JP2009283888A - Surface emitting laser element, surface emitting laser array, optical scanning device, and image forming apparatus - Google Patents

Abstract

The present invention suppresses "negative droop characteristics" in a surface emitting laser element.
By selective oxidation of a resonator structure including an active layer 105, a semiconductor DBR (lower semiconductor DBR103, upper semiconductor DBR107) provided between the resonator structure, and a selective oxidation layer containing Al. It has an oxidation confinement structure formed inside the upper semiconductor DBR 107 and capable of simultaneously confining the injected current and the transverse mode of the oscillation light. The thickness of the selective oxidation layer is 28 nm, and the temperature at which the threshold current is minimized is about 17 ° C. When a square wave current pulse having a pulse period of 1 ms and a pulse width of 500 μs is supplied, the light output P1 at 10 ns after supply and the light output P2 at 1 μs after supply are used, and (P1-P2) / P2 = −0.05.
[Selection] Figure 1

Description

  The present invention relates to a surface emitting laser element, a surface emitting laser array, an optical scanning device, and an image forming apparatus. More specifically, the present invention relates to a surface emitting laser element that emits light in a direction perpendicular to a substrate, and the surface emitting laser element. The present invention relates to a surface-emitting laser array in which the surface-emitting laser is integrated, an optical scanning device having the surface-emitting laser element or the surface-emitting laser array, and an image forming apparatus including the optical scanning device.

  In recent years, surface emitting laser elements (surface emitting semiconductor laser elements) that generate laser oscillation in a direction perpendicular to the substrate have been intensively studied. The surface-emitting laser element has a lower oscillation threshold current than the edge-emitting laser element, and can obtain a circular high-quality outgoing beam shape. In addition, since the surface emitting laser element can extract the laser output in a direction perpendicular to the substrate, it can be easily integrated in a two-dimensional manner with high density, a light source for parallel optical interconnection, and a high-speed, high-definition electrophotographic system. The application to etc. is examined.

  The surface emitting laser element has a constricted structure in order to increase current inflow efficiency. As this constriction structure, a constriction structure by selective oxidation of Al (aluminum) (hereinafter also referred to as “oxidized constriction structure” for convenience. For example, see Non-Patent Document 1 and Non-Patent Document 2) is often used. Yes.

  Non-Patent Document 3 discloses a printer using a 780 nm band VCSEL array (surface emitting laser array).

  Patent Document 1 discloses that a difference (detuning amount) between an oscillation wavelength determined by the length of the resonator and a gain peak wavelength determined by the composition of the active layer is a predetermined amount at a predetermined temperature, and a temperature range higher than the predetermined temperature. In particular, a surface emitting laser element having an oscillation wavelength and a gain peak wavelength that coincide with each other is disclosed.

  Patent Document 2 discloses a multi-spot image forming apparatus having a multi-spot light source.

JP 2004-319643 A JP 11-48520 A K. D. Choquette, K.M. L. Lear, R.M. P. Schneider, Jr. K. M.M. Geib, “Cavity characteristics of selective oxidised vertical-cavity lasers”, Applied Physics Letters, vol. 66, no. 25, pp. 3413-3415, 1995 K. D. Choquette, R.A. P. Schneider, Jr. K. L. Lear, K.M. M.M. Geib, “Low threshold voltage vertical-cavity lasers fabricated by selective oxidation,” “Electronics Letters, No. 4”. 24, Vol. 30, pp. 2043-2044, 1994 H. Nakayama, T .; Nakamura, M .; Funada, Y. et al. Ohashi, M .; Kato, “780 nm VCSELs for Home Networks and Printers”, Electronic Components and Technology Conference Processings, 54th, Vol. 2, June, 2004, pp. 1371-1375

  In electrophotography and the like, the rising behavior in the response waveform of the light output of the light source when the drive current is supplied to the light source (time change of the light output, hereinafter also referred to as “light waveform”) is extremely large in image quality. Influence. For example, not only the rise time in the optical waveform, but also the light quality may deteriorate slightly even after the light output reaches a certain light quantity at the beginning of the rise.

  This is the contour of the image that is formed at the rise and fall of the optical waveform, and the contour of the image changes when the amount of light changes, particularly during the rise and after it has been considered to have risen substantially. This is because the image quality becomes unclear and the image quality lacks visual clarity.

  For example, if the time required to scan one line of A4 paper width (vertical) of about 300 mm is 300 μs, the width of about 1 mm is scanned in a time of 1 μs. It is said that the range in which the visual sensitivity of the human eye is highest with respect to fluctuations in image density is 1 to 2 mm. Therefore, if the image density fluctuates in a width of about 1 mm, the density change is sufficient to be detected by the human eye, giving an impression that the outline is unclear.

  FIG. 36 shows an optical waveform when a surface emitting laser element having an oxidized constricting structure is driven under a pulse condition of a pulse width of 500 μs and a duty of 50% (pulse period 1 ms). As shown in FIG. 36, when viewed on a relatively long time scale, the light output shows a peak immediately after rising, and then the light output decreases and becomes stable. This change in light output is due to self-heating of the surface emitting laser element, and is generally called “droop characteristic”.

  By the way, when the inventors have made a detailed examination, as shown in FIG. 37 in which the vicinity of the rising edge of the optical waveform in FIG. 36 is enlarged, when viewed on a short time scale, the light different from the “droop characteristic”. I got a new finding that there was a change in output.

  In FIG. 37, the optical output does not rise even after 10 ns, and rises substantially after about 200 ns. However, the light output gradually increases during the period up to about 1 μs. Such a phenomenon (characteristic) has been newly found by the present inventors. In this specification, such characteristics are referred to as “negative droop characteristics”. It should be noted that such a “negative droop characteristic” is not observed in the conventional edge-emitting laser element.

  The inventors focused on the “negative droop characteristic” and examined the cause in detail, and found that this phenomenon is closely related to the optical confinement strength of the transverse mode in the oxidized constriction structure. .

  The present invention has been made on the basis of the novel findings obtained by the inventors described above. From the first viewpoint, the present invention is a surface emitting laser element that emits light in a direction perpendicular to a substrate, and includes an active layer An oxide including at least an oxide provided by sandwiching a part of the selective oxidation layer including aluminum and surrounding the current passing region; A semiconductor distributed Bragg reflector including therein a constriction structure capable of simultaneously confining an injection current and a transverse mode of oscillation light, and the thickness of the selectively oxidized layer is at least 25 nm, and the threshold current of oscillation The surface emitting laser element is characterized in that the temperature at which the oscillation threshold current is minimized is 25 ° C. or less in relation to the temperature.

  According to this, it is possible to suppress the “negative droop characteristic” regardless of the pulse period.

  From a second viewpoint, the present invention is a surface emitting laser array in which the surface emitting laser elements of the present invention are integrated.

  According to this, since the surface emitting laser element of the present invention is integrated, it is possible to suppress the “negative droop characteristic” regardless of the pulse period.

  From a third aspect, the present invention is an optical scanning device that scans a surface to be scanned with light, the light source having the surface-emitting laser element of the present invention; a deflector that deflects the light from the light source; A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned.

  According to this, since the surface-emitting laser element of the present invention is included, as a result, it becomes possible to perform highly accurate optical scanning.

  According to a fourth aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with light, a light source having the surface emitting laser array of the present invention; a deflector that deflects light from the light source; A scanning optical system that condenses the light deflected by the deflector onto the surface to be scanned.

  According to this, since the surface emitting laser array according to the present invention is provided, as a result, it is possible to perform highly accurate optical scanning.

  According to a fifth aspect of the present invention, there is provided at least one image carrier; and at least one optical scanning device according to the invention that scans light including image information on the at least one image carrier. An image forming apparatus.

  According to this, since at least one optical scanning device of the present invention is provided, a high-quality image can be formed.

“First Embodiment”
FIG. 1 is a cross-sectional view showing a schematic configuration of a surface emitting laser element 100 according to the first embodiment of the present invention. In this specification, the laser oscillation direction is defined as the Z-axis direction, and two directions orthogonal to each other in a plane perpendicular to the Z-axis direction are described as the X-axis direction and the Y-axis direction.

  The surface-emitting laser element 100 is a surface-emitting laser element having a designed oscillation wavelength of 780 nm band. On the substrate 101, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, A plurality of semiconductor layers such as the upper semiconductor DBR 107 and the contact layer 109 are sequentially stacked. Hereinafter, a structure in which the plurality of semiconductor layers are stacked is also referred to as a “first stacked body” for convenience.

  The substrate 101 is an n-GaAs single crystal substrate.

  The buffer layer 102 is a layer made of n-GaAs.

The lower semiconductor DBR 103 has 40.5 pairs of a low refractive index layer made of n-Al _0.9 Ga _0.1 As and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. Yes. And, in order to reduce the electrical resistance, a composition gradient layer having a thickness of 20 nm is provided between the low refractive index layer and the high refractive index layer, in which the composition is gradually changed from one composition to the other composition. It has been. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ. By the way, the optical thickness and the actual thickness of the layer have the following relationship. When the optical thickness is λ / 4, the actual thickness d of the layer is d = λ / 4N (where N is the refractive index of the medium of the layer).

The lower spacer layer 104 is a layer made of non-doped Al _0.6 Ga _0.4 As.

The active layer 105 is a multiple quantum well active layer of Al _0.15 Ga _0.85 As / Al _0.6 Ga _0.4 As.

The upper spacer layer 106 is a layer made of non-doped Al _0.6 Ga _0.4 As.

  A portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and the thickness thereof is set to be an optical thickness of one wavelength. The active layer 105 is provided at the center of the resonator structure at a position corresponding to the antinode in the standing wave distribution of the electric field so that a high stimulated emission probability can be obtained. This resonator structure is sandwiched between the lower semiconductor DBR 103 and the upper semiconductor DBR 107.

The upper semiconductor DBR 107 has 24 pairs of a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index layer made of p-Al _0.3 Ga _0.7 As. And, in order to reduce the electrical resistance, a composition gradient layer having a thickness of 20 nm is provided between the low refractive index layer and the high refractive index layer, in which the composition is gradually changed from one composition to the other composition. It has been. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

  The contact layer 109 is a layer made of p-GaAs.

