Vertical cavity light emitting device

Abstract

To provide a vertical resonator type light-emitting element which has high durability by preventing deterioration of a semiconductor layer including an active layer.SOLUTION: A vertical resonator type light-emitting element in the present invention comprises: a gallium nitride based semiconductor wafer; a first multilayer film reflector formed on the wafer and configured by alternately laminating an In containing nitride semiconductor layer containing In in a composition and an In non-containing nitride semiconductor layer not containing In; a semiconductor structure layer including an active layer consisting of a nitride semiconductor; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator 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 centralizing a current in one region of the active layer. An uppermost layer of the first multilayer film reflector is the In containing nitride semiconductor layer and in a region of the uppermost layer along a top face of the In containing nitride semiconductor layer, a hydrogen impurity concentration is higher than that in the other regions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

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

[0005] In such a vertical cavity light emitting device, stress occurs due to differences in lattice constants between the multilayer reflector and the semiconductor layer including the active layer disposed on the multilayer reflector, or between layers in the semiconductor layer, and thermal stress occurs within the vertical cavity light emitting device due to heat generated from the active layer when the vertical cavity light emitting device is operated.

[0006] One of the problems with vertical cavity light emitting devices is that such stress can cause damage such as dislocations in the active layer and the surrounding semiconductor layers that serve as the current path to the active layer, deteriorating these layers and reducing their durability.

[0007] The present invention has been made in view of the above-mentioned points, and has as its object to provide a vertical cavity light emitting device having high durability by preventing deterioration of semiconductor layers including an active layer. [Means for solving the problem]

[0008] a semiconductor structure layer including: a first semiconductor layer formed on the first multilayer reflector and made of a nitride semiconductor having a first conductivity type; an active layer formed on the first semiconductor layer and made of a nitride semiconductor; 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 reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer reflector; and a current constriction structure formed between the first multilayer reflector and the second multilayer reflector and concentrating current in one region of the active layer, wherein the first multilayer reflector has a higher hydrogen impurity concentration in a region along an upper surface of the uppermost In-containing nitride semiconductor layer of the first multilayer reflector than in other regions. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a surface-emitting laser according to a first embodiment; [Figure 2] 1 is a cross-sectional view of a surface-emitting laser according to a first embodiment. [Figure 3] This shows the results of SIMS measurement of the vicinity of the top surface of the AlInN layer, which is the top layer of the first multilayer reflector. [Figure 4]1 is a cross-sectional view of a laser device using a surface-emitting laser according to a first embodiment. [Figure 5] This is a TEM image of the vicinity of the top surface of the AlInN layer, which is the top layer of the first multilayer reflector. [Figure 6] Figure 5 shows an enlarged portion of the TEM image. [Figure 7] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0012] The substrate 11 is a gallium nitride semiconductor substrate, for example, a GaN substrate. The substrate 11 is a so-called C-plane substrate, in which the C-plane is exposed on the upper surface. The substrate 11 is, for example, a substrate whose upper surface has a rectangular shape.

[0013] The first multilayer reflector 13 is a semiconductor multilayer reflector made of semiconductor layers grown on the substrate 11. The first multilayer reflector 13 is formed by alternately stacking semiconductor films having an AlInN composition and semiconductor films having a GaN composition, which has a higher refractive index than the semiconductor films having an AlInN composition. In other words, the first multilayer reflector 13 is a distributed Bragg reflector (DBR) made of semiconductor materials.

[0014] The semiconductor structure layer 15 is a laminated structure made up of multiple semiconductor layers formed on the first multilayer reflector 13. The semiconductor structure layer 15 has an n-type semiconductor layer (first semiconductor layer) 17 formed on the first multilayer reflector 13, a light-emitting layer (or active layer) 19 formed on the n-type semiconductor layer 17, and a p-type semiconductor layer (second semiconductor layer) 21 formed on the active layer 19.

[0015] The n-type semiconductor layer 17, which serves as a semiconductor layer of a first conductivity type, is a semiconductor layer formed on the first multilayer reflector 13. The n-type semiconductor layer 17 has a GaN composition and is doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower portion 17A and a cylindrical upper portion 17B disposed thereon (a mesa-shaped structure having a lower portion 17A having a planar shape similar to the top surface of the first multilayer reflector 13 and a mesa-shaped upper portion 17B disposed thereon). Specifically, for example, the n-type semiconductor layer 17 has a cylindrical upper portion 17B protruding 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.

[0016] The active layer 19 is formed on the upper portion 17B of the n-type semiconductor layer 17 and has a quantum well structure including a well layer having an InGaN composition and a barrier layer having a GaN composition. In the surface-emitting laser 10, light is generated in the active layer 19.

[0017] The p-type semiconductor layer 21, which serves as a semiconductor layer of a second conductivity type, is a semiconductor layer having a GaN composition formed on the active layer 19. The p-type semiconductor layer 21 is doped with Mg as a p-type impurity.

