Vertical resonator type light-emitting element

Abstract

To provide a vertical resonator type light-emitting element having high light emission efficiency and output and being capable of stably emitting single-mode light.SOLUTION: A vertical resonator type light-emitting element 10 comprises: a gallium nitride semiconductor substrate; a first multilayer film reflector 13 consisting of a nitride semiconductor formed on the gallium nitride semiconductor substrate; a semiconductor structure layer 15 including an active layer 19 consisting of a nitride semiconductor formed on the first multilayer film reflector; a second multilayer film reflector 31 formed on the semiconductor structure layer and configuring a resonator in a clearance with the first multilayer film reflector; and a current constriction structure formed between the first multilayer film reflector and the second multilayer film reflector and concentrating a current into one region of the active layer. The vertical resonator type light-emitting element also comprises a recessed reflection structure 12R disposed on a bottom face of the gallium nitride semiconductor substrate or in a lower region than the bottom face, extending to the outside of the one region in a top view in a direction vertical to a top face of the gallium nitride semiconductor substrate and including a recessed reflection surface opposed to the first multilayer film reflector.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vertical cavity light-emitting device such as a vertical cavity surface emitting laser (VCSEL).

Background Art

[0002] Conventionally, as one of semiconductor lasers, a vertical cavity semiconductor surface emitting laser (hereinafter, also simply referred to as a surface emitting laser) having a semiconductor layer that emits light by applying a voltage and multilayer mirrors facing each other across the semiconductor layer is known. 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

Summary of the Invention

Problems 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 mirrors. For example, in a surface emitting laser, when a voltage is applied to a semiconductor layer via an electrode, light emitted from the semiconductor layer resonates in the optical resonator, and laser light is generated.

[0005] However, as an example of a problem, a vertical cavity semiconductor laser device has a lower emission efficiency than a horizontal resonator type semiconductor laser having a resonator in the in-plane direction of a semiconductor layer including an active layer.

[0006] Furthermore, light emitted from vertical-cavity semiconductor laser elements tends to have multimode lateral modes rather than single modes. Therefore, obtaining stable single-mode lateral light was difficult.

[0007] The present invention has been made in view of the above-mentioned points, and aims to provide a vertical resonator type light-emitting element that has high luminous efficiency and output and is capable of stably emitting single-mode light. [Means for solving the problem]

[0008] The vertical resonator type light-emitting element according to the present invention comprises a gallium nitride semiconductor substrate, a first multilayer reflector made of a 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 reflector, an active layer made of a nitride semiconductor formed on the first semiconductor layer, and a second semiconductor layer made of a nitride semiconductor formed on the active layer and having a second conductivity type opposite to the first conductivity type, and formed on the semiconductor structure layer, The gallium nitride semiconductor substrate is characterized by having a reflective structure which includes a second multilayer reflector that forms a resonator with a first multilayer reflector, and a current-constricting structure formed between the first multilayer reflector and the second multilayer reflector that concentrates current in a region of the active layer, and which is disposed on the lower surface or a region below the lower surface of the gallium nitride semiconductor substrate, and which extends beyond the region of the first in a top view taken from a direction perpendicular to the upper surface of the gallium nitride semiconductor substrate and has a concave reflective surface facing the first multilayer reflector. [Brief explanation of the drawing]

[0009] [Figure 1] Perspective view of the surface-emitting laser of Example 1 [Figure 2] This is a top view of the surface-emitting laser of Example 1. [Figure 3] This is a cross-sectional view of the surface-emitting laser of Example 1. [Figure 4] This is a top view of the surface-emitting laser in the first modification. [Figure 5] This is a cross-sectional view of a surface-emitting laser in modified example 2. [Figure 6] This is a cross-sectional view of the surface-emitting laser in modified example 3. [Figure 7] This is a cross-sectional view of a modified surface-emitting laser. [Figure 8] This is a cross-sectional view of the surface-emitting laser of Example 2. [Modes for carrying out the invention]

[0010] The following describes embodiments of the present invention in detail. 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 type light-emitting elements such as vertical-cavity type light-emitting diodes. [Examples]

[0011] Figure 1 is a perspective view of a vertical cavity surface-emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser, hereinafter also simply referred to as a surface-emitting laser) 10 according to Example 1.

[0012] The substrate 11 is a gallium nitride-based semiconductor substrate, such as an undoped GaN substrate. The substrate 11 is, for example, a substrate with a rectangular top surface shape. The top surface of the substrate 11 is a surface that is 0.5° off-center from the C-plane in the M-plane direction. Furthermore, the top surface of the substrate 11 is hardly off-center from the C-plane in the A-plane direction, and the off-angle from the C-plane to the A-plane direction is 0 ± 0.01°. In the following description, the axis passing through the center of the top surface of the substrate 11 and perpendicular to the top surface will be described as the central axis AX1.

[0013] In the surface-emitting laser 10, the substrate 11 is also placed inside the resonator, so it is preferable that it has high light transmittance. For this reason, it is preferable that the substrate 11 is undoped.

[0014] The convex portion 11P is a convex portion formed in a circular region centered on the central axis AX1 of the lower surface of the substrate 11 and consisting of a downwardly convex curved surface. In this embodiment, the convex portion 11P has a plano-convex lens shape. Also, in this embodiment, the optical axis of the lens shape formed by the convex portion 11P coincides with the central axis AX1.

[0015] The back multilayer film mirror 12 (two-dot chain line in the figure) is a dielectric multilayer film mirror made of a dielectric film formed on the surface of the convex portion 11P. The back multilayer film mirror 12 is a dielectric multilayer film mirror in which a low refractive index dielectric film made of SiO2 and a high refractive index dielectric film made of Nb2O5 and having a higher refractive index than the low refractive index dielectric film are alternately laminated.

[0016] In other words, the back multilayer film mirror 12 is a distributed Bragg reflector (DBR) made of a dielectric material. In this embodiment, the back multilayer film mirror 12 is composed of 4 pairs of Nb2O5 / SiO2 layers formed on the surface of the convex portion 11P. A concave reflecting structure 12R having an upwardly concave concave reflecting surface 12RS is formed by the back multilayer film mirror 12 and the convex portion 11P. In other words, the upper surface of the back multilayer film mirror 12 is the concave reflecting surface 12RS.

