JP2007219561A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical modulator of an electric field absorption type which is high in a signal-to-noise ratio of optical modulation even at a high temperature and enables ≥10 GHz high speed modulation and to provide a semiconductor light emitting device. <P>SOLUTION: The semiconductor optical modulator is provided with an n type Al<SB>0.4</SB>Ga<SB>0.6</SB>As clad layer 102, a lower GaAs optical waveguide layer 103, a multiple quantum well structure 301, an upper GaAs optical waveguide layer 105, a first p type Al<SB>0.4</SB>Ga<SB>0.6</SB>As clad layer 302, a p type AlAs layer 303, a second p type Al<SB>0.4</SB>Ga<SB>0.6</SB>As clad layer 108, and a p type GaAs cap layer 109 sequentially on an n type GaAs substrate 101. The multiple quantum well structure 301 is formed by laminating GaInNAs as well layers and GaInP as barrier layers in three periods. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device.

Conventionally, for example, Patent Document 1 discloses a semiconductor optical modulator using an InGaAsP-based multiple quantum well structure. That is, the InP / InGaAsP-based multiple quantum well structure is also used as an optical modulator using the quantum confined Stark effect. The quantum confined Stark effect is a phenomenon in which the energy band gap between exciton electron-hole pairs is reduced when a voltage is applied to the quantum well layer. When no voltage is applied to the quantum well structure, the light absorption coefficient is 0. However, when a voltage is applied, the energy band gap of the quantum well layer is reduced by the quantum confined Stark effect, and light absorption is increased. Thereby, an electroabsorption optical modulator capable of modulating the light intensity can be formed.
JP-A-10-228005

  However, in an electroabsorption semiconductor optical modulator using a conventional InP / InGaAsP-based multiple quantum well structure, the conduction band discontinuity between the InP barrier layer and the InGaAsP quantum well layer is relatively small. There is a problem in that electrons leak from the quantum well layer and excitons are broken. In particular, since electron leakage becomes significant during high-temperature operation, the amount of change in the band gap due to the quantum confined Stark effect becomes small, and the amount of change in the light absorption coefficient becomes small. For this reason, there has been a problem that the S / N ratio of light modulation is significantly reduced.

  An object of the present invention is to provide an electroabsorption type semiconductor optical modulator and a semiconductor light emitting device that have a high S / N ratio of light modulation even at high temperatures and are capable of high-speed modulation of 10 GHz or more.

  In order to achieve the above object, the present invention has the following configuration. That is,

  According to a first aspect of the present invention, a surface emitting semiconductor laser element and a semiconductor optical modulator having a light absorption layer having a multiple quantum well structure are monolithically integrated in a stacking direction on a single crystal semiconductor substrate. The modulator is characterized by being located in the resonator of the surface emitting semiconductor laser element or in the semiconductor distributed Bragg reflector of the surface emitting semiconductor laser element.

  According to a second aspect of the present invention, a surface emitting semiconductor laser element and a semiconductor optical modulator including a light absorption layer are monolithically integrated in a stacking direction on a single crystal semiconductor substrate. It is characterized in that it is located in a semiconductor distributed Bragg reflector opposite to the light emitting surface of the surface emitting semiconductor laser element.

  According to a third aspect of the present invention, a surface emitting semiconductor laser element and a semiconductor optical modulator including a light absorption layer are monolithically integrated in a stacking direction on a single crystal semiconductor substrate. It is located in the semiconductor distributed Bragg reflector of the surface emitting semiconductor laser element, and at least one of the modulation electrodes of the semiconductor optical modulator is positioned at one cycle or less of the semiconductor distributed Bragg reflector adjacent to the semiconductor optical modulator. It is characterized by being provided.

  According to a fourth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to third aspects, AlAs or AlGaAs is used as an electrical insulating layer between the semiconductor optical modulator and the surface emitting semiconductor laser element. It is characterized by using a selectively oxidized layer.

  According to a fifth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to third aspects, the distributed Bragg reflector of the surface emitting semiconductor laser element includes a high refractive index layer, a low refractive index layer, The composition gradient layer is provided between the layers, and the layer thickness of the composition gradient layer is 30 to 50 nm.

  According to the first aspect of the present invention, since the semiconductor optical modulator is located in the resonator of the surface emitting semiconductor laser element or in the semiconductor distributed Bragg reflector, the S / N of the light intensity modulation of the semiconductor optical modulator is obtained. The N ratio can be increased.

  According to the second aspect of the present invention, the semiconductor optical modulator is positioned in the semiconductor distributed Bragg reflector on the opposite side of the light emitting surface of the surface emitting semiconductor laser element, so that the semiconductor optical modulator When the light absorption coefficient is changed, the reflectivity of the distributed Bragg reflector on the high reflectivity side is lowered, so that the threshold current can be changed more greatly.

  According to the invention of claim 3, at least one of the modulation electrodes of the semiconductor optical modulator is provided at a position of one cycle or less of the semiconductor distributed Bragg reflector adjacent to the semiconductor optical modulator. It is possible to reduce the influence of the delay due to the resistance and capacitance of the semiconductor distributed Bragg reflector and to operate at a higher frequency.

  According to a fourth aspect of the invention, in the semiconductor light emitting device according to any one of the first to third aspects, AlAs or an electrical insulating layer between the semiconductor optical modulator and the surface emitting semiconductor laser element is used. By using a layer in which AlGaAs is selectively oxidized, the withstand voltage between the semiconductor optical modulator and the surface emitting semiconductor laser element can be increased and the reliability can be improved.

According to the invention described in claim 5, the distributed Bragg reflector of the surface emitting semiconductor laser element is provided with the composition gradient layer between the high refractive index layer and the low refractive index layer, and the composition gradient layer Therefore, even when a bias is applied to the semiconductor optical modulator via the distributed Bragg reflector, the resistance and capacitance of the distributed Bragg reflector are reduced, so that the semiconductor light has a higher modulation frequency. It becomes possible to operate the modulator.

(First embodiment)
The semiconductor optical modulator according to the first embodiment of the present invention is an electroabsorption semiconductor light having a multiple quantum well structure as a light absorption layer, and having a p-side electrode and an n-side electrode for applying an electric field to the multiple quantum well structure. In the modulator, the multiple quantum well structure is composed of a quantum well layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb and a barrier layer made of any material of GaAs, GaInP, and GaInAsP. It is characterized by having.

  When a mixed crystal semiconductor containing As and N as group V elements such as GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb forms a heterojunction with GaAs, GaInAsP, and GaInP, the band discontinuity ratio on the conduction band side with respect to the valence band side is increased. It is known that it can be enlarged. On the other hand, on the InP substrate, which is a conventional material system, InAlAs is the material having the largest energy band gap among the bulk single crystals that can be formed. In the present invention, since a GaAs substrate is used, GaInAsP and A material having a larger energy band gap such as GaInP can be used for the barrier layer. Therefore, the confinement of electrons in the quantum well layer can be strengthened, and exciton divergence can be suppressed even at high temperature operation. Accordingly, the band gap change amount due to the quantum confined Stark effect can be increased even during high-temperature operation, and the S / N of light modulation does not decrease.

  Further, in the conventional material system, since the band discontinuity on the valence band side is large, the hole confinement in the InGaAsP quantum well layer is too strong, and holes having a large effective mass are accumulated in the quantum well layer, There is also a problem that the modulation characteristics are deteriorated. On the other hand, in a mixed crystal semiconductor containing As and N as group V elements such as GaNAs, GaInNAs, GaNASSb, GaInNAsSb, etc., the valence band edge position decreases as the N composition increases. Therefore, when a heterojunction is formed with a barrier layer such as GaAs, GaInAsP, or GaInP, an increase in valence band discontinuity can be suppressed. Therefore, it is difficult for holes to accumulate in the quantum well layer, and high-speed modulation of 10 GHz or more is possible.

  N and Al are chemically active, and when a quantum well layer containing N as a constituent element and a barrier layer containing Al as a constituent element are in direct contact with each other and crystal growth is performed, N is segregated at the interface. Therefore, in the first embodiment, GaAs, GaInAsP, and GaInP that do not contain Al as a constituent element are employed as the barrier layer, thereby suppressing N segregation at the interface and forming a high-quality quantum well structure. .

  As the barrier layer, GaAs, GaInAsP, and GaInP not containing Al are used as the constituent elements, but other III-V group elements such as B, N, and Sb may be included.

<Example 1>
FIGS. 1A and 1B are diagrams showing a configuration example of a semiconductor optical modulator according to the present invention. 1A is a cross-sectional view seen from the front, and FIG. 1B is a cross-sectional view seen from the side.

Referring to FIG. 1, this semiconductor optical modulator includes an n-type Al _0.4 Ga _0.6 As cladding layer 102, a GaAs lower optical waveguide layer 103, a multiple quantum well structure 301, a GaAs on an n-type GaAs substrate 101. Upper optical waveguide layer 105, p-type Al _0.4 Ga _0.6 As first cladding layer 302, p-type AlAs layer 303, p-type Al _0.4 Ga _0.6 As second cladding layer 108, p-type GaAs cap Layers 109 are sequentially stacked.

  Here, the multiple quantum well structure 301 is configured by stacking three periods using GaInNAs as a well layer and GaInP as a barrier layer.

A ridge waveguide is formed by etching in a stripe shape from the surface of the p-type GaAs cap layer 109 to the middle of the n-type Al _0.4 Ga _0.6 As cladding layer 102. Further, the p-type AlAs layer 303 is selectively oxidized from the side surface of the ridge stripe to form an AlO _x insulating region 304.

A p-side electrode 110 is formed on the p-type GaAs cap layer 109, and an n-side electrode 111 is formed on the back surface of the n-type GaAs substrate 101. Further, non-reflective films 112 and 113 having a reflectance of 0.2% or less are formed on both end faces T ₁ and T ₂ of the element formed by cleavage.

The semiconductor optical modulator of FIG. 1, the laser light incident from the rear end face T ₁ is the light intensity in the process of propagating through the waveguide including a multiple quantum well structure 301 where the light absorption coefficient changes with respect to the wavelength of the incident light modulated, and has a structure that is emitted from the front end face T ₂ of the opposite side. In the direction perpendicular to the substrate 101, the GaAs optical waveguide layers 103 and 105 have an SCH structure sandwiched between clad layers 102, 302, and 108 having a low refractive index. Further, in the horizontal direction with respect to the substrate 101, light is confined in a ridge waveguide formed by etching.

  In the semiconductor optical modulator having such a configuration, when a reverse bias is applied to the multiple quantum well structure 301, the energy band gap of the multiple quantum well structure 301 is reduced due to the quantum confined Stark effect. Thereby, when no voltage is applied, the multiple quantum well structure 301 is transparent to incident light, but light absorption increases by applying a voltage. Therefore, it operates as an electroabsorption optical modulator.

Here, the non-reflective films 112 and 113 formed on the both end faces T ₁ and T ₂ reduce reflection loss when light is input to or output from the optical modulator. In addition, the AlO _x insulating region 304 formed by selective oxidation has a surface leakage current generated in the multiple quantum well structure 301 exposed on the side surface of the ridge stripe by separating the current path from the side surface of the ridge stripe in the vicinity of the multiple quantum well structure 301. It works to decrease.

  The electroabsorption semiconductor optical modulator shown in FIG. 1 is characterized in that a GaInNAs quantum well layer is provided as an absorption layer on a GaAs substrate 101. Therefore, it corresponds to a long wavelength band of 1.3 μm or 1.55 μm used for optical fiber transmission.

  Since GaInNAs can form a single crystal thin film on the GaAs substrate 101, GaInP, which is a wide gap material, can be used for the barrier layer. Therefore, the electron confinement with respect to the GaInNAs quantum well layer can be strengthened, and exciton divergence can be suppressed even at high temperature operation. Accordingly, the band gap change amount due to the quantum confined Stark effect can be increased even during high-temperature operation, and the S / N of optical modulation does not decrease.

  In addition, in a mixed crystal semiconductor containing As and N as group V elements such as GaInNAs, the valence band edge position decreases as the N composition is increased. Therefore, when a heterojunction is formed with a GaInP barrier layer, an increase in band discontinuity on the valence band side can be suppressed. Therefore, it is difficult for holes to accumulate in the GaInNAs quantum well layer, and modulation can be performed at a high frequency of 10 to 50 GHz.

  Further, N and Al are chemically active, and when a layer containing N as a constituent element and a layer containing Al as a constituent element are in direct contact with each other for crystal growth, N segregates at the interface. Therefore, in the multiple quantum well structure 301 of Example 1, by using GaInP that does not contain Al as a constituent element for the barrier layer, it is possible to suppress N segregation at the interface between the GaInNAs quantum well layer and the barrier layer, High quality quantum well structure is formed. As the barrier layer not containing Al, GaAs or GaInAsP can be used in addition to GaInP. In addition to GaInNAs, it is possible to use GaNAs, GaInNAs, GANASSb, and GaInNAsSb as the quantum well layer.

  In FIG. 1, a semiconductor optical modulator as one element is shown, but a monolithic array can be formed on the same substrate by forming a plurality of ridge stripe structures.

  In addition, a surface-type electroabsorption optical modulator that allows light to enter and exit in a direction perpendicular to the substrate can also be configured using the multiple quantum well structure 301.

(Second Embodiment)
Further, the semiconductor optical modulator of the second embodiment of the present invention is an electroabsorption type comprising a multiple quantum well structure as a light absorption layer, and a p-side electrode and an n-side electrode for applying an electric field to the multiple quantum well structure. In the semiconductor optical modulator, the multiple quantum well structure includes a quantum well layer made of any one of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb, Al _a Ga _1-a As (0 <a ≦ 1), (Al _{b Ga 1-b) InP (} 0 <b ≦ 1), and _(a Al c Ga 1-c) InAsP (0 <c ≦ 1) barrier layer constituted of any material of the quantum well layer and a barrier layer And an intermediate layer made of any material of GaAs, GaInP, and GaInAsP.

In the configuration of the second embodiment, Al _a Ga _1-a As (0 <a ≦ 1), (Al _b Ga _1-b ) InP (0 <b ≦ 1), Any material of (Al _c Ga _1-c ) InAsP (0 <c ≦ 1) is used. The material is a material having a larger band gap than GaAs, GaInAsP, and GaInP used for the barrier layer in the first embodiment. Therefore, the electron confinement with respect to the quantum well layer can be further strengthened, and high temperature operation is possible.

  In the second embodiment, Al is used as a constituent element for the barrier layer, but an intermediate layer made of GaAs, GaInAsP, and GaInP that does not contain N and Al as constituent elements between the barrier layer and the quantum well layer. A thin layer is provided. By this intermediate layer, it is possible to suppress the segregation of N at the interface between the barrier layer and the quantum well layer, and to form a high-quality quantum well structure.