[0018] The n-electrode 23 is a metal electrode provided on an upper surface 17S of a lower portion 17A of the n-type semiconductor layer 17 and electrically connected to the n-type semiconductor layer 17. The n-electrode 23 is formed in a ring shape so as to surround an upper portion 17B of the n-type semiconductor layer 17. The n-electrode 23 is in electrical contact with the n-type semiconductor layer 17 and forms a first electrode layer that supplies a current from the outside to the semiconductor structure layer 15.

[0019] Insulating layer 25 is a layer made of an insulator and formed on p-type semiconductor layer 21. Insulating layer 25 is made of a substance, such as SiO2, that has a lower refractive index than the material that forms p-type semiconductor layer 21. Insulating layer 25 is formed in a ring shape on p-type semiconductor layer 21, and has an opening (not shown) in the center that exposes p-type semiconductor layer 21.

[0020] The transparent electrode 27 is a light-transmitting metal oxide film formed on the upper surface of the insulating layer 25. The transparent electrode 27 covers the entire upper surface of the insulating layer 25 and the entire upper surface of the p-type semiconductor layer 21 exposed from an opening formed in the central part of the insulating layer 25. As the metal oxide film forming the transparent electrode 27, for example, ITO or IZO, which is light-transmitting to light emitted from the active layer 19, can be used.

[0021] The p-electrode 29 is a metal electrode formed on the transparent electrode 27. The p-electrode 29 is electrically connected to the upper surface of the p-type semiconductor layer 21 exposed from the opening in the insulating layer 25 via the transparent electrode 27. The transparent electrode 27 and the p-electrode 29 form a second electrode layer that is in electrical contact with the p-type semiconductor layer 21 and supplies current from the outside to the semiconductor structure layer 15. In this embodiment, the p-electrode 29 is formed in a ring shape on the upper surface of the transparent electrode 27 along the outer edge of the upper surface.

[0022] The second multilayer reflector 31 is a cylindrical multilayer reflector formed in an area surrounded by the p-electrode 29 on the upper surface of the transparent electrode 27. The second multilayer reflector 31 is a dielectric multilayer reflector in which low-refractive-index dielectric films made of SiO2 and high-refractive-index dielectric films made of Nb2O5 and having a higher refractive index than the low-refractive-index dielectric films are alternately stacked. In other words, the second multilayer reflector 31 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0023] Fig. 2 is a cross-sectional view taken along line 2-2 in Fig. 1. As described above, the surface-emitting laser 10 has a substrate 11 which is a GaN substrate, and a first multilayer film reflector 13 is formed on the substrate 11. The lower surface of the substrate 11 may be coated with an AR coating.

[0024] The first multilayer reflector 13 is formed by providing a buffer layer (not shown) having a GaN composition on the upper surface of the substrate 11, depositing the low-refractive-index semiconductor film 13A made of AlInN on the buffer layer, and then alternately depositing high-refractive-index semiconductor film 13B made of GaN and the low-refractive-index semiconductor film 13A in this order. The uppermost layer of the first multilayer reflector 13 is the high-refractive-index semiconductor film 13B made of GaN.

[0025] For example, in this embodiment, the first multilayer reflector 13 is made of 41 pairs of AlInN layers / GaN layers stacked on a 1 μm thick GaN underlayer formed on the upper surface of the substrate 11. In other words, the first multilayer reflector 13 is a stack of 41 AlInN layers and 41 GaN layers stacked alternately, with the bottom layer being an AlInN layer and the top layer being a GaN layer.

[0026] In other words, the first multilayer reflector 13 is a laminated body in which In-containing nitride semiconductor layers containing In in their composition and In-free nitride semiconductor layers not containing In are alternately laminated.

[0027] The uppermost layer of low-refractive-index semiconductor film 13A, which is the AlInN layer of first multilayer reflector 13, has a high concentration of hydrogen, an impurity, in a region along its top surface, in other words, in a region along the interface with the GaN layer of high-refractive-index semiconductor film 13B, the uppermost layer of first multilayer reflector 13. In other words, the region along the top surface of the uppermost AlInN layer of first multilayer reflector 13 has a higher hydrogen impurity concentration than other regions, i.e., the central portion in the thickness direction of the AlInN layer. Furthermore, this hydrogen impurity concentration is higher than the GaN layer formed directly above it, i.e., high-refractive-index semiconductor film 13B, and n-type semiconductor layer 17, which will be described later.

[0028] 3 is a graph showing the results of measurements by secondary ion mass spectrometry (SIMS) showing the densities (atoms / cc) of aluminum (Al), indium (In), hydrogen (H), and gallium (Ga) in the region above the uppermost layer of low-refractive-index semiconductor film 13A of first multilayer reflector 13, i.e., along the interface with the GaN layer of high-refractive-index semiconductor film 13B. In this graph, the horizontal axis represents depth in the layer thickness direction, the left vertical axis represents hydrogen density, and the right vertical axis represents densities of gallium, aluminum, and indium.

