Surface emitting laser, array light source, and projection device

Abstract

To provide a surface emitting laser capable of suppressing oscillation of higher-order transverse modes.SOLUTION: The surface emitting laser includes, in order, a first reflector 20, a first conductivity-type semiconductor layer 31, an active layer 34, a second conductivity-type semiconductor layer 32, a transparent electrode 36, and a second reflector 40. The surface of the second conductivity-type semiconductor layer 32 on the side of the transparent electrode 36 has a central portion 50 protruding relative to a peripheral portion 52, and the thickness of the transparent electrode 36 at the central portion 50 is smaller than the thickness of the transparent electrode 36 at the peripheral portion 52.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a surface-emitting laser, an array light source, and a light projecting device. [Background technology]

[0002] In a surface-emitting laser such as a surface-emitting laser using a nitride semiconductor layer, it is known to use a transparent electrode between a semiconductor layer on an active layer and an upper reflecting mirror.

[0003] Patent Document 1 describes that when a convex portion that protrudes from the center relative to the periphery is provided on the surface of the semiconductor layer on the active layer facing the transparent electrode, the transparent electrode becomes thin on the side of the convex portion, and that to prevent this, the height of the convex portion is made smaller than the thickness of the transparent electrode. Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 does not describe the relationship between the thickness of the transparent electrode provided on the top surface of the convex portion and the thickness of the transparent electrode in the peripheral portion, and the drawings show the transparent electrodes in the central portion and the peripheral portion as having the same thickness. In this case, there is a possibility that higher-order transverse modes may occur.

[0005] An object of the present invention is to provide a surface-emitting laser, an array light source, and a light projecting device that can suppress oscillation in higher-order transverse modes. [Means for solving the problem]

[0006] According to an embodiment of the present invention, a light emitting device includes, in order, a first reflecting mirror, a first conductivity type semiconductor layer, an active layer, a second conductivity type semiconductor layer, a transparent electrode, and a second reflecting mirror, wherein the surface of the second conductivity type semiconductor layer facing the transparent electrode has a central portion that protrudes relative to an outer periphery, and the thickness of the transparent electrode at the central portion is smaller than the thickness of the transparent electrode at the outer periphery. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a surface-emitting laser, an array light source, and a light projector that can suppress oscillation in higher-order transverse modes. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a surface-emitting laser according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a main part of the surface-emitting laser according to the first embodiment of the present invention. [Figure 3] 3(a) and 3(b) are plan views showing transparent electrodes in the first embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a main part of a surface-emitting laser according to a reference example. [Figure 5] 5(a) and 5(b) are diagrams showing the light intensity and refractive index with respect to the position in the surface-emitting laser according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of a main part of a surface-emitting laser according to Modification 1 of the first embodiment of the present invention. [Figure 7] FIG. 7 is a cross-sectional view of a main part of a surface-emitting laser according to Modification 2 of the first embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view of a main part of a surface-emitting laser according to a third modification of the first embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing Δn / nA for each sample. [Figure 10] FIG. 10 is a plan view showing an array light source according to the second embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing a projection device according to the third embodiment of the present invention. [Figure 12] FIG. 12 is a perspective view showing a head mounted display according to a fourth embodiment of the present invention. [Figure 13] FIG. 13 is a cross-sectional view of the inside of the front and temples of a head-mounted display according to a fourth embodiment of the present invention. [Figure 14]FIG. 14 is a diagram showing a biometric authentication device according to a fifth embodiment of the present invention. [Figure 15] FIG. 15 is a diagram showing a floodlight device according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are examples for embodying the technical ideas of the invention, and the present invention is not limited to the described configurations and numerical values. In each drawing, the same components are given the same reference numerals, and duplicated explanations may be omitted as appropriate. The size, positional relationship, etc. of each component shown in each drawing may be exaggerated to facilitate understanding of the invention.

