Vertical cavity light emitting device

Abstract

To provide a vertical resonator type light-emitting device capable of suppressing an increase of a driving voltage in a long period conduction, and realize a long life.SOLUTION: A vertical resonator type light-emitting device includes: a substrate 11 of a gallium nitride semiconductor; a first multilayer film reflector 13 formed by a nitride semiconductor; a translucent electrode layer in which a first semiconductor layer 17 having a first conductivity type, an active layer 19, and a second semiconductor layer 21 having a second conductivity type are laminated in this order, is formed onto an upper surface of a region of the second semiconductor layer, is electrically connected to the second semiconductor layer, and is isolated from the second semiconductor layer in other regions; and a translucent insulation layer that is formed so as to cover the region onto the translucent electrode layer, and is arranged to between a second multilayer film reflector 29 and a translucent electrode layer of the second semiconductor layer in the other region onto the second semiconductor layer. A thickness of the translucent electrode layer in a step of the other region on an upper surface of a semiconductor structure layer is larger than that other than the step, and includes a flatness over the upper surface of the second semiconductor 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] Conventionally, as one type of semiconductor laser, a vertical cavity type semiconductor surface emitting laser (hereinafter also simply referred to as a surface emitting laser) has been known, which 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 therebetween. For example, Patent Document 1 discloses a surface emitting laser using a nitride semiconductor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-98328 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in a vertical cavity light emitting element such as a surface emitting laser, an insulating film that defines an emission 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 transparent 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 transparent electrode film is formed so as to generate a step at the opening edge of the insulating film.

[0006] However, if a step occurs in the translucent electrode film as described above, abnormalities such as cracks may occur in the step portion of the translucent electrode during long-term current flow, which may result in an increase in driving voltage or problems such as short circuits or open circuits.

[0007] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a vertical cavity light emitting device which suppresses an increase in driving voltage during long-term energization and has a long life. [Means for solving the problem]

[0008] A vertical cavity light emitting device according to the present invention comprises a gallium nitride based semiconductor substrate, a first multilayer film 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 film 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, and a semiconductor structure 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 contacting the second semiconductor layer in another region surrounding the first region other than the first region. The semiconductor structure layer has a translucent electrode layer insulated from the semiconductor layer, a second multilayer film reflector formed on the translucent electrode layer to cover a certain region and forming a resonator between the first multilayer film reflector and the second multilayer film reflector, and a translucent insulator layer disposed between the second semiconductor layer and the translucent electrode layer in another region surrounding the certain region on the second semiconductor layer and insulating the second semiconductor layer from the translucent electrode layer, wherein a step is formed in another region on the top surface of the semiconductor structure layer, the thickness of the translucent electrode layer at the step is thicker than the thickness of the translucent electrode layer in places other than the step, and flatness is provided from the top surface of the translucent insulator layer to the top surface of the second semiconductor layer in the certain region.

[0009] A vertical cavity light emitting device according to the present invention comprises a gallium nitride semiconductor substrate, a first multilayer reflector made of nitride semiconductors formed on the substrate, a semiconductor structure layer including 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, and a light transmissive 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, the first multilayer reflector is formed on the transparent electrode layer to cover a region thereof and forms a resonator between itself and the first multilayer reflector; and a transparent insulator layer is 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 on the outside of the second multilayer reflector, the second semiconductor layer having an inactivated region in the other region thereof which is formed by partially removing the surface of the second semiconductor layer and in which the impurities imparting the second conductivity type to the second semiconductor layer are inactivated on the surface of the second semiconductor layer after the removal, and the thickness of the transparent electrode layer at the inner edge is thicker than the thickness of the transparent electrode layer at locations other than the inner edge. [Brief description of the drawings]

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

[0011] The following is a detailed description of an embodiment of the present invention. In the following description, a semiconductor surface-emitting laser element is taken 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. EXAMPLES

[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, for example, a GaN substrate. The substrate 11 is, for example, a substrate having a rectangular top surface shape. On the substrate 11, a first multilayer film reflector 13 made of a semiconductor layer grown on the substrate 11 is formed.

