Vertical resonator type 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 a vertical cavity light emitting device such as a vertical cavity surface emitting laser (VCSEL).

Background Art

[0002] Conventionally, as one of semiconductor lasers, a vertical cavity semiconductor surface emitting laser (hereinafter, also simply referred to as a surface emitting laser) having a semiconductor layer that emits light by applying a voltage and multilayer mirrors facing each other with the semiconductor layer interposed therebetween is known. For example, Patent Document 1 discloses a surface emitting laser using a nitride semiconductor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, in a vertical cavity light emitting device such as a surface emitting laser, an insulating film that defines a light emitting region is formed on the upper surface of the semiconductor layer, and a translucent electrode film such as ITO that is electrically in 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 the light emitting region of the semiconductor layer, and a translucent electrode film 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 that a step is generated at the opening end of the insulating film.

[0006] However, if a step is present in the transparent electrode film as described above, abnormalities such as cracks may occur at the step portion of the transparent electrode during long-term energization, and an increase in the driving voltage or malfunctions such as short / open may occur.

[0007] The present invention has been made in view of the above points, and an object thereof is to provide a vertical cavity surface emitting laser (VCSEL) with a long lifespan that suppresses an increase in the driving voltage during long-term energization.

Means for Solving the Problems

[0008] The vertical cavity surface emitting laser (VCSEL) according to the present invention includes a gallium nitride-based semiconductor substrate, a first multilayer film mirror made of a nitride semiconductor formed on the substrate, a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film mirror, an active layer made of a nitride semiconductor formed on the first semiconductor layer, and a second semiconductor layer made of a nitride semiconductor formed on the active layer and having a second conductivity type opposite to the first conductivity type, a semiconductor structure layer, a transparent electrode layer formed on the 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 a region on the other region of the upper surface of the transparent electrode layer, a second multilayer film mirror formed on the transparent electrode layer so as to cover one region and constituting a resonator with the first multilayer film mirror, and a transparent insulator layer disposed between the second semiconductor layer and the transparent electrode layer in another region on the second semiconductor layer, the transparent insulator layer having an inner edge with a step outside one region, the second semiconductor layer having, in another region, an inactivated region formed by partially removing the surface of the second semiconductor layer and in which impurities adding the second conductivity type to the second semiconductor layer are inactivated, and the metal conductor layer being formed so as to cover the inner edge of the transparent insulator layer via the transparent electrode layer.

[0009] In addition, the vertical cavity surface emitting laser according to the present invention includes a gallium nitride-based semiconductor substrate, a first multilayer mirror made of a nitride semiconductor formed on the substrate, a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer mirror, an active layer made of a nitride semiconductor formed on the first semiconductor layer, and a second semiconductor layer made of a nitride semiconductor having a second conductivity type opposite to the first conductivity type formed on the active layer. The semiconductor structure layer includes a light-transmitting electrode layer formed on the 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; a metal conductor layer formed on the upper surface of the light-transmitting electrode layer above the other region; a second multilayer mirror formed on the light-transmitting electrode layer so as to cover the one region and constituting a resonator with the first multilayer mirror; and a light-transmitting insulator layer disposed between the second semiconductor layer and the light-transmitting electrode layer in another region on the second semiconductor layer. The semiconductor structure layer has an annular groove formed in another region and surrounding the second multilayer mirror in a plan view. The second semiconductor layer has an inactivated region formed by partially removing the surface of the second semiconductor layer in another region and inactivating impurities adding the second conductivity type to the surface of the second semiconductor layer after the removal. The metal conductor layer is formed so as to cover the inner edge of the light-transmitting insulator layer via the light-transmitting electrode layer.

Brief Description of Drawings

[0010]

Figure 1

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Figure 11

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. In the following description, a semiconductor surface-emitting laser element will be described as an example (semiconductor laser), but the present invention can be applied not only to surface-emitting lasers but also to various vertical cavity surface-emitting elements such as vertical cavity surface-emitting diodes.

Example

[0012] FIG. 1 is a perspective view of a vertical cavity surface-emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser, hereinafter also simply referred to as a surface-emitting laser) 10 according to Example 1.

[0013] The substrate 11 is a gallium nitride-based semiconductor substrate, for example, a GaN substrate. The substrate 11 is, for example, a substrate having a rectangular upper surface shape. On the substrate 11, a first multilayer film mirror 13 made of a semiconductor layer grown on the substrate 11 is formed.

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

[0015] In addition, the upper surface of the substrate 11, that is, the surface on which the buffer layer having a composition of GaN is provided, is preferably a C-plane or a plane offset within 0.5° from the C-plane. This is because the crystallinity of the semiconductor structure layer 15 described later becomes good.

[0016] The semiconductor structure layer 15 is a laminated structure body composed of a plurality of semiconductor layers formed on the first multilayer film reflector 13. The semiconductor structure layer 15 has an n-type semiconductor layer (first semiconductor layer) 17 of the first conductivity type formed on the first multilayer film 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 the 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 composition of GaN and is a semiconductor layer doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower part 17A and a cylindrical upper part 17B arranged thereon. Specifically, for example, the n-type semiconductor layer 17 has a cylindrical upper part 17B protruding from the upper surface of the prismatic lower part 17A. In other words, the n-type semiconductor layer 17 has a mesa-shaped structure including the upper part 17B.

[0018] The active layer 19 is formed on the upper portion 17B of the n-type semiconductor layer 17, and is a layer having a quantum well structure including a well layer having an InGaN composition and a barrier layer having a GaN composition. In the surface-emitting laser 10, light is generated in the active layer 19.

[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 laminated on the mesa-shaped structure.

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

[0021] The insulating layer 25 as a light-transmissive insulating layer is a layer made of an insulator formed on the p-type semiconductor layer 21. The insulating layer 25 is formed of a substance having a refractive index lower than that of the material forming the p-type semiconductor layer 21, such as SiO2. The insulating layer 25 is formed in an annular shape on the p-type semiconductor layer 21 and has an opening (not shown) that exposes the p-type semiconductor layer 21 at the central portion.