[0029] Referring to FIG. 3, the low refractive index semiconductor film 13A, which is the uppermost layer of the first multilayer film reflector 13, has a hydrogen concentration of 1E18 / cm in a region along the interface with the high refractive index semiconductor film 13B (the region sandwiched between the dashed lines in FIG. 3). 3 In the region away from the interface of the low refractive index semiconductor film 13A and the GaN layer formed directly thereon, that is, in the region away from the interface of the high refractive index semiconductor film 13B, the refractive index exceeds 1E17 / cm 3 The concentration difference is more than 10 times as follows:

[0030] The inventors of the present application have found that if the low-refractive-index semiconductor film 13A having an AlInN composition has a portion with a high concentration of hydrogen impurities, basal plane dislocations (hereinafter also simply referred to as plane dislocations) are likely to occur in the portion with a high concentration of hydrogen impurities when stress is applied to the low-refractive-index semiconductor film 13A. In other words, it has been found that in the surface-emitting laser 10 of this embodiment, basal plane dislocations are likely to occur due to stress load in the region along the upper surface of the low-refractive-index semiconductor film 13A of the first multilayer reflector 13.

[0031] As described above, the semiconductor structure layer 15 is formed on the first multilayer film reflector 13. The semiconductor structure layer 15 is a laminated body in which an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 are formed in this order. A protrusion 21P that protrudes upward is formed in the center of the top surface of the p-type semiconductor layer 21.

[0032] Insulating layer 25 is formed to cover the region of the upper surface of p-type semiconductor layer 21 except for protruding portion 21P. As described above, insulating layer 25 is made of a material having a lower refractive index than p-type semiconductor layer 21. Insulating layer 25 has opening 25H that exposes protruding portion 21P. For example, opening 25H and protruding portion 21P have the same shape, and the inner surface of opening 25H and the outer surface of protruding portion 21P are in contact with each other.

[0033] Transparent electrode 27 is formed so as to cover insulating layer 25 and the upper surface of protruding portion 21P exposed from opening 25H of insulating layer 25. That is, transparent electrode 27 is in electrical contact with p-type semiconductor layer 21 in a region of the upper surface of p-type semiconductor layer 21 exposed by opening 25H. In other words, the region of the upper surface of p-type semiconductor layer 21 exposed through opening 25H serves as electrical contact surface 21S that brings p-type semiconductor layer 21 and transparent electrode 27 into electrical contact.

[0034] As described above, p-electrode 29 is a metal electrode and is formed along the outer edge of the upper surface of transparent electrode 27. That is, p-electrode 29 is in electrical contact with transparent electrode 27. Therefore, p-electrode 29 is in electrical contact or connection with p-type semiconductor layer 21 via transparent electrode 27 at electrical contact surface 21S exposed by opening 25H in the upper surface of p-type semiconductor layer 21.

[0035] The second multilayer reflector 31 is formed on the upper surface of the transparent electrode 27 in a region above the opening 25H of the insulating layer 25, in other words, in a region above the electrical contact surface 21S, i.e., in the central portion of the upper surface of the transparent electrode 27. The lower surface of the second multilayer reflector 31 faces the upper surface of the first multilayer reflector 13, with the transparent electrode 27 and the semiconductor structure layer 15 sandwiched between them. The arrangement of the first multilayer reflector 13 and the second multilayer reflector 31 forms a resonator OC that resonates light emitted from the active layer 19.

[0036] In the surface-emitting laser 10, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 31. Therefore, part of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 31 passes through the first multilayer reflector 13 and the substrate 11 and is extracted to the outside.

[0037] Here, we will explain the operation of the surface-emitting laser 10. When a voltage is applied between the n-electrode 23 and the p-electrode 29 in the surface-emitting laser 10, a current flows in the semiconductor structure layer 15 as shown by the thick dashed-dotted line in Fig. 2, and light is emitted from the active layer 19. The light emitted from the active layer 19 is repeatedly reflected between the first multilayer film reflector 13 and the second multilayer film reflector 31, and reaches a resonance state (i.e., laser oscillation occurs).

[0038] In the surface-emitting laser 10, current is injected into the p-type semiconductor layer 21 only from the portion exposed by the opening 25H, i.e., the electrical contact surface 21S. In addition, since the p-type semiconductor layer 21 is very thin, current does not diffuse in the in-plane direction within the p-type semiconductor layer 21, i.e., in the direction along the in-plane of the semiconductor structure layer 15.

[0039] Therefore, in the surface-emitting laser 10, current is supplied only to the region of the active layer 19 directly below the electrical contact surface 21S defined by the opening 25H, and light is emitted only from that region. That is, in the surface-emitting laser 10, the opening 25H forms a current confinement structure that limits the range of current supply in the active layer 19.

[0040] In other words, in the surface-emitting laser 10, a current confinement structure is formed between the first multilayer reflector 13 and the second multilayer reflector 31, which confines the current so that it flows only in a central region CA, which is a columnar region of the active layer 19 with the electrical contact surface 21S as its bottom surface, i.e., concentrates the current in one region of the active layer. The central region CA, which includes the region in the active layer 19 through which the current flows, is defined by the electrical contact surface 21S.