  Japanese Unexamined Patent Publication No. 2000-89180 discloses a quantum well modulator using GaInNAs as a quantum well layer and using a II-VI group compound semiconductor having a large energy band gap such as ZnCdSSe or ZnMgSSe as a barrier layer. However, in the present invention, the barrier layer is formed of the same group III-V compound semiconductor as that of the quantum well layer instead of the group II-VI compound semiconductor, whereby the constituent elements are formed at the interface between the quantum well layer and the barrier layer. Interdiffusion is small and a good interface can be formed.

  Note that the intermediate layer made of any one of the above GaAs, GaInP, and GaInAsP materials may contain B, Sb, and the like. What is important is that N and Al are not contained.

(Third embodiment)
According to another aspect of the present invention, there is provided a semiconductor light emitting device including a semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb on a GaAs substrate (GaAs single crystal substrate); The semiconductor optical modulator described in the second embodiment is integrated.

  A semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb can be formed on a GaAs substrate in a wavelength band of 1.2 to 1.6 μm. It has been proved that the semiconductor laser has a very high characteristic temperature of 150 to 200 K and a good temperature characteristic.

  The semiconductor optical modulator of the first or second embodiment can also be formed on a GaAs substrate, and high-speed optical modulation of 10 GHz or more, which exceeds the direct modulation frequency of the semiconductor laser element, is possible.

  The semiconductor light emitting device of the present invention includes a semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb on a GaAs substrate, and the electroabsorption type of the first or second embodiment. The semiconductor laser device of 1.2 to 1.6 μm band having a high characteristic temperature and capable of high-speed modulation of 10 GHz or more can be formed by integrating the semiconductor optical modulator.

(Fourth embodiment)
According to another aspect of the present invention, there is provided a semiconductor light emitting device including a semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb on a GaAs substrate (GaAs single crystal substrate); The semiconductor optical modulator described in the second embodiment is monolithically integrated.

  A semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb can be formed on a GaAs substrate in a wavelength band of 1.2 to 1.6 μm. It has been proved that the semiconductor laser has a very high characteristic temperature of 150 to 200 K and a good temperature characteristic.

  The semiconductor optical modulator of the first or second embodiment can also be formed on a GaAs substrate, and high-speed optical modulation of 10 GHz or more, which exceeds the direct modulation frequency of the semiconductor laser element, is possible.

  The semiconductor light emitting device of the present invention includes a semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb on a GaAs substrate, and the electroabsorption type of the first or second embodiment. By forming the semiconductor optical modulator in a monolithic manner, a 1.2 to 1.6 μm band semiconductor laser device having a high characteristic temperature and capable of high-speed modulation of 10 GHz or more can be formed. Then, by forming the semiconductor laser element and the optical modulator monolithically, the semiconductor laser device can be reduced in size.

<Example 2>
FIG. 2 is a diagram showing a configuration example of a semiconductor light emitting device according to the present invention. The semiconductor light emitting device of FIG. 2 is configured as an optical modulator integrated semiconductor laser device, and a semiconductor laser element portion A that generates laser light and an electric field absorption that modulates the intensity of the laser light generated by the semiconductor laser element portion A. The type semiconductor optical modulator B is monolithically integrated on the same n-type GaAs substrate 101.

Here, the semiconductor laser element portion A is formed on an n-type GaAs substrate 101, an n-type Al _0.4 Ga _0.6 As cladding layer 102, a GaAs lower optical waveguide layer 103, a multiple quantum well active layer 401, a GaAsP diffraction grating. A layer 402, a p-type Al _0.4 Ga _0.6 As cladding layer 404, and a p-type GaAs cap layer 109 are sequentially stacked. The multi-quantum well active layer 401 is composed of GaInNAs as a well layer and GaAs as a barrier layer.

On the other hand, the electroabsorption semiconductor optical modulator B includes an n-type Al _0.4 Ga _0.6 As clad layer 102, a GaAs lower optical waveguide layer 103, a multiple quantum well structure 401, and a GaAsP upper portion on an n-type GaAs substrate 101. An optical waveguide layer 403, a p-type Al _0.4 Ga _0.6 As cladding layer 404, and a p-type GaAs cap layer 109 are sequentially stacked. The GaAsP upper optical waveguide layer 403 has a lattice constant smaller than that of the GaAs substrate, and has a tensile strain of about 0.5%, for example.

Then, protons are injected between the semiconductor laser element part A and the electroabsorption semiconductor optical modulator B from the surface until reaching the n-type Al _0.4 Ga _0.6 As cladding layer 102, and a high resistance region 405 is formed. As a result, the semiconductor laser element portion A and the electroabsorption semiconductor optical modulator B are electrically insulated.

  A p-side electrode 406 is formed on the p-type GaAs cap layer 109 of the semiconductor laser element part A, and a p-side electrode 407 is formed on the p-type GaAs cap layer 109 of the electroabsorption semiconductor optical modulator B. An n-side common electrode 111 is formed on the back surface of the n-type GaAs substrate 101.

  Further, non-reflective films 112 and 113 having a reflectance of 0.2% or less are formed on both end faces of the element (semiconductor light emitting device) formed by cleavage.

  In the semiconductor light emitting device of FIG. 2, carriers are injected into the multiple quantum well active layer 401 by applying a forward bias to the p-side electrode 406 and the n-side electrode 111 in the semiconductor laser element portion A. Carriers injected into the multiple quantum well active layer 401 recombine in the GaInNAs well layer, and light of 1.3 μm band corresponding to the energy band gap of the GaInNAs well layer is emitted. The light generated in the multiple quantum well active layer 401 is reflected in the process of being guided through the optical waveguide including the GaAsP diffraction grating layer 402, and laser oscillation is performed at a wavelength that satisfies the Bragg resonance condition.

  The light laser-oscillated by the semiconductor laser element A is guided through the GaAs lower optical waveguide layer 103 and the GaAsP diffraction grating layer 402 and input to the electroabsorption semiconductor optical modulator B. In the electroabsorption semiconductor optical modulator B, the band gap wavelength of the multiple quantum well structure 401 is shifted to a short wavelength due to the influence of the tensile strain of the adjacent GaAsP upper optical waveguide layer 403.

  On the other hand, in the semiconductor laser element part A, since the diffraction grating is formed in the GaAsP layer 402 and has a fine uneven shape, the tensile strain of the GaAsP layer is relieved. Therefore, the energy band gap of the multiple quantum well active layer 401 of the semiconductor laser element part A is not affected by the strain of the GaAsP layer 402.

  As a result, the energy band gap of the multiple quantum well structure of the electroabsorption semiconductor optical modulator B is about several tens of meV larger than the energy band gap of the multiple quantum well active layer 401 of the semiconductor laser element portion A. Therefore, when no bias is applied to the p-side electrode 407 and the n-side electrode 111 of the electroabsorption semiconductor optical modulator B, the multiple quantum well structure 401 is transparent to the laser light.

  On the other hand, when a reverse bias is applied to the p-side electrode 407 and the n-side electrode 111, the energy band gap of the multiple quantum well structure 401 is reduced by the quantum confined Stark effect and absorbs laser light. Therefore, the light intensity of the laser light can be modulated by turning on and off the bias voltage between the p-side electrode 407 and the n-side electrode 111.

  The antireflective films 112 and 113 formed on the end face function to suppress laser oscillation in the Fabry-Perot mode.

Since the semiconductor laser element portion A of the light emitting device of FIG. 2 uses a 1.3 μm band GaInNAs quantum well layer as an active layer, Al _0.4 Ga _0.6 As, which is a wide gap material, is used as a cladding layer. It is possible. In this case, the height of the electron confinement barrier between the active layer and the cladding layer can be increased, and electron overflow from the quantum well layer to the cladding layer can be suppressed. As a result, a high characteristic temperature of 150K or more can be obtained, and the increase in threshold current can be reduced even during high temperature operation.

  In the electroabsorption semiconductor optical modulator B, a multiple quantum well structure 401 having GaInNAs as a quantum well layer and GaAs as a barrier layer is used as an absorption layer. It is known that GaInNAs can increase the band discontinuity ratio on the conduction band side with respect to the valence band side when a heterojunction is formed with GaAs. Therefore, compared to the conventional InP / InGaAsP multiple quantum well structure, the electron confinement with respect to the GaInNAs quantum well layer can be strengthened, and exciton divergence can be suppressed even at high temperature operation. Therefore, the amount of change in the band gap due to the quantum confined Stark effect can be increased even during high temperature operation, and a decrease in the S / N ratio of light modulation can be prevented.

  In this manner, an optical modulator integrated semiconductor laser device having excellent temperature characteristics can be realized as a semiconductor light emitting device.

  Furthermore, when an electric field is applied to the semiconductor optical modulator, the light modulation frequency can be increased compared to the case where the semiconductor laser is modulated by current injection. Therefore, as shown in FIG. 2, by integrating the electroabsorption type semiconductor optical modulator, the laser light is modulated at a higher modulation frequency (10 to 50 GHz) than when the semiconductor laser is directly modulated by current injection. be able to. The semiconductor laser element and the semiconductor optical modulator are monolithically integrated on the same substrate, so that the device size can be reduced.

(Fifth embodiment)
In the semiconductor light emitting device of the present invention, the semiconductor laser element can be configured as a surface emitting semiconductor laser element.

  When the light intensity is modulated not by direct modulation of the semiconductor laser but by using an optical modulator, the semiconductor laser element is continuously energized. Accordingly, in order to suppress power consumption and heat generation, it is important to reduce the threshold current of the semiconductor laser element. In the third embodiment, since the surface emitting semiconductor laser element is used, the threshold current of the semiconductor laser element can be lowered to 5 mA or less as compared with the case where the end surface type semiconductor laser element is used. Therefore, the operating current of the semiconductor light emitting device can be reduced and the power consumption can be reduced.

  The planar semiconductor laser device of the present invention includes an active layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb on a GaAs substrate. Therefore, a distributed Bragg reflector (DBR) in which GaAs high refractive index layers and AlAs or AlGaAs low refractive index layers are alternately stacked can be used as the reflecting mirror. In the InP / InGaAsP material system, which is a conventional material system, it is necessary to use a quaternary mixed crystal of InGaAsP for the high refractive index layer, which increases the thermal resistance of the DBR.

  In addition, since the difference in refractive index between InP and InGaAsP is small, a large number of layers are required to obtain high reflectivity. In contrast, a DBR using a GaAs / AlGaAs material has a low thermal resistance and a large difference in refractive index between a high refractive index layer and a low refractive index layer, so that a high reflectance can be obtained with a small number of layers. Therefore, it is advantageous for heat dissipation. Therefore, it operates stably even at the time of high temperature operation which is the subject of the present invention.

<Example 3>
FIGS. 3A and 3B are diagrams showing another configuration example of the semiconductor light emitting device according to the present invention. 3A is a view from the top, and FIG. 3B is a cross-sectional view from the side.

  3A and 3B, on a Si substrate 1001, a surface emitting laser array 1002, an optical waveguide 1004 having a 45 ° mirror 1003 on one surface, and an electroabsorption semiconductor optical modulator array 1005. An optical fiber 1006 is provided.

  The surface emitting laser array 1002 includes a vertical cavity surface emitting laser configured by laminating a GaAs / AlGaAs lower DBR, a resonator structure including a GaInNAs active layer, and a GaAs / AlGaAs upper DBR on a GaAs substrate. For example, they are integrated in a four-element monolithic manner. The oscillation wavelength is in a 1.3 μm band suitable for transmission of a silica-based optical fiber.

  An optical waveguide 1004 provided with a 45 ° mirror 1003 on one surface is formed of quartz material, Si, polymer material, or the like. The electroabsorption type semiconductor optical modulator array 1005 is formed by integrating the end face type semiconductor optical modulators shown in FIG. 1 in a four-element monolithic manner.

  In the semiconductor light emitting device having such a configuration, light emitted upward from each surface emitting laser of the surface emitting laser array 1002 is bent by the 45 ° mirror 1003 and is incident on the optical waveguide 1004. The light incident on the optical waveguide 1004 is guided through the optical waveguide 1004 and is incident on the semiconductor optical modulator array 1005. At this time, the surface emitting laser and the semiconductor optical modulator have a one-to-one correspondence. The optical signals whose light intensity is modulated by the semiconductor optical modulator array 1005 are output to the outside through the optical fibers 1006, respectively.

  In the semiconductor light emitting device shown in FIG. 3, by modulating the optical signal at 10 GHz by the semiconductor optical modulator array 1005, it is possible to transmit an optical signal of up to 40 Gbps through four channels.

  In FIG. 3, the surface emitting laser array 1002 includes an active layer made of GaInNAs on a GaAs substrate. Therefore, a distributed Bragg reflector (DBR) in which GaAs high refractive index layers and AlGaAs low refractive index layers are alternately stacked can be used as the reflecting mirror. In the InP / InGaAsP material system, which is a conventional material system, it is necessary to use a quaternary mixed crystal of InGaAsP for the high refractive index layer, which increases the thermal resistance of the DBR. In addition, since the difference in refractive index between InP and InGaAsP is small, a large number of layers are required to obtain high reflectivity.

  In contrast, a DBR using a GaAs / AlGaAs material has a low thermal resistance and a large difference in refractive index between a high refractive index layer and a low refractive index layer, so that a high reflectance can be obtained with a small number of layers. Therefore, it is advantageous for heat dissipation. Therefore, it operates stably even at the time of high temperature operation which is the subject of the present invention.

  When the light intensity is modulated not by direct modulation of the semiconductor laser but by using an optical modulator, the semiconductor laser element is continuously energized. Accordingly, in order to suppress power consumption and heat generation, it is important to reduce the threshold current of the semiconductor laser element. In the semiconductor light emitting device shown in FIG. 3, since the surface emitting semiconductor laser element 1002 is used, the threshold current of the semiconductor laser element should be lowered to 5 mA or less as compared with the case of using the end surface type semiconductor laser element. Can do. Therefore, the operating current of the semiconductor light emitting device can be reduced and the power consumption can be reduced.

In addition, the multiple quantum well structure that is the absorption layer of the electroabsorption semiconductor optical modulator 1005 includes GaInNAs as a quantum well layer and Al _0.2 Ga _0.8 As as a barrier layer, thereby forming a GaInNAs quantum well. The confinement of electrons to the layer can be strengthened. Accordingly, exciton divergence can be suppressed even during high-temperature operation, and the amount of band gap change due to the quantum confined Stark effect can be increased. Therefore, it is possible to prevent a decrease in light modulation S / N even during high temperature operation.

  That is, in the semiconductor light emitting device of FIG. 3, a surface emitting semiconductor laser including a GaInNAs active layer and an electroabsorption semiconductor optical modulator having a GaInNAs quantum well layer as an absorption layer are integrated on a Si substrate 1001. It is possible to realize a 1.3 μm band semiconductor laser device having good temperature characteristics and capable of high-speed modulation of 10 GHz or more.