[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 of the insulating layer 25 via a transparent electrode layer 31 (described later in FIG. 3) made of a metal oxide film such as ITO or IZO.

[0023] The second multilayer film mirror 29 is a dielectric multilayer film mirror in which a low refractive index dielectric film made of SiO2 and a high refractive index dielectric film made of Nb2O5 and having a higher refractive index than the low refractive index dielectric film are alternately laminated. In other words, the second multilayer film mirror 29 is a distributed Bragg reflector (DBR) made of a dielectric material.

[0024] FIG. 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 mirror 29 is formed on the p electrode 27.

[0025] The insulating layer 25 has an opening 25H which is a circular opening exposing the p-type semiconductor layer 21 of the insulating layer 25 described above. As shown in FIG. 2, the opening 25H is formed at the center of the insulating layer 25 when viewed from above the surface emitting laser 10, and is covered with the second multilayer film mirror 29 when viewed from above the surface emitting laser 10. In other words, the opening 25H is covered with the second multilayer film mirror 29 on the top surface of the p-type semiconductor layer 21. Further in other words, the opening 25H is formed in a region of the insulating layer 25 facing the lower surface of the second multilayer film mirror 29.

[0026] The p electrode 27 is formed at 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 an opening larger than the opening 25H. For example, the shape of the opening 27H is a circular shape concentric with the shape of the opening 25H.

[0027] As shown in FIG. 2, an annular step 15S is formed on the upper surface of the p-type semiconductor layer 21, that is, on the upper surface of the semiconductor structure layer 15. The step 15S is formed in the region outside the opening 25H and the opening 27H. That is, the step 15S is a step provided in an annular shape 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 outside the second multilayer film mirror 29 on the upper surface of the p-type semiconductor layer 21.

[0029] FIG. 3 is a cross-sectional view of the surface-emitting laser 10 taken along line 3-3 of FIG. 2. As described above, the surface-emitting laser 10 has a substrate 11 that is a GaN substrate, and a first multilayer film mirror 13 is formed on the substrate 11. An AR coat in which Nb2O5 and SiO2 are laminated may be provided on the lower surface of the substrate 11.

[0030] A semiconductor structure layer 15 is formed on the first multilayer film mirror 13. The semiconductor structure layer 15 is a laminate in which an n-type semiconductor layer 17, an active layer 19, and a p-type semiconductor layer 21 are formed in 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 at the center of the upper surface of the p-type semiconductor layer 21.

[0032] The insulating layer 25 is formed so as to cover the upper surface of the p-type semiconductor layer 21. The insulating layer 25 is made of a material having a refractive index lower than that of the p-type semiconductor layer 21 as described above. The insulating layer 25 has an opening 25H that exposes 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 is in contact with the outer surface of the protruding portion 21P. Further, 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 at the same height. That is, the upper surfaces of the insulating layer 25 and the protruding portion 21P have flatness in the region inside the step 15S. Here, the same height does not necessarily mean exactly the same height, and may include unevenness and steps within a range that is insensitive to the light emitted from the active layer 19, that is, the standing wave (laser light) generated between the first multilayer mirror 13 and the second multilayer mirror 29.

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

[0034] The p - electrode 27 is a metal electrode as described above and is formed to cover the transparent electrode layer 31. That is, the p - electrode 27 is in electrical contact with the transparent electrode layer 31. Therefore, the p - electrode 27 is in electrical contact or connection with the p - type semiconductor layer 21 via the transparent electrode layer 31 in the 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 at its central portion that exposes the transparent electrode layer 31. The opening 27H is an opening having a width (or diameter) larger than that of the opening 25H. Also, as shown in FIG. 3, the p - electrode 27 is formed to cover the step 15S.

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

[0036] Here, the operation of the surface - emitting laser 10 will be described. In the surface - emitting laser 10, when a voltage is applied between the n - electrode 23 and the p - electrode 27, as shown by the thick two - dot chain line in the figure, a current flows in the semiconductor structure layer 15, 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 mirror 13 and the second multilayer film mirror 29 and reaches a resonant state (laser oscillation occurs).

[0037] In the surface - emitting laser 10, current is injected only from the portion of the p - type semiconductor layer 21 exposed by the opening 25H. Also, 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, that is, in the direction along the in - plane of the semiconductor structure layer 15. Therefore, in the surface - emitting laser 10, current is supplied only to the region directly below the opening 25H in the active layer 19, and light is emitted only from this region. That is, in the surface - emitting laser 10, the opening 25H serves as a current constriction structure that limits the current supply range in the active layer 19.

[0038] As described above, in this embodiment, the first multilayer film mirror 13 has a reflectance slightly lower than that of the second multilayer film mirror 29. Therefore, part of the light resonated between the first multilayer film mirror 13 and the second multilayer film mirror 29 is transmitted through the first multilayer film mirror 13 and the substrate 11 and taken out 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 each layer of the lower surface of the substrate 11 and the semiconductor structure layer 15.

[0039] In addition, the protruding portion 21P of the p-type semiconductor layer 21 and the opening 25H of the insulating layer 25 of the semiconductor structure layer 15 define the light-emitting center which is the center of the light-emitting region in the active layer 19, and define the central axis (light-emitting 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] In addition, the light-emitting region of the active layer 19 is, for example, a region having a predetermined width in which light of a predetermined intensity or more is emitted within the active layer 19, and the center thereof is the light-emitting center. Also, for example, the light-emitting region of the active layer 19 is a region in which a current of a predetermined density or more is injected within the active layer 19, and the center thereof is the light-emitting center. Also, a straight line perpendicular to the in-plane direction of each layer of the upper surface of the substrate 11 or the semiconductor structure layer 15 passing through the light-emitting center is the central axis AX. The light-emitting central axis AX is a straight line extending along the resonator length direction of the resonator OC constituted by the first multilayer film mirror 13 and the second multilayer film mirror 29. Also, the central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 10.

