JP2009170775A - Semiconductor light emitting device, manufacturing method thereof, and optical tomographic imaging apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element which emits low-coherence light having a center wavelength band of 0.90 to 1.15 μm, formation of a wide-band quantum well layer and formation of an upper clad layer of high crystal quality being compatibly achieved without removing a mask for selective growth. <P>SOLUTION: Disclosed is the semiconductor light emitting element 1 which emits low-coherence light having the center wavelength band of 0.90 to 1.15 μm and has a GaAs substrate 11 and an InGaAs quantum well layer 15, the semiconductor light emitting element being characterized in that the InGaAs quantum well layer 15 is formed at a growth temperature of ≤600°C by performing selective growth, and an InGaP upper clad layer 17 is formed at a growth temperature of ≥600°C without removing the mask for selective growth. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, a manufacturing method thereof, and an optical tomographic imaging apparatus using the same, and more specifically, a semiconductor light emitting device using selective growth, a manufacturing method thereof, and an optical tomographic image using the same. The present invention relates to a conversion device.

  An OCT (Optical Coherence Tomography) apparatus that uses optical interference with low-coherence light when acquiring a tomographic image of a living tissue has been put into practical use (Patent Document 1).

  As a light source wavelength of the OCT apparatus, a 0.8 μm band is mainly used. This is a wavelength selected as a result of mainly considering absorption characteristics in the living body. However, in recent years, it has been clarified that in the OCT apparatus that detects backscattered reflected light, the scattering characteristics also regulate the measurement depth. Therefore, recently, in order to minimize the total loss of light in the living tissue expressed by the sum of absorption loss and scattering loss, the 1.3 μm band as a light source wavelength has attracted attention. This is a result of considering that the scattering intensity of Rayleigh scattering mainly occurring in the living tissue is inversely proportional to the fourth power of the wavelength. For this reason, after the OCT apparatus for ophthalmology has been put into practical use, research and development using light in the 1.3 μm band has been advanced for OCT apparatuses for endoscopes.

  However, when an OCT apparatus is applied to an endoscope, it must be considered that many parts to be measured are covered with a substance containing a lot of moisture. For example, the stomach wall is covered with gastric juice and gastric mucosa, and the colon wall is covered with mucus and intestinal mucosa. The bladder wall is covered with urine or physiological saline used for measurement. Therefore, in the measurement target covered with a substance containing a large amount of moisture as described above, since the light in the 1.3 μm band is easily affected by absorption by water, a tomographic image up to a desired measurement depth cannot be acquired. Or the problem that the reliability of the acquired tomographic image falls arises.

  Therefore, in the case of acquiring a tomographic image of a measured part covered with a substance containing a lot of moisture in Patent Document 2, the present applicant takes into consideration the light absorption characteristics, scattering characteristics, and dispersion characteristics of biological tissue. It has been clarified that the low coherence light for the OCT apparatus is optimal when the center wavelength band is 0.90 μm or more and 1.15 μm or less.

On the other hand, the resolution in the optical axis direction of the tomographic image is determined by the coherence length of the light source, and the resolution improves as the coherence length becomes shorter. Since the coherence length Δz of the low-coherence light is expressed by the following equation using the center wavelength λc and the spectral half-value width Δλ, it can be said that it is preferable that the light source for the OCT apparatus has a wider band.
Δz = 2ln2 · λc ² / (π · Δλ)

  Therefore, a superluminescent diode (SLD) that is low in cost and has an emission spectrum close to a Gaussian shape is promising as a candidate for a semiconductor light-emitting element constituting a low-coherence light source. As one of methods for manufacturing an SLD having a broad emission spectrum, there is a method of forming a structure that generates light having different emission wavelengths in the waveguide direction of emitted light in a semiconductor light emitting device.

Specifically, the selective growth is used to form an active layer in which the film thickness and composition of the quantum well are changed along the waveguide direction of the emitted light, thereby emitting light in the waveguide direction of the emitted light. This is a method of obtaining a structure that generates light having different wavelengths. In this method, when two selective growth masks formed of SiO ₂ or the like having different widths are formed at an interval and crystal growth is performed thereon, the growth rate and composition of the growth region sandwiched between the masks are masked. It utilizes a phenomenon that changes depending on the width. Therefore, by changing the mask width, the thickness and composition of the active layer grown can be changed along the waveguide direction of the emitted light.
JP 11-325849 A JP 2007-184557 A JP 2006-267071 A

  However, although this method can be used to obtain a semiconductor light emitting device having a broad emission spectrum, a semiconductor light emitting device that emits low coherence light having a central wavelength band of 0.90 μm or more and 1.15 μm or less is manufactured. There are the following problems.

