Vertical cavity light emitting device

Abstract

To provide a vertical resonator type light emitting device capable of stably emitting light in a specific polarization direction.SOLUTION: A vertical resonator type light emitting device includes: a gallium-nitride-based semiconductor substrate; a first multilayer reflector formed on the substrate; one semiconductor layer having a first conductivity type formed on the first multilayer reflector; a semiconductor structure layer including an active layer formed on the first semiconductor layer and a second semiconductor layer formed on the active layer and having a second conductivity type opposite the first conductivity type; a second multilayer reflector formed on the semiconductor structural layer and constituting a resonator together with the first multilayer reflector; and a current constriction structure formed between the first multilayer reflector and the second multilayer reflector and concentrating current in one region of the active layer. A diffraction grating consisting of a plurality of mutually parallel slit structures is formed in a region overlapping with the one region when viewed from a normal direction of an upper surface of the gallium-nitride-based semiconductor substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to vertical cavity light emitting devices such as vertical cavity surface emitting lasers (VCSELs). [Background technology]

[0002] A vertical cavity semiconductor surface emitting laser (hereinafter also simply referred to as a surface emitting laser) has been known as one type of semiconductor laser, and has a semiconductor layer that emits light when a voltage is applied thereto and multilayer film reflectors that face each other with the semiconductor layer sandwiched therebetween. For example, Patent Document 1 discloses a vertical cavity semiconductor laser having an n-electrode and a p-electrode connected to an n-type semiconductor layer and a p-type semiconductor layer, respectively. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-98328 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in a vertical cavity light emitting device such as a surface emitting laser, an optical resonator is formed by opposing reflecting mirrors. For example, in a surface emitting laser, when a voltage is applied to a semiconductor layer via electrodes, light emitted from the semiconductor layer resonates within the optical resonator, generating laser light.

[0005] However, one example of a problem with vertical cavity semiconductor laser elements is that they have lower light emission efficiency than horizontal cavity semiconductor lasers that have a cavity in the in-plane direction of a semiconductor layer including an active layer.

[0006] Furthermore, the light emitted from vertical cavity semiconductor laser devices using GaN-based substrates is often elliptically polarized or linearly polarized with varying polarization directions, and it is difficult to stabilize the polarization direction during operation, as the polarization direction changes depending on the driving current and operating temperature.

[0007] The present invention has been made in consideration of the above-mentioned points, and aims to provide a vertical cavity light emitting device that has high luminous efficiency and is capable of stably emitting light in a specific polarization direction. [Means for solving the problem]

[0008] a first multilayer reflector formed on the substrate and made of nitride semiconductors; a semiconductor structure layer including a first semiconductor layer formed on the first multilayer reflector and made of nitride semiconductors and having a first conductivity type; an active layer formed on the first semiconductor layer and made of nitride semiconductors; and a second semiconductor layer formed on the active layer and made of nitride semiconductors and having a second conductivity type opposite to the first conductivity type; a second multilayer reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer reflector; and a current constriction structure formed between the first multilayer reflector and the second multilayer reflector and concentrating current in one region of the active layer, wherein a diffraction grating consisting of a plurality of slit structures parallel to each other is formed in a region overlapping with the one region when viewed from the normal direction of the top surface of the gallium nitride semiconductor substrate. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a surface-emitting laser according to a first embodiment; [Figure 2] 1 is a top view of a surface-emitting laser according to a first embodiment. [Figure 3] 1 is a cross-sectional view of a surface-emitting laser according to a first embodiment. [Figure 4] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a second embodiment. [Figure 5]FIG. 10 is a cross-sectional view of a surface-emitting laser according to a third embodiment. [Figure 6] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a fourth embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a fifth embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail embodiments of the present invention. In the following description, a semiconductor surface-emitting laser element will be used as an example, but the present invention can be applied not only to surface-emitting lasers but also to various vertical-cavity light-emitting elements such as vertical-cavity light-emitting diodes. [Example]

[0011] FIG. 1 is a perspective view of a vertical cavity surface emitting laser (VCSEL, hereinafter also simply referred to as a surface emitting laser) 10 according to a first embodiment.

[0012] The substrate 11 is a gallium nitride semiconductor substrate, such as a GaN substrate. The substrate 11 is, for example, a substrate having a rectangular top surface. The substrate 11 is a coreless substrate manufactured so that dislocations are uniformly distributed throughout the substrate and no cores, which are clusters of dislocation defects, are formed.

[0013] The upper surface of substrate 11 is a surface that is off-axis from the C-plane toward the M-plane by 0.5°. The upper surface of substrate 11 is also barely off-axis from the C-plane toward the A-plane, and the off-axis angle from the C-plane toward the A-plane is 0±0.01°.

[0014] In a region including the central part of the upper surface of the substrate 11, slit grooves GV1 are formed as a plurality of slit structures each extending in the direction along the m-axis and arranged in a lattice pattern.

[0015] The first multilayer reflector 13 is a semiconductor multilayer reflector made of semiconductor layers grown on the substrate 11. The first multilayer reflector 13 is formed by alternately stacking low-refractive-index semiconductor films having an AlInN composition and high-refractive-index semiconductor films having a GaN composition and a higher refractive index than the low-refractive-index semiconductor films. In other words, the first multilayer reflector 13 is a distributed Bragg reflector (DBR) made of semiconductor materials.

[0016] The first multilayer film reflector 13 is formed, for example, by providing a buffer layer having a GaN composition on the upper surface of the substrate 11 and alternately depositing the high-refractive-index semiconductor films and the low-refractive-index semiconductor films on the buffer layer.

[0017] The semiconductor structure layer 15 is a laminated structure made up of multiple semiconductor layers formed on the first multilayer reflector 13. The semiconductor structure layer 15 has an n-type semiconductor layer (first semiconductor layer) 17 formed on the first multilayer reflector 13, a light-emitting layer (or active layer) 19 formed on the n-type semiconductor layer 17, and a p-type semiconductor layer (second semiconductor layer) 21 formed on the active layer 19.

[0018] The n-type semiconductor layer 17, which serves as a semiconductor layer of a first conductivity type, is a semiconductor layer formed on the first multilayer film reflector 13. The n-type semiconductor layer 17 has a GaN composition and is doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower portion 17A and a cylindrical upper portion 17B disposed thereon. Specifically, for example, the n-type semiconductor layer 17 has a cylindrical upper portion 17B protruding from a top surface 17S of the prismatic lower portion 17A. In other words, the n-type semiconductor layer 17 has a mesa-shaped structure including the upper portion 17B.