[0041] Here, an exemplary configuration of each layer of the first multilayer film mirror 13, the semiconductor structure layer 15, and the second multilayer film mirror 29 in the surface-emitting laser 10 will be described. In this embodiment, the first multilayer film mirror 13 is composed of a 1-um 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 an n-GaN layer doped with Si having a layer thickness of 1580 nm. The active layer 19 consists of an active layer with a multiple quantum well structure in which a 4-nm InGaN layer and a 5-nm GaN layer are stacked in 4 pairs, and the peak of the emission spectrum emitted from the active layer 19 is adjusted to be about 440 nm. On the active layer 19, an electron barrier layer of Mg-doped AlGaN is formed, and on it, a p-type semiconductor layer 21 consisting of a 50-nm p-GaN layer is formed. The second multilayer film mirror 29 is formed by stacking 10.5 pairs of 45-nm Nb2O5 and 76-nm SiO2. The resonance wavelength in this case was 440 nm.

[0043] Further, the p-type semiconductor layer 21 has a layer thickness of 50 nm at the protruding portion 21P and a layer thickness of 30 nm in the region from the outer peripheral end of the protruding portion 21P to the step 15S. Also, the insulating layer 25 made of SiO2 has a layer thickness of 20 nm, that is, in the region from the inner peripheral end in contact with the side surface of the protruding portion 21P of the insulating layer 25 to the step 15S, the upper surface of the insulating layer 25 is configured to be disposed at the same height position as the upper surface of the protruding portion 21P of the p-type semiconductor layer 21.

[0044] Further, the translucent electrode layer 31 formed on the semiconductor structure layer 15 is a layer made of 20-nm ITO, and the second multilayer film mirror 29 is formed on the translucent electrode layer 31 and the p electrode 27 with a 40-nm Nb2O5 spacer layer interposed therebetween. The p electrode 27 is formed by laminating Ti (100 nm), Pt (100 nm), and Au (500 nm) in this order.

[0045] Note that the p-type semiconductor layer 21, the insulating layer 25, the translucent electrode layer 31, and the p electrode 27 at the portion of the step 15S are preferably steps having an inclination with respect to the central axis AX of the surface-emitting laser 10. Also, 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 translucent electrode layer 31 during long-term energization.

[0046] Also, the back surface of the substrate 11 is a polished surface, and a two-layer AR coat of Nb2O5 and SiO2 is formed on the polished surface.

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

[0048] Hereinafter, the optical characteristics inside the surface-emitting laser 10 will be described. 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. Also, the layer thicknesses of the other layers between the first multilayer film mirror 13 and the second multilayer film mirror 29 are the same within the same layer at any location in the plane.

[0049] Therefore, the equivalent refractive index (which is the optical distance between the first multilayer film mirror 13 and the second multilayer film mirror 29 and corresponds to the resonance wavelength) in the resonator OC formed between the first multilayer film mirror 13 and the second multilayer film mirror 29 of the surface-emitting laser 10 is different between the central region CA as a cylindrical region defined by the opening 25H in the upper surface shape and the peripheral region PA as other cylindrical regions 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 film mirror 13 and the second multilayer film mirror 29, the equivalent refractive index of the peripheral region PA is lower than that of the central region CA, that is, the equivalent resonance wavelength in the central region CA is longer than the equivalent resonance wavelength in the peripheral region PA. Note that, as described above, light is emitted in the region directly below the protruding portion 21P in the active layer 19. That is, the light-emitting region where 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, in the surface-emitting laser 10, a central region CA including the light-emitting region of the active layer 19 and a peripheral region PA surrounding the central region CA and having a refractive index lower than that of the central region CA are formed. As a result, light loss due to the standing wave in the central region CA diverging (radiating) into the peripheral region PA is suppressed. That is, a large amount of light remains in the central region CA, and laser light is extracted to the outside in that state. Therefore, a large amount of light is concentrated in the central region CA around the light-emitting central axis AX of the resonator OC, and high-output and high-density laser light can be generated and emitted.

[0052] As described above, in the surface-emitting laser 10 of Example 1, the translucent electrode layer 31 is formed so as to have a step. In other words, a step is formed in the translucent electrode layer 31 by the step 15S. Thereafter, the p electrode 27 is formed so as to cover the step.

[0053] As described above, the surface-emitting laser 10 of Example 1 includes a gallium nitride-based semiconductor substrate 11, a first multilayer film mirror 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 film mirror 13, an active layer 19 made of a nitride semiconductor formed on the n-type semiconductor layer 17, and a p-type semiconductor layer 21 made of a nitride semiconductor having a p-type conductivity type opposite to the n-type conductivity type formed on the active layer 19, a semiconductor structure layer 15 including the p-type semiconductor layer 21, a translucent electrode layer 31 formed on the upper surface of the p-type semiconductor layer 21, electrically contacting the central region CA of the p-type semiconductor layer 21, and insulated from the p-type semiconductor layer 21 in a peripheral region PA surrounding a region other than the central region CA, a p electrode 27 formed on the upper surface of the translucent electrode layer 31 above the peripheral region PA, and a second multilayer film mirror 29 formed on the translucent electrode layer 31 so as to cover the central region CA and constituting a resonator OC with the first multilayer film mirror 13. A step 15S is formed in the peripheral region PA on the upper surface of the semiconductor structure layer 15, and the p electrode 27 is formed so as to cover the translucent electrode layer 31 on the step 15S.

[0054] Further, the step 15S has an inclined surface with an angle of 45° or less with respect to the upper surface of the semiconductor structure layer 15. Also, 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 existing around the mesa-shaped structure.

[0055] FIG. 4 shows a cross-sectional view of the surface-emitting laser 10A according to Modification 1 of Embodiment 1.