(Sixth embodiment)
In the semiconductor light emitting device of the present invention, the semiconductor laser element is configured as a surface emitting semiconductor laser element, and the surface emitting semiconductor laser element and the electroabsorption semiconductor optical modulator are integrated monolithically in the stacking direction. You can also. That is, it can also be configured as a planar semiconductor optical device that inputs and outputs light in a direction perpendicular to the main plane of the GaAs single crystal substrate. In this case, it is not necessary to form the light input / output surface as a cleaved surface. Therefore, it is possible to form the planar semiconductor light emitting device on the GaAs single crystal substrate in a monolithic two-dimensional array. Thereby, the planar semiconductor light emitting devices can be integrated in parallel at high density.

  Since the planar semiconductor light emitting device of the present invention can be formed on a GaAs substrate, a distributed Bragg reflector (DBR) in which GaAs high refractive index layers and AlAs or AlGaAs low refractive index layers are alternately stacked is used as the reflecting mirror. be able to. In the InP / InGaAsP material system, which is a conventional material system, it is necessary to use a quaternary mixed crystal of InGaAsP for the high refractive index layer, which increases the thermal resistance of the DBR.

  In addition, since the difference in refractive index between InP and InGaAsP is small, a large number of layers are required to obtain high reflectivity. In contrast, a DBR using a GaAs / AlGaAs material has a low thermal resistance and a large difference in refractive index between a high refractive index layer and a low refractive index layer, so that a high reflectance can be obtained with a small number of layers. Therefore, it is advantageous for heat dissipation. Therefore, it operates stably even at the time of high temperature operation which is the subject of the present invention.

<Example 4>
FIG. 4A is a diagram showing another configuration example of the semiconductor light emitting device according to the present invention. The semiconductor light emitting device of FIG. 4A is a surface semiconductor light emitting device (optical modulator integrated surface emitting semiconductor laser). Device), a surface emitting semiconductor laser and an electroabsorption semiconductor optical modulator are monolithically integrated in the stacking direction. That is, the electroabsorption semiconductor optical modulator B that modulates the laser light intensity is inserted in the middle of the p-side DBR (distributed Bragg reflector) in the surface emitting semiconductor laser.

Specifically, in FIG. 4A, an n-type GaAs / Al _0.8 Ga _0.2 As DBR 201, an n-type GaAs lower spacer layer 202, a GaInNAs / GaAs multiple quantum well are formed on an n-type GaAs substrate 101. Active layer 203, p-type Al _0.2 Ga _0.8 As carrier blocking layer 204, p-type GaAs upper spacer layer 205, p-type AlAs layer 501, first DBR 502 of p-type GaAs / Al _0.8 Ga _0.2 As Are sequentially stacked.

An AlO _x insulating layer 503 is formed on the first DBR 502 of p-type GaAs / Al _0.8 Ga _0.2 As, and further, an electroabsorption semiconductor optical modulator is formed on the AlO _x insulating layer 503. An n-type GaAs contact layer 504, an n-type Al _0.4 Ga _0.6 As clad layer 505, a multiple quantum well structure 506, and a p-type Al _0.4 Ga _0.6 As clad layer 507 are stacked. Yes.

Here, the AlO _x insulating layer 503 functions to electrically insulate the surface emitting semiconductor laser from the electroabsorption semiconductor optical modulator B.

Further, the stacked structure of the multiple quantum well structure 506 is as shown in FIG. 4B, for example. That is, in the example of FIG. 4B, the multiple quantum well structure 506 is alternately stacked with GaInNAs as the quantum well layer 506a and Al _0.2 Ga _0.8 As as the barrier layer 506b. A GaAs intermediate layer 506c having a thickness of 2 nm is provided at the interface between the GaInNAs quantum well layer 506a and the Al _0.2 Ga _0.8 As barrier layer 506b.

Thus, between the GaInNAs quantum well layer 506a containing N as a constituent element and the Al _0.2 Ga _0.8 As barrier layer 506b containing Al as a constituent element, a GaAs intermediate that does not contain N and Al as constituent elements. By providing the layer 506c, N segregation at the interface is suppressed and a high-quality quantum well structure is formed.

The layer thickness of the AlO _x insulating layer 503, the layer thickness of the n-type GaAs contact layer 504, the n-type Al _0.4 Ga _0.6 As cladding layer 505, the multiple quantum well structure 506, the p-type Al _0.4 Ga _0. The total thickness of the ₆ As cladding layer 507 is set so that the phase matching condition is satisfied with respect to the laser oscillation wavelength (that is, an integral multiple of 1/4 optical wavelength thickness). .

4A, a second DBR 508 of p-type GaAs / Al _0.8 Ga _0.2 As is stacked on the p-type Al _0.4 Ga _0.6 As cladding layer 507. Yes.

In FIG. 4A, the stacked structure sequentially stacked in this manner is dry-etched in three steps to form a columnar structure. The first stage from the top is formed so that the surface of the n-type GaAs contact layer 504 is exposed, and the second stage is the outermost surface of the first DBR 502 of p-type GaAs / Al _0.8 Ga _0.2 As. The third stage is etched to a depth that reaches the DBR 201 of n-type GaAs / Al _0.8 Ga _0.2 As.

In addition, the p-type AlAs layer 501 at the periphery of the columnar structure is selectively oxidized from the side surface exposed by etching to form an AlO _x insulating region 509. Further, the AlO _x insulating layer 503 that electrically insulates the surface emitting semiconductor laser and the electroabsorption semiconductor optical modulator B is formed by oxidizing the crystal-grown AlAs layer from the etching side surface. This oxidation process can be performed simultaneously with the selective oxidation process for forming the AlO _x insulating region 509.

  In FIG. 4A, a modulation p-side electrode 510 is formed on the surface of the p-type second DBR 508 which is the outermost surface of the columnar structure. A modulation n-side electrode 511 is formed on the first terrace surface where the surface of the n-type GaAs contact layer 504 is exposed by etching. A p-side electrode 110 for laser driving is formed on the second terrace surface where the surface of the p-type first DBR 502 is exposed by etching. An n-side electrode 111 for driving the laser is formed on the back surface of the n-type GaAs substrate 101 except for an opening for taking out laser light to the outside.

In the configuration of FIG. 4, in the surface emitting semiconductor laser, carriers are injected into the GaInNAs / GaAs multiple quantum well active layer 203 by applying a forward bias to the p-side electrode 110 and the n-side electrode 111. At this time, the current is confined to a region narrower than the columnar structure by the AlO _x insulating region 509 formed by selective oxidation. Thereby, the current can be concentrated and the threshold current can be reduced.

  The carriers injected into the GaInNAs / GaAs multiple quantum well active layer 203 are recombined to emit light, and light in the 1.3 μm band corresponding to the band gap of the GaInNAs well layer is emitted. The light generated in the GaInNAs / GaAs multiple quantum well active layer 203 resonates in the resonator composed of the n-type DBR 201, the p-type first DBR 502, and the p-type second DBR 508 to oscillate.

  In the electroabsorption semiconductor optical modulator B, when no bias is applied to the p-side electrode 510 and the n-side electrode 511, the multiple quantum well structure 506 is transparent to the laser light. Therefore, since the reflected light from the p-type second DBR 508 in addition to the p-type first DBR 502 returns to the active region of the surface emitting semiconductor laser portion, a high reflectance of 99% or more necessary for laser oscillation can be obtained.

  On the other hand, when a reverse bias is applied to the p-side electrode 510 and the n-side electrode 511, the energy band gap of the multiple quantum well structure 506 is reduced by the quantum confined Stark effect and absorbs laser light. Therefore, the reflectivity of the p-side DBR is effectively reduced, and laser oscillation is stopped. Thereby, the light intensity of the laser beam can be modulated.

In the semiconductor light emitting device of FIG. 4, in a 1.3 μm band GaInNAs surface emitting semiconductor laser formed on a GaAs substrate 101, a GaInNAs well layer and a p-type Al _0.4 Ga _0.6 As carrier blocking layer 204 are provided. The conduction band discontinuity can be increased to 200 meV or more. Therefore, an electronic overflow can be suppressed even during high temperature operation. Further, the DBR can be formed of a GaAs / AlGaAs-based material having a low thermal resistance and a high reflectivity of 99% or more with a smaller number of layers. Accordingly, it is possible to form a surface emitting semiconductor laser having good temperature characteristics in the 1.3 μm band.

In addition, the multiple quantum well structure 506 that is an absorption layer of the electroabsorption semiconductor optical modulator B includes a GaInNAs quantum well layer and Al _0.2 Ga _0.8 As as a barrier layer, thereby forming a GaInNAs quantum well. The confinement of electrons to the layer can be strengthened. Accordingly, exciton divergence can be suppressed even during high-temperature operation, and the amount of band gap change due to the quantum confined Stark effect can be increased. Therefore, it is possible to prevent a decrease in light modulation S / N even during high temperature operation.

  In the semiconductor light emitting device of FIG. 4, a surface emitting semiconductor laser including a GaInNAs active layer and an electroabsorption semiconductor optical modulator B having a GaInNAs quantum well layer as an absorption layer are monolithically integrated on a GaAs substrate 101. As a result, it is possible to realize a 1.3 μm band semiconductor laser device having good temperature characteristics and capable of high-speed modulation of 10 GHz or more.

  Further, the semiconductor light emitting device of FIG. 4 uses a vertical cavity surface emitting laser capable of lowering the threshold current as compared with the end face type optical modulator integrated semiconductor laser device shown in FIG. The threshold current of the semiconductor laser device can be reduced. Further, the surface emitting semiconductor laser can be monolithically formed into a two-dimensional array, which is advantageous for high-density parallel integration.

(Seventh embodiment)
The semiconductor light emitting device according to the seventh embodiment of the present invention is the semiconductor light emitting device described in the sixth embodiment, wherein the semiconductor optical modulator is located in the resonator of the surface emitting semiconductor laser element. In this case, the semiconductor optical modulator is configured as a planar semiconductor optical modulator that inputs and outputs light in a direction perpendicular to the substrate.

  When the semiconductor optical modulator is located in the resonator of the surface emitting semiconductor laser element, the multiple quantum well structure is transparent to light when no bias is applied to the semiconductor optical modulator. Accordingly, since there is no light absorption loss in the resonator of the surface emitting semiconductor laser element, laser oscillation occurs with a low threshold current. On the other hand, when a reverse bias is applied to the semiconductor optical modulator, the energy band gap of the multiple quantum well structure is reduced by the quantum confined Stark effect to absorb light. Therefore, the light absorption loss of the resonator increases, and the threshold current of the surface emitting semiconductor laser element increases.

  Therefore, when the injection current is made constant, the laser oscillation state and the laser oscillation stop state can be switched between when the reverse bias is not applied to the semiconductor optical modulator and when it is applied. Thereby, even when the light absorption layer of the semiconductor light modulator is thinned to 1 μm or less and the change in the light absorption coefficient is small, the light intensity of the laser light can be greatly changed. Therefore, the S / N ratio of the light intensity modulation can be increased.

  Further, a semiconductor laser element including an active layer made of any material of GaNAs, GaInNAs, GaNASSb, and GaInNAsSb may be formed in a wavelength band of 1.2 to 1.6 μm suitable for transmission of a quartz optical fiber. it can. It has been proved that the semiconductor laser has a very high characteristic temperature of 150 to 200 K and a good temperature characteristic. Furthermore, the semiconductor optical modulator of the first or second embodiment can strengthen the electron confinement with respect to the quantum well layer, and can operate at a high temperature.

  Therefore, it is possible to realize a long-wavelength surface emitting semiconductor laser device having a high characteristic temperature and capable of high-speed optical modulation of 10 GHz or more, which exceeds the direct modulation frequency of the semiconductor laser element.

<Example 5>
FIG. 5 is a diagram showing another configuration example of the semiconductor light-emitting device according to the present invention. The semiconductor light-emitting device of FIG. 5 is configured as a surface-type semiconductor light-emitting device (optical modulator integrated surface-emitting semiconductor laser device). The surface emitting semiconductor laser and the electroabsorption semiconductor optical modulator are monolithically integrated in the stacking direction. That is, the electroabsorption semiconductor optical modulator that modulates the laser light intensity is inserted in the middle of the resonator structure in the surface emitting semiconductor laser.

Specifically, in FIG. 5, an n-type GaAs / Al _0.8 Ga _0.2 As DBR 201, an n-type GaAs lower spacer layer 202, a GaInNAs / GaAs multiple quantum well active layer 203 is formed on an n-type GaAs substrate 101. , First GaAs upper spacer layer 1101, p-type AlAs layer 501, second GaAs upper spacer layer 1102, p-type GaAs contact layer 1103, multiple quantum well structure 506, n-type GaAs / Al _0.8 Ga _0.2 The upper DBR 1104 of As is sequentially stacked.

The stacked structure of the multiple quantum well structure 506 is, for example, as shown in FIG. That is, in the example of FIG. 4B, the multiple quantum well structure 506 is alternately stacked with GaInNAs as the quantum well layer 506a and Al _0.2 Ga _0.8 As as the barrier layer 506b. A GaAs intermediate layer 506c having a thickness of 2 nm is provided at the interface between the GaInNAs quantum well layer 506a and the Al _0.2 Ga _0.8 As barrier layer 506b.

Thus, between the GaInNAs quantum well layer 506a containing N as a constituent element and the Al _0.2 Ga _0.8 As barrier layer 506b containing Al as a constituent element, a GaAs intermediate that does not contain N and Al as constituent elements. By providing the layer 506c, N segregation at the interface is suppressed and a high-quality quantum well structure is formed.

  A region sandwiched between the n-type DBR 201 and the n-type upper DBR 1104 constitutes a resonator structure of the surface emitting semiconductor laser element. Lower GaAs spacer layer 202, GaInNAs / GaAs multiple quantum well active layer 203, first GaAs spacer layer 1101, p-type AlAs layer 501, second GaAs spacer layer 1102, p-type GaAs contact layer 1103, multiple quantum well structure 506 The total layer thickness is set to be an integral multiple of ½ optical wavelength thickness with respect to the laser oscillation wavelength.

In FIG. 5, the stacked structure sequentially stacked in this way is dry-etched in two steps to form a columnar structure. The first stage from the top is formed so that the surface of the p-type GaAs contact layer 1103 is exposed, and the second stage is etched to a depth reaching the DBR 201 of n-type GaAs / Al _0.8 Ga _0.2 As. ing.

In addition, the p-type AlAs layer 501 at the periphery of the columnar structure is selectively oxidized from the side surface exposed by etching to form an AlO _x insulating region 503. As a result, the current is confined to a region narrower than the first-stage mesa size, thereby reducing the threshold current.

  In FIG. 5, a modulation n-side electrode 511 is formed on the surface of the n-type upper DBR 1104 that is the outermost surface of the columnar structure, except for a region from which light is extracted. A p-side common electrode 110 is formed on the first terrace surface where the surface of the p-type GaAs contact layer 1103 is exposed by etching. An n-side electrode 111 for driving the laser is formed on the back surface of the n-type GaAs substrate 101.