[0017] The first multilayer film mirror 13 is a semiconductor multilayer film mirror made of a semiconductor layer grown on the substrate 11. The first multilayer film mirror 13 is formed by alternately laminating a low refractive index semiconductor film having a composition of AlInN and a high refractive index semiconductor film having a composition of GaN and having a higher refractive index than the low refractive index semiconductor film. In other words, the first multilayer film mirror 13 is a distributed Bragg reflector (DBR) made of a semiconductor material.

[0018] The first multilayer 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 film and the low refractive index semiconductor film on the buffer layer. In this embodiment, the first multilayer reflector 13 consists of 35 pairs of GaN / AlInN layers laminated on a 1 μm GaN underlayer formed on the upper surface of the substrate 11. The first multilayer reflector 13 with such a configuration has a reflectivity of about 80% for light emitted from the active layer 19.

[0019] The semiconductor structure layer 15 is a stacked structure consisting of multiple semiconductor layers formed on the first multilayer reflecting mirror 13. The semiconductor structure layer 15 includes an n-type semiconductor layer (first semiconductor layer) 17 formed on the first multilayer reflecting mirror 13, an emissive 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.

[0020] The n-type semiconductor layer 17, as the first conductive semiconductor layer, is a semiconductor layer formed on the first multilayer reflecting mirror 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 part 17A and a cylindrical upper part 17B positioned above it. Specifically, for example, the n-type semiconductor layer 17 has a cylindrical upper part 17B that protrudes from the upper surface 17S of the prismatic lower part 17A. In other words, the n-type semiconductor layer 17 has a mesa-shaped structure including the upper part 17B.

[0021] The active layer 19 is formed on the upper part 17B of the n-type semiconductor layer 17 and is a layer having 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. In this embodiment, the active layer 19 is formed such that its light-emitting center is located on the central axis AX1.

[0022] The p-type semiconductor layer 21, which serves as the second conductive semiconductor layer, 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.

[0023] The n-electrode 23 is a metal electrode provided on the upper surface 17S of the lower part 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 an annular shape so as to surround the upper part 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 an external current to the semiconductor structure layer 15.

[0024] The insulating layer 25 is a layer made of an insulator formed on the p-type semiconductor layer 21. The insulating layer 25 is made of a material having a lower refractive index than the material forming the p-type semiconductor layer 21, such as SiO2. The insulating layer 25 is formed in an annular shape on the p-type semiconductor layer 21 and has an opening (not shown) in its central portion that exposes the p-type semiconductor layer 21.

[0025] The transparent electrode 27 is a translucent 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 through 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 are translucent to light emitted from the active layer 19, can be used.

[0026] 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, which is exposed through 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 electrically contacts the p-type semiconductor layer 21 and supplies an external current to the semiconductor structure layer 15. In this embodiment, the p electrode 29 is formed in an annular shape on the upper surface of the transparent electrode 27 along the outer edge of the upper surface.

[0027] The second multilayer reflector 31 is a cylindrical multilayer reflector formed in the region 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 a low refractive index dielectric film made of SiO2 and a high refractive index dielectric film made of Nb2O5, which has a higher refractive index than the low refractive index dielectric film, are alternately stacked. In other words, the second multilayer reflector 31 is a distributed Bragg reflector (DBR) made of dielectric material.

[0028] In this embodiment, the second multilayer reflector 31 consists of a Nb2O5 spacer layer formed on the upper surface of the transparent electrode 27, and 10.5 pairs of Nb2O5 / SiO2 layers deposited on the spacer layer. The second multilayer reflector 31 with this configuration has a reflectance of 99% or more with respect to the light emitted from the active layer 19. The reflectance of this second multilayer reflector 31 is higher than that of the first multilayer reflector 13.

[0029] Figure 2 is a top view of the surface-emitting laser 10. In Figure 2, the axis aligned with the m-axis direction within the same plane as the top surface of the substrate 11 is defined as the transverse axis AX2. As described above, the surface-emitting laser 10 has a semiconductor structure layer 15 including an n-type semiconductor layer 17, an active layer 19 with a circular top surface shape, and a p-type semiconductor layer 21, all formed on a substrate 11 having a rectangular top surface shape (see Figure 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 reflector 31 are formed on the transparent electrode 27.

[0030] 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 described above. As shown in Figure 2, the opening 25H is formed in the central part of the insulating layer 25 when viewed from above the surface-emitting laser 10 and is covered by the second multilayer reflector 31 when viewed from above the surface-emitting laser 10. In other words, the opening 25H is formed in the region of the insulating layer 25 that faces the lower surface of the multilayer reflector 31. In this embodiment, the opening 25H has a diameter of 10 μm.

[0031] The opening 25H is circular with its center on the central axis AX1. Therefore, the p-type semiconductor layer 21 is electrically connected to the transparent electrode 27 via an electrical contact surface 21S located in a circular region exposed from the opening 25H on the upper surface of the p-type semiconductor layer 21.

[0032] As shown in Figure 2, the protrusion 11P (thick dashed line in the figure) is a circle with its center on the central axis AX1 when viewed from above. The protrusion 11P is formed over a region facing the electrical contact surface 21S on the lower surface of the substrate 11. The protrusion 11P is formed so as to overlap the electrical contact surface 21S when viewed from above, i.e., from the direction normal to the upper surface of the substrate 11, and extends beyond the outer edge, i.e., contour, of the electrical contact surface 21S. In this embodiment, the protrusion 11P extends outside the p electrode 29 when viewed from above, i.e., outside the upper part 17B of the n-type semiconductor layer 17.

[0033] Figure 3 is a cross-sectional view of the surface-emitting laser 10 along line 3-3 in Figure 2. As described above, the surface-emitting laser 10 has a substrate 11 which is a GaN substrate, and a first multilayer reflecting mirror 13 is formed on the substrate 11.

[0034] Furthermore, as described above, a back surface multilayer reflector 12, which serves as a third multilayer reflector, is formed on the surface of the protrusion 11P on the lower surface of the substrate 11. Therefore, the protrusion 11P and the back surface multilayer reflector 12 form a concave reflective structure 12R having an upwardly concave reflective surface facing the active layer 19 and the second multilayer reflector 31.

[0035] This upwardly concave reflective surface causes light that has passed downward from the direction of the active layer 19 through the first multilayer reflecting mirror 13 to be reflected upward and focused toward the central axis AX1. In other words, the back surface multilayer reflecting mirror 12 has the function of focusing the light that has passed through the first multilayer reflecting mirror 13 and reached the back surface multilayer reflecting mirror 12 into a region along the central axis AX1.