  Next, a method for manufacturing the surface emitting laser element 100 will be briefly described.

(1-1) The first stacked body is formed by crystal growth by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE). At this time, a selective oxidation layer made of p-AlAs is inserted into one of the low refractive index layers in the upper semiconductor DBR 107 with a thickness of 28 nm.

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and arsine (AsH ₃ ) gas is used as Group V materials. Further, carbon tetrabromide (CBr ₄ ) is used as a p-type dopant material, and hydrogen selenide (H ₂ Se) is used as an n-type dopant material.

(1-2) A square resist pattern having a side of 20 μm is formed on the surface of the first laminate.

(1-3) A square columnar mesa is formed by using an ECR etching method using Cl ₂ gas and a square resist pattern as a photomask. Here, the bottom surface of the etching is positioned in the lower semiconductor DBR 103.

(1-4) The photomask is removed.

(1-5) The first stacked body is heat-treated in water vapor to selectively oxidize a part of the selectively oxidized layer in the mesa. Then, an unoxidized region 108b surrounded by the oxide layer 108a is left in the center of the mesa. As a result, an oxidized constriction structure is formed that restricts the drive current path of the light emitting part to only the central part of the mesa. The non-oxidized region 108b is a current passage region (current injection region). Here, one side of the current passing region is 4.5 μm.

(1-6) The protective layer 111 made of SiN is formed using a chemical vapor deposition method (CVD method).

(1-7) Flatten with polyimide 112.

(1-8) Open P-side electrode contact window on top of mesa. Here, after masking with a photoresist, the opening at the top of the mesa is exposed to remove the photoresist at that portion, and then the polyimide 112 and the protective layer 111 are etched and opened with BHF.

(1-9) A resist pattern having a square shape with a side of 8 μm is formed in a region to be a light emitting portion on the upper part of the mesa, and a p-side electrode material is deposited. As the electrode material on the p side, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(1-10) The electrode material of the light emitting part is lifted off, and the p-side electrode 113 is formed.

(1-11) After polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), an n-side electrode 114 is formed. Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au.

(1-12) Ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, the mesa becomes a light emitting part.

(1-13) Cut for each chip.

  When a square wave current pulse having a pulse period of 1 ms and a pulse width of 500 μs is supplied to the surface emitting laser element 100 manufactured in this manner, the light output at 10 ns after supply is P1, and the light output at 1 μs after supply. Was P2, it was (P1-P2) /P2=-0.05. Hereinafter, the value (unit:%) of (P1−P2) / P2 × 100 is also referred to as “droop rate”. Therefore, in the surface emitting laser element 100 according to the first embodiment, the droop rate is −5%.

  FIG. 2 shows the relationship between the thickness of the selective oxidation layer and the droop rate in the surface emitting laser element. According to this, when the thickness of the selective oxidation layer decreases, the droop rate decreases exponentially, and the “negative droop characteristic” appears remarkably. In addition, variation in the droop rate for each element becomes remarkable. And in order to make droop rate -10% or more, it is necessary to make the thickness of a selective oxidation layer into 25 nm or more. When a surface emitting laser element having a droop rate smaller than −10% is used, the image output from the laser printer becomes unclear at least partially when observed with the naked eye.

  By the way, the inventors examined in detail the optical waveforms when a conventional surface emitting laser element having an oxidized constriction structure is driven by various square wave current pulses. FIG. 3 shows an optical waveform when the pulse period is 1 ms and the duty is 50%, and FIG. 4 shows an optical waveform when the pulse period is 100 ns and the duty is 50%.

  Looking at the optical waveform of FIG. 3, after rising, the optical output gradually increases, and a “negative droop characteristic” appears. Further, even after 60 ns, the light output does not reach 100% (1.5 mW). On the other hand, in the optical waveform of FIG. 4, the output after the rise is stable, and the “negative droop characteristic” is not seen.

  As described above, when a square wave current pulse is supplied to a conventional surface emitting laser element, even when the duty is the same, a “negative droop characteristic” is observed when the pulse period is long, and when the pulse period is short, It was found that the “droop characteristics of” was not observed.

  When the pulse period is different, the internal temperature of the surface emitting laser element is considered to be different. That is, when the pulse period is long, the time during which heat is generated and the time during which the pulse is cooled are both long, so that the internal temperature of the surface emitting laser element varies greatly. On the other hand, when the pulse period is short, the continuous cooling time cannot be taken sufficiently, so that the fluctuation of the internal temperature of the surface emitting laser element is small and stable on average at a higher temperature. In other words, under the driving conditions where “negative droop characteristics” can be seen, the internal temperature of the surface emitting laser element varies greatly, and “negative droop characteristics” is a phenomenon caused by the internal temperature of the surface emitting laser element. Can think.

  When the internal temperature of the surface emitting laser element changes, the electric field strength distribution in the lateral direction of the oscillation mode (hereinafter also referred to as “lateral mode distribution” for convenience) changes.

  The transverse mode distribution of the surface emitting laser element can be estimated by calculating the electric field intensity distribution from the following Helmholtz equations (Equations (1) and (2)).

  However, since the equations (1) and (2) are difficult to solve analytically, numerical analysis by a finite element method using a computer is usually performed. There are various types of finite element solvers that can be used, and commercially available VCSEL simulators (for example, LASER MOD) can be used.

  As an example, a fundamental transverse mode distribution in a surface emitting laser element having an oscillation wavelength band of 780 nm is calculated.

In the surface emitting laser element used for the calculation, the active layer has an Al _0.12 Ga _0.88 As / Al _0.3 Ga _0.7 As triple quantum well structure with a thickness of 8 nm / 8 nm, and each spacer layer has Al _0.6 Ga _0.4 As. The lower semiconductor DBR is composed of 40.5 pairs of Al _0.3 Ga _0.7 As (high refractive index layer) / AlAs (low refractive index layer), and the upper semiconductor DBR is Al _0.3 Ga _0.7 As. It consists of 24 pairs of (high refractive index layer) / Al _0.9 Ga _0.1 As (low refractive index layer).

  This surface emitting laser element has a cylindrical mesa shape with a diameter of 25 μm, and mesa etching is performed up to the interface between the lower semiconductor DBR and the lower spacer layer, and the etched region is occupied by the atmosphere. It was. That is, a simple etched mesa structure was used. The diameter of the portion of the lower semiconductor DBR that is not mesa-etched is 35 μm, which is the maximum lateral width considered in the calculation. The material of the selectively oxidized layer is AlAs, and the position of the selectively oxidized layer is in the low refractive index layer having an optical thickness of 3λ / 4 in the upper semiconductor DBR, and the electric field intensity distribution is 3 from the active layer. The position of the second clause.

  Note that the calculation does not consider the gain of the active layer and the absorption by the semiconductor material, and only the eigenmode distribution determined by the structure is obtained. The surface emitting laser element has a uniform temperature of 300K. Further, the values shown in FIG. 5 were used for the refractive indexes of the respective materials.

  The calculation result of the fundamental transverse mode distribution in the active layer when the thickness of the oxide layer in the oxide confinement structure is 30 nm and the diameter of the current passage region (hereinafter also referred to as “oxidation confinement diameter”) is 4 μm is as follows. It is shown in FIG. The horizontal axis x in FIG. 6 represents the position from the center in the radial direction (lateral direction), and x = 0 corresponds to the center of the mesa. Hereinafter, for convenience, the oxide layer in the oxidized constriction structure is also simply referred to as “oxide layer”.

  Since the refractive index of the oxide layer is about 1.6 and is smaller than the refractive index of the surrounding semiconductor layer (about 3), a so-called built-in effective refractive index difference Δneff is laterally formed inside the surface emitting laser element. Exists (see FIG. 7).

  Oscillation modes such as the fundamental transverse mode are confined in the lateral direction by this effective refractive index difference Δneff. At this time, the lateral spread of the oscillation mode is determined by the magnitude of Δneff. The larger the Δneff is, the smaller the lateral spread is (see FIGS. 8A and 8B).

  When current (driving current) is injected into this surface emitting laser element, the current concentrates in the mesa center, and the temperature at the center of the mesa, particularly near the active layer, is caused by Joule heat or non-radiative recombination in the active layer region. It rises locally with respect to the surrounding area. The semiconductor material has the property that when the temperature rises, the band gap energy decreases and the refractive index increases. For this reason, when the temperature of the central portion of the mesa rises locally, the refractive index of the central portion increases with respect to the peripheral region, and lateral light confinement becomes strong.

  As shown in FIG. 8A, when the built-in effective refractive index difference Δneff is small and the temperature of the central portion of the mesa rises locally, as shown in FIG. The change in the difference Δneff increases and the transverse mode distribution changes greatly. In this case, the overlap between the gain region in which current injection is performed and the lateral mode increases, and the optical confinement factor Γl in the lateral direction increases. As a result, the light intensity in the gain region increases, the stimulated emission rate increases, and the oscillation threshold current (hereinafter, also simply referred to as “threshold current” for convenience) decreases.

As described above, in the surface emitting laser element in which the built-in effective refractive index difference Δneff is small and the lateral light confinement at room temperature is insufficient, when the internal temperature rises, the IL curve is The light emission efficiency is improved by shifting to the low current side (see FIG. 10). In this case, the optical output at the same drive current value increases with time, and a “negative droop characteristic” is observed (see FIG. 11). FIG. 10 shows an IL characteristic that is predicted at time t = t ₀ seconds before the internal temperature rises, and an I- characteristic that is predicted at time t = t ₁ seconds when the pulse is applied and the internal temperature sufficiently rises. The L characteristic is shown. As the temperature rises, the light emission efficiency is improved and the threshold current is reduced. Therefore, the IL characteristic at t ₁ second is shifted to the low current side with respect to t ₀ second. Since the drive current value I _op of the pulse is constant, the light output becomes larger in the case of t ₁ second. The optical waveform in this case is shown in FIG.

