Vertical resonator light-emitting element

Abstract

A vertical resonator-type light-emitting element with high luminous efficiency is provided. The present invention is characterized by comprising: a substrate; a first multilayer thin-film reflector formed on the substrate; a semiconductor structure layer comprising a first semiconductor layer of a first conductivity type formed on the first multilayer thin-film reflector, a light-emitting layer formed on the first semiconductor layer, and a second semiconductor layer of a second conductivity type opposite to the first conductivity type and formed on the light-emitting layer; an electrode layer formed on the upper surface of the semiconductor structure layer and electrically contacting the second semiconductor layer of the semiconductor structure layer in a region of the upper surface; and a second multilayer thin-film reflector formed to cover a region on the electrode layer and to constitute a resonator with the first multilayer thin-film reflector, the semiconductor structure layer having a recessed structure comprising one or more recessed portions penetrating the light-emitting layer from the upper surface in a region surrounding the region.

Description

Technical Field

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

[0002] Conventionally, as one type of semiconductor laser, a vertical cavity type semiconductor surface emitting laser (hereinafter also referred to as a surface emitting laser) is known. This type of laser includes a semiconductor layer that emits light when a voltage is applied and a multilayer reflector that is opposed to each other and has a semiconductor layer interposed therebetween. For example, Patent Document 1 discloses a vertical cavity type semiconductor laser having an n-electrode and a p-electrode connected to an n-type semiconductor layer and a p-type semiconductor layer, respectively.

[0003] Citation List

[0004] Patent Literature

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-98328 Summary of the Invention

[0006] Technical issues

[0007] For example, an optical resonator having opposing reflectors is formed in a vertical cavity light-emitting element such as a surface-emitting laser. For example, in a surface-emitting laser, by applying a voltage to a semiconductor layer via an electrode, light emitted from the semiconductor layer resonates in the optical resonator to generate laser light.

[0008] However, as an example of a problem, for example, a vertical cavity type semiconductor laser element has lower light emission efficiency than a horizontal cavity type semiconductor laser element having a resonator in a plane direction of a semiconductor layer including an active layer.

[0009] The present invention has been made in view of the above problems, and its object is to provide a vertical cavity light emitting element with high luminous efficiency.

[0010] Technical Solution

[0011] The vertical cavity light-emitting element of the present invention includes a substrate, a first multilayer reflector, a semiconductor structure layer, an electrode layer, and a second multilayer reflector. The first multilayer reflector is formed on the substrate. The semiconductor structure layer includes a first semiconductor layer, a light-emitting layer, and a second semiconductor layer. A first semiconductor layer having a first conductivity type is formed on the first multilayer reflector. The light-emitting layer is formed on the first semiconductor layer. The second semiconductor layer is formed on the light-emitting layer and has a second conductivity type opposite to the first conductivity type. The electrode layer is formed on the upper surface of the semiconductor structure layer and is in electrical contact with the second semiconductor layer of the semiconductor structure layer in an area of the upper surface. The second multilayer reflector is formed to cover an area on the electrode layer and forms a resonator with the first multilayer reflector. The semiconductor structure layer has a recessed structure, wherein the recessed structure includes one or more recessed portions that pass through the light-emitting layer from the upper surface in an area surrounding an area. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a perspective view of a surface emitting laser according to a first embodiment.

[0013] Figure 2 is a top view of the surface emitting laser according to the first embodiment.

[0014] Figure 3 is a cross-sectional view of a surface emitting laser according to a first embodiment.

[0015] Figure 4 is a perspective view of a surface emitting laser according to a second embodiment.

[0016] Figure 5 is a cross-sectional view of a surface emitting laser according to a second embodiment.

[0017] Figure 6 is a perspective view of a surface emitting laser according to a third embodiment.

[0018] Figure 7 is a top view of a surface emitting laser according to a third embodiment.

[0019] Figure 8 is a cross-sectional view of a surface emitting laser according to a third embodiment.

[0020] Figure 9 is a perspective view of a surface emitting laser according to a fourth embodiment.

[0021] Figure 10 is a cross-sectional view of a surface emitting laser according to a fourth embodiment.

[0022] Figure 11 is a top view of a surface emitting laser according to a modification.

[0023] Figure 12 is a top view of a surface emitting laser according to a modification.

[0024] Figure 13 is a top view of a surface emitting laser according to a modification.

[0025] Figure 14 is a perspective view of a surface emitting laser according to a fifth embodiment.

[0026] Figure 15 is a top view of a surface emitting laser according to a fifth embodiment.

[0027] Figure 16 is a top view of a surface emitting laser according to a modification. DETAILED DESCRIPTION

[0028] The following describes an embodiment of the present invention in detail. Although a semiconductor surface-emitting laser element (semiconductor laser) is used as an example in the following description, the present invention is applicable not only to surface-emitting lasers but also to various vertical cavity light-emitting elements such as vertical cavity light-emitting diodes.

[0029] Implementation Method 1

[0030] Figure 1 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 Embodiment 1. FIG.

[0031] The substrate 11 is a gallium nitride-based semiconductor substrate (eg, a GaN substrate). The substrate 11 has, for example, a rectangular upper surface. On the substrate 11, a first multilayer reflector 13 composed of semiconductor layers grown on the substrate 11 is formed.

[0032] The first multilayer reflector 13 is a semiconductor multilayer reflector in which a low-refractive-index semiconductor thin film having an AlInN composition and a high-refractive-index semiconductor thin film having a GaN composition and having a refractive index higher than that of the low-refractive-index semiconductor thin film are alternately stacked. In other words, the first multilayer reflector 13 is a distributed Bragg reflector (DBR) made of semiconductor materials. For example, a buffer layer having a GaN composition is provided on the upper surface of the substrate 11, and the high-refractive-index semiconductor thin film and the low-refractive-index semiconductor thin film are alternately formed on the buffer layer to form the first multilayer reflector 13.

[0033] Note that the upper surface of the substrate 11 (i.e., the surface on which the buffer layer having a GaN composition is provided) is preferably a C-plane or a surface within 0.5° offset from the C-plane. This is to provide, for example, satisfactory crystallinity of the semiconductor structure layer 15, which will be described later.

[0034] The semiconductor structure layer 15 is a stacked structure composed of multiple semiconductor layers formed on the first multilayer reflector 13. The semiconductor structure layer 15 includes 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.

[0035] The n-type semiconductor layer 17 is a semiconductor layer formed on the first multilayer reflector 13. The n-type semiconductor layer 17 is a semiconductor layer having a GaN composition and doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower portion 17A and a columnar upper portion 17B disposed on the lower portion 17A. Specifically, for example, the n-type semiconductor layer 17 has a columnar upper portion 17B that protrudes from an upper 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.

[0036] The active layer 19 is a layer 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 .

[0037] The p-type semiconductor layer 21 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.

[0038] N-electrode 23 is a metal electrode provided on upper surface 17S of lower portion 17A of n-type semiconductor layer 17 and electrically connected to n-type semiconductor layer 17. N-electrode 23 is formed in a ring shape to surround upper portion 17B of n-type semiconductor layer 17.

[0039] The insulating layer 25 is a layer composed of an insulator formed on the p-type semiconductor layer 21. The insulating layer 25 is formed, for example, from a material (e.g., SiO2) having a lower refractive index than the material forming the p-type semiconductor layer 21. The insulating layer 25 is formed in a ring shape on the p-type semiconductor layer 21 and has an opening (not shown) in the center that exposes the p-type semiconductor layer 21.