  When a GaAs substrate and an InGaAs quantum well layer are used in this wavelength band, the material that can be used for the cladding layer is a system containing Al such as AlGaAs or InGaP because of the band gap.

  However, the former material system containing Al is unsuitable for use because the adsorption to the selective growth mask is too strong and a polycrystal is generated on the mask, which adversely affects the light output characteristics.

On the other hand, the latter In _x Ga _1-x P is lattice-matched to the GaAs substrate only at X = 0.5. Therefore, when trying to broaden the emission spectrum by selective growth, after forming an InGaAs quantum well layer by applying strong modulation to the composition of In and Ga, and forming an InGaP upper cladding layer under the same conditions, In this case, the same compositional modulation occurs, resulting in lattice mismatch with the GaAs substrate. As a result, crystal degradation occurs from the lattice mismatched upper clad layer, and the durability and reliability of the semiconductor light emitting device are lowered. If the method of forming the upper cladding layer after removing the selective growth mask (that is, without using selective growth) is used, the problem of lattice mismatch does not occur. However, this method cannot be used at all, considering that the series of layer formation steps must be stopped at an inappropriate place, and that most of the active layer must be exposed to the outside air. It is clear.

  That is, in a semiconductor light-emitting device that emits low-coherence light having a central wavelength band of 0.90 μm or more and 1.15 μm or less and that uses selective growth, a quantum spectrum having a broad emission spectrum without removing the selective growth mask. It has been very difficult to achieve both the formation of the well layer and the formation of the upper cladding layer having a high crystal quality. For example, as shown in Patent Document 3 by the present applicant, when an InGaP upper cladding is formed by selective growth, there is a problem in characteristics such as light emission efficiency.

  The present invention has been made in view of the above problems, and has higher durability in a semiconductor light emitting device that emits low coherence light in a central wavelength band of 0.90 μm or more and 1.15 μm or less and uses selective growth. An object of the present invention is to provide a reliable semiconductor light emitting device and a method for manufacturing the same, and to provide a higher performance optical tomographic imaging apparatus using the semiconductor light emitting device according to the present invention.

  In order to achieve the above object, the present applicant has focused on the fact that the composition modulation of In and Ga can be controlled by the growth temperature in selective growth, and has reached the present invention.

That is, the method for manufacturing a semiconductor light emitting device according to the present invention includes:
A first step of forming a selective region by forming a selective growth mask whose width changes stepwise or continuously on a lower clad layer formed on a conductive GaAs substrate;
A second step of forming at least one quantum well layer composed of InGaAs on the selected region;
In a method for manufacturing a semiconductor light emitting device, comprising at least a third step of forming an upper cladding layer made of InGaP on a quantum well layer in this order,
The second step is performed at a growth temperature of less than 600 ° C., the third step is performed at a growth temperature of 600 ° C. or more without removing the selective growth mask, and at least the second to third steps are performed. The process is performed without exposure to the atmosphere.

  Here, the “mask for selective growth whose width changes stepwise or continuously” is a mask used for selective growth, and the length of the mask in the direction perpendicular to the waveguide direction of the emitted light. Means one that changes along the waveguide direction stepwise or continuously.

  Then, performing the third step “without removing the selective growth mask” means that the third step is performed without performing at least the step for removing the selective growth mask before the third step. Is meant to be performed.

  “Do not expose to the atmosphere” means that a semiconductor light emitting element in the middle of manufacture is taken out from the thin film growth apparatus to the atmosphere, or a thin film growth apparatus in which a semiconductor light emitting element in the middle of manufacture is present is not filled with air. It means to do. In this case, movement between apparatuses via a vacuum path or a path filled with an inert gas is included.

  In the method for manufacturing a semiconductor light emitting device according to the present invention, the growth temperature in the second step is in the range of 500 ° C. to less than 600 ° C., and the growth temperature in the third step is in the range of 600 ° C. to 750 ° C. Is preferred.

  Furthermore, the semiconductor light-emitting device according to the present invention is manufactured by the above-described method for manufacturing a semiconductor light-emitting device, and is preferably a superluminescent diode or a semiconductor optical amplifier.

  Moreover, it is preferable to have a sloped waveguide structure in which the light exit surface is inclined with respect to the resonator axis.

Furthermore, the optical tomographic imaging apparatus according to the present invention is:
A light source that emits low coherence light;
A splitting means for splitting the low-coherence light into measurement light and reference light, an irradiation optical system for irradiating the measurement light to the measurement object,
A multiplexing means for multiplexing the reflected light from the measurement object when the reference light or the measurement light is irradiated and the reference light;
Based on the light intensity of the interference light between the combined reflected light and the reference light, the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially coincide with each other at a plurality of depths of the measurement target. In an optical tomographic imaging apparatus comprising image acquisition means for detecting the intensity of reflected light at a position and acquiring a tomographic image of a measurement object based on the intensity at these depth positions,
The light source unit includes the semiconductor light emitting element described above as a light source of low coherence light.