  On the other hand, as shown in FIG. 8B, when the built-in effective refractive index difference Δneff is large, even if the temperature of the central portion of the mesa rises locally, as shown in FIG. The change in the effective refractive index difference Δneff is small and the transverse mode distribution does not change much.

  As described above, in a surface emitting laser element having a large built-in effective refractive index difference Δneff and sufficiently large lateral light confinement at room temperature, the lateral mode distribution is stable even when the internal temperature rises, and the luminous efficiency is increased. Almost no change occurs. In this case, the optical output at the same drive current value is almost constant over time, and “negative droop characteristics” are not observed.

  As an index representing the strength of light confinement in the lateral direction, there is a light confinement factor in the lateral direction (hereinafter simply referred to as “light confinement factor” for convenience). The larger the value of the optical confinement factor, the sharper the electric field intensity distribution is concentrated in the gain region. In other words, the larger the value of the light confinement coefficient at room temperature, the more the light is confined by the oxidized confinement structure, and the electric field against disturbance such as local temperature change (refractive index change) in the gain region. It means that the intensity distribution is stable.

  Here, the optical confinement factor is defined as “the ratio of the integrated intensity of the electric field in the region having the same radius as the current passing region to the integrated intensity of the electric field in the diametrical cross section passing through the center of the surface emitting laser element” as described above. Based on the basic transverse mode distribution calculated as described above, the following equation (3) was used. Here, a corresponds to the radius of the current passage region.

  FIG. 12 shows the results of calculation of the fundamental transverse mode optical confinement factor at room temperature in the surface-emitting laser element of the 780 nm band with respect to the thicknesses of various selective oxidation layers and oxidation confinement diameters. The optical confinement coefficient depends on the thickness of the selective oxidation layer and the oxidized constriction diameter, and takes a higher value as the selective oxidation layer is thicker and the oxidized constriction diameter is larger.

  FIG. 13 shows the calculation result of FIG. 12 with the optical confinement factor as the vertical axis and the thickness of the selective oxidation layer as the horizontal axis. Looking at the change in the optical confinement factor with respect to the increase in the thickness of the selective oxidation layer, even if the oxidation confinement diameter is different, the change is abrupt in the region where the thickness of the selective oxidation layer is 25 nm or less, and 25 nm or more. It can be seen that there is a saturation tendency.

  FIG. 14 shows the result of actually manufacturing a plurality of surface emitting laser elements having different thicknesses of selective oxidation layers and different oxidation constriction diameters and evaluating their droop characteristics. In FIG. 14, a droop rate of −10% or more is represented by “◯”, and a droop rate smaller than −10% is represented by “x”.

  From FIG. 12 and FIG. 14, it is understood that a droop rate of −10% or more is obtained in the element structure in which the optical confinement coefficient of the fundamental transverse mode at room temperature is 0.9 or more. Further, the oxidation confinement diameter that is generally used is in the range of 4.0 μm to 5.0 μm, and as shown in FIG. An optical confinement factor of 9 or more can be ensured.

  FIG. 15 shows an optical waveform of the surface emitting laser element in which the fundamental transverse mode optical confinement coefficient at room temperature is about 0.983. The droop rate at this time was about −4.3%.

  FIG. 16 shows an optical waveform of the surface emitting laser element in which the fundamental transverse mode optical confinement coefficient at room temperature is about 0.846. The droop rate at this time was about -62.8%.

  Thus, by setting the optical confinement coefficient of the fundamental transverse mode at room temperature to 0.9 or more, the “negative droop characteristic” can be suppressed.

  As described above, since the optical confinement factor of the fundamental transverse mode is determined mainly depending on two of the oxidized constriction diameter and the thickness of the selective oxidation layer, the combination of the oxidation constriction diameter and the thickness of the selective oxidation layer is determined. How you choose is important.

  When the inventors tried various fitting methods, the calculation result of FIG. 12 shows that the oxidized constriction diameter (d [μm]) and the thickness of the selective oxidation layer (t [nm]) are variables. As a result, it was possible to perform fitting in these secondary forms. The following equation (4) is the result of fitting the optical confinement factor (Γ) of the fundamental transverse mode in a quadratic form of the oxidized constriction diameter d and the thickness t of the selective oxidation layer. By substituting the specific values of FIG. 12, the optical confinement factor of the fundamental transverse mode of FIG. 12 can be obtained with an error of approximately 1%.

Γ (d, t) = (− 2.54d ² −0.14t ² −0.998d · t + 53.4d + 12.9t−216) (4)

  As described above, in order to effectively suppress the “negative droop characteristic”, it is necessary to set the optical confinement factor to 0.9 or more. Here, the oxidation in which the optical confinement factor is 0.9 or more is required. The combination (range) of the constriction diameter (d) and the thickness (t) of the selective oxidation layer can be obtained from the above equation (4). That is, this range is a combination of d and t that satisfies the inequality of Γ (d, t) ≧ 0.9, and more specifically is expressed as the following equation (5).

−2.54d ² −0.14t ² −0.998d · t + 53.4d + 12.9t−216 ≧ 0.9 (5)

  Therefore, by selecting the oxidized constriction diameter (d) and the thickness (t) of the selective oxidation layer so that the above equation (5) is satisfied, the optical confinement coefficient in the fundamental transverse mode becomes 0.9 or more. An element in which the “negative droop characteristic” is suppressed can be obtained.

  By the way, it has not been known so far that Δneff affects the droop characteristic, and has been revealed for the first time by the inventors of the present application.

  In general, the effective refractive index difference Δneff at room temperature increases as the thickness of the selective oxidation layer is thicker and the position of the selective oxidation layer is closer to the active layer. When these two influences are compared, the influence degree of the thickness of the selective oxidation layer is much larger.

  Therefore, the intensity of lateral light confinement at room temperature is mainly determined by the thickness of the selectively oxidized layer. And it can be said that the thickness of the selective oxidation layer necessary for suppressing the “negative droop characteristic” is 25 nm or more.

  In the selective oxidation process of the selective oxidation layer, the oxidation proceeds slightly in the vertical direction as well as in the direction parallel to the substrate surface. Therefore, when the cross section of the mesa after selective oxidation is observed with an electron microscope, the thickness of the oxide layer is not uniform, the thickness at the outer periphery of the mesa is thick, and the oxidation tip is thin. However, in the region from the oxidation tip to the outer peripheral direction of the mesa to 2 to 3 μm, the thickness of the oxide layer is substantially the same as the thickness of the selective oxidation layer. Since the oscillation light is mainly affected by the effective refractive index difference of the oxidation front end portion, by actually controlling the thickness of the selective oxidation layer to a desired value (25 nm or more), The thickness of the oxide layer can be set to a desired value.

  FIG. 17 shows a lateral mode distribution due to self-heating in a surface emitting laser element having a structure (oxidized confinement diameter 4 μm, thickness of a selective oxidation layer 20 nm) in which the optical confinement coefficient is about 0.788 at room temperature (27 ° C.). It shows how it changes. Here, the calculation is performed assuming that the temperature is 27 ° C. in the entire region of the surface emitting laser element in the room temperature state. Further, since the temperature of the current injection region of the active layer is considered to rise significantly in the operating state, the resonance region (a region composed of a spacer layer and an active layer sandwiched between a pair of semiconductor DBRs (see FIG. 18)). The calculation was performed with only the refractive index of the current injection portion defined by the oxide layer as the value at 60 ° C. As a result when the temperature of only the current injection portion in the resonance region is set to 60 ° C., the distribution of the fundamental transverse mode is narrower than that at 27 ° C., and a large change is observed. When only the current injection part in the resonance region is set to 60 ° C., the optical confinement factor of the fundamental transverse mode is about 0.987, and the change rate of the optical confinement factor of the fundamental transverse mode is 25% compared to the case of 27 ° C. is there. Thus, if the fundamental transverse mode distribution is not stable against self-heating, a “negative droop characteristic” is observed, which is not preferable.

  FIG. 19 shows a fundamental transverse mode distribution due to self-heating in a surface emitting laser device having a structure (oxidation confinement diameter 4 μm, selective oxidation layer thickness 30 nm) in which the optical confinement coefficient of the fundamental transverse mode at room temperature is about 0.973. Shows how changes occur. The change between the two states is slight. When only the current injection part in the resonance region is set to 60 ° C., the optical confinement coefficient in the transverse mode is about 0.994, and the rate of change of the optical confinement coefficient in the fundamental transverse mode is 2.2% compared to 27 ° C. It is.

  FIG. 20 shows that for various surface emitting laser elements having different element structures, only the optical confinement factor (Γl) of the fundamental transverse mode at room temperature and the temperature of the current injection portion in the resonance region are locally set to 60 ° C. It is the result of calculating the ratio of the optical confinement coefficient (Γl ′) of the fundamental transverse mode in the case. Actually, various surface-emitting laser elements were manufactured and measured, and when the value of Γl ′ / Γl was 1.1 or less (change rate of 10% or less), the droop coefficient was −5% or more, A good optical waveform could be obtained.

  On the contrary, when the value of Γl ′ / Γl exceeds 1.1, the “negative droop characteristic” is clearly seen, and the droop rate decreases as the value of Γl ′ / Γl increases.

  From these, the rate of change of the optical confinement coefficient in the fundamental transverse mode is set to within 10% when only the temperature of the current injection portion in the resonance region is locally 60 ° C. with respect to the optical confinement coefficient in the fundamental transverse mode at room temperature. Thus, the “negative droop characteristic” can be further suppressed.

  In the surface emitting laser element 100 according to the first embodiment, the optical confinement factor of the fundamental transverse mode at room temperature (27 ° C.) was about 0.974. In addition, when only the temperature of the current injection portion in the resonator structure was locally 60 ° C., the optical confinement factor was about 0.996. That is, the rate of change of the optical confinement factor was 2.2%.

  Further, when the internal temperature of the surface emitting laser element changes, the detuning amount also changes. Therefore, the relationship between the detuning amount and the “negative droop characteristic” will be described next.

