JP2008227469A - Red surface emitting laser element, image forming apparatus, and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel red surface emitting laser element that can decrease the amount of leakage current. <P>SOLUTION: A red surface emitting laser element 3000 constituted of a multilayer film includes a first reflector 302, a second reflector 308 constituted of a p-type semiconductor multilayer film, an active layer 305 between the first reflector and the second reflector, and a p-type semiconductor spacer layer 307 between the active layer and the second reflector, the p-type semiconductor spacer layer having a thickness of 100 nm or more and 350 nm or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a red surface emitting laser element, an image forming apparatus using the red surface emitting laser element, and an image display device.

A. Usefulness of Red Surface Emitting Laser Element A surface emitting laser element (particularly a vertical cavity surface emitting laser is called VCSEL) can extract light in a direction perpendicular to the surface of a semiconductor substrate, and is a two-dimensional array. It is said that it is relatively easy to realize.

  When a two-dimensional array is formed, parallel processing is possible by the emitted multi-beams, and therefore various industrial applications are expected with the intention of increasing the density and speed.

  For example, when a surface emitting laser array is used as an exposure light source of an electrophotographic printer, the printing speed can be increased by parallel processing of printing processes using multi-beams.

  The surface emitting lasers currently in practical use are elements that mainly output laser light in the infrared region (wavelength λ = 0.75 μm to 1 μm). If the oscillation wavelength is shortened, the beam diameter can be further reduced, so that a higher resolution image can be obtained.

  The red surface emitting laser outputs light with a wavelength shorter than the infrared region (about 0.6 μm to about 0.73 μm), and the wavelength is sensitive to the sensitivity of amorphous Si that can be applied to the photosensitive drum of an electrophotographic printer. It is also a very high wavelength.

  Therefore, there is a demand for practical use of a red surface emitting laser in order to employ it in a photosensitive drum using amorphous Si and enable high-speed and high-resolution image printing.

  In addition, the effect of the combination of high resolution by shortening the wavelength and parallel processing by multi-beam is significant, and not only for application to electrophotographic printers, but also in various fields including image display devices such as laser displays. Expected to contribute to

B. Basic structure of red surface emitting laser In order to generate light having a wavelength in the red region, a semiconductor material called AlGaInP is usually used. This material is lattice-matched to GaAs, which is a material constituting the growth substrate, and the band gap can be controlled by changing the composition ratio of Al and Ga.

  In order to cause laser oscillation, it is necessary to inject a current higher than the threshold current into the laser element, and carriers such as electrons and holes are injected into the active layer by the current injection, thereby causing recombination of light emission (radiative recombination). Converted to light.

C. Specific Prior Art A red surface emitting laser is formed by sandwiching a resonator region including an AlGaInP active layer with a multilayer reflector using AlGaAs, which is a different semiconductor material. As the substrate, a GaAs substrate in which the active layer and the multilayer reflector are lattice-matched is used.

  Crawford et al. Of Sandia National Laboratories published an element configuration of a single wavelength resonator structure in 1995 (Non-patent Document 1).

  This one-wavelength resonator structure is the most commonly used resonator length in a surface emitting laser that outputs an infrared wavelength laser. In the case of a red surface emitting laser, the one-wavelength resonator length is Is approximately 200 nm (in the case of a wavelength of 680 nm) in layer thickness.

  Specifically, an active layer having a multiple quantum well structure of 40 nm to 50 nm is disposed in the central region of the one-wavelength resonator length. Then, on both sides, a p-type AlGaInP layer and an n-type AlGaInP layer which are spacer layers are arranged at 80 nm or less, respectively.

  In addition, an undoped spacer layer may be further used between the active layer and a p-type (or n-type) spacer layer which is a doped layer. In such a case, the p-type (or The layer thickness of the (n-type) AlGaInP spacer layer is about 50 nm.

  In fact, even in Non-Patent Document 1, it can be seen that the p-type AlGaInP layer and the n-type AlGaInP layer have a thickness of about 50 nm.

In this document, it can be read that the maximum light emission intensity in the mode of wavelength 675 nm is 2.8 mW (20 ° C.) using an element having an oxidized constriction diameter of 15 μmφ.
M.M. H. Crawford et al. , IEEE PHOTOTONICS TECHNOLOGY LETTERS, Vol. 7, no. 7 (1995) 724 R. P. Schneider et al. , IEEE PHOTOTONICS TECHNOLOGY LETTERS, Vol. 6, no. 3 (1994) 313 D. Bour et al. , Journal of Quantum Electronics, Vol. 29, no. 5 (1993) 1337

  By the way, when using a red surface emitting laser element as a light source for electrophotography, excellent operating characteristics at high temperatures are required.

  However, in the case of the element structure described in Non-Patent Document 1, it is described that, for example, when the environmental temperature is increased from 20 ° C. to 40 ° C., the maximum light emission intensity is significantly reduced. Specifically, it is described that in the mode with a wavelength of 675 nm, the maximum emission intensity is reduced to about 1.0 mW (the output is reduced to 40%).

  Further, according to the knowledge of the present inventors, even when the ambient temperature is 20 ° C., when the current injection amount is increased for the purpose of high output operation, the internal temperature of the element is 20 ° C. with the increase of the current injection amount. It becomes higher temperature. In such a case, the light emission intensity does not increase or further decreases as the current injection amount increases, and the maximum light emission intensity that can be used is limited.

  Such a decrease in light emission intensity is considered to be caused by a significant increase in leakage current that does not contribute to light emission as the temperature rises.

  Accordingly, an object of the present invention is to provide a novel red surface emitting laser element capable of reducing leakage current, and an image forming apparatus and an image display apparatus using the same.

According to the first aspect of the present invention, a red surface emitting laser element including a laminated film includes:
A first reflector,
a second reflecting mirror comprising a p-type semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror, and an intermediate layer interposed between the active layer and the second reflecting mirror and having a thickness in the stacking direction of 100 nm to 350 nm. A p-type semiconductor spacer layer,
It is characterized by having.

According to a second aspect of the present invention, a red surface emitting laser element including a laminated film is provided.
A first reflector,
a second reflecting mirror comprising a p-type AlGaAs semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror, and an intermediate layer interposed between the active layer and the second reflecting mirror and having a thickness in the stacking direction of 100 nm to 350 nm. A p-type AlInP semiconductor spacer layer or a p-type AlGaInP semiconductor spacer layer,
It is characterized by having.

According to a third aspect of the present invention, there is provided a red surface emitting laser element including a laminated film,
A first reflector;
a second reflecting mirror comprising a p-type semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror;
A p-type semiconductor spacer layer interposed between the active layer and the second reflecting mirror;
The conduction band edge at the X point of the p-type semiconductor multilayer film is lower than the p-type semiconductor spacer layer, and the thickness of the p-type semiconductor spacer layer in the stacking direction is 100 nm or more and 350 nm or less. And

  Another image forming apparatus or image display apparatus according to the present invention reflects and scans the red surface emitting laser element according to the first to third aspects of the present invention and the laser light output from the laser element. And an optical deflector.

  ADVANTAGE OF THE INVENTION According to this invention, the novel red surface emitting laser element which can reduce a leakage current, and an image forming apparatus and image display apparatus using the same are provided.

A. First, the background of the present invention will be described.

  a) As described above, in the configuration of the red surface emitting laser described in Non-Patent Document 1, the operating characteristics at a high temperature are remarkably deteriorated.

  As a cause of this, the present inventors considered that the leakage current suddenly increased due to the influence of heat, and the light emission efficiency significantly decreased.

  In order to confirm this, the present inventors first decided to study based on a generally considered band diagram.

  b) The band diagram described in the paper (Non-Patent Document 2) on the red VCSEL reported from the same Sandia National Laboratory as that of Non-Patent Document 1 is cited and shown in FIG.

Specifically, an active layer, an AlInP spacer layer (the spacer layer may be expressed as a cladding layer), and a DBR region (AlAs and Al _0.5 Ga ₀ ) composed of a semiconductor multilayer film constituting a reflecting mirror. _.5 As multilayer)). Note that DBR is a reflecting mirror used to constitute a resonator, and is an abbreviation for Distributed Bragg Reflector.

  It can be seen that the components of the DBR region are drawn higher than the AlInP constituting the spacer layer with respect to the band edge of the conduction band (CB side in FIG. 6).

  That is, in this band diagram, the electrons that have overcome the hetero barrier formed by the AlInP spacer layer with respect to the active layer are shown as potentials that are difficult to diffuse beyond the thickness of the AlInP layer.

