Vertical cavity light emitting device

Abstract

To provide a vertical resonator type light-emitting device of which the lifetime is prolonged by suppressing a rise of a drive voltage during long-term electrification.SOLUTION: A vertical resonator type light-emitting device comprises: a semiconductor structure layer including a substrate of a gallium nitride based semiconductor, a first multilayer film reflector, a first semiconductor layer of a first conductivity type, an active layer and a second semiconductor layer of a second conductivity type; a translucent electrode layer which is electrically in contact with the second semiconductor layer in one region of a top face of the second semiconductor layer and insulated from the second semiconductor layer in the other region surrounding the one region; a metal conductor layer formed on the other region of the top face of the translucent electrode layer; a second multilayer film reflector covering one region on the translucent electrode layer; and a translucent insulator layer disposed between the second semiconductor layer and the translucent electrode layer in the other region. The translucent insulator layer includes an inner edge having a step outside of one region. The second semiconductor layer includes an inactivated region in which an impurity is inactivated. The metal conductor layer is formed so as to cover the inner edge of the translucent insulator layer via the translucent electrode layer.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 surface emitting laser that uses a nitride semiconductor. [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 insulating film that defines a light emitting region is formed on the upper surface of a semiconductor layer, and a light-transmitting electrode film such as ITO that is in electrical contact with the semiconductor layer is formed on the insulating film.

[0005] For example, Patent Document 1 discloses a vertical cavity light emitting device in which an opening is formed in a region corresponding to a light emitting region of a semiconductor layer, and a translucent electrode film made of ITO is formed on an insulating film formed so as to surround the light emitting region. In the vertical cavity light emitting device of Patent Document 1, the translucent electrode film is formed so as to create a step at the edge of the opening of the insulating film.

[0006] However, if steps occur in the translucent electrode film as described above, abnormalities such as cracks may occur in the stepped portions of the translucent electrode during long-term electrical conduction, which may result in an increase in driving voltage or short / open circuits.

[0007] The present invention has been made in view of the above points, and has as its object to provide a vertical cavity light emitting device that suppresses an increase in drive voltage during long-term power supply and has a long life. [Means for solving the problem]

[0008] A vertical cavity light emitting device according to the present invention comprises a semiconductor structure layer including a gallium nitride semiconductor substrate, a first multilayer reflector made of nitride semiconductors formed on the substrate, a first semiconductor layer made of nitride semiconductors having a first conductivity type formed on the first multilayer reflector, an active layer made of nitride semiconductors formed on the first semiconductor layer, and a second semiconductor layer formed on the active layer and made of nitride semiconductors having a second conductivity type opposite to the first conductivity type, a transparent electrode layer formed on an upper surface of the second semiconductor layer, electrically contacting the second semiconductor layer in one region of the second semiconductor layer and insulated from the second semiconductor layer in another region surrounding the first region other than the first region, and a light emitting element on another region of the upper surface of the transparent electrode layer. a metal conductor layer formed in region A, a second multilayer reflector formed on the transparent electrode layer so as to cover region A and constituting a resonator between itself and the first multilayer reflector, and a transparent insulator layer disposed between the second semiconductor layer and the transparent electrode layer in another region on the second semiconductor layer, wherein the transparent insulator layer has an inner edge with a step outside region A, and the second semiconductor layer has, in the other region, an inactivated region formed by partially removing the surface of the second semiconductor layer and in which the impurities that impart the second conductivity type to the second semiconductor layer are inactivated on the surface of the second semiconductor layer after the removal, and the metal conductor layer is formed so as to cover the inner edge of the transparent insulator layer via the transparent electrode layer.

[0009] A vertical cavity light emitting device according to the present invention comprises a gallium nitride based semiconductor substrate, a first multilayer reflector made of nitride semiconductors formed on the substrate, a first semiconductor layer made of nitride semiconductors having a first conductivity type formed on the first multilayer reflector, an active layer made of nitride semiconductors formed on the first semiconductor layer, and a second semiconductor layer formed on the active layer and made of nitride semiconductors having a second conductivity type opposite to the first conductivity type, a transparent electrode layer formed on an upper surface of the second semiconductor layer, electrically contacting the second semiconductor layer in one region of the second semiconductor layer and insulated from the second semiconductor layer in another region surrounding the one region other than the first region, and a transparent electrode layer formed on the upper surface of the transparent electrode layer above the other region. a metal conductor layer disposed between the first semiconductor layer and the first multilayer reflector; a second multilayer reflector formed on the translucent electrode layer so as to cover one region and constituting a resonator between itself and the first multilayer reflector; and a translucent insulator layer disposed in another region on the second semiconductor layer between the second semiconductor layer and the translucent electrode layer, wherein the semiconductor structure layer has an annular groove formed in the other region and surrounding the second multilayer reflector in a plan view, and the second semiconductor layer has an inactivated region in the other region that is formed by partially removing the surface of the second semiconductor layer and in which an impurity that imparts a second conductivity type to the second semiconductor layer is inactivated on the surface of the second semiconductor layer after the removal, and the metal conductor layer is formed so as to cover the inner edge of the translucent insulator layer via the translucent electrode layer. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of a surface-emitting laser according to a first embodiment; [Figure 2] 1 is a top view of a surface-emitting laser according to a first embodiment. [Figure 3] 1 is a cross-sectional view of a surface-emitting laser according to a first embodiment. [Figure 4] FIG. 2 is a cross-sectional view of a surface-emitting laser according to a first modified example of the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a second modification of the first embodiment. [Figure 6] FIG. 10 is a top view of the surface-emitting laser according to the second embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a second embodiment. [Figure 8] FIG. 10 is a perspective view of a surface-emitting laser according to a third embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a third modified example of the first embodiment. [Figure 11] FIG. 10 is a cross-sectional view of a surface-emitting laser according to a fourth modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes in detail the embodiments of the present invention. In the following description, a semiconductor surface-emitting laser element is used as an example (semiconductor laser), 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]

[0012] 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.

[0013] The substrate 11 is a gallium nitride semiconductor substrate, such as a GaN substrate. The substrate 11 has, for example, a rectangular top surface. A first multilayer film reflector 13 made of semiconductor layers grown on the substrate 11 is formed on the substrate 11.

[0014] The first multilayer reflector 13 is a semiconductor multilayer reflector in which low-refractive-index semiconductor films having an AlInN composition and high-refractive-index semiconductor films having a GaN composition and a higher refractive index than the low-refractive-index semiconductor films are alternately stacked. In other words, the first multilayer reflector 13 is a distributed Bragg reflector (DBR) made of semiconductor material. For example, a buffer layer having a GaN composition is provided on the upper surface of the substrate 11, and the first multilayer reflector 13 is formed by alternately depositing the high-refractive-index semiconductor films and the low-refractive-index semiconductor films on the buffer layer.