  In the edge-emitting laser element, since the resonance longitudinal mode is densely present, laser oscillation occurs at the gain peak wavelength λg. On the other hand, in the surface emitting laser element, the resonance wavelength is usually one wavelength, and only a single longitudinal mode can exist in the reflection band of the semiconductor DBR. Further, since laser oscillation occurs at the resonance wavelength λr, the emission characteristics of the surface emitting laser element depend on the relationship between the resonance wavelength λr and the gain peak wavelength λg of the active layer.

Here, the detuning amount Δλ ₀ is defined by the following equation (6). λr ₀ is a resonance wavelength, and λg ₀ is a gain peak wavelength. The subscript 0 means a value when CW (Continuous Wave Oscillation) driving is performed with a threshold current at room temperature. Hereinafter, when there is no subscript 0, in other cases, for example, a value when operating at a threshold current or more is meant.

Δλ ₀ = λr ₀ −λg ₀ (6)

FIG. 21A shows the case of Δλ ₀ > 0, and FIG. 21B shows the case of Δλ ₀ <0.

Since the oscillation wavelength is determined not by the gain peak wavelength but by the resonance wavelength, the laser characteristics of the surface emitting laser element greatly depend on the positive / negative of Δλ ₀ and its value. For example, the threshold current at room temperature tends to increase as the absolute value of Δλ ₀ increases.

  Both the resonance wavelength and the gain peak wavelength change to the longer wavelength side as the temperature rises. At this time, the change in the resonance wavelength is caused by the change in the refractive index of the material constituting the resonator structure, and the change in the gain peak wavelength is caused by the change in the band gap energy of the active layer material. However, the rate of change in the band gap energy is about an order of magnitude greater than the rate of change in the refractive index. Therefore, the light emission characteristics at the time of temperature change are determined mainly depending on the amount of change in the gain peak wavelength. Note that the temperature change rate of the resonance wavelength is about 0.05 nm / K, and the change with respect to the temperature can be substantially ignored.

In the surface emitting laser element, when the internal temperature (temperature of the active layer) rises due to a change in injection current or the like, the gain peak wavelength shifts to the long wavelength side. Therefore, when Δλ ₀ > 0 (see FIG. 21A), the absolute value of Δλ (degree of detuning) decreases once and then increases.

  In general, in a surface emitting laser element, the oscillation efficiency (light emission efficiency) is highest when the gain peak wavelength and the resonance wavelength coincide with each other.

When Δλ ₀ > 0 and the element temperature (environment temperature) is increased from room temperature and the threshold current is measured, the threshold current starts to decrease as the element temperature increases. The threshold current becomes the minimum value when the gain peak wavelength matches the resonance wavelength, and starts to increase when the temperature is further increased. That is, a temperature at which the threshold current is minimum exists on the higher temperature side than room temperature.

In the case of Δλ ₀ <0 (see FIG. 21B), the absolute value of Δλ only increases as the internal temperature (the temperature of the active layer) increases, so the device temperature is increased from room temperature. When the threshold current is measured, the threshold current only increases as the element temperature increases.

In this case, when the element temperature is lowered from room temperature, the gain peak wavelength Δλg is shifted to the short wavelength side. Therefore, when the threshold temperature is measured by lowering the element temperature from room temperature, the threshold current starts to decrease and becomes minimum when the gain peak wavelength and the resonance wavelength coincide. When the temperature is further lowered, the threshold current starts to increase. That is, when Δλ ₀ <0, the temperature at which the threshold current is minimum exists on the lower temperature side than room temperature.

Δλ ₀ is different from each other (Δλ ₀ <0, Δλ ₀ ≈0, Δλ ₀ > 0). The result of measuring the oscillation threshold current of three elements while changing the element temperature (environment temperature) is shown as an example. 22. The vertical axis in FIG. 22 is a value obtained by normalizing the oscillation threshold current (Ith) at each temperature with the oscillation threshold current (Ith (25 ° C.)) at 25 ° C. (room temperature). FIG. 22 shows that the threshold current is lower than room temperature when Δλ ₀ <0, near the room temperature when Δλ ₀ ≈0, and higher than room temperature when Δλ ₀ > 0. It can actually be confirmed that it is minimum.

In conventional surface-emitting laser elements, Δλ ₀ > 0 is usually set so that the threshold current at high temperatures is low in order to prevent degradation of light emission characteristics at high temperature and high power operation.

However, when a conventional surface emitting laser element set to Δλ ₀ > 0 is driven by a square wave current pulse, the IL characteristic shifts to the low current side as the internal temperature increases, and the threshold current decreases. Therefore, the light output at the same drive current value increases with time. That is, a “negative droop characteristic” occurs. On the other hand, when Δλ ₀ <0, the IL characteristic shifts to the high current side as the internal temperature rises, so that the light output does not rise. That is, the “negative droop characteristic” does not occur. Thus, in order to suppress the “negative droop characteristic”, it is necessary to set Δλ ₀ <0 in addition to the thickness of the oxide layer so that the threshold current does not become minimum at a temperature of room temperature or higher. .

In order to set λ ₀ to a desired value, it is necessary to know the gain peak wavelength λg ₀ . In the edge-emitting laser element, the oscillation wavelength coincides with the gain peak wavelength, so that the gain peak wavelength can be known from the oscillation wavelength. However, in the surface emitting laser element, the resonance wavelength is determined by the structure, so that it is difficult to estimate the gain peak wavelength as in the edge emitting laser element.

  Therefore, (1) an edge-emitting laser device having the same active layer is manufactured and a gain peak wavelength is estimated from an oscillation wavelength at room temperature, or (2) a double heterostructure having the same active layer is manufactured, Either a method of estimating the gain peak wavelength from the photoluminescence wavelength (PL wavelength) is taken.

When the method (1) is employed, as an example, an oxide film stripe type edge emitting laser element having the same active layer structure and a stripe width of 40 μm and a resonator length of 500 μm is fabricated, and the room temperature of the edge emitting laser element is obtained. The wavelength at the threshold current of CW oscillation at ₁ is used as the gain peak wavelength λg ₀ .

Further, when the method (2) is adopted, the wavelength at the time of laser oscillation is shifted to the long wavelength side (wavelength shift) with respect to the PL wavelength, so adjustment for this is necessary. The wavelength shift is due to differences in excitation processes such as photoexcitation and current excitation, and the influence of heat generated by current in the case of current excitation. Generally, an oscillation wavelength in the edge emitting laser element, 10 nm approximately with respect to the PL wavelength lambda _PL, a long wavelength. Therefore, the wavelength shift amount in this case is 10 nm.

  Therefore, considering the PL wavelength as a reference, the above equation (6) becomes the following equation (7).

Δλ ₀ = λ _r0 −λ _g0 = λ _r0 − (λ _PL +10) = λ _r0 −λ _PL −10 (7)

  The wavelength shift amount of 10 nm is a general value, but may be changed according to the material system used.

A plurality of surface-emitting laser elements having different Δλ ₀ were manufactured, and the temperature at which the threshold current in each surface-emitting laser element was minimum was determined. The result is shown in FIG. From FIG. 23, it can be seen that when Δλ ₀ is actually 0, the threshold current is minimum at room temperature.

  Next, a plurality of surface emitting laser elements having different thicknesses of the selective oxidation layers (30, 31, and 34 nm) were manufactured, and the temperature and the droop rate at which the threshold current in each surface emitting laser element was minimized were determined. FIG. 24 shows the relationship between the droop rate and the temperature at which the threshold current is minimized for each thickness of the selective oxidation layer.

  In FIG. 24, attention is first focused on surface emitting laser elements having the same selective oxidation layer thickness. In any thickness, in a surface emitting laser element having a temperature at which the threshold current is minimized at 25 ° C. or less, the absolute value of the droop rate is small (close to 0) and is substantially constant. On the other hand, in a surface emitting laser element having a minimum threshold current temperature of 25 ° C. or higher, the droop rate decreases as the temperature at which the threshold current is minimum increases.

  A surface-emitting laser element whose temperature at which the threshold current is minimum is higher than room temperature is an element whose oscillation efficiency is improved when the temperature of the active layer is increased by current injection. The droop characteristic of “ Furthermore, the higher the temperature at which the threshold current is minimum, the higher the surface emitting laser element, the lower the efficiency at the initial stage of current injection.

  Next, in FIG. 24, attention is paid to the difference in thickness of the selective oxidation layer. In a surface emitting laser element having a temperature at which the threshold current is minimized at 25 ° C. or lower, the droop rate becomes closer to 0 as the thickness of the selective oxidation layer increases, and “negative droop characteristics” are suppressed. This is because, as described above, the thicker the selective oxidation layer is, the larger the optical confinement coefficient by the oxide layer is, and the fundamental transverse mode is more stable with respect to temperature changes.

  Each of the surface emitting laser elements shown in FIG. 24 has a selective oxidation layer having a thickness of 25 nm or more. Therefore, in the surface emitting laser element having a minimum threshold current temperature of 25 ° C. or less, the droop rate Becomes -10% or more, and the "negative droop characteristic" is effectively suppressed.

  Thus, in common with the detuning amount and the optical confinement factor, in order to suppress the “negative droop characteristic”, the surface emission is higher when the temperature of the active layer is higher than when it is at room temperature. It is important to set so that the efficiency (light emission efficiency) of the laser element is not improved.

In the surface emitting laser device 100 according to the first embodiment, the PL wavelength of the active layer is set to 772 nm, the detuning amount Δλ ₀ at room temperature is set to −2 nm, and the threshold current is minimum at about 17 ° C. It is trying to become.

  Various surface-emitting laser elements having different optical confinement factors from each other were manufactured after setting the temperature at which the threshold current is actually minimized to 25 ° C. or less, and the optical confinement factor was about 0.degree. At 9, the droop rate was about -5%. Increasing the optical confinement factor further increased the droop rate with the increase.

  On the other hand, in the surface emitting laser element having an optical confinement factor smaller than 0.9, the droop rate tends to decrease as the optical confinement factor decreases, and a surface emitting laser element having a droop rate of −70% or less was also observed. .