[0014] The first multilayer reflector 13 is a semiconductor multilayer reflector in which a low refractive index semiconductor film having an AlInN composition and a high refractive index semiconductor film having a GaN composition and a higher refractive index than the low refractive index semiconductor film 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 film and the low refractive index semiconductor film 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 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 film 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 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 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 is a semiconductor layer having a GaN composition and doped with Si as an n-type impurity. The n-type semiconductor layer 17 has a prismatic lower portion 17A and a 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 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 a ring shape so as to surround the upper portion 17B of the n-type semiconductor layer 17. In other words, the n-electrode 23, which is in electrical contact with the n-type semiconductor layer 17, is formed on the upper surface around the mesa-shaped structure of the n-type semiconductor layer 17. 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] Insulating layer 25, which serves as a light-transmitting insulator layer, is a layer made of an insulator formed on p-type semiconductor layer 21. Insulating layer 25 is made of a substance, such as SiO2, having a lower refractive index than the material forming 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 of 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 film reflector 29 is a dielectric multilayer film reflector 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 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 exposing the p-type semiconductor layer 21 of the insulating layer 25 described above. 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 film reflector 29 when viewed from above the surface-emitting laser 10. In other words, the opening 25H is covered by the second multilayer film reflector 29 on the upper surface of the p-type semiconductor layer 21. In further other words, the opening 25H is formed in a region of the insulating layer 25 facing the lower surface of the second multilayer film 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 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. In other words, the step 15S is a step that is 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 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 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 from 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. 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 exposing the protruding portion 21P. For example, the opening 25H is circular as shown in FIG. 2. 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 so as to be at the same height. That is, in the region inside the step 15S, the upper surface of the insulating layer 25 and the upper surface of the protruding portion 21P have flatness. Note that the same height here does not mean a completely same height, and may include unevenness or steps in 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 film reflector 13 and the second multilayer film reflector 29.

[0033] The light-transmitting electrode layer 31 is a layer made of a light-transmitting 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 light-transmitting 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 light-transmitting electrode layer 31 is formed of a metal oxide such as ITO or IZO that is light-transmitting to the light emitted from the active layer 19. The light-transmitting electrode layer 31 is formed so as to transfer the shape 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 light-transmitting 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 connected to 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 exposing the translucent electrode layer 31 in the center. 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 so as to cover the step 15S.

[0035] In the surface-emitting laser 10, the first multilayer reflector 13 has a reflectance slightly lower than that of the second multilayer reflector 29. Therefore, a 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, the operation of the surface-emitting laser 10 will be described. 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 resonant state (laser oscillation).

[0037] In the surface-emitting laser 10, a current is injected into the p-type semiconductor layer 21 only from a portion exposed by the opening 25H. In addition, since the p-type semiconductor layer 21 is very thin, the 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, a current is supplied only to a 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 reflectance slightly lower than that of the second multilayer reflector 29. Therefore, a 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 (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] The light emitting region of the active layer 19 is, for example, a region having a predetermined width in the active layer 19 where light of a predetermined intensity or more is emitted, and the center of the region is the light emitting center. The light emitting region of the active layer 19 is, for example, a region in the active layer 19 where a current of a predetermined density or more is injected, and the center of the region is the light emitting center. A straight line passing through the light emitting center and perpendicular to the 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 resonator length direction of the resonator OC formed by the first multilayer film reflector 13 and the second multilayer film reflector 29. 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 reflector 13, the semiconductor structure layer 15, and the second multilayer reflector 29 in the surface-emitting laser 10 will be described. In this embodiment, the first multilayer reflector 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 a Si-doped n-GaN layer with a thickness of 1580 nm. The active layer 19 is made of a multi-quantum well structure in which four pairs of 4 nm InGaN layers and 5 nm GaN layers are stacked, and the peak of the spectrum of the light emitted from the active layer 19 is adjusted to be about 440 nm. 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 thereon. The second multilayer reflector 29 is made of 10.5 pairs of 45 nm Nb2O5 and 76 nm SiO2 stacked. The resonant wavelength in this case was 440 nm.

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

[0044] 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 40 nm Nb2O5 spacer layer sandwiched therebetween. 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, the insulating layer 25, the light-transmitting electrode layer 31 and the 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 flow.

[0046] The back 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-mentioned configuration of the surface emitting laser 10 of this embodiment is merely one 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 lower refractive index than the p-type semiconductor layer 21. Moreover, the layer thicknesses of the other layers between the first multilayer film reflector 13 and the second multilayer film reflector 29 are the same anywhere in the plane if they are in the same layer.