[0015] 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 plane off-axis within 0.5° from the C-plane, because this improves the crystallinity of the semiconductor structure layer 15, which will be described later.

[0016] The semiconductor structure layer 15 is a laminated structure made up of a plurality of semiconductor layers formed on the first multilayer reflector 13. The semiconductor structure layer 15 has an n-type semiconductor layer (first semiconductor layer) 17 of a first conductivity type 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 of a second conductivity type formed on the active layer 19.

[0017] The n-type semiconductor layer 17 is a semiconductor layer formed on the first multilayer film reflector 13. The n-type semiconductor layer 17 has a GaN composition and is doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower portion 17A and a cylindrical upper portion 17B disposed thereon. Specifically, for example, the n-type semiconductor layer 17 has a cylindrical upper portion 17B protruding from the top surface 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.

[0018] 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.

[0019] 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. That is, in the semiconductor structure layer 15, a mesa-shaped structure is formed on the upper surface of the n-type semiconductor layer 17, and the active layer 19 and the p-type semiconductor layer 21 are stacked on the mesa-shaped structure.

[0020] N-electrode 23 as an electrode layer is a metal electrode provided on the upper surface 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 so as to surround upper portion 17B of n-type semiconductor layer 17. In other words, n-electrode 23, which is in electrical contact with n-type semiconductor layer 17, is formed on the upper surface surrounding the mesa-shaped structure of n-type semiconductor layer 17. Note that n-electrode 23 may be a so-called electrode layer formed in a layer shape on the upper surface of n-type semiconductor layer 17.

[0021] Insulating layer 25, which serves as a light-transmitting insulator layer, 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.

[0022] The p-electrode 27 as a metal conductor layer is a metal electrode formed on the insulating layer 25. The p-electrode 27 is electrically connected to the upper surface of the p-type semiconductor layer 21 exposed from the opening in the insulating layer 25 via a light-transmitting electrode layer 31 (described later in FIG. 3) made of a metal oxide film such as ITO or IZO.

[0023] The second multilayer reflector 29 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 29 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0024] 2 is a top view of the surface-emitting laser 10. As described above, the surface-emitting laser 10 has a semiconductor structure layer 15 including an n-type semiconductor layer 17 formed on a substrate 11 having a rectangular top surface shape, an active layer 19 having a circular top surface shape, and a p-type semiconductor layer 21 (see FIG. 1). An insulating layer 25 and a p-electrode 27 are formed on the p-type semiconductor layer 21. A second multilayer film reflector 29 is formed on the p-electrode 27.

[0025] The insulating layer 25 has an opening 25H, which is a circular opening that exposes the p-type semiconductor layer 21 of the insulating layer 25. As shown in Fig. 2, the opening 25H is formed in the center of the insulating layer 25 when viewed from above the surface-emitting laser 10, and is covered by the second multilayer reflector 29 when viewed from above 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 insulating layer 25 facing the lower surface of the second multilayer reflector 29.

[0026] The p-electrode 27 is formed in the center of the insulating layer 25 when viewed from above the surface-emitting laser 10, and has an opening 27H surrounding the opening 25H. That is, the opening 27H is larger than the opening 25H. For example, the shape of the opening 27H is a circle that is concentric with the shape of the opening 25H.

[0027] 2, an annular step 15S 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 step 15S is formed in a region outside the openings 25H and 27H. That is, the step 15S is an annular step when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0028] In this embodiment, the step 15S is formed on the upper surface of the p-type semiconductor layer 21 outside the second multilayer film reflector 29.

[0029] Fig. 3 is a cross-sectional view of the surface-emitting laser 10 taken along line 3-3 in Fig. 2. As described above, the surface-emitting laser 10 has the substrate 11, which is a GaN substrate, and the first multilayer film reflector 13 is formed on the substrate 11. The lower surface of the substrate 11 may be coated with an AR coating made of a laminate of Nb2O5 and SiO2.

[0030] A semiconductor structure layer 15 is formed on the first multilayer film reflector 13. The semiconductor structure layer 15 is a laminated body in which an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 are formed in this order.

[0031] The step 15S formed in the semiconductor structure layer 15 is formed so as to surround a protruding portion 21P that protrudes from the center of the upper surface of the p-type semiconductor layer 21.

[0032] The insulating layer 25 is formed to cover the upper surface of the p-type semiconductor layer 21. 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 exposing the protruding portion 21P. For example, as shown in FIG. 2, the opening 25H is circular. For example, the opening 25H and the protruding portion 21P have the same shape, and the inner surface of the opening 25H and the outer surface of the protruding portion 21P are in contact with each other. In addition, in the region inside the step 15S, the upper surface of the insulating layer 25 and the upper surface of the protruding portion 21P are formed to be flush with each other. That is, in the region inside the step 15S, the upper surfaces of the insulating layer 25 and the protruding portion 21P are flat. Note that the "same height" mentioned here does not mean a completely flush height, but may include unevenness or steps in a range that is insensitive to the light emitted from the active layer 19, i.e., the standing wave (laser light) generated between the first multilayer film reflector 13 and the second multilayer film reflector 29.

[0033] The translucent electrode layer 31 is a layer made of a translucent conductor and formed so as to cover the insulating layer 25 and the protruding portion 21P exposed from the opening 25H of the insulating layer 25. That is, the translucent electrode layer 31 is in electrical contact with the p-type semiconductor layer 21 in a region of the upper surface of the p-type semiconductor layer 21 exposed by the opening 25H. The translucent electrode layer 31 is formed of a metal oxide such as ITO or IZO that is translucent to light emitted from the active layer 19. The translucent electrode layer 31 is formed so as to transfer the shapes of the upper surface of the insulating layer 25 on the lower surface side and the upper surface of the protruding portion 21P. That is, the translucent electrode layer 31 has a step at a location corresponding to the step 15S.

[0034] As described above, the p-electrode 27 is a metal electrode and is formed so as to cover the translucent electrode layer 31. That is, the p-electrode 27 is in electrical contact with the translucent electrode layer 31. Therefore, the p-electrode 27 is in electrical contact or connection with the p-type semiconductor layer 21 via the translucent electrode layer 31 in a region exposed by 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 translucent electrode layer 31. The opening 27H is an opening with a width (or diameter) larger than that of the opening 25H. Furthermore, as shown in FIG. 3, the p-electrode 27 is formed so as to cover the step 15S.