[0010] (First embodiment) First, a first embodiment will be described. The first embodiment relates to a surface-emitting laser. Fig. 1 is a cross-sectional view showing a surface-emitting laser according to the first embodiment of the present invention.

[0011] The surface-emitting laser 100 according to the first embodiment is a vertical cavity surface-emitting laser (VCSEL) that employs, for example, a nitride semiconductor layer. The surface-emitting laser 100 includes a substrate 10, a first reflecting mirror 20, a resonator 30, a second reflecting mirror 40, a transparent electrode 36, and electrodes 12 and 14.

[0012] Light is emitted in a direction perpendicular to the surface of the substrate 10. The light emission direction is perpendicular to the surface of the substrate 10 and is also called the vertical direction. A plane parallel to the surface of the substrate 10 is a plane perpendicular to the light emission direction, and a direction parallel to a plane parallel to the surface of the substrate 10 is also called the planar direction or horizontal direction.

[0013] The substrate 10 is a semiconductor substrate on which a nitride semiconductor layer can be formed. The substrate 10 may be, for example, a gallium nitride (GaN) substrate or a substrate in which a GaN template layer is formed on a heterogeneous substrate. The heterogeneous substrate may be, for example, a sapphire substrate, a silicon (Si) substrate, a gallium arsenide (GaAs) substrate, or a silicon carbide (SiC) substrate. The nitride semiconductor layer on the substrate 10 is formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride Vapor Phase Epitaxy).

[0014] The first reflecting mirror 20 is provided on the substrate 10, and is, for example, a distributed Bragg reflector (DBR) configured by laminating a plurality of n-type nitride semiconductor layers.

[0015] The resonator 30 is provided on the first reflecting mirror 20 and includes semiconductor layers 31 and 32 and an active layer 34. The active layer 34 is sandwiched between the semiconductor layers 31 and 32. The semiconductor layer 31 is an n-type semiconductor layer, and the semiconductor layer 32 is a p-type semiconductor layer. The semiconductor layers 31 and 32 are, for example, GaN layers or aluminum gallium nitride (AlGaN) layers.

[0016] The active layer 34 has, for example, a quantum well structure having an InGaN layer and a GaN layer, or a quantum well structure having an InGaN layer and an AlGaN layer. The thickness of the resonator 30 is an integer multiple of the wavelength λ, where λ is the wavelength of the oscillating light. This causes the light to resonate within the resonator 30 and produce laser oscillation. The light emission efficiency is highest when the active layer 34 is located at a position corresponding to the antinode of the electric field in the standing wave.

[0017] The transparent electrode 36 is provided on the resonator 30. The transparent electrode 36 is a conductor transparent to the oscillation light, such as an ITO (Indium Tin Oxide) layer, an ATO (Antimony doped Tin Oxide) layer, or a GZO (Gallium doped Zinc Oxide) layer. When the transparent electrode 36 is provided at a position that is a node of the electric field in the standing wave, the light absorption by the transparent electrode 36 is minimized.

[0018] The second reflecting mirror 40 is provided on the transparent electrode 36. The first reflecting mirror 20 and the second reflecting mirror 40 face each other in the vertical direction, sandwiching the resonator 30 therebetween. The second reflecting mirror 40 is a distributed Bragg reflector formed by laminating dielectric layers.

[0019] At least a part of the semiconductor layer 31, the active layer 34, and the semiconductor layer 32 of the resonator 30 are provided on a mesa 58. By including at least the active layer 34 in the mesa 58, it is possible to suppress lateral leakage of light generated in the active layer 34.

[0020] The electrode 12 is provided on the semiconductor layer 31 to surround the mesa 58 and is in electrical contact with the semiconductor layer 31. The electrode 12 is, for example, a Ti film and an Al film from the semiconductor layer 31 side. The electrode 14 is provided on the transparent electrode 36 to surround the central portion 50 and is in electrical contact with the transparent electrode 36. The electrode 14 is, for example, a Ni film and an Au film from the transparent electrode 36 side. The central portion 50 is a region that includes at least the center of the mesa 58.