[0019] The active layer 19 is formed on the upper portion 17B of the n-type semiconductor layer 17 and has a quantum well structure including a well layer having an InGaN composition and a barrier layer having a GaN composition. In the surface-emitting laser 10, light is generated in the active layer 19.

[0020] The p-type semiconductor layer 21, which serves as a semiconductor layer of a second conductivity type, is a semiconductor layer having a GaN composition formed on the active layer 19. The p-type semiconductor layer 21 is doped with Mg as a p-type impurity.

[0021] The n-electrode 23 is a metal electrode provided on an upper surface 17S of a lower portion 17A of the n-type semiconductor layer 17 and electrically connected to the n-type semiconductor layer 17. The n-electrode 23 is formed in a ring shape so as to surround an upper portion 17B of the n-type semiconductor layer 17. The n-electrode 23 is in electrical contact with the n-type semiconductor layer 17 and forms a first electrode layer that supplies a current from the outside to the semiconductor structure layer 15.

[0022] Insulating layer 25 is a layer made of an insulator and formed on p-type semiconductor layer 21. Insulating layer 25 is made of a substance, such as SiO2, that has a lower refractive index than the material that forms p-type semiconductor layer 21. Insulating layer 25 is formed in a ring shape on p-type semiconductor layer 21, and has an opening (not shown) in the center that exposes p-type semiconductor layer 21.

[0023] The transparent electrode 27 is a light-transmitting metal oxide film formed on the upper surface of the insulating layer 25. The transparent electrode 27 covers the entire upper surface of the insulating layer 25 and the entire upper surface of the p-type semiconductor layer 21 exposed from an opening formed in the central part of the insulating layer 25. As the metal oxide film forming the transparent electrode 27, for example, ITO or IZO, which is light-transmitting to light emitted from the active layer 19, can be used.

[0024] The p-electrode 29 is a metal electrode formed on the transparent electrode 27. The p-electrode 29 is electrically connected to the upper surface of the p-type semiconductor layer 21 exposed from the opening in the insulating layer 25 via the transparent electrode 27. The transparent electrode 27 and the p-electrode 29 form a second electrode layer that is in electrical contact with the p-type semiconductor layer 21 and supplies current from the outside to the semiconductor structure layer 15. In this embodiment, the p-electrode 29 is formed in a ring shape on the upper surface of the transparent electrode 27 along the outer edge of the upper surface.

[0025] The second multilayer reflector 31 is a cylindrical multilayer reflector formed in an area surrounded by the p-electrode 29 on the upper surface of the transparent electrode 27. The second multilayer reflector 31 is a dielectric multilayer reflector in which low-refractive-index dielectric films made of Al2O3 and high-refractive-index dielectric films made of Ta2O5 and having a higher refractive index than the low-refractive-index dielectric films are alternately stacked. In other words, the second multilayer reflector 31 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0026] 2 is a top view of the surface-emitting laser 10. As described above, the surface-emitting laser 10 has a semiconductor structure layer 15 including an n-type semiconductor layer 17 formed on a substrate 11 having a rectangular top surface shape, an active layer 19 having a circular top surface shape, and a p-type semiconductor layer 21 (see FIG. 1). An insulating layer 25 and a transparent electrode 27 are formed on the p-type semiconductor layer 21. A p-electrode 29 and a second multilayer film reflector 31 are formed on the transparent electrode 27.

[0027] In FIG. 2, the axis passing through the center of the surface-emitting laser 10 and extending in the m-axis direction of the substrate 11, that is, the axis along which the slit groove GV1 formed in the upper surface of the substrate 11 extends, is the axis AX1.

[0028] The insulating layer 25 has an opening 25H, which is a circular opening that exposes the p-type semiconductor layer 21 of the insulating layer 25. As shown in Fig. 2, the opening 25H is formed in the center of the insulating layer 25 when viewed from above the surface-emitting laser 10, and is covered by the second multilayer film reflector 31 when viewed from above the surface-emitting laser 10. In other words, the opening 25H is formed in a region of the insulating layer 25 that faces the lower surface of the multilayer film reflector 31.

[0029] Opening 25H is circular and has its center on axis AX1. Therefore, p-type semiconductor layer 21 is electrically connected to transparent electrode 27 via electrical contact surface 21S in the circular region of the upper surface of p-type semiconductor layer 21 that is exposed through opening 25H.

[0030] 2, the slit grooves GV1 extend parallel to each other and are formed across the region facing the electrical contact surface 21S across the semiconductor structure layer 15 and the multilayer film reflector 13. In other words, the slit groove GV1 is formed so as to overlap with the electrical contact surface 21S in a top view, i.e., in the normal direction of the upper surface of the substrate 11.

[0031] Fig. 3 is a cross-sectional view of the surface-emitting laser 10 taken along line 3-3 in Fig. 2. As described above, the surface-emitting laser 10 has the substrate 11, which is a GaN substrate, and the first multilayer film reflector 13 is formed on the substrate 11. The lower surface of the substrate 11 may be coated with an AR coating.

[0032] Each of the slit grooves GV1 formed in the upper surface of the substrate 11 forms a gap together with the lower surface of the first multilayer reflector 13. In other words, the first multilayer reflector 13 is formed so as to cover the slit groove GV1, and the semiconductor material forming the first multilayer reflector 13 is not filled in the slit groove GV1. That is, a diffraction grating structure consisting of a plurality of gaps extending in the direction of the axis AX1 (the direction perpendicular to the paper surface in FIG. 3) is formed between the first multilayer reflector 13 and the substrate 11.

[0033] A semiconductor structure layer 15 is formed on the first multilayer film reflector 13. The semiconductor structure layer 15 is a laminated body in which an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 are formed in this order. A protrusion 21P that protrudes upward is formed in the center of the top surface of the p-type semiconductor layer 21.

[0034] Insulating layer 25 is formed to cover the region of the upper surface of p-type semiconductor layer 21 except for protruding portion 21P. As described above, insulating layer 25 is made of a material having a lower refractive index than p-type semiconductor layer 21. Insulating layer 25 has opening 25H that exposes protruding portion 21P. For example, opening 25H and protruding portion 21P have the same shape, and the inner surface of opening 25H and the outer surface of protruding portion 21P are in contact with each other.

[0035] Transparent electrode 27 is formed so as to cover insulating layer 25 and the upper surface of protruding portion 21P exposed from opening 25H of insulating layer 25. That is, transparent electrode 27 is in electrical contact with p-type semiconductor layer 21 in a region of the upper surface of p-type semiconductor layer 21 exposed by opening 25H. In other words, the region of the upper surface of p-type semiconductor layer 21 exposed through opening 25H serves as electrical contact surface 21S that brings p-type semiconductor layer 21 and transparent electrode 27 into electrical contact.