  The semiconductor light emitting device according to the present invention emits low coherence light having a central wavelength band of 0.90 μm or more and 1.15 μm or less, and has a GaAs substrate and an InGaAs quantum well layer. The InGaAs quantum well layer is formed at a growth temperature of 600 ° C. or lower, and the InGaP upper cladding layer is formed at a growth temperature of 600 ° C. or higher without removing the selective growth mask. Thereby, it is possible to control so that In and Ga in the InGaAs quantum well layer are compositionally modulated, and In and Ga in the InGaP upper cladding layer are not compositionally modulated. As a result, the formation of a quantum well layer having a broad emission spectrum and the formation of an upper cladding layer having a high crystal quality can be achieved, thereby improving the durability and reliability of the semiconductor light emitting device. By using the semiconductor light emitting element according to the present invention, the performance of the optical tomographic imaging apparatus can be improved.

  Hereinafter, although the best embodiment in the present invention is described using a drawing, the present invention is not limited to this.

“Semiconductor Light-Emitting Element and Manufacturing Method Thereof”
First, control of composition modulation of In and Ga by the growth temperature will be described.
FIG. 1 is a graph showing the relationship between the compositional modulation of InGaAs and the width of the selective growth mask at growth temperatures of 550 ° C., 585 ° C., 600 ° C., and 635 ° C. As a result, it has been found that the effect of compositional modulation by selective growth varies depending on the growth temperature. That is, when selective growth is performed at growth temperatures of 550 ° C. and 585 ° C., compositional modulation and film thickness modulation occur depending on the selective growth mask width. However, when selective growth is performed at growth temperatures of 600 ° C. and 635 ° C., the diffusion lengths of In and Ga are substantially the same and the composition ratio does not change. Therefore, wavelength modulation in this temperature region is effective only for film thickness modulation. Can be seen.

  FIG. 2 is a graph showing the same relationship as In FIG. 1 for InGaP. From this, it can be seen that InGaP also has the same effect as InGaAs by controlling the growth temperature.

  The composition amount was determined by Auger electron spectroscopy, and the thicknesses of the InGaAs layer and the InGaP layer were 200 mm in order to evaluate the critical film thickness or less.

  From these, it can be seen that a change occurs in the diffusion length of In and Ga around 600 ° C., and the effect of the composition modulation appears. Furthermore, in the III-V group semiconductor compound which has In and Ga in a III group system, it has shown that the growth temperature which becomes this boundary does not depend on the kind of V group system. Therefore, by utilizing this phenomenon in selective growth, the InGaAs quantum well layer is formed at a growth temperature below 600 ° C. to enhance the effect of composition modulation, and the InGaP upper clad layer is formed at a temperature above 600 ° C. Thus, it is possible to control such that the composition is not modulated.

  An example of the growth temperature profile at that time is shown in FIG. In this case, the InGaAs quantum well layer is formed at a growth temperature of 580 ° C., then the growth temperature is increased to 650 ° C., and the InGaP upper cladding layer is formed at a growth temperature of 650 ° C. By using this method, in the manufacture of a semiconductor light emitting device that emits low coherence light having a central wavelength band of 0.90 μm or more and 1.15 μm or less, formation of a quantum well layer having a broad emission spectrum and a high crystal quality upper portion It is possible to achieve both formation of the cladding layer.

Next, the semiconductor light emitting device and the manufacturing method thereof according to the first embodiment will be described.
4 to 7 are schematic perspective views illustrating the manufacturing process of the semiconductor light emitting device according to the present embodiment. FIG. 7 is a schematic perspective view of the semiconductor light emitting device 1 according to the present embodiment manufactured through this process. In the semiconductor light emitting device 1 according to the present embodiment shown in FIG. 7, the device end surface on the far side in the drawing is the rear end surface 1R, and the device end surface on the near side in the drawing is the front end surface (end surface on the light output side) 1F. In the present embodiment, the rear end surface 1R and the front end surface 1F are both perpendicular to the substrate surface of the semiconductor substrate 11, and the rear end surface 1R and the front end surface 1F are parallel to each other.
The layer configuration of the semiconductor light emitting device 1 according to the present embodiment will be explained below.