[0041] 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 resonating between the first multilayer reflector 13 and the second multilayer reflector 31 passes through the first multilayer reflector 13 and the substrate 11 and is extracted to the outside. In this way, the surface-emitting laser 10 emits light from the lower surface of the substrate 11 in a direction perpendicular to the in-plane direction of the lower surface of the substrate 11 and each layer of the semiconductor structure layer 15. In other words, the lower surface of the substrate 11 serves as the light-emitting surface of the surface-emitting laser 10.

[0042] The electrical contact surface 21S of the p-type semiconductor layer 21 of the semiconductor structure layer 15 and the opening 25H of the insulating layer 25 define an emission center, which is the center of the light-emitting region in the active layer 19, and define a central axis (emission central axis) AX of the resonator OC. The central axis AX 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.

[0043] The light emitting region of the active layer 19 is, for example, a region having a predetermined width in the active layer 19 from which light of a predetermined intensity or more is emitted, the center of which is the light emitting center. Also, for example, the light emitting region of the active layer 19 is a region in the active layer 19 into which a current of a predetermined density or more is injected, the center of which is the light emitting center. A straight line passing through the light emitting center and perpendicular to the in-plane direction of the upper surface of the substrate 11 or each layer of the semiconductor structure layer 15 is the central axis AX.

[0044] The light emission central axis AX is a straight line extending along the cavity length direction of the cavity OC formed by the first multilayer reflector 13 and the second multilayer reflector 31. The central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 10.

[0045] Here, we will explain exemplary configurations of the first multilayer reflector 13, the semiconductor structure layer 15, and the second multilayer reflector 31 in the surface-emitting laser 10. In this example, the first multilayer reflector 13 is made of a 1 μm GaN underlayer formed on the upper surface of the substrate 11, and 41 pairs of AlInN layers (50 nm) and GaN layers (45 nm).

[0046] The n-type semiconductor layer 17 is a GaN layer with a thickness of 558 nm. The active layer 19 has a multi-quantum well structure in which five pairs of 4 nm GaInN layers and 5 nm GaN layers are stacked. An Mg-doped AlGaN electron barrier layer is formed on the active layer 19, and a p-type semiconductor layer 21 made of a 50 nm p-GaN layer is formed on top of that. The second multilayer reflector 31 is made by stacking 10.5 pairs of Nb2O5 and SiO2. The resonant wavelength in this case was 440 nm.

[0047] Insulating layer 25 is a 20 nm layer made of SiO2. In other words, protruding portion 21P on the upper surface of p-type semiconductor layer 21 protrudes by 20 nm from the surrounding area. That is, p-type semiconductor layer 21 has a layer thickness of 50 nm at protruding portion 21P and a layer thickness of 30 nm in other regions. In addition, the upper surface of insulating layer 25 is configured to be located at the same height as the upper surface of protruding portion 21P of p-type semiconductor layer 21. Note that these configurations are merely examples.

[0048] The following describes the optical characteristics inside the surface-emitting laser 10. As described above, in the surface-emitting laser 10, the insulating layer 25 has a lower refractive index than the p-type semiconductor layer 21. Between the first multilayer reflector 13 and the second multilayer reflector 31, the layer thicknesses of the active layer 19 and the n-type semiconductor layer 17 are the same anywhere in the plane if they are in the same layer.

[0049] Therefore, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 31, which corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 31 of the surface-emitting laser 10 differs between the cylindrical central region CA with the electrical contact surface 21S as its bottom surface and the cylindrical peripheral region PA around it, due to the difference in refractive index between the p-type semiconductor layer 21 and the insulating layer 25.

[0050] Specifically, between the first multilayer reflector 13 and the second multilayer reflector 31, the equivalent refractive index of the peripheral region PA is lower than the equivalent refractive index of the central region CA, i.e., the equivalent resonant wavelength in the central region CA is smaller than the equivalent resonant wavelength in the peripheral region PA. Note that light is emitted from the active layer 19 in the region directly below the opening 25H and the electrical contact surface 21S. That is, the light-emitting region from which light is emitted in the active layer 19 is the portion of the active layer 19 that overlaps with the central region CA, in other words, the region that overlaps with the electrical contact surface 21S in a top view.

[0051] As described above, the surface-emitting laser 10 is formed with a central region CA including the light-emitting region of the active layer 19, and a peripheral region PA surrounding the central region CA and having a lower refractive index than the central region CA. This suppresses optical loss caused by standing waves in the central region CA diverging (radiating) to the peripheral region PA. That is, much light remains in the central region CA, and laser light is extracted in this state. Therefore, much light is concentrated in the central region CA around the light-emitting central axis AX of the resonator OC, enabling the generation and emission of high-power, high-density laser light.

[0052] [Structure of laser device 100 incorporating 10 surface-emitting laser elements] 4 shows a cross-sectional view of a laser device 100 in which a surface-emitting laser 10 is mounted on a support substrate 50. The cross-sectional view of FIG. 4 shows a cross-section along the same cross-sectional line as the cross-section shown in FIG.