[0036] As described above with respect to Figure 1, a semiconductor structural layer 15 is formed on the first multilayer reflecting mirror 13. The semiconductor structural layer 15 is a laminate in which an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 are formed in that order. A protruding portion 21P is formed in the center of the upper surface of the p-type semiconductor layer 21, protruding upward.

[0037] In this embodiment, the n-type semiconductor layer 17 is a Si-doped n-GaN layer with a thickness of 350 nm. The active layer 19 is an active layer with a multiple quantum well structure in which four pairs of 3 nm GaInN layers and 4 nm GaN layers are stacked. On the active layer 19, a 120 nm undoped GaN layer and a 10 nm Mg-doped AlGaN (Al composition 30%) electron barrier layer are formed, and on top of that, a p-type semiconductor layer 21 is formed, consisting of a p-GaN layer with a thickness of 83 nm in the portion where the protrusion 21P is formed.

[0038] The insulating layer 25 is formed to cover the area of ​​the upper surface of the p-type semiconductor layer 21 other than the protruding portion 21P. As described above, the insulating layer 25 is made of a material having a lower refractive index than the p-type semiconductor layer 21. The insulating layer 25 has an opening 25H that exposes the protruding portion 21P. For example, the opening 25H and the protruding portion 21P have similar shapes, and the inner surface of the opening 25H and the outer surface of the protruding portion 21P are in contact.

[0039] The insulating layer 25 is a 20 nm thick layer of SiO2. The upper surface of the insulating layer 25 is positioned at the same height as the upper surface of the protrusion 21P of the p-type semiconductor layer 21. In other words, the protrusion 21P on the upper surface of the p-type semiconductor layer 21 protrudes 20 nm from the surrounding region. Therefore, the p-type semiconductor layer 21 has a thickness of 83 nm at the protrusion 21P and a thickness of 63 nm in the other regions.

[0040] The transparent electrode 27 is formed to cover the insulating layer 25 and the upper surface of the protruding portion 21P that is exposed through the opening 25H of the insulating layer 25. In other words, the transparent electrode 27 is in electrical contact with the p-type semiconductor layer 21 in the region exposed by the opening 25H on the upper surface of the p-type semiconductor layer 21. To put it another way, the region exposed through the opening 25H on the upper surface of the p-type semiconductor layer 21 is the electrical contact surface 21S that brings about electrical contact between the p-type semiconductor layer 21 and the transparent electrode 27.

[0041] As described above, the p electrode 29 is a metal electrode and is formed along the outer edge of the upper surface of the transparent electrode 27. That is, the p electrode 29 is in electrical contact with the transparent electrode 27. Therefore, the p electrode 29 is in electrical contact or connected to the p-type semiconductor layer 21 via the transparent electrode 27 at the electrical contact surface 21S exposed by the opening 25H on the upper surface of the p-type semiconductor layer 21.

[0042] The second multilayer reflector 31 is formed on the upper surface of the transparent electrode 27, in the region above the opening 25H of the insulating layer 25, in other words, in the region above the electrical contact surface 21S, i.e., 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 and the upper surface of the back multilayer reflector 12, with the transparent electrode 27 and the semiconductor structural layer 15 in between. A first resonator OC1 is formed between the first multilayer reflector 13 and the second multilayer reflector 31, and a second resonator OC2 is formed between the back multilayer reflector 12 and the second multilayer reflector 31. The resonators OC that resonate the light emitted from the active layer 19 include these first resonators OC1 and OC2.

[0043] In the surface-emitting laser 10, the reflectivity of the second multilayer mirror 31 is slightly higher than the reflectivity of the reflective structure consisting of the back-surface multilayer mirror 12 and the first multilayer mirror 13. Therefore, a portion of the light that resonates between the back-surface multilayer mirror 12, the first multilayer mirror 13, and the second multilayer mirror 31 is transmitted through the first multilayer mirror 13, the substrate 11, and the back-surface multilayer mirror 12 and extracted to the outside.

[0044] The operation of the surface-emitting laser 10 will now be explained. When a voltage is applied between the n electrode 23 and the p electrode 29 in the surface-emitting laser 10, a current flows within the semiconductor structure layer 15, as shown by the thick dashed arrow 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 mirror 13 and the back surface multilayer mirror 12 and the second multilayer mirror 31, until it reaches a resonance state (i.e., laser oscillation occurs).

[0045] In the surface-emitting laser 10, current is injected into the p-type semiconductor layer 21 only from the portion exposed by the aperture 25H, i.e., the electrical contact surface 21S. Furthermore, because the p-type semiconductor layer 21 is very thin, the current does not diffuse within the p-type semiconductor layer 21 in the in-plane direction, i.e., in the direction along the in-plane direction of the semiconductor structure layer 15.

[0046] 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 aperture 25H, and light is emitted only from that region. In other words, in the surface-emitting laser 10, the aperture 25H forms a current-constricting structure that limits the current supply range in the active layer 19. That is, in the surface-emitting laser, a current-constricting structure is formed by the p-type semiconductor layer 21 and the insulating layer 25.

[0047] In other words, in the surface-emitting laser 10, a current-constricting structure is formed between the first multilayer mirror 13 and the second multilayer mirror 31 such that current flows only through the central region CA, which is a columnar region of the active layer 19 with the electrical contact surface 21S as its base. That is, the current is concentrated in one region of the active layer. The central region CA, which includes the area in the active layer 19 through which current flows, is defined by the electrical contact surface 21S.

[0048] As described above, in this embodiment, the first multilayer reflector 13 has a lower reflectivity than the second multilayer reflector 31. Therefore, a portion of the light arriving from the second multilayer reflector 31 and the active layer 19 and reaching the first multilayer reflector 13 is transmitted to the back multilayer reflector 12, causing resonance to occur between the second multilayer reflector 31 and the back multilayer reflector 12. Some of this resonated light passes through the first multilayer reflector 13, the back multilayer reflector 12, and the substrate 11 and is extracted to the outside.

[0049] 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 (excluding the protrusions 11P) and each layer of the semiconductor structural layer 15. In other words, the lower surface of the substrate 11 is the light-emitting surface of the surface-emitting laser 10.

[0050] Furthermore, 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 the light emission center, which is the center of the light emission region in the active layer 19, and define the central axis (light emission center axis) of the resonator OC. The central axis 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. In this embodiment, the light emission center axis of the resonator OC and the central axis AX1 are assumed to be the same. In the following description, the central axis AX1 will also be referred to as the light emission center axis AX1.