[0035] In the surface-emitting laser 10, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 29. Therefore, part of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 29 passes through the first multilayer reflector 13 and the substrate 11 and is extracted to the outside.

[0036] 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 27 in the surface-emitting laser 10, a current flows in the semiconductor structure layer 15 as shown by the thick two-dot chain line in the figure, and light is emitted from the active layer 19. The light emitted from the active layer 19 is repeatedly reflected between the first multilayer film reflector 13 and the second multilayer film reflector 29, and reaches a resonance state (laser oscillation).

[0037] 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. Furthermore, because 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 direction of the semiconductor structure layer 15. Therefore, in the surface-emitting laser 10, current is supplied only to the region of the active layer 19 directly below 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.

[0038] As described above, in this embodiment, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 29. Therefore, part of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 29 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.

[0039] The protruding portion 21P 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 protruding portion 21P of the p-type semiconductor layer 21 and extends along a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0040] 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, and its center 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, and its center is the light-emitting center. A straight line passing through the light-emitting center and perpendicular to the upper surface of the substrate 11 or the in-plane direction of each layer of the semiconductor structure layer 15 is the central axis AX. The light-emitting central axis AX is a straight line extending along the cavity length direction of the cavity OC formed by the first multilayer reflecting mirror 13 and the second multilayer reflecting mirror 29. The central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 10.

[0041] Here, we will explain 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. In this example, the first multilayer reflector 13 is made of a 1 μm thick GaN underlayer formed on the upper surface of the substrate 11, and 42 pairs of n-GaN layers (45 nm) and AlInN layers (50 nm).

[0042] The n-type semiconductor layer 17 is a 1580 nm thick Si-doped n-GaN layer. The active layer 19 has a multi-quantum well structure with four pairs of 4 nm InGaN layers and 5 nm GaN layers stacked together. The peak of the spectrum of the light emitted from the active layer 19 is adjusted to approximately 440 nm. An Mg-doped AlGaN electron barrier layer is formed on the active layer 19, and a p-type semiconductor layer 21 consisting of a 50 nm p-GaN layer is formed on top of that. The second multilayer reflector 29 is formed by stacking 10.5 pairs of 45 nm Nb2O5 and 76 nm SiO2. The resonant wavelength in this case was 440 nm.

[0043] Furthermore, p-type semiconductor layer 21 has a layer thickness of 50 nm at protruding portion 21P, and a layer thickness of 30 nm in a region from the outer peripheral edge of protruding portion 21P to step 15S. Insulating layer 25 made of SiO2 has a layer thickness of 20 nm; that is, in a region from the inner peripheral edge of insulating layer 25 in contact with the side surface of protruding portion 21P to step 15S, 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.

[0044] The light-transmitting electrode layer 31 formed on the semiconductor structure layer 15 is a 20 nm layer made of ITO, and a second multilayer film reflector 29 is formed on the light-transmitting electrode layer 31 and the p-electrode 27, sandwiching a 40 nm NbO spacer layer. The p-electrode 27 is formed by laminating Ti (100 nm), Pt (100 nm), and Au (500 nm) in this order.

[0045] The p-type semiconductor layer 21, insulating layer 25, light-transmitting electrode layer 31, and p-electrode 27 in the step 15S are preferably inclined with respect to the central axis AX of the surface-emitting laser 10. The inclination angle of the inclination is preferably 45° or more with respect to the central axis AX. In other words, the inclination angle is preferably 45° or less with respect to the upper surface of the semiconductor structure layer 15. By providing an inclination to the step, it is possible to improve the long-term reliability, such as the crack resistance of the light-transmitting electrode layer 31, during long-term current application.

[0046] The rear surface of the substrate 11 is a polished surface, and a two-layer AR coating of Nb2O5 and SiO2 is formed on the polished surface.

[0047] The above-described configuration of the surface-emitting laser 10 of this embodiment is merely an example.

[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 refractive index lower than that of the p-type semiconductor layer 21. Furthermore, the thicknesses of the other layers between the first multilayer film reflector 13 and the second multilayer film reflector 29 are the same anywhere within the plane if they are within the same layer.

[0049] Therefore, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 29, which corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 29 of the surface-emitting laser 10 differs between the central region CA, which is one cylindrical region whose top surface shape is defined by the opening 25H, and the peripheral region PA, which is another cylindrical region 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 29, 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 resonance wavelength in the central region CA is longer than the equivalent resonance wavelength in the peripheral region PA. As described above, light is emitted from the region directly below the protrusion 21P in the active layer 19. In other words, 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.

[0051] Thus, 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] As described above, in the surface-emitting laser 10 of Example 1, a step is formed in the translucent electrode layer 31. In other words, the step 15S forms a step in the translucent electrode layer 31. Then, the p-electrode 27 is formed to cover the step.

[0053] As described above, the surface-emitting laser 10 of Example 1 includes a substrate 11 made of a gallium nitride semiconductor, a first multilayer reflector 13 made of a nitride semiconductor formed on the substrate 11, an n-type semiconductor layer 17 made of a nitride semiconductor having a first conductivity type formed on the first multilayer reflector 13, an active layer 19 made of a nitride semiconductor formed on the n-type semiconductor layer 17, and a semiconductor structure layer 15 including a p-type semiconductor layer 21 formed on the active layer 19 and made of a nitride semiconductor having a p-type conductivity type opposite to the n-type conductivity type, and a semiconductor structure layer 15 formed on an upper surface of the p-type semiconductor layer 21 and including a central region of the p-type semiconductor layer 21. The semiconductor structure layer 15 has a light-transmitting electrode layer 31 that is in electrical contact with the p-type semiconductor layer 21 in the area CA and is insulated from the p-type semiconductor layer 21 in the peripheral area PA that surrounds areas other than the central area CA, a p-electrode 27 formed on the upper surface of the light-transmitting electrode layer 31 above the peripheral area PA, and a second multilayer film reflector 29 formed on the light-transmitting electrode layer 31 so as to cover the central area CA and to form a resonator OC between itself and the first multilayer film reflector 13, and a step 15S is formed in the peripheral area PA on the upper surface of the semiconductor structure layer 15, and the p-electrode 27 is formed so as to cover the light-transmitting electrode layer 31 on the step 15S.

[0054] The step 15S has an inclined surface that forms an angle of 45° or less with respect to the upper surface of the semiconductor structure layer 15. The n-type semiconductor layer 17 has a mesa-shaped structure on its upper surface, and the active layer 19 and the p-type semiconductor layer are stacked on the mesa-shaped structure. The surface-emitting laser 10 has an n-electrode 23 that is in electrical contact with the n-type semiconductor layer 17 on the upper surface of the n-type semiconductor layer 17 that is present around the mesa-shaped structure.