In the semiconductor light emitting device 1, an n-type GaAs buffer layer 12 and an n-type In _0.49 Ga _0.51 P lower cladding layer 13 are sequentially formed on the upper surface of an n-type (first conductivity type) GaAs substrate 11 from the substrate side. Are stacked. On the lower cladding layer 13, an undoped GaAs lower light guide layer 14, an InGaAs / GaAs quantum well active layer 15, an undoped GaAs upper light guide layer 16, and a p-type (second conductivity type) In _0.49 Ga _{0. A} striped ridge structure 20 having a laminated structure of ₅₁ P upper cladding layer 17 is formed. The ridge width d of the ridge structure portion 20 is 5 μm. A p-type GaAs contact layer 18 is formed on the ridge structure portion 20 on the upper surface except for both side end surfaces of the ridge structure portion 20. An SiO ₂ current confinement layer 19 is formed so as to cover the lower cladding layer 13 and the ridge structure portion 20 except for a part on the contact layer 18 (current confinement portion 23). Further, a p-type electrode 25 is formed on the current confinement layer 19 and an n-type electrode 26 is formed on the lower surface of the substrate 11 so as to fill the current confinement portion 23.

  The quantum well active layer 15 has an alternately stacked structure of InGaAs quantum well layers and barrier layers (for example, GaAs). In this case, the quantum well active layer 15 may have a single quantum well structure with one InGaAs quantum well layer or a multiple quantum well structure with two or more InGaAs quantum well layers.

  In the present embodiment, among the layers forming the ridge structure portion 20, the InGaAs quantum well layer in the quantum well active layer 15 has a composition and a film thickness, and the other layers have a film thickness. The wave direction is changed stepwise or continuously. Thus, the InGaAs quantum well layer has a compressive strain that changes stepwise or continuously, and the other layers are configured to lattice match. In addition, the layer composition of the semiconductor light emitting element 1 and the film thickness of each layer can be appropriately designed according to the wavelength characteristics of the emitted light. Further, the ridge structure portion 20 is formed by two regions (referred to as an e region and an f region, respectively) aligned in the light guiding direction (FIG. 7), and the film thickness of the e region on the light output side. Is getting thicker. At the boundary between the e region and the f region, both the composition and the film thickness are inclined so that the composition and the film thickness continuously change between the two regions. The width in the waveguide direction of the emitted light in the e region and the f region is not particularly limited and can be appropriately designed according to the wavelength characteristics of the emitted light.

The method for manufacturing the semiconductor light emitting device 1 according to the present embodiment will be described below.
With reference to FIGS. 4 to 7, an example of a method for manufacturing the semiconductor light emitting device 1 according to the present embodiment will be described. In the present embodiment, the semiconductor light emitting device 1 is manufactured by selective growth using a patterned selective growth mask.

First, an n-type (first conductivity type) GaAs substrate 11 is prepared, and an n-type GaAs buffer layer 12 and an n-type In _0.49 Ga _0.51 P lower cladding layer 13 are sequentially formed on substantially the entire surface of the substrate 11. . Next, a SiO ₂ selective growth mask M having a pattern corresponding to the ridge structure 20 is formed on the n-type lower cladding layer 13 (FIG. 4), and the selective growth mask M is patterned by photolithography. Thereafter, with the selective growth mask M formed, an undoped GaAs lower light guide layer 14, an InGaAs / GaAs quantum well active layer 15, and an undoped GaAs upper light guide layer 16 are sequentially formed at a growth temperature of 580 ° C. Then, the growth is interrupted to raise the growth temperature to 650 ° C. (FIG. 3). Then, a p-type (second conductivity type) In _0.49 Ga _0.51 P upper clad layer 17 and a p-type GaAs contact layer 18 are sequentially formed (FIG. 5), and the selective growth mask M is removed to make a minute. After removing the polycrystal (FIG. 6), the contact layer 18 is removed leaving only the upper portion of the ridge structure 20 by lithography and etching. Then, a SiO ₂ current confinement layer 19 is formed, a window opening stripe having a width of about 2 μm is formed in a portion corresponding to the upper portion of the ridge structure portion 20 by a lithography process, and a p-type electrode 25 is further formed on the lower surface of the substrate 11. The n-type electrode 26 is formed on the semiconductor light emitting device 1 to complete the semiconductor light emitting device 1 (FIG. 7). The steps from the formation of the lower light guide layer 14 to the formation of the contact layer 18 are performed consistently with one thin film growth apparatus without being exposed to the atmosphere.

  In this embodiment, the method for forming each semiconductor layer and various films is not particularly limited, and examples thereof include a metal organic chemical vapor deposition method (MOCVD method) and a molecular beam epitaxy method.

  Since the ridge structure 20 is selectively grown by the selective growth mask M as shown in FIG. 4, the composition and film thickness of each layer are stepwise in the waveguide direction of the emitted light as described above. Or it becomes the structure changed continuously.