The element structure in Non-Patent Document 1 is a structure in which a multilayer reflector is adjacent to an active layer via a p-type Al _0.25 Ga _0.25 In _0.5 P spacer layer. Specifically, the multilayer reflector is a multilayer reflector in which 34 pairs of a p-type AlAs layer of about 50 nm and a p-type Al _0.5 Ga _0.5 As layer of about 50 nm are repeated.

  In such a case, the total of the p-type AlInP spacer layer and the p-type DBR layer, which is the thickness of the p-type layer, is 3 μm or more.

  Thus, if the p-type DBR region having a higher band edge of the conduction band than the p-type spacer layer is sufficiently thick, carrier electrons injected into the active layer from the n-type semiconductor layer are adjacent to the active layer. The probability of leakage as a leakage current exceeding the p-type spacer layer is extremely low.

  In other words, the concentration gradient of the electrons over the AlInP spacer layer in the spacer layer becomes gentler than that in the case where the p-type DBR region does not exist.

  Since the magnitude of the diffusion current related to the leak is determined by the electron concentration gradient, the diffusion current component of the leakage current due to the electrons over the spacer layer is very large assuming the band diagram shown in FIG. It will be less.

  c) However, as described above, the red surface emitting laser element has been further studied on the basis that the temperature characteristics are poor.

  In the red surface emitting laser, the resonator region sandwiched between the upper and lower multilayer reflectors generally includes AlGaInP, while the multilayer reflector includes AlGaAs. That is, the resonator region and the multilayer mirror region are made of different materials.

  As the p-type layer, there are both a p-type semiconductor spacer layer (for example, a p-type AlGaInP spacer layer) and a p-type DBR region (for example, an AlGaAs layer). The layer is made of AlGaAs.)

  That is, even if the conductivity types are common to each other, in order to examine in detail the effect on the leakage current when different materials are stacked in this way, examine the band edge position of the conduction band, which is the potential felt by electrons, in detail. There is a need to.

Specifically, with respect to the p-type spacer layer and the p-type DBR region constituting the red surface emitting laser element,
(1) Since p-type doping is performed, the Fermi level of each layer is located almost at the band edge of the valence band,
(2) _Al x is used as a p-type semiconductor spacer layer _{Ga 1-x In 0.5 P (} 0.25 ≦ x ≦ 0.55, particularly 0.35 ≦ x ≦ 0.5 area of) or, DBR Al _y Ga _1-y As (0.4 ≦ y ≦ 1) constituting the region is not a direct transition type semiconductor but an indirect transition type semiconductor, and the band edge in the conduction band is not a Γ point but an X point. Being
Considering both of these simultaneously, the potential of electrons should be examined. Note that the Γ point is a region in the direct transition semiconductor where the bottom of the band edge in the conduction band is supposed to exist.

  As a result of taking the above two points (1) and (2) into consideration, it has been found that the electron potential, that is, the band edge lineup at the X point in the conduction band, is as shown by the solid line 1010 in FIG. The horizontal axis of FIG. 1 shows the layer thickness of the element, and the vertical axis shows the band offset amount based on GaAs. The positive side region is the conduction band side, and the negative side region is the valence band side. Show.

In the figure, reference numeral 1050 indicates a p-type semiconductor spacer layer, and reference numeral 1060 indicates only one pair of p-type DBR regions (actually, this pair is repeated). In FIG. 1, p-type Al _0.35 Ga _0.15 In _0.5 P is used as an example of the p-type semiconductor spacer layer 1050, and p-type Al _0.9 Ga _{0 is used} as an example of the p-type DBR region 1060. _.1 depicts the band structure for a pair of As and p-type Al _0.5 Ga _0.5 As.

  For comparison, FIG. 1 also shows the band edge (dashed line 1020) of the conduction band at the Γ point, the lineup 1090 of the band edge of the valence band, and the pseudo-Fermi level (1092, 1093). . For the sake of simplicity, FIG. 1 does not show spikes, notches, and the like due to band edge energy discontinuities. Since the study is on the p-type layer, the band lineup is determined so that the Fermi levels existing in the vicinity of the valence band in the p-doped layer match.

Further, in Al _0.9 Ga _0.1 As constituting the p-type DBR region 1060 which is a p-type semiconductor multilayer film region, the point X (1010 in FIG. 1) is the Γ point (1020 in FIG. 1). It can be seen that it has a significantly lower band edge than. Specifically, it can be seen that in the p-type Al _0.9 Ga _0.1 As layer adjacent to the p-type AlGaInP spacer layer, the band edge potential of the conduction band drops by about 200 meV.

  That is, a band diagram (FIG. 1) different from the band diagram (FIG. 6) shown in Non-Patent Document 2 is constructed.

  d) Consider the leakage current again based on the band diagram shown in FIG.

Let us consider electrons existing in the p-type semiconductor spacer layer 1050 by overcoming the hetero-barrier which is the difference between the band edges of the active layer 1070 and the p-type semiconductor spacer layer 1050. The electrons actually feel a drop in the potential at the band edge of Al _0.9 Ga _0.1 As that is a constituent element of the adjacent p-type DBR region 1060. In FIG. 1, reference numeral 1075 denotes an undoped barrier layer provided as necessary.

Therefore, in the vicinity of the interface between the p-type semiconductor spacer layer 1050 and the p-type Al _0.9 Ga _{0.1 As} 1061, most of the electrons fall to the p-type Al _0.9 Ga _0.1 As layer side, and the p-type semiconductor spacer layer There are almost no electrons with the same energy as the inside.

  Therefore, the electron concentration gradient in the p-type semiconductor spacer layer 1050 becomes very large, and the diffusion current component can have a very large value.

  That is, the p-type DBR region 1060 cannot actually function sufficiently as a barrier against carrier electrons leaking beyond the p-type semiconductor spacer layer 1050.

  e) In other words, the effective p-type layer thickness that contributes to suppressing the leakage current that exceeds the p-type semiconductor spacer layer is not the thickness including the thickness in the p-type DBR region, but p This is only the thickness of the type semiconductor spacer layer.

  Based on this new knowledge, the leakage current was calculated from the following (Equation 1) in order to investigate the leakage current.

The leakage current density (J _leak ) is formed by the diffusion component and drift component of electrons leaked from the active layer to the p-type semiconductor spacer layer, and is given by the following equation (Non-patent Document 3).

Here, q is the charge amount, D _n is the electron diffusion constant, _mn is the effective mass of the electron, k is the Boltzmann constant, h is the Planck constant, T is the temperature, and ΔE is the heterobarrier. L _n is the electron diffusion length, Z is the effective electric field length, σ _p is the conductivity of the p-type spacer layer, J _total is the total injected current density, and x _p is the p-type cladding layer thickness.

FIG. 2A shows the leak current (solid line 2091) using the above (Equation 1), with the layer thickness of the p-type semiconductor spacer layer taken on the horizontal axis and the left vertical axis normalized. Note that the composition of the spacer layer is premised on AlGaInP (for example, Al _0.5 In _0.5 P or Al _0.35 Ga _0.25 In _0.5 P).

  As is apparent from the figure, when the thickness of the p-type semiconductor spacer layer is about 80 nm or less, the leakage current (particularly the diffusion current component) increases rapidly, leading to a decrease in light emission efficiency and high temperature operation. It is presumed that it will be difficult to obtain characteristic degradation and high output operation.

  Based on the above-described knowledge, when the layer thickness of the p-type semiconductor spacer layer of about 50 nm, which is the thickness of the spacer layer read from Non-Patent Document 1, is examined, it can be seen that the configuration is extremely weak against leakage current.

  At present, the p-type AlGaInP spacer layer used as a standard for a red surface emitting laser has a thickness of about 50 nm. For better high-temperature operation characteristics, the p-type spacer layer is made thicker. I realized that I needed to do it.

B. First Embodiment (Red Surface Emitting Laser Element)
A red surface emitting laser element including a laminated film according to the present embodiment will be described with reference to FIG.

  The laser element 3000 in FIG. 1 includes a first reflecting mirror 302, a second reflecting mirror 308 configured to include a p-type semiconductor multilayer film, and between the first reflecting mirror 302 and the second reflecting mirror 308. An active layer 305 interposed therebetween. Furthermore, a p-type semiconductor spacer layer 307 is interposed between the active layer 305 and the second reflecting mirror 308 and has a thickness of 100 nm to 350 nm. Here, the significance of setting the thickness of the p-type semiconductor spacer layer to 100 nm or more and 350 nm or less will be described. The layer thickness is the thickness in the stacking direction.