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

[0057] Also, as shown in FIG. 5, the insulating layer 25 may further include a first insulating layer 25A for forming a step (step 25AS in the figure), and an insulating layer 25 may be additionally stacked on the upper surface of the annular region surrounding the protruding portion 21P of the p-type semiconductor layer 21 and the first insulating layer 25A. Note that the insulating layer 25 for forming the step 25AS may be an insulating layer made of a material different from that of the insulating layer 25.

[0058] Note that when the translucent electrode is formed so as not to generate a step, the capacitance of the current path of the semiconductor layer increases, and the modulation speed may decrease. Also, when the capacitance increases, the amount of heat generated by the semiconductor layer during driving increases, and the semiconductor layer may melt, resulting in problems such as a short circuit.

[0059] That is, by forming this step to increase the distance between the p - electrode 27 and the surface of the semiconductor layer 21, the capacitance between the p - electrode 27 and the surface of the semiconductor layer 21 during the driving of the surface - emitting laser 10 can be reduced, and it becomes possible to prevent a decrease in the modulation speed. Also, due to this reduction in capacitance, it becomes possible to reduce the amount of heat generated during driving, and it also becomes possible to prevent the occurrence of problems such as melting of the semiconductor structure layer 15.

[0060] Further, the light - transmitting electrode layer 31 on the step 15S is covered with the p - electrode 27 which is a metal layer. Thereby, it becomes possible to prevent the occurrence of abnormalities such as cracks in the stepped portion of the light - transmitting electrode layer 31 during long - term energization. Also, even if a crack occurs in the stepped portion of the light - transmitting electrode layer 31 during long - term energization, since the p - electrode 27 is formed so as to cover the step, the conduction 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 light - transmitting electrode layer 31, it becomes possible to prevent the occurrence of abnormalities such as open.

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

Embodiment

[0062] Hereinafter, the surface - emitting laser 20 which is the second embodiment of the present invention will be described.

[0063] FIG. 6 shows a top view of the surface - emitting laser 20 of the second embodiment. Also, FIG. 7 is a cross - sectional view of the surface - emitting laser 20 taken along the line 5 - 5 of FIG. 6.

[0064] The surface-emitting laser 20 has basically the same configuration as the surface-emitting laser 10 of Example 1 and has the same appearance. However, the surface-emitting laser 20 is different from the surface-emitting laser 10 in that no step is provided outside the central region CA of the semiconductor structure layer 15, and a step is formed by the insulating layer 25 formed outside the central region CA. Further, the surface-emitting laser 20 is different from the surface-emitting laser 10 in that an inactivation region layer 21A in which p-type impurities are inactivated is provided outside the protruding portion 21P of the p-type semiconductor layer 21.

[0065] The inactivation region layer 21A can be formed, for example, by performing dry etching while leaving the region of the protruding portion 21P of the p-type semiconductor layer 21. When dry etching is performed on a semiconductor containing impurities such as the p-type semiconductor layer 21, the surface thereof is roughened. As a result, the p-type impurities in the etched portion are inactivated, and the inactivation region layer 21A is formed. Further, in the inactivation region layer 21A, the p-type semiconductor layer 21 is partially removed by dry etching. In other words, the inactivation region layer 21A has an opening 21H which is a circular opening exposing the p-type semiconductor layer 21 of the inactivation region layer 21A. Incidentally, the etching amount partially removed by dry etching in the inactivation region layer 21A is, for example, 4 nm.

[0066] Further, an insulating layer 25 as a light-transmitting insulator layer is formed outside the central region CA on the upper surface of the p-type semiconductor layer 21. Further, the insulating layer 25 has a step 25S formed at the inner edge thereof. The light-transmitting electrode layer 31 and the p electrode 27 are formed such that a step occurs at a portion corresponding to the step 25S. That is, the p electrode 27 is formed so as to cover the step portion of the light-transmitting electrode layer 31 caused by the step 25S. Further in other words, the p electrode 27 is formed so as to cover the inner edge of the light-transmitting insulating layer 25, that is, the portion of the step 25S, via the light-transmitting electrode layer 31.

[0067] Similar to the above-described Example 1, by forming the step 25S to increase the distance between the p - electrode 27 and the surface of the semiconductor layer 21, the capacitance between the p - electrode 27 and the semiconductor layer 21 during the driving of the surface - emitting laser 20 can be reduced, and it becomes possible to prevent a decrease in the modulation speed. Further, due to this reduction in capacitance, it becomes possible to reduce the amount of heat generated during driving, and it also becomes possible to prevent the occurrence of problems such as melting of the semiconductor structure layer 15.

[0068] Also, the transparent electrode layer 31 and the p - electrode 27 in the portion of the step 25S are preferably steps having an inclination with respect to the central axis AX of the surface - emitting laser 20. Further, the inclination angle of the insulating layer 25 in the portion of 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 becomes possible to improve the long - term reliability such as crack resistance during long - term energization of the transparent electrode layer formed on the step 25S of the insulating layer 25.

[0069] As described above, the surface-emitting laser 20 of Example 2 includes a gallium nitride-based semiconductor substrate 11, a first multilayer film mirror 13 made of a nitride semiconductor formed on the substrate 11, an n-type semiconductor layer 17 made of a nitride semiconductor having an n-type conductivity type formed on the first multilayer film mirror 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 made of a nitride semiconductor having a p-type conductivity type opposite to the n-type conductivity type and formed on the active layer 19; an insulating layer 25 formed on the upper surface of the p-type semiconductor layer 21 and formed in a region surrounding the central region CA of the p-type semiconductor layer 21; a transparent electrode layer 31 formed across the upper surface of the p-type semiconductor layer 21 and the upper surface of the passivation 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 transparent electrode layer 31 above the peripheral region PA; and a second multilayer film mirror 29 formed on the transparent electrode layer 31 so as to cover the central region CA and constituting a resonator OC with the first multilayer film mirror 13. The p electrode 27 is formed so as to cover the inner edge of the insulating layer 25 via the transparent electrode layer 31.