[0036] As described above, p-electrode 29 is a metal electrode and is formed along the outer edge of the upper surface of transparent electrode 27. That is, p-electrode 29 is in electrical contact with transparent electrode 27. Therefore, p-electrode 29 is in electrical contact or connection with p-type semiconductor layer 21 via transparent electrode 27 at electrical contact surface 21S exposed by opening 25H in the upper surface of p-type semiconductor layer 21.

[0037] The second multilayer reflector 31 is formed on the upper surface of the transparent electrode 27 in a region above the opening 25H of the insulating layer 25, in other words, in a region above the electrical contact surface 21S, i.e., in the central portion of the upper surface of the transparent electrode 27. The lower surface of the second multilayer reflector 31 faces the upper surface of the first multilayer reflector 13, with the transparent electrode 27 and the semiconductor structure layer 15 sandwiched between them. The arrangement of the first multilayer reflector 13 and the second multilayer reflector 31 forms a resonator OC that resonates light emitted from the active layer 19.

[0038] In the surface-emitting laser 10, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 31. Therefore, part of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 31 passes through the first multilayer reflector 13 and the substrate 11 and is extracted to the outside.

[0039] Here, we will explain the operation of the surface-emitting laser 10. When a voltage is applied between the n-electrode 23 and the p-electrode 29 in the surface-emitting laser 10, a current flows in the semiconductor structure layer 15 as shown by the thick dashed line in the figure, and light is emitted from the active layer 19. The light emitted from the active layer 19 is repeatedly reflected between the first multilayer film reflector 13 and the slit groove GV1 and the second multilayer film reflector 31, and reaches a resonance state (i.e., laser oscillation occurs).

[0040] In the surface-emitting laser 10, current is injected into the p-type semiconductor layer 21 only from the portion exposed by the opening 25H, i.e., the electrical contact surface 21S. In addition, since the p-type semiconductor layer 21 is very thin, current does not diffuse in the in-plane direction within the p-type semiconductor layer 21, i.e., in the direction along the in-plane of the semiconductor structure layer 15.

[0041] Therefore, in the surface-emitting laser 10, current is supplied only to the region of the active layer 19 directly below the electrical contact surface 21S defined by the opening 25H, and light is emitted only from that region. That is, in the surface-emitting laser 10, the opening 25H forms a current confinement structure that limits the range of current supply in the active layer 19.

[0042] In other words, in the surface-emitting laser 10, a current confinement structure is formed between the first multilayer reflector 13 and the second multilayer reflector 31, which confines the current so that it flows only in a central region CA, which is a columnar region of the active layer 19 with the electrical contact surface 21S as its bottom surface, i.e., concentrates the current in one region of the active layer. The central region CA, which includes the region in the active layer 19 through which the current flows, is defined by the electrical contact surface 21S.

[0043] As described above, in this embodiment, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 31. Therefore, a portion of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 31 is transmitted through the slit groove GV1 and also resonates between the second multilayer reflector 31 and the slit groove GV1. A portion of this resonated light is transmitted through the first multilayer reflector 13, the slit groove GV1, and the substrate 11 and extracted to the outside. In this way, the surface-emitting laser 10 emits light from the lower surface of the substrate 11 in a direction perpendicular to the in-plane direction of the lower surface of the substrate 11 and each layer of the semiconductor structure layer 15. In other words, the lower surface of the substrate 11 serves as the light-emitting surface of the surface-emitting laser 10.

[0044] The electrical contact surface 21S of the p-type semiconductor layer 21 of the semiconductor structure layer 15 and the opening 25H of the insulating layer 25 define an emission center, which is the center of the light-emitting region in the active layer 19, and define a central axis (emission central axis) AX2 of the resonator OC. The central axis AX2 of the resonator OC passes through the center of the electrical contact surface 21S of the p-type semiconductor layer 21 and extends along a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0045] The light emitting region of the active layer 19 is, for example, a region having a predetermined width in the active layer 19 from which light of a predetermined intensity or more is emitted, the center of which is the light emitting center. Also, for example, the light emitting region of the active layer 19 is a region in the active layer 19 into which a current of a predetermined density or more is injected, the center of which is the light emitting center. A straight line passing through the light emitting center and perpendicular to the in-plane direction of the upper surface of the substrate 11 or each layer of the semiconductor structure layer 15 is the central axis AX2.

[0046] The light emission central axis AX2 is a straight line extending along the cavity length direction of the cavity OC formed by the first multilayer reflector 13 and the second multilayer reflector 31. The central axis AX2 corresponds to the optical axis of the laser light emitted from the surface-emitting laser 10.

[0047] Here, we will explain exemplary configurations of the first multilayer reflector 13, the semiconductor structure layer 15, and the second multilayer reflector 31 in the surface-emitting laser 10. In this example, the first multilayer reflector 13 is made of a 1 μm GaN underlayer formed on the upper surface of the substrate 11, and 42 pairs of n-GaN and AlInN layers.

[0048] The n-type semiconductor layer 17 is an n-GaN layer with a thickness of 1580 nm. The active layer 19 has a multi-quantum well structure in which four pairs of 4 nm GaInN layers and 5 nm GaN layers are stacked. An Mg-doped AlGaN electron barrier layer is formed on the active layer 19, and a p-type semiconductor layer 21 made of a 50 nm p-GaN layer is formed on top of that. The second multilayer reflector 31 is made by stacking 10.5 pairs of Nb2O5 and SiO2. The resonant wavelength in this case was 440 nm.

[0049] Insulating layer 25 is a 20 nm layer made of SiO2. In other words, protruding portion 21P on the upper surface of p-type semiconductor layer 21 protrudes by 20 nm from the surrounding area. That is, p-type semiconductor layer 21 has a layer thickness of 50 nm at protruding portion 21P and a layer thickness of 30 nm in other regions. In addition, the upper surface of insulating layer 25 is configured to be located at the same height as the upper surface of protruding portion 21P of p-type semiconductor layer 21. Note that these configurations are merely examples.

[0050] The following describes the optical characteristics inside the surface-emitting laser 10. As described above, in the surface-emitting laser 10, the insulating layer 25 has a lower refractive index than the p-type semiconductor layer 21. Between the first multilayer reflector 13 and the second multilayer reflector 31, the layer thicknesses of the active layer 19 and the n-type semiconductor layer 17 are the same anywhere in the plane if they are in the same layer.

[0051] Therefore, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 31, which corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 31 of the surface-emitting laser 10 differs between the cylindrical central region CA with the electrical contact surface 21S as its bottom surface and the cylindrical peripheral region PA around it, due to the difference in refractive index between the p-type semiconductor layer 21 and the insulating layer 25.