In the configuration of FIG. 5, carriers are injected into the GaInNAs / GaAs multiple quantum well active layer 203 by applying a forward bias to the p-side electrode 110 and the n-side electrode 111 in the surface emitting semiconductor laser. At this time, the current is confined to a region narrower than the columnar structure by the AlO _x insulating region 503 formed by selective oxidation. The carriers injected into the GaInNAs / GaAs multiple quantum well active layer 203 are recombined to emit light, and light in the 1.3 μm band corresponding to the band gap of the GaInNAs well layer is emitted. The light generated in the GaInNAs / GaAs multiple quantum well active layer 203 resonates in the resonator formed by the n-type DBR 201 and the n-type upper DBR 1104 and oscillates. The laser light is extracted from vertically above the GaAs substrate 101.

  In the electroabsorption semiconductor optical modulator, when no bias is applied to the p-side electrode 110 and the n-side electrode 511, the multiple quantum well structure 506 is transparent to light. Therefore, laser oscillation occurs because there is no light absorption loss in the resonator of the surface emitting semiconductor laser. On the other hand, when a reverse bias is applied to the p-side electrode 110 and the n-side electrode 511, the energy band gap of the multiple quantum well structure 506 is reduced by the quantum confined Stark effect and absorbs light. Therefore, the light absorption loss in the resonator increases and laser oscillation stops. Thereby, when the light intensity of the laser light is modulated, the S / N ratio of the light intensity modulation can be increased.

  In the semiconductor light emitting device of FIG. 5, the 1.3 μm band GaInNAs surface emitting semiconductor laser formed on the GaAs substrate 101 has a low thermal resistance, and a high reflectance of 99% or more can be obtained with a smaller number of layers. A DBR can be formed of a GaAs / AlGaAs material. Accordingly, it is possible to form a surface emitting semiconductor laser having good temperature characteristics in the 1.3 μm band. Further, the threshold current can be reduced as compared with the case of using an end face type semiconductor laser element.

In addition, the multiple quantum well structure 506 that is an absorption layer of the electroabsorption semiconductor optical modulator is configured by using GaInNAs as a quantum well layer and Al _0.2 Ga _0.8 As as a barrier layer, thereby forming a GaInNAs quantum well layer. The electron confinement with respect to can be strengthened. Accordingly, exciton divergence can be suppressed even during high-temperature operation, and the amount of band gap change due to the quantum confined Stark effect can be increased. Therefore, it is possible to prevent a decrease in light modulation S / N even during high temperature operation.

  In the semiconductor light emitting device of FIG. 5, a surface emitting semiconductor laser including a GaInNAs active layer and an electroabsorption semiconductor optical modulator having a GaInNAs quantum well layer as an absorption layer are monolithically integrated on a GaAs substrate 101. Thus, it is possible to realize a 1.3 μm band semiconductor laser device having good temperature characteristics and capable of high-speed modulation of 10 GHz or more.

(Eighth embodiment)
The semiconductor light emitting device according to the eighth embodiment of the present invention is the semiconductor light emitting element described in the sixth embodiment, wherein the semiconductor optical modulator is located in the distributed Bragg reflector of the surface emitting semiconductor laser element. . In this case, the semiconductor optical modulator is configured as a planar semiconductor optical modulator that inputs and outputs light in a direction perpendicular to the substrate.

  When the semiconductor optical modulator is located in the distributed Bragg reflector of the surface emitting semiconductor laser element, the multiple quantum well structure is transparent to light when no bias is applied to the semiconductor optical modulator. Accordingly, since the reflected light from the distributed Bragg reflector outside the semiconductor optical modulator returns to the active region of the surface emitting semiconductor laser element, a high reflectivity of 99% or more necessary for laser oscillation can be obtained.

  On the other hand, when a reverse bias is applied to the semiconductor optical modulator, the energy band gap of the multiple quantum well structure is reduced by the quantum confined Stark effect to absorb light. Therefore, the reflectivity of the distributed Bragg reflector is effectively reduced, the threshold current is increased, and laser oscillation is stopped. Thereby, even when the light absorption layer of the semiconductor light modulator is as thin as 1 μm or less, the light intensity of the laser light can be greatly changed, and the S / N ratio of the light intensity modulation can be increased.

  The position where the semiconductor optical modulator is provided in the distributed Bragg reflector is preferably a position where the light intensity distribution is strong in the distributed Bragg reflector. That is, it is desirable to provide the antinode on the side close to the resonator. When the semiconductor light modulator is provided at a position where the light intensity distribution is strong, the effect of light absorption by the semiconductor light modulator is increased in the laser element, so that the laser light intensity can be modulated with a smaller change in absorption coefficient.

  When the semiconductor optical modulator is provided in the resonator, it is necessary to form one electrode of the surface emitting semiconductor laser element and one electrode of the semiconductor optical modulator in the resonator. Therefore, the carrier overflowed from the active layer to the resonator flows into the electrode. On the other hand, when the semiconductor optical modulator is provided in the distributed Bragg reflector, carriers overflowing from the active layer to the resonator are blocked by the low refractive index layer of the distributed Bragg reflector having a large band gap. Therefore, carrier confinement in the active layer can be increased.

(Ninth embodiment)
In the semiconductor light emitting device of the present invention, the semiconductor optical modulator can be positioned in the distributed Bragg reflector on the substrate side of the surface emitting semiconductor laser element.

  As a method of forming a current confinement structure of a surface emitting semiconductor laser element, a method of forming an AlOx insulating region by selectively oxidizing an AlAs layer with water vapor from the side surface is common. When the semiconductor optical modulator is provided in the distributed Bragg reflector (upper) on the side opposite to the substrate, the lower electrode of the semiconductor optical modulator and the upper electrode of the surface emitting semiconductor laser element are arranged on the terrace in the middle of the upper distributed Bragg reflector. Must be formed on top. Therefore, the mesa size formed by etching the active layer and the AlAs layer in the surface emitting semiconductor laser element is increased by the amount of the terrace.

  On the other hand, when the semiconductor optical modulator is provided in the distributed Bragg reflector (lower part) on the substrate side, the upper electrode of the semiconductor optical modulator and the lower electrode of the surface emitting semiconductor laser element are lower than the active layer and the AlAs layer. Can be formed on the terrace. Therefore, the mesa size formed by etching the active layer and the AlAs layer can be further reduced.

  That is, in order to form the same current confinement area, when the semiconductor optical modulator is provided in the distributed Bragg reflector (upper part) on the side opposite to the substrate, the distance for selective oxidation must be increased. If the distance for selective oxidation becomes longer, a slight difference in oxidation rate causes variations in the current confinement area, resulting in variations in the threshold current of the surface emitting semiconductor laser element.

  On the other hand, by providing the semiconductor optical modulator in the distributed Bragg reflector (lower part) on the substrate side, the distance for oxidizing the AlAs layer from the side surface can be made smaller, so that the selective oxidation can be easily controlled and the current confinement area varies. Can be suppressed.

  The above effect is similarly obtained whether the conductivity type of the substrate is n-type or p-type. In addition, the same effect is obtained when the electrode has three terminals or four terminals. However, the AlAs layer to be selectively oxidized needs to be provided on the p-type side at least from the active layer. The important point is that the terrace for forming one electrode of the semiconductor light modulator and one electrode of the surface emitting semiconductor laser element is formed by providing the semiconductor light modulator in the distributed Bragg reflector on the substrate side. This is a point that can be provided below the AlAs layer.

<Example 6>
FIG. 6 is a diagram showing another configuration example of the semiconductor light emitting device according to the present invention. The semiconductor light emitting device of FIG. 6 is configured as a surface type semiconductor light emitting device (optical modulator integrated type surface emitting semiconductor laser device). The surface emitting semiconductor laser and the electroabsorption semiconductor optical modulator are monolithically integrated in the stacking direction. That is, the electroabsorption semiconductor optical modulator that modulates the laser light intensity is inserted in the middle of a substrate-side DBR (distributed Bragg reflector) in the surface emitting semiconductor laser.

Specifically, in FIG. 6, an n-type GaAs / Al _0.8 Ga _0.2 As lower DBR 1201, a multiple quantum well structure 506, a p-type GaAs / Al _0.8 Ga ₀ are formed on an n-type GaAs substrate 101. _.2 As lower DBR 1202, p-type AlAs layer 501, GaAs lower spacer layer 202, GaInNAs / GaAs multiple quantum well active layer 203, GaAs upper spacer layer 205, n-type GaAs / Al _0.8 Ga _0.2 As upper portion DBR 1203 is sequentially stacked.

Further, the stacked structure of the multiple quantum well structure 506 is as shown in FIG. 4B, for example. That is, in the example of FIG. 4B, the multiple quantum well structure 506 is alternately stacked with GaInNAs as the quantum well layer 506a and Al _0.2 Ga _0.8 As as the barrier layer 506b. A GaAs intermediate layer 506c having a thickness of 2 nm is provided at the interface between the GaInNAs quantum well layer 506a and the Al _0.2 Ga _0.8 As barrier layer 506b.

Thus, between the GaInNAs quantum well layer 506a containing N as a constituent element and the Al _0.2 Ga _0.8 As barrier layer 506b containing Al as a constituent element, a GaAs intermediate that does not contain N and Al as constituent elements. By providing the layer 506c, N segregation at the interface is suppressed and a high-quality quantum well structure is formed.

  The layer thickness of the multiple quantum well structure 506 is set so that the phase matching condition is satisfied with respect to the laser oscillation wavelength (that is, an integral multiple of the quarter optical wavelength thickness).

In FIG. 6, the stacked structure sequentially stacked in this manner is dry-etched so that the outermost surface of the lower DBR 1202 of p-type GaAs / Al _0.8 Ga _0.2 As is exposed, thereby forming a columnar structure. ing.

In addition, the p-type AlAs layer 501 at the periphery of the columnar structure is selectively oxidized from the side surface exposed by etching to form an AlO _x insulating region 503.

  In FIG. 6, an n-side electrode 1204 for driving the laser is formed on the surface of the n-type upper DBR 1203 that is the outermost surface of the columnar structure, except for a region where light is extracted. A p-side common electrode 510 is formed on the terrace surface where the surface of the p-type lower DBR 1202 is exposed by etching. A modulation n-side electrode 111 is formed on the back surface of the n-type GaAs substrate 101.

In the configuration of FIG. 6, carriers are injected into the GaInNAs / GaAs multiple quantum well active layer 203 by applying a forward bias to the p-side electrode 510 and the n-side electrode 1204 in the surface emitting semiconductor laser. At this time, the current is confined to a region narrower than the columnar structure by the AlO _x insulating region 509 formed by selective oxidation. Thereby, the current can be concentrated and the threshold current can be reduced.

  The carriers injected into the GaInNAs / GaAs multiple quantum well active layer 203 are recombined to emit light, and light in the 1.3 μm band corresponding to the band gap of the GaInNAs well layer is emitted. The light generated in the GaInNAs / GaAs multiple quantum well active layer 203 resonates in the resonator composed of the n-type upper DBR 1203, the p-type lower DBR 1202, and the n-type lower DBR 1201 and oscillates. The laser light is extracted from vertically above the GaAs substrate 101.

  In the electroabsorption semiconductor optical modulator, when no bias is applied to the p-side electrode 510 and the n-side electrode 111, the multiple quantum well structure 506 is transparent to light. Accordingly, since the reflected light from the n-type lower DBR 1201 in addition to the p-type lower DBR 1202 returns to the active region of the surface emitting semiconductor laser portion, a high reflectivity of 99% or more necessary for laser oscillation is obtained.

  On the other hand, when a reverse bias is applied to the p-side electrode 510 and the n-side electrode 111, the energy band gap of the multiple quantum well structure 506 is reduced due to the quantum confined Stark effect and absorbs light. Therefore, the reflectivity of the DBR on the substrate side (lower part) is effectively reduced, and laser oscillation is stopped. Thereby, the light intensity of the laser beam can be modulated.

  In the semiconductor light emitting device shown in FIG. 6, the semiconductor optical modulator is provided in a distributed Bragg reflector (lower part) on the substrate side, which is the upper electrode of the semiconductor optical modulator and the lower electrode of the surface emitting semiconductor laser element. The p-side electrode 510 can be formed on the terrace below the active layer 203 and the AlAs layer 501. Therefore, the mesa size formed by etching the active layer 203 and the AlAs layer 501 can be further reduced.

  That is, in order to form the same current confinement area, when the semiconductor optical modulator is provided in the distributed Bragg reflector (upper part) on the side opposite to the substrate, the distance for selective oxidation must be increased. If the distance for selective oxidation becomes longer, a slight difference in oxidation rate causes variations in the current confinement area, resulting in variations in the threshold current of the surface emitting semiconductor laser element.

  On the other hand, by providing the semiconductor optical modulator in the distributed Bragg reflector (lower part) on the substrate side, the distance for oxidizing the AlAs layer 501 from the side surface can be made smaller, so that the selective oxidation can be easily controlled and the current confinement area can be reduced. Variations can be suppressed.

(Tenth embodiment)
In the semiconductor light emitting device according to the tenth embodiment of the present invention, a surface emitting semiconductor laser element and a semiconductor optical modulator having a multiple quantum well structure as a light absorption layer are monolithically integrated on a single crystal semiconductor substrate in the stacking direction. The semiconductor optical modulator is located in the resonator of the surface emitting semiconductor laser element or in the semiconductor distributed Bragg reflector of the surface emitting semiconductor laser element.

  When a surface-type semiconductor optical modulator and a surface-emitting semiconductor laser device are stacked serially in the stacking direction, the light oscillated by the surface-emitting semiconductor laser device is absorbed by the light absorption layer of the semiconductor optical modulator and attenuated. For this purpose, a thickness of several tens of μm or more is required, which is difficult to manufacture. When the thickness of the light absorption layer is thin, the difference in light intensity between when the laser light is transmitted through the semiconductor optical modulator and when it is absorbed becomes small, and the S / N ratio of the light intensity modulation is lowered.

  On the other hand, in the tenth embodiment, when the semiconductor optical modulator is located in the resonator of the surface emitting semiconductor laser element or in the semiconductor distributed Bragg reflector, and no bias is applied to the semiconductor optical modulator. The multiple quantum well structure is transparent to light. Accordingly, since there is no light absorption loss in the surface emitting semiconductor laser element, laser oscillation occurs with a low threshold current. On the other hand, when a reverse bias is applied to the semiconductor optical modulator, the energy band gap of the multiple quantum well structure is reduced by the quantum confined Stark effect to absorb light. Therefore, the light absorption loss in the surface emitting semiconductor laser element increases, and the threshold current of the surface emitting semiconductor laser element increases.