[0070] Further, the passivation 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 protruding portion 21P of the p-type semiconductor layer 21, which is a region where etching has not been performed, that is, a region where the passivation region layer 21A is not provided, functions as a low-resistance region.

[0071] The p-type semiconductor layer 21 functions as a current constriction layer that constricts the current path 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 injection of current into the active layer 19 is suppressed.

[0072] That is, in the surface-emitting laser 20, current is injected only from the portion of the p-type semiconductor layer 21 that is exposed by the opening 21H. Further, since the p-type semiconductor layer 21 is very thin, current hardly diffuses in the in-plane direction within the p-type semiconductor layer 21, that is, 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 directly under the opening 21H in the active layer 19, and light is emitted only from this region. That is, in the surface-emitting laser 20, the opening 21H serves as a current constriction structure that limits the current supply range 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, 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 mirror 13 and the second multilayer film mirror 29, reaching a resonant state (laser oscillation).

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

[0075] Therefore, the equivalent refractive index (the optical distance between the first multilayer film mirror 13 and the second multilayer film mirror 29, corresponding to the resonant wavelength) in the resonator OC formed between the first multilayer film mirror 13 and the second multilayer film mirror 29 of the surface-emitting laser 20 differs between the columnar central region CA whose upper surface shape is defined by the opening 21H and the surrounding cylindrical peripheral region PA due to the difference in refractive index between the p-type semiconductor layer 21 and the insulating layer 25.

[0076] Specifically, between the first multilayer film mirror 13 and the second multilayer film mirror 29, the equivalent refractive index of the peripheral region PA is lower than that of the central region CA, that is, 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 active layer 19 in the region directly below the opening 21H. That is, the light-emitting region where light is emitted from the active layer 19 is the portion of the active layer 19 that overlaps with the central region CA.

[0077] In addition, in the second embodiment, the case where the high-resistance region layer forming the current constriction structure is the inactivation region layer 21A in which the p-type semiconductor layer 21 is inactivated by dry etching has been described. However, the configuration of the high-resistance region layer is not limited to this. For example, as the high-resistance region layer, it may be the surface layer of a GaN layer that has been ion-implanted into the p-type semiconductor layer 21 and subjected to a high-resistance treatment. Also, for example, the high-resistance region layer may be an insulating layer such as SiO2.

[0078] As described above, according to the second embodiment, the translucent electrode layer 31 on the step 25S is covered with the p electrode 27 which is a metal layer. Thereby, it becomes possible to prevent the occurrence of abnormalities such as cracks in the stepped portion of the translucent electrode layer 31 during long-term energization. Also, even if a crack occurs in the stepped portion of the translucent electrode layer 31 during long-term energization, since the p electrode 27 is formed so as to cover the step, the conduction 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 becomes possible to prevent the occurrence of abnormalities such as open circuits.

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

Embodiment

[0080] Hereinafter, a surface emitting laser 30 which is the third embodiment of the present invention will be described.

[0081] FIG. 8 shows a perspective view of the surface-emitting laser 30 of Example 3. Further, FIG. 9 shows a cross-sectional view of the surface-emitting laser 20 cut along the same cross-section as 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 is different 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] As shown in FIG. 9, an annular groove 15G is formed on the upper surface of the p-type semiconductor layer 21, that is, on the upper surface of the semiconductor structure layer 15. The groove 15G is formed in a region outside the opening 25H and the opening 27H. That is, the groove 15G is a groove provided annularly 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 outside the second multilayer film mirror 29 on the upper surface of the p-type semiconductor layer 21. That is, on the upper surface of the p-type semiconductor layer 21, the groove 15G is exposed from the peripheral region PA where the second multilayer film mirror 29 is formed.

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

[0086] Thus, in the surface-emitting laser 30 of Example 3, the groove 15G is formed so as to penetrate the active layer 19. In other words, a gap is formed in the active layer 19 by the groove 15G.

[0087] The insulating layer 25 is formed so as to cover the upper surface of the p-type semiconductor layer 21 and the inner surface of the groove 15G. The insulating layer 25 is made of a material having a refractive index lower than that of the p-type semiconductor layer 21 as described above. 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 the third embodiment, the groove 15G is formed so as to penetrate the active layer 19. In other words, a gap is formed in the active layer 19 by the groove 15G. This groove 15G is formed after the semiconductor structure layer 15 is formed. Thereafter, the insulating layer 25 is formed before the transparent electrode layer 31, the p-electrode 27, and the second multilayer film mirror 29 are formed.

[0089] Therefore, after the semiconductor structure layer 15 is formed, by forming the groove 15G leading to the active layer 19, a space or a gap is formed in the direction along the in-plane of the active layer 19. This gap relaxes the strain generated in the in-layer direction of the active layer 19 or in the layer-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 crystal structure is distorted due to the difference in lattice constants between InGaN and GaN that form the quantum well structure, resulting in a piezoelectric polarization and 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 reasons for the low internal quantum efficiency.

[0091] In the surface-emitting laser 30, a groove 15G leading to the active layer 19 is formed in the semiconductor structure layer 15. It is considered that the strain generated in the in-layer direction of the active layer 19 during the growth of the active layer 19 is relaxed by the gap formed by this groove, and the internal quantum efficiency in the active layer 19 is improved.

[0092] Here, the operation of the surface-emitting laser 30 will be described. In the surface-emitting laser 30, when a voltage is applied between the n-electrode 23 and the p-electrode 27, 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 mirror 13 and the second multilayer film mirror 29 and reaches a resonant state (laser oscillation).

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

[0094] As described above, in this embodiment, the first multilayer film mirror 13 has a slightly lower reflectivity than the second multilayer film mirror 29. Therefore, a part of the light resonated between the first multilayer film mirror 13 and the second multilayer film mirror 29 is transmitted through the first multilayer film mirror 13 and the substrate 11 and taken out 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 each layer of the lower surface of the substrate 11 and the semiconductor structure layer 15.