[0053] In the laser device 100, the surface-emitting laser 10 is bonded to a support substrate 50 by bonding portions 51 and 53 formed of an AuSn eutectic. The bonding portion 51 bonds the p-electrode 29 and the second multilayer film reflector 31 to the support substrate 50. The bonding portion 51 is formed so as to cover the upper surfaces of the p-electrode 29 and the second multilayer film reflector 31. Wiring (not shown) that supplies current to the p-electrode is formed on the portion of the surface of the support substrate 50 that is covered by the bonding portion 51.

[0054] Bonding portion 53 bonds n-electrode 23 to supporting substrate 50. Bonding portion 53 is spaced apart from bonding portion 51 so as to be insulated from bonding portion 51. Wiring (not shown) that supplies current to the n-electrode is formed on the portion of the surface of supporting substrate 50 that is covered by bonding portion 51.

[0055] When a current is supplied to the surface-emitting laser 10 while the laser device 100 is in operation, heat is generated in the region of the semiconductor structure layer 15 directly below the opening 25H through which the current flows into the active layer 19, and thermal distortion occurs as a result. When stress due to this thermal distortion is applied to the interface between the semiconductor structure layer 15 and the first multilayer film reflector 13, planar dislocations occur in a region along the top surface of the uppermost layer of the low-refractive-index semiconductor film 13A of the first multilayer film reflector 13.

[0056] Fig. 5 is a TEM image (50,000x magnification) of region A surrounded by a dashed line in Fig. 4, and was taken after laser device 100 was driven. In Fig. 5, line L1 is a line along the right-end side surface of opening 25H in Fig. 4. Therefore, in Fig. 5, the region to the left of line L1 is the region directly below opening 25H.

[0057] 5. FIG. 6 is a further enlarged TEM image (150,000 times) of a portion of the region along the interface between the first multilayer film reflector 13 and the semiconductor structure layer 15 in FIG.

[0058] 5 and 6, after the laser device 100 is driven, planar dislocations (black portions in the figures) are observed in a region IF (the region surrounded by the two-dot chain line in FIG. 5 and the region sandwiched between the two-dot chain lines in FIG. 6) that is along the boundary between the low-refractive-index semiconductor film 13A and the high-refractive-index semiconductor film 13B of the first multilayer reflector 13 and to the left of the line L1. In other words, the planar dislocations are formed in a region along the top surface of the first multilayer reflector 13 that overlaps with the opening 25H when viewed from the normal direction to the top surface of the substrate 11, i.e., in a region that overlaps with a region where current flows in a concentrated manner in the semiconductor structure layer 15. On the other hand, no planar dislocations are formed in a region to the right of the line L1 that does not overlap with the opening 25H when viewed from the normal direction, i.e., does not overlap with a region where current flows in a concentrated manner.

[0059] This is because, when the laser device 100 is operated, current flows in the region directly below the opening 25H in the semiconductor structure layer 15, generating heat and distortion in that region, which in turn places stress on the region IF directly below the opening 25H.

[0060] In addition, in FIGS. 5 and 6, the interface between the high refractive index semiconductor film 13B and the n-type semiconductor layer 17 cannot be seen because they are both made of GaN.

[0061] As described above, the uppermost layer of the low refractive index semiconductor film 13A of the first multilayer reflector 13 contains a large amount of hydrogen as an impurity, and a region where planar dislocations due to stress are likely to occur is formed.

[0062] In particular, the formation of a layer of a material with a different lattice constant on the upper surface of the n-type semiconductor layer 13B increases the likelihood of planar dislocations. The difference in lattice constant is also influenced by the n-type semiconductor layer 17, which is formed as thick as 558 nm (500 nm or more), because the high refractive index semiconductor film 13B directly above it is thin at 45 nm (50 nm or less). In this example, the n-type semiconductor layer 17 is nGaN, but even if it contains a few percent of In, Al, or the like, it is estimated that the difference in lattice constant will still have an effect of increasing the likelihood of planar dislocations.

[0063] It is believed that planar dislocations were generated in this region due to stress caused by the distortion in the semiconductor layer described above. Since planar dislocations hardly occurred outside the opening 25H, where little heat and thermal stress are generated in the semiconductor structure layer 15, it is also assumed that planar dislocations are generated by thermal distortion and thermal stress generated in the semiconductor structure layer 15 during operation.

[0064] The occurrence of these planar dislocations relieves the strain and internal stress that occur in the semiconductor structure layer 15 during operation, particularly during the initial operation, and makes it difficult for strain-induced damage to occur in the semiconductor structure layer 15, particularly in the active layer 19. This improves the durability of the surface-emitting laser 10.

[0065] Furthermore, the formation of the above-mentioned planar dislocations on the uppermost layer of the low-refractive-index semiconductor film 13A of the first multilayer reflector 13 prevents the dislocations from propagating into the semiconductor structure layer 15 inside the first multilayer reflector 13. Specifically, when a dislocation generated in the first multilayer reflector 13 propagates toward the semiconductor structure layer 15, the dislocation is bent in a direction along the interface between the low-refractive-index semiconductor film 13A and the semiconductor structure layer 15, preventing the dislocation from entering the semiconductor structure layer 15.