[0049] Therefore, the equivalent refractive index (which is the optical distance between the first multilayer film reflector 13 and the second multilayer film reflector 29 and corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer film reflector 13 and the second multilayer film reflector 29 of the surface-emitting laser 10 differs between the central region CA, which is a cylindrical region whose upper surface shape is defined by the opening 25H, and the peripheral region PA, which is the other cylindrical region surrounding 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 that of the central region CA, i.e., the equivalent resonant wavelength in the central region CA is longer than the equivalent resonant wavelength in the peripheral region PA. As described above, the region from which light is emitted in the active layer 19 is directly below the convex portion 21P. 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] In this manner, in the surface emitting laser 10, a central area CA including the light emitting region of the active layer 19 and a peripheral area PA surrounding the central area CA and having a lower refractive index than the central area CA are formed. This suppresses optical loss caused by standing waves in the central area CA diverging (radiating) to the peripheral area PA. That is, a lot of light remains in the central area CA, and in this state, the laser light is extracted to the outside. Therefore, a lot of light is concentrated in the central area 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, 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 the first embodiment 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 translucent electrode layer 31 that is in electrical contact with the p-type semiconductor layer 21 in the central region CA and is insulated from the p-type semiconductor layer 21 in the peripheral region PA that surrounds the regions 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 reflector 29 formed on the translucent electrode layer 31 so as to cover the central region 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 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] Moreover, 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. Moreover, 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 laminated on the mesa-shaped structure, and the surface-emitting laser 10 has an n-electrode 23 in electrical contact with the n-type semiconductor layer 17 on the upper surface of the n-type semiconductor layer 17 present around the mesa-shaped structure.

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

[0056] 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 and in the region. However, instead, as shown in FIG. 4, the p-type semiconductor layer 21 may be etched all over except for the protruding portion 21P, the insulating layer 25 may be formed in the region, and the step 25S may be formed in the insulating layer 25.

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

[0058] If the transparent electrode is formed without a step, the capacitance of the current path of the semiconductor layer increases, which may decrease the 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 cause 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 can be reduced when the surface-emitting laser 10 is driven, and it becomes possible to prevent a decrease in the modulation speed. Furthermore, this reduction in capacitance makes it possible to reduce the amount of heat generated during operation, and it becomes possible to prevent the occurrence of defects such as melting of the semiconductor structure layer 15.

[0060] In addition, the translucent 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 the occurrence of abnormalities such as cracks in the step portion of the translucent electrode layer 31 during long-term current application. Even if a crack occurs in the step 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 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 is possible to prevent the occurrence of abnormalities such as open circuits.

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

[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 a surface-emitting laser 20 of Example 2. Also, 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 a basically similar configuration to the surface-emitting laser 10 of Example 1, and has a similar appearance. However, the surface-emitting laser 20 differs from the surface-emitting laser 10 in that there is no step outside the central region CA of the semiconductor structure layer 15, but the step is 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 there is an inactivated region layer 21A in which p-type impurities are inactivated outside the protruding portion 21P of the p-type semiconductor layer 21.

[0065] The inactivated 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. The surface of a semiconductor containing impurities, such as the p-type semiconductor layer 21, is roughened by performing dry etching. As a result, the p-type impurities in the etched portion are inactivated, and the inactivated region layer 21A is formed. In addition, in the inactivated region layer 21A, the p-type semiconductor layer 21 is partially removed by dry etching. In other words, the inactivated region layer 21A has an opening 21H that is a circular opening that exposes the p-type semiconductor layer 21 of the inactivated region layer 21A. The amount of etching that is partially removed by dry etching in the inactivated region layer 21A is, for example, 4 nm.

[0066] Further, an insulating layer 25 is formed as a translucent insulator layer 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 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 generated 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, the capacitance between the p-electrode 27 and the semiconductor layer 21 can be reduced when the surface-emitting laser 20 is driven, and a decrease in the modulation speed can be prevented. Furthermore, this decrease in capacitance makes it possible to reduce the amount of heat generated during driving, and prevents the occurrence of defects such as melting of the semiconductor structure layer 15.