[0095] Note that the protruding portion 21P of the p-type semiconductor layer 21 and the opening 25H of the insulating layer 25 in the semiconductor structure layer 15 define the light-emitting center, which is the center of the light-emitting region in the active layer 19, and define the central axis (light-emitting 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 within the active layer 19 where light with a predetermined intensity or more is emitted, and the center thereof is the light-emitting center. Also, for example, the light-emitting region of the active layer 19 is a region where a current with a predetermined density or more is injected within the active layer 19, and the center thereof is the light-emitting center. Further, a straight line perpendicular to the in-plane direction of each layer of the upper surface of the substrate 11 or the semiconductor structure layer 15 passing through the light-emitting center is the central axis AX. The light-emitting central axis AX is a straight line extending along the resonator length direction of the resonator OC constituted by the first multilayer film mirror 13 and the second multilayer film mirror 29. Also, the central axis AX corresponds to the optical axis of the laser light emitted from the surface-emitting laser 30.

[0097] Here, an exemplary configuration of each layer of the first multilayer film mirror 13, the semiconductor structure layer 15, and the second multilayer film mirror 29 in the surface-emitting laser 30 and exemplary dimensions of the groove 15G will be described. In the present embodiment, the first multilayer film mirror 13 is composed of a 1-μm GaN underlayer formed on the upper surface of the substrate 11, and 42 pairs of n-GaN layers and AlInN layers.

[0098] The n-type semiconductor layer 17 is an n-GaN layer with a layer thickness of 1580 nm. The active layer 19 is composed of an active layer having a multiple quantum well structure in which 4 pairs of 4-nm InGaN layers and 5-nm GaN layers are stacked. On the active layer 19, an electron barrier layer of Mg-doped AlGaN is formed, and a p-type semiconductor layer 21 composed of a 50-nm p-GaN layer is formed thereon. The second multilayer film mirror 29 is formed by stacking 10.5 pairs of Nb2O5 and SiO2. The resonance 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 transparent electrode layer 31 formed on the semiconductor structure layer 15 is a layer composed of 20-nm ITO, and the second multilayer film mirror 29 is formed on the transparent electrode layer 31 and the p-electrode 27 with a 40-nm Nb2O5 spacer layer interposed therebetween.

[0100] Also, the back surface of the substrate 11 is a polished surface, and a two-layer AR coat of Nb2O5 and SiO2 is formed on the polished surface.

[0101] Further, the p-type semiconductor layer 21 may have a layer thickness of 50 nm at the protruding portion 21P and a layer thickness of 30 nm in other regions. That is, the p-type semiconductor layer 21 may have different layer thicknesses at the protruding portion 21P and other portions. Also, the upper surface of the insulating layer 25 is configured to be disposed at the same height position as the upper surface of the protruding portion 21P of the p-type semiconductor layer 21.

[0102] Note that, in FIG. 9, the groove 15G is shown as being formed in a direction perpendicular to the upper surface of the p-type semiconductor layer 21. However, the p-type semiconductor layer 21, the insulating layer 25, the transparent electrode layer 31, and the p electrode 27 in the groove 15G and the portion of the groove 15G preferably have steps with side surfaces inclined with respect to the central axis AX of the surface-emitting laser 30. Further, 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 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 anti-cracking property of the transparent electrode layer 31 during long-term energization.

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

[0104] Hereinafter, the optical characteristics inside the surface-emitting laser 30 will be described. 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. Also, the layer thicknesses of the other layers between the first multilayer film mirror 13 and the second multilayer film mirror 29 are the same within the same layer at any location in the plane.

[0105] Therefore, the equivalent refractive index (the optical distance between the first multilayer mirror 13 and the second multilayer mirror 29, corresponding to the resonance wavelength) in the resonator OC formed between the first multilayer mirror 13 and the second multilayer mirror 29 of the surface-emitting laser 30 is different between the columnar central region CA whose upper surface shape is defined by the opening 25H and the surrounding cylindrical peripheral region PA due to the difference in refractive index between the p-type semiconductor layer 21 and the insulating layer 25.

[0106] Specifically, between the first multilayer mirror 13 and the second multilayer mirror 29, the equivalent refractive index of the peripheral region PA is lower than that of the central region CA, that is, the equivalent resonance wavelength in the central region CA is smaller than the equivalent resonance wavelength of the peripheral region PA. As described above, light is emitted from the active layer 19 in the region directly below the opening 25H. That is, the light-emitting region where light is emitted from the active layer 19 is the portion of the active layer 19 that overlaps with the central region CA.

[0107] In addition, in the present Example 3, the case where the groove 15G is formed in an annular shape outside the central region CA in a top view has been described. However, the groove 15G may have a groove structure including intermittently formed recesses instead of a complete annular shape. That is, the groove 15G may have a concave structure including a plurality of recesses. In other words, the groove 15G may have an intermittently formed annular structure. For example, the groove 15G may have an intermittently formed annular structure surrounding the region exposed by the opening 25H on the upper surface of the p-type semiconductor layer 21.

[0108] When the groove 15G is formed by a plurality of recesses, in order to evenly relieve the strain in the active layer 19, it is desirable that the groove 15G is formed in two or more directions when viewed from the above-described emission central axis AX. That is, when the groove 15G is formed by a plurality of recesses, in a top view of the surface-emitting laser 30, the recesses are formed in two or more directions when viewed from the emission region including the emission central axis AX, and it is preferable to have a structure in which the emission region is sandwiched by the recesses. In order to evenly relieve the strain in the active layer 19, the recesses forming the groove 15G are more preferably arranged rotationally symmetrically with respect to the emission central axis AX. In other words, the recesses forming the groove 15G are preferably provided rotationally symmetrically when 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 concave structure including one or a plurality of grooves 15G penetrating the active layer 19 from above in a region surrounding the central region CA of the semiconductor structure layer 15. Also, the p-electrode 27 is formed so as to cover the inner surfaces of the one or a plurality of grooves 15G.