[0052] Specifically, between the first multilayer reflector 13 and the second multilayer reflector 31, the equivalent refractive index of the peripheral region PA is lower than the equivalent refractive index of the central region CA, i.e., the equivalent resonant wavelength in the central region CA is smaller than the equivalent resonant wavelength in the peripheral region PA. Note that light is emitted from the active layer 19 in the region directly below the opening 25H and the electrical contact surface 21S. That is, the light-emitting region from which light is emitted in the active layer 19 is the portion of the active layer 19 that overlaps with the central region CA, in other words, the region that overlaps with the electrical contact surface 21S in a top view.

[0053] As described above, the surface-emitting laser 10 includes a central region CA including the light-emitting region of the active layer 19, and a peripheral region PA surrounding the central region CA and having a lower refractive index than the central region CA. This reduces optical loss caused by standing waves in the central region CA diverging (radiating) to the peripheral region PA. That is, much light remains in the central region CA, and laser light is extracted in this state. Therefore, much light is concentrated in the central region CA around the light-emitting central axis AX2 of the resonator OC, enabling the generation and emission of high-power, high-density laser light.

[0054] As described above, in the surface-emitting laser 10 of this embodiment, the top surface of the substrate 11 is a surface that is offset from the C-plane by 0.5° in the M-plane direction. When a semiconductor layer is grown on a growth surface offset from the M-plane of the substrate 11, as in the surface-emitting laser 10 of this embodiment, the optical gain of light polarized in the m-axis direction is greater than that of light polarized in other directions, and therefore laser light polarized in the m-axis direction is more likely to oscillate. Therefore, the light emitted from the central region CA of the surface-emitting laser 10 is dominated by light polarized in the m-axis direction.

[0055] Furthermore, in the surface-emitting laser 10, a diffraction grating consisting of a hollow space formed by a plurality of grooves GV1, each extending in a direction along the m-axis and arranged in a lattice pattern, is formed in a region including the central part of the upper surface of the substrate 11.

[0056] The diffraction grating formed by this slit groove 41 provides high reflectivity to light whose polarization direction is the extension direction of each of the slit grooves GV1 that form the diffraction grating, i.e., the m-axis direction, in the central region CA of the reflection structure formed by the first multilayer film reflector 13.

[0057] That is, the formation of the slit groove GV1 increases the reflectance of light polarized in the m-axis direction compared to light polarized in other directions, and the light polarized in the m-axis direction is more likely to oscillate preferentially. That is, the slit groove GV1 reduces the loss of light polarized along the m-axis direction of the surface-emitting laser 10.

[0058] Therefore, in the surface-emitting laser 10, the upper surface of the substrate 11 is offset from the C-plane to the M-plane, and the semiconductor structure layer 15 is grown thereon, and a diffraction grating structure consisting of slit grooves GV1 extending along the m-axis is formed on the upper surface of the substrate 11. With this configuration, the surface-emitting laser 10 can stably obtain emitted light in which light having one polarization direction, specifically the polarization direction along the m-axis direction, is dominant.

[0059] In order to provide the diffraction grating structure formed by the slit grooves GV1 with high reflectivity for light polarized in the m-axis direction, it is preferable that the slit grooves GV1 have a width approximately equal to the wavelength of light emitted from the active layer 19. It is also preferable that the slit grooves GV1 are arranged at intervals approximately equal to the wavelength of light emitted from the active layer 19.

[0060] The slit grooves GV1 may extend further outward than the area facing the opening 25H, that is, the central area CA. The slit grooves GV1 may also be arranged up to the outside of the central area CA.

[0061] When the surface-emitting laser 10 of Example 1 was actually driven to check the polarization direction of the emitted light, it was confirmed that when driven with a drive current of 3 mA to 13 mA, emitted light in which the polarization direction is dominated by light in the m-axis direction can be stably obtained under conditions where the device temperature is 20°C to 80°C.

[0062] As described above, the surface-emitting laser of the present invention has high light-emitting efficiency and can stably obtain emitted light with a specific polarization direction, which is very effective when the emitted light from the surface-emitting laser is used in a device having an optical system using a liquid crystal or a polarizer. [Manufacturing method] An example of a method for manufacturing the surface-emitting laser 10 will be described below. First, an n-GaN substrate having an upper surface with a crystal plane tilted from the C-plane to the M-plane as described above is prepared as the substrate 11, and a slit groove GV1 is formed on the upper surface by exposure patterning and dry etching. Next, an n-GaN (1 μm thick) layer is formed as an underlayer on the upper surface of the substrate 11 by metalorganic vapor phase epitaxy (MOVPE). Thereafter, 42 pairs of n-GaN / AlInN layers are formed on the underlayer to form the first multilayer reflector 13.

[0063] Next, Si-doped n-GaN (layer thickness 1580 nm) is formed on the first multilayer reflector 13 to form the n-type semiconductor layer 17, and four pairs of layers made of GaInN (layer thickness 4 nm) and GaN (layer thickness 5 nm) are stacked on top of that to form the active layer 19.

[0064] Next, an electron barrier layer made of Mg-doped AlGaN is formed on the active layer 19 (not shown), and a p-GaN layer (layer thickness 50 nm) is formed on the electron barrier layer to form the p-type semiconductor layer 21.

[0065] Next, the p-type semiconductor layer 21, the active layer 19, and the surrounding areas of the n-type semiconductor layer 17 are etched to form a mesa shape that exposes the top surface 17S of the n-type semiconductor layer 17 in the surrounding areas. In other words, this step completes the semiconductor structure layer 15 having a cylindrical portion made up of the n-type semiconductor layer 17, the active layer 19, and the p-type semiconductor layer 21 shown in FIG. 1.

[0066] Next, the periphery of the central portion of the upper surface of the p-type semiconductor layer 21 is etched to form a protruding portion 21P. Thereafter, a film of SiO2 is formed on the semiconductor structure layer 15, and a portion of it is removed to form an opening 25H, thereby forming the insulating layer 25. In other words, SiO2 is buried in the etched-away portion of the upper surface of the p-type semiconductor layer 21.

[0067] Next, a 20 nm ITO film is formed on the insulating layer 25 to form the transparent electrode 27, and an Au film is formed on the upper surface of the transparent electrode 27 and the upper surface 17S of the n-type semiconductor layer 17 to form the p-electrode 29 and the n-electrode 23, respectively.

[0068] Next, a 40 nm Nb2O5 film is formed on the transparent electrode 27 as a spacer layer (not shown), and 10.5 pairs of layers, each consisting of Nb2O5 / SiO2, are formed on the spacer layer to form the second multilayer film reflector 31.