[0066] In this way, in the surface-emitting laser 10, dislocations generated in the first multilayer film reflector 13 are prevented from propagating to the semiconductor structure layer 15, particularly the active layer 19. This also prevents damage to the semiconductor structure layer 15, and improves the durability of the surface-emitting laser 10.

[0067] The planar dislocations propagate in the equivalent m-axis directions: [1-100], [10-10], [01-10], [-1100], [-1010], and [0-110], and in the equivalent a-axis directions: [1-210], [2-1-10], [11-20], [-1210], [-2110], and [-1-120].

[0068] [Manufacturing method] The following describes an example of a method for manufacturing the surface-emitting laser 10. First, an n-GaN substrate with the C-plane exposed on the upper surface as described above is prepared as the substrate 11.

[0069] Next, a GaN (100 nm thick) layer is formed as an underlayer (not shown) by metalorganic chemical vapor deposition (MOCVD) on the upper surface of the substrate 11. After that, an AlInN / GaN layer, i.e., 41 pairs of the above-mentioned low-refractive-index semiconductor film 13A and high-refractive-index semiconductor film 13B, are formed on the underlayer to form the first multilayer film reflector 13.

[0070] In forming the first multilayer film reflector 13, the growth substrate temperature is first set to 800°C and N2 is used as the carrier gas. After the substrate temperature stabilizes, trimethylindium (TMI), trimethylaluminum (TMA), and NH3 are supplied, and a low-refractive-index semiconductor film 13A, which is an AlInN layer, is grown to a thickness of 50 nm on the underlayer. Thereafter, the supply of the organometallic material (MO material) is stopped. During the formation of this low-refractive-index semiconductor film 13A, the In composition of the AlInN layer, which is the low-refractive-index semiconductor film 13A, is set to 18.5 at%.

[0071] Next, triethylgallium (TEG) and NH3 were supplied to grow a 1 nm cap layer (not shown) made of GaN on the low refractive index semiconductor film 13A. The supply of the metal-organic materials was then stopped. The carrier gas was then changed from N2 to H2, and the substrate temperature was raised from 800°C to 1100°C over 3 minutes. Then, TMG and NH3 were supplied to grow a 44 nm GaN layer. The supply of the metal-organic materials was then stopped to form the high refractive index semiconductor film 13B including the cap layer (not shown).

[0072] The first multilayer film reflector 13 is formed by repeatedly forming the low refractive index semiconductor film 13A and the high refractive index semiconductor film 13B.

[0073] When forming the uppermost high-refractive-index semiconductor film 13B, the carrier gas is H2 and the temperature is raised to 1100°C over a period of 3 minutes, thereby introducing a high concentration of hydrogen into the upper surface of the low-refractive-index semiconductor film 13A directly below it. As a result, a region with a high amount of hydrogen impurities and prone to basal plane dislocations as described above is formed in the region along the interface between the uppermost layer of the low-refractive-index semiconductor film 13A of the first multilayer reflector 13 and the high-refractive-index semiconductor film 13B.

[0074] In order to promote hydrogen uptake so that the region along the interface between low-refractive-index semiconductor film 13A and high-refractive-index semiconductor film 13B becomes a region where basal plane dislocations are likely to occur, the difference between the growth temperature of low-refractive-index semiconductor film 13A and the growth temperature of n-type semiconductor layer 17 was set to 250° C. or more. In addition, the temperature rise time from the growth temperature of low-refractive-index semiconductor film 13A to the growth temperature of n-type semiconductor layer 17 was set to 2.5 minutes or more.

[0075] Next, an n-type semiconductor layer 17 is formed on the first multilayer reflector 13, specifically on the upper surface of the uppermost low refractive index semiconductor film 13A. TMG, NH, and disilane (SiH) are supplied as source gases to grow Si-doped n-GaN to a thickness of 558 nm.

[0076] Next, the active layer 19 is formed on the n-type semiconductor layer 17 by stacking five pairs of layers made of GaInN (layer thickness 3 nm) and GaN (layer thickness 6 nm).

[0077] Next, an electron barrier layer (20 nm) made of Mg-doped AlGaN is formed on the active layer 19 (not shown), and a p-GaN layer (layer thickness 50 nm) is formed on the electron barrier layer to form the p-type semiconductor layer 21.

[0078] Next, the p-type semiconductor layer 21, the active layer 19, and the surrounding areas of the n-type semiconductor layer 17 are etched to form a mesa shape that exposes the top surface 17S of the n-type semiconductor layer 17 in the surrounding areas. In other words, this step completes the semiconductor structure layer 15 having a cylindrical portion made up of the n-type semiconductor layer 17, the active layer 19, and the p-type semiconductor layer 21 shown in FIG. 1.