[0055] FIG. 4 shows a cross-sectional view of a surface-emitting laser 10A according to a first modification of the first embodiment.

[0056] 3, in order to form the step 15S, an annular region (corresponding to the peripheral region PA when viewed from above) of the p-type semiconductor layer 21 surrounding the protruding portion 21P is etched, and an insulating layer 25 is formed on the upper surface of the p-type semiconductor layer 21 outside the region and the step 15S. However, instead, as shown in FIG. 4, the entire surface of the p-type semiconductor layer 21 except for the protruding portion 21P may be etched, and an insulating layer 25 may be formed in the region, and the step 25S may be formed in the insulating layer 25.

[0057] 5, insulating layer 25 may be formed by laminating a first insulating layer 25A for forming a step (step 25AS in the figure) and an additional insulating layer 25 on the annular region of p-type semiconductor layer 21 surrounding protruding portion 21P and on the upper surface of first insulating layer 25A. Note that insulating layer 25 for forming step 25AS may be formed of a material other than insulating layer 25.

[0058] If the transparent electrode is formed without creating a step, the capacitance of the current path in the semiconductor layer increases, which may result in a decrease in modulation speed. Furthermore, if the capacitance increases, the amount of heat generated by the semiconductor layer during operation increases, which may cause the semiconductor layer to melt and result in a short circuit or other problems.

[0059] That is, by forming this step and increasing the distance between the p-electrode 27 and the surface of the semiconductor layer 21, it is possible to reduce the capacitance between the p-electrode 27 and the surface of the semiconductor layer 21 when the surface-emitting laser 10 is operating, and to prevent a decrease in modulation speed. Furthermore, this reduction in capacitance makes it possible to reduce the amount of heat generated during operation, and to prevent problems such as melting of the semiconductor structure layer 15 from occurring.

[0060] Furthermore, the transparent electrode layer 31 on the step 15S is covered with the p-electrode 27, which is a metal layer. This makes it possible to prevent abnormalities such as cracks from occurring in the step portion of the transparent electrode layer 31 during long-term current application. Even if a crack occurs in the step portion of the transparent electrode layer 31 during long-term current application, the p-electrode 27 is formed so as to cover the step, so that conduction between the p-electrode 27 and the p-type semiconductor layer 21 is maintained. Therefore, even if a crack occurs in the step portion of the transparent electrode layer 31, it is possible to prevent abnormalities such as an open circuit from occurring.

[0061] Therefore, according to the first embodiment, it is possible to prevent the occurrence of problems such as an increase in driving voltage during long-term power supply and short / open circuits, and to provide a vertical cavity surface emitting laser 10 with a long life. [Example]

[0062] Second Embodiment A surface-emitting laser 20 according to a second embodiment of the present invention will now be described.

[0063] Fig. 6 shows a top view of the surface-emitting laser 20 of Example 2. Fig. 7 is a cross-sectional view of the surface-emitting laser 20 taken along line 5-5 in Fig. 6.

[0064] The surface-emitting laser 20 has basically the same configuration and similar appearance as the surface-emitting laser 10 of Example 1. However, the surface-emitting laser 20 differs from the surface-emitting laser 10 in that the surface-emitting laser 20 does not have a step outside the central region CA of the semiconductor structure layer 15, but has a step formed by an insulating layer 25 formed outside the central region CA. The surface-emitting laser 20 also differs from the surface-emitting laser 10 in that a passivation region layer 21A in which p-type impurities are passivated is provided outside the protruding portion 21P of the p-type semiconductor layer 21.

[0065] The passivation region layer 21A can be formed, for example, by dry etching, leaving the region of the protruding portion 21P of the p-type semiconductor layer 21. The surface of a semiconductor containing impurities, such as the p-type semiconductor layer 21, is roughened by dry etching. This inactivates the p-type impurities in the etched portion, forming the passivation region layer 21A. Furthermore, the p-type semiconductor layer 21 is partially removed by dry etching in the passivation region layer 21A. In other words, the passivation region layer 21A has an opening 21H, which is a circular opening that exposes the p-type semiconductor layer 21 of the passivation region layer 21A. The amount of etching partially removed by dry etching in the passivation region layer 21A is, for example, 4 nm.

[0066] Furthermore, an insulating layer 25 serving as a translucent insulator layer is formed outside the central region CA on the upper surface of the p-type semiconductor layer 21. Furthermore, a step 25S is formed on the inner edge of the insulating layer 25. The translucent electrode layer 31 and the p-electrode 27 are formed so that a step is generated in a portion corresponding to the step 25S. That is, the p-electrode 27 is formed so as to cover the step portion of the translucent electrode layer 31 caused by the step 25S. In other words, the p-electrode 27 is formed so as to cover the inner edge of the translucent insulating layer 25, i.e., the portion of the step 25S, via the translucent electrode layer 31.

[0067] As in the above-described first embodiment, by forming the step 25S to increase the distance between the p-electrode 27 and the surface of the semiconductor layer 21, it is possible to reduce the capacitance between the p-electrode 27 and the semiconductor layer 21 when the surface-emitting laser 20 is driven, and to prevent a decrease in modulation speed. Furthermore, this reduction in capacitance makes it possible to reduce the amount of heat generated during driving, and to prevent problems such as melting of the semiconductor structure layer 15.

[0068] Furthermore, the translucent electrode layer 31 and the p-electrode 27 at the step 25S are preferably inclined with respect to the central axis AX of the surface-emitting laser 20. The inclination angle of the insulating layer 25 at the step 25S is preferably 45° or more with respect to the central axis AX. In other words, the inclination angle is preferably 45° or less with respect to the upper surface of the semiconductor structure layer 15. By providing an inclination to the step, it is possible to improve the long-term reliability, such as crack resistance, of the translucent electrode layer formed on the step 25S of the insulating layer 25 during long-term current application.