[0068] Moreover, the translucent electrode layer 31 and the p-electrode 27 in 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 in 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 the second embodiment includes the substrate 11 made of a gallium nitride semiconductor, the first multilayer reflector 13 made of a nitride semiconductor formed on the substrate 11, the n-type semiconductor layer 17 made of a nitride semiconductor having an n-type conductivity formed on the first multilayer reflector 13, the active layer 19 made of a nitride semiconductor formed on the n-type semiconductor layer 17, and the semiconductor structure layer 15 including the p-type semiconductor layer 21 formed on the active layer 19 and made of a nitride semiconductor having a 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 protruding portion 21P of the p-type semiconductor layer 21, which is a region where no etching has been performed, i.e., 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 constriction layer that constricts the path of a 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 a current is injected into the active layer 19. On the other hand, the inactivated region layer 21A of the p-type semiconductor layer 21 functions as a non-current injection region where the injection of a current 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. In addition, 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, i.e., in the direction along the in-plane direction 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, in the surface-emitting laser 20, 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 reflector 13 and the second multilayer film reflector 29, and reaches a resonant state (laser oscillation).

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

[0075] Therefore, the equivalent refractive index (which is the optical distance between the first multilayer film reflector 13 and the second multilayer film reflector 29, and corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer film reflector 13 and the second multilayer film reflector 29 of the surface-emitting laser 20 differs between the cylindrical central region CA, whose upper surface shape is defined by the opening 21H, and the cylindrical peripheral region PA therearound, 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 that of the central region CA, i.e., the equivalent resonant wavelength in the central region CA is longer than the equivalent resonant wavelength in the peripheral region PA. As described above, the region from which light is emitted in the active layer 19 is directly below the opening 21H. 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 in which the p-type semiconductor layer 21 is inactivated 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 is subjected to a high resistance treatment by ion implantation into the p-type semiconductor layer 21. 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. This makes it possible to prevent the occurrence of abnormalities such as cracks in the step portion of the translucent electrode layer 31 during long-term current application. Even if a crack occurs in the step 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 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 is possible to prevent the occurrence of abnormalities such as an open circuit.

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

[0080] Third Embodiment 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 a basically similar configuration to the surface-emitting laser 10 of the first embodiment, 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 on the upper surface of the p-type semiconductor layer 21, i.e., the upper surface of the semiconductor structure layer 15. The groove 15G is formed in an area outside the openings 25H and 27H. That is, the groove 15G is a groove that is provided in an annular shape 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 film 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 film 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 protruding 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 manner, in the surface emitting laser 30 of the third embodiment, 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 so as 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 side surface of the opening 25H and the outer side 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 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 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 groove 15G is formed to reach the active layer 19, thereby forming a space or gap in a direction along the in-plane of the active layer 19. This gap relieves distortion that occurs in the in-plane 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 crystal structure is distorted due to the difference in lattice constant between InGaN and GaN that form the quantum well structure, which generates piezoelectric polarization and generates a piezoelectric field. The generation of this piezoelectric field reduces the recombination probability of the electrons and holes injected into the active layer 19, which is one of the factors that reduces the 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. It is believed that the gap created by this groove relieves distortion that occurs in the in-layer direction of the active layer 19 during the growth of the active layer 19, thereby improving the internal quantum efficiency of the active layer 19.

[0092] Here, the operation of the surface-emitting laser 30 will be described. 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 resonant state (laser oscillation).

[0093] In the surface-emitting laser 30, a current is injected into the p-type semiconductor layer 21 only from a portion exposed by the opening 25H. In addition, 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, i.e., in the direction along the in-plane direction of the semiconductor structure layer 15. Therefore, in the surface-emitting laser 30, a 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 reflectance slightly lower than that of the second multilayer reflector 29. Therefore, a 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 (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 in the active layer 19 where light of a predetermined intensity or more is emitted, and the center of the region is the light emitting center. The light emitting region of the active layer 19 is, for example, a region in the active layer 19 where a current of a predetermined density or more is injected, and the center of the region is the light emitting center. A straight line passing through the light emitting center and perpendicular to the in-plane direction of the upper surface of the substrate 11 or 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 resonator length direction of the resonator OC formed by the first multilayer film reflector 13 and the second multilayer film reflector 29. 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 reflector 13, the semiconductor structure layer 15, and the second multilayer film reflector 29 and an exemplary dimension of the groove 15G in the surface-emitting laser 30 will be described. In this embodiment, the first multilayer film reflector 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 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 is made of an active layer with a multiple 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 thereon. The second multilayer film reflector 29 is made of 10.5 pairs of Nb2O5 and SiO2 stacked. 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 um, a depth of 120 nm, and a width of 2 um. 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 Nb2O5 with a thickness of 40 nm sandwiched therebetween.