[0069] When the back surface of the substrate 11 is provided with an AR coating, the back surface of the substrate 11 is polished last, and an AR coating made of Nb2O5 / SiO2 is formed on the polished surface, thereby completing the surface-emitting laser 10. [Example]

[0070] Second Embodiment A surface-emitting laser 40 according to a second embodiment of the present invention will now be described. The surface-emitting laser 40 differs from the surface-emitting laser 10 in that, instead of the slit groove GV1, a slit groove GV2 is formed on the lower surface of the substrate 11, i.e., on the light-emitting surface of the surface-emitting laser 40.

[0071] FIG. 4 is a cross-sectional view showing a cut surface when the surface-emitting laser 40 is cut along the same cutting line as shown in FIG. 2, that is, a cut surface corresponding to FIG.

[0072] 4, in the surface-emitting laser 40, a plurality of slit grooves GV2 are formed in a region within a central region CA on the lower surface of the substrate 11. In other words, a plurality of slit grooves GV2 are formed on the lower surface of the substrate 11 in a region facing the opening 25H and the electrical contact surface 21S on the lower surface of the substrate 11, i.e., in a region from which emitted light is emitted.

[0073] In other words, in the surface-emitting laser 40, a plurality of slit grooves GV2 are formed on the lower surface of the substrate 11, and the formation area thereof overlaps with the area in which the slit grooves GV1 of the surface-emitting laser 10 of Example 1 are formed when viewed from above.

[0074] The slit grooves GV2 of the surface-emitting laser 40 are grooves, i.e., slit-shaped recesses, that extend parallel to the axis AX1 on the lower surface of the substrate 11 and are arranged in a direction perpendicular to the axis AX1. That is, the slit grooves GV2 are grooves that extend parallel to each other along the m-axis direction on the lower surface of the substrate 11.

[0075] The slit grooves GV2 provide the same effect as the slit grooves GV1 in the above-described Example 1. That is, the diffraction grating formed by the slit grooves GV2 provides high reflectance to light whose polarization direction is the extension direction of each of the slit grooves GV2 forming the diffraction grating, in the central area CA of the reflection structure formed by the first multilayer film reflecting mirror 13 and the substrate 11.

[0076] In other words, the diffraction grating formed by the slit grooves GV2 provides the reflective structure formed by the multilayer film reflector 13 and the substrate n11 with high reflectance for light whose polarization direction is in the m-axis direction.

[0077] Therefore, by forming the slit groove GV2, the reflectance of light whose polarization direction is the m-axis direction is increased compared to light having other polarization directions, and in the surface-emitting laser 40, light whose polarization direction is the m-axis direction tends to oscillate preferentially.

[0078] Therefore, according to the surface-emitting laser 40, by forming a diffraction grating structure consisting of slit grooves GV2 on the lower surface of the substrate 11, further polarization control of the emitted light can be performed, and it is possible to stably obtain emitted light in which the light polarization direction is predominant in the m-axis direction, similar to the surface-emitting laser 10 of Example 1.

[0079] The slit groove GV2 can be formed, for example, by performing an etching process such as dry etching on the lower surface of the substrate 11 after polishing the lower surface of the substrate 11 in the final step of the manufacturing method of the surface-emitting laser 10 of Example 1 described above.

[0080] The slit grooves GV2 may extend further outward than the area facing the opening 25H, that is, the central area CA. The slit grooves GV2 may also be arranged up to the outside of the central area CA. [Example]

[0081] Hereinafter, a surface-emitting laser 50 according to a third embodiment of the present invention will be described. The surface-emitting laser 50 differs from the surface-emitting laser 40 in that a convex portion is formed on the lower surface of the substrate 11, i.e., the light-emitting surface of the surface-emitting laser 50, and the slit groove GV2 described in the second embodiment is formed on the surface of the convex portion.

[0082] Fig. 5 is a cross-sectional view showing a cut surface when the surface-emitting laser 50 is cut along the same cutting line as shown in Fig. 2, i.e., a cut surface corresponding to Fig. 3. As shown in Fig. 5, in the surface-emitting laser 50, a convex portion 51 having a downwardly convex lens shape is formed in a region including a region facing the opening 25H and the electrical contact surface 21S on the lower surface of the substrate 11, i.e., in a central region CA.

[0083] The convex portion 51 has a convex lens shape with the central axis AX2 as its vertex as described in Example 1. A plurality of slit grooves GV2 are formed on the surface of the convex portion 51, and each extends in the m-axis direction, similar to the surface-emitting laser 40 of Example 2.

[0084] According to the surface-emitting laser 50 of Example 3, the provision of the convex portion 51 can increase the amount of light reflected toward the central area CA by the reflective structure formed by the first multilayer film reflector 13 and the substrate 11. As a result, according to the surface-emitting laser 50, it is possible to further increase the light oscillation efficiency in the central area CA, which produces the main part of the emitted light.

[0085] For example, the convex portion 51 can be formed by depositing resist in the same shape as the convex portion 51 on the back surface of the substrate 11, and then dry etching the entire back surface of the substrate 11 to transfer the shape of the resist to the back surface of the substrate 11.

[0086] In the above description, the convex portion 51 has a convex lens shape, but the shape of the convex portion 51 may be any other shape as long as the light reflected by the reflective structure formed by the first multilayer film reflecting mirror 13 and the substrate 11 is collected in the central area CA. For example, the convex portion 51 may have a parabolic shape that is convex downward.

[0087] The slit grooves GV2 may extend further outward than the region facing the opening 25H, i.e., the central region CA. The slit grooves GV2 may be arranged up to the outside of the central region CA. The slit grooves GV2 may extend up to the outside of the protrusions 51. The slit grooves GV2 may be arranged up to the outside of the protrusions 51. [Example]

[0088] A surface-emitting laser 60 according to a fourth embodiment of the present invention will now be described. The surface-emitting laser 60 differs from the surface-emitting laser 10 in that a slit groove GV3 is formed in the upper surface of the first multilayer reflector 13 instead of the slit groove GV1. That is, in the surface-emitting laser 60, a hollow slit groove GV3 is formed along the interface between the first multilayer reflector 13 and the semiconductor structure layer 15.

[0089] In other words, in the surface-emitting laser 60, a hollow diffraction grating structure consisting of slit grooves GV3 is formed along the interface between the first multilayer film reflector 13 and the semiconductor structure layer 15.