[0040] P electrode 27 is a metal electrode formed on insulating layer 25. P electrode 27 is electrically connected to the upper surface of p-type semiconductor layer 21 exposed from the above-mentioned opening of insulating layer 25 via a transparent electrode (not illustrated) made of a metal oxide thin film such as ITO or IZO.

[0041] The second multilayer reflector 29 is a dielectric multilayer reflector in which a low-refractive-index dielectric thin film made of Al2O3 and a high-refractive-index dielectric thin film made of Ta2O5 and having a higher refractive index than the low-refractive-index dielectric thin film are alternately stacked. In other words, the second multilayer reflector 29 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0042] Figure 2 1 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 upper surface shape, an active layer 19 having a circular upper surface, and a p-type semiconductor layer 21 (see FIG. Figure 1 On the p-type semiconductor layer 21, an insulating layer 25 and a p-electrode 27 are formed. On the p-electrode 27, a second multilayer reflector 29 is formed.

[0043] The insulating layer 25 has an opening 25H which is a circular opening of the insulating layer 25 for exposing the p-type semiconductor layer 21. Figure 2 As shown, the opening 25H is formed at the center of the insulating layer 25 when viewed from the upper side of the surface emitting laser 10, and the opening 25H is covered by the second multilayer reflector 29 when viewed from the upper side of the surface emitting laser 10. In other words, the opening 25H is covered by the second multilayer reflector 29 at the upper surface of the p-type semiconductor layer 21. In other words, the opening 25H is formed in a region of the insulating layer 25 that is opposite to the lower surface of the second multilayer reflector 29.

[0044] When viewed from the upper side of the surface emitting laser 10, the p-electrode 27 is formed at the center of the insulating layer 25 and has an opening 27H surrounding the opening 25H. That is, the opening 27H is larger than the opening 25H. For example, the opening 27H has a circular shape concentric with the shape of the opening 25H.

[0045] like Figure 2 As shown by the dashed line, a circular groove 15G is formed on the upper surface of the p-type semiconductor layer 21 (i.e., the upper surface of the semiconductor structure layer 15). The groove 15G is formed in the area outside the opening 25H and the opening 27H. In other words, the groove 15G is an annular groove when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0046] In the present embodiment, the groove 15G is formed so as to be covered by the second multilayer reflector 29 on the upper surface of the p-type semiconductor layer 21. That is, in the present embodiment, the groove 15G is formed at a position opposite to the lower surface of the second multilayer reflector 29.

[0047] Figure 3 It is along Figure 2 3-3 in FIG. 3 is a cross-sectional view of the surface emitting laser 10. As described above, the surface emitting laser 10 has the substrate 11 as a GaN substrate, and the first multilayer reflector 13 is formed on the substrate 11. Note that the lower surface of the substrate 11 may be applied with an AR coating.

[0048] The semiconductor structure layer 15 is formed on the first multilayer reflector 13. The semiconductor structure layer 15 is a stacked body made by sequentially forming an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21.

[0049] The groove 15G formed in the semiconductor structure layer 15 is formed around a protrusion 21P protruding from the center of the upper surface of the p-type semiconductor layer 21 and passes through the active layer 19 from the upper surface of the p-type semiconductor layer 21 to reach the n-type semiconductor layer 17 .

[0050] Therefore, in the surface emitting laser 10 according to Embodiment 1, the groove 15G is formed to pass through the active layer 19 . In other words, the groove 15G forms a gap in the active layer 19 .

[0051] The insulating layer 25 is formed to cover the upper surface of the p-type semiconductor layer 21 and the inner surface of the groove 15G. As described above, the insulating layer 25 is made of a material having a refractive index lower than that of the p-type semiconductor layer 21. The insulating layer 25 has an opening 25H that exposes the protrusion 21P. For example, Figure 2 As shown, the opening 25H has a circular shape. For example, the opening 25H and the protrusion 21P have similar shapes, and the inner surface of the opening 25H and the outer surface of the protrusion 21P are in contact with each other.

[0052] The light-transmitting electrode layer 31 is a layer made of a light-transmitting conductor, and is formed so as to cover the insulating layer 25 and the protrusion 21P exposed from the opening 25H of the insulating layer 25. That is, the light-transmitting electrode layer 31 is in electrical contact with the p-type semiconductor layer 21 in the region exposed through the opening 25H on the upper surface of the p-type semiconductor layer 21. The light-transmitting electrode layer 31 is formed, for example, of a metal oxide (e.g., ITO or IZO) having semi-transparency with respect to the emitted light from the active layer 19.

[0053] As described above, the p-electrode 27 is a metal electrode and is formed to cover the light-transmitting electrode layer 31. That is, the p-electrode 27 is in electrical contact with the light-transmitting electrode layer 31. Therefore, the p-electrode 27 is in electrical contact or connection with the p-type semiconductor layer 21 via the light-transmitting electrode layer 31 in the region exposed through the opening 25H on the upper surface of the p-type semiconductor layer 21. The p-electrode 27 has an opening 27H in the center that exposes the light-transmitting electrode layer 31. The opening 27H is wider than the opening 25H.

[0054] The second multilayer reflector 29 is formed to cover the opening 27H and the groove 15G. The second multilayer reflector 29 is formed to fill the space formed by the opening 27H and is in contact with the light-transmitting electrode layer 31. The second multilayer reflector 29 is formed to fill the space formed by the groove 15G.

[0055] In the surface emitting laser 10, the reflectivity of the first multilayer reflector 13 is slightly lower than that of the second multilayer reflector 29. Therefore, a portion of light resonating between the first multilayer reflector 13 and the second multilayer reflector 29 passes through the substrate 11 and the first multilayer reflector 13 to be taken out to the outside.

[0056] As described above, in the surface-emitting laser 10 according to Embodiment 1, the groove 15G is formed to pass through the active layer 19. In other words, the groove 15G forms a gap in the active layer 19. The groove 15G is formed after forming the semiconductor structure layer 15. Thereafter, the insulating layer 25 is formed before forming the light-transmitting electrode layer 31, the p-electrode 27, and the second multilayer reflector 29.

[0057] Therefore, after forming the semiconductor structure layer 15, the groove 15G reaching the active layer 19 is formed to form a space or gap in the direction along the plane of the active layer 19. This gap reduces the distortion generated in the layer direction of the active layer 19 or the layer surface direction of the semiconductor structure layer 15 when the active layer 19 is formed.

[0058] Specifically, when forming active layer 19, the crystal structure of active layer 19 is distorted due to the difference in lattice constants between InGaN and GaN forming the quantum well structure, thereby causing piezoelectric polarization and generating a piezoelectric field. The generation of this piezoelectric field reduces the probability of recombination of electrons and holes injected into the light-emitting layer, thereby reducing the internal quantum efficiency.

[0059] In the surface emitting laser 10, a groove 15G reaching the active layer 19 is formed in the semiconductor structure layer 15. It is believed that the gap formed by the groove reduces the distortion generated in the intra-layer direction of the active layer 19 during the growth of the active layer 19, and therefore the internal quantum efficiency in the active layer 19 is improved.

[0060] Here, the operation of the surface emitting laser 10 will be described. In the surface emitting laser 10, when a voltage is applied between the n-electrode 23 and the p-electrode 27, a current flows inside the semiconductor structure layer 15 as shown by the single-dot chain thick 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 reflector 13 and the second multilayer reflector 29 to reach a resonant state (oscillate in laser light).