  A dotted line 2095 in FIG. 2A is drawn to find the degree (inclination) of the change in the region where the normalized leakage current significantly increases with respect to the change in the thickness of the p-type semiconductor spacer layer. It is a dotted line.

  As the layer thickness of the p-type semiconductor spacer layer 307, a layer thickness corresponding to the region 2591 having a very large inclination should be avoided, and in view of the fact that it slightly varies depending on the composition ratio of the material constituting the spacer layer, it is 100 nm or more. It can be seen that it is better to have a layer thickness of.

  On the other hand, the dotted line 2096 is drawn to find the degree of change (slope) of the region 2592 in which the change in the normalized leakage current is very gradual with respect to the change in the thickness of the p-type semiconductor spacer layer 307. It is a dotted line. As is apparent from this dotted line 2096, it can be seen that in the region where the thickness of the p-type spacer layer exceeds 350 nm, the change in the thickness of the spacer layer hardly affects the leakage current.

Further, a solid line 2091 in FIG. 2B shows how the loss inside the resonator changes with respect to the thickness of the p-type spacer layer. Here, the loss due to the mirror is not taken into consideration, but only the loss lost by free carrier absorption in the p-type spacer layer and the p-type DBR layer is taken into consideration, and it is allocated to the entire resonator length. As is clear from the figure, the greater the thickness of the p-type spacer layer, the greater the loss inside the resonator. From this point of view, it is necessary to select a spacer layer thickness that is as thin as possible. Even if the thickness of the p-type semiconductor spacer layer is 350 nm, it can be seen that the increase in the loss inside the resonator is 20% or less (the intracavity loss at 350 nm is 12.5 cm ⁻¹ , the resonator at 50 nm). The internal loss was calculated as 10.5 cm ⁻¹ ).

  From the above viewpoint, it can be seen that the p-type semiconductor spacer layer preferably has a thickness of 100 nm or more and 350 nm.

  In the above description, the specific composition ratio of the p-type semiconductor spacer layer is omitted as appropriate.

  In FIG. 2 (a), the normalized leakage current is calculated as the normalized leakage current by paying attention to the following parts in the above (Equation 1) and assuming the other parts are the same.

Here, the thickness of the p-type layer is calculated as the thickness of the p-type AlGaInP spacer layer (x _p = 40 to 700 nm). The values used for the calculation are calculated using 1 × 10 ¹⁸ cm ⁻³ as the p doping amount, 1 μm as the electron diffusion length L _n , and ³ kA / cm ² as the _total injection current density J _total . Further, the value of the temperature T is not considered in the calculation in order to obtain a value normalized with respect to the spacer layer. As for internal light absorption, free carrier absorption is calculated for the entire device including the multilayer reflector in the p-type DBR region.

  The p-type semiconductor spacer layer and the p-type semiconductor multilayer film (p-type DBR region) will be described in detail below.

  The conduction band at the X point of the two layers where the band edge of the conductor at the X point of the p-type semiconductor spacer layer 307 is a repeating unit constituting the p-type DBR region (1060 in FIG. 1 and 308 in FIG. 3). The material is selected so that the edge is higher than the higher layer. That is, the material is selected so that the conduction band edge at the point X of the p-type DBR region is lower than the p-type semiconductor spacer layer.

  Further, the p-type semiconductor spacer layer 307 can be composed of a layer made of a composition containing Al, In, and P.

When the composition of the p-type semiconductor spacer layer is Al _x Ga _y In _1-xy P, the range of x and y is preferably as follows.

  First, from the viewpoint of lattice matching with a GaAs material, the proportion of In in the above composition formula (corresponding to “1-xy” in the above relational expression) is in the range of 0.45 to 0.55, preferably Should be in the range of 0.48 to 0.50.

  From the former range, 0.45 ≦ x + y ≦ 0.55, and from the latter range, 0.50 ≦ x + y ≦ 0.52.

Furthermore, from the viewpoint of securing a hetero barrier between the active layer and the p-type semiconductor spacer, considering that Al _0.2 Ga _0.3 In _0.5 P is generally used for the barrier layer in the active layer, The x is preferably in the following range. Specifically, the ratio (x) in the Al composition is 0.25 or more, preferably 0.30 or more, and more preferably 0.35 or more. Note that the upper limit of the proportion (x) of the Al composition is 0.55 or less, preferably 0.52 or less in consideration of lattice matching.

Further, considering that the proportion of Ga may be 0, a preferable composition of the p-type semiconductor spacer layer is Al _x Ga _y In _1-xy P. Here, x and y satisfy the following three relational expressions, that is, 0.45 ≦ x + y ≦ 0.55, 0.25 ≦ x ≦ 0.55, and 0 ≦ y ≦ 0.30. The value to be

More preferably, the p-type semiconductor spacer layer is made of Al _x Ga _y In _1-xy P (0.50 ≦ x + y ≦ 0.52, 0.35 ≦ x ≦ 0.52, 0 ≦ y ≦ 0. 17).

  Of course, the present invention does not exclude the case where the above composition contains other impurities as long as epitaxial growth is possible.

Further, when the In ratio is 0.5, that is, in the case of a p-type Al _z Ga _1-z In _0.5 P spacer layer, for example, z is appropriately set within the range of 0.35 ≦ z ≦ 0.5. Can be determined. In the range of z, a crystal having a relatively high crystallinity is easily formed, and a band offset with the active layer can be secured as large as possible.

  Note that the p-type semiconductor spacer layer 307 may use a so-called multiple quantum barrier structure (MQB: Multi Quantum Barrier).

Of the two layers constituting the p-type DBR region 308, which is a repeating unit, the layer with the higher band edge of the conductor (when both layers use AlGaAs, the layer with the larger Al composition) Is selected from Al _x Ga _1-x As (0.70 ≦ x ≦ 1.0, preferably 0.8 ≦ x ≦ 1.0).

  The p-type semiconductor multilayer film constituting the second reflecting mirror is constituted by laminating a set of a first layer and a second layer having different refractive indexes from each other a plurality of times. As described above, at least one of the first and second layers can be a layer made of a composition containing Al, Ga, and As.

The composition of the layer with the lower band edge of the conductor among the two layers serving as the repeating unit is Al _x Ga _1-x As (0.40 ≦ x ≦ 0.70, preferably 0.45 ≦ x ≦ 0.60). Although depending on the wavelength of light emitted from the active layer, x is set to 0.4 or more so that the wavelength is not absorbed, and is appropriately determined from the viewpoint of ensuring a sufficient refractive index with the other layer constituting the DBR. For example, in Al _x Ga _1-x As, x = 0.5 is a preferable mode.

  In FIG. 1, among the layers constituting the DBR region 308 which is a p-type semiconductor multilayer film, the layer having the higher conductor band edge at the point X is drawn so as to be adjacent to the p-type semiconductor spacer layer 1050. Although not necessarily adjacent. For example, of the layers constituting the DBR region, the layer with the lower band edge of the conductor at the point X may be adjacent to the p-type spacer layer.

(A) Resonator structure In order to ensure the thickness of the p-type semiconductor spacer layer described above, a resonator length longer than a commonly used single wavelength resonator, for example, a 1.5 wavelength resonator length or more is employed. It is preferable to do.

  The layer thickness of the p-type semiconductor spacer layer (1050 in FIG. 1 and 307 in FIG. 3) is preferably 100 nm to 350 nm, and preferably a p-type AlGaInP spacer layer having a thickness of 150 nm to 300 nm. Good.

  As a preferable resonator length, a resonator having a good separation such as 1.5 wavelength or 2 wavelengths can be considered. In order to realize this, it is preferable to increase the thickness of the p-type semiconductor spacer layer so that the resonator length becomes longer at intervals of 0.5 wavelength. The 0.5 wavelength corresponds to approximately 100 nm, and when combined with a conventional p-type AlGaInP layer thickness of about 60 nm, a value of 160 nm (in the case of adding 0.5 wavelength) and a value of 260 nm (in the case of adding one wavelength) Is calculated. Therefore, the thickness of the p-type semiconductor spacer layer is more preferably 150 nm or more and 300 nm or less from the viewpoint of including the case where 0.5 wavelength is added and the case where 1 wavelength is added.

  As described above, the resonator structure according to the present embodiment is preferably 1.5 wavelength resonator length or more, and the upper limit thereof is 4 wavelength resonator length or less, preferably 3.5 wavelength resonator length or less, more preferably 2.5 wavelength resonator length or less. The resonator length is the thickness in the stacking direction of the region between the first and second reflecting mirrors.

  On the other hand, in FIG. 3, an n-type semiconductor spacer layer 303 located on the substrate 301 side of the active layer 305 may be provided as necessary.