  Therefore, when the injection current is made constant, the laser oscillation state and the laser oscillation stop state can be switched between when the reverse bias is not applied to the semiconductor optical modulator and when it is applied. Thereby, even when the light absorption layer of the semiconductor light modulator is thinned to 1 μm or less and the change in the light absorption coefficient is small, the light intensity of the laser light can be greatly changed. Therefore, the S / N ratio of the light intensity modulation can be increased. When a reverse bias is applied to the semiconductor optical modulator, the optical output is greatly reduced by increasing the threshold current even if laser oscillation does not necessarily stop. Therefore, it is also possible to modulate the light intensity with the laser oscillated.

  Japanese Patent Application Laid-Open No. 5-152673 reports a structure in which a semiconductor optical modulator and a surface emitting semiconductor laser element are monolithically integrated. In Japanese Patent Application Laid-Open No. 5-152675, laser light oscillated by a surface emitting semiconductor laser element is externally modulated by a semiconductor optical modulator, and the laser oscillated light is absorbed by the semiconductor optical modulator to obtain a light intensity. Is changing. Therefore, the problem that the S / N ratio of the light intensity modulation is lowered when the light absorption layer is thin has not been sufficiently solved. On the other hand, in the tenth embodiment, the internal loss of the semiconductor laser is changed by the light absorption layer of the semiconductor optical modulator, and the light output can be greatly changed by a slight change in the absorptance.

<Example 7>
FIG. 14 is a diagram showing a configuration example of another semiconductor light emitting device according to the present invention. The semiconductor light emitting device of FIG. 14 has a lower DBR 1402 of p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As, GaAs / Al _0.2 Ga _{0. 8} As multiple quantum well light absorption layer 1403, n-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As DBR 1404, Al _0.2 Ga _0.8 As lower spacer layer 1405, GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406, Al _0.2 Ga _0.8 As upper spacer layer 1407, p-type AlAs layer 501, p-type Al _0.2 Ga _0.8 As / Al _{0 .9} Ga _0.1 As upper DBR 1408 are sequentially stacked.

The stacked structure sequentially stacked in this manner is dry-etched to form a columnar structure. The columnar structure is etched to a depth that reaches the DBR 1404 of n-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As.

Then, the p-type AlAs layer 501 at the periphery of the columnar structure is selectively oxidized from the side surface exposed by etching to form an AlO _x insulating region 509. As a result, the current is confined in a region narrower than the mesa size.

In FIG. 14, the p-side electrode is formed on the surface of the upper DBR 1408 of p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As, which is the outermost surface of the columnar structure, except for the region for extracting light. 1413 is formed. An n-side common electrode 1412 is formed on the terrace surface whose surface is exposed by etching. A p-side electrode 1411 is formed on the back surface of the p-type GaAs substrate 1401.

In the configuration of FIG. 14, carriers are injected into the GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406 by applying a forward bias to the p-side electrode 1413 and the n-side electrode 1412. At this time, the current is confined to a region narrower than the columnar structure by the AlO _x insulating region 509 formed by selective oxidation. Carriers injected into the GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406 recombine with light to emit light in the 0.85 μm band. The light generated in the GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406 resonates in a resonator composed of the p-type lower DBR 1402, the n-type DBR 1404, and the p-type upper DBR 1408. Laser oscillation. The semiconductor light emitting device of FIG. 14 is a surface emitting semiconductor laser element that can extract laser light from vertically above a GaAs substrate 1401.

In the configuration of FIG. 14, when no bias is applied to the p-side electrode 1411 and the n-side electrode 1412, the GaAs / Al _0.2 Ga _0.8 As multiple quantum well light absorption layer 1403 has a GaAs / Al _{0 The} band gap is designed to be transparent to the light generated in the _.2 Ga _0.8 As multiple quantum well active layer 1406. Therefore, in the surface emitting semiconductor laser element, the GaAs / Al _0.2 Ga _0.8 As multiple quantum well light absorption layer 1403 oscillates with a low threshold current without causing light absorption loss.

On the other hand, when a reverse bias is applied to the p-side electrode 1411 and the n-side electrode 1412, the energy band gap of the GaAs / Al _0.2 Ga _0.8 As multiple quantum well light absorption layer 1403 is reduced by the quantum confined Stark effect. As a result, the light generated in the GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406 is absorbed. As a result, the internal light absorption loss of the surface emitting semiconductor laser element increases, thereby increasing the threshold current of the laser.

Therefore, a current value injected from the p-side electrode 1413 and the n-side electrode 1412 to the GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1406 is not applied to the p-side electrode 1411 and the n-side electrode 1412. In this case, the bias current is applied to the p-side electrode 1411 and the n-side electrode 1412 when the threshold current value is set between the threshold current value when the reverse bias is applied to the p-side electrode 1411 and the n-side electrode 1412. If not, laser oscillation occurs. If a reverse bias is applied to the p-side electrode 1411 and the n-side electrode 1412, the laser oscillation stops. As a result, the output light can be changed greatly.

  In Example 7, the output light intensity can be changed greatly even if the change in the absorption coefficient of the light absorption layer is small, compared to the method in which the light intensity is changed by absorbing the laser-oscillated light in the light absorption layer. The modulation S / N ratio can be increased.

Compared with the case where the semiconductor laser element is directly modulated, the method of modulating by applying an electric field to the GaAs / Al _0.2 Ga _0.8 As multiple quantum well light absorption layer 1403 can be operated at a high modulation frequency. it can. Therefore, modulation can be performed at 10 GHz or more exceeding the limit of the direct modulation frequency of the surface emitting semiconductor laser element, for example, 20 to 50 GHz, and can be used for a large capacity optical transmission system.

  In Example 7, an example of a 0.85 μm band surface emitting semiconductor laser element using a GaAs / AlGaAs-based material was shown, but the present invention is not limited to this material system, and the InGaAs / AlGaAs-based or GaInP / AlGaInP is not limited thereto. The present invention can be applied to surface emitting semiconductor lasers such as an InGaN / InGaN / AlGaN system and a GaInNAsSb / AlGaAs system.

(Eleventh embodiment)
In the semiconductor light emitting device according to the eleventh embodiment of the present invention, the surface emitting semiconductor laser element and the semiconductor optical modulator including the light absorption layer are monolithically integrated on the single crystal semiconductor substrate in the stacking direction. The semiconductor optical modulator is located in the semiconductor distributed Bragg reflector opposite to the light emitting surface of the surface emitting semiconductor laser element.

  In the surface emitting semiconductor laser device, in order to reduce the threshold current, the reflectance of the distributed Bragg reflector is generally increased to 99% or more. In particular, the distributed Bragg reflector on the side opposite to the light exit surface does not need to extract light to the outside, and is designed with a very high reflectivity, for example, 99.9%. On the other hand, the reflectance of the distributed Bragg reflector on the light exit surface side is set lower than that of the distributed Bragg reflector on the side opposite to the light exit surface in order to increase the light extraction efficiency.

  In the eleventh embodiment, the semiconductor optical modulator is located in the semiconductor distributed Bragg reflector on the side opposite to the light exit surface that requires higher reflectivity. Therefore, when the light absorption coefficient is changed by the semiconductor optical modulator, the reflectance of the distributed Bragg reflector on the high reflectance side is lowered, so that the threshold current can be changed more greatly.

(Twelfth embodiment)
In the semiconductor light emitting device according to the twelfth embodiment of the present invention, the surface emitting semiconductor laser element and the semiconductor optical modulator including the light absorption layer are monolithically integrated on the single crystal semiconductor substrate in the stacking direction. The semiconductor optical modulator is located in the semiconductor distributed Bragg reflector of the surface emitting semiconductor laser element, and at least one of the modulation electrodes of the semiconductor optical modulator is a semiconductor distributed Bragg reflector adjacent to the semiconductor optical modulator. It is characterized by being provided at a position of one cycle or less.

  The semiconductor distributed Bragg reflector is formed by alternately stacking high refractive index layers and low refractive index layers having different band gap energies. For this reason, a hetero spike occurs at the interface between the high refractive index layer and the low refractive index layer, preventing carrier injection and increasing the resistance. In addition, the depletion layer formed at the heterointerface increases the capacitive component of the distributed Bragg reflector. Accordingly, the semiconductor distributed Bragg reflector deteriorates the high-frequency transmission characteristics due to high resistance and capacitance.

  On the other hand, in the twelfth embodiment, the modulation electrode that changes the light absorption coefficient of the light absorption layer of the semiconductor light modulator is positioned at one cycle or less of the semiconductor distributed Bragg reflector adjacent to the semiconductor light modulator. Is provided. Therefore, when a bias is applied to the modulation electrode, an electric field is applied to the light absorption layer without passing through the semiconductor distributed Bragg reflector for more than one period, so that the influence of delay due to resistance and capacitance is reduced, and operation is performed at higher frequencies. It becomes possible to make it.

<Example 8>
FIG. 15 is a diagram showing a configuration example of another semiconductor light emitting device according to the present invention. 15 includes an n-type GaAs / Al _0.8 Ga _0.2 As DBR 201, an n-type GaAs lower spacer layer 202, a GaInNAs / GaAs multiple quantum well active layer 203 on an n-type GaAs substrate 101. A p-type GaAs upper spacer layer 205, a p-type AlAs layer 501, and a p-type GaAs layer 1501 are sequentially stacked.

An AlO _x insulating layer 503 is formed on the p-type GaAs layer 1501. Further, an n-type GaAs layer 1502 constituting an electroabsorption semiconductor optical modulator is formed on the AlO _x insulating layer 503. A quantum well structure 506 and a p-type GaAs layer 1503 are stacked.

Here, the AlO _x insulating layer 503 functions to electrically insulate the surface emitting semiconductor laser from the electroabsorption semiconductor optical modulator.

Further, the stacked structure of the multiple quantum well structure 506 is as shown in FIG. 4B, for example. That is, in the example of FIG. 4B, the multiple quantum well structure 506 is alternately stacked with GaInNAs as the quantum well layer 506a and Al _0.2 Ga _0.8 As as the barrier layer 506b. A GaAs intermediate layer 506c having a thickness of 2 nm is provided at the interface between the GaInNAs quantum well layer 506a and the Al _0.2 Ga _0.8 As barrier layer 506b.

In FIG. 15, a p-type GaAs / Al _0.8 Ga _0.2 As DBR 508 is further stacked on the p-type GaAs layer 1503.

In FIG. 15, the stacked structure sequentially stacked in this way is dry-etched into four steps to form a columnar structure. The first stage from the top is formed so that the surface of the p-type GaAs layer 1503 is exposed, the second stage is formed so that the surface of the n-type GaAs layer 1502 is exposed, and the third stage is p The surface of the type GaAs layer 1501 is formed so as to be exposed, and the fourth stage is etched to a depth reaching the DBR 201 of n type GaAs / Al _0.8 Ga _0.2 As.

In addition, the p-type AlAs layer 501 at the periphery of the columnar structure is selectively oxidized from the side surface exposed by etching to form an AlO _x insulating region 509. In addition, the AlO _x insulating layer 503 that electrically insulates the surface emitting semiconductor laser and the electroabsorption semiconductor optical modulator is formed by oxidizing the crystal-grown AlAs layer from the etching side surface. This oxidation process can be performed simultaneously with the selective oxidation process for forming the AlO _x insulating region 509.

  In FIG. 15, a modulation p-side electrode 510 is formed on the first terrace surface where the surface of the p-type GaAs layer 1503 is exposed by etching, and the surface of the n-type GaAs layer 1502 is exposed by etching. A modulation n-side electrode 511 is formed on the terrace surface of the step. A p-side electrode 110 for laser driving is formed on the third terrace surface where the surface of the p-type GaAs layer 1501 is exposed by etching. An n-side electrode 111 for driving the laser is formed on the back surface of the n-type GaAs substrate 101.

In the configuration of FIG. 15, carriers are injected into the GaInNAs / GaAs multiple quantum well active layer 203 by applying a forward bias to the p-side electrode 110 and the n-side electrode 111. At this time, the current is confined to a region narrower than the columnar structure by the AlO _x insulating region 509 formed by selective oxidation. The carriers injected into the GaInNAs / GaAs multiple quantum well active layer 203 are recombined for light emission, and 1.3 μm band light corresponding to the band gap of the GaInNAs well layer is emitted. Then, the light generated in the GaInNAs / GaAs multiple quantum well active layer 203 resonates in the resonator constituted by the n-type DBR 201 and the p-type DBR 508 and oscillates.

  In the electroabsorption semiconductor optical modulator, when a bias is not applied to the p-side electrode 510 and the n-side electrode 511, the multiple quantum well structure 506 can generate light with respect to the light generated in the GaInNAs / GaAs multiple quantum well active layer 203. It is transparent. Accordingly, there is no light absorption loss and laser oscillation is performed with a low threshold current.

  On the other hand, when a reverse bias is applied to the p-side electrode 510 and the n-side electrode 511, the energy band gap of the multiple quantum well structure 506 is reduced due to the quantum confined Stark effect, and is generated in the GaInNAs / GaAs multiple quantum well active layer 203. Absorbs light. Therefore, the reflectivity of the p-side DBR is effectively reduced and the threshold current is increased. Thereby, the light intensity of the output laser beam can be modulated.

  Further, in the semiconductor light emitting device of FIG. 15, modulation electrodes 510 and 511 for changing the light absorption coefficient of the multiple quantum well structure 506 of the semiconductor optical modulator are provided on the GaAs layers 1502 and 1503 adjacent to the semiconductor optical modulator. It has been. Therefore, when a bias is applied to the modulation electrode, an electric field is applied to the multiple quantum well structure 506 without passing through the semiconductor distributed Bragg reflector, so that the influence of delay due to the resistance and capacitance of the semiconductor distributed Bragg reflector is eliminated. The semiconductor optical modulator can be operated at a high frequency.

(13th Embodiment)
In any of the sixth to twelfth semiconductor light emitting devices described above, a layer obtained by selectively oxidizing AlAs or AlGaAs may be used as the electrical insulating layer between the semiconductor optical modulator and the surface emitting semiconductor laser element.

  A pn reverse bias junction is generally used for electrical insulation between the semiconductor optical modulator and the surface emitting semiconductor laser element. However, in the pn reverse bias junction, tunneling, breakdown, or the like may occur due to crystal defects or the like, and a large current may flow through the active layer of the surface emitting semiconductor laser device, thereby destroying the device.

On the other hand, a layer obtained by selectively oxidizing AlAs or AlGaAs can form AlO _x which is a good insulator. Therefore, the withstand voltage between the semiconductor optical modulator and the surface emitting semiconductor laser element can be improved to 20 V or more, for example.