[0051] The light-emitting region of the active layer 19 is, for example, a region within the active layer 19 having a predetermined width in which light of a predetermined intensity or greater is emitted, and its center is the light-emitting center. Alternatively, for example, the light-emitting region of the active layer 19 is a region within the active layer 19 in which a current of a predetermined density or greater is injected, and its center is the light-emitting center. Furthermore, the light-emitting center axis AX1 is a straight line perpendicular to the in-plane direction of the upper surface of the substrate 11 or each layer of the semiconductor structure layer 15 that passes through the light-emitting center.

[0052] The light emission central axis AX1 is a straight line extending along the length direction of the resonator OC, which is composed of the first multilayer reflector 13, the back surface multilayer reflector 12, and the second multilayer reflector 31. The light emission central axis AX1 also corresponds to the optical axis of the laser beam emitted from the surface-emitting laser 10.

[0053] The optical characteristics of the inside of the surface-emitting laser 10 are described below. As mentioned above, in the surface-emitting laser 10, the insulating layer 25 has a lower refractive index than the p-type semiconductor layer 21. Furthermore, between the back surface multilayer reflector 12 and the first multilayer reflector 13 and the second multilayer reflector 31, the layer thickness of the active layer 19 and the n-type semiconductor layer 17 is the same at any point in the plane as long as it is within the same layer.

[0054] Therefore, the equivalent refractive index (which is the optical distance between the back surface multilayer reflector 12 and the first multilayer reflector 13 and the second multilayer reflector 31, and corresponds to the resonant wavelength) in the resonator OC formed between the back surface multilayer reflector 12 and 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 base and the surrounding cylindrical peripheral region PA, due to the difference in refractive index between the p-type semiconductor layer 21 and the insulating layer 25.

[0055] Specifically, between the back surface multilayer reflector 12 and the first multilayer reflector 13 and the second multilayer reflector 31, the equivalent refractive index of the peripheral region PA is lower than that of the central region CA. That is, the equivalent resonant wavelength in the central region CA is smaller than the equivalent resonant wavelength of the peripheral region PA. Light is emitted from the active layer 19 in the region directly below the aperture 25H and the electrical contact surface 21S. In other words, the light-emitting region of the active layer 19 is the part of the active layer 19 that overlaps with the central region CA, or in other words, the region that overlaps with the electrical contact surface 21S when viewed from above.

[0056] Thus, in the surface-emitting laser 10, a p-type semiconductor layer 21 and an insulating layer 25 that form a current-constricting structure form 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.

[0057] This suppresses optical loss caused by standing waves in the central region CA diverging (radiating) to the surrounding region PA. In other words, a large amount of light remains in the central region CA, and the laser light is extracted to the outside in that state.

[0058] In other words, in the surface-emitting laser 10, a light confinement structure is also formed by the p-type semiconductor layer 21 and the insulating layer 25 that form a current-constricting structure, which keeps the light confined to the central region.

[0059] Furthermore, in the surface-emitting laser 10, light that passes through the first multilayer reflector 13 and reaches the back multilayer reflector 12 is focused in the central region CA by the concave reflective surface 12RS of the concave reflective structure 12R formed by the back multilayer reflector 12. In other words, the light is also retained in the central region CA by the back multilayer reflector 12.

[0060] Therefore, the current-constricting structure and the back-surface multilayer reflector 12 concentrate a large amount of light into the central region CA around the light-emitting central axis AX1 of the resonator OC, enabling the generation and emission of high-power and high-density laser light.

[0061] Furthermore, in the surface-emitting laser 10, as described above, the resonator OC is formed by the back surface multilayer reflector 12, the first multilayer reflector 13, and the second multilayer reflector 31. This makes it easy to increase the light output by enlarging the current-injection region, the region in the active layer 19 through which current flows, while maintaining the light emitted from the surface-emitting laser 10 in single mode.

[0062] For example, consider a configuration in which the back surface multilayer reflector 12 is removed from the surface-emitting laser 10 of the present application, and the reflectivity of the first multilayer reflector 13 and the second multilayer reflector 31 is made close to form a resonator using only these (hereinafter also referred to as the comparative configuration). In this case, the inventors of the present application have found that unless the diameter of the aperture 25H, which forms a current constriction structure that limits the flow of current into the active layer 19 and defines the light-emitting region, is made to be approximately 5.5 μm or less, the extracted light is unlikely to be single-mode.

[0063] In other words, in the comparative configuration that simply uses a structure to form a current-constricting structure to confine light and control the transverse mode to a single mode, it was found that the current injection region had to be kept small. This is because increasing the current injection region of the active layer and raising the optical output causes spatial hole burning to occur near the light emission center of the active layer, reducing the optical gain near that light emission center.

[0064] This spatial hole burning is a phenomenon in which the light density becomes excessively high in a specific region of the active layer, leading to increased stimulated emission, and consequently, the injected carriers are consumed in that high-light-density region, resulting in a decrease in carrier density.

[0065] In the comparative configuration described above, when attempting to increase the optical output, if the aperture 25H is enlarged beyond 5.5 μm, the optical confinement effect caused by the current-constricting structure leads to excessive concentration of light around the light-emitting center of the active layer, resulting in an excessively high optical density and causing hole burning. In a surface-emitting laser, when this hole burning occurs, the optical gain of the resonator in the width direction becomes multi-peaked, and the transverse modes of the extracted light become multi-mode.

[0066] In the surface-emitting laser 10 of this embodiment, as described above, a reflective structure that reflects light upward is formed by the back surface multilayer reflector 12 and the first multilayer reflector 13, and a reflective structure that reflects light downward is formed by the second multilayer reflector 31, thereby forming a resonator.

[0067] Thus, in the surface-emitting laser 10, some of the light from the first resonator OC1, which consists of the first multilayer reflecting mirror 13 and the second multilayer reflecting mirror 31, is directed downwards by passing through the first multilayer reflecting mirror 13. As a result, a second resonator OC2 is formed between the back surface multilayer reflecting mirror 12, which has a concave reflective surface 12RS that reflects light while focusing toward the central axis AX1, and the second multilayer reflecting mirror 31.

[0068] In this way, the light density in the region around the light emission central axis AX1 can be reduced in the active layer 19 compared to the case where the first resonator OC1 is formed only between the first multilayer mirror 13 and the second multilayer mirror 31, thereby suppressing the occurrence of spatial hole burning.