  Since the leak current of holes to the n-type semiconductor spacer layer (for example, composed of AlGaInP) is sufficiently small, the thickness of the n-type spacer layer 303 is sufficient to be about 40 nm to 80 nm even when it is provided. It is.

  That is, the resonator structure in the invention according to the present embodiment can form a resonator including the active layer 305, the p-type semiconductor spacer layer 307, and the n-type semiconductor spacer layer 303. The active layer 305 can have an asymmetric structure that is not located at the center in the resonator length direction.

  In particular, it is preferable that the p-type semiconductor spacer layer 307 is thicker than the n-type semiconductor spacer layer 303. The asymmetric structure means a configuration in which the p-type semiconductor spacer layer 307 is thicker than the n-type semiconductor spacer layer 303 and the active layer 305 does not exist in the center of the resonator. However, when designing the device structure, it is preferable to design the device so that the center of the active layer is located at the antinode of the internal light intensity standing wave existing inside the device.

  In addition, the layers 304 and 306 adjacent to the active layer 307 in FIG. 3 are each an undoped spacer layer (or a spacer layer having a lower impurity concentration than the p-type and n-type semiconductor spacer layers 307 and 303). It is. These two layers 304 and 306 are not essential layers in the present invention, but are necessary for functioning as a barrier layer for impurity diffusion from the p-type semiconductor spacer layer 307 and the n-type semiconductor spacer layer 303 to the active layer 305. It is preferable to provide according to the above. The thicknesses of these layers 304 and 306 are, for example, in the range of 10 nm to 50 nm, preferably 20 nm to 40 nm.

In an AlGaInP semiconductor laser, for example, red light emission can be obtained by using a GaInP quantum well structure as an active layer. As the p-type semiconductor spacer layer 307, for example, an Al _0.35 Ga _0.15 In _0.5 P layer or an Al _0.5 In _0.5 P layer can be used.

  The layer structure of the red surface emitting laser according to the present invention will be described below with specific materials.

For example, a spacer layer 307 (0.2 ≦ x ≦ 0.5) made of p-type Al _x Ga _0.5-x In _0.5 P having a thickness of about 170 nm is used. On the other hand, since there is almost no amount of holes having a large effective mass that can overcome the n-type Al _x Ga _0.5-x In _0.5 P layer 303 (0.2 ≦ x ≦ 0.5) and contribute to the leakage current. As for the thickness of the n-type AlGaInP layer, about 50 nm is sufficient as usual.

  The thickness of the active layer 305 is set to 40 nm to 50 nm by using a suitable multiple quantum well structure in a surface emitting laser. Therefore, it is preferable to design the active layer 305 as a 1.5 wavelength resonator length even if it is the shortest in the entire resonator. .

  Since the active layer 305 is disposed at the antinode of the internal electric field strength distribution, it is not located at the center of the 1.5 wavelength resonator length. Therefore, when attention is paid to the resonator structure, this structure is not a symmetric structure often found in a normal single wavelength resonator but an asymmetric structure.

  On the other hand, in the case of the symmetric structure, there is a case where it is easier to adjust the position of the active layer to the antinode of the internal electric field strength while adjusting the resonance wavelength to a desired value during crystal growth. Therefore, it is possible to increase the thickness of the n-type AlGaInP spacer layer to the same thickness as that of the p-type AlGaInP layer, for example, about 170 nm, and to form a symmetrical resonator. In this case, according to the above example, the resonator length is a two-wavelength resonator. Since free carrier absorption in the n-type spacer layer is less than that in the p-layer, the problem of light absorption caused by increasing the thickness of the n-layer is not as serious as in the p-layer.

  In this way, it is possible to provide a novel red surface emitting laser element that can reduce the leakage current and does not significantly increase the light absorption due to the thicker spacer layer.

(B) Other Configurations In FIG. 3, a substrate 301 (for example, a GaAs substrate) is illustrated, but may be omitted as necessary. For example, after a laminated film is grown on a substrate such as GaAs, the substrate can be removed or transferred to another transparent substrate such as a Si substrate, SOI substrate, or glass, a Ge substrate, or a plastic substrate. From the viewpoint of heat dissipation, it is preferable to transfer the light emitting element to a Si substrate or an SOI substrate. At the time of transfer, it is possible to use a technique of growing the above-described element constituent layer after polishing or grinding is used to remove the growth substrate, or after an etching sacrificial layer is formed on the growth substrate.

  The p-type semiconductor multilayer film 308 constituting the second reflecting mirror can be composed of a composition containing Al and As. The p-type semiconductor multilayer film 308 is configured by laminating a set of a first layer and a second layer having different refractive indexes from each other a plurality of times, and at least one of the first and second layers. One may be a layer made of a composition containing Al, Ga, and As.

  The material of the second reflecting mirror is not limited to a material made of AlAs or AlGaAs, and is not particularly limited as long as it is made of a semiconductor material lattice-matched to GaAs.

  The first reflecting mirror 302 can be composed of an n-type semiconductor multilayer film. Further, an n-type AlGaInP spacer layer (303 in FIG. 3) may be provided between the first reflecting mirror and the active layer.

  The first reflecting mirror 302 is not necessarily an n-type DBR as long as current can be injected into the red surface emitting laser element 3000. If a bonding technique or the like is used, a photonic crystal or the like can be used instead of a reflecting mirror made of a semiconductor multilayer film.

  Furthermore, in FIG. 3, separate spacer layers 304 and 306 are provided between the active layer 305 and the p-type or n-type spacer layers 303 and 307, but this may be omitted as necessary. it can. In FIG. 3, the n-type DBR region 302 is provided on the substrate 301 side, and the p-type DBR region 308 is provided on the active layer. For example, a p-type DBR region or a p-type spacer layer is provided between the active layer and the substrate.

  Examples of the configuration of the active layer 305 include a quantum well active layer including a layer made of GaInP and a layer made of AlGaInP. In the present invention, there is no limitation as long as a red color (wavelength in the range of 0.6 μm to 0.73 μm, more preferably in the range of wavelength of 0.63 μm to 0.72 μm) can be output. For example, a double hetero structure or a quantum dot structure can be adopted as the active layer, and AlGaInPN or the like can be used as the material system. Furthermore, as will be described later with reference to FIGS. 8 and 10, a plurality of active layers can be used. For example, the number of active layers is appropriately selected to be two as shown in FIG. 8 or the like, and further to three or more. As described above, a resonator is configured including the active layer 305, the p-type semiconductor spacer layer 307, and the n-type semiconductor spacer layer 303, and the active layer extends in the resonator length direction. An asymmetrical structure that is not centrally arranged can also be used.

  Here, the p-type AlGaInP spacer layer 307 may be thicker than the n-type AlGaInP spacer layer 303.

  In the present invention, the layer thickness configuration of the DBR region is preferably designed so as to constitute a vertical cavity surface emitting laser. However, if the surface emitting output is possible, it is strictly vertical. There is no need.

  The present invention is suitably used for a laser element that requires good operating characteristics at high temperatures. In particular, it is effective for a laser element that emits light with a high emission intensity and a single transverse mode.

C. Second Embodiment A red surface emitting laser element including a laminated film according to the second embodiment has the following characteristics. A description will be given with reference to FIG. 3 as in the first embodiment.

  The element is interposed between the first reflecting mirror 302, the second reflecting mirror 308 configured to include a p-type AlGaAs semiconductor multilayer film, and the first reflecting mirror and the second reflecting mirror. And an active layer 305. The p-type AlInP semiconductor spacer layer or the p-type AlGaInP semiconductor spacer layer 307 is interposed between the active layer 305 and the second reflecting mirror 308 and has a thickness in the stacking direction of 100 nm to 350 nm. .

  In addition, as long as the thickness is in the said range as the whole p-type semiconductor spacer layer, it can also be set as the structure containing both AlInP and AlGaInP, for example.

  With such a configuration, a novel red surface emitting laser element capable of reducing leakage current is provided.

  The notation of AlGaAs or AlGaInP indicates that the former includes Al, Ga, and As, and the latter includes Al, Ga, In, and P as constituents of each layer. Each composition ratio is not particularly limited as long as each layer can be epitaxially grown and red light emission can be realized. Of course, the matters described in the first embodiment can be applied to the laser element in the present embodiment as long as there is no contradiction.

D. Third Embodiment A red surface emitting laser element including a laminated film according to the third embodiment has the following characteristics. It demonstrates using FIG. 3 similarly to the above-mentioned embodiment.

  A first reflecting mirror 302; a second reflecting mirror 308 configured to include a p-type semiconductor multilayer film; and an active layer 305 interposed between the first reflecting mirror 302 and the second reflecting mirror 308. And a p-type semiconductor spacer layer 307 interposed between the active layer and the second reflecting mirror.