[0069] As described above, the surface-emitting laser 20 of Example 2 includes the semiconductor structure layer 15 including the substrate 11 made of a gallium nitride semiconductor, the first multilayer reflector 13 made of a nitride semiconductor and formed on the substrate 11, the n-type semiconductor layer 17 made of a nitride semiconductor having n-type conductivity and formed on the first multilayer reflector 13, the active layer 19 made of a nitride semiconductor and formed on the n-type semiconductor layer 17, and the p-type semiconductor layer 21 formed on the active layer 19 and made of a nitride semiconductor having p-type conductivity opposite to the n-type conductivity, and the p-type semiconductor layer 22 formed on the upper surface of the p-type semiconductor layer 21. The semiconductor device has an insulating layer 25 formed in a region surrounding a central region CA of 1, a light-transmitting electrode layer 31 formed across the upper surface of the p-type semiconductor layer 21 and the upper surface of the inactivated region layer 21A and in contact with the p-type semiconductor layer 21 in the central region CA, a p-electrode 27 formed on the upper surface of the light-transmitting electrode layer 31 above the peripheral region PA, and a second multilayer film reflector 29 formed on the light-transmitting electrode layer 31 so as to cover the central region CA and which constitutes a resonator OC between itself and the first multilayer film reflector 13, and the p-electrode 27 is formed so as to cover the inner edge of the insulating layer 25 via the light-transmitting electrode layer 31.

[0070] Moreover, the inactivated region layer 21A functions as a high-resistance region having a higher electrical resistance than the p-type semiconductor layer 21. On the other hand, the region that has not been etched, i.e., the protruding portion 21P of the p-type semiconductor layer 21, which is a region where the inactivated region layer 21A is not provided, functions as a low-resistance region.

[0071] The p-type semiconductor layer 21 functions as a current confinement layer that constricts the path of current injected into the active layer 19. The protruding portion 21P of the p-type semiconductor layer 21 functions as a current injection region where current is injected into the active layer 19. On the other hand, the passivation region layer 21A of the p-type semiconductor layer 21 functions as a non-current injection region where current injection into the active layer 19 is suppressed.

[0072] That is, in the surface-emitting laser 20, current is injected into the p-type semiconductor layer 21 only from the portion exposed by the opening 21H. Moreover, because the p-type semiconductor layer 21 is very thin, current hardly diffuses 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. Therefore, in the surface-emitting laser 20, current is supplied only to the region of the active layer 19 directly below the opening 21H, and light is emitted only from that region. That is, in the surface-emitting laser 20, the opening 21H forms a current confinement structure that limits the range of current supply in the active layer 19.

[0073] Therefore, when a voltage is applied between the n-electrode 23 and the p-electrode 27 in the surface-emitting laser 20, a current flows in the semiconductor structure layer 15 as shown by the thick two-dot chain line in the figure, and light is emitted from the active layer 19. The light emitted from the active layer 19 is repeatedly reflected between the first multilayer film reflector 13 and the second multilayer film reflector 29, and reaches a resonance state (laser oscillation).

[0074] As described above, the thickness of the p-type semiconductor layer 21 in the central region CA (low resistance region) is greater than the thickness of the p-type semiconductor layer 21 in the peripheral region PA (high resistance region).

[0075] Therefore, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 29, which corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 29 of the surface-emitting laser 20 differs between the cylindrical central region CA whose top surface shape is defined by the opening 21H 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.

[0076] 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 the equivalent refractive index of the central region CA, i.e., the equivalent resonance wavelength in the central region CA is longer than the equivalent resonance wavelength in the peripheral region PA. As described above, light is emitted from the region directly below the opening 21H in the active layer 19. In other words, 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.

[0077] In the second embodiment, the high-resistance region layer forming the current confinement structure is an inactivated region layer 21A obtained by inactivating the p-type semiconductor layer 21 by dry etching. However, the configuration of the high-resistance region layer is not limited to this. For example, the high-resistance region layer may be a surface layer of a GaN layer that has been subjected to a high-resistance treatment by ion implantation into the p-type semiconductor layer 21. Alternatively, the high-resistance region layer may be an insulating layer such as SiO2.

[0078] As described above, according to Example 2, the transparent electrode layer 31 on the step 25S is covered with the p-electrode 27, which is a metal layer. This makes it possible to prevent abnormalities such as cracks from occurring in the step portion of the transparent electrode layer 31 during long-term current application. Even if a crack occurs in the step portion of the transparent electrode layer 31 during long-term current application, the p-electrode 27 is formed so as to cover the step, so that conduction between the p-electrode 27 and the p-type semiconductor layer 21 is maintained. Therefore, even if a crack occurs in the step portion of the transparent electrode layer 31, it is possible to prevent abnormalities such as an open circuit from occurring.

[0079] Therefore, according to the second embodiment, it is possible to prevent the occurrence of problems such as an increase in driving voltage during long-term power supply and short / open circuits, and to provide a vertical cavity surface-emitting laser 20 with a long life. [Example]

[0080] A surface-emitting laser 30 according to a third embodiment of the present invention will now be described.

[0081] Fig. 8 shows a perspective view of a surface-emitting laser 30 of Example 3. Fig. 9 shows a cross-sectional view of the surface-emitting laser 20 cut along the same cross section as that shown in Example 1 above.

[0082] The surface-emitting laser 30 has basically the same configuration as the surface-emitting laser 10 of Example 1, but differs from the surface-emitting laser 10 in that an annular groove 15G is formed outside the central region CA of the semiconductor structure layer 15.

[0083] 9, an annular groove 15G is formed in 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 a region outside the openings 25H and 27H. That is, the groove 15G is an annular groove when viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0084] In this embodiment, the groove 15G is formed on the upper surface of the p-type semiconductor layer 21 outside the second multilayer reflector 29. That is, on the upper surface of the p-type semiconductor layer 21, the groove 15G is exposed from the peripheral region PA where the second multilayer reflector 29 is formed.

[0085] The groove 15G formed in the semiconductor structure layer 15 is formed so as to surround the protruding portion 21P that protrudes from the center of the upper surface of the p-type semiconductor layer 21, and extends from the upper surface of the p-type semiconductor layer 21 through the active layer 19 to the n-type semiconductor layer 17.

[0086] In this way, in the surface-emitting laser 30 of Example 3, the grooves 15G are formed so as to penetrate through the active layer 19. In other words, gaps are formed in the active layer 19 by the grooves 15G.

[0087] 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 lower refractive index than the p-type semiconductor layer 21. The insulating layer 25 has an opening 25H that exposes the protruding portion 21P. For example, as shown in FIG. 8, the opening 25H is circular. For example, the opening 25H and the protruding portion 21P have the same shape, and the inner surface of the opening 25H and the outer surface of the protruding portion 21P are in contact with each other.

[0088] As described above, in the surface-emitting laser 30 of Example 3, the groove 15G is formed to penetrate the active layer 19. In other words, the groove 15G forms a gap in the active layer 19. The groove 15G is formed after the semiconductor structure layer 15 is formed. Thereafter, the insulating layer 25 is formed before the light-transmitting electrode layer 31, the p-electrode 27, and the second multilayer film reflector 29 are formed.