  The second step is included in the step of forming the InGaAs / GaAs quantum well active layer 15. As described above, the quantum well active layer 15 has a single quantum well structure or a multiple quantum well structure. At this time, it is sufficient that at least one InGaAs quantum well layer is formed so as to cause compositional modulation at a growth temperature of less than 600 ° C. This is because if there is at least one InGaAs quantum well layer having compositional modulation, it is possible to broaden the emission spectrum of the semiconductor light emitting device. In the case where the quantum well active layer 15 has a multiple quantum well structure, all InGaAs quantum well layers are caused to undergo compositional modulation at a growth temperature of less than 600 ° C. from the viewpoint of light emission characteristics of the semiconductor light emitting device. More preferably, it is formed.

Then, in the third step of forming the In _0.49 Ga _0.51 P upper cladding layer 17 at a growth temperature of 650 ° C., the composition of the upper cladding layer 17 is modulated without removing the selective growth mask M. I try not to make it happen.

  The growth temperature in the second step is preferably in the range of 500 ° C. to less than 600 ° C., and the growth temperature in the third step is preferably in the range of 600 ° C. to 750 ° C. Here, the reason why the lower limit of the growth temperature in the second step is set to 500 ° C. is because the crystal quality of the InGaAs quantum well layer deteriorates, and the upper limit of the growth temperature in the third step is set to 750 ° C. This is because the crystal quality deteriorates in the same manner when a thermal history higher than this is applied to the InGaAs quantum well layer.

  In the present embodiment, the growth interruption is performed when the growth temperature is raised, but the growth interruption is not necessarily required. For example, in forming the InGaAs / GaAs quantum well active layer 15, a method of increasing the temperature while forming the last barrier layer may be used. In this way, it is possible to prevent re-evaporation of the material from the uppermost layer due to the growth interruption, and to continuously perform a series of layer formation. For example, in the case of a GaAs barrier layer, such a method can be used because even if the growth temperature is changed during formation of the layer, there is no influence of compositional modulation or the like.

  Furthermore, in the present invention, at least the second step to the third step are performed without exposure to the atmosphere. However, in the case of this embodiment, it is preferable to perform the steps from the formation of the lower light guide layer 14 to the formation of the contact layer 18 as described above without exposing to the atmosphere. It is more desirable to do it consistently. More generally, it is more desirable to form a thin film between the formation and removal of the selective growth mask M without exposing it to the atmosphere with one thin film growth apparatus. By doing so, particle contamination due to exposure to the atmosphere can be prevented, so that there is an effect of preventing quality deterioration of the structure close to the InGaAs / GaAs quantum well active layer 15.

The selective growth technique is a method in which a semiconductor crystal is vapor-phase grown only in a region not masked by a selective growth mask (dielectric such as SiO ₂ ). In the case of a mixed crystal semiconductor crystal, by changing the mask width, the concentration gradient in the gas phase of each source species containing atoms constituting the mixed crystal semiconductor crystal and the effective movement distance due to surface migration change, and the composition and A gradient can be given to the film thickness. Therefore, the semiconductor light emitting device 1 having two regions having different compositions and film thicknesses in the waveguide direction of the emitted light can be manufactured in a lump without dividing into regions by selective growth. The modulation control of the composition and film thickness of the ridge structure portion 20 can be performed by changing the mask pattern (mask width, inter-mask width, etc.) so as to obtain a desired composition and film thickness. The pattern of the selective growth mask M shown in FIG. 4 is an example of a pattern used when the semiconductor light emitting element 1 is configured.

  The width of the selective growth mask M may be determined in accordance with the film thickness and composition of the ridge structure portion 20, and the width of the film on which the film thickness is desired to be relatively increased may be increased. As shown in the drawing, in the present embodiment, the width of the selective growth mask M is increased so that the film thickness is increased in the e region on the light output side.

Hereinafter, the operation in the present embodiment will be described.
The semiconductor light emitting device 1 according to the present invention emits low coherence light having a central wavelength band of 0.90 μm or more and 1.15 μm or less, has a GaAs substrate and an InGaAs quantum well layer, and uses InGaAs quantum wells by selective growth. The well layer is formed at a growth temperature of 580 ° C., and the InGaP upper cladding layer is formed at a growth temperature of 650 ° C. without removing the selective growth mask.

  Thereby, it is possible to control so that the In and Ga in the InGaAs quantum well layer are compositionally modulated and the In and Ga in the InGaP upper cladding layer are not compositionally modulated while the selective growth mask M is left. That is, the InGaAs quantum well layer can have a structure in which the band gap changes along the waveguide direction of the emitted light, and the upper cladding layer 17 is entirely lattice-matched without compositional modulation. It can be. As a result, the formation of a quantum well layer having a broad emission spectrum and the formation of an upper cladding layer having a high crystal quality can be compatible, thereby improving the durability and reliability of the semiconductor light emitting device.