  A layer obtained by selectively oxidizing AlAs or AlGaAs is also used for a current confinement structure of a surface emitting semiconductor laser element. Thereby, the selective oxidation process for current confinement of the surface emitting semiconductor laser element and the selective oxidation process for insulation between the semiconductor optical modulator and the surface emitting semiconductor laser element can be performed in a common process. At this time, if the selective oxidation distance for current confinement of the surface-emitting semiconductor laser element is different from the selective oxidation distance for insulation between the semiconductor optical modulator and the surface-emitting semiconductor laser element, the current confinement of the surface-emitting semiconductor laser element The selective oxidation rate can be adjusted by changing the layer thickness and Al composition between the AlAs or AlGaAs layer for use and the AlAs or AlGaAs layer for insulation between the semiconductor optical modulator and the surface emitting semiconductor laser element. That is, for example, by reducing the thickness of the AlAs or AlGaAs layer, the oxidation rate can be lowered. Further, the oxidation rate can be lowered as the Al composition of the AlGaAs layer is reduced.

  In the embodiment described above, an n-type substrate is used as the substrate, but a p-type substrate can also be used. In the surface emitting semiconductor laser device, a tunnel junction can be formed in the vicinity of the active layer, and current can be injected into the active layer.

(Fourteenth embodiment)
The semiconductor light emitting device according to the fourteenth embodiment of the present invention is the semiconductor light emitting device according to any one of the sixth to twelfth described above, wherein the distributed Bragg reflector of the surface emitting semiconductor laser element includes a high refractive index layer and a low refractive index layer. A composition gradient layer is provided between the refractive index layer and the thickness of the composition gradient layer is 30 to 50 nm.

FIG. 16 shows the calculation result of the resistance value of the distributed Bragg reflector when the doping concentration of each layer is 7 × 10 ¹⁷ cm ^{−3 in the} GaAs / AlAs distributed Bragg reflector (4 periods) including the composition gradient layer. FIG. From FIG. 16, it can be seen that when the thickness of the composition gradient layer is greater than 30 nm, the resistance value of the distributed Bragg reflector rapidly decreases and approaches the bulk resistance value (dotted line in FIG. 16).

  FIG. 17 is a diagram showing a change in reflectance of the distributed Bragg reflector with respect to a change in film thickness of the composition gradient layer in a 1.3 μm band GaAs / AlAs distributed Bragg reflector (23 periods). Compared with the tangent line shown in FIG. 17, the reflectance changes abruptly when the thickness of the composition gradient layer is 50 nm or more. For this reason, the oscillation threshold current of the surface emitting laser element suddenly increases correspondingly.

  Therefore, by setting the thickness of the composition gradient layer to 30 to 50 nm, a distributed Bragg reflector having a low resistance and a high reflectance can be formed.

  Further, by providing the composition gradient layer, a notch for trapping carriers does not occur at the interface between the high refractive index layer and the low refractive index layer, so that the capacity of the distributed Bragg reflector is reduced.

  As a result, even when a bias is applied to the semiconductor optical modulator via the distributed Bragg reflector, the resistance and capacitance of the distributed Bragg reflector can be reduced, so that it can be operated at a high modulation frequency.

(Fifteenth embodiment)
Further, the wavelength tunable laser device of the present invention includes an ASE (amplitude spontaneous emission) radiation source and a wavelength demultiplexer for wavelength-demultiplexing light generated by the ASE radiation source in a resonator constituted by a pair of reflecting mirrors. And an optical gate array that selects and amplifies light of each wavelength demultiplexed through the wavelength demultiplexer, and a semiconductor optical modulator that modulates the intensity of the light that has passed through the optical gate array. The above-described semiconductor optical modulator according to the present invention (first or second embodiment) is used as a device.

  Here, as the ASE radiation light source, one using the following semiconductor optical amplifier can be used.

  That is, the semiconductor optical amplifier includes a GaAs substrate (for example, a GaAs single crystal substrate), a gain region, a p-side electrode and an n-side electrode for injecting a current into the gain region, and the gain region includes GaNAs, GaInNAs, GaNAsSb, A material using a semiconductor layer made of any material of GaInNAsSb can be used.

  A mixed crystal semiconductor containing As and N as group V elements such as GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb can grow a single crystal thin film on a GaAs substrate, and the transmission loss of a quartz optical fiber is low. It is known to have a band gap wavelength of ˜1.6 μm band. Therefore, it has a gain for 1.3 μm or 1.55 μm laser light used for optical fiber transmission.

  It is known that a mixed crystal semiconductor containing As and N as a group V element can increase the band discontinuity ratio on the conduction band side with respect to the valence band side when forming a heterojunction with an AlGaAs or AlGaInP-based material. . In addition, since it can be formed on a GaAs substrate, a material having a large energy band gap such as AlGaAs or AlGaInP can be used for the cladding layer. Therefore, the conduction band discontinuity between the gain region made of any material of GaNAs, GaInNAs, GaNASSb, and GaInNAsSb and the clad layer can be as large as 200 meV or more.

  For this reason, even when the external environment temperature increases, electrons overflowing from the gain region to the cladding layer do not increase rapidly, and a decrease in gain due to a temperature increase can be suppressed. Therefore, in a semiconductor optical amplifier having a gain region made of any material of GaNAs, GaInNAs, GaNASSb, and GaInNAsSb, the change in optical gain can be reduced with respect to the external environment temperature.

Further, the gain coefficient of the InGaAsP layer on the InP substrate, which is a conventional material system, is as low as about 500 cm ⁻¹ (refer to the document “IEEE J. Quantum Electron., Vol. 27, pp 1804-1811”). On the other hand, the gain coefficient of the GaInNAs layer (1.2 μm band) on the GaAs substrate has been reported to be as high as 2243 cm ⁻¹ (see “Jpn. J. Appl. Phys., Vol. 35, pp. 206-”). 209 ").

Figure 7 is a prototype end face type LD for the GaInNAs of 1.3μm band and the active layer on a GaAs substrate, is the result obtained experimentally threshold current density _{J th} and the relationship of the total loss α of the semiconductor laser . From FIG. 7, it was found that the gain coefficient G ₀ of the GaInNAs layer can be as high as 1500 cm ⁻¹ even in the 1.3 μm band. Therefore, the GaInNAs layer on the GaAs substrate has a higher gain coefficient than the InGaAsP material on the InP substrate, and is suitable for use as a gain region of a semiconductor optical amplifier in the 1.2 to 1.3 μm band. Yes.

  In the semiconductor optical amplifier, the gain region has a multi-quantum well structure in which a plurality of quantum well layers made of any material of GaNAs, GaInNAs, GANASSb, and GaInNAsSb are stacked. A plurality of quantum well layers having different energy band gaps are stacked.

  Thus, when the gain region of the semiconductor optical amplifier is composed of a quantum well layer made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb, the change in the optical amplification factor is reduced with respect to the external environment temperature. it can.

  Furthermore, the energy band gap of a quantum well layer can be made different by changing the mixed crystal composition or well width of each quantum well layer. In this case, each quantum well layer has gain for different wavelength bands. Therefore, a multiple quantum well structure in which quantum well layers with different energy band gaps are combined can have a wide amplification band by overlapping the gain bands of the quantum well layers. Such a broadband optical amplifier can be applied to a wavelength division multiplexing optical transmission system having a relatively wide wavelength interval.

  It is important to equalize the gain of each quantum well layer when combining (deleting) the amplification band (correction of errors) by combining quantum well layers having different energy band gaps. However, when the energy band gap is different, the gain coefficient of the quantum well layer is different, and the height of the carrier confinement barrier to the quantum well layer is also changed.

  On the other hand, in the semiconductor optical amplifier, since the quantum well layer is configured by using GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb, the same energy band gap can be obtained by controlling the strain amount and N composition applied to the quantum well layer. The gain coefficient can be changed as it is.

  Also, the conduction band edge position of the quantum well layer can be lowered by increasing the N composition, and the conduction band edge position can be raised by increasing the Sb composition. As a result, the height of the electron confinement barrier in the quantum well layer can be made uniform. Therefore, it is possible to make the gain coefficients of quantum well structures having different energy band gaps uniform.

  FIGS. 8A and 8B are diagrams showing a configuration example of the above-described semiconductor optical amplifier. 8A is a cross-sectional view seen from the front, and FIG. 8B is a cross-sectional view seen from the side.

Referring to FIG. 8, this semiconductor optical amplifier includes an n-type Al _0.4 Ga _0.6 As cladding layer 102, a GaAs lower optical waveguide layer 103, a GaInNAs / GaAs multiple quantum well active layer on an n-type GaAs substrate 101. 104, a GaAs upper optical waveguide layer 105, and a p-type Ga _0.5 In _0.5 P first cladding layer 106 are sequentially stacked.

  Here, the GaInNAs / GaAs multiple quantum well active layer 104 is configured, for example, by laminating three cycles of a GaInNAs quantum well layer having a thickness of 7 nm and a GaAs barrier layer having a thickness of 10 nm.

An n-type Al _0.5 In _0.5 P current blocking layer 107 is formed on both sides of the stripe region for current injection on the p-type Ga _0.5 In _0.5 P first cladding layer 106. . This is because, after the n-type Al _0.5 In _0.5 P current blocking layer 107 is grown on the p-type Ga _0.5 In _0.5 P first cladding layer 106, the stripe region is converted into a sulfuric acid-based etching solution. Can be formed by chemical etching. That is, since the sulfuric acid-based etching solution etches AlInP and does not etch GaInP, only the n-type Al _0.5 In _0.5 P current blocking layer 107 can be etched.

Then, on the n-type Al _0.5 In _0.5 P current blocking layer 107 and the p-type Ga _0.5 In _0.5 P first cladding layer 106 in the stripe region, the p-type Al _0.4 Ga _{0.6 is formed.} An As second cladding layer 108 and a p-type GaAs cap layer 109 are sequentially stacked.

A p-side electrode 110 is formed on the p-type GaAs cap layer 109, and an n-side electrode 111 is formed on the back surface of the n-type GaAs substrate 101. Further, non-reflective films 112 and 113 having a reflectance of 0.2% or less are formed on both end faces T ₁ and T ₂ of the element formed by cleavage.

The semiconductor optical amplifier of FIG. 8 is a traveling wave type. That is, the laser beam incident from the rear end face T ₁ is optically amplified in the process of propagating through the waveguide including a GaInNAs / GaAs multiple quantum well active layer 104 having a gain with respect to the wavelength of the incident light, the front end surface of the opposite side It has a structure that is emitted from the T _2. In the direction perpendicular to the substrate 101, an SCH structure in which GaAs optical waveguide layers 103 and 105 are sandwiched between cladding layers 102, 106, and 108 having a low refractive index is formed.

Further, in the direction horizontal to the substrate 101, the refractive index of the n-type Al _0.5 In _0.5 P current blocking layer 107 provided outside the stripe region is lower than that of the p-type cladding layers 106 and 108. An effective refractive index difference is formed inside and outside the stripe region to confine light in the stripe region. Note that the n-type Al _0.5 In _0.5 P current blocking layer 107 is transparent to light propagating through the waveguide, and therefore does not absorb light during wave guiding.

  In the semiconductor optical amplifier of FIG. 8, by applying a forward bias, holes and electrons are injected into the GaInNAs / GaAs multiple quantum well active layer 104 from the p-side electrode 110 and the n-side electrode 111, respectively, and an inversion distribution occurs. It is formed. Therefore, stimulated emission light is generated in resonance with the incident light, and the light is amplified.

  Further, in the semiconductor optical amplifiers of FIGS. 8A and 8B, the non-reflective films 112 and 113 formed on both end surfaces suppress laser oscillation in the Fabry-Perot mode, and suppress laser oscillation to flatten the gain. It has a function as a means. In the example of FIG. 8, the antireflection films 112 and 113 are formed on both end faces as laser oscillation suppressing means for suppressing laser oscillation in the Fabry-Perot mode, but in addition, the direction of the stripe structure is perpendicular to the light emitting end face. A method of tilting from the direction, a method of forming a window structure in the vicinity of the light emitting end face, a method of providing a light absorption region in the vicinity of the light emitting end face, a method of using these methods in combination with a non-reflective film, and the like can also be used.

  The semiconductor optical amplifier of FIG. 8 includes GaInNAs on a GaAs substrate 101 as a gain region (quantum well layer). GaInNAs grown on a GaAs substrate has a band gap wavelength of 1.2 to 1.6 μm. Therefore, it has a gain with respect to wavelengths of 1.3 μm and 1.55 μm used for optical fiber transmission. It is known that GaInNAs can increase the band discontinuity ratio of the conduction band to the valence band when a heterojunction is formed with AlGaAs or an AlGaInP-based material.

  Further, since it can be formed on a GaAs substrate, wide gap GaInP or AlGaAs can be used for the cladding layer. Therefore, the conduction band discontinuity between the GaInNAs gain region and the cladding layer can be increased to 200 meV or more. For this reason, even when the external environment temperature increases, electrons overflowing from the gain region to the cladding layer do not increase rapidly, and a decrease in gain due to a temperature increase can be suppressed. Therefore, it is possible to reduce the change in the optical amplification factor with respect to the external environment temperature.

  In FIG. 8, a GaInNAs material is used as a long wavelength band gain region (quantum well layer) formed on the GaAs substrate 101, but instead of this, any material of GaNAs, GaNAsSb, and GaInNAsSb may be used. Even in this case, the same effect can be obtained.

  In FIG. 8, a semiconductor optical amplifier is used as a single element. However, a one-dimensional array can be formed monolithically on the same substrate by forming a plurality of stripe regions.

FIG. 9 is a diagram showing another configuration example of the semiconductor optical amplifier. In the example of FIG. 9, the semiconductor optical amplifier is configured as a planar semiconductor optical amplifier. That is, referring to FIG. 9, this semiconductor optical amplifier has an n-type GaAs / Al _0.8 Ga _0.2 As DBR 201, an n-type GaAs lower spacer layer 202, a GaInNAs / GaAs multiple layer on an n-type GaAs substrate 101. A quantum well active layer 203, a p-type Al _0.4 Ga _0.6 As carrier blocking layer 204, a p-type GaAs upper spacer layer 205, and a p-type GaAs / Al _0.8 Ga _0.2 As DBR 206 are sequentially stacked. ing.

Here, the n-type DBR 201 and the p-type DBR 206 alternately use GaAs, which has a high refractive index, and Al _0.8 Ga _0.2 As, which has a low refractive index, at an optical thickness of ¼ of the operating wavelength. It is the reflecting mirror formed by laminating.

The total thickness of the n-type GaAs lower spacer layer 202, the GaInNAs / GaAs multiple quantum well active layer 203, the p-type Al _0.4 Ga _0.6 As carrier blocking layer 204, and the p-type GaAs upper spacer layer 205 is summed. Is designed to be an integral multiple of an optical thickness of ½ the operating wavelength.

  In the semiconductor optical amplifier of FIG. 9, the high resistance region 207 is formed by injecting protons in the vicinity of the active layer excluding the circular current injection region.

  In FIG. 9, the p-side electrode 110 is formed on the p-type DBR 206, and the n-side electrode 111 is formed on the back surface of the n-type GaAs substrate 101. In the p-side electrode 110 and the n-side electrode 111, the upper and lower electrodes in the current injection region are removed to form an opening in order to cause light to enter and exit, respectively.