[0089] Therefore, after the semiconductor structure layer 15 is formed, the grooves 15G reaching the active layer 19 are formed, thereby forming spaces or gaps in the direction along the in-plane of the active layer 19. These gaps relieve strain that occurs in the in-layer direction of the active layer 19 or in the in-plane direction of the semiconductor structure layer 15 during the formation of the active layer 19.

[0090] Specifically, when the active layer 19 is formed, the difference in lattice constant between the InGaN and GaN that form the quantum well structure causes distortion of the crystal structure, resulting in piezoelectric polarization and the generation of a piezoelectric field. The generation of this piezoelectric field reduces the recombination probability of electrons and holes injected into the active layer 19, which is one of the causes of a low internal quantum efficiency.

[0091] In the surface-emitting laser 30, a groove 15G is formed in the semiconductor structure layer 15, reaching the active layer 19. The gap created by this groove relieves strain that occurs in the active layer 19 in the in-layer direction during growth of the active layer 19, and it is believed that this improves the internal quantum efficiency of the active layer 19.

[0092] Here, we will explain the operation of the surface-emitting laser 30. When a voltage is applied between the n-electrode 23 and the p-electrode 27 in the surface-emitting laser 30, a current flows in the semiconductor structure layer 15 as shown by the thick two-dot chain line in the figure, and light is emitted from the active layer 19. The light emitted from the active layer 19 is repeatedly reflected between the first multilayer film reflector 13 and the second multilayer film reflector 29, and reaches a resonance state (laser oscillation).

[0093] In the surface-emitting laser 30, current is injected into the p-type semiconductor layer 21 only from the portion exposed by the opening 25H. Furthermore, because the p-type semiconductor layer 21 is very thin, current hardly diffuses in the in-plane direction within the p-type semiconductor layer 21, i.e., in the direction along the in-plane direction of the semiconductor structure layer 15. Therefore, in the surface-emitting laser 30, current is supplied only to the region of the active layer 19 directly below the opening 25H, and light is emitted only from that region. That is, in the surface-emitting laser 30, the opening 25H forms a current confinement structure that limits the range of current supply in the active layer 19.

[0094] As described above, in this embodiment, the first multilayer reflector 13 has a reflectivity slightly lower than that of the second multilayer reflector 29. Therefore, part of the light resonating between the first multilayer reflector 13 and the second multilayer reflector 29 passes through the first multilayer reflector 13 and the substrate 11 and is extracted to the outside. In this way, the surface-emitting laser 30 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.

[0095] The protruding portion 21P 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 protruding portion 21P of the p-type semiconductor layer 21 and extends along a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0096] 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, and its center 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, and its center is the light-emitting center. A straight line passing through the light-emitting center and perpendicular to the upper surface of the substrate 11 or the in-plane direction of each layer of the semiconductor structure layer 15 is the central axis AX. The light-emitting central axis AX is a straight line extending along the cavity length direction of the cavity OC formed by the first multilayer reflecting mirror 13 and the second multilayer reflecting mirror 29. The central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 30.

[0097] Here, we will explain exemplary configurations of the first multilayer reflector 13, the semiconductor structure layer 15, and the second multilayer reflector 29, as well as exemplary dimensions of the grooves 15G, in the surface-emitting laser 30. In this example, the first multilayer reflector 13 is made of a 1 μm thick GaN underlayer formed on the upper surface of the substrate 11, and 42 pairs of n-GaN and AlInN layers.

[0098] The n-type semiconductor layer 17 is an n-GaN layer with a thickness of 1580 nm. The active layer 19 has a multi-quantum well structure in which four pairs of 4 nm InGaN 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 29 is made by stacking 10.5 pairs of Nb2O5 and SiO2. The resonant wavelength in this case was 440 nm.

[0099] 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 ITO with a thickness of 20 nm, and the second multilayer film reflector 29 is formed on the light-transmitting electrode layer 31 and the p-electrode 27 with a spacer layer of NbO sandwiched therebetween with a thickness of 40 nm.

[0100] The rear surface of the substrate 11 is a polished surface, and a two-layer AR coating of Nb2O5 and SiO2 is formed on the polished surface.

[0101] Furthermore, p-type semiconductor layer 21 may have a layer thickness of 50 nm in protruding portion 21P and a layer thickness of 30 nm in other regions. That is, p-type semiconductor layer 21 may have a different layer thickness in protruding portion 21P than in other portions. Furthermore, 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.

[0102] 9, the groove 15G is depicted as if it were formed perpendicular to the top surface of the p-type semiconductor layer 21. However, the groove 15G and the p-type semiconductor layer 21, insulating layer 25, translucent electrode layer 31, and p-electrode 27 in the groove 15G portion preferably form a step having a side surface inclined with respect to the central axis AX of the surface-emitting laser 30. The inclination angle of the side surface is preferably 45° or more with respect to the central axis AX. In other words, the inclination angle of the side surface is preferably 45° or less with respect to the top surface of the semiconductor structure layer 15. By providing an inclination to the step, it is possible to improve the long-term reliability, such as the crack resistance of the translucent electrode layer 31, during long-term current application.

[0103] The above-described configuration of the surface-emitting laser 30 of this embodiment is merely an example.

[0104] The following describes the optical characteristics inside the surface-emitting laser 30. As described above, in the surface-emitting laser 30, the insulating layer 25 has a refractive index lower than that of the p-type semiconductor layer 21. Furthermore, the thicknesses of the other layers between the first multilayer film reflector 13 and the second multilayer film reflector 29 are the same anywhere within the plane if they are within the same layer.

[0105] Therefore, the equivalent refractive index (the optical distance between the first multilayer reflector 13 and the second multilayer reflector 29, which corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer reflector 13 and the second multilayer reflector 29 of the surface-emitting laser 30 differs between the cylindrical central region CA whose top surface shape is defined by the opening 25H 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.

[0106] 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 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. As described above, light is emitted from the region directly below the opening 25H in the active layer 19. In other words, 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.

[0107] In the third embodiment, the groove 15G is formed in a ring shape outside the central region CA in a top view. However, the groove 15G may have a groove structure including intermittently formed recesses rather than a complete ring shape. That is, the groove 15G may have a recessed structure including a plurality of recesses. In other words, the groove 15G may have an intermittently formed ring structure. For example, the groove 15G may have an intermittently formed ring structure surrounding a region exposed by the opening 25H on the top surface of the p-type semiconductor layer 21.