  Furthermore, the step of removing the selective growth mask M can be omitted, and the step of exposure to the atmosphere can be reduced, and a consistent thin film can be formed. Therefore, the manufacturing process can be simplified and the cost can be reduced.

  The light emission characteristics of the semiconductor light emitting device 1 according to the present invention and the conventional semiconductor light emitting device manufactured at 580 ° C. without changing the growth temperature of the quantum well active layer and the upper cladding layer were as follows. . In the conventional type, cracks occurred in the InGaP upper clad layer having the wider ridge width and light emission could not be observed. However, in the semiconductor light emitting device 1 according to the present invention, the composition of In and Ga is stabilized and a high quality InGaP upper clad layer is formed. Since the external quantum efficiency is 0.3 W / A, the light emission characteristics are remarkably improved. Furthermore, the center wavelength was 1.102 μm, the spectrum half width was 186.3 nm, and the maximum output was 19.6 mW, so that sufficient performance as an OCT light source could be obtained.

  As described above, according to the present invention, it is possible to obtain a semiconductor light emitting device having a broad spectrum and high output of a spectral half width of 200 nm and an output of about 10 mW, and providing a light source that can withstand a practical level of an ultra high resolution OCT apparatus. It becomes possible.

  The semiconductor light emitting device 1 according to the present embodiment can also be used as a super luminescent diode (SLD) or a semiconductor optical amplifier (SOA).

(Design change example)
The semiconductor light emitting device 1 according to the present embodiment is not limited to the above configuration, and can be appropriately changed in design.
In the above embodiment, the semiconductor light emitting device 1 has the buried ridge stripe structure, but may have other structures such as an internal stripe structure.

  In the above embodiment, the optical waveguide has a waveguide structure extending in the direction substantially the same as the normal direction of the element end faces 1F and 1R. However, at least a part of the optical waveguide is in the normal direction of the element end faces 1F and 1R. An oblique waveguide structure extending obliquely may be used.

  In the above embodiment, the ridge structure 20 is manufactured by the selective growth technique, but the manufacturing method is not limited.

  Moreover, in the said embodiment, although it was set as the structure from which the light emission wavelength differs in two area | regions of the waveguide direction of the light to inject | emitted, the number of area | regions is not restrict | limited and it can design suitably according to the wavelength characteristic of the light to inject | emits.

Furthermore, since the semiconductor light emitting device 1 according to the present embodiment has a configuration in which a plurality of continuous regions emitting different wavelengths are provided in the waveguide direction of emitted light on the same substrate, a single semiconductor substrate is used. In addition, it can be applied to a semiconductor optical integrated device in which a plurality of optical devices having different functions are integrated.

"Optical tomography system"
With reference to the drawings, an optical tomographic imaging apparatus including the semiconductor light emitting device 1 of the above embodiment will be described. FIG. 8 is a schematic configuration diagram of the optical tomographic imaging apparatus according to the present embodiment.

  An optical tomographic imaging apparatus 200 shown in FIG. 8 acquires a tomographic image to be measured by the above-described TD-OCT (Time Domain Optical Coherence Tomography) measurement. The optical tomographic imaging apparatus 200 emits a laser beam La and collects light. A light source unit (light source unit) 210 composed of a lens 51, a light splitting means 2 for splitting a laser beam La emitted from the light source unit 210 and propagating through an optical fiber FB1, and a laser beam La passing through the light beam measuring unit L1 The light splitting means 3 that splits the light into the reference light L2, the optical path length adjusting means 220 that adjusts the optical path length of the reference light L2 split by the light splitting means 3 and propagated through the optical fiber FB3, and the light splitting means 3 The optical probe 230 for irradiating the measuring object S with the measuring light L1 propagated through the optical fiber FB2, and the measuring light L1 is irradiated from the optical probe 230 to the measuring object S. When the reflected light L3 from the measurement object and the reference light L2 are combined, the combining means 4 (also serving as the light splitting means 3) combines the reflected light L3 and the reference light. Interference light detection means 240 for detecting interference light L4 with L2.

  The light source 50 is an SLD that emits low-coherent light La having a center wavelength (λc) of 1.1 μm and a spectral half width of 75 nm, and the light source unit 210 transmits the light emitted from the light source 50 and the light source 50 to the optical fiber FB1. And an optical system 51 for making the light incident inside. This light source 50 is the semiconductor light emitting device 1 of the above embodiment.