  As already described with reference to FIG. 1, the conduction band edge at the point X of the p-type semiconductor multilayer film is made lower than that of the p-type semiconductor spacer layer 307. Further, the p-type semiconductor spacer layer 307 is characterized in that the thickness in the stacking direction is not less than 100 nm and not more than 350 nm.

  Even if the leakage current cannot be sufficiently reduced by the presence of the second reflecting mirror including the p-type semiconductor multilayer film, the leakage current can be reduced by setting the thickness of the p-type semiconductor spacer layer 307 to 100 nm to 350 nm. Can be reduced (FIG. 2A).

  Needless to say, the items described in the first embodiment can be applied to the laser element in the present embodiment as long as there is no contradiction.

E. Fourth embodiment (image forming apparatus and image display apparatus)
The red surface emitting laser element described in the first to third embodiments can be applied to, for example, an image forming apparatus or an image display apparatus.

  When applied to an image forming apparatus, as shown in FIG. 9, the red surface emitting laser element 914 and an optical deflector 910 for reflecting and scanning the laser beam output from the laser element are included. Is done. The configuration of the optical deflector is not particularly limited as long as it has a function of reflecting laser light and a function of scanning the reflection direction.

  As such an optical deflector, for example, a polygon mirror, a polygon mirror, or a reflector configured by swinging a thin piece made of Si or the like by using MEMS technology can be used.

  The electrophotographic apparatus includes, for example, a drum-shaped photosensitive member 900, a charger 902, a developing unit 904, and a fixing unit 908 for forming an electrostatic latent image by the beam deflected by the optical deflector. Although it is included, the details will be described in the embodiments described later.

  Of course, when the red surface emitting laser element according to the present invention is used in an image display device such as a display, it can be configured in combination with the deflector.

  In addition, a plurality of the above-described red surface emitting laser elements can be arranged in an array and applied to the image forming apparatus or the like as a multi-beam.

Example 1
The first embodiment of the present invention will be described below.

  FIG. 3 shows a schematic cross-sectional view of the layer structure of the red surface emitting laser according to the present invention.

The VCSEL structure in this example is
n-type GaAs substrate 301,
n-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 As multilayer reflector 302,
n-type Al _0.35 Ga _0.15 In _0.5 P spacer layer 303,
Undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304,
Ga _0.56 In _0.44 P / Al _0.25 Ga _0.25 In _0.5 P quantum well active layer 305,
Undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306, p-type Al _0.5 In _0.5 P spacer layer 307,
p-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 As multilayer mirror 308,
A p-type GaAs contact layer 309 is used.

  Here, a red surface emitting laser that oscillates at 680 nm is formed.

First, an n-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 As multilayer mirror 302 and a p-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 The As multilayer reflector 308 will be described. Each of the Al _0.9 Ga _0.1 As layer and the Al _0.5 Ga _0.5 As layer is formed to have an optical thickness of ¼ wavelength.

In order to lower the electrical resistance, a composition gradient layer of about 20 nm can be provided between the Al _0.9 Ga _0.1 As layer and the Al _0.5 Ga _0.5 As layer.

  In this case, it is formed to have an optical thickness of ¼ wavelength including the composition gradient layer. The p-type multilayer mirror 308 is doped with an impurity serving as an acceptor, for example, C or Zn so that a current flows. The n-type multilayer mirror is doped with an impurity serving as a donor, for example, Si or Se. Then, in order to reduce the light absorption in the multilayer reflector as much as possible, modulation doping is performed in which the doping amount is low at the antinode of the standing wave of the internal electric field strength distribution existing in the multilayer reflector and the doping amount is increased at the node. You may go.

  In this embodiment, since an element structure that extracts light from the epitaxial layer, that is, from the p-type layer side, is adopted, the p-type multilayer mirror 308 has approximately 36 pairs and is optimal in light extraction efficiency. A reflecting mirror is formed. On the other hand, since it is not necessary to extract light on the n side, the reflectance is increased as much as possible by repeating about 60 pairs, and the threshold current is decreased.

By the way, in the p-side multilayer reflector 308, for example, an Al _0.98 Ga _0.02 As layer of about 30 nm is inserted between 1 to 3 pairs counted from the active layer side, and this layer is selectively oxidized. By doing so, a current confinement structure can also be formed.

  Next, the formation of the resonator will be described.

  In order to set the thickness of the p-type AlGaInP layer 307 to 100 nm or more and 350 nm or less, this embodiment adopts a 1.5 wavelength resonator length as shown in FIG. 4 instead of the normally used single wavelength resonator.

  Since the emission wavelength is 680 nm and 1.5 wavelengths, the optical thickness is 1020 nm. The resonator is entirely formed of an AlGaInP layer, but since AlGaInP with various compositions such as an active layer, a barrier layer, and a spacer layer is used, the layer thickness is determined according to its refractive index, and 1.5 wavelength resonance It is necessary to make it a captain.

  In order to maximize the interaction between light and carriers, the active layer needs to be disposed on the antinode 403 of the standing wave. That is, the active layer 305 is disposed at 1/3 position within 1020 nm, the n layer is disposed on the short side (left side in FIG. 4), and the p layer is disposed on the long side (right side in FIG. 4).

  Considering the above conditions, an actual example is shown below.

The active layer 305 is formed of four 6 nm GaInP quantum wells and three 6 nm Al _0.25 Ga _0.25 In _0.5 P barrier layers, and the actual layer thickness is 42 nm.

Since the refractive index of the GaInP layer and the Al _0.25 Ga _0.25 In _0.5 P layer at the emission wavelength of 680 nm is 3.56 and 3.37, respectively, the optical thickness in this active layer is 146 nm. Become.

The half length of the active layer region is 73 nm, and the optical layer is formed by an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 and an n-type Al _0.35 Ga _0.15 In _0.5 P layer 303. The target thickness may be 340 nm, which is 1/3 of 1020 nm.

The layer thickness of the undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 is 20 nm, and the layer thickness of the n-type Al _0.35 Ga _0.15 In _0.5 P layer 303 is 60.5 nm. Since the refractive indices are 3.37 and 3.30, respectively, the optical thickness of these two layers is 267 nm.

  In other words, the sum of the active layer 305 and 73 nm, which is half of the active layer 305, is 340 nm as the optical thickness, and the center of the active layer 305 is located at the antinode 403 of the standing wave as shown in FIG.

On the p side, 73 nm, which is half the optical thickness of the active layer 305, and an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _0.5 In _0.5 P layer 307 Therefore, the remaining optical thickness may be 680 nm.

Although the n-side with _Al 0.35 _Ga 0.15 _{In 0.5} P layer using _{Al 0.5 In} 0.5 P layer in order to increase the possible hetero barrier in the p-side, 1 × ^{10 18} Doping is performed up to about cm ⁻³ . Zn or Mg is used as the dopant.

The barrier layer 306 is 20 nm, and the p-type Al _0.5 In _0.5 P layer 307 is 167.6 nm. Since the refractive indexes are 3.37 and 3.22, respectively, the optical thickness of these two layers is 607 nm, and the sum of the optical thickness of half of the active layer 305 and 73 nm is the optical thickness. 680 nm.

  As described above, the optical thicknesses of the n layer including the undoped barrier layer, the active layer, and the p layer including the undoped barrier layer are 267 nm, 146 nm, and 607 nm (total 1020 nm), respectively. It matches.

  The thickness of the p layer (not the optical thickness but the actual layer thickness) is also 167.6 nm, which is 100 nm or more and 350 nm or less.

  A multilayer reflector is formed on both sides of the resonator. The multilayer mirror is configured on both the n side and the p side so that it becomes an antinode of the standing wave at the interface between the resonator and the multilayer mirror.

Specifically, a low refractive index material, here an Al _0.9 Ga _0.1 As layer 402 is adjacent to the resonator, and next to it is a high refractive index material, here Al _0.5 Ga _0.5 As. The layers 401 are formed so as to be arranged, and the necessary numbers (p-side 36 pairs, n-side 60 pairs) are repeated.

  In actual device fabrication, a wafer having the above layer thickness is first formed by a crystal growth technique.

  For example, a layer structure is formed by an organic metal compound growth apparatus or a molecular beam epitaxy apparatus. After the wafer structure is formed, a laser element 5000 as shown in FIG. 5 is completed by a normal semiconductor process technique. In FIG. 5, layers having the same functions as the layers described in FIG. 3 are given the same numbers.