[0061] In the surface-emitting laser 10, current is injected into the p-type semiconductor layer 21 only from the portion exposed through the opening 25H. Because the p-type semiconductor layer 21 is quite thin, current hardly diffuses in the in-plane direction (i.e., along the plane of the semiconductor structure layer 15) within the p-type semiconductor layer 21. Therefore, in the surface-emitting laser 10, current is supplied only to the area directly below the opening 25H in the active layer 19, and light is emitted only from this area. In other words, in the surface-emitting laser 10, the opening 25H has a current-limiting structure that limits the current supply range in the active layer 19.

[0062] As described above, in the embodiment, the reflectivity of the first multilayer reflector 13 is slightly lower than the reflectivity of the second multilayer reflector 29. Therefore, a portion of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 29 is transmitted through the substrate 11 and the first multilayer reflector 13 to be extracted to the outside. As a result, 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 the corresponding layer of the semiconductor structure layer 15.

[0063] The protrusion 21P of the p-type semiconductor layer 21 of the semiconductor structure layer 15 and the opening 25H of the insulating layer 25 define the emission center as the center of the light-emitting region in the active layer 19, thereby defining the central axis (emission center axis) AX of the resonator OC. The central axis AX of the resonator OC passes through the center of the protrusion 21P of the p-type semiconductor layer 21 and extends in a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0064] Note that the light-emitting region of the active layer 19 refers to, for example, a region of predetermined width within the active layer 19 from which light having a predetermined intensity or greater is emitted, and the center of the region is the light-emitting center. For example, the light-emitting region of the active layer 19 refers to a region within the active layer 19 into which a current having a predetermined density or greater is injected, and the center of the region 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 the corresponding layer of the semiconductor structure layer 15 is the central axis AX. The light-emitting center axis AX is a straight line extending along the resonator length direction of the resonator OC formed by the first multilayer reflector 13 and the second multilayer reflector 29. The central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 10.

[0065] Here, exemplary configurations of the first multilayer reflector 13, the semiconductor structure layer 15, and the second multilayer reflector 29 in the surface emitting laser 10, as well as exemplary dimensions of the groove 15G, will be described. In the embodiment, the first multilayer reflector 13 is made of a 1 μm GaN-based layer and 42 pairs of n-GaN and AlInN layers formed on the upper surface of the substrate 11.

[0066] The n-type semiconductor layer 17 is a 1580nm thick n-GaN layer. The active layer 19 comprises a multi-quantum well structure comprising four pairs of 4nm thick GaInN layers and a 5nm thick GaN layer. A Mg-doped AlGaN electron barrier layer is formed on the active layer 19, and a p-type semiconductor layer 21 comprising a 50nm thick p-GaN layer is formed thereon. The second multilayer reflector 29 is a stack of 10.5 pairs of Nb2O5 and SiO2. The resonant wavelength in this case is 440nm.

[0067] The groove 15G formed in the semiconductor structure layer 15 has an outer diameter of 8 μm, a depth of 120 nm, and a width of 2 μm. The light-transmitting electrode layer 31 formed on the semiconductor structure layer 15 is a layer made of 20 nm ITO, and the second multilayer reflector 29 is formed on the light-transmitting electrode layer 31 and the p-electrode 27 with a 40 nm Nb2O5 spacer layer interposed therebetween.

[0068] The back surface of the substrate 11 is a polished surface on which a two-layer AR coating of Nb2O5 and SiO2 is formed.

[0069] The p-type semiconductor layer 21 may have a thickness of 50 nm at the protrusion 21P and a thickness of 30 nm at other portions. That is, the p-type semiconductor layer 21 may have different thicknesses at the protrusion 21P and other regions. The upper surface of the insulating layer 25 is arranged at the same height as the upper surface of the protrusion 21P of the p-type semiconductor layer 21. This is merely an example.

[0070] The following describes the optical characteristics inside the surface emitting laser 10. As described above, in the surface emitting laser 10, the refractive index of the insulating layer 25 is lower than the refractive index of the p-type semiconductor layer 21. The layer thicknesses of the other layers between the first multilayer reflector 13 and the second multilayer reflector 29 are the same at any position within the plane as long as they are in the same layer.

[0071] Therefore, due to the refractive index difference between the p-type semiconductor layer 21 and the insulating layer 25, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 29, and corresponding to the resonant wavelength) in the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 29 of the surface emitting laser 10 is different in the cylindrical central area CA having the upper surface shape defined by the opening 25H and the tubular peripheral area PA around the central area CA.

[0072] Specifically, between the first multilayer reflector 13 and the second multilayer reflector 29, the equivalent refractive index of the peripheral region PA is lower than that of the central region. That is, the equivalent resonant wavelength of the central region CA is shorter than the equivalent resonant wavelength of the peripheral region PA. Note that, as described above, the region that emits light in the active layer 19 is the region directly below the opening 25H. In other words, the region that emits light in the active layer 19 is the portion that overlaps with the central region CA of the active layer 19, in other words, the region within the opening 25H of the insulating layer 25 in a top view.

[0073] Therefore, in the surface-emitting laser 10, 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 are formed. This reduces optical losses caused by the diffusion (radiation) of standing waves within the central region CA into the peripheral region PA. In other words, a large amount of light remains in the central region CA, in which state the laser light LB is extracted to the outside. Therefore, a large amount of light is concentrated in the central region CA in the peripheral area of the light-emitting center axis AX of the resonator OC, ensuring the generation and emission of high-output and high-density laser light.

[0074] As described above, in the surface emitting laser 10 of the embodiment, the groove 15G that reaches from the upper surface of the p-type semiconductor layer 21 to the active layer 19 is formed in the semiconductor structure layer 15. By virtue of the groove 15G, the distortion generated in the intralayer direction of the active layer 19 is reduced in the active layer 19, and the internal quantum efficiency in the active layer 19 is improved, thereby ensuring improved luminous efficiency.

[0075] (Manufacturing Method)

[0076] The following describes an example method for manufacturing the surface-emitting laser 10. First, a c-plane n-GaN substrate is prepared as the substrate 11, and an n-GaN layer (1 μm thick) is formed on the substrate by metal-organic vapor phase epitaxy (MOVPE) as a base layer. Subsequently, a pair of n-GaN / AlInN layers is formed on the base layer 42 to form the first multilayer reflector 13.

[0077] Next, an n-type semiconductor layer 17 is formed by forming n-GaN doped with Si (with a layer thickness of 1580 nm) on the first multilayer reflector 13, and then an active layer 19 is formed by stacking four pairs of layers made of GaInN (with a layer thickness of 4 nm) and GaN (with a layer thickness of 5 nm) on the n-type semiconductor layer 17.

[0078] Next, an electron barrier layer (not shown) composed of Mg-doped AlGaN is formed on the active layer 19 , and then a p-GaN layer (50 nm thick) is formed on the electron barrier layer to form the p-type semiconductor layer 21 .

[0079] Next, the periphery of the p-type semiconductor layer 21, the active layer 19, and the n-type semiconductor layer 17 is etched to form a mesa shape so that the upper surface 17S of the n-type semiconductor layer 17 is exposed in the periphery. In other words, in this process, the process is completed. Figure 1 The semiconductor structure layer 15 includes a columnar portion made of an n-type semiconductor layer 17 , an active layer 19 and a p-type semiconductor layer 21 .

[0080] Next, a groove 15G is formed by etching from the upper surface of the p-type semiconductor layer 21 through the active layer 19. Subsequently, the insulating layer 25 is formed by forming a SiO2 film on the semiconductor structure layer 15 and removing a portion of the film to form an opening 25H.