[0069] Specifically, the surface-emitting laser 10 employs not only an optical confinement structure formed between the first multilayer mirror 13 and the second multilayer mirror 31, but also another lateral optical confinement structure that focuses light to the central region CA using the back surface multilayer mirror 12. Furthermore, as described above, since the reflectivity of the first multilayer mirror 13 is low, the optical confinement effect caused by the current narrowing structure, which is strongly generated in the first resonator OC1 between the first multilayer mirror 13 and the second multilayer mirror 31, becomes milder than in conventional designs.

[0070] In the surface-emitting laser 10, the optical confinement effect due to the current-constricting structure is less pronounced compared to the comparative configuration in which resonance occurs only in the first resonator OC1 between the first multilayer reflector 13 and the second multilayer reflector 31. Instead, the back surface multilayer reflector 12, which has a concave reflective surface 12RS that reflects light that has passed through the first multilayer reflector 13 and gone downwards upwards and toward the central axis AX1, compensates for the less pronounced optical confinement effect due to the current-constricting structure.

[0071] Thus, by performing light confinement in combination with the current-constricting structure described above and the back-surface multilayer reflecting mirror 12, light is sufficiently confined in the central region CA, but light does not become excessively concentrated in the region near the central axis AX1 of the active layer 19, and the light density does not become excessively high. As a result, even if the current injection region of the active layer 19 is enlarged, hole burning due to excessively high light density becomes less likely to occur.

[0072] Thus, in the surface-emitting laser 10, even if the aperture 25H is enlarged and the current injection region of the active layer 19 is enlarged, hole burning does not occur, and the light intensity distribution of the emitted light is more likely to maintain a Gaussian distribution. In other words, in the surface-emitting laser 10, the transverse modes of the emitted light are more likely to be kept as single modes.

[0073] Furthermore, it is preferable that the radius of curvature R of the concave reflective surface 12RS of the concave reflective structure 12R satisfies the following equation (1).

[0074]

number

[0075] Here, Z is originally the distance between the reflective surface of the concave reflective structure and the active layer 19, but since the distance between the active layer 19 and the lower surface of the second multilayer mirror 31 is small enough to approximate, it is taken as the distance between the reflective surface of the concave reflective structure 12R and the lower surface of the second multilayer mirror 31 (see Figure 3).

[0076] Also, n eq The equivalent refractive index due to the semiconductor between the reflective surface of the concave reflective structure 12R and the lower surface of the second multilayer mirror 31 is λ. lasing This is the wavelength of light emitted from the active layer 19.

[0077] This relationship was derived based on ω0, which is half the beam spot diameter, in the light intensity distribution in the plane perpendicular to the emission direction of the light emitted from the surface-emitting laser 10 in the first resonator OC1, and the distance from the peak position to the position where the light intensity at the peak is 1 / e, i.e., 1 / 2 of the beam spot diameter, and the following equation (2).

[0078]

number

[0079] Furthermore, equation (1) above is derived from equation (2) above, which shows the relationship between ω0 and R. Specifically, it is derived by introducing the condition that the spot diameter ω0 of the light output by the first resonator OC1 is a maximum of 1.65 μm, and that it is preferable for the spot diameter of the light output by the second resonator OC2 to be larger than this into equation (1).

[0080] Furthermore, as described above, in the surface-emitting laser 10 of this embodiment, the upper surface of the substrate 11 is a surface that is 0.5° off-center from the C-plane 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 with a polarization direction in the m-axis direction becomes greater than that of light with a polarization direction in other directions, so laser light with a polarization direction 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 has a large amount of light with a polarization direction in the m-axis direction. In other words, the surface-emitting laser 10 has a large amount of light with a polarization direction along the lateral axis AX2.

[0081] As described above, the surface-emitting laser of the present invention makes it easy to increase the emission output while maintaining the transverse mode of the emitted light as a single mode. Furthermore, it has high luminous efficiency and makes it possible to stably obtain emitted light with a specific polarization direction. This is very effective when the emitted light of the surface-emitting laser is used in a device having an optical system using liquid crystal or polarizer. [Manufacturing method] The following describes an example of a manufacturing method for the surface-emitting laser 10. First, as the substrate 11, a GaN substrate is prepared in which the upper surface has a crystal plane that is inclined from the C plane to the M plane, as described above.

[0082] Next, a GaN (1 μm thick) layer is formed as a base layer on the upper surface of the substrate 11 by metal-organic vapor deposition (MOVPE). Then, 35 pairs of n-GaN / AlInN layers are deposited on the base layer to form the first multilayer reflecting mirror 13.

[0083] Next, an n-type semiconductor layer 17 is formed on the first multilayer reflecting mirror 13 by forming a Si-doped n-GaN (layer thickness 350 nm), and an active layer 19 is formed on top of it by stacking four pairs of layers made of GaInN (layer thickness 3 nm) and GaN (layer thickness 4 nm).

[0084] Next, an electron barrier layer (10 nm) made of Mg-doped AlGaN (Al composition 30%) is formed on the active layer 19 (not shown), and a p-GaN layer (layer thickness 83 nm) is deposited on the electron barrier layer to form a p-type semiconductor layer 21.

[0085] 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 in which the upper surface 17S of the n-type semiconductor layer 17 is exposed in the surrounding areas. In other words, in this process, the semiconductor structure layer 15 having a cylindrical portion consisting of the n-type semiconductor layer 17, the active layer 19, and the p-type semiconductor layer 21 shown in Figure 1 is completed.

[0086] Next, the area around the center of the upper surface of the p-type semiconductor layer 21 is etched to form a protrusion 21P. Then, a 20 nm film of SiO2 is deposited on the semiconductor structural layer 15, and a portion of it is removed to form an opening 25H, thereby forming an insulating layer 25. In other words, SiO2 is embedded in the etched portion of the upper surface of the p-type semiconductor layer 21.

[0087] Next, a 20 nm layer of ITO is deposited on the insulating layer 25 to form a transparent electrode 27, and Au is deposited on the upper surface of the transparent electrode 27 and the upper surface 17S of the n-type semiconductor layer 17 to form a p electrode 29 and an n electrode 23, respectively.

[0088] Next, a 38 nm layer of Nb2O5 is deposited on the transparent electrode 27 as a spacer layer (not shown), and 10.5 pairs of layers, each consisting of Nb2O5 / SiO2, are deposited on the spacer layer to form a second multilayer reflecting mirror 31.