[0021] 2 is a cross-sectional view of the main parts of the surface-emitting laser according to the first embodiment of the present invention, which mainly shows an enlarged view of the first reflecting mirror 20, the resonator 30, the transparent electrode 36, and the second reflecting mirror 40.

[0022] The first reflecting mirror 20 includes a plurality of alternately stacked low-refractive index layers 22 and a plurality of high-refractive index layers 24. The refractive index of the low-refractive index layers 22 is lower than the refractive index of the high-refractive index layers 24. The low-refractive index layers 22 and the high-refractive index layers 24 are, for example, AlN layers and GaN layers, respectively, AlGaN layers and GaN layers, or AlInN layers and InN layers, respectively.

[0023] The second reflecting mirror 40 includes a plurality of alternately stacked low refractive index layers 42 and a plurality of alternately stacked high refractive index layers 44. The refractive index of the low refractive index layers 42 is lower than the refractive index of the high refractive index layers 44. The low refractive index layers 42 and the high refractive index layers 44 are, for example, silicon oxide (SiO2) layers and tantalum oxide (Ta2O5) layers, respectively, or silicon oxide (SiO2) layers and niobium oxide (Nb2O5) layers, respectively.

[0024] The optical thickness of the low refractive index layers 22, 42 and the high refractive index layers 24, 44 is approximately λ / 4, where λ is the wavelength of the oscillating light. As a result, the first reflecting mirror 20 and the second reflecting mirror 40 Bragg-reflect the light of wavelength λ.

[0025] The surface of the semiconductor layer 32 in the resonator 30 facing the transparent electrode 36 has a central portion 50 that protrudes relative to an outer periphery 52, forming a convex portion 54. The surface of the transparent electrode 36 facing the second reflecting mirror 40 is flat at the outer periphery 52 and the central portion 50. The semiconductor layer 32 and the transparent electrode 36 are in electrical contact at the outer periphery 52 and the central portion 50. The side surface of the convex portion 54 may be inclined as shown in FIG. 2 or may be vertical as shown in FIG. 1.

[0026] The thickness of the transparent electrode 36 in the central portion 50 is T36A, the thickness of the transparent electrode 36 in the peripheral portion 52 is T36B, and the height of the protrusions 54 is T54. In this case, T36B = T36A + T54. This makes the upper surface of the transparent electrode 36 flat. For example, by making the electrical contact resistance between the transparent electrode 36 and the semiconductor layer 32 lower in the central portion 50 than in the peripheral portion 52, the current is confined to the central portion 50.

[0027] The total thickness of the resonator 30 and the transparent electrode 36 in the central portion 50 is T30A, and the total thickness of the resonator 30 and the transparent electrode 36 in the peripheral portion 52 is T30B. The oscillating light is reflected by the first reflecting mirror 20 and the second reflecting mirror 40 and resonates in the resonator 30. The resonator length, which determines the resonant wavelength, is the total thickness of the resonator 30 and the transparent electrode 36. In other words, the thicknesses T30A and T30B correspond to the resonator lengths in the central portion 50 and the peripheral portion 52, respectively. This causes stimulated emission and laser light oscillation.

[0028] 3(a) and 3(b) are plan views showing a transparent electrode according to a first embodiment of the present invention. As shown in FIGS. 3(a) and 3(b), an outer peripheral portion 52 is provided to surround a central portion 50. In FIG. 3(a), the central portion 50 has a circular planar shape. As a result, the polarization of the emitted laser light is not controlled.

[0029] In FIG. 3(b), the planar shape of the central portion 50 is elliptical. This polarizes the emitted laser light. The planar shape of the central portion 50 may be a circle, an ellipse, or a polygon such as a rectangle. By making the planar shape of the central portion 50 different in two orthogonal directions, such as an ellipse or a rectangle, the polarization of the laser light can be controlled.