[0081] Next, a 20 nm thick ITO film is formed on the insulating layer 25 to form the light-transmitting electrode layer 31 , and then an Au film is formed on the light-transmitting electrode layer 31 and the upper surface 17S of the n-type semiconductor layer 17 to form the p-electrode 27 and the n-electrode 23 .

[0082] Next, a 40 nm Nb2O5 film is formed as a spacer layer (not shown) on the p-electrode 27 and the light-transmitting electrode layer 31, and then a second multilayer reflector 29 is formed by forming 10.5 pairs of thin films made of Nb2O5 / SiO2 layers on the spacer layer.

[0083] Next, the back surface of the substrate 11 is polished, and then, by forming an AR coating made of Nb2O5 / SiO2 on the polished surface, the surface emitting laser 10 is completed.

[0084] Implementation Method 2

[0085] A surface emitting laser 40 as Embodiment 2 of the present invention is described below. The surface emitting laser 40 differs from the surface emitting laser 10 in that the groove 15G of the semiconductor structure layer 15 is formed outside the second multilayer reflector 29 in a plan view.

[0086] Figure 4 A perspective view of a surface emitting laser 40 according to Embodiment 2 is illustrated. Figure 5 A cross-sectional view of the surface emitting laser 40 cut along a cross section similar to that shown in the above-described embodiment 1 is illustrated. Figure 4 and Figure 5 As shown, in the surface emitting laser 40, the groove 15G of the semiconductor structure layer 15 is formed outside the second multilayer reflector 29 on the upper surface of the p-type semiconductor layer 21. That is, on the upper surface of the p-type semiconductor layer 21, the groove 15G is exposed from the second formation region.

[0087] A groove structure 27G inheriting the shape of the groove 15G is formed on the upper surface of the p-electrode 27 formed on the p-type semiconductor layer 21 via the insulating layer 25. That is, the groove structure 27G is formed on the groove 15G in a shape substantially the same as that of the groove 15G.

[0088] like Figure 5 As shown, in surface-emitting laser 40, similar to surface-emitting laser 10, a groove 15G is formed in semiconductor structure layer 15, extending from the upper surface of p-type semiconductor layer 21 to active layer 19. This groove 15G reduces distortion within active layer 19, improving the internal quantum efficiency of active layer 19 and thereby ensuring improved luminous efficiency. In surface-emitting laser 40, there is no need to form second multilayer reflector 29 on p-electrode 27. In other words, since second multilayer reflector 29 does not need to be formed across a level difference, the accuracy of forming second multilayer reflector 29 can be further improved.

[0089] Implementation 3

[0090] The following describes a surface emitting laser 50 as Embodiment 3 of the present invention. The surface emitting laser 50 is different from the surface emitting laser 10 in that an electrode connected to the n-type semiconductor layer 17 is provided on the back surface of a substrate 51 or the like.

[0091] Figure 6 : is a perspective view of a surface emitting laser 50. The substrate 51 is a substrate having a rectangular upper surface shape, for example. The substrate 51 is a substrate made of a conductive material such as n-GaN. On the back surface of the substrate 51, an n-electrode 52 made of metal is formed.

[0092] On substrate 51, a first multilayer reflector 53 is formed, which is composed of semiconductor layers grown on substrate 51. The first multilayer reflector 53 is a conductive semiconductor multilayer reflector in which low-refractive-index semiconductor thin films having an AlInN composition and high-refractive-index semiconductor thin films having a GaN composition and a refractive index higher than that of the low-refractive-index semiconductor thin films are alternately stacked. In other words, the first multilayer reflector 53 is a distributed Bragg reflector (DBR) made of semiconductor materials. For example, a buffer layer having a GaN composition is provided on the upper surface of substrate 51, and the high-refractive-index semiconductor thin films and low-refractive-index semiconductor thin films are alternately formed on the buffer layer to form the first multilayer reflector 53.

[0093] The semiconductor structure layer 15 is a stacked structure composed of multiple semiconductor layers formed on the first multilayer reflector 53. The semiconductor structure layer 15 includes an n-type semiconductor layer (first semiconductor layer) 17 formed on the first multilayer reflector 53, 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.

[0094] The n-type semiconductor layer 17 is a semiconductor layer formed on the first multilayer reflector 53. The n-type semiconductor layer 17 is a semiconductor layer having a GaN composition and doped with Si as an n-type impurity.

[0095] The active layer 19 is a layer formed on 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 50 , light is generated in the active layer 19 .

[0096] The p-type semiconductor layer 21 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.

[0097] The insulating layer 25 is a layer composed of an insulator formed on the p-type semiconductor layer 21. The insulating layer 25 is formed, for example, from a material (e.g., SiO2) having a lower refractive index than the material forming the p-type semiconductor layer 21. The insulating layer 25 is formed in a ring shape on the p-type semiconductor layer 21 and has an opening (not shown) in the center that exposes the p-type semiconductor layer 21.

[0098] P electrode 27 is a metal electrode formed on insulating layer 25. P electrode 27 is electrically connected to the upper surface of p-type semiconductor layer 21 exposed from the above-mentioned opening of insulating layer 25 via a transparent electrode (not illustrated) made of a metal oxide thin film such as ITO or IZO.

[0099] The second multilayer reflector 29 is a dielectric multilayer reflector in which a low-refractive-index dielectric thin film made of Al2O3 and a high-refractive-index dielectric thin film made of Ta2O5 and having a higher refractive index than the low-refractive-index dielectric thin film are alternately stacked. In other words, the second multilayer reflector 29 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0100] Figure 7 is a top view of the surface emitting laser 50. As described above, the surface emitting laser 50 has a semiconductor structure layer 15 including an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 formed on a substrate 51 having a rectangular upper surface shape (see FIG. Figure 6On the p-type semiconductor layer 21, an insulating layer 25 and a p-electrode 27 are formed. On the p-electrode 27, a second multilayer reflector 29 is formed.

[0101] The insulating layer 25 has an opening 25H which is a circular opening of the insulating layer 25 for exposing the p-type semiconductor layer 21. Figure 7 As shown, the opening 25H is formed at the center of the insulating layer 25 when viewed from the upper surface of the surface emitting laser 10, and the opening 25H is covered by the second multilayer reflector 29 when viewed from the upper surface of the surface emitting laser 10. In other words, the opening 25H is covered by the second multilayer reflector 29 on the upper surface of the p-type semiconductor layer 21. In other words, the opening 25H is formed in a region of the upper surface of the p-type semiconductor layer 21 that is opposite to the lower surface of the second multilayer reflector 29.

[0102] When viewed from the upper surface of the surface-emitting laser 50, the p-electrode 27 is formed at the center of the insulating layer 25 and has an opening 27H surrounding the opening 25H. That is, the opening 27H is larger than the opening 25H. For example, the opening 27H has a circular shape concentric with the shape of the opening 25H.

[0103] like Figure 7 As shown by the dashed line, a circular groove 15G is formed on the upper surface of the p-type semiconductor layer 21 (i.e., the upper surface of the semiconductor structure layer 15). The groove 15G is formed in the area outside the opening 25H and the opening 27H. In this embodiment, the groove 15G is formed so that the upper surface of the p-type semiconductor layer 21 is covered by the second multilayer reflector 29. In other words, in this embodiment, the groove 15G is formed at a position opposite the lower surface of the second multilayer reflector 29.

[0104] Figure 8 It is along Figure 7 8 is a cross-sectional view of the surface emitting laser 50 taken along line 8 - 8 in FIG. As described above, the surface emitting laser 50 has the substrate 51 as an n-GaN substrate, and the first multilayer reflector 53 is formed on the substrate 51 .