[0089] Next, the back surface of the substrate 11 is polished to a thickness of 200 μm or less, and then a protrusion 11P is formed on the back surface of the substrate 11. The protrusion 11P is formed by a reflow process so that the central axis of its lens shape coincides with the light emission central axis AX1. The protrusion 11P may also be formed using exposure patterning and dry etching.

[0090] Specifically, for example, the protrusion 11P may be formed by depositing a resist on the back surface of the substrate 11 in a shape similar to the protrusion 11P, dry etching the entire back surface of the substrate 11, and transferring the shape of the resist to the back surface of the substrate 11.

[0091] [Example 1] The following describes a surface-emitting laser 40, which is a modification 1 of the surface-emitting laser 10 of Embodiment 1 of the present invention. Modification 1 differs from the surface-emitting laser 10 in that the convex portion 11P is not circular, that is, the concave reflective surface formed by the concave reflective structure 12R is not circular.

[0092] Figure 4 is a top view of the surface-emitting laser 40 of the modified example 1. As shown in Figure 4, in the surface-emitting laser 40, the top surface shape of the convex portion 11P has an elliptical shape with the major axis in the same direction as the lateral axis AX2. That is, the convex portion 11P has an elliptical top surface shape with the major axis along the m-axis direction when viewed from above.

[0093] In the surface-emitting laser 40, if the convex portion 11P is elliptical in shape with its major axis in the m-axis direction, that is, if the reflective surface of the concave reflective structure 12R is reflective with an elliptical upper surface shape having its major axis in the m-axis direction, the inventors of the present invention have found that the optical gain of light with a polarization direction along the m-axis direction in the central region CA of the light has a polarization direction along the m-axis direction becomes higher and the loss in the m-axis direction becomes lower.

[0094] Therefore, with the surface-emitting laser 40, it is possible to extract a large amount of light having a polarization direction along the m-axis from the lower surface of the substrate 11 which is the light-emitting surface of the surface-emitting laser 10, and to suppress the emission of light with polarization directions other than along the m-axis. Thus, with the surface-emitting laser 40, it is possible to further suppress the variation in the polarization direction of the light extracted from the light-emitting surface in the in-plane direction of the light-emitting surface.

[0095] Furthermore, the shape of the convex portion 11P, which further suppresses variations in polarization direction, in other words, the shape of the upper surface of the concave reflective structure 12R, may be any other shape as long as the longitudinal direction is along the horizontal axis AX2. In other words, the shape of the upper surface of the convex portion 11P may be any shape other than an ellipse as long as the longitudinal direction is along the horizontal axis AX2.

[0096] For example, the upper surface shape of the protrusion 11P may be rectangular or rectangular with its longitudinal direction along the lateral axis AX2. Alternatively, for example, the upper surface shape of the protrusion 11P may be oval with the same contour as a running track, with its longitudinal direction along the lateral axis AX2. Alternatively, for example, the upper surface shape of the protrusion 11P may be rhombic with its longitudinal direction along the axis AX2.

[0097] [Differentiation 2] Hereinafter, a surface-emitting laser 50, which is a modified example 2 of the surface-emitting laser 10 of Example 1 of the present invention, will be described with reference to Figure 5. The surface-emitting laser 50 of Modified Example 2 differs from the surface-emitting laser 10 of Example 1 in that it does not have a back surface multilayer reflecting mirror 12.

[0098] Figure 5 is a cross-sectional view showing the cross-section obtained when the surface-emitting laser 50 is cut along the same cutting line as shown in Figure 2, i.e., the cross-section corresponding to Figure 3. As shown in Figure 5, the surface-emitting laser 50 does not have a back-surface multilayer reflecting mirror 12, but instead has a diffraction grating 53 (indicated by the dashed line in the figure) made up of multiple slit grooves 51 formed on the surface of the convex portion 11P. That is, the convex portion 11P and the diffraction grating 53 form a concave reflective structure 55R having a concave reflective surface 55RS. These slit grooves 51 have a longitudinal direction in the same direction as the transverse axis AX2 (see Figure 2), which is an axis along the direction perpendicular to the plane of the paper in Figure 5. That is, the slit grooves 51 have a longitudinal direction in the direction along the m-axis when viewed from above.

[0099] The diffraction grating 53 formed by these slit grooves 51 provides high reflectivity for light whose polarization direction is in the direction of extension of each slit groove 51 that forms the diffraction grating, i.e., the m-axis direction. In other words, the formation of the diffraction grating 53 made of slit grooves 51 increases the reflectivity of light whose polarization direction is in the m-axis direction compared to light with other polarization directions, making it easier for light whose polarization direction is in the m-axis direction to oscillate preferentially.

[0100] Therefore, with the surface-emitting laser 50, by forming a diffraction grating 53 consisting of slit grooves 51 on the lower surface of the substrate 11 to form a concave reflective structure 55R, it is possible to further control the polarization of the emitted light and stably obtain emitted light in which light having a polarization direction 1 is dominant.

[0101] The slit groove 51 can be formed in the final step of the manufacturing process for the surface-emitting laser 10 of Embodiment 1 described above by performing an etching process such as dry etching on the lower surface of the substrate 11.

[0102] [Difference 3] Hereinafter, a surface-emitting laser 60, which is a modification 3 of Embodiment 1 of the present invention, will be described with reference to Figure 6. The surface-emitting laser 60 differs from the surface-emitting laser 10 of Embodiment 1 in that, in order to form the current-constricting structure described above, a tunnel junction structure is formed in the semiconductor structural layer 15 instead of the insulating layer 25. Specifically, the structure of the surface-emitting laser 60 above the p-type semiconductor layer 21 differs from that of the surface-emitting laser 10.

[0103] Figure 6 is a cross-sectional view showing the cross-section obtained when the surface-emitting laser 60 is cut along the same cutting line as shown in Figure 2, i.e., the cross-section corresponding to Figure 3. As shown in Figure 6, in the surface-emitting laser 60, a tunnel junction layer 61 is formed on the protruding portion 21P of the p-type semiconductor layer 21. That is, in the surface-emitting laser 60, the tunnel junction layer 61 is formed in the central region CA within the semiconductor structural layer 15.

[0104] The tunnel junction layer 61 includes a highly doped p-type semiconductor layer 61A, which is 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 61B, which is formed on the highly doped p-type semiconductor layer 61A and has a higher impurity concentration than the n-type semiconductor layer 17.