  As described above, according to the surface-emitting laser device 100 according to the first embodiment, the resonator structure including the active layer 105 and the semiconductor DBR (lower semiconductor) provided between the resonator structures. DBR103 and upper semiconductor DBR107). In the upper semiconductor DBR 107, the oxide layer 108a including at least an oxide generated by oxidizing a part of the selectively oxidized layer including Al surrounds the current passing region 108b, and the injection current and the transverse mode of the oscillation light are simultaneously displayed. It contains an oxidized constriction structure that can be confined. The selective oxidation layer has a thickness of 28 nm, and the temperature at which the threshold current is minimized is about 17 ° C. Thereby, it becomes possible to suppress the “negative droop characteristic” regardless of the pulse period.

  Further, when a square wave current pulse having a pulse period of 1 ms and a pulse width of 500 μs is supplied, (P1−P2) /P2=−0.05, and it is possible to further suppress the “negative droop characteristic”. Become.

  Further, in the surface emitting laser element 100, the transverse optical confinement factor of the fundamental transverse mode in the oxidized constriction structure at room temperature is about 0.974, and the “negative droop characteristic” can be further improved.

  Further, in the surface emitting laser element 100, when only the temperature of the current injection portion in the resonator structure is changed from room temperature to 60 ° C., the rate of change of the optical confinement coefficient is 2.2%, and “negative droop characteristic” Can be further improved.

  Further, in the surface emitting laser element 100, the gain peak wavelength in the oscillation threshold current at room temperature is 2 nm longer than the resonance wavelength of the resonator structure, so that the “negative droop characteristic” can be further improved.

“Second Embodiment”
FIG. 25 is a sectional view showing a schematic configuration of the surface emitting laser element 100A according to the second embodiment of the present invention.

  The surface-emitting laser element 100A is a surface-emitting laser element having a design oscillation wavelength of 780 nm band. On the substrate 201, a buffer layer 202, a lower semiconductor DBR 203, a lower spacer layer 204, an active layer 205, an upper spacer layer 206, A plurality of semiconductor layers such as the upper semiconductor DBR 207 and the contact layer 209 are sequentially stacked. Hereinafter, a structure in which the plurality of semiconductor layers are stacked is also referred to as a “second stacked body” for convenience.

  The substrate 201 is an n-GaAs single crystal substrate, and is a so-called tilted substrate in which the normal direction of the main surface is tilted by 15 ° in the [111] A direction with respect to the [100] direction.

  The buffer layer 202 is a layer made of n-GaAs.

The lower semiconductor DBR 203 has 40.5 pairs of a low refractive index layer made of n-AlAs and a high refractive index layer made of n-Al _0.3 Ga _0.7 As. And between each refractive index layer, in order to reduce an electrical resistance, the composition inclination layer of thickness 20nm which changed the composition gradually toward the other composition from one composition is provided. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

The lower spacer layer 204 is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  The active layer 205 has a quantum well layer made of GaInAsP and a barrier layer made of GaInP.

  By the way, the quantum well layer is obtained by introducing As into a GaInP mixed crystal in order to obtain an oscillation wavelength in the 780 nm band, and has a compressive strain. The barrier layer increases the band gap by introducing tensile strain, realizes high carrier confinement, and forms a strain compensation structure for the quantum well layer. The composition of the quantum well layer is set such that the oscillation wavelength at the CW oscillation threshold current in the end face LD structure is equal to the resonance wavelength of the surface emitting laser element. That is, the PL wavelength is adjusted to be 770 nm in consideration of the difference (about 10 nm) from the end face LD oscillation wavelength.

  Here, since an inclined substrate is used as the substrate 201, anisotropy is introduced into the gain in the active layer, and the polarization direction can be aligned in a specific direction (polarization control).

The upper spacer layer 206 is a layer made of non-doped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P.

  A portion composed of the lower spacer layer 204, the active layer 205, and the upper spacer layer 206 is also called a resonator structure, and the thickness thereof is set to be an optical thickness of one wavelength. The active layer 205 is provided at the center of the resonator structure, which is a position corresponding to the antinode in the standing wave distribution of the electric field, so that a high stimulated emission probability can be obtained. This resonator structure is sandwiched between the lower semiconductor DBR 203 and the upper semiconductor DBR 207.

  The upper semiconductor DBR 207 includes a first upper semiconductor DBR 207a and a second upper semiconductor DBR 207b.

The first upper semiconductor DBR 207a includes a low refractive index layer made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and p- (Al _0.1 Ga _0.9 ) _0.5. One pair of high refractive index layers made of In _0.5 P (also referred to as “first pair”) is included. The first upper semiconductor DBR 207a has a larger band gap energy than the AlGaAs layer, and functions as a block layer for electrons injected into the active region.

  Here, since an inclined substrate is used for the substrate 201, generation of hill-like defects (hillocks) of the AlGaInP material can be suppressed, crystallinity can be improved, and generation of natural superlattices can be suppressed, A decrease in gap energy can be prevented. Therefore, the first upper semiconductor DBR 207a can keep a large band gap energy and functions well as an electron blocking layer.

The second upper semiconductor DBR 207b includes a pair of a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index layer made of p-Al _0.3 Ga _0.7 As (“second 23 pairs) (also referred to as “pairs”).

  Between each refractive index layer in the upper semiconductor DBR, there is provided a composition gradient layer having a thickness of 20 nm in which the composition is gradually changed from one composition to the other composition in order to reduce electric resistance. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ.

  The contact layer 209 is a layer made of p-GaAs.

  Next, a method for manufacturing the surface emitting laser element 100A will be briefly described.

(2-1) The second laminate is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxial growth (MBE). At this time, a selective oxidation layer made of p-AlAs in the middle of the second upper semiconductor DBR 207b and at the position of the third standing wave node from the active layer 205 (third pair from the resonator structure). Is inserted at a thickness of 30 nm.

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and arsine (AsH ₃ ) gas is used as Group V materials. Further, carbon tetrabromide (CBr ₄ ) is used as a p-type dopant material, and hydrogen selenide (H ₂ Se) is used as an n-type dopant material. A phosphine (PH ₃ ) gas is used as the Group V P raw material for the AlGaInAsP-based material, and dimethyl zinc (DMZn) is used as the p-type dopant raw material for AlGaInP.

  In addition, in a plurality of layers (region A in FIG. 26) close to the resonator structure in the lower semiconductor DBR 203, the doping concentration of the n-type dopant is adjusted to be relatively low with respect to other regions. is doing.

Specifically, in the lower semiconductor DBR 203, four pairs from the region in contact with the lower spacer layer 204 are set as a low doping concentration region, and the doping concentration is relatively low with respect to the remaining 37.5 pairs. Specifically, in the low doping concentration region, the doping concentration is ³ to 7.5 × 10 ¹⁷ [cm ⁻³ ] at a site corresponding to the constant composition layer (each refractive index layer) and the antinode of the standing wave distribution. ] In the range of 3 × 10 ¹⁷ to 1 × 10 ¹⁸ [cm ⁻³ ] in the region corresponding to the node of the standing wave distribution. For the remaining 37.5 pairs, the doping concentration of the portion corresponding to the anti-constant layer (each refractive index layer) and the antinode of the standing wave distribution is within the range of 1 to 3 × 10 ¹⁸ [cm ⁻³ ]. The doping concentration of the portion corresponding to the node of the standing wave distribution is adjusted within the range of 1 to 5 × 10 ¹⁸ [cm ⁻³ ].

  In the layer close to the resonator structure in the first upper semiconductor DBR 207a and the second upper semiconductor DBR 207b (region B in FIG. 26), the doping concentration of the p-type dopant is relative to other regions. The concentration is adjusted to be low.

Specifically, in the upper semiconductor DBR, four pairs from the region in contact with the upper spacer layer 206 are set as a low doping concentration region, and the doping concentration is relatively low with respect to the remaining 20 pairs. The specific doping concentration is about 2 to 1.3 × 10 ¹⁸ [cm ⁻³ ] in the region corresponding to the anti-constant layer (each refractive index layer) and the antinode of the standing wave distribution in the low doping concentration region. Within the range, the region corresponding to the node of the standing wave distribution is in the range of 2 × 10 ¹⁷ to 4 × 10 ¹⁸ [cm ⁻³ ]. For the remaining 20 pairs, the doping concentration of the portion corresponding to the anti-composition layer (each refractive index layer) and the antinode of the standing wave distribution is 1 × 10 ^{18 to} 1.5 × 10 ¹⁸ [cm ⁻³ ]. Within the range, the doping concentration of the portion corresponding to the node of the standing wave distribution is set to 4 × 10 ¹⁸ [cm ⁻³ ] or more.

(2-2) A square resist pattern having a side of 25 μm is formed on the surface of the laminate.

(2-3) A square columnar mesa is formed by using an ECR etching method using Cl ₂ gas and a square resist pattern as a photomask. Here, the bottom surface of the etching is located in the lower spacer layer 204.

(2-4) The photomask is removed.

(2-5) The second laminate is heat-treated in water vapor to selectively oxidize a part of the selectively oxidized layer in the mesa. Then, an unoxidized region 208b surrounded by the oxide layer 208a is left in the center of the mesa. As a result, an oxidized constriction structure is formed that restricts the drive current path of the light emitting part to only the central part of the mesa. The non-oxidized region 208b is a current passage region (current injection region). Here, one side of the current passage region is 4 μm.

(2-6) The protective layer 211 made of SiO ₂ is formed by using a chemical vapor deposition method (CVD method).

(2-7) Open P-side electrode contact window on top of mesa. Here, after masking with a photoresist, the opening at the top of the mesa is exposed to remove the photoresist at that portion, and then the protective layer 211 is etched and opened with BHF.

(2-8) A square resist pattern having a side of 10 μm is formed in a region to be a light emitting portion on the upper part of the mesa, and a p-side electrode material is deposited. As the electrode material on the p side, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(2-9) The electrode material of the light emitting part is lifted off to form the p-side electrode 213.