[0105] A protrusion 51P is formed on the back surface 51A of the substrate 51. When viewed from the normal direction of the substrate 51, the protrusion 51P is formed in the area corresponding to the protrusion 21P. The protrusion 51P is a protrusion left after the back surface 51A is polished and the peripheral area of the protrusion 51P is removed by dry etching. Therefore, the upper surface of the protrusion 51P is a polished surface, and the peripheral area of the protrusion 51P on the back surface 51A of the substrate 51 has a surface that is dry-etched to the polished surface. The n-electrode 52 is formed in the peripheral area of the protrusion 51P on the back surface 51A of the substrate 51 (i.e., the area other than the protrusion 51P). Because the protrusion 51P has an upper surface that serves as an opening, the emitted light is emitted to the outside through the opening, so that the n-electrode 52 does not block the emitted light. In other words, the protrusion 51P has a structure that protrudes from the opening of the n-electrode 52.

[0106] The anti-reflection layer 55 is formed so as to cover the protrusion 51P in the back surface 51A of the substrate 51. The anti-reflection layer 55 is composed of, for example, a dielectric multilayer thin film and has a structure in which, for example, Ta2O5 layers and SiO2 layers are alternately stacked multiple times. The anti-reflection layer 55 is a so-called AR coating that suppresses reflection of light emitted from the active layer 19 at the upper surface of the protrusion 51P of the substrate 51.

[0107] A semiconductor structure layer 15 is formed on the first multilayer reflector 53. The semiconductor structure layer 15 is a stacked structure made by sequentially forming an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21.

[0108] The p-type semiconductor layer 21 has a protrusion 21P protruding upward in a columnar shape at the center of the upper surface of the p-type semiconductor layer 21. The groove 15G formed in the semiconductor structure layer 15 is formed to surround the protrusion 21P of the upper surface of the p-type semiconductor layer 21 and pass through the active layer 19 from the upper surface of the p-type semiconductor layer 21 to reach the n-type semiconductor layer 17.

[0109] Therefore, in the surface emitting laser 50 according to Embodiment 3, similarly to the surface emitting lasers 10 and 40 in the above-described embodiments, the groove 15G is formed to pass through the active layer 19. In other words, the groove 15G forms a gap in the active layer 19.

[0110] The insulating layer 25 is formed to cover the upper surface of the p-type semiconductor layer 21 and the inner surface of the groove 15G. As described above, the insulating layer 25 is made of a material having a refractive index lower than that of the p-type semiconductor layer 21. The insulating layer 25 has an opening 25H that exposes the protrusion 21P. For example, Figure 7 As shown, the opening 25H has a circular shape. For example, the opening 25H and the protrusion 21P have similar shapes, and the inner surface of the opening 25H and the outer surface of the protrusion 21P are in contact with each other.

[0111] The light-transmitting electrode layer 31 is a layer made of a light-transmitting conductor, and is formed to cover the insulating layer 25 and the protrusion 21P exposed from the opening 25H of the insulating layer 25. The light-transmitting electrode layer 31 is formed of, for example, a metal oxide (e.g., ITO or IZO) having translucency with respect to the emitted light from the active layer 19.

[0112] As described above, the p-electrode 27 is a metal electrode and is formed to cover the light-transmitting electrode layer 31. The p-electrode 27 has an opening 27H at the center that exposes the light-transmitting electrode layer 31. The opening 27H is wider than the opening 25H.

[0113] The second multilayer reflector 29 is formed to cover the opening 27H and the groove 15G. The second multilayer reflector 29 is formed to fill the space formed by the opening 27H and is in contact with the light-transmitting electrode layer 31. The second multilayer reflector 29 is formed to fill the space formed by the groove 15G.

[0114] In the surface emitting laser 50, the reflectivity of the first multilayer reflector 53 is slightly lower than that of the second multilayer reflector 29. Therefore, a portion of light resonating between the first multilayer reflector 53 and the second multilayer reflector 29 is transmitted through the first multilayer reflector 53 and the substrate 51 and is taken out to the outside.

[0115] As described above, in the surface-emitting laser 50 according to Embodiment 3, the groove 15G is formed so as to pass through the active layer 19. In other words, the groove 15G forms a gap in the active layer 19. The groove 15G is formed after forming the semiconductor structure layer 15. Thereafter, the insulating layer 25 is formed before forming the light-transmitting electrode layer 31, the p-electrode 27, and the second multilayer reflector 29.

[0116] Therefore, after forming the semiconductor structure layer 15, the groove 15G reaching the active layer 19 is formed to form a gap in the direction in the plane of the active layer 19. This gap reduces the distortion generated in the intra-layer direction of the active layer 19 or the in-plane direction of the semiconductor structure layer 15 when the active layer 19 is formed.

[0117] Specifically, as described above, when active layer 19 is formed, the active layer 19 has a distorted crystal structure due to the difference in lattice constants between InGaN and GaN forming the quantum well structure. This leads to piezoelectric polarization and causes a piezoelectric field. This piezoelectric field reduces the probability of recombination of electrons and holes injected into the light-emitting layer, thereby reducing the internal quantum efficiency.

[0118] In the surface emitting laser 50, a groove 15G reaching the active layer 19 is formed in the semiconductor structure layer 15. The gap formed by the groove is considered to reduce the distortion generated in the intra-layer direction of the active layer 19 during the growth of the active layer 19, thereby improving the internal quantum efficiency in the active layer 19.

[0119] Here, the operation of the surface emitting laser 50 will be described. In the surface emitting laser 50, when a voltage is applied between the n-electrode 52 and the p-electrode 27, a current flows inside the semiconductor structure layer 15 as shown by a single-dot chain thick 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 reflector 53 and the second multilayer reflector 29 to reach a resonant state (oscillate in laser light).

[0120] In the surface-emitting laser 50, similar to the case of the surface-emitting laser 10, current is injected into the p-type semiconductor layer 21 only from the portion exposed through the opening 25H. Since the p-type semiconductor layer 21 is quite thin, current hardly diffuses in the in-plane direction (i.e., along the plane of the semiconductor structure layer 15) within the p-type semiconductor layer 21. Therefore, in the surface-emitting laser 50, current is supplied only to the area directly below the opening 25H in the active layer 19, and light is emitted only from this area. In other words, in the surface-emitting laser 50, the opening 25H has a current-limiting structure that limits the current supply range in the active layer 19.

[0121] As described above, in the embodiment, the reflectivity of the first multilayer reflector 53 is slightly lower than the reflectivity of the second multilayer reflector 29. Therefore, a portion of the light resonating between the first multilayer reflector 53 and the second multilayer reflector 29 is transmitted through the first multilayer reflector 53 and the substrate 51 and is extracted to the outside through the protrusion 51P. Therefore, the surface-emitting laser 50 emits light in a direction perpendicular to the lower surface of the substrate 51 and the in-plane direction of the corresponding layer of the semiconductor structure layer 15.

[0122] Since the light emission center axis AX and the like are the same as those of the surface emitting laser 10 according to Embodiment 1, description of the light emission center axis AX and the like will be omitted.

[0123] The following describes exemplary configurations of the first multilayer reflector 53, the semiconductor structure layer 15, and the second multilayer reflector 29 in the surface emitting laser 50, as well as exemplary dimensions of the groove 15G. In the embodiment, the first multilayer reflector 53 is made of a 1 μm GaN-based layer and 42 pairs of n-GaN and AlInN layers formed on the surface of the substrate 51.