[0090] Fig. 6 is a cross-sectional view showing a cut surface when the surface-emitting laser 60 is cut along the same cutting line as shown in Fig. 2, i.e., a cut surface corresponding to Fig. 3. As shown in Fig. 6, in the surface-emitting laser 60, a plurality of slit grooves GV3 are formed in a region facing the opening 25H and the electrical contact surface 21S in the lower surface of the n-type semiconductor layer 17, i.e., in a central region CA. In other words, in the surface-emitting laser 60, a plurality of slit grooves GV3 are formed in the lower surface of the n-type semiconductor layer 17, and the formation region overlaps with the region where the slit groove GV1 of the surface-emitting laser 10 of Example 1 is formed in top view.

[0091] The slit grooves GV3 of the surface-emitting laser 60 are grooves, i.e., slit-shaped recesses, that extend parallel to the axis AX1 (see FIG. 2) on the upper surface of the multilayer film reflector 13 and are arranged in a direction perpendicular to the axis AX1. That is, the slit grooves GV3 are grooves that extend parallel to each other along the m-axis direction at the interface between the multilayer film reflector 13 and the semiconductor structure layer 15, and form a diffraction grating structure made up of slits that extend along the m-axis direction.

[0092] The slit groove GV3 provides the same effect as the slit groove GV1 in the above-described first embodiment. That is, the diffraction grating formed by the slit groove GV3 provides high reflectance to light whose polarization direction is the extension direction of each of the slit grooves GV3, i.e., the m-axis direction, in the central region CA of the reflection structure formed by the first multilayer film reflecting mirror 13 and the substrate 11. Therefore, by forming the slit groove GV3, the reflectance of light whose polarization direction is the m-axis direction is higher than that of light whose polarization direction is other than the m-axis direction, and light whose polarization direction is the m-axis direction is more likely to oscillate preferentially.

[0093] Therefore, according to the surface-emitting laser 60, by forming a diffraction grating structure consisting of slit grooves GV3 at the interface between the first multilayer film reflector 13 and the semiconductor structure layer 15, it is possible to control the polarization of the emitted light and stably obtain emitted light in which light having one polarization direction is dominant, as in the surface-emitting laser 10 of Example 1.

[0094] In the surface-emitting laser 60, the diffraction grating structure consisting of the slit grooves GV3 is formed in the region between the first multilayer reflector 13 and the second multilayer reflector 31. That is, in the surface-emitting laser 60, the slit grooves GV3 forming the diffraction grating structure are provided closer to the active layer 19 than in the surface-emitting lasers 10, 40, and 50 of the first to third embodiments.

[0095] Therefore, in the surface-emitting laser 60, the intensity of the emitted light from the active layer 19 in the region where the slit grooves GV3 are formed is greater than in the surface-emitting lasers 10, 40, and 50 of the other embodiments. Therefore, the diffraction grating structure formed by the slit grooves GV3 can reflect more light, and the polarization control effect described above is greater than in the surface-emitting lasers of the other embodiments. Therefore, in the surface-emitting laser 60, it is possible to stably obtain emitted light in which light having one polarization direction is more dominant than in the surface-emitting lasers of the other embodiments.

[0096] The slit groove GV3 can be formed by forming a GaN layer as the top layer of the first multilayer reflector 13, etching the top GaN layer to form the groove GV3, growing and flattening a GaN layer so as to cover the portion from which the GaN has been removed, i.e., so as not to fill the slit groove GV3, and then growing an n-GaN layer on the flattened surface to form the n-type semiconductor layer 17.

[0097] The slit grooves GV3 may extend further outward than the area facing the opening 25H, that is, the central area CA. The slit grooves GV3 may also be arranged up to the outside of the central area CA.

[0098] The diffraction grating structure formed by the slit grooves GV3 does not have to be a hollow structure. That is, a buried type (buried structure) diffraction grating structure in which the slit grooves GV3 are filled with a semiconductor material may be provided.

[0099] When providing this embedded diffraction grating structure, in the manufacture of the surface-emitting laser 60, the top layer of the first multilayer reflector 13 is an AlInN layer, a slit groove GV3 is formed in the top AlInN layer by etching, a GaN layer is grown and planarized so as to fill the slit groove GV3, and an n-GaN layer is grown on the planarized surface to form the n-type semiconductor layer 17.

[0100] Depending on the growth conditions when growing a GaN layer on the slit grooves GV3, the slit grooves GV3 can be filled with GaN or left hollow, so the diffraction grating structure formed by the slit grooves GV3 can be either a buried structure or a hollow structure.

[0101] Of course, even if the diffraction grating structure formed by the slit grooves GV3 is an embedded structure, the same polarization control effect as that of a hollow diffraction grating structure can be achieved. [Example]

[0102] A surface-emitting laser 70 according to a fifth embodiment of the present invention will now be described. The surface-emitting laser 70 differs from the surface-emitting laser 10 according to the first embodiment in that, in order to form the current confinement structure described above, a tunnel junction structure is formed in the semiconductor structure layer 15 instead of the insulating layer 25. Specifically, the surface-emitting laser 70 differs from the surface-emitting laser 10 in the structure above the p-type semiconductor layer 21.

[0103] Furthermore, the surface-emitting laser 70 differs from the surface-emitting laser 10 in that, instead of the slit groove GV1, a groove GV4 formed along the interface between the semiconductor structure layer 15 and the second multilayer film reflector 75 is used to form the diffraction grating structure.

[0104] Fig. 7 is a cross-sectional view showing a cut surface of the surface-emitting laser 70 cut along the same cutting line as shown in Fig. 2, i.e., a cut surface corresponding to Fig. 3. As shown in Fig. 7, in the surface-emitting laser 70, a tunnel junction layer 71 is formed on the protruding portion 21P of the p-type semiconductor layer 21. That is, in the surface-emitting laser 70, the tunnel junction layer 71 is formed in a central region CA in the semiconductor structure layer 15.

[0105] The tunnel junction layer 71 includes a highly doped p-type semiconductor layer 71A which is a p-type semiconductor layer formed on the p-type semiconductor layer 21 and has a higher impurity concentration than the p-type semiconductor layer 21, and a highly doped n-type semiconductor layer 71B which is an n-type semiconductor layer formed on the highly doped p-type semiconductor layer 71A and has a higher impurity concentration than the n-type semiconductor layer 17.

[0106] The n-type semiconductor layer 73 is formed on the p-type semiconductor layer 21 and the tunnel junction layer 71. The n-type semiconductor layer 73 is formed so as to bury the tunnel junction layer 71 on the upper surface of the p-type semiconductor layer 21. In other words, the n-type semiconductor layer 73 is formed so as to cover the side surfaces of the protruding portion 21P and the side surfaces and upper surface of the tunnel junction layer 71.

[0107] The second multilayer film reflector 75 is formed on the upper surface of the n-type semiconductor layer 73, and is an n-type semiconductor layer having a doping concentration similar to that of the n-type semiconductor layer 17. That is, the n-type semiconductor layer 73 has a doping concentration lower than that of the highly doped n-type semiconductor layer 71B.