[0100] The back 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 at protruding portion 21P and a layer thickness of 30 nm in other regions. That is, p-type semiconductor layer 21 may have a layer thickness different between protruding portion 21P and 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 shown as being formed perpendicular to the top surface of the p-type semiconductor layer 21. However, the groove 15G and the p-type semiconductor layer 21, the insulating layer 25, the light-transmitting electrode layer 31, and the p-electrode 27 in the groove 15G portion are preferably steps having side surfaces 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 light-transmitting electrode layer 31 during long-term current application.

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

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

[0105] Therefore, the equivalent refractive index (which is the optical distance between the first multilayer film reflector 13 and the second multilayer film reflector 29 and corresponds to the resonant wavelength) within the resonator OC formed between the first multilayer film reflector 13 and the second multilayer film reflector 29 of the surface-emitting laser 30 differs between the cylindrical central region CA, whose upper surface shape is defined by the opening 25H, and the cylindrical peripheral region PA therearound, 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 that of the central region CA, i.e., the equivalent resonant wavelength in the central region CA is smaller than the equivalent resonant wavelength of the peripheral region PA. As described above, the region from which light is emitted in the active layer 19 is directly below the opening 25H. 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 recesses formed intermittently, 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 a ring structure formed intermittently. For example, the groove 15G may have a ring structure formed intermittently that surrounds the region exposed by the opening 25H of the upper surface of the p-type semiconductor layer 21.

[0108] In addition, 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 above-mentioned light-emitting central axis AX in order to uniformly relieve the distortion in the active layer 19. That is, when the groove 15G is formed by a plurality of recesses, it is preferable to form the recesses in two or more directions as viewed from the light-emitting region including the light-emitting central axis AX in the top view of the surface-emitting laser 30, and to sandwich the light-emitting region between the recesses. In order to uniformly relieve the distortion 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 provided 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 upper surface 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 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 embodiment.

[0111] According to the third embodiment, the translucent electrode layer 31 on the groove 15G is covered with the p-electrode 27, which is a metal layer. This makes it possible to prevent the occurrence of abnormalities such as cracks in the step portion of the translucent electrode layer 31 during long-term current application. Even if a crack occurs in the step 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 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 is possible to prevent the occurrence of abnormalities such as open circuits.

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

[0113] In addition, as described above, in the surface-emitting laser 30 of this embodiment, the semiconductor structure layer 15 is formed with the groove 15G extending from the upper surface of the p-type semiconductor layer 21 to the active layer 19. The groove 15G relieves distortion occurring 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 the light-emitting efficiency to be realized.

[0114] In any of the first, second and third embodiments, the step 15S, 25S or groove 15G is provided on the outer side of 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 the second multilayer film reflector 29 is formed so as to cover the steps 15S, 25S or the groove 15G, it is possible to obtain the same effects as those of the respective embodiments. In addition, in the case of a structure having the groove 15G as in the third embodiment, the second multilayer film reflector 29 is formed so as to fill the space formed by the groove 15G.

[0116] In addition, in all of Examples 1, 2 and 3, a 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, the substrate 11 may be made of a conductive material such as n-GaN, and an n-electrode made of a metal may be formed on the back surface of the substrate 11.

[0117] At this time, a back surface protrusion is formed on the back surface of the substrate 11. The back surface protrusion is formed in a region corresponding to the protrusion 21P when viewed from the normal direction of the substrate 11. This back surface protrusion is a convex portion that remains after the back surface is polished and the periphery of the back surface protrusion is removed by dry etching. Therefore, the top surface of the back surface protrusion is a polished surface, and the region around the back surface protrusion on the back surface of the substrate 11 is a surface obtained by dry etching the polished surface. The n-electrode is formed in the region around the back surface protrusion, i.e., the region excluding the back surface protrusion. This is because the top surface of the back surface protrusion of the substrate 11 becomes an opening through which the emitted light is released to the outside, and the emitted light is not blocked by the n-electrode. In other words, the back 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, except for the area corresponding to the central region CA when viewed from a direction perpendicular to the top surface of the substrate 11.