[0124] The n-type semiconductor layer 17 is a 1580nm thick Si-doped n-GaN layer. The active layer 19 comprises an active layer having a multi-quantum well structure, stacking four pairs of 4nm GaInN layers and 5nm GaN layers. An Mg-doped AlGaN electron barrier layer is formed on the active layer 19, and a 50nm thick p-GaN layer is formed on top of the active layer 19. The second multilayer reflector 29 is a stack of 10.5 pairs of Nb2O5 and SiO2.

[0125] The groove 15G formed in the semiconductor structure layer 15 has an outer diameter of 20 μm, a depth of 120 nm, and a width of 1 μm. The light-transmitting electrode layer 31 formed on the semiconductor structure layer 15 is a layer made of 20 nm ITO, and the second multilayer reflector 29 is formed on the light-transmitting electrode layer 31 and the p-electrode 27 with a 40 nm Nb2O5 spacer layer interposed therebetween.

[0126] The p-type semiconductor layer 21 may have a thickness of 50 nm at the protrusion 21P and a thickness of 30 nm at other portions. That is, the p-type semiconductor layer 21 may have different thicknesses at the protrusion 21P and other regions. The upper surface of the insulating layer 25 is arranged at the same height as the upper surface of the protrusion 21P of the p-type semiconductor layer 21. This is merely an example.

[0127] Since the optical characteristics are similar to those of the surface emitting laser 10 , description of the optical characteristics inside the surface emitting laser 50 is omitted.

[0128] As described above, similar to the surface emitting laser 10 according to Embodiment 1, in the surface emitting laser 50 of the embodiment, the groove 15G that reaches from the upper surface of the p-type semiconductor layer 21 to the active layer 19 is formed in the semiconductor structure layer 15. With this groove 15G, the distortion generated in the intra-layer direction of the active layer 19 is reduced in the active layer 19, the internal quantum efficiency in the active layer 19 is improved, thereby ensuring improved luminous efficiency.

[0129] Implementation 4

[0130] The following describes a surface emitting laser 60 according to Embodiment 4 of the present invention. The surface emitting laser 60 differs from the surface emitting laser 50 in that the groove 15G of the semiconductor structure layer 15 is formed outside the second multilayer reflector 29 in a plan view.

[0131] Figure 9 A perspective view of a surface emitting laser 60 according to Embodiment 4 is illustrated. Figure 10 A cross-sectional view of the surface emitting laser 60 cut along a cross section similar to that shown in the above-described embodiment 3 is illustrated. Figure 9and Figure 10 As shown, in the surface emitting laser 60, the groove 15G of the semiconductor structure layer 15 is formed outside the second multilayer reflector 29 on the upper surface of the p-type semiconductor layer 21. That is, on the upper surface of the p-type semiconductor layer 21, the groove 15G is exposed outside the second multilayer reflector.

[0132] On the upper surface of the p-type semiconductor layer 21 formed via the insulating layer 25, a groove structure 27G is formed by inheriting the shape of the groove 15G. That is, the groove structure 27G is formed on the groove 15G in a shape substantially the same as that of the groove 15G. Figure 10 As shown, in the surface-emitting laser 60, similar to the surface-emitting laser 10, a groove 15G is formed in the semiconductor structure layer 15, extending from the upper surface of the p-type semiconductor layer 21 to the n-type semiconductor layer 17. This groove 15G reduces the distortion generated in the active layer 19 in the layer direction, improving the internal quantum efficiency (e.g., slope efficiency) in the active layer 19, thereby ensuring improved luminous efficiency. Note that in the surface-emitting laser 60, there is no need to form the second multilayer reflector 29 on the p-electrode 27. In other words, since the second multilayer reflector 29 does not need to be formed across the level difference, the formation accuracy of the second multilayer reflector 29 can be further improved.

[0133] (Modification of Semiconductor Structure Layer)

[0134] In the above embodiment, the case where the groove 15G formed in the semiconductor structure layer 15 has a circular ring shape has been described. However, the groove 15G may have other shapes.

[0135] For example, Figure 11 As shown, the groove 15G may be a groove structure including a discontinuously formed recessed portion GV (or groove GV) in the annular region CR (the region surrounded by a single-dot chain line in the figure) rather than a perfect ring. In other words, the groove 15G may have a recessed structure including a plurality of recessed portions. In other words, the groove 15G may have a discontinuously formed annular structure. For example, the groove 15G may have a discontinuously formed annular structure surrounding the region exposed by the opening 25H on the upper surface of the p-type semiconductor layer 21.

[0136] Note that when groove 15G is formed by multiple recesses, in order to uniformly reduce distortion of the active layer 19, the multiple recesses are preferably formed in two or more directions when viewed from the aforementioned emission center axis AX. That is, when groove 15G is formed by multiple recesses, in a top view of the surface-emitting laser 10, the recesses are preferably formed in two or more directions when viewed from the light-emitting region containing the emission center axis AX, with the light-emitting region sandwiched between the recesses. In order to uniformly reduce distortion of the active layer 19, the recesses forming groove 15G are also preferably arranged rotationally symmetrically with respect to the emission center axis AX. In other words, the recesses forming groove 15G are preferably arranged rotationally symmetrically when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0137] Note that, as described above, the polarization of light emitted from the surface emitting laser of the above embodiment can also be controlled by changing the shape of the groove 15G (for example, by forming the groove 15G with a plurality of recessed portions) to reduce the degree of anisotropy of the active layer 19 twist. Figure 11 In the case of the surface emitting laser shown in , when viewed from the opening 25H (i.e., from the central area CA), the distortion of the active layer 19 is further reduced in the direction in which the depressed portion GV forming the groove 15G exists. This allows for improvement of the optical gain in the direction in which the depressed portion GV forming the groove 15G exists when viewed from the opening 25H (left-right direction in the figure), and allows for acquisition of a large amount of light with a polarization direction along this direction.

[0138] In order to reduce the distortion of the above-mentioned active layer 19 and to make the above-mentioned distortion less anisotropic so as to control the polarization of the light emitted from the surface emitting laser, it is preferred to form a groove 15G near the light-emitting center axis AX. Therefore, for example, as with the surface emitting laser 10 according to embodiment 1 and the surface emitting laser 50 according to embodiment 3, it is preferred that the groove 15G is formed below the second multilayer reflector 29. Note that in order to reduce the distortion of the active layer 19, the groove 15G or the plurality of grooves GV are preferably formed at a distance of, for example, within 50 μm from the outer edge of the light-emitting region. That is, the annular region CR where the groove 15G is formed is preferably set at a distance of within 50 μm from the outer edge of the light-emitting region or the central region CA.

[0139] In the above embodiment, although circular laser light is emitted from the surface-emitting laser as an example, a configuration that emits ring-shaped laser light may be employed. Specifically, when viewed from above in the surface-emitting laser of the above embodiment, a circular insulating layer may be formed at the center of the opening 25H of the insulating layer 25. In other words, the insulating layer 25 may have a ring-shaped aperture, and through this ring-shaped aperture, the upper surface of the p-type semiconductor layer 21 may be exposed, and the light-transmitting electrode layer 31 and the p-type semiconductor layer 21 may be in electrical contact with each other.

[0140] In this case, an inner recess IG may be formed inside the groove 15G of the semiconductor structure layer 15 . Similar to the groove 15G, the inner recess IG also passes through the active layer 19 from the upper surface of the p-type semiconductor layer 21 .