[0110] In addition, as described above, by changing the shape of the groove 15G, such as 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 Example 3, the translucent electrode layer 31 on the groove 15G is covered with the p-electrode 27 which is a metal layer. Thereby, it becomes possible to prevent the occurrence of abnormalities such as cracks at the step portion of the translucent electrode layer 31 during long-term energization. Also, even if a crack occurs in the step portion of the translucent electrode layer 31 during long-term energization, since the p-electrode 27 is formed so as to cover the step, the 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 translucent electrode layer 31, it becomes possible to prevent the occurrence of abnormalities such as an open.

[0112] Therefore, according to this Example 3, it is possible to prevent the occurrence of an increase in the driving voltage and problems such as short circuit / open during long-term energization, and it becomes possible to provide a long-life vertical cavity surface-emitting laser 30.

[0113] In addition, as described above, in the surface-emitting laser 30 of this embodiment, a groove 15G extending from the upper surface of the p-type semiconductor layer 21 to the active layer 19 is formed in the semiconductor structure layer 15. By this groove 15G, in the active layer 19, the strain generated in the in-layer direction of the active layer 19 is relaxed, the internal quantum efficiency in the active layer 19 is improved, and an improvement in the light emission efficiency can be realized.

[0114] Note that in any of the first, second, and third embodiments, the step 15S, 25S, or groove 15G is provided outside the second multilayer film mirror 29 from the central axis AX, and the case where the step 15S, 25S, or groove 15G is exposed in a top view of the surface-emitting laser has been described. However, the step 15S, 25S, or groove 15G may be provided so as to be covered by the second multilayer film mirror 29.

[0115] Even in a configuration in which the second multilayer film mirror 29 is formed so as to cover the step 15S, 25S, or groove 15G, it is possible to obtain the same effects as in each of the embodiments. Further, in the case of the structure having the groove 15G as in the third embodiment, the second multilayer film mirror 29 is formed so as to fill the space formed by the groove 15G.

[0116] Also, in any of the first, second, and third embodiments, the surface-emitting laser in which the n-electrode 23 is formed on the upper surface of the substrate 11 has been described. However, the n-electrode 23 may be formed on the back surface of the substrate 11. In this case, a substrate 11 made of a material such as conductive n-GaN may be used, and an n-electrode made of metal may be formed on the back surface of the substrate 11.

[0117] At this time, a back surface protruding portion is formed on the back surface of the substrate 11. The back surface protruding portion is formed in a region corresponding to the protruding portion 21P when viewed from the normal direction of the substrate 11. This back surface protruding portion is a convex portion remaining because the periphery of the back surface protruding portion was removed by dry etching after the back surface was polished. Therefore, the top surface of the back surface protruding portion is a polished surface, and the region around the back surface protruding portion on the back surface of the substrate 11 is a surface where the polished surface has been dry etched. The n electrode is formed in the region around the back surface protruding portion, that is, the region excluding the back surface protruding portion. The back surface protruding portion of the substrate 11 serves as an opening through which the light emitted from its top surface is emitted to the outside and does not block the emitted light by the n electrode. That is, the back surface protruding portion has a structure protruding from the opening of the n electrode.

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

[0119] Also, in any of the first, second, and third embodiments, a surface emitting laser having a current confinement structure by the insulating layer 25 or the passivation region layer 21A has been described. 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 by a tunnel junction layer formed with a highly doped p-type semiconductor layer having an impurity concentration higher than that of the p-type semiconductor layer 21 in the central region CA on the p-type semiconductor layer 21 and a highly doped n-type semiconductor layer having an impurity concentration higher than that of the n-type semiconductor layer 17 formed on the highly doped p-type semiconductor layer.

[0121] In other words, in the region outside the central region CA, it is provided in the layer below the translucent electrode layer 31, and as long as the p electrode 27 is formed so that a step is formed in the step portion of the translucent electrode layer 31 due to the step and the step portion of the translucent electrode layer 31 is covered.

[0122] Also, in any of Examples 1, 2, and 3, a light guide layer may be included, which is provided over the transparent electrode layer 31 across the central region CA and the peripheral region PA and has a first transparent insulating layer having a convex portion on the central axis AX, and a second transparent insulating layer provided on the first transparent insulating layer within the peripheral region PA and having a refractive index smaller than that of the first transparent insulating layer.

[0123] Thereby, the optical loss due to the standing wave in the resonator OC diverging (radiating) outward from the central region CA is suppressed. That is, a large amount of light remains in the central region CA, and the laser light is extracted to the outside in that state. Therefore, a large amount of light is concentrated near the central axis AX, and a laser beam having a stable single-peak or multi-peak intensity distribution can be generated and emitted.

[0124] Also, in any of Examples 1, 2, and 3, the case where the p-electrode 27 covers the step of the transparent electrode layer 31 and is integrally formed has been described. However, the p-electrode 27 may have a first p-electrode that covers the step portion of the transparent electrode layer 31 to extend the life of the transparent electrode layer 31, and a second p-electrode that is formed at 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 transparent electrode layer 31 and a portion that is connected to the mounting substrate.

[0125] Also, in any of Examples 1, 2, and 3, the case where the p-electrode 27 is formed so as to cover the step of the transparent electrode layer 31 has been described. However, the protective film that covers the step of the transparent electrode layer 31 is not limited to the p-electrode 27.

[0126] FIG. 10 shows a cross-sectional view of the surface-emitting laser 10B according to Modification Example 3 of Example 1.

[0127] For example, as shown in FIG. 10, a second transparent electrode layer 31A made of the same material as the transparent electrode layer 31 may be additionally laminated only on the stepped portion of the transparent electrode layer 31. In other words, the film thickness of the stepped portion of the transparent electrode layer 31 may be, for example, twice the film thickness of the transparent electrode layer 31. This makes it possible to less likely cause cracks to occur in the stepped portion of the transparent electrode layer 31 during long-term energization. In this modification, the case where the second transparent electrode layer 31A is additionally laminated only on the portion corresponding to the step 15S has been described, but the range where the second transparent electrode layer 31A is laminated is not limited thereto. For example, the second transparent electrode layer 31A may be formed in a range excluding the central region CA which is the light-emitting region. In other words, it may be formed so as to cover at least the portion corresponding to the step 15S. This modification 3 is also applicable to Examples 2 and 3.