  The semiconductor optical amplifier of FIG. 9 is a surface type that allows light to enter and exit in a direction perpendicular to the main surface of the substrate. That is, light is incident from the p-side electrode 110 side, and multiple reflections occur between the p-type DBR 206 and the n-type DBR 201 including the GaInNAs / GaAs multiple quantum well active layer 203 having a gain with respect to the wavelength of the incident light. Amplified and output from the n-type GaAs substrate 101 side.

  Therefore, the resonant optical amplifier has a high gain with respect to the wavelength resonating between the p-type DBR 206 and the n-type DBR 201. Note that the reflectance of the n-type DBR 201 is reduced to 70 to 90% so that the semiconductor optical amplifier itself does not oscillate even at high injection.

Similarly to the semiconductor optical amplifier of FIG. 8, the planar semiconductor optical amplifier of FIG. 9 includes GaInNAs on the GaAs substrate 101 as a gain region. Therefore, it corresponds to a long wavelength band of 1.3 μm or 1.55 μm used for optical fiber transmission. The conduction band discontinuity between the GaInNAs well layer and the p-type Al _0.4 Ga _0.6 As carrier blocking layer 204 can be increased to 200 meV or more.

  Therefore, even if the external environment temperature becomes high, electrons do not overflow suddenly from the GaInNAs well layer, and a decrease in gain due to temperature rise can be suppressed. Therefore, it is possible to reduce the change in the optical amplification factor with respect to the external environment temperature.

  Further, since the semiconductor optical amplifier of FIG. 9 is a surface type, it is not necessary to form the light incident / exit surface as a cleavage plane unlike the semiconductor optical amplifier of FIG. Therefore, it is also possible to monolithically integrate semiconductor optical amplifiers on a GaAs substrate to form a two-dimensional array. Therefore, it is advantageous for high-density parallel integration.

  In FIG. 9, light is amplified by transmitting from the front surface to the back surface of the substrate. However, light is input and output from the front surface side of the substrate using an n-type DBR 201 having a high reflectance of 99% or more. It is also possible to construct a reflective amplifier.

  Thus, the semiconductor optical amplifier described above can be used as an ASE radiation source. In other words, the above-described semiconductor optical amplifier forms an inversion distribution by injecting current into the gain region. And the reflectance of the end surface which inputs and outputs light is suppressed to less than 1% so that the light does not resonate. Therefore, spontaneous emission light generated in the gain region is amplified by stimulated emission, and high output ASE is generated. Therefore, it can be used as a light source that emits ASE by suppressing laser oscillation at a high injection with no signal light incident on the semiconductor optical amplifier.

  In the semiconductor optical amplifier described above, the gain region is made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb, so that the conduction band discontinuity between the gain region and the cladding layer is increased to 200 meV or more. Can do. Therefore, even when the external environment temperature becomes high, electrons overflowing from the gain region to the cladding layer do not increase rapidly. Therefore, high output ASE can be generated even at high temperatures.

  In the wavelength tunable laser device of the present invention, the optical gate array can be formed by arranging a plurality of the above-described semiconductor optical amplifiers on a GaAs substrate (GaAs single crystal substrate).

  That is, when no bias current is injected into the semiconductor optical amplifier, the gain region absorbs incident light. On the other hand, when light is incident on the semiconductor optical amplifier with a bias current injected, the light can be amplified by about 10 to 20 dB. Therefore, the semiconductor optical amplifier functions as an optical gate that controls the passage / shielding of incident light by a bias current. Then, by arranging a plurality of such semiconductor optical amplifiers on the substrate, it is possible to form an optical gate array for selecting a passage channel for parallel optical signals.

  The gain region of the semiconductor optical amplifier constituting the optical gate array is made of any material of GaNAs, GaInNAs, GaNAsSb, and GaInNAsSb when the semiconductor optical amplifier described above is used for the semiconductor optical amplifier. Therefore, the conduction band discontinuity between the gain region and the cladding layer can be increased to 200 meV or more. Therefore, even if the external environment temperature is high, electrons overflowing from the gain region to the cladding layer do not increase rapidly, and a high optical gain can be maintained even at high temperatures. Therefore, an optical gate array that operates stably with respect to the external environment temperature can be formed without deteriorating the S / N ratio of the optical signal passing through the optical gate.

  In the wavelength tunable laser device having such a configuration, light generated by the ASE radiation source is ASE (amplitude spontaneous emission) having a wide emission spectrum width. The light generated by the ASE radiation source is spatially branched into each wavelength component in the process of being guided through the wavelength demultiplexer. As the wavelength demultiplexer, for example, an arrayed waveguide element is used.

  The light passing through the wavelength demultiplexer is input to the optical gate array. The light input to each semiconductor optical amplifier constituting the optical gate array is light having a narrow spectral width with the wavelength selected by the wavelength demultiplexer, and each has a different wavelength. In the optical gate array, only a light having a selected wavelength is selected and amplified by applying a bias current only to a semiconductor optical amplifier corresponding to a desired wavelength from different wavelengths. Light of other wavelengths is absorbed and attenuated in the process of being guided through an unbiased semiconductor optical amplifier.

  The light of the wavelength selected by the optical gate array resonates in a resonator composed of the rear end face side of the ASE radiation light source and the front end face side of the optical gate array, and laser oscillates. Accordingly, the wavelength is selected by being digitally divided in accordance with the number of semiconductor optical amplifiers constituting the optical gate array.

  An ASE light source using the semiconductor optical amplifier described above can operate at high temperature and high output. The optical gate array using the semiconductor optical amplifier described above operates stably with respect to the external environment temperature. Therefore, by configuring the wavelength tunable laser device using the above-described ASE radiation light source device using the semiconductor optical amplifier and the optical gate array, a light source that is stable against changes in the external environment temperature can be formed. And since precise temperature control by an electronic cooling device is not required, it can manufacture at low cost.

<Example 9>
FIG. 10 is a diagram showing a configuration example of a wavelength tunable laser device according to the present invention. Referring to FIG. 10, the tunable laser apparatus includes an ASE radiation light source 601 that generates light, a wavelength demultiplexer 602 that demultiplexes light generated by the ASE radiation light source 601 on a Si substrate 606, and a semiconductor. The optical amplifier 604 includes an optical gate array 603 formed by monolithically integrating the array, and a multiplexer 605 that couples the light output from the optical gate array 603 into one optical waveguide. The light output from the multiplexer 605 is modulated by the semiconductor optical modulator 607 and output.

  The wavelength tunable laser device having such a configuration operates as follows. That is, the light generated by the ASE radiation light source 601 is ASE with a wide emission spectrum width. The light generated by the ASE light source 601 is spatially branched into each wavelength component in the process of being guided through the wavelength demultiplexer 601 and output. An arrayed waveguide element can be used as the wavelength demultiplexer 602. The light that has passed through the wavelength demultiplexer 602 is input to the optical gate array 603. The optical gate array 603 is formed by monolithically integrating n-channel traveling wave semiconductor optical amplifiers 604 in an array.

  The light input to each semiconductor optical amplifier 604 of the optical gate array 603 is light whose wavelength is selected by the wavelength demultiplexer 602, and the wavelengths are different from λ1 to λn, respectively. In the optical gate array 603, a bias current is applied only to the semiconductor optical amplifier corresponding to the desired wavelength from among the wavelengths λ1 to λn, thereby selecting and amplifying only the light of the selected wavelength. Light of other wavelengths is absorbed and attenuated in the process of being guided through an unbiased semiconductor optical amplifier.

  The light of the wavelength selected by the optical gate array 603 resonates in a resonator constituted by the rear end face of the ASE radiation light source 601 and the front end face of the semiconductor optical amplifier 604, and laser oscillation occurs. The selected wavelength is digitally divided in accordance with the number of semiconductor optical amplifiers 604 constituting the optical gate array 603. The light output from the optical gate array 603 is coupled to the common optical waveguide by the multiplexer 605, and the light output from the multiplexer 605 is modulated by the semiconductor optical modulator 607 and emitted to the outside.

  FIGS. 11A and 11B are diagrams showing a configuration example of the ASE radiation light source 601 used in the wavelength tunable laser apparatus shown in FIG. FIG. 11A is a cross-sectional view seen from the front, and FIG. 11B is a view seen from the top. Referring to FIG. 11A, the stacked structure of the ASE radiation light source 601 has the same structure as that of the semiconductor optical amplifier shown in FIG.

Then, the front end surface T ₂ of the element formed by cleavage is formed reflectance of 0.2% or less of the non-reflection film 703, a high reflection film 702 of reflectivity of 99% on the rear end surface T ₁ is formed Has been. Also, the stripe region 704 for current injection, in the front end face T ₂ near that emits light has a structure in which inclined 10 ° from a direction perpendicular to the device end face.

  FIG. 11C is a diagram showing the structure of the GaInNAs / GaAs multiple quantum well structure 701 which is the active region in FIG. Referring to FIG. 11C, a GaInNAs / GaAs multiple quantum well structure 701 has a structure in which a GaAs barrier layer 706 is sandwiched above and below four GaInNAs well layers 705a, 705b, 705c, and 705d.

  The band gap wavelengths of the four GaInNAs well layers are different by changing the mixed crystal composition and the well width. The band gap wavelengths of the well layers 705a, 705b, 705c, and 705d can be set to 1.20 μm for 705a, 1.24 μm for 705b, 1.28 μm for 705c, and 1.32 μm for 705d, for example.

  The ASE radiation source in FIG. 11 applies the semiconductor optical amplifier shown in FIG. That is, in FIG. 11, when a forward bias current is applied to the p-side electrode 110 and the n-side electrode 111, holes and electrons are recombined in the multiple quantum well active layer 701, and spontaneous emission and stimulated emission occur. .

Since the front end face T ₂ antireflection coating 703 is formed, the light generated in the multi-quantum well active layer 701 is suppressed resonance due to multiple reflections, and is emitted from the front end face T ₂ without laser oscillation. At this time, the spontaneous emission light is optically amplified by the inversion distribution of the gain region itself and emitted as ASE.

When using a semiconductor optical amplifier as ASE radiation source, there is no need to input the signal light from the rear end face T ₁ to the element. Therefore, by forming a high reflection film 702 of 99% reflectance on the rear end face _{T 1} in ASE radiation source shown in FIG. 11, and to release the ASE efficiently from the front end surface _{T 2.}

Further, as shown in FIG. 11B, the stripe region 704 into which current is injected has a structure inclined by 10 ° from the direction perpendicular to the end face in the vicinity of the light emitting end face. Therefore, to further reduce the light components return to reflected by the gain region in the front end face T _2, it is prevented from lasing in the cavity formed by both end faces of the semiconductor optical amplifier.

In the ASE radiation source shown in FIG. 11, since the gain region is composed of GaInNAs quantum well layers, the conduction band discontinuity between the gain region and the Al _0.4 Ga _0.6 As cladding layer is 200 meV or more. And can be enlarged. Therefore, even when the external environment temperature becomes high, electrons overflowing from the gain region to the cladding layer do not increase rapidly. Therefore, it is possible to generate the high output ASE while maintaining the inversion distribution state even at a high temperature.

  In the ASE radiation source of FIG. 11, as shown in FIG. 11C, the band gap wavelengths of the four GaInNAs well layers 705a, 705b, 705c, and 705d constituting the multiple quantum well active layer 701 that is the gain region. Are formed differently. Therefore, each GaInNAs well layer 705a, 705b, 705c, 705d has a gain with respect to a different wavelength band.

  Therefore, the multiple quantum well active layer 701 in which GaInNAs well layers having different energy band gaps are combined can have a wide amplification band of 1.20 to 1.32 μm by overlapping the gain bands of the respective well layers. . Therefore, since the ASE radiation source of FIG. 11 can generate a broadband ASE, the wavelength variation of the wavelength tunable laser device shown in FIG. 10 can be expanded.

  In the wavelength tunable laser device of FIG. 10, the optical gate array 603 is configured by monolithically integrating n traveling wave semiconductor optical amplifiers 604 as shown in FIG. 8 on a GaAs substrate. Here, the number of arrays is set to 8, for example.

  In this case, the optical gate array 603 can select eight wavelengths from a wavelength range of 1.20 to 1.32 μm. Further, in order to form a resonator with the rear end face of the ASE radiation light source 601 and the front end face of the semiconductor optical amplifier 604, a low reflection film having a reflectance of 10% is formed on the front end face of the semiconductor optical amplifier 604.

In the optical gate array 603, the gain region of the semiconductor optical amplifier 604 is composed of GaInNAs, and the conduction band discontinuity between the gain region and the Al _0.4 Ga _0.6 As cladding layer may be increased to 200 meV or more. it can. Therefore, even if the external environment temperature is high, electrons overflowing from the gain region to the cladding layer do not increase rapidly, and a high optical gain can be maintained even at high temperatures. Therefore, it is possible to prevent the S / N ratio of the optical signal passing through the optical gate array from deteriorating and to operate stably with respect to the external environment temperature.

  As described above, the wavelength tunable laser apparatus of FIG. 10 uses, as active elements, the ASE radiation source 601 capable of high-temperature and high-power operation and the optical gate array 603 that operates stably with respect to the external environment temperature. Yes. Therefore, a stable light source can be formed against changes in the external environment temperature. Further, since it is not necessary to precisely control the temperature of the device by the electronic cooling device, it can be manufactured at a low cost.

  By the way, in the wavelength tunable laser device of the present invention, the light intensity of the wavelength-demultiplexed light is modulated by the electroabsorption semiconductor optical modulator 607. The modulation frequency when applying an electric field can increase the modulation frequency of light as compared with the case where modulation is performed by current injection. Therefore, the modulation frequency of the laser device can be increased.

  Further, in the wavelength tunable laser device of the present invention, the S / N ratio of the light modulation can be improved even at high temperature operation by using the electrolytic absorption type semiconductor optical modulator of the present invention (first or second embodiment) described above. A drop can be prevented and stable operation can be achieved. Moreover, high-speed modulation of 10 GHz or more is possible.

(Sixteenth embodiment)
Further, the multi-wavelength laser device of the present invention selects and amplifies the wavelength demultiplexer and light of each wavelength demultiplexed through the wavelength demultiplexer in the resonator constituted by a pair of reflecting mirrors. A semiconductor optical amplifier and a semiconductor optical modulator that modulates the intensity of light amplified by the semiconductor optical amplifier are provided, and the semiconductor optical modulator of the present invention (first or second embodiment) described above is used as the semiconductor optical modulator. It is characterized in that a vessel is used.

  Here, the semiconductor optical amplifier described above (for example, the semiconductor optical amplifier of FIGS. 8 and 9) can be used as the semiconductor optical amplifier.