  A post is formed by photolithography and semiconductor etching, and a current confinement layer 502 is formed by selective oxidation. Thereafter, an insulator film 503 is deposited, and only a region in contact with the p-GaAs contact layer 309 is opened to form a p-side electrode 504. Finally, an n-side electrode 501 is formed on the back surface of the wafer to complete the device.

  As described above, the device manufactured based on the present invention can be operated at high temperature and high power, and the application of the red surface emitting laser is greatly expanded, and its ripple effect is very large.

  The above is a method for manufacturing a single element.

  When manufacturing a plurality of elements integrated in an array, for example, in order to arrange 32 elements of 4 × 8 in an array at a pitch of 50 μm, use a photomask that provides the desired element arrangement from the beginning. To do. Then, using the same epiwafer as described above and performing the same element formation step, a plurality of elements in an array can be formed simultaneously. That is, a red surface emitting laser array can be easily obtained by using a mask having a necessary pattern.

  Here, an n-type GaAs substrate is used to form an element structure with a p-type layer on top, but a p-type GaAs substrate may be used to form an element structure with an n-type layer on top.

(Example 2)
The second embodiment of the present invention will be described below.

  In FIG. 7, the cross-sectional schematic diagram of the layer structure of the red surface emitting laser element 7000 based on this invention is shown.

The VCSEL structure in this example is
n-type GaAs substrate 301,
n-type AlAs / Al _0.5 Ga _0.5 As multilayer mirror 701,
n-type Al _0.35 Ga _0.15 In _0.5 P spacer layer 303,
Undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304,
First Ga _0.56 In _0.44 P / Al _0.25 Ga _0.25 In _0.5 P quantum well active layer 702,
Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703,
Second Ga _0.56 In _0.44 P / Al _0.25 Ga _0.25 In _0.5 P quantum well active layer 704,
Undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306,
p-type Al _0.35 Ga _0.15 In _0.5 P spacer layer 705,
p-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 As multilayer mirror 308,
p-type GaAs contact layer 309
Consists of. Here, a red surface emitting laser that oscillates at 680 nm is formed.

In the n-type multilayer mirror 701, AlAs, which is a material having a low thermal resistance, is used instead of Al _0.9 Ga _0.1 As as a layer constituting the reflecting mirror in order to reduce the thermal resistance of the element.

The p-type Al _0.9 Ga _0.1 As / Al _0.5 Ga _0.5 As multilayer mirror 308 is the same as in the first embodiment (FIG. 3).

  As shown in FIG. 7, in this embodiment, a periodic gain structure using two multiple quantum well structures is used. As a result, the light confinement ratio is increased, the mode gain is increased, and a high light emission output is easily obtained.

  In addition to the periodic gain structure, a 2.5 wavelength resonator is used as the resonator length as shown in FIG. 8 in order to make the thickness of the p-type AlGaInP layer not less than 100 nm and not more than 350 nm.

  Hereinafter, the layer structure of the resonator will be described with reference to FIG.

  Since the resonance wavelength is 680 nm, when the resonator length is 2.5 wavelengths, the optical thickness is 1700 nm.

  The resonator is entirely formed of an AlGaInP layer, but since AlGaInP with various compositions such as an active layer, a barrier layer, and a spacer layer is used, the layer thickness is determined according to the refractive index, and a 2.5 wavelength resonator Need to be long.

  In order to maximize the interaction between light and carriers, the active layers 702 and 704 need to be disposed on the antinode 403 of the internal light intensity standing wave. That is, active layers are arranged at 1/5 and 2/5 positions within 1700 nm, an n layer is arranged on the short side (left side in FIG. 8), and a p layer is arranged on the long side (right side in FIG. 8). .

  Considering the above conditions, an actual example is shown below.

The first active layer 702 and the second active layer 704 are formed of four 6 nm GaInP quantum wells and three 6 nm Al _0.25 Ga _0.25 In _0.5 P barrier layers, and the actual layer thickness is 42 nm. Become. Since the refractive index of the GaInP layer and the Al _0.25 Ga _0.25 In _0.5 P layer at 680 nm is 3.56 and 3.37, respectively, the optical path length in this active layer is 146 nm.

The optical path is 73 nm, which is half the length of the active layer region, and an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 and an n-type Al _0.35 Ga _0.15 In _0.5 P layer 303. The length should be 340 nm.

The layer thickness of the undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 is 20 nm, and the layer thickness of the n-type Al _0.35 Ga _0.15 In _0.5 P layer 303 is 60.5 nm. Since the refractive indexes are 3.37 and 3.30, respectively, the optical thickness of these two layers is 267 nm, and the total thickness is 340 nm with 73 nm which is half of the optical thickness of the first active layer 702. .

That is, as shown in FIG. 8, the center of the first active layer 702 is located on the antinode 403 of the standing wave. Subsequently, the optical thickness of half of the first active layer 702 is 73 nm, the optical thickness of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 and the optical thickness of half of the second active layer 704. It may be 340 nm at 73 nm.

Since the refractive index of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 is 3.37, if the thickness is 57.6 nm, the optical thickness of this intermediate barrier layer is 194 nm. It becomes. The total thickness of the first and second active layers 702 and 703 and the half of the optical thickness is 340 nm. Therefore, the center of the second active layer 704 is located at the antinode 403 of the standing wave as shown in FIG.

  By the way, a part of the AlGaInP intermediate barrier layer 703 may be doped with Mg or Zn to be p-type to increase the efficiency of hole injection into the first active layer 702.

The p-side has an optical thickness of 73 nm, which is half that of the active layer 704, and an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _0.5 In _0.5 P layer 705. Therefore, the remaining optical thickness may be 1020 nm.

The barrier layer 306 is 20 nm, and the p-type Al _0.5 In _0.5 P layer 705 is 273.2 nm. Since the refractive indexes are 3.37 and 3.22, respectively, the optical thickness of these two layers is 947 nm, and the total of the optical thickness of 73 nm, which is half the optical thickness of the second active layer 704, is 1020 nm. . The total optical thickness of the n layer including the undoped barrier layer, the two active layers including the intermediate barrier layer, and the p layer including the undoped barrier layer is 267 nm, 486 nm, and 947 nm, respectively, and the total is 1700 nm and 2.5 wavelengths. It matches the optical thickness in the case of a resonator. The thickness of the p-type AlGaInP layer is also 273.2 nm, which is not less than 100 nm and not more than 300 nm.

  A multilayer reflector is formed on both sides of the resonator. The multilayer reflector is configured on both the n side and the p side so that it becomes an antinode of the standing wave at the interface between the resonator and the multilayer reflector.

Specifically, a low refractive index material, here an AlAs layer 801 on the n side, an Al _0.9 Ga _0.1 As layer 402 on the p side is adjacent to the resonator, and a high refractive index material next to the resonator. The Al _0.5 Ga _0.5 As layer 401 is formed so as to be arranged on both the n side and the p side. Then, the necessary numbers (about 36 pairs on the p side and 60 pairs on the n side) are repeated.

  Hereinafter, as shown in the first embodiment, an element may be manufactured or arrayed.

(Example 3)
In the third embodiment, an embodiment of an application example using the red surface emitting laser array according to the present invention will be described.

  FIG. 9 shows a structural diagram of an electrophotographic recording type image forming apparatus in which the red surface emitting laser array according to the present invention is mounted. FIG. 9A is a top view of the image forming apparatus, and FIG. 9B is a side view of the apparatus.

  In FIG. 9, 900 is a photosensitive member, 902 is a charger, 904 is a developing unit, 906 is a transfer charger, 908 is a fixing unit, 910 is a polygon mirror, and 912 is a motor. Reference numeral 914 denotes a red surface emitting laser array, 916 denotes a reflecting mirror, 920 denotes a collimator lens, and 922 denotes an f-θ lens.

  In FIG. 9, a motor 912 drives the rotary polygon mirror 910 to rotate. The rotary polygon mirror 910 in this embodiment includes six reflecting surfaces.

  Reference numeral 914 denotes a red surface emitting laser array which is a recording light source. The red surface emitting laser array 914 is turned on or off according to an image signal by a laser driver (not shown), and the laser light thus modulated is transmitted from the red surface emitting laser array 914 through a collimator lens 920 to a rotating polygon mirror. Irradiated toward 910.