  The optical path length adjusting means 220 is a mirror that is movable in the direction of arrow A in the figure so as to change the distance between the collimator lens 61 that collimates the reference light L2 emitted from the optical fiber FB3 and the collimator lens 61. 63 and mirror moving means 64 for moving the mirror 63, and has a function of changing the optical path length of the reference light L2 in order to change the measurement position in the measurement object S in the depth direction. . The reference light L 2 whose optical path length has been changed by the optical path length adjusting means 220 is guided to the multiplexing means 4.

  The optical probe 230 includes a cylindrical probe outer cylinder 55 whose tip is closed, and one optical fiber 53 disposed in the inner space of the probe outer cylinder 55 so as to extend in the axial direction of the outer cylinder 55. A prism mirror 57 that deflects the light L emitted from the tip of the optical fiber 53 in the circumferential direction of the probe outer cylinder 55, and the light L emitted from the tip of the optical fiber 53 is arranged on the outer circumference of the probe outer cylinder 55. A rod lens 58 that condenses light so as to converge on the measurement target S as a body to be scanned, and a motor 54 that rotates the prism mirror 57 about the axis of the optical fiber 53 are provided.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light La guided from the light source unit 210 through the optical fiber FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively. The measurement light L1 is guided through the optical fiber FB2, and the reference light L2 is guided through the optical fiber FB3. The light splitting means 3 in this example also functions as the multiplexing means 4.

  An optical probe 230 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 230. The optical probe 230 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 31.

  Further, the multiplexing means 4 is composed of a 2 × 2 optical fiber coupler as described above, and the reference light L2 that has been subjected to frequency shift and change of the optical path length by the optical path length adjusting means 230, and the reflected light L3 from the measurement object S. Are combined and emitted to the interference light detection means 240 side via the optical fiber FB4.

  The interference light detection means 240 detects the light intensity of the interference light L4. The light detectors 40a and 40b that measure the light intensity of the interference light L4, the detection value of the light detector 40a, and the light detector 40b. And an arithmetic unit 41 that performs balance detection by adjusting the input balance of the detected values. Specifically, when the difference between the total optical path length of the measuring light L1 and the reflected light L3 reflected or backscattered at a point on the measuring object S and the optical path length of the reference light L2 is shorter than the coherence length of the light source Only an interference signal with an amplitude proportional to the amount of reflected light is detected. By scanning the optical path length by the optical path length adjusting unit 220, the reflection point position (depth) of the measurement target S from which the interference signal is obtained changes, and the interference light detection unit 240 reflects the reflection at each measurement position of the measurement target S. A rate signal is detected. The information on the measurement position is output from the optical path length adjustment unit 220 to the image acquisition unit 250. Based on the information on the measurement position in the mirror moving unit 64 and the signal detected by the interference light detection unit 240, the image acquisition unit 250 obtains the reflected light intensity distribution information in the depth direction of the measurement target S.

  Hereinafter, the operation of the optical tomographic imaging apparatus 200 having the above configuration will be described. When acquiring a tomographic image, the optical path length is adjusted so that the measuring object S is positioned within the measurable region by first moving the mirror 63 in the direction of arrow A. Thereafter, the light La is emitted from the light source unit 210, and the light La is split into the measurement light L1 and the reference light L2 by the light splitting means 3. The measurement light L1 is emitted from the optical probe 230 into the body cavity and irradiated to the measurement object S.

  Then, the reflected light L3 from the measuring object S is combined with the reference light L2 reflected by the reflecting mirror 62 to generate interference light L4.

  The interference light L4 is split by the light splitting means 3 (multiplexing means 4), one of which is input to the photodetector 40a and the other is input to the photodetector 40a.

  The interference light detection means 240 adjusts the input balance between the detection value of the light detector 40 a and the detection value of the light detector 40 b to perform balance detection, detects the light intensity of the interference light L 4, and sends it to the image acquisition means 250. Output.

  Based on the detected light intensity of the interference light L4, the image acquisition means 250 obtains reflected light intensity information at a predetermined depth of the measuring object S. Next, the optical path length adjustment unit 330 changes the optical path length of the reference light L2, similarly detects the light intensity of the interference light L4, and acquires reflected light intensity information at different predetermined depths. By repeating such an operation, the reflected light intensity information in the depth direction (one-dimensional) of the measuring object S can be acquired.

  Then, if the measurement light L1 is scanned on the measurement target S by rotating the prism mirror 57 by the motor 54 of the optical probe 230, the depth direction of the measurement target S in each portion along the scanning direction. Since information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measuring object S to scan in the second direction orthogonal to the scanning direction, the second object is obtained. It is also possible to obtain a tomographic image of a tomographic plane including the direction.