[0108] Such a stacked structure of the p-type semiconductor layer 21, the tunnel junction layer 71, and the n-type semiconductor layer 73 generates a tunnel effect in the tunnel junction layer 71. As a result, in the surface-emitting laser 70, a current flows only through the tunnel junction layer 71 between the p-type semiconductor layer 21 and the n-type semiconductor layer 73, forming a current confinement structure in which the current is confined to the central region CA.

[0109] The second multilayer reflector 75 is a semiconductor multilayer reflector made of semiconductor layers formed on the n-type semiconductor layer 73. The second multilayer reflector 75 is formed by alternately stacking low-refractive-index semiconductor films having an AlInN composition and high-refractive-index semiconductor films having a GaN composition and a higher refractive index than the low-refractive-index semiconductor films, and has the properties of an n-type semiconductor. In other words, the second multilayer reflector 75 is a distributed Bragg reflector (DBR) made of semiconductor material.

[0110] The second n-electrode 77 is a metal electrode formed along the periphery of the upper surface of the second multilayer reflector 75. In the surface-emitting laser 70, the second multilayer reflector 75 is conductive, so that a current flows from the second n-electrode 77 through the second multilayer reflector 75, the n-type semiconductor layer 73, the tunnel junction layer 71, the p-type semiconductor layer 21, the active layer 19, and the n-type semiconductor layer 17 to the n-electrode 23.

[0111] In the surface-emitting laser 70, the slit groove GV4 is formed in a region immediately above the tunnel junction layer 71 on the upper surface of the n-type semiconductor layer 73, and is a groove extending in the m-axis direction. The second multilayer film reflecting mirror 75 on the slit groove GV4 is laminated so as to cover the slit groove GV4. That is, the inside of the slit groove GV4 is hollow, and the slit groove GV4 forms a diffraction grating structure consisting of a hollow space.

[0112] The slit groove GV4 provides the same effect as the slit groove GV1 in the first embodiment described above. That is, the diffraction grating formed by the slit groove GV4 provides high reflectance to light whose polarization direction is the extension direction of each of the slit grooves GV4 forming the diffraction grating, i.e., the m-axis direction, in the central region CA of the reflection structure formed by the second multilayer film reflecting mirror 75. Therefore, by forming the slit groove GV4, the reflectance of light whose polarization direction is the m-axis direction is higher than that of light whose polarization direction is other than the m-axis direction, and light whose polarization direction is the m-axis direction is more likely to oscillate preferentially.

[0113] Therefore, according to the surface-emitting laser 70, by forming a diffraction grating structure consisting of slit grooves GV4 on the upper surface of the n-type semiconductor layer 73, polarization control of the emitted light can be performed, and it is possible to stably obtain emitted light in which light having one polarization direction is dominant, as with the surface-emitting laser 10 of Example 1.

[0114] In the surface-emitting laser 60, the slit groove GV4 is formed along the interface between the semiconductor structure layer 15 and the second multilayer film reflector 75. That is, in the surface-emitting laser 70, the slit groove GV4 forming the diffraction grating structure is provided closer to the active layer 19 than in the surface-emitting lasers 10, 40, and 50 of the first to third embodiments.

[0115] Therefore, in the surface-emitting laser 70, the intensity of the emitted light from the active layer 19 in the region where the slit grooves GV4 are formed is greater than in the surface-emitting lasers 10, 40, and 50 of Examples 1 to 3. Therefore, the diffraction grating structure formed by the slit grooves GV4 can reflect more light, and the polarization control effect described above is greater than in the surface-emitting lasers of the other Examples. Therefore, in the surface-emitting laser 70, it is possible to stably obtain emitted light in which light having one polarization direction is more dominant than in the surface-emitting lasers of Examples 1 to 3.

[0116] The slit groove GV4 can be formed by forming the slit groove GV4 on the upper surface of the n-type semiconductor layer 73 by etching, then forming and flattening an n-GaN layer, which is also a part of the n-type semiconductor layer 73, so as to cover the slit groove GV4, and then forming the multilayer film reflector 75.

[0117] The slit grooves GV4 may extend not only in the central area CA but also outward. The slit grooves GV4 may also be arranged up to the outside of the central area CA.

[0118] 8, the slit groove GV4 may be formed on the lower surface of the multilayer reflector 75. In this case, the first n-AlInN layer of the multilayer reflector 75 is etched to form a groove for forming the slit groove, an n-GaN layer is formed on top of it to cover the groove and flatten it, and then the thin film layer of the multilayer reflector 75 is formed, thereby forming the slit groove GV4.

[0119] In the above-described first to fourth embodiments, the insulating layer 25 is provided on the upper surface of the p-type semiconductor layer 21 to form the electrical contact surface 21S and the insulating region around it, thereby causing current confinement and forming a region with a low refractive index. However, instead of providing the insulating layer 25, other methods may be used to cause current confinement and form a region with a low refractive index.

[0120] For example, the insulating region, the low refractive index region, and the electrical contact surface 21S may be formed by etching the upper surface of the p-type semiconductor layer 21 on which the insulating layer 25 is provided in the above embodiment. Alternatively, the insulating region, the low refractive index region, and the electrical contact surface 21S may be formed by implanting ions into the upper surface of the p-type semiconductor layer 21 on which the insulating layer 25 is provided, thereby producing a current confinement effect similar to that achieved by forming the insulating layer 25 in the above embodiment. When implanting ions, for example, B ions, Al ions, or oxygen ions are implanted into the p-type semiconductor layer 21.

[0121] In the above-described embodiment, the upper surface of substrate 11 is offset from the C-plane toward the M-plane by 0.5°, i.e., the off-angle from the C-plane toward the M-plane is 0.5°. However, the off-angle is not limited to this angle. For example, an off-angle of approximately 0.3° to 0.8° is sufficient to obtain the polarization control effect described above. Furthermore, if the off-angle of the upper surface of substrate 11 is 0.8° or less, the semiconductor multilayer film constituting first multilayer film reflector 13 can be formed to have a stable and sufficient reflectance.

[0122] Furthermore, in the above-described embodiment, a coreless substrate is used as the substrate 11, but a striped-core substrate may also be used. In this case, when viewed from above, the direction of the stripes of the core of the substrate 11 and the tilt direction of the crystal plane on the upper surface of the substrate 11 are parallel or perpendicular to each other. That is, in the above-described embodiment, the m-axis direction of the substrate 11 and the direction of the stripes of the core of the substrate 11 are parallel or perpendicular to each other.