[0030] (Reference example) Fig. 4 is a cross-sectional view of a main portion of a surface-emitting laser according to a reference example. As shown in Fig. 4, in the surface-emitting laser 110 according to the reference example, a thickness T36A of the transparent electrode 36 at the central portion 50 is equal to a thickness T36B of the transparent electrode 36 at the peripheral portion 52. The surface of the transparent electrode 36 facing the second reflecting mirror 40 has a convex portion 56 where the central portion 50 protrudes relative to the peripheral portion 52. Therefore, the total thickness T30A of the resonator 30 and the transparent electrode 36 at the central portion 50 is greater than the total thickness T30B of the resonator 30 and the transparent electrode 36 at the peripheral portion 52.

[0031] Let nA and nB be the effective refractive indices of the central portion 50 and the peripheral portion 52, respectively, and Δn=nA-nB. Δn / nA is approximately (λA-λB) / λA. λA and λB are the resonance wavelengths of the central portion 50 and the peripheral portion 52, respectively. When Δn is positive, a waveguide structure is formed. When Δn becomes large and positive, the oscillating light is confined in the central portion 50. Therefore, in the surface-emitting laser 110 of the reference example, the oscillating light is confined in the central portion 50. The zeroth-order transverse mode has a peak of light intensity in the central portion 50. The higher-order transverse modes have peaks of light intensity in the peripheral portion 52. Therefore, when the oscillating light is confined in the central portion 50, the zeroth-order transverse mode is generated, and the generation of higher-order transverse modes can be suppressed.

[0032] The transparent electrode 36 is a conductor and has a larger absorption coefficient of the oscillating light than the semiconductor layer 32. For example, the light absorption coefficient of gallium nitride in the visible range is several hundred cm -1 The optical absorption coefficient of ITO in the visible range is several thousand cm -1 Therefore, when the thickness T36A of the transparent electrode 36 in the central portion 50 increases, the oscillating light is more easily absorbed. On the other hand, when the transparent electrode 36 is made thinner, the height T54 of the convex portions 54 is reduced to improve the coverage of the transparent electrode 36 on the convex portions 54. This reduces Δn, and the oscillating light is less confined to the central portion 50.

[0033] In the surface-emitting laser 100 of the first embodiment, as shown in FIG. 2, the thickness T36A of the transparent electrode 36 at the central portion 50 is smaller than the thickness T36B of the transparent electrode 36 at the peripheral portion 52. As a result, the oscillating light is less likely to be absorbed at the central portion 50. On the other hand, the oscillating light is more likely to be absorbed by the transparent electrode 36 at the peripheral portion 52. This makes it possible to increase the threshold carrier density for laser oscillation at the peripheral portion 52. This makes it possible to suppress the occurrence of higher-order transverse modes that increase light intensity at the peripheral portion 52. Therefore, oscillation in a single transverse mode can be obtained.

[0034] In the first embodiment, the transparent electrode 36 (portion with thickness T36B) of the peripheral portion 52 is provided so as to surround the transparent electrode 36 (portion with thickness T36A) of the central portion 50. The transparent electrode 36 of the peripheral portion 52, i.e., the transparent electrode 36 having a thickness greater than that of the transparent electrode 36 of the central portion 50, may be provided in at least a portion on the outer periphery side of the transparent electrode 36 of the central portion 50. In this case, the transparent electrode 36 of the peripheral portion 52 may be divided into multiple portions.

[0035] In the peripheral portion 52, the surface of the transparent electrode 36 on the semiconductor layer 32 includes a flat portion. A thickness T36B of the transparent electrode 36 on this flat portion is greater than a thickness T36A of the transparent electrode 36 in the central portion 50.

[0036] 5(a) and 5(b) are diagrams showing the light intensity and refractive index versus position in the surface-emitting laser according to the first embodiment of the present invention. 5(a) and 5(b) show the central portion 50 and the peripheral portion 52, respectively. The position on the horizontal axis indicates the position in the vertical direction in FIG. 2. 30, 36