  The light generated by the semiconductor optical amplifier provided in the resonator constituted by the pair of reflecting mirrors is ASE having a wide emission spectrum width. The light generated by the semiconductor optical amplifier is input to the wavelength demultiplexer, guided through the wavelength demultiplexer, and returned to the semiconductor optical amplifier. At this time, since the light returning to the semiconductor optical amplifier is light having a narrow spectral width by spatially branching the wavelength by the wavelength demultiplexer, only light having a specific wavelength is amplified.

  By repeating this, the light selected by the wavelength demultiplexer oscillates in the resonator. By providing a plurality of semiconductor optical amplifiers at positions where the wavelength demultiplexer outputs different wavelengths, it is possible to realize a multi-wavelength laser device that performs laser oscillation at different wavelengths.

  The above-described semiconductor optical amplifier can reduce the change in optical amplification factor with respect to the external environment temperature, and has a high amplification factor stably even at high temperatures. Therefore, by using the semiconductor optical amplifier described above for a multi-wavelength laser device, it is possible to form a multi-wavelength laser device that is stable against changes in external environmental temperature. Moreover, since precise temperature control by an electronic cooling device is not required, it can be manufactured at low cost.

  By the way, in the multi-wavelength laser device of the present invention, the light intensity of the wavelength-demultiplexed light is modulated by the electroabsorption semiconductor optical modulator. The modulation frequency when applying an electric field can increase the modulation frequency of light as compared with the case where modulation is performed by current injection. Therefore, the modulation frequency of the laser device can be increased.

  Further, in the multi-wavelength laser device of the present invention, by using the electroabsorption semiconductor optical modulator of the present invention (first or second embodiment) described above, the S / N ratio of the light modulation can be improved even at high temperature operation. A drop can be prevented and stable operation can be achieved. Moreover, high-speed modulation of 10 GHz or more is possible.

(Seventeenth embodiment)
Further, the present invention is an optical transmission system of a wavelength division multiplexing system including an optical transmission module that transmits optical signals of a plurality of wavelengths, an optical fiber that transmits the optical signal, and an optical reception module that receives the optical signal. The multi-wavelength laser device of the present invention described above is used for the optical transmission module.

  The wavelength division multiplexing method is a method of increasing transmission capacity by multiplexing in one optical fiber with optical signals of a plurality of wavelengths and transmitting in parallel. In this case, optical signal sources having different wavelengths are required, and a low-cost multi-wavelength light source is required. In the wavelength division multiplexing optical transmission system of the present invention, the above-described multi-wavelength laser device is used for the optical transmission module.

  As described above, the multi-wavelength laser device of the present invention operates with stable optical output and modulation characteristics against changes in the external environment temperature. Therefore, precise temperature control by an electronic cooling device is not required, and a multi-wavelength laser device can be manufactured at low cost. Therefore, it is possible to reduce the cost of a wavelength division multiplexing optical transmission system using this.

<Example 10>
FIG. 12 is a diagram illustrating a configuration example of an optical transmission system according to the present invention. The optical transmission system of FIG. 12 includes an optical transmission module 801, an optical reception module 802, and an optical fiber cable 803.

  Here, as the optical fiber cable 803, a single mode fiber having quartz as a core and a clad can be used. The optical transmission module 801 includes a drive control circuit 805 and a multi-wavelength laser device 804, and multiplexes optical signals of a plurality of different wavelengths in one optical fiber and transmits them in parallel. A wavelength division division method that increases the transmission capacity is adopted. The optical receiving module 802 includes a receiving device 806 and a receiving circuit 807.

  In the optical transmission system having such a configuration, the electrical signal input to the optical transmission module 801 is first input to the drive control circuit 805. In the drive control circuit 805, current is injected into the laser of each wavelength of the multi-wavelength laser device 804 to oscillate, and the laser light intensity is modulated according to the signal. The multi-wavelength laser device 804 independently modulates laser light having a plurality of wavelengths and sends an optical signal to one optical fiber cable 803.

  The optical signal is guided through the optical fiber cable 803 and input to the light receiving device 806 in the optical receiving module 802. In the light receiving device 806, after the optical signal is separated into separate wavelength components by the wavelength demultiplexer, the light of each wavelength component is converted into an electrical signal by a photodiode, an avalanche photodiode or the like. After that, the reception circuit 807 amplifies and shapes the electric signal and outputs it.

  FIG. 13 is a diagram showing the configuration of the multi-wavelength laser apparatus 804 used in the optical transmission system shown in FIG. In FIG. 12, reference numeral 604 denotes a semiconductor optical amplifier that has a function of generating ASE and amplifying the generated ASE. A plurality of semiconductor optical amplifiers 604 are monolithically integrated on the same substrate.

  Reference numeral 602 denotes a wavelength demultiplexer that demultiplexes light generated by the semiconductor optical amplifier 604. In the wavelength demultiplexer 602, a highly reflective film 901 is formed on the side opposite to the side where the semiconductor optical amplifier 604 is provided. Reference numeral 902 denotes an electro-absorption semiconductor optical modulator that modulates the intensity of each light demultiplexed by the wavelength demultiplexer 602, and reference numeral 605 denotes a light beam demultiplexed by the wavelength demultiplexer 602. A multiplexer coupled to the optical waveguide. Reference numeral 606 denotes a Si substrate on which the above components are arranged.

  The operation of the multi-wavelength laser device having such a configuration is as follows. That is, the light generated by the semiconductor optical amplifier 604 is ASE with a wide emission spectrum width. The light generated by the semiconductor optical amplifier 604 is input to the wavelength demultiplexer 602, guided by the wavelength demultiplexer 602, reflected by the highly reflective film 901 provided on the opposite side, and again guided through the wavelength demultiplexer 602. And return to the semiconductor optical amplifier 604.

  At this time, since the light returning to the semiconductor optical amplifier 604 is light having a narrow spectral width by spatially branching the wavelength by the wavelength demultiplexer 602, only light having a specific wavelength is amplified. A low reflection film having a reflectance of 10% is formed on the front end face of the semiconductor optical amplifier 604, and the high reflection film 901 and the front end face of the semiconductor optical amplifier 604 constitute a resonator to cause laser oscillation.

  A plurality of semiconductor optical amplifiers 604 are provided at positions where the wavelength demultiplexer 602 outputs different wavelengths, and a multi-wavelength laser device can be realized by amplifying light of different wavelengths and causing laser oscillation. In the example of FIG. 13, a four-element semiconductor optical amplifier is used, and laser oscillation is performed at 1.20 μm, 1.24 μm, 1.28 μm, and 1.32 μm, respectively.

In the multiwavelength laser device of FIG. 13, the semiconductor optical amplifier 604 uses the semiconductor optical amplifier shown in FIG. Therefore, since the gain region is composed of a GaInNAs quantum well layer, the conduction band discontinuity between the gain region and the Al _0.4 Ga _0.6 As cladding layer can be increased to 200 meV or more. Therefore, even when the external environment temperature becomes high, electrons overflowing from the gain region to the cladding layer do not increase rapidly. Therefore, a high optical gain can be maintained even at high temperatures, and the operation is stable with respect to the external environment temperature.

  In the multiwavelength laser apparatus of FIG. 13, an electroabsorption semiconductor optical modulator 902 is provided to modulate the laser light intensity. Here, as the electroabsorption optical modulator, the semiconductor optical modulator of the present invention (for example, the electroabsorption semiconductor optical modulator as shown in FIG. 1) is used. As a result, the S / N ratio does not decrease even during high temperature operation, and the operation is stable. Accordingly, it is possible to form a multi-wavelength laser device that is stable against changes in the external environment temperature. Moreover, since precise temperature control by an electronic cooling device is not required, it can be manufactured at low cost.

  Further, the electroabsorption semiconductor optical modulator of FIG. 1 can perform high-speed modulation of 10 to 50 GHz. In the optical transmission system of FIG. 12, large-capacity transmission of a maximum of 100 Gbit / s is possible by modulating four wavelengths of laser light at 25 GHz.

The wavelength division multiplexing optical transmission system shown in FIG. 12 uses a low-cost multi-wavelength laser apparatus that operates stably with respect to optical output and modulation characteristics with respect to changes in the external environment temperature. Therefore, an optical transmission system capable of large capacity transmission of 100 Gbit / s can be constructed at low cost and with high reliability.

It is a figure which shows the structural example of the semiconductor optical modulator based on this invention. It is a figure which shows the structural example of the semiconductor light-emitting device based on this invention. It is a figure which shows the other structural example of the semiconductor light-emitting device based on this invention. It is a figure which shows the other structural example of the semiconductor light-emitting device based on this invention. It is a figure which shows the other structural example of the surface type semiconductor light-emitting device based on this invention. It is a figure which shows the other structural example of the surface type semiconductor light-emitting device based on this invention. And prototype facet semiconductor lasers for the GaInNAs of 1.3μm band and the active layer on a GaAs substrate, is a diagram showing a result of experimentally determined the relationship between the threshold current density J _th and the total loss α of the semiconductor laser . It is a figure which shows the structural example of the semiconductor optical amplifier which concerns on this invention. It is a figure which shows the other structural example of the semiconductor optical modulator based on this invention. It is a figure which shows the structural example of the wavelength tunable laser apparatus which concerns on this invention. It is a figure which shows the structural example of the ASE radiation light source used for the wavelength tunable laser apparatus of FIG. It is a figure which shows the structural example of the optical transmission system which concerns on this invention. It is a figure which shows the structural example of the multiwavelength laser apparatus used for the optical transmission system shown in FIG. It is a figure which shows the other structural example of the semiconductor light-emitting device based on this invention. It is a figure which shows the other structural example of the semiconductor light-emitting device based on this invention. It is a figure which shows the relationship between the resistivity of a distributed Bragg reflector, and a composition gradient layer thickness. It is a figure which shows the relationship between the change rate of the reflectance of a distributed Bragg reflector, and composition gradient layer thickness.

Explanation of symbols

101: n-type GaAs substrate 102: n-type AlGaAs cladding layer 103: GaAs lower optical waveguide layer 104: GaInNAs / GaAs multiple quantum well active layer 105: GaAs upper optical waveguide layer 106: p-type GaInP first cladding layer 107: n-type AlInP blocking layer 108: p-type AlGaAs second cladding layer 109: p-type GaAs cap layer 110: p-side electrode 111: n-side electrode 112: rear end face non-reflective film 113: front end face non-reflective film 201: n-type GaAs / AlGaAs DBR
202: n-type GaAs lower spacer layer 203: GaInNAs / GaAs multiple quantum well active layer 204: p-type AlGaAs carrier block layer 205: p-type GaAs upper spacer layer 206: p-type GaAs / AlGaAs DBR
207: high resistance region 301: multiple quantum well structure 302: p-type AlGaAs first cladding layer 303: p-type AlAs
304: AlO _x insulating region 401: GaAsP diffraction grating layer 402: GaAsP upper optical waveguide layer 403: p-type AlGaAs cladding layer 404: high resistance region 405: p-side electrode 406: p-side electrode 501: p-type AlAs layer 502: p Type GaAs / AlGaAs first DBR
503: AlO _x insulating layer 504: n-type GaAs contact layer 505: n-type AlGaAs cladding layer 506: multiple quantum well structure 506a: GaInNAs quantum well layer 506b: AlGaAs barrier layer 506c: GaAs intermediate layer 507: p-type AlGaAs cladding layer 508 : P-type GaAs / AlGaAs second DBR
509: AlO _x insulating region 510: modulation p-side electrode 511: modulation n-side electrode 601: ASE light source 602: duplexer 603: optical gate array 604: semiconductor optical amplifier 605: multiplexer 606: Si substrate 701 GaInNAs / GaAs multiple quantum well active layer 702: non-reflective film 703: highly reflective film 704: stripe region 705a, b, c, d: GaInNAs well layer 706: GaAs barrier layer 801: optical transmitter module 802: optical receiver module 803: Optical fiber cable 804: Multi-wavelength laser device 805: Drive control circuit 806: Light receiving device 807: Receiving circuit 901: High reflection film 902: Electroabsorption optical modulator 1001: Si substrate 1002: Surface emitting laser array 1003: 45 ° mirror 1004: Optical waveguide 1005: Optical modulator array 1 06: optical fiber 1101: first upper GaAs spacer layer 1102: second upper GaAs spacer layer 1103: p-type GaAs contact layer 1104: n-type GaAs / AlGaAs upper DBR
1201: n-type GaAs / AlGaAs lower DBR
1202: p-type GaAs / AlGaAs DBR
1203: n-type GaAs / AlGaAs upper DBR
1204: n-side electrode

1401: p-type GaAs substrate 1402: p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As lower DBR
_{1403: GaAs / Al 0.2 Ga 0.8} As multiple quantum well optical absorption layer 1404: n-type _{Al 0.2 Ga 0.8 As / Al 0.9} Ga 0.1 As DBR
1405: Al _0.2 Ga _0.8 As lower spacer layer 1406: GaAs / Al _0.2 Ga _0.8 As multiple quantum well active layer 1407: Al _0.2 Ga _0.8 As upper spacer layer 1408: p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As upper DBR
1411: p-side electrode 1412: n-side electrode 1413: p-side electrode 1501: p-type GaAs layer 1502: n-type GaAs layer 1503: p-type GaAs layer

Claims (5)

A surface-emitting semiconductor laser element and a semiconductor optical modulator having a light absorption layer having a multiple quantum well structure are monolithically integrated in a stacking direction on a single crystal semiconductor substrate. The semiconductor optical modulator is a surface-emitting semiconductor laser. A semiconductor light-emitting device, which is located in a resonator of an element or in a semiconductor distributed Bragg reflector of a surface-emitting semiconductor laser element. A surface emitting semiconductor laser element and a semiconductor optical modulator including a light absorption layer are monolithically integrated in a stacking direction on a single crystal semiconductor substrate, and the semiconductor optical modulator is a light emitting surface of the surface emitting semiconductor laser element. The semiconductor light emitting device is located in the semiconductor distributed Bragg reflector on the opposite side of the semiconductor light emitting device. A surface emitting semiconductor laser element and a semiconductor optical modulator including a light absorption layer are monolithically integrated in a stacking direction on a single crystal semiconductor substrate. The semiconductor optical modulator is a semiconductor distribution Bragg of the surface emitting semiconductor laser element. It is located in the reflecting mirror, and at least one of the modulation electrodes of the semiconductor optical modulator is provided at a position of one cycle or less of the semiconductor distributed Bragg reflecting mirror adjacent to the semiconductor optical modulator. Semiconductor light emitting device. 4. The semiconductor light emitting device according to claim 1, wherein a layer obtained by selectively oxidizing AlAs or AlGaAs is used as an electrical insulating layer between the semiconductor optical modulator and the surface emitting semiconductor laser element. A semiconductor light emitting device. 4. The semiconductor light emitting device according to claim 1, wherein the distributed Bragg reflector of the surface emitting semiconductor laser element includes a composition gradient layer between the high refractive index layer and the low refractive index layer. And a layer thickness of the composition gradient layer is 30 to 50 nm.

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