[0105] The n-type semiconductor layer 63 is formed on the p-type semiconductor layer 21 and the tunnel junction layer 61. The n-type semiconductor layer 63 is formed to embed the tunnel junction layer 61 on the upper surface of the p-type semiconductor layer 21. In other words, the n-type semiconductor layer 63 is formed to cover the side surface of the protrusion 21P and the side and upper surface of the tunnel junction layer 61.

[0106] The second multilayer reflector 65 is formed on the upper surface of the n-type semiconductor layer 63 and is an n-type semiconductor layer having the same doping concentration as the n-type semiconductor layer 17. That is, the n-type semiconductor layer 63 has a lower doping concentration than the highly doped n-type semiconductor layer 61B.

[0107] In this stacked structure of p-type semiconductor layer 21, tunnel junction layer 61, and n-type semiconductor layer 63, a tunneling effect occurs in the tunnel junction layer 61. As a result, in the surface-emitting laser 60, current flows only in the tunnel junction layer 61 between the p-type semiconductor layer 21 and the n-type semiconductor layer 63, forming a current-constricting structure in which the current is narrowed to the central region CA.

[0108] The second multilayer reflector 65 is a semiconductor multilayer reflector consisting of semiconductor layers formed on an n-type semiconductor layer 63. The second multilayer reflector 65 is formed by alternately stacking a low refractive index semiconductor film having an AlInN composition and a high refractive index semiconductor film having a GaN composition and a higher refractive index than the low refractive index semiconductor film, and thus possesses the characteristics of an n-type semiconductor. In other words, the second multilayer reflector 65 is a distributed Bragg reflector (DBR) made of semiconductor material.

[0109] The p-side electrode 67 is a metal electrode formed along the peripheral edge of the upper surface of the second multilayer reflector 65. In the surface-emitting laser 60, since the second multilayer reflector 65 is conductive, current flows from the p-side electrode 67 through the second multilayer reflector 65, the n-type semiconductor layer 63, the tunnel junction layer 61, the p-type semiconductor layer 21, the active layer 19, and the n-type semiconductor layer 17 to the n-side electrode 23.

[0110] In a semiconductor structure layer having this configuration, current flows from the p-GaN layer to the n-type semiconductor layer 17 only from the tunnel junction layer. Therefore, it is possible to produce a current confinement effect similar to that when the insulating layer 25 described above is formed. Furthermore, because the refractive index is different in the tunnel junction layer 61 and the surrounding region, it is also possible to produce a light confinement effect similar to that in Example 1.

[0111] In other words, by forming a tunnel junction layer 61 in the same region as the electrical contact surface 21S described above when viewed from above, it becomes possible to obtain the same current constriction effect and light confinement effect as when the electrical contact surface 21S is formed.

[0112] In the above-described examples 1 and modifications 1 to 3, the n-electrode 23 was formed on the n-type semiconductor layer 17, but instead, the n-side electrode may be formed on the back surface of the substrate 11.

[0113] Figure 7 shows a cross-sectional view of the surface-emitting laser 10 of Example 1, in which the n-side electrode 68 is formed in the region surrounding the convex portion 11P, i.e., the region outside the concave reflective structure 12R, instead of the n-electrode 23. In this case, the substrate 11 becomes the path for the current, so the substrate 11 must be doped.

[0114] However, as mentioned above, in the surface-emitting laser 10, the substrate 11 is also placed inside the resonator, so it is preferable that the substrate 11 has high light transmittance. Therefore, it is preferable that the n-type dopant used to dope the substrate 11 is Si rather than oxygen, and that the dopant concentration is low. For example, in the substrate 11, the Si dopant concentration in the regions within the first resonator OC1 and the second resonator OC2 is 2 × 10⁻¹⁶. 18 / cm 3 Preferably, the following areas occupy 80%, and more preferably, 1 × 10 18 / cm 3 Preferably, the following areas account for 80%.

[0115] Specifically, since a high dopant concentration is required in the area where the n-side electrode is formed, for example, the dopant concentration is increased only in that area, and the dopant concentration is decreased in the other areas including the resonator OC, thereby forming a substrate 11 that satisfies the above dopant concentration conditions. Note that since the area where the n-side electrode is formed is the area outside the resonator OC, the dopant can be oxygen.

[0116] The above-described modifications 1 to 3 and the example in which the n-side electrode is formed on the back surface of the substrate 11 are all combinable. [Examples]

[0117] The following describes the surface-emitting laser 70, which is an embodiment 2 of the present invention. Figure 8 is a cross-sectional view showing the cross-section obtained when the surface-emitting laser 79 is cut along the same cutting line as shown in Figure 2, i.e., the cross-section corresponding to Figure 3.

[0118] As shown in Figure 8, in the surface-emitting laser 70, instead of providing a convex portion 11P on the back surface of the substrate 11 to form a concave reflective structure 12R, an output coupler 71 having a concave reflective surface 71RS is positioned below the substrate 11 to form a concave reflective structure 71R. In other words, the output coupler 71 is positioned below the substrate 11 at a distance.

[0119] The output coupler 71 consists of a transparent substrate 72 having a concave surface 72S facing the lower surface of the substrate 11, and an external multilayer reflector 73 which is a dielectric covering the concave surface 72S.

[0120] In the surface-emitting laser 70, a concave reflective structure 71R corresponding to the concave reflective structure 12R of the surface-emitting laser 10 is formed by a transparent substrate 72 and an external multilayer reflector 73. In the surface-emitting laser 70, a second resonator OC2 is formed between the second multilayer reflector 31 and the external multilayer reflector 73.

[0121] In addition, in the surface-emitting laser 10, an AR coating made of, for example, four pairs of Nb2O5 / SiO2 is formed on the back surface of the substrate 11 to prevent light reflection from occurring on the back surface of the substrate 11.

[0122] This configuration, which uses an output coupler 71 instead of a concave reflective structure 12R formed by a protrusion 11P on the lower surface of the substrate 11, is advantageous when the concave reflective structure 12R must be large for design purposes in the surface-emitting laser 10.

[0123] For example, when forming multiple surface-emitting lasers 10 on a wafer and separating them into individual pieces, if the concave reflective structure 12R needs to be made larger, the number of surface-emitting lasers 10 that can be manufactured per wafer may be limited by the size of the convex portion 11P. In such cases, by replacing the concave reflective structure 12R with the concave reflective structure 71R of an external output coupler 71, the concave reflective structure can be made larger without reducing the number of surface-emitting lasers that can be manufactured per wafer.