[0108] In addition, when the groove 15G is formed by a plurality of recesses, it is desirable that they are formed in two or more directions as viewed from the above-mentioned light-emitting central axis AX in order to uniformly relieve strain in the active layer 19. That is, when the groove 15G is formed by a plurality of recesses, it is preferable that the recesses are formed in two or more directions as viewed from the light-emitting region including the light-emitting central axis AX in a top view of the surface-emitting laser 30, so that the light-emitting region is sandwiched between the recesses. In order to uniformly relieve strain in the active layer 19, it is more preferable that the recesses forming the groove 15G are arranged rotationally symmetrically with respect to the light-emitting central axis AX. In other words, it is preferable that the recesses forming the groove 15G are arranged rotationally symmetrically as viewed from a direction perpendicular to the in-plane direction of the semiconductor structure layer 15.

[0109] That is, the step of the surface-emitting laser 30 of Example 3 is a recessed structure including one or more grooves 15G penetrating the active layer 19 from the top surface in a region surrounding the central region CA of the semiconductor structure layer 15. In addition, the p-electrode 27 is formed so as to cover the inner surface of the one or more grooves 15G.

[0110] As described above, by changing the shape of the groove 15G, for example, by forming the groove 15G with a plurality of recesses, it is also possible to control the polarization of the light emitted from the surface-emitting laser of the above-described embodiment.

[0111] According to the third embodiment, the translucent electrode layer 31 above the groove 15G is covered with the p-electrode 27, which is a metal layer. This makes it possible to prevent abnormalities such as cracks from occurring in the stepped portion of the translucent electrode layer 31 during long-term current application. Even if a crack occurs in the stepped portion of the translucent electrode layer 31 during long-term current application, the p-electrode 27 is formed so as to cover the step, so that electrical continuity between the p-electrode 27 and the p-type semiconductor layer 21 is maintained. Therefore, even if a crack occurs in the stepped portion of the translucent electrode layer 31, it is possible to prevent abnormalities such as an open circuit from occurring.

[0112] Therefore, according to the third embodiment, it is possible to prevent the occurrence of problems such as an increase in driving voltage during long-term power supply and short / open circuits, and to provide a vertical cavity surface-emitting laser 30 with a long life.

[0113] Additionally, as described above, in the surface-emitting laser 30 of this embodiment, the semiconductor structure layer 15 is formed with a groove 15G extending from the upper surface of the p-type semiconductor layer 21 to the active layer 19. The groove 15G relieves strain generated in the active layer 19 in the in-layer direction, improving the internal quantum efficiency of the active layer 19 and enabling an improvement in light-emitting efficiency to be realized.

[0114] In any of Examples 1, 2, and 3, the step 15S, 25S, or groove 15G is provided outside the second multilayer film reflector 29 from the central axis AX, and the step 15S, 25S, or groove 15G is exposed when viewed from above the surface-emitting laser. However, the step 15S, 25S, or groove 15G may be provided so as to be covered by the second multilayer film reflector 29.

[0115] Even in a configuration in which second multilayer film reflector 29 is formed so as to cover steps 15S, 25S or groove 15G, it is possible to obtain the same effects as those of the respective embodiments. Furthermore, in the case of a structure having groove 15G as in embodiment 3, second multilayer film reflector 29 is formed so as to fill the space formed by groove 15G.

[0116] Furthermore, in all of Examples 1, 2, and 3, the surface-emitting laser has been described in which n-electrode 23 is formed on the upper surface of substrate 11. However, n-electrode 23 may be formed on the back surface of substrate 11. In this case, substrate 11 may be made of a conductive material such as n-GaN, and an n-electrode made of metal may be formed on the back surface of substrate 11.

[0117] In this case, a rear surface protrusion is formed on the rear surface of substrate 11. The rear surface protrusion is formed in a region corresponding to protrusion 21P when viewed from the normal direction of substrate 11. This rear surface protrusion is a convex portion that remains after the rear surface is polished and the area around the rear surface protrusion is removed by dry etching. Therefore, the top surface of the rear surface protrusion is a polished surface, and the area around the rear surface protrusion on the rear surface of substrate 11 is a surface where the polished surface has been dry-etched. The n-electrode is formed in the area around the rear surface protrusion, i.e., the area excluding the rear surface protrusion. This is because the top surface of the rear surface protrusion of substrate 11 serves as an opening through which emitted light is released to the outside, and the emitted light is not blocked by the n-electrode. In other words, the rear surface protrusion is structured to protrude from the opening of the n-electrode.

[0118] That is, the substrate 11 has an n-type conductivity, and the surface-emitting lasers 10, 20, and 30 have an n-electrode on the surface of the substrate 11 opposite the semiconductor structure layer 15, excluding the area corresponding to the central region CA when viewed from a direction perpendicular to the top surface of the substrate 11.

[0119] Furthermore, in each of Examples 1, 2, and 3, the surface-emitting laser has been described as having a current confinement structure formed by the insulating layer 25 or the passivation region layer 21 A. However, the configuration of the current confinement structure is not limited to these.

[0120] For example, the surface-emitting laser may be configured to have a current confinement structure formed by a tunnel junction layer in which a highly doped p-type semiconductor layer having a higher impurity concentration than the p-type semiconductor layer 21 is formed in a central region CA on the p-type semiconductor layer 21, and a highly doped n-type semiconductor layer formed on the highly doped p-type semiconductor layer and having a higher impurity concentration than the n-type semiconductor layer 17 is formed.

[0121] In other words, the p-electrode 27 is provided in a layer below the translucent electrode layer 31 in an area outside the central area CA, and a step is formed in the translucent electrode layer 31 at the step portion, and the p-electrode 27 is formed so as to cover the step portion of the translucent electrode layer 31.

[0122] Furthermore, any of Examples 1, 2 and 3 may have an optical guide layer including: a first light-transmitting insulating layer provided on the light-transmitting electrode layer 31 across the central region CA and the peripheral region PA, the first light-transmitting insulating layer having a convex portion on the central axis AX; and a second light-transmitting insulating layer provided on the first light-transmitting insulating layer in the peripheral region PA, the second light-transmitting insulating layer having a refractive index smaller than that of the first light-transmitting insulating layer.

[0123] This suppresses optical loss caused by the standing waves in the resonator OC diverging (radiating) outward from the central region CA. That is, much of the light remains in the central region CA, and the laser light is extracted in this state. Therefore, much of the light is concentrated near the central axis AX, and a laser light having a stable unimodal or multimodal intensity distribution can be generated and emitted.

[0124] Furthermore, in all of Examples 1, 2, and 3, the case has been described in which the p-electrode 27 covers the step of the translucent electrode layer 31 and is formed integrally therewith. However, the p-electrode 27 may have a first p-electrode that covers the step of the translucent electrode layer 31 to extend the life of the translucent electrode layer 31, and a second p-electrode that is formed on the outer edge of the semiconductor structure layer 15 and is electrically connected to the mounting substrate. In other words, the p-electrode 27 may be separated into a portion that protects the translucent electrode layer 31 and a portion that is connected to the mounting substrate.