  The rotating polygon mirror 910 rotates in the direction of the arrow, and the laser beam output from the red surface emitting laser array 914 is a deflected beam that continuously changes the emission angle on the reflecting surface as the rotating polygon mirror 910 rotates. Reflected. The reflected light is subjected to correction of distortion and the like by the f-θ lens 922, irradiated to the photosensitive member 900 through the reflecting mirror 916, and scanned on the photosensitive member 900 in the main scanning direction. At this time, images of a plurality of lines corresponding to the red surface emitting laser array 914 are formed in the main scanning direction of the photosensitive drum 900 by reflection of the beam light through one surface of the rotary polygon mirror 910. In this embodiment, a 4 × 8 red surface emitting laser array 914 is used, and images for four lines are formed simultaneously.

  The photosensitive drum 900 is charged in advance by a charger 902 and is sequentially exposed by scanning with a laser beam to form an electrostatic latent image. The photosensitive member 900 is rotated in the direction of the arrow, and the formed electrostatic latent image is developed by the developing unit 904. The developed visible image is transferred to a transfer paper (not shown) by the transfer charging unit 906. Is transcribed. The transfer paper onto which the visible image has been transferred is conveyed to a fixing device 908, and after being fixed, is discharged outside the apparatus.

  In this embodiment, a 4 × 8 red surface emitting laser array is used, but the present invention is not limited to this, and an m × n red surface emitting laser array (m, n: natural number) may be used.

  As described above, by using the red surface emitting laser array according to the present invention for an electrophotographic recording type image forming apparatus, it is possible to obtain an image forming apparatus capable of high-speed and high-definition printing.

  Furthermore, there are cases where laser operation up to 60 ° C. is required while achieving a single transverse mode, such as application of an electrophotographic light source. Generally, in order to achieve the single transverse mode, it is necessary to narrow the light emitting region (4 μm diameter or less), and even with the same current injection amount, the actual current density is further increased and the leakage current is further increased. .

  According to the present invention, a novel red surface emitting laser element with improved temperature characteristics is provided, which is extremely useful.

  In addition, FIG. 11 demonstrates an example in the case of comprising a laser display using the element based on this invention. In FIG. 11, reference numeral 1202 denotes a first deflection unit, 1211 denotes a second deflection unit, and 1210 denotes a scanning locus on the reflection plane of the second deflection unit by the first deflection unit 1202. Reference numeral 1212 denotes light deflected by the second deflecting unit 211, reference numeral 1213 denotes a certain plane, reference numeral 1214 denotes a range scanned by the deflecting light on a certain plane 1213, and reference numeral 1215 denotes a trajectory of a scanning line on the certain plane 1213. Is. Reference numeral 1201 denotes a laser element according to the present invention. Reference numeral 1203 indicates the traveling direction of the output light from the laser element 1201. Reference numerals 1205 and 1206 denote the traveling directions of the laser light deflected by the first deflecting means 1202.

  The first deflecting unit 1202 and the second deflecting unit 1210 deflect light in the horizontal direction and the vertical direction, respectively. Thus, the range in which the deflected light spreads becomes a two-dimensional region.

Example 4
The fourth embodiment of the present invention will be described below.

  This embodiment also uses a periodic gain structure that uses two multiple quantum well structures. As a result, the light confinement ratio is increased, the mode gain is increased, and a high light emission output is easily obtained.

  Further, in addition to the periodic gain structure, in order to make the thickness of the p-type AlGaInP layer not less than 100 nm and not more than 350 nm, a two-wavelength resonator is used as the resonator length as shown in FIG.

  Hereinafter, the layer structure of the resonator will be described with reference to FIG.

  Since the resonance wavelength is 680 nm, when the resonator length is two wavelengths, the optical thickness is 1360 nm. Although the resonator is entirely formed of an AlGaInP layer, AlGaInP with various compositions such as an active layer, a barrier layer, and a spacer layer is used. It is necessary to let In order to maximize the interaction between light and carriers, the active layers 702 and 704 need to be disposed on the antinode 403 of the internal light intensity standing wave. That is, active layers are arranged at 1/4 and 1/2 positions within 1360 nm, an n layer is arranged on the short side (left side in FIG. 10), and a p layer is arranged on the long side (right side in FIG. 10). .

  Considering the above conditions, an actual example is shown below.

The first active layer 702 and the second active layer 704 are formed of four 6 nm GaInP quantum wells and three 6 nm Al _0.25 Ga _0.25 In _0.5 P barrier layers, and the actual layer thickness is 42 nm. Become.

Since the refractive indexes of the GaInP layer and the Al _0.25 Ga _0.25 In _0.5 P layer at a wavelength of 680 nm are 3.56 and 3.37, respectively, the optical path lengths in this active layer are 146 nm, respectively. The optical path is 73 nm, which is half the length of the active layer region, and an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 and an n-type Al _0.35 Ga _0.15 In _0.5 P layer 303. The length should be 340 nm.

The layer thickness of the undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 304 is 20 nm, and the layer thickness of the n-type Al _0.35 Ga _0.15 In _0.5 P layer 303 is 60.5 nm. Since the refractive indexes are 3.37 and 3.30, respectively, the optical thickness of these two layers is 267 nm, and the total thickness is 340 nm with 73 nm which is half of the optical thickness of the first active layer 702. . That is, as shown in FIG. 10, the center of the first active layer 702 is located on the antinode 403 of the standing wave. Subsequently, the optical thickness of half of the first active layer 702 is 73 nm, the optical thickness of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 and the optical thickness of half of the second active layer 704. It may be 340 nm at 73 nm. Since the refractive index of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 is 3.37, if the thickness is 57.6 nm, the optical thickness of this intermediate barrier layer is 194 nm. It becomes. Thus, the total of the optical thicknesses of the first and second active layers 702 and 703 is 340 nm. Therefore, the center of the second active layer 704 is located at the antinode 403 of the standing wave as shown in FIG. By the way, a part of the AlGaInP intermediate barrier layer 703 may be doped with Mg or Zn to be p-type to increase the efficiency of hole injection into the first active layer 702.

The p-side has an optical thickness of 73 nm, which is half that of the active layer 704, and an undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _0.5 In _0.5 P layer 705. Therefore, the remaining optical thickness may be 680 nm. If the barrier layer 306 is 20 nm and the p-type Al _0.5 In _0.5 P layer 705 is 167.6 nm, the refractive index is 3.37 and 3.22, respectively. The thickness is 607 nm. The total of 607 nm and 73 nm, which is half the optical thickness of the second active layer 704, is 680 nm. The total thickness of the two active layers including the n-layer including the undoped barrier layer and the intermediate barrier layer, and the optical thickness of the p-layer including the undoped barrier layer are 267 nm, 486 nm, and 607 nm, respectively. It matches the optical thickness in the case of. The thickness of the p-type AlGaInP layer is also 167.6 nm, which is not less than 100 nm and not more than 300 nm. A multilayer reflector is formed on both sides of the resonator. The multilayer reflector is configured on both the n side and the p side so that it becomes an antinode of the standing wave at the interface between the resonator and the multilayer reflector. Specifically, a low refractive index material, here an AlAs layer 801 on the n side, an Al _0.9 Ga _0.1 As layer 402 on the p side is adjacent to the resonator, and a high refractive index material next to the resonator. The Al _0.5 Ga _0.5 As layer 401 is formed so as to be arranged on both the n side and the p side. Then, the necessary numbers (about 36 pairs on the p side and 60 pairs on the n side) are repeated.

In FIG. 12, the relationship between the environmental temperature and the maximum output regarding the red surface emitting laser manufactured by the multilayer structure described in the present embodiment is shown by a solid line. Specifically, it is the configuration described in FIG. 10 and its explanatory text, and the p-type semiconductor spacer layer 705 is a p-type Al _0.5 In _0.5 P layer 705 (layer thickness 167.6 nm). However, as the 801 layer in FIG. 10, Al _0.9 Ga _0.1 As is used instead of the AlAs layer. In the example shown by the dotted line in FIG. 12, the composition of the p-type semiconductor spacer layer is a p-type Al _0.35 Ga _0.15 In _0.5 P layer and the layer thickness is 60.5 nm as a conventional laser. It is a thing. The other layer configurations show the characteristics of the element when the same element as that shown by the solid line in FIG. 12 is used.

  As described above, as the environmental temperature increases, the leakage current increases and the light output tends to decrease. The conventional device (dotted line in FIG. 12) does not oscillate at an ambient temperature of 75.2 ° C., but the laser device of this example can oscillate up to 84.1 ° C. Further, when the maximum outputs of both were compared at 60 ° C., it was found that the device of the present invention had about 40% higher light output than the conventional device. That is, it can be seen that a red surface emitting laser capable of operating at a high temperature can be realized with a leakage current reduced as compared with the prior art.

  Note that an AlAs layer having a low thermal resistance can also be adopted as the low refractive index layer constituting the lower DBR located on the substrate side. In such a case, since heat generated in the laser element can be easily escaped, a situation in which the heat rise inside the element is suppressed as much as possible can be realized.