[0079] Next, the periphery of the central portion of the upper surface of the p-type semiconductor layer 21 is etched to form a protruding portion 21P. Thereafter, a film of SiO2 is formed on the semiconductor structure layer 15, and a portion of it is removed to form an opening 25H, thereby forming the insulating layer 25. In other words, SiO2 is buried in the etched-away portion of the upper surface of the p-type semiconductor layer 21.

[0080] Next, a 20 nm ITO film is formed on the insulating layer 25 to form the transparent electrode 27, and an Au film is formed on the upper surface of the transparent electrode 27 and the upper surface 17S of the n-type semiconductor layer 17 to form the p-electrode 29 and the n-electrode 23, respectively.

[0081] Next, a 40 nm Nb2O5 film is formed on the transparent electrode 27 as a spacer layer (not shown), and 10.5 pairs of layers, each consisting of Nb2O5 / SiO2, are formed on the spacer layer to form the second multilayer film reflector 31.

[0082] When the back surface of the substrate 11 is provided with an AR coating, the back surface of the substrate 11 is polished last, and an AR coating made of Nb2O5 / SiO2 is formed on the polished surface, thereby completing the surface-emitting laser 10. [Example]

[0083] A surface-emitting laser 70 according to a second embodiment of the present invention will now be described. The surface-emitting laser 70 differs from the surface-emitting laser 10 according to the first embodiment in that, in order to form the current confinement structure described above, a tunnel junction structure is formed in the semiconductor structure layer 15 instead of the insulating layer 25. Specifically, the surface-emitting laser 70 differs from the surface-emitting laser 10 in the structure above the p-type semiconductor layer 21.

[0084] Fig. 7 is a cross-sectional view showing a cut surface when the surface-emitting laser 70 is cut along the same cutting line as shown in Fig. 1, i.e., a cut surface corresponding to Fig. 2. As shown in Fig. 7, in the surface-emitting laser 70, a tunnel junction layer 71 is formed on the protruding portion 21P of the p-type semiconductor layer 21. That is, in the surface-emitting laser 70, the tunnel junction layer 71 is formed in a central region CA in the semiconductor structure layer 15.

[0085] The tunnel junction layer 71 includes a highly doped p-type semiconductor layer 71A which is a p-type semiconductor layer formed on the p-type semiconductor layer 21 and has a higher impurity concentration than the p-type semiconductor layer 21, and a highly doped n-type semiconductor layer 71B which is an n-type semiconductor layer formed on the highly doped p-type semiconductor layer 71A and has a higher impurity concentration than the n-type semiconductor layer 17.

[0086] The n-type semiconductor layer 73 is formed on the p-type semiconductor layer 21 and the tunnel junction layer 71. The n-type semiconductor layer 73 is formed so as to bury the tunnel junction layer 71 on the upper surface of the p-type semiconductor layer 21. In other words, the n-type semiconductor layer 73 is formed so as to cover the side surfaces of the protruding portion 21P and the side surfaces and upper surface of the tunnel junction layer 71.

[0087] The n-type semiconductor layer 73 is an n-type semiconductor layer having a doping concentration similar to that of the n-type semiconductor layer 17. That is, the n-type semiconductor layer 73 has a doping concentration lower than that of the highly doped n-type semiconductor layer 71B.

[0088] Such a stacked structure of the p-type semiconductor layer 21, the tunnel junction layer 71, and the n-type semiconductor layer 73 generates a tunnel effect in the tunnel junction layer 71. As a result, in the surface-emitting laser 70, a current flows only through the tunnel junction layer 71 between the p-type semiconductor layer 21 and the n-type semiconductor layer 73, forming a current confinement structure in which the current is confined to the central region CA.

[0089] The p-side electrode 75 is a metal electrode formed along the periphery of the upper surface of the n-type semiconductor layer 73. In the surface-emitting laser 70, a current flows through the p-side electrode 75, the n-type semiconductor layer 73, the tunnel junction layer 71, the p-type semiconductor layer 21, the active layer 19, and the n-type semiconductor layer 17 to the n-electrode 23.

[0090] The second multilayer reflector 77 is formed in an area surrounded by the p-side electrode 75 on the upper surface of the n-type semiconductor layer 73, and is a distributed Bragg reflector (DBR) having a configuration similar to that of the second multilayer reflector 31 of the surface-emitting laser 10 of Example 1.

[0091] In the surface-emitting laser 70 having such a current confinement structure using a tunnel junction layer, it is possible to obtain the same effect as that described for the surface-emitting laser 10 of Example 1, which is obtained by forming a region in which basal plane dislocations are likely to occur in the first multilayer film reflector 13.

[0092] In the above-described first embodiment, the insulating layer 25 is provided on the upper surface of the p-type semiconductor layer 21 to form the electrical contact surface 21S and the insulating region around it, thereby causing current confinement and forming a region with a low refractive index. However, instead of providing the insulating layer 25, other methods may be used to cause current confinement and form a region with a low refractive index.