[0125] In addition, in all of Examples 1, 2, and 3, the p-electrode 27 is formed to cover the steps of the translucent electrode layer 31. However, the protective film that covers the steps of the translucent electrode layer 31 is not limited to the p-electrode 27.

[0126] FIG. 10 is a cross-sectional view of a surface-emitting laser 10B according to a third modification of the first embodiment.

[0127] For example, as shown in FIG. 10 , a second translucent electrode layer 31A made of the same material as the translucent electrode layer 31 may be additionally laminated only on the step portion of the translucent electrode layer 31. In other words, the thickness of the step portion of the translucent electrode layer 31 may be, for example, twice the thickness of the translucent electrode layer 31. This makes it possible to prevent cracks from occurring in the step portion of the translucent electrode layer 31 during long-term current application. Note that in this modification, the case where the second translucent electrode layer 31A is additionally laminated only on the portion corresponding to the step 15S has been described, but the area where the second translucent electrode layer 31A is laminated is not limited to this. For example, the second translucent electrode layer 31A may be formed in an area excluding the central region CA, which is the light-emitting area. In other words, it is sufficient that the second translucent electrode layer 31A is formed so as to cover at least the portion corresponding to the step 15S. Modification 3 can also be applied to Examples 2 and 3.

[0128] FIG. 11 is a cross-sectional view of a surface-emitting laser 10C according to a fourth modification of the first embodiment.

[0129] As in the second modification, the dielectric film 33 may be formed only on the stepped portion of the translucent electrode layer 31. The dielectric film 33 may be formed of, for example, SiO2, SiN xThe dielectric film 33 is preferably a dielectric film made of a material such as Al2O3 or Al2O3. The dielectric film 33 is preferably a dielectric film that is less reactive with the translucent electrode layer 31 than the high-refractive-index dielectric film (Nb2O5 in this embodiment) used in the spacer layer (not shown). As described above, protecting the step portion of the translucent electrode layer 31 with a dielectric layer can reduce the likelihood of cracks occurring in the step portion of the translucent electrode layer 31 during long-term current application. While this modification describes the case where the dielectric film 33 is additionally laminated only on the portion corresponding to the step 15S, the area where the dielectric film 33 is laminated is not limited thereto. For example, the dielectric film 33 may be formed in an area excluding the central region CA, which is the light-emitting region. In other words, it is sufficient that the dielectric film 33 is formed to cover at least the portion corresponding to the step 15S. In this case, however, the dielectric film 33 is preferably formed so as not to impede electrical contact between the p-electrode 27 and the translucent electrode layer 31. That is, it is preferable that the p-electrode 27 and the translucent electrode layer 31 are configured to be in electrical contact with each other in at least one portion. The fourth modification can also be applied to the second and third embodiments.

[0130] Furthermore, the various numerical values, dimensions, materials, etc. in the above-described embodiments and modifications are merely examples, and can be selected appropriately depending on the application and the surface-emitting laser to be manufactured. [Explanation of symbols]

[0131] 10, 20, 30 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 27p electrode 29 Second multilayer mirror 31 Transparent electrode layer 33 Dielectric layer

Claims

1. a gallium nitride semiconductor substrate; a first multilayer reflector made of nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a transparent electrode layer formed on an upper surface of the second semiconductor layer, electrically contacting the second semiconductor layer in one region of the second semiconductor layer, and insulated from the second semiconductor layer in another region surrounding the one region other than the one region; a metal conductor layer formed on the upper surface of the translucent electrode layer in a region above the other region; a second multilayer reflector formed on the transparent electrode layer so as to cover the first region and constituting a resonator between itself and the first multilayer reflector; a transparent insulator layer disposed between the second semiconductor layer and the transparent electrode layer in the other region on the second semiconductor layer, the first region is an upper surface of a protrusion that protrudes upward from the other region, the light-transmitting insulator layer has an inner edge with a step outside the first region, the second semiconductor layer includes, in the other region, a passivation region in which an impurity imparting the second conductivity type to the second semiconductor layer is inactivated; The vertical cavity light emitting device is characterized in that the metal conductor layer is formed so as to cover the inner edge of the translucent insulator layer via the translucent electrode layer.

2. 2. The vertical cavity light emitting device of claim 1, wherein the passivation region is a region containing an oxide.

3. The passivation region is made of Si and O ２ 3. The vertical cavity light emitting device according to claim 2, comprising at least one of the following:

4. 4. The vertical cavity light emitting device according to claim 1, wherein the thickness of said metal conductor layer is greater than the thickness of said transparent electrode layer.

5. 5. The vertical cavity light emitting device according to claim 1, wherein an equivalent refractive index in the cavity formed between the first multilayer film reflector and the second multilayer film reflector in the other region is lower than an equivalent refractive index in the cavity formed between the first multilayer film reflector and the second multilayer film reflector in the one region.

6. 6. The vertical cavity light emitting device according to claim 1, further comprising an anti-reflection layer on the lower surface of the substrate.

7. 7. The vertical cavity light emitting device according to claim 1, wherein the transparent electrode layer is made of ITO or IZO.

8. a gallium nitride semiconductor substrate; a first multilayer reflector made of nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film reflector; an active layer made of a nitride semiconductor formed on the first semiconductor layer; and a second semiconductor layer formed on the active layer and made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type; a transparent electrode layer formed on an upper surface of the second semiconductor layer, electrically contacting the second semiconductor layer in one region of the second semiconductor layer, and insulated from the second semiconductor layer in another region surrounding the one region other than the one region; a metal conductor layer formed on the upper surface of the translucent electrode layer above the other region; a second multilayer reflector formed on the transparent electrode layer so as to cover the first region and constituting a resonator between itself and the first multilayer reflector; a transparent insulator layer disposed between the second semiconductor layer and the transparent electrode layer in the other region on the second semiconductor layer, the first region is an upper surface of a protrusion that protrudes upward from the other region, the semiconductor structure layer has an annular groove formed in the other region and surrounding the second multilayer film reflector in a plan view; the second semiconductor layer includes, in the other region, a passivation region in which an impurity imparting the second conductivity type to the second semiconductor layer is inactivated; The vertical cavity light emitting device is characterized in that the metal conductor layer is formed so as to cover the inner edge of the translucent insulator layer via the translucent electrode layer.

9. 9. The vertical cavity light emitting device according to claim 8, wherein the groove penetrates the active layer of the semiconductor structure layer.

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