  Examples of various p-type spacer layer thicknesses applicable to the present invention are shown in Table 1. Table 1 shows an active layer, a p-side undoped barrier layer, an n-type spacer layer, an n-side undoped barrier layer, and a resonator length for realizing the thickness of the p-type spacer layer within a range of 100 nm to 350 nm. 16 types of examples are shown.

here,
Al _0.5 In _0.5 P layer as a p-type spacer layer,
Al _0.35 Ga _0.15 In _0.5 P layer as an n-type spacer layer,
As the undoped barrier layer, an Al _0.25 Ga _0.25 In _0.5 P layer is used on both the p-side and the n-side.

When a quadruple Ga _0.5 In _0.5 P / Al _0.25 Ga _0.25 In _0.5 P quantum well is used as the active layer, the layer thickness is 42 nm. On the other hand, when the periodic gain structure is used, the double period gain structure includes the intermediate undoped barrier layer and the thickness is 141.6 nm, and the triple period gain structure includes the two intermediate undoped barrier layers and the thickness is 241.2 nm.

  In Examples 1, 2, and 4, there were only two types of p-type spacer layer thicknesses of 167.6 nm and 273.2 nm. As shown in Table 1, by appropriately adjusting the resonator length, active layer thickness, undoped barrier layer, and n-type spacer layer thickness, the p-type spacer layer thickness is set within a desired value range (100 nm to 350 nm). can do.

  Two conditions are that the resonator length is an integral multiple of half the design wavelength and that the center of the active layer coincides with the antinode of the light distribution (the antinode of the internal light intensity standing wave). Is attached, the p-type spacer layer thickness does not take a continuous value. As shown in Table 1, it is possible to adjust the p-type spacer layer thickness defined in the present invention by adjusting the layer thickness of the undoped barrier layer.

It is a figure which shows the lineup of the band edge of the active layer of a red surface emitting laser element, a p-type semiconductor spacer layer, and a p-type semiconductor multilayer film area | region. The relationship between the normalized leak current (FIG. 2A) and the optical loss inside the resonator (FIG. 2B) with respect to the p-type semiconductor spacer layer thickness is shown. It is a typical sectional view for showing layer composition of a red surface emitting laser concerning a 1st embodiment of the present invention. 3 is a schematic cross-sectional view showing a resonator structure in Example 1. FIG. 1 is a schematic cross-sectional view showing a laser element in Example 1. FIG. The band diagram described in Non-Patent Document 2 is cited and described. 6 is a schematic cross-sectional view showing a layer configuration of a red surface emitting laser in Example 2. FIG. 6 is a schematic cross-sectional view illustrating a resonator structure in Example 2. FIG. 1 is a schematic diagram for explaining an image forming apparatus according to the present invention. 10 is a schematic cross-sectional view showing a resonator structure in Example 4. FIG. It is a schematic diagram for demonstrating the image display apparatus which concerns on this invention. 6 is a graph showing temperature characteristics of a laser obtained in Example 4.

Explanation of symbols

Reference Signs List 301 substrate 302 first reflecting mirror 305 active layer 307 p-type semiconductor spacer layer 308 second reflecting mirror 401 Al _0.5 Ga _0.5 As high refractive index layer 402 Al _0.9 Ga _0.1 As low refractive index Layer 403 antinode of internal electric field strength standing wave 501 n-side electrode 502 oxidation constriction layer 503 dielectric film 504 p-side electrode 701 n-type AlAs / Al _0.5 Ga _0.5 As multilayer mirror 702 first Ga _{0. 56} In _0.44 P / Al _0.25 Ga _0.25 In _0.5 P quantum well active layer 703 Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 704 Second Ga _0.56 In _{0 .44} P / Al _0.25 Ga _0.25 In _0.5 P quantum well active layer 705 p-type Al _0.5 In _0.5 P spacer layer 801 AlAs low refractive index layer 900 photoconductor 902 Charging device 904 Developing device 906 Transfer charging device 908 Fixing device 910 Rotating polygon mirror 912 Motor 914 Red surface emitting laser array 916 Reflecting mirror 920 Collimator lens 922 f-θ lens

Claims (20)

A red surface emitting laser element comprising a laminated film,
A first reflector,
a second reflecting mirror comprising a p-type semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror; and an active layer interposed between the active layer and the second reflecting mirror and having a thickness of 100 nm to 350 nm. a p-type semiconductor spacer layer,
A red surface emitting laser element characterized by comprising:   2. The red surface emitting laser element according to claim 1, wherein the p-type semiconductor spacer layer has a thickness of 150 nm to 300 nm.   3. The red surface emitting laser element according to claim 1, wherein the p-type semiconductor spacer layer is a layer made of a composition containing Al, In, and P. 4. The p-type semiconductor spacer layer includes Al _x Ga _y In _1-xy P (0.45 ≦ x + y ≦ 0.55, 0.25 ≦ x ≦ 0.55, 0 ≦ y ≦ 0.30). 4. The red surface emitting laser element according to claim 1, wherein the red surface emitting laser element is configured. The p-type semiconductor spacer layer includes Al _x Ga _y In _1-xy P (0.50 ≦ x + y ≦ 0.52, 0.35 ≦ x ≦ 0.52, 0 ≦ y ≦ 0.17). 5. The red surface emitting laser element according to claim 4, wherein the red surface emitting laser element is configured.   6. The red surface emitting laser element according to claim 1, wherein the p-type semiconductor multilayer film constituting the second reflecting mirror is made of a composition containing Al and As. 7.   The p-type semiconductor multilayer film constituting the second reflecting mirror is configured by laminating a set of a first layer and a second layer having different refractive indexes from each other a plurality of times. 7. The red surface emitting laser element according to claim 1, wherein at least one of the second layers is a layer made of a composition containing Al, Ga, and As. 8.   8. The red surface emitting laser element according to claim 1, wherein the second reflecting mirror is made of a semiconductor material lattice-matched to GaAs. 9.   9. The red surface emitting laser element according to claim 1, wherein the active layer is a quantum well active layer including a layer made of GaInP and a layer made of AlGaInP. 10.   10. The first reflecting mirror is formed of an n-type semiconductor multilayer film, and an n-type semiconductor spacer layer is provided between the first reflecting mirror and the active layer. The red surface emitting laser element according to any one of the above.   11. The red surface emitting laser element according to claim 1, further comprising another spacer layer between the p-type semiconductor spacer layer and the active layer. 11.   A resonator is configured including the active layer, the p-type semiconductor spacer layer, and the n-type semiconductor spacer layer, and the active layer has an asymmetric structure that is not located in the center of the resonator length direction. The red surface emitting laser element according to claim 10, wherein the red surface emitting laser element is provided.   13. The red surface emitting laser element according to claim 12, wherein a thickness of the p-type semiconductor spacer layer is larger than a thickness of the n-type semiconductor spacer layer.   2. The red surface emitting laser element according to claim 1, wherein the number of the active layers interposed between the first reflecting mirror and the second reflecting mirror is plural.   15. The resonator according to claim 1, wherein a resonator length including the active layer is not less than 1.5 wavelength resonator length and not more than 4 wavelength resonator length. Red surface emitting laser element. A red surface emitting laser element comprising a laminated film,
A first reflector,
a second reflecting mirror comprising a p-type AlGaAs semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror; and an active layer interposed between the active layer and the second reflecting mirror and having a thickness of 100 nm to 350 nm. a p-type AlInP semiconductor spacer layer or a p-type AlGaInP semiconductor spacer layer,
A red surface emitting laser element characterized by comprising: A red surface emitting laser element comprising a laminated film,
A first reflector;
a second reflecting mirror comprising a p-type semiconductor multilayer film;
An active layer interposed between the first reflecting mirror and the second reflecting mirror;
A p-type semiconductor spacer layer interposed between the active layer and the second reflecting mirror;
The conduction band edge at the point X of the p-type semiconductor multilayer film is lower than the p-type semiconductor spacer layer, and the thickness of the p-type semiconductor spacer layer is 100 nm or more and 350 nm or less. Surface emitting laser element.   It has the said red surface emitting laser element as described in any one of Claim 1 to 17, and the optical deflector for reflecting and scanning the laser beam output from this laser element, It is characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 18, comprising a photoconductor for forming an electrostatic latent image by light deflected by the light deflector, a charger, a developing device, and a fixing device.   18. An image display comprising: the red surface emitting laser element according to claim 1; and an optical deflector for reflecting and scanning the laser beam output from the laser element. apparatus.

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