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

[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 an impurity concentration higher than that of the p-type semiconductor layer 21 in a 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 are formed on the highly doped p-type semiconductor layer.

[0121] In other words, in the region outside the central region CA, the p-electrode 27 is provided in a layer below the translucent electrode layer 31, 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] In addition, any of Examples 1, 2 and 3 may have a light 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) from the central area CA to the outside. In other words, a lot of light remains in the central area CA, and the laser light is extracted to the outside in this state. Therefore, a lot of 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] Also, in all of Examples 1, 2 and 3, the case has been described in which the p-electrode 27 covers the step of the light-transmitting 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 light-transmitting electrode layer 31 to extend the life of the light-transmitting 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 light-transmitting 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 step of the translucent electrode layer 31. However, the protective film that covers the step 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 film thickness of the step portion of the translucent electrode layer 31 may be, for example, twice the film thickness of the translucent electrode layer 31. This makes it possible to make it difficult for cracks to occur in the step portion of the translucent electrode layer 31 during long-term current application. 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 range in which 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 a range excluding the central region CA, which is the light-emitting region. 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. The modification 3 is also applicable to the second and third embodiments.

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

[0129] As in the second modification, the dielectric film 33 may be formed only on the step portion of the translucent electrode layer 31. The dielectric film 33 may be formed of, for example, SiO2, SiN xor a dielectric film made of a material such as Al2O3. The dielectric film 33 is preferably a dielectric film that is less reactive to the transparent electrode layer 31 than the high refractive index dielectric film (Nb2O5 in this embodiment) used in the spacer layer (not shown). As described above, by protecting the step portion of the transparent electrode layer 31 with the dielectric layer, it is possible to make it difficult for cracks to occur in the step portion of the transparent electrode layer 31 during long-term current application. 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 the dielectric film 33 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. In other words, it is preferable that the dielectric film 33 is configured so that the p-electrode 27 and the transparent electrode layer 31 are electrically contacted in at least one portion. The fourth modified example is also applicable to the second and third embodiments.

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

[0131] 10, 20, 30 Surface Emitting Laser 11 Substrate 13 First multilayer mirror 15 Semiconductor structure 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 mirror made of a nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer 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 second multilayer film reflector formed on the light-transmitting electrode layer so as to cover the first region and forming a resonator between the second multilayer film reflector and the first multilayer film reflector; a transparent insulator layer disposed between the second semiconductor layer and the transparent electrode layer in another region surrounding the first region on the second semiconductor layer, and insulating the second semiconductor layer from the transparent electrode layer; a step is formed in the other region of the upper surface of the semiconductor structure layer, a thickness of the translucent electrode layer at the step is greater than a thickness of the translucent electrode layer at a portion other than the step; A vertical cavity light emitting device having flatness from an upper surface of the light transmissive insulating layer to an upper surface of the second semiconductor layer in the first region.

2. The vertical cavity light emitting device according to claim 1 , wherein the step has an inclined surface with an angle of 45° or less with respect to the upper surface of the semiconductor structure layer.

3. A gallium nitride semiconductor substrate; a first multilayer mirror made of a nitride semiconductor formed on the substrate; a semiconductor structure layer including: a first semiconductor layer made of a nitride semiconductor having a first conductivity type formed on the first multilayer 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 second multilayer film reflector formed on the light-transmitting electrode layer so as to cover the first region and forming a resonator between the second multilayer film reflector and the first multilayer film 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 transparent insulator layer has an inner edge having a step on the outer side of the second multilayer film reflector, the second semiconductor layer includes, in the other region, an inactivated region that is formed by partially removing a surface of the second semiconductor layer and in which an impurity that imparts the second conductivity type to the second semiconductor layer is inactivated on the surface of the second semiconductor layer after the removal, 2. A vertical cavity light emitting device, wherein the thickness of the translucent electrode layer at the inner edge is greater than the thickness of the translucent electrode layer at any other location than the inner edge.

4. 4. The vertical cavity light emitting device according to claim 3, wherein the inner edge of the transparent insulating layer has an inclined surface with an angle of 45 degrees or less with respect to the upper surface of the semiconductor structure layer.

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

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