[0128] Further, FIG. 11 shows a cross-sectional view of the surface-emitting laser 10C according to Modification 4 of Example 1.

[0129] Similar to Modification 2, a dielectric film 33 may be formed only on the stepped portion of the transparent electrode layer 31. The dielectric film 33 is, for example, SiO2, SiN xIt is a dielectric film made of a material such as Al2O3. Note that the dielectric film 33 is preferably a dielectric film that is less reactive with respect to the transparent electrode layer 31 than the high refractive index dielectric film (Nb2O5 in this embodiment) used for the spacer layer (not shown). As described above, by protecting the stepped portion of the transparent electrode layer 31 with a dielectric layer, it is possible to make it difficult for cracks to occur in the stepped portion of the transparent electrode layer 31 during long-term energization. Note that in this modified example, the case where the dielectric film 33 is additionally laminated only on the portion corresponding to the step 15S has been described, but the range in which the dielectric film 33 is laminated is not limited to this. For example, the dielectric film 33 may be formed in a range excluding the central region CA which is the light emitting region. In other words, it is sufficient that it is formed so as to cover at least the portion corresponding to the step 15S. However, in this case, the dielectric film 33 is preferably formed so as not to inhibit the electrical contact between the p electrode 27 and the transparent electrode layer 31. That is, it is preferably configured such that the p electrode 27 and the transparent electrode layer 31 are in electrical contact at at least one portion. This modified example 4 is also applicable to Examples 2 and 3.

[0130] Also, the various numerical values, dimensions, materials, etc. in the above-described examples and modified examples are merely illustrative, and can be appropriately selected according to the application and the surface-emitting laser to be manufactured.

Explanation of Reference Numerals

[0131] 10, 20, 30 Surface-emitting laser 11 Substrate 13 First multilayer film mirror 15 Semiconductor structure layer 17 n-type semiconductor layer 19 Active layer 21 p-type semiconductor layer 23 n electrode 25 Insulating layer 27 p electrode 29 Second multilayer film mirror 31 Transparent electrode layer 33 Dielectric layer

Claims

1. A gallium nitride-based semiconductor substrate, A first multilayer film mirror made of a nitride semiconductor formed on the substrate, A first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film mirror, an active layer made of a nitride semiconductor formed on the first semiconductor layer, and a second semiconductor layer made of a nitride semiconductor formed on the active layer and having a second conductivity type opposite to the first conductivity type, a semiconductor structure layer including: A translucent electrode layer formed on the 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 a region on the other region on the upper surface of the translucent electrode layer, A second multilayer film mirror formed on the translucent electrode layer so as to cover the one region, and constituting a resonator with the first multilayer film mirror, A translucent insulator layer disposed between the second semiconductor layer and the translucent electrode layer in the other region on the second semiconductor layer, having: The translucent insulator layer has an inner edge having a step outside the one region, The second semiconductor layer is formed by partially removing the surface of the second semiconductor layer in the other region, and has an inactivated region in which impurities adding the second conductivity type to the second semiconductor layer are inactivated on the surface of the second semiconductor layer after the removal, The metal conductor layer is formed so as to cover the inner edge of the translucent insulator layer via the translucent electrode layer, a vertical cavity surface emitting laser device characterized by that.

2. The vertical cavity surface emitting laser device according to claim 1, wherein the inactivated region is a region containing an oxide.

3. The inactivation region contains at least one of Si and O ２ The vertical cavity surface emitting laser according to claim 2, characterized in that it contains at least one of Si and O

4. The vertical cavity surface emitting laser device according to any one of claims 1 to 3, wherein the thickness of the metal conductor layer is thicker than the thickness of the translucent electrode layer.

5. The vertical cavity surface emitting laser device according to any one of claims 1 to 4, wherein an equivalent refractive index in a resonator formed between the first multilayer film mirror and the second multilayer film mirror in the other region is lower than an equivalent refractive index in a resonator formed between the first multilayer film mirror and the second multilayer film mirror in the one region.

6. The vertical cavity surface emitting laser according to any one of claims 1 to 5, characterized in that an antireflection layer is provided on the lower surface of the substrate.

7. The vertical cavity surface emitting laser according to any one of claims 1 to 6, characterized in that the transparent electrode layer is made of ITO or IZO.

8. A substrate of a gallium nitride-based semiconductor, A first multilayer film mirror made of a nitride semiconductor formed on the substrate, A first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer film mirror, an active layer made of a nitride semiconductor formed on the first semiconductor layer, and a second semiconductor layer made of a nitride semiconductor formed on the active layer and having a second conductivity type opposite to the first conductivity type. A semiconductor structure layer including: A transparent electrode layer formed on the upper surface of the second semiconductor layer, electrically contacting the second semiconductor layer in one region of the second semiconductor layer, and insulating 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 transparent electrode layer above the other region, A second multilayer film mirror formed on the transparent electrode layer so as to cover the one region and constituting a resonator with the first multilayer film mirror, A transparent insulating layer disposed between the second semiconductor layer and the transparent electrode layer in the other region on the second semiconductor layer, The semiconductor structure layer has an annular groove formed in the other region and surrounding the second multilayer film mirror in plan view, In the other region, the second semiconductor layer is formed by partially removing the surface of the second semiconductor layer, and an impurity adding the second conductivity type to the second semiconductor layer after the removal is inactivated in the inactivated region. The second semiconductor layer is provided with, The vertical cavity surface emitting laser, characterized in that the metal conductor layer is formed so as to cover the inner edge of the transparent insulating layer via the transparent electrode layer.

9. The vertical cavity surface emitting laser according to claim 8, characterized in that the groove penetrates the active layer of the semiconductor structure layer.

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