[0141] Figure 12 1 is a top view of a modified example in which a columnar inner recess IG is formed in the surface emitting laser 10 according to Embodiment 1. FIG. Figure 13 1 is a top view of a modified example in which a cylindrical inner depressed portion IG is formed in the surface emitting laser 10 according to Embodiment 1. Therefore, forming the inner depressed portion IG allows further reduction in the distortion of the active layer 19 .

[0142] Implementation 5

[0143] The following describes a surface-emitting laser 70 according to Embodiment 5 of the present invention. The surface-emitting laser 70 of this embodiment differs from the surface-emitting laser 10 according to Embodiment 1 in that a C-plane GaN substrate tilted (offset) from the c-plane in the m-plane (1-100) direction is used as the substrate 11, and in that the groove 15G is different. Note that the surface-emitting laser 70 can be formed by a manufacturing method similar to that of the surface-emitting laser 10 according to Embodiment 1.

[0144] Figure 14 It is a perspective view when viewed from the front and obliquely above of the surface emitting laser 70 . Figure 15 70 is a top view of the surface emitting laser 70. As described above, the surface emitting laser 70 has the substrate 11, the upper surface of which is a surface shifted from the c-plane of the GaN crystal plane to the m-plane.

[0145] Specifically, the upper surface of the substrate 11 is a surface inclined at 0.4° from the c-plane toward the m-plane. In other words, the substrate 11 is a GaN substrate having a main surface inclined at 0.4° from the c-plane toward the m-plane. Figure 15, axis AX1 is an axis along the m-axis direction perpendicular to the m-plane of substrate 11 and within a plane including the upper surface of substrate 11 , and axis AX2 is an axis perpendicular to axis AX1 and within a plane including the upper surface of substrate 11 .

[0146] In the surface-emitting laser 70, the groove 15G is composed of two grooves GV extending parallel to each other along the axis AX2. In other words, the groove 15G is composed of two grooves GV extending across the axis AX2. That is, along the direction along the axis AX1, the grooves 15G are arranged so as to sandwich the opening 25H of the insulating layer 25 that overlaps the light-emitting region of the active layer 19.

[0147] On the upper surface of the p-type semiconductor layer 21, each of the grooves GV extends upward from the area directly below the second multilayer reflector 29 to the outside of the second multilayer reflector 29. In other words, both end portions of the corresponding groove GV are provided outside the second multilayer reflector 29. Therefore, the groove structure 27G having a shape similar to that of the groove 15G also extends upward from the area directly below the second multilayer reflector 29 to the outside of the second multilayer reflector 29.

[0148] In the surface emitting laser 70, no groove GV is formed in the region along the axis AX2 when viewed from the opening 25H. That is, in the surface emitting laser 70, the groove GV is formed only in the region along the axis AX1 when viewed from the opening 25H.

[0149] The following describes the polarization direction of light emitted from the surface-emitting laser 70. 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 70 of this embodiment, the optical gain becomes greater when the polarization direction is in the m-axis direction than in the other directions. Therefore, laser light with a polarization direction in the m-axis direction tends to oscillate easily. Therefore, a large amount of light emitted from the central area CA of the surface-emitting laser 70 has a polarization direction in the m-axis direction.

[0150] Furthermore, as described above, the surface emitting laser 70 has a groove structure 27G in which the grooves GV are formed only in the region along the direction of the axis AX1 along the m-axis direction when viewed from the opening 25H. Therefore, in the direction in which the grooves GV are formed, that is, in the direction along the axis AX1 when viewed from the opening 25H, that is, in the central region CA as the light emitting region, the distortion of the active layer 19 is significantly reduced.

[0151] According to the surface-emitting laser 70, this increases the gain around the direction along the axis AX1 along the m-axis direction, thereby allowing a large amount of laser light having a polarization direction along the m-axis direction to be obtained in addition to the above-mentioned offset effect. Note that in order to obtain the above-mentioned offset effect, the upper surface of the substrate 11 is preferably tilted from the c-plane toward the m-plane in a range of 0.1° to 0.5°.

[0152] Although the surface emitting laser 70 is formed by growing the semiconductor structure layer 15 by a method similar to that of the surface emitting laser 10 according to the above-described embodiment 1, by performing heat treatment after forming the groove 15G, a surface emitting laser capable of obtaining a larger amount of laser light having a polarization direction in the direction along the m-axis direction can be obtained.

[0153] Specifically, after forming the groove 15G, before forming the insulating layer 25, heat treatment is performed at a temperature of, for example, 500° C., which enables formation of a surface emitting laser capable of obtaining a larger amount of laser light having a polarization direction along the m-axis direction. This is considered to be because the heat treatment improves the conductivity in the current path in the direction along the axis AX1 among the current paths to the active layer 19 in the p-type semiconductor layer 21.

[0154] The improvement in conductivity in the current path in the direction along the axis AX1 is due to the desorption of hydrogen from p-GaN forming the p-type semiconductor layer 21 exposed in the groove 15G, and thus the conductivity of the p-type semiconductor layer 21 around the portion exposed from the groove 15G is improved.

[0155] In addition to increasing the polarization direction of laser light along the axis AX due to reducing the distortion of the active layer 19 on the axis AX1 and the offset of the growth surface of the substrate 11, performing the above-mentioned heating treatment allows further increasing the polarization direction of laser light along the axis AX in the surface emitting laser 70.

[0156] Note that the heat treatment performed after forming groove 15G and before forming insulating layer 25 only needs to be performed at a temperature at which hydrogen is desorbed from p-GaN forming p-type semiconductor layer 21. Specifically, for example, heat treatment at 400°C or higher is preferably performed to desorb hydrogen from p-GaN.

[0157] In order to enhance the effect of increasing the polarization direction of light along the axis AX, it is preferable to form the groove 15G symmetrically with respect to the axis AX2. The groove 15G preferably has a shape along the outer edge of the light emitting region. Therefore, also in the surface emitting laser 70, as Figure 16 As shown, it is preferred to form a Figure 11 The groove 15G is shown in an arc shape.

[0158] In the above embodiment, in order to reduce the distortion of the active layer 19, the groove 15G is preferably formed in a circular region 50 μm or less from the outer edge of the light-emitting region. In order to control the polarization direction of the above-mentioned laser light, the groove 15G is preferably formed in a region where the luminous intensity of the active layer is 1.8% or less of the peak luminous intensity of the active layer when the surface-emitting laser is observed from above.

[0159] In other words, the region where the groove 15G is formed (eg, Figure 16 The annular region CR) is preferably a region that is 50 μm or less from the outer edge of the light emitting region and is a region where the light emission intensity of the active layer is 1.8% or less of the light emission peak of the active layer when the surface emitting laser is observed from above.

[0160] This is because the confinement effect of the groove 15G that confines the light emitted from the active layer 19 to the inside of the region where the groove 15G is formed is not produced. Compared with the case where the confinement effect is not produced, the confinement effect causes the polarization direction to fluctuate in directions other than the direction along the axis AX1, so it is preferable not to produce the confinement effect.

[0161] Note that groove 15G is preferably formed so as not to overlap opening 25H in the direction along axis AX2. Therefore, the twist reduction of active layer 19 in the direction along axis AX2 is suppressed, and the generation of light having a polarization direction in the direction along axis AX2 is reduced.

[0162] In other words, increasing the difference in twist reduction between the direction along axis AX1 and the direction along axis AX2 in active layer 19 to increase the anisotropy of twist reduction allows increasing the proportion of light having a polarization direction in the direction along axis AX1 in the light emitted from surface emitting laser 70.