[0124] In the above-described embodiment, the upper surface of the substrate 11 was described as being 0.5° off-center from the C-plane in the M-plane direction, i.e., the off-angle from the C-plane to the M-plane direction is 0.5°. However, the off-angle is not limited to this angle. If the off-angle is, for example, around 0.3° to 0.8°, the polarization control effect described above can be sufficiently obtained. Furthermore, if the off-angle of the upper surface of the substrate 11 is 0.8° or less, the semiconductor multilayer film constituting the first multilayer reflector 13 can be formed stably with sufficient reflectivity.

[0125] Furthermore, although the above embodiment described a case where the upper surface of the substrate 11 is turned off in the direction from the C plane to the M plane, the upper surface of the substrate 11 may be turned off in the direction from the C plane to the A plane, and may not be turned off at all in the direction of the C plane.

[0126] In this case, in order to obtain the polarization control effect described above, for the same reasons as described for the range of the off-angle of the C-plane, the off-angle from the C-plane towards the A-plane is preferably about 0.3° to 0.8°, and the off-angle from the C-plane towards the M-plane is preferably 0 ± 0.1°. Note that when the upper surface of the substrate 11 is off-center from the C-plane to the A-plane, in the description of the longitudinal direction of the upper surface shape of the protrusion 11P in the modified example 1 and the longitudinal direction of the slit groove 51 in the modified example 2, please understand that the lateral axis AX2 corresponds to the a-axis.

[0127] When the upper surface of the substrate 11 is turned off from the C-plane towards the A-plane, a large amount of light with a polarization direction along the a-axis can be extracted, and the emission of light with polarization directions other than along the a-axis can be suppressed. Therefore, the surface-emitting laser 10 makes it possible to 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.

[0128] Furthermore, if the effect of suppressing variations in the deflection direction due to the above-mentioned off-angle is not required, the substrate 11 may be a C-surface substrate with a C-surface exposed on its upper surface.

[0129] The various numerical values, dimensions, materials, etc., in the above-described examples are merely illustrative and can be appropriately selected depending on the application and the surface-emitting laser being manufactured. [Explanation of Symbols]

[0130] 10, 40, 50, 60, 70-plane emitting lasers 11 circuit boards 12 Back multilayer reflective mirror 12R concave reflective structure 13. First multilayer reflecting mirror 15 Semiconductor structural layers 17 n-type semiconductor layer 19 Active layer 21 p-type semiconductor layer 23 n electrode 25 Insulating layer 27 Transparent electrode 29p electrode 51 Slit groove 53 Diffraction Grating 55R concave reflective structure 31. Second multilayer reflecting mirror 61 Tunnel junction layer 63 n-type semiconductor layer 65. Second multilayer reflecting mirror 67 Second n electrode 71 Output coupler 71R concave reflective structure 72 Transparent substrate 73 External multilayer reflector

Claims

1. A gallium nitride semiconductor substrate; a first multilayer reflector made of a nitride semiconductor formed on the gallium nitride based semiconductor 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 the second multilayer film reflector and the first multilayer film reflector; a current confinement structure formed between the first multilayer film reflector and the second multilayer film reflector for concentrating a current in one region of the active layer; a concave reflection structure that is disposed on the lower surface of the gallium nitride semiconductor substrate or in a region below the lower surface, extends beyond the first region in a top view seen from a direction perpendicular to the upper surface of the gallium nitride semiconductor substrate, and has a concave reflection surface that faces the first multilayer film reflector; 4. A vertical cavity light emitting device, comprising: a concave reflecting surface having a shape such that light reflected by the concave reflecting surface is concentrated on the current confinement structure.

2. 2. The vertical cavity light emitting device according to claim 1, wherein the concave reflective structure comprises a convex portion formed on the underside of the gallium nitride based semiconductor substrate and extending outside the first region when viewed from the top, and a third multilayer film reflector covering a surface of the convex portion to form the concave reflective surface.

3. 2. The vertical cavity light emitting device according to claim 1, wherein the concave reflective structure is a diffraction grating formed on the underside of the gallium nitride based semiconductor substrate and extending beyond the one region when viewed from above, and comprising a plurality of slit grooves formed parallel to each other on the surface of the convex portion to form the concave reflective surface.

4. 2 . The vertical cavity light emitting device according to claim 1 , wherein the concave reflective structure is a member disposed below the gallium nitride based semiconductor substrate and spaced apart from the substrate, the member having the concave reflective surface.

5. 5. The vertical cavity light emitting device according to claim 1, further comprising: a first electrode formed in a region of the lower surface of the gallium nitride based semiconductor substrate that is outer than the concave reflective structure when viewed from above; and a second electrode formed on the upper surface of the semiconductor structure layer, and the gallium nitride based semiconductor substrate is doped with an n-type dopant.

6. 6. The vertical cavity light emitting device of claim 5, wherein the n-type dopant is Si.

7. 7. The vertical cavity light emitting device according to claim 5, wherein a dopant concentration is higher in a region of said gallium nitride based semiconductor substrate that is in contact with said first electrode than in other regions.

8. 3. The vertical cavity light emitting device according to claim 2, wherein 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 the concave reflective surface has a longitudinal direction in the m-axis direction when the top surface is offset to the M-plane, and has a longitudinal direction in the a-axis direction when the top surface is offset to the A-plane.

9. 4. The vertical cavity light emitting device according to claim 3, wherein 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 grooves 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.

10. 10. The vertical cavity light emitting device according to claim 8, 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.

11. The radius of curvature R of the concave reflecting surface of the concave reflecting structure is expressed by Z, the distance between the concave reflecting surface and the active layer is expressed by n ｅｑ 11. The vertical cavity light emitting device according to claim 1, wherein the following formula is satisfied when the wavelength of light emitted from the active layer is λlasing: [0010]

12. A vertical cavity light emitting device as described in claim 1, characterized in that the concave reflective surface is shaped so that light reflected by the concave reflective surface is not concentrated on the active layer.

13. The vertical resonator type light-emitting element as described in Claim 12, characterized in that the concave reflective surface is shaped so that light reflected by the concave reflective surface passes through the light-emitting center of the active layer and is reflected while being narrowed toward a light-emitting central axis extending in a direction perpendicular to the in-plane direction of the semiconductor structure layer.

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