(2-10) After polishing the back side of the substrate 201 to a predetermined thickness (for example, about 100 μm), the n-side electrode 214 is formed. Here, the n-side electrode 214 is a multilayer film made of AuGe / Ni / Au.

(2-11) Ohmic conduction is established between the p-side electrode 213 and the n-side electrode 214 by annealing. Thereby, the mesa becomes a light emitting part.

(2-12) Cut for each chip.

  When a square wave current pulse having a pulse period of 1 ms and a pulse width of 500 μs was supplied to the surface emitting laser element 100A thus manufactured, the droop rate was −1%.

  Further, in the surface emitting laser element 100A, the optical confinement coefficient in the fundamental transverse mode at room temperature was 0.978.

  As described above, in order to suppress the “negative droop characteristic” in the surface emitting laser element having the oxidized constriction structure, the optical confinement in the transverse mode is performed against the refractive index change caused by the local temperature change inside the element. It is effective to set a large optical confinement factor by the oxide layer so as to be strong. However, when the optical confinement factor is increased, the optical confinement is good not only for the fundamental transverse mode but also for the higher order transverse mode, and higher order mode oscillation is likely to occur. Therefore, suppression of “negative droop characteristics” and improvement of single mode output are in a trade-off relationship.

  FIG. 27 shows the relationship between the optical confinement factor of the fundamental (0th order) transverse mode and the diameter of the mesa in the surface emitting laser element structure having an oscillation wavelength band of 780 nm. The primary transverse mode is one of the higher order transverse modes. The relationship between the mode optical confinement factor and the mesa diameter is shown in FIG. 27 and 28, the selective oxidation layer having a thickness of 30 nm is provided in the third pair from the resonator structure in the semiconductor DBR, and at the position of the node of the standing wave distribution. The oxidized constriction diameter is 4 μm, and the surface emitting laser element structure is entirely at room temperature.

  First, referring to FIG. 27, by setting the thickness of the selectively oxidized layer to 30 nm, the optical confinement coefficient in the fundamental transverse mode is 0.9 or more in the range of the mesa diameter of 15 to 30 μm. It is possible to effectively suppress the “droop characteristics”. In addition, referring to FIG. 28, it can be seen that the optical confinement factor tends to decrease as the mesa diameter increases. Since the primary transverse mode is orthogonal to the fundamental transverse mode, the spatial overlap with the fundamental transverse mode (that is, the spatial overlap with the current injection region) can be reduced by increasing the size of the mesa. . FIG. 29 shows this state, and shows the electric field strength distribution of each primary transverse mode when the mesa diameter is 18 μm and 25 μm. As shown in FIG. 29, the electric field strength distribution is shifted to the periphery by increasing the diameter of the mesa.

  The optical confinement factor of the primary transverse mode is an index indicating the ease of oscillation of the primary transverse mode, and the smaller the value, the more difficult the primary transverse mode oscillates. Therefore, by increasing the diameter of the mesa, the oscillation of the primary transverse mode is suppressed and the single mode output is increased.

  As shown in FIG. 28, the optical confinement factor of the first-order transverse mode decreases as the mesa diameter increases, but shows a saturation tendency when the mesa diameter is 22 μm or more. In other words, the size of the mesa diameter of 22 μm is an important value that greatly changes the behavior of the first-order transverse mode. Accordingly, in the case of a cylindrical mesa, the diameter is 22 μm or more, and in the case of a quadrangular prism-shaped mesa, the length of one side of a quadrangle (cross section) is set to 22 μm or more, thereby effectively oscillating the primary transverse mode. It is possible to suppress. In addition, since the optical confinement coefficient of the fundamental transverse mode at this time maintains a value of 0.9 or more (see FIG. 27), it is possible to improve the single mode output while suppressing the “negative droop characteristic”. Is possible.

  Further, as described above, the “negative droop characteristic” occurs due to a local temperature change in the center of the mesa. Therefore, the first method of suppressing the “negative droop characteristic” is to increase the optical confinement coefficient at room temperature to improve the stability of the transverse mode distribution due to local temperature change in the center of the mesa. The second method is to suppress a local temperature rise in the central part of the mesa.

  Specifically, the second method is to improve the power conversion efficiency of the surface emitting laser element and reduce the heat generation inside the surface emitting laser element. By the way, in a semiconductor material, there exists an absorption process (hereinafter also referred to as “free carrier absorption”) due to free carriers, which is one factor that decreases power conversion efficiency. The light energy absorbed by free carrier absorption becomes carrier kinetic energy and is finally converted into lattice vibration energy, so that free carrier absorption itself increases the temperature in the vicinity of the center of the mesa. Free carrier absorption depends on the electric field strength and carrier concentration of light, and becomes more significant as the carrier concentration is higher and the electric field strength is higher.

  The electric field intensity of the oscillation light in the surface emitting laser element is large in the vicinity of the active layer and gradually attenuates as the distance from the active layer increases. Therefore, when free carrier absorption occurs at a high electric field strength, the power conversion efficiency is greatly reduced and heat generation is increased.

  Furthermore, if free carrier absorption is large, it is necessary to increase the injection current into the active layer in order to compensate for the energy of the absorbed light (decrease in light output). The internal temperature of the light emitting laser element is further raised.

  Therefore, when the doping concentration in the region having a large electric field strength adjacent to the resonator structure of the semiconductor DBR is relatively low with respect to other regions, free carrier absorption is reduced, and the surface emitting laser element is reduced. It is possible to improve the power conversion efficiency. As a result, local temperature rise inside the surface emitting laser element can be reduced, so that the cause of “negative droop characteristics” such as changes in the fundamental transverse mode distribution and detuning amount can be reduced. Is possible.

  In the surface emitting laser element having the oxidized constricting structure, the current injection region of the active layer is limited to a relatively small region by the oxide layer, and thus the current passing region in the oxidized constricting structure is likely to have a high resistance. In addition, since the current passing region necessarily has a spatial overlap with the light emitting region, there is a possibility that the current passing region generates heat due to current injection, and the temperature of the light emitting region at the center of the mesa increases. As described above, this temperature rise causes “negative droop characteristics”.

  The inventors have taken into consideration the optical confinement factor of the fundamental transverse mode, the heat generation inside the device, the influence of the stress of the oxide layer, etc., and the details of the device structure with less negative droop characteristics and excellent long-term reliability It was examined. As a result, the position of the selectively oxidized layer is set in the third or fourth pair of semiconductor DBRs from the resonator structure (the position corresponding to the third or fourth node from the active layer in the standing wave distribution). It was found to be effective.

  Since the oxide layer in the oxide confinement structure has a function of simultaneously performing current confinement and optical confinement, it is advantageous to be closer to the active layer for the purpose of reducing the threshold current. In addition, if the oxide layer has the same thickness and the same oxidized constriction diameter, the optical confinement factor of the fundamental transverse mode can be increased closer to the active layer, which is effective in suppressing “negative droop characteristics”.

  However, it has been found that an element in which the position of the selective oxidation layer is the first pair and the second pair from the resonator structure has difficulty in terms of long-term reliability. Normally, the volume of the selective oxidation layer shrinks in the selective oxidation process. Further, the oxidized constriction structure has a large resistance, and becomes a heat source when energized. Therefore, in the structure in which the selective oxidation layer is provided in the first pair or the second pair from the resonator structure, the stress due to the contraction of the selective oxidation layer and the heat from the oxidation constriction structure may affect the active layer. There is. In this case, the occurrence and proliferation of dislocations in the active layer became significant, and the lifetime of the surface emitting laser element was short.

  On the other hand, when the position of the selective oxidation layer is the third pair or the fourth pair from the resonator structure, the lifetime of the surface emitting laser element is significantly increased, and sufficient reliability can be obtained.

  However, when the position of the selective oxidation layer is set to the fifth pair or more from the resonator structure, the threshold current increases and the input power increases, so that the amount of heat generated inside the surface emitting laser element increases, There was a tendency for the “droop characteristics” to increase slightly.

  As described above, by reducing the position of the selective oxidation layer to the third or fourth pair from the resonator structure, it is possible to simultaneously realize the reduction of “negative droop characteristics” and the improvement of long-term reliability. I found it possible.

  As described above, according to the surface emitting laser element 100A according to the second embodiment, the resonator structure including the active layer 205 and the semiconductor DBR (lower semiconductor) provided with the resonator structure interposed therebetween. DBR 203 and upper semiconductor DBR 207). In the upper semiconductor DBR 207, the oxide layer 208a including at least an oxide generated by oxidizing a part of the selective oxidation layer including Al surrounds the current passing region 208b, and the injection current and the transverse mode of the oscillation light are simultaneously displayed. It contains an oxidized constriction structure that can be confined. The thickness of the selective oxidation layer is 30 nm, and when a square wave current pulse with a pulse period of 1 ms and a pulse width of 500 μs is supplied, (P1−P2) /P2=−0.01. Thereby, it becomes possible to suppress the “negative droop characteristic” regardless of the pulse period.

  Further, in the surface emitting laser element 100A, a partial region of the semiconductor DBR adjacent to the resonator structure has a low doping concentration. The electric field strength in the semiconductor DBR is halved at about the fourth pair from the active layer. Therefore, free carrier absorption can be effectively reduced by setting the doping concentration in a region with a large electric field strength to a low concentration. Since the absorption loss is reduced, the oscillation threshold current is reduced and the slope efficiency is improved, so that the drive current can be reduced. That is, since less input power is required, heat generation can be reduced. Therefore, the “negative droop characteristic” can be further suppressed.

  It should be noted that the doping concentration may be different between the constant composition layer (each refractive index layer) and the portion corresponding to the antinode of the standing wave distribution within the above range. Further, in the low doping concentration region, the doping concentration may be different for each pair within the above range. For example, in a low doping concentration region, free carrier absorption can be effectively reduced by setting a region close to the spacer layer and having a large electric field strength to have a lower concentration.

  Further, in the surface emitting laser element 100A, since the length of one side in the cross-sectional shape orthogonal to the laser oscillation direction of the mesa is 25 μm, the single mode output can be increased to 2 mW.