[0163] Note that, although the case where the upper surface of the substrate 11 is shifted from the c-plane to the m-plane, which is a non-polar plane, has been described in Embodiment 5, the upper surface of the substrate 11 may be shifted from the c-plane to the a-plane, which is another non-polar plane. In this case, in the surface-emitting laser 70 according to Embodiment 5, the axis AX1 becomes the axis along the a-axis, and when viewed from the opening 25H, the groove GV is formed in a region in the direction along the axis AX1.

[0164] As described above, the surface-emitting laser according to Embodiment 5 can obtain light including a large amount of linearly polarized light having a polarization direction in a specific direction, that is, light with aligned polarization directions. Therefore, since the emitted light from the surface-emitting laser 70 according to Embodiment 5 itself is light with aligned polarization directions, it is possible to minimize light loss caused by using an optical system such as liquid crystal or a polarizing element, and it is easy to obtain light with a specific polarization direction.

[0165] For example, the surface emitting laser according to Embodiment 5 (eg, the surface emitting laser 70 ) is useful in the case of obtaining sensor light (eg, light used for communication such as Li-Fi) that requires alignment of polarization directions.

[0166] In the above embodiment, although the insulating layer 25 is provided to generate current confinement by forming an insulating region and to form a region with a low refractive index, instead of providing the insulating layer 25, current confinement can be generated and the region with a low refractive index can be generated by another method. For example, by etching the surface of the semiconductor structure layer 15 provided with the insulating layer 25 in the above embodiment, the insulating region and the region with a low refractive index can be formed. By implanting ions on the surface of the semiconductor structure layer 15 provided with the insulating layer 25, the insulating region and the region with a low refractive index can be formed, producing an effect similar to that of forming the insulating layer 25 in the above embodiment. When performing ion implantation, for example, B ions, Al ions, or oxygen ions are implanted into the semiconductor structure layer 15.

[0167] In the surface emitting laser element as described above, the semiconductor structure layer 15 can be formed by sequentially stacking a p-GaN layer, an active layer similar to the active layer of the above embodiment, and an n-GaN layer on the n-type semiconductor layer 17. In this case, in the p-GaN layer, the active layer is formed by the n-GaN layer. + -GaN layer and p + A tunnel junction layer composed of GaN may be formed in a portion overlapping the central region CA of the above embodiment in a region in contact with the n-type semiconductor layer 17 in a plan view.

[0168] In the semiconductor structure layer having this structure, current flows from the p-GaN layer to the n-type semiconductor layer 17 only from a portion of the tunnel junction layer. Therefore, current confinement similar to that in the case of forming the insulating layer 25 described above can be generated.

[0169] Various values, dimensions, materials, and the like in the above-described embodiments are merely examples and may be appropriately selected corresponding to the intended use and the surface emitting laser to be manufactured.

[0170] Description of Reference Numerals

[0171] 10, 40, 50, 60, 70 surface emitting lasers

[0172] 11, 51 base plate

[0173] 13.53 First multilayer reflector

[0174] 15 Semiconductor structure layer

[0175] 17 N-type semiconductor layer

[0176] 19 Active layer

[0177] 21 P-type semiconductor layer

[0178] 23, 52 n electrode

[0179] 25 Insulation layer

[0180] 27 p electrode

[0181] 29 Second multilayer reflector

[0182] 31 light-transmitting electrode layer

Claims

1. A vertical cavity light-emitting element, comprising: Gallium nitride-based semiconductor substrate; a first multilayer reflector made of a nitride semiconductor and formed on the substrate; a semiconductor structure layer, the semiconductor structure layer comprising a first semiconductor layer, an active layer, and a second semiconductor layer, wherein the first semiconductor layer made of a nitride semiconductor having a first conductivity type is formed on the first multilayer reflector, the active layer made of a nitride semiconductor is formed on the first semiconductor layer, and the second semiconductor layer is formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a first electrode layer, the first electrode layer being in electrical contact with the first semiconductor layer of the semiconductor structure layer; a second electrode layer, the second electrode layer being formed on the upper surface of the semiconductor structure layer, the second electrode layer being in electrical contact with the second semiconductor layer of the semiconductor structure layer in a region of the upper surface; as well as a second multilayer reflector, the second multilayer reflector being formed to cover the one region on the second electrode layer, the second multilayer reflector and the first multilayer reflector forming a resonator, The semiconductor structure layer has a recessed structure, wherein the recessed structure includes one or more recessed portions, and the one or more recessed portions pass through the active layer from the upper surface in a region surrounding the one region, and Wherein, when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer, the recessed structure is arranged to overlap with the second multilayer reflector.

2. The vertical cavity light emitting device according to claim 1, wherein: When viewed from a direction perpendicular to an in-plane direction of the semiconductor structure layer, the one or more recessed portions are arranged rotationally symmetrically.

3. The vertical cavity light emitting device according to claim 1, wherein: When viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer, the one or more recessed portions are grooves arranged in a ring shape.

4. The vertical cavity light emitting device according to claim 1, wherein: The area outside the one area of the upper surface of the semiconductor structure layer and the inner surfaces of the one or more recessed portions are covered with an insulating layer.

5. The vertical cavity light emitting device according to claim 1, wherein: The one region of the upper surface of the semiconductor structure layer is a ring-shaped region and has another recessed structure. The another recessed structure includes one or more recessed portions passing through the active layer from the upper surface in the one region.

6. The vertical cavity light emitting device according to claim 1, wherein: The first semiconductor layer includes a mesa structure including the active layer and the second semiconductor layer, and The first electrode layer is provided on an upper surface of the first semiconductor layer existing around the mesa-shaped structure.

7. The vertical cavity light emitting device according to claim 1, wherein: The gallium nitride-based semiconductor substrate has a first conductivity type, and The first electrode layer is provided on a surface of the substrate on the opposite side to the semiconductor structure layer, and is provided at a position other than a region corresponding to the one region when viewed from a normal direction of the substrate.

8. The vertical cavity light emitting device according to claim 7, wherein: When viewed from the normal direction of the substrate, the first electrode layer has a shape including an opening in a region corresponding to the one region, and The gallium nitride-based semiconductor substrate has a protruding portion in which a portion of the substrate protrudes from the opening.

9. The vertical cavity light emitting device according to claim 1, wherein: The first multilayer reflector is formed on the C-plane of the gallium nitride-based semiconductor substrate or on a surface offset from the C-plane by less than 0.5°.

10. The vertical cavity light emitting device according to claim 1, wherein: The recessed structure is an annular structure consisting of a plurality of intermittent grooves surrounding the one region.

11. The vertical cavity light emitting device according to claim 1, wherein: The surface of the gallium nitride-based semiconductor substrate on which the first multilayer reflector is formed is a surface of a crystal plane offset from the c-plane to one of the m-plane and the a-plane, and when observed from the one region, one or more groove portions extend on the upper surface of the semiconductor structure layer to a region in a direction along an axis perpendicular to the one crystal plane, and are not formed in a region in a direction perpendicular to the direction along the one axis.

12. The vertical cavity light emitting device according to claim 11, wherein: The one crystal plane is the m-plane.

13. The vertical cavity light emitting device according to claim 11, wherein: The one or more groove portions have a shape along an outer edge of the one region.

14. The vertical cavity light emitting device according to claim 1, wherein: The region around the one region is a region that is 50 μm or less from an outer edge of the one region and in which the luminous intensity of the active layer is 1.8% or less of the peak luminous intensity of the active layer when the vertical cavity light-emitting element is observed from above.

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