The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measuring object S to scan in the second direction orthogonal to the scanning direction, the second object is obtained. It is also possible to obtain a tomographic image of a tomographic plane including the direction.
As described in the background section, the performance of the optical tomographic imaging apparatus largely depends on the broadband property of the light source. Since the optical tomographic imaging apparatus 200 according to the present embodiment is configured using the semiconductor light emitting element 1 according to the present embodiment having a wide band and high output, it is possible to acquire a clear and high-definition tomographic image. it can.

(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate. In the above-described embodiment, an optical tomographic imaging apparatus that acquires an image by TD-OCT measurement is described as an example, but the present invention can also be applied to other optical tomographic imaging apparatuses.

  The semiconductor light emitting device of the present invention can be particularly preferably used for a low coherence light source for an optical image tomography apparatus such as an OCT apparatus. The semiconductor light emitting device of the present invention can be preferably used as a light source for various applications in fields such as communication, measurement, medical care, printing, and image processing in addition to the light source for the optical image tomography apparatus.

Diagram showing the relationship between growth temperature and composition change in InGaAs layers The figure which shows the relationship between the growth temperature and composition variation in an InGaP layer Conceptual diagram showing an example of growth temperature profile with controlled compositional modulation Sectional drawing which shows the manufacturing process of the semiconductor light-emitting device by embodiment (the 1) Sectional drawing which shows the manufacturing process of the semiconductor light-emitting device by embodiment (the 2) Sectional drawing which shows the manufacturing process of the semiconductor light-emitting device by embodiment (the 3) Sectional drawing which shows the structure of the semiconductor light-emitting device by embodiment (the 4) Schematic configuration diagram showing an optical tomographic imaging apparatus according to an embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor light emitting element 11 1st conductivity type (n type) GaAs substrate 12 1st conductivity type (n type) GaAs buffer layer 13 1st conductivity type (n type) InGaP lower clad layer 14 Undoped GaAs lower light guide layer 15 InGaAs / GaAs quantum well active layer 16 Undoped GaAs upper light guide layer 17 Second conductivity type (p-type) InGaP upper cladding layer 18 Second conductivity type (p-type) GaAs contact layer 19 SiO ₂ current confinement layer 20 Ridge structure portion 21 p-type Electrode 22 N-type electrode 23 Current constriction part 200 Optical tomographic imaging apparatus 210 Light source unit (light source part)
2, 3 Division means 230 Irradiation probe (irradiation optical system)
4 Multiplexing means 250 Image acquisition means S Measurement object La Low coherence light (broadband light)
L1 Measurement light L2 Reference light L3 Reflected light L4 Interference light d Width of ridge structure

Claims (7)

A first step of forming a selective region by forming a selective growth mask whose width changes stepwise or continuously on a lower clad layer formed on a conductive GaAs substrate;
A second step of forming at least one quantum well layer composed of InGaAs on the selected region;
In a method for manufacturing a semiconductor light emitting device, comprising at least a third step of forming an upper cladding layer made of InGaP on the quantum well layer in this order,
The second step is performed under a growth temperature of less than 600 ° C., the third step is performed under a growth temperature of 600 ° C. or more without removing the selective growth mask, and at least the second step To the third step without performing exposure to the atmosphere.   2. The semiconductor according to claim 1, wherein a growth temperature in the second step is in a range of 500 ° C. to less than 600 ° C., and a growth temperature in the third step is in a range of 600 ° C. to 750 ° C. 3. Manufacturing method of light emitting element.   A semiconductor light emitting device manufactured by the method for manufacturing a semiconductor light emitting device according to claim 1.   4. The semiconductor light emitting device according to claim 3, wherein the semiconductor light emitting device is a superluminescent diode.   4. The semiconductor light-emitting device according to claim 3, wherein the semiconductor light-emitting device is a semiconductor optical amplifier.   6. The semiconductor light emitting device according to claim 3, wherein the light emitting surface has a sloped waveguide structure in which the light emitting surface is inclined with respect to the resonator axis. A light source that emits low coherence light;
A dividing unit that divides the low-coherence light into measurement light and reference light; and an irradiation optical system that irradiates the measurement object with the measurement light.
A multiplexing means for multiplexing the reflected light from the measurement object when irradiated with the reference light or the measurement light, and the reference light;
Based on the light intensity of the interference light between the reflected light and the reference light combined, the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially match In an optical tomographic imaging apparatus comprising image acquisition means for detecting the intensity of reflected light at a plurality of depth positions and acquiring a tomographic image of a measurement object based on the intensity at these depth positions,
An optical tomographic imaging apparatus, wherein the light source unit includes the semiconductor light emitting element according to claim 3 as a light source of the low coherence light.

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