  Further, in the surface emitting laser element 100A, the selective oxidation layer is provided in the third pair of upper semiconductor DBRs 207 from the resonator structure. As a result, while maintaining a practical threshold current, the portion that generates heat due to the high resistance accompanying current confinement can be moved away from the active layer 205, the thermal resistance can be reduced, and local heat generation in the center of the mesa can be reduced. . In addition, the influence of strain inherent in the oxide layer 208a on the active layer 205 can be reduced, the device life can be extended, and long-term reliability can be improved. Note that the selective oxidation layer may be provided in the upper semiconductor DBR 207 in the fourth pair from the resonator structure.

“Third Embodiment”
FIG. 30 shows a schematic configuration of a surface emitting laser array 500 according to the third embodiment of the present invention.

  In the surface emitting laser array 500, a plurality (32 in this case) of light emitting units are arranged on the same substrate. Here, the description will be made assuming that the right direction in FIG. 30 is the + M direction and the downward direction is the + S direction.

  As shown in FIG. 31, the surface-emitting laser array 500 includes eight light emitting units along the T direction, which is a direction that forms an inclination angle α (0 ° <α <90 °) from the M direction toward the S direction. Have four rows of light emitting sections arranged at equal intervals. These four light emitting section rows are arranged at equal intervals d in the S direction so that they are equally spaced c when all the light emitting sections are orthogonally projected onto a virtual line extending in the S direction. That is, the 32 light emitting units are two-dimensionally arranged. In this specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

  Here, the interval c is 3 μm, the interval d is 24 μm, and the light emitting portion interval X in the M direction (see FIG. 31) is 30 μm.

  Each light emitting portion has the same structure as the surface emitting laser element 100 described above, as shown in FIG. The surface emitting laser array 500 can be manufactured by a method similar to that of the surface emitting laser element 100 described above.

  Thus, since the surface emitting laser array 500 according to the third embodiment is a surface emitting laser array in which the surface emitting laser elements 100 are integrated, the same effects as the surface emitting laser element 100 can be obtained. Can do.

  In addition, it is preferable that the groove | channel between two light emission parts shall be 5 micrometers or more for the electrical and spatial separation of each light emission part. This is because if it is too narrow, it becomes difficult to control etching during production. Further, the mesa size (length of one side) is preferably 10 μm or more. This is because if it is too small, heat will be accumulated during operation and the characteristics may be deteriorated.

  In the third embodiment, the surface emitting laser array has 32 light emitting units. However, the present invention is not limited to this.

  Further, a surface emitting laser array in which the surface emitting laser elements 100A are integrated may be used.

  In the first to third embodiments, the case where the mesa shape in the cross section perpendicular to the laser oscillation direction is square has been described. However, the present invention is not limited to these, and for example, a circle, an ellipse, or a rectangle It can be of any shape.

  Moreover, although the said 1st-3rd embodiment demonstrated the case where the oscillation wavelength of a light emission part was a 780 nm band, it is not limited to this. For example, wavelength bands such as a 650 nm band, an 850 nm band, a 980 nm band, a 1.3 μm band, and a 1.5 μm band may be used.

“Fourth Embodiment”
FIG. 33 shows a schematic configuration of a laser printer 1000 as an image forming apparatus according to the fourth embodiment of the present invention.

  The laser printer 1000 includes an optical scanning device 1010, a photosensitive drum 1030, a charging charger 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, a toner cartridge 1036, a paper feeding roller 1037, a paper feeding tray 1038, A registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, a communication control device 1050, a printer control device 1060 that comprehensively controls the above-described units, and the like are provided. These are housed in predetermined positions in the printer housing 1044.

  The communication control device 1050 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The photosensitive drum 1030 is a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. The photosensitive drum 1030 rotates in the direction of the arrow in FIG.

  The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning unit 1035 are each disposed in the vicinity of the surface of the photosensitive drum 1030. Then, along the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in this order.

  The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030.

  The optical scanning device 1010 irradiates the surface of the photosensitive drum 1030 charged by the charging charger 1031 with a light beam modulated based on image information from the host device. As a result, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 1030. The latent image formed here moves in the direction of the developing roller 1032 as the photosensitive drum 1030 rotates. The configuration of the optical scanning device 1010 will be described later.

  The toner cartridge 1036 stores toner, and the toner is supplied to the developing roller 1032.

  The developing roller 1032 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030 to visualize the image information. Here, the latent image to which the toner is attached (hereinafter also referred to as “toner image” for the sake of convenience) moves in the direction of the transfer charger 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038, and the paper feed roller 1037 takes out the recording paper 1040 one by one from the paper feed tray 1038 and conveys it to the registration roller pair 1039. The registration roller pair 1039 temporarily holds the recording paper 1040 taken out by the paper supply roller 1037, and in the gap between the photosensitive drum 1030 and the transfer charger 1033 according to the rotation of the photosensitive drum 1030. Send it out.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording sheet 1040 transferred here is sent to the fixing roller 1041.

  In the fixing roller 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. The recording paper 1040 fixed here is sent to the paper discharge tray 1043 via the paper discharge roller 1042 and is sequentially stacked on the paper discharge tray 1043.

  The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030.

  The cleaning unit 1035 removes the toner remaining on the surface of the photosensitive drum 1030 (residual toner). The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position facing the charging charger 1031 again.

  Next, the configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 34 as an example, the optical scanning device 1010 includes a deflector side scanning lens 11a, an image plane side scanning lens 11b, a polygon mirror 13, a light source 14, a coupling lens 15, an aperture plate 16, an anamorphic. A lens 17, a reflection mirror 18, a scanning control device (not shown), and the like are provided. These are assembled at predetermined positions in the housing 30.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 14 includes the surface-emitting laser array 500 as an example, and can emit 32 light beams simultaneously. Here, the surface emitting laser array 500 is arranged so that the M direction coincides with the main scanning corresponding direction and the S direction coincides with the sub scanning corresponding direction.

  The coupling lens 15 makes the light beam emitted from the light source 14 weak divergent light.

  The aperture plate 16 has an aperture and defines the beam diameter of the light beam through the coupling lens 15.

  The anamorphic lens 17 forms an image of the light beam that has passed through the opening of the aperture plate 16 in the sub-scanning corresponding direction in the vicinity of the deflection reflection surface of the polygon mirror 13 via the reflection mirror 18.

  The optical system arranged on the optical path between the light source 14 and the polygon mirror 13 is also called a pre-deflector optical system. In the fourth embodiment, the pre-deflector optical system includes a coupling lens 15, an aperture plate 16, an anamorphic lens 17, and a reflection mirror 18.

  As an example, the polygon mirror 13 has a hexahedral mirror having an inscribed circle radius of 18 mm, and each mirror serves as a deflecting reflection surface. The polygon mirror 13 deflects the light flux from the reflection mirror 18 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The deflector-side scanning lens 11 a is disposed on the optical path of the light beam deflected by the polygon mirror 13.

  The image plane side scanning lens 11b is disposed on the optical path of the light beam via the deflector side scanning lens 11a. Then, the light beam that has passed through the image plane side scanning lens 11b is irradiated onto the surface of the photosensitive drum 1030, and a light spot is formed. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 13 rotates. That is, the photoconductor drum 1030 is scanned. The moving direction of the light spot at this time is the “main scanning direction”. The rotation direction of the photosensitive drum 1030 is the “sub-scanning direction”.

  The optical system arranged on the optical path between the polygon mirror 13 and the photosensitive drum 1030 is also called a scanning optical system. In the fourth embodiment, the scanning optical system includes a deflector side scanning lens 11a and an image plane side scanning lens 11b. At least one folding mirror is disposed on at least one of the optical path between the deflector side scanning lens 11a and the image plane side scanning lens 11b and the optical path between the image plane side scanning lens 11b and the photosensitive drum 1030. May be.

  In the surface emitting laser array 500, since the intervals between the light emitting portions when the respective light emitting portions are orthogonally projected onto a virtual line extending in the sub-scanning corresponding direction are equal intervals c, the lighting timing is adjusted to adjust the light emitting portions on the photosensitive drum 1030. It can be considered that the configuration is the same as the case where the light emitting units are arranged at equal intervals in the sub-scanning direction.

  Since the distance c is 3 μm, if the magnification of the optical system of the optical scanning device 1010 is about 1.8, high-density writing of 4800 dpi (dot / inch) can be performed. Of course, it is possible to increase the density by increasing the number of light emitting portions in the main scanning direction, making the array arrangement in which the distance d is narrowed and the distance c is further reduced, or by reducing the magnification of the optical system. Quality printing is possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

  In this case, the laser printer 1000 can perform printing without decreasing the printing speed even if the writing dot density increases. Further, when the writing dot density is the same, the printing speed can be further increased.

  As described above, according to the optical scanning device 1010 according to the fourth embodiment, since the light source 14 includes the surface-emitting laser array 500, high-accuracy optical scanning can be performed.

  In addition, according to the laser printer 1000 according to the fourth embodiment, since the optical scanning device 1010 is provided, it is possible to form a high-quality image as a result.

  In the fourth embodiment, the light source 14 has 32 light emitting units. However, the present invention is not limited to this.

  In the fourth embodiment, the light source 14 has a surface emitting laser array. However, the present invention is not limited to this, and is equivalent to the surface emitting laser element 100 or the surface emitting laser element 100A. You may have a surface emitting laser element.

  In the fourth embodiment, instead of the surface emitting laser array 500, a surface emitting laser array in which light emitting units similar to the light emitting units in the surface emitting laser array 500 are arranged one-dimensionally may be used.

  In the fourth embodiment, instead of the surface emitting laser array 500, a surface emitting laser array in which the surface emitting laser elements 100A are integrated may be used.

  In the fourth embodiment, the case of the laser printer 1000 as the image forming apparatus has been described. However, the present invention is not limited to this. In short, an image forming apparatus including the optical scanning device 1010 can form a high-quality image as a result.