[0093] For example, the insulating region, the low refractive index region, and the electrical contact surface 21S may be formed by etching the upper surface of the p-type semiconductor layer 21 on which the insulating layer 25 is provided in the above embodiment. Alternatively, the insulating region, the low refractive index region, and the electrical contact surface 21S may be formed by implanting ions into the upper surface of the p-type semiconductor layer 21 on which the insulating layer 25 is provided, thereby producing a current confinement effect similar to that achieved by forming the insulating layer 25 in the above embodiment. When implanting ions, for example, B ions, Al ions, or oxygen ions are implanted into the p-type semiconductor layer 21.

[0094] In the above-described embodiment, the top layer of the first multilayer reflector is the GaN layer of the high-refractive-index semiconductor film 13B, but it may be the AlInN layer of the low-refractive-index semiconductor film 13A. In this case, planar dislocations occur at the interface between the AlInN layer, which is the top layer, and the n-type semiconductor layer.

[0095] The various numerical values, dimensions, materials, etc. in the above-described embodiments are merely examples, and can be appropriately selected depending on the application and the surface-emitting laser to be manufactured. [Explanation of symbols]

[0096] 10, 70 Surface-emitting laser 11 Circuit Board 13 First multilayer mirror 15 Semiconductor structural layer 17 n-type semiconductor layer 19 Active layer 21 p-type semiconductor layer 23 n electrode 25 insulating layer 27 Transparent electrode 29p electrode 31 Second multilayer mirror 71 Tunnel junction layer 73 n-type semiconductor layer 75 p side electrode 77 Second multilayer mirror

Claims

1. a gallium nitride semiconductor substrate; a first multilayer reflector formed on the substrate and including alternately stacked In-containing nitride semiconductor layers containing In in their composition and In-free nitride semiconductor layers not containing In; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer film reflector; a current confinement structure formed between the first multilayer reflector and the second multilayer reflector, for concentrating current in one region of the active layer; a hydrogen impurity concentration in a region along an upper surface of the In-containing nitride semiconductor layer formed on the top of the first multilayer reflector is 10 times or more that in other regions, and is 10 times or more that of the In-free nitride semiconductor layer formed directly thereon and the first semiconductor layer or the first semiconductor layer formed directly thereon.

2. In a region along the upper surface of the In-containing nitride semiconductor layer formed on the top of the first multilayer film reflector, a hydrogen impurity concentration is 1E18 / cm ３ 2. The vertical cavity light emitting device according to claim 1, wherein the above-mentioned portions are formed.

3. 3. The vertical cavity light emitting device according to claim 1, wherein the In-containing nitride semiconductor layer has an AlInN composition, and the In-free nitride semiconductor layer has a GaN composition.

4. 4. The vertical cavity light emitting device according to claim 1, wherein the uppermost layer of said first multilayer reflector is said In-free nitride semiconductor layer.

5. 4. The vertical cavity light emitting device according to claim 1, wherein the uppermost layer of said first multilayer reflector is said In-containing nitride semiconductor layer.

6. a gallium nitride based semiconductor substrate; and a first multilayer film reflector formed on the substrate, the first multilayer film reflector including In-containing nitride semiconductor layers containing In as a composition and In-free nitride semiconductor layers not containing In alternately stacked; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a second multilayer film reflector formed on the semiconductor structure layer and constituting a resonator between itself and the first multilayer film reflector; a current confinement structure formed between the first multilayer reflector and the second multilayer reflector, for concentrating current in one region of the active layer; a vertical cavity light emitting device, characterized in that planar dislocations are formed in a region along an upper surface of the In-containing nitride semiconductor layer formed on the topmost part of the first multilayer reflector, the region overlapping with the first region when viewed from the normal direction to the upper surface of the gallium nitride based semiconductor substrate, and a hydrogen impurity concentration in the region along the upper surface is 10 times or more that in other regions.

7. The vertical cavity light emitting device according to claim 6 , wherein the planar dislocations are formed after the vertical cavity light emitting device is driven.

8. 8. The vertical cavity light emitting device according to claim 6, wherein the planar dislocations are not formed in a region along the top surface of the In-containing nitride semiconductor layer formed on the top of the first multilayer reflector and not overlapping with the first region when viewed from the normal direction of the top surface of the gallium nitride based semiconductor substrate.

9. 9. The vertical cavity light emitting device according to claim 6, wherein a region along the top surface of the In-containing nitride semiconductor layer formed on the top of the first multilayer reflector has a higher hydrogen impurity concentration than other regions.

10. In a region along the upper surface of the In-containing nitride semiconductor layer formed on the top of the first multilayer film reflector, a hydrogen impurity concentration is 1E18 / cm ３ 10. The vertical cavity light emitting device according to claim 9, wherein the above-mentioned portions are formed.

11. 11. The vertical cavity light emitting device according to claim 6, wherein the In-containing nitride semiconductor layer has an AlInN composition, and the In-free nitride semiconductor layer has a GaN composition.

12. 12. The vertical cavity light emitting device according to claim 6, wherein the uppermost layer of the first multilayer reflector is the In-free nitride semiconductor layer.

13. 12. The vertical cavity light emitting device according to claim 6, wherein the uppermost layer of the first multilayer reflector is the In-containing nitride semiconductor layer.

Images