[0123] Furthermore, in the above embodiment, the upper surface of the substrate 11 is described as being off-axis from the C-plane toward the M-plane, but it is also acceptable for the upper surface of the substrate 11 to be off-axis from the C-plane toward the A-plane and not be off-axis at all in the M-plane direction.

[0124] In this case, for the same reasons as those described above regarding the range of the off-angle of the C-plane, in order to obtain the polarization control effect, the off-angle from the C-plane toward the A-plane is preferably about 0.3° to 0.8°, and the off-angle from the C-plane toward the M-plane is preferably 0±0.1°. Note that when the upper surface of the substrate 11 is off-angled from the C-plane toward the A-plane, the description of the shape of the electrical contact surface 21S in the above embodiment should be interpreted as AX1 corresponding to the a-axis.

[0125] When the top surface of the substrate 11 is off-axis from the C-plane to the A-plane, it is possible to extract a large amount of light polarized along the a-axis direction and suppress the emission of light polarized in directions other than the a-axis. Therefore, the surface-emitting laser 10 can suppress variations in the polarization direction of the light extracted from the light emitting surface in the in-plane direction of the light emitting surface.

[0126] Furthermore, in the above embodiment, the case where the top surface of substrate 11 is offset from the C-plane toward the M-plane or the A-plane has been described, but the top surface of substrate 11 does not have to be offset from the C-plane. Even in this case, the diffraction grating structure formed by the above-described slit grooves GV1, GV2, GV3, and GV4 preferentially oscillates light having a polarization direction parallel to the slit grooves, making it possible to obtain output light in which light having a polarization direction parallel to the slit grooves is dominant.

[0127] In the third embodiment, a case has been described in which the protrusions 51 are formed and the slit grooves GV2 are formed on the lower surface of the protrusions 51. However, the protrusions 51 may be formed on the lower surface of the substrate of a surface-emitting laser of any other embodiment other than the third embodiment. Even when the protrusions 51 are formed on the surface-emitting laser of any other embodiment, the effect of the protrusions 51 of increasing the amount of light reflected in the central region CA is obtained. In other words, even when the protrusions 51 are formed on the surface-emitting laser of any other embodiment, it is possible to obtain the effect of further increasing the light oscillation efficiency in the central region CA, which produces the main part of the emitted light.

[0128] The various numerical values, dimensions, materials, etc. in the above-described embodiments are merely examples, and can be appropriately selected depending on the application and the surface-emitting laser to be manufactured. [Explanation of symbols]

[0129] 10, 40, 50, 60, 70 Surface-emitting laser 11 Circuit Board 13 First multilayer mirror 15 Semiconductor structural layer 17 n-type semiconductor layer 19 Active layer 21 p-type semiconductor layer 23 n electrode 25 insulating layer 27 Transparent electrode 29p electrode 31 Second multilayer mirror 71 Tunnel junction layer 73 n-type semiconductor layer 75 Second multilayer mirror 77 Second n-electrode

Claims

1. a gallium nitride semiconductor substrate; a first multilayer reflector made of nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer film reflector; a current confinement structure formed between the first multilayer reflector and the second multilayer reflector, for concentrating current in one region of the active layer; a diffraction grating having a plurality of slit structures parallel to each other is formed in a region overlapping with the first region when viewed from a normal direction of the top surface of the gallium nitride based semiconductor substrate, 2. A vertical cavity light emitting device, wherein each of the plurality of slit structures is a recess formed on the rear surface of the substrate.

2. The vertical cavity light emitting device described in claim 1, characterized in that the upper surface of the gallium nitride semiconductor substrate is a surface offset from the c-plane to either the m-plane or the a-plane crystal plane, and each of the multiple slit structures extends in the m-axis direction when the upper surface is offset to the m-plane, and extends in the a-axis direction when the upper surface is offset to the a-plane.

3. 3. The vertical cavity light emitting device according to claim 2, wherein the top surface of the gallium nitride based semiconductor substrate is a surface offset from the c-plane by an angle of 0.8° or less to the m-plane when the top surface is offset to the m-plane, and is a surface offset from the c-plane by an angle of 0.8° or less to the a-plane when the top surface is offset to the a-plane.

4. 4. The vertical cavity light emitting device according to claim 2, wherein the gallium nitride based semiconductor substrate is a stripe-core substrate, and the direction in which the core of the gallium nitride based semiconductor substrate extends is along the m-axis when the top surface is offset to the m-plane, and along the a-axis when the top surface is offset to the a-plane.

5. 5. The vertical cavity light emitting device according to claim 1, wherein a region of the lower surface of the gallium nitride based semiconductor substrate that overlaps with the first region when viewed from the normal direction of the upper surface of the gallium nitride based semiconductor substrate has a convex lens shape that is convex downward.

6. a gallium nitride semiconductor substrate; a first multilayer reflector made of nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer film reflector; a current confinement structure formed between the first multilayer reflector and the second multilayer reflector, for concentrating current in one region of the active layer; a diffraction grating having a plurality of slit structures parallel to each other is formed in a region overlapping with the first region when viewed from a normal direction of the top surface of the gallium nitride based semiconductor substrate, A vertical cavity light emitting device characterized in that the top surface of the gallium nitride semiconductor substrate is a surface offset from the c-plane to either the m-plane or the a-plane crystal plane, and each of the plurality of slit structures extends in the m-axis direction when the top surface is offset to the m-plane, and extends in the a-axis direction when the top surface is offset to the a-plane.

7. 7. The vertical cavity light emitting device according to claim 6, wherein the top surface of the gallium nitride based semiconductor substrate is a plane offset from the c-plane by an angle of 0.8° or less to the m-plane when the top surface is offset to the m-plane, and is a plane offset from the c-plane by an angle of 0.8° or less to the a-plane when the top surface is offset to the a-plane.

8. 8. The vertical cavity light emitting device according to claim 6, wherein the gallium nitride based semiconductor substrate is a stripe-core substrate, and the direction in which the core of the gallium nitride based semiconductor substrate extends is along the m-axis when the top surface is offset to the m-plane, and along the a-axis when the top surface is offset to the a-plane.

9. a gallium nitride semiconductor substrate; a first multilayer reflector made of nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer film reflector; a current confinement structure formed between the first multilayer reflector and the second multilayer reflector, for concentrating current in one region of the active layer; a diffraction grating having a plurality of slit structures parallel to each other is formed in a region overlapping with the first region when viewed from a normal direction of the top surface of the gallium nitride based semiconductor substrate, A vertical cavity light emitting device, characterized in that a region of the lower surface of the gallium nitride based semiconductor substrate that overlaps with the first region when viewed from the normal direction of the upper surface of the gallium nitride based semiconductor substrate has a convex lens shape that is convex downward.

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