  For example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  As an example, as shown in FIG. 35, a color printer 2000 including a plurality of photosensitive drums may be used.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow). The black “photosensitive drum K1, charging device K2, "Developing device K4, cleaning unit K5, and transfer device K6", cyan "photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6", and magenta "photosensitive drum" M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6 ”,“ photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6 ”for yellow, and light A scanning device 2010, a transfer belt 2080, a fixing unit 2030, and the like are provided.

  Each photoconductor drum rotates in the direction of the arrow in FIG. 35, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photoconductor drum along the rotation direction. Each charging device uniformly charges the surface of the corresponding photosensitive drum. The surface of each photoconductive drum charged by the charging device is irradiated with light by the optical scanning device 2010, and an electrostatic latent image is formed on each photoconductive drum. Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is transferred onto the recording paper on the transfer belt 2080 by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 2030.

  The optical scanning device 2010 has a light source similar to the light source 14 for each color. Therefore, the same effect as that of the optical scanning device 1010 can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, the same effect as the laser printer 1000 can be obtained.

  By the way, in the color printer 2000, color misregistration may occur due to a manufacturing error or a position error of each component. However, since the optical scanning device 2010 includes a plurality of light emitting units arranged two-dimensionally, it is turned on. By selecting the light emitting unit to be used, the color misregistration correction accuracy can be increased.

  As described above, the surface-emitting laser element and the surface-emitting laser array of the present invention are suitable for suppressing “negative droop characteristics”. Moreover, the optical scanning device of the present invention is suitable for performing high-precision optical scanning. The image forming apparatus of the present invention is suitable for forming a high quality image.

It is a figure for demonstrating schematic structure of the surface emitting laser element which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the relationship between the thickness of a to-be-selected oxidation layer in a surface emitting laser element at 25 degreeC, and a droop rate. It is a figure for demonstrating the optical waveform when the conventional surface emitting laser element is driven by the square wave current pulse of 1 ms of pulse periods and 50% of a duty. It is a figure for demonstrating the optical waveform when the conventional surface emitting laser element is driven by the square wave current pulse of pulse period 100ns and duty 50%. It is a figure for demonstrating each refractive index used for calculation. It is a figure for demonstrating the fundamental transverse mode distribution obtained by calculation. It is a figure for demonstrating built-in effective refractive index difference (DELTA) neff. FIG. 8A and FIG. 8B are diagrams for explaining the built-in effective refractive index difference Δneff, respectively. FIG. 9A and FIG. 9B are diagrams for explaining the effective refractive index difference Δneff when the internal temperature rises. It is a figure for demonstrating the shift of the IL curve by the raise of internal temperature in the surface emitting laser element with insufficient light confinement of the horizontal direction at room temperature. It is a figure for demonstrating the optical waveform at the time of FIG. FIG. 6 is a diagram (part 1) for explaining the relationship between the optical confinement coefficient, the thickness of the selective oxidation layer, and the oxidized constriction diameter. FIG. 6 is a diagram (part 2) for explaining the relationship between the optical confinement factor, the thickness of the selective oxidation layer, and the oxidized constriction diameter. FIG. 6 is a diagram (No. 3) for explaining the relationship between the optical confinement factor, the thickness of the selective oxidation layer, and the oxidized constriction diameter; It is a figure for demonstrating the optical waveform of the surface emitting laser element in which the optical confinement coefficient of a fundamental transverse mode in 25 degreeC is about 0.983. It is a figure for demonstrating the optical waveform of the surface emitting laser element in which the optical confinement coefficient of a fundamental transverse mode in 25 degreeC is about 0.846. In the surface emitting laser element in which the optical confinement coefficient at 27 ° C. is about 0.788, it is a diagram for explaining the change in the fundamental transverse mode distribution when only the temperature of the current injection portion in the resonance region becomes 60 ° C. is there. It is a figure for demonstrating the heat_generation | fever area | region in FIG. In the surface emitting laser element in which the optical confinement coefficient at 27 ° C. is about 0.973, it is a diagram for explaining the change in the fundamental transverse mode distribution when only the temperature of the current injection portion in the resonance region becomes 60 ° C. is there. It is a figure for demonstrating the relationship between the change rate of an optical confinement coefficient, and the thickness of a to-be-selected oxidation layer when only the current injection part in a resonance area | region changes from 27 degreeC to 60 degreeC. FIG. 21A is a diagram for explaining Δλ ₀ > 0, and FIG. 21B is a diagram for explaining Δλ ₀ <0. It is a figure for demonstrating the relationship between an oscillation threshold current and measured temperature. It is a figure for demonstrating the relationship between the amount of detuning and the temperature where threshold current becomes the minimum. It is a figure for demonstrating the relationship between droop rate and the temperature from which threshold current becomes the minimum. It is a figure for demonstrating schematic structure of the surface emitting laser element which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating a low doping concentration area | region. It is a figure for demonstrating the relationship between the optical confinement coefficient of a fundamental (0th order) transverse mode, and a mesa diameter. It is a figure for demonstrating the relationship between the optical confinement coefficient of a primary transverse mode, and a mesa diameter. It is a figure for demonstrating the difference in the electric field strength distribution of the primary transverse mode by the difference in mesa diameter. It is a figure for demonstrating the surface emitting laser array which concerns on the 3rd Embodiment of this invention. It is a figure for demonstrating the two-dimensional arrangement | sequence of the light emission part in FIG. It is AA sectional drawing of FIG. It is a figure for demonstrating schematic structure of the laser printer which concerns on the 4th Embodiment of this invention. It is the schematic which shows the optical scanning device in FIG. It is a figure for demonstrating schematic structure of a color printer. It is a figure for demonstrating the optical waveform of the conventional surface emitting laser element. FIG. 37 is an enlarged view of the vicinity of the rise in FIG. 36.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11a ... Deflector side scanning lens (a part of scanning optical system), 11b ... Image surface side scanning lens (a part of scanning optical system), 13 ... Polygon mirror (deflector), 14 ... Light source, 100 ... Surface emitting laser Element 100A ... Surface emitting laser element 103 ... Lower semiconductor DBR (part of semiconductor distributed Bragg reflector) 104 ... Lower spacer layer (part of resonator structure) 105 ... Active layer 106 ... Upper spacer layer (Part of the resonator structure), 107 ... upper semiconductor DBR (part of the semiconductor distributed Bragg reflector), 108a ... oxide layer (part of the constriction structure), 108b ... current passing region (one part of the constriction structure) Part), 203 ... lower semiconductor DBR (part of semiconductor distributed Bragg reflector), 204 ... lower spacer layer (part of resonator structure), 205 ... active layer, 206 ... upper spacer layer (of resonator structure) part 207, upper semiconductor DBR (part of the semiconductor distributed Bragg reflector), 208a, oxide layer (part of the constricted structure), 208b, current passing region (part of the constricted structure), 500, surface emitting laser array , 1000 ... Laser printer (image forming apparatus), 1010 ... Optical scanning apparatus, 1030 ... Photosensitive drum (image carrier), 2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning apparatus, K1, C1, M1, Y1... Photosensitive drum (image carrier).

Claims (12)

A surface emitting laser element that emits light in a direction perpendicular to a substrate,
A resonator structure including an active layer;
An oxide including at least an oxide generated by oxidizing a part of the selective oxidation layer containing aluminum, which is provided across the resonator structure, surrounds the current passing region, and a transverse mode of injected current and oscillation light. A semiconductor distributed Bragg reflector including therein a constricted structure capable of simultaneously confining
The selectively oxidized layer has a thickness of at least 25 nm;
A surface emitting laser element characterized in that the temperature at which the oscillation threshold current is minimized is 25 ° C. or less in the relationship between the oscillation threshold current and the temperature.   When a square wave current pulse having a pulse period of 1 ms and a pulse width of 500 μs is supplied, the optical output P1 at 10 ns after supply and the optical output P2 at 1 μs after supply are used, and (P1−P2) / P2 ≧ − The surface emitting laser element according to claim 1, wherein a relationship of 0.1 is satisfied. Using the width d [μm] of the current passing region and the thickness t [nm] of the oxide surrounding the current passing region, −2.54d ² −0.14t ² −0.998d · t + 53.4d + 112. The surface emitting laser element according to claim 1, wherein a relationship of 9t−216 ≧ 0.9 is satisfied.   When only the temperature of the current injection part in the resonator structure is changed from room temperature to 60 ° C., the change rate of the optical confinement coefficient in the transverse direction of the fundamental transverse mode in the constriction structure is 10% or less. 4. The surface emitting laser element according to claim 2, wherein A part of the plurality of semiconductor layers including the resonator structure and the semiconductor distributed Bragg reflector has a columnar or quadrangular columnar mesa shape extending in the light emission direction,
5. The surface-emitting laser element according to claim 1, wherein a diameter of the cylinder or a length of one side of the quadrangular column in a cross section perpendicular to the laser oscillation direction is at least 22 μm. .   The impurity doping concentration in the region adjacent to the resonator structure in the semiconductor distributed Bragg reflector is relatively lower than the impurity doping concentration in other regions in the semiconductor distributed Bragg reflector. The surface emitting laser element according to claim 1, wherein the surface emitting laser element is characterized in that The semiconductor distributed Bragg reflector has a plurality of pairs consisting of a low refractive index layer and a high refractive index layer,
The said selective oxidation layer is provided in the said semiconductor structure Bragg reflector in the 3rd pair or the 4th pair from the said resonator structure, The Claim 1 characterized by the above-mentioned. The surface emitting laser element described.   A surface emitting laser array in which the surface emitting laser elements according to any one of claims 1 to 7 are integrated. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the surface emitting laser element according to claim 1;
A deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the deflector onto the surface to be scanned. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the surface emitting laser array according to claim 8;
A deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the deflector onto the surface to be scanned. At least one image carrier;
An image forming apparatus comprising: at least one optical scanning device according to claim 9 or 10 that scans light including image information on the at least one image carrier.   The image forming apparatus according to claim 11, wherein the image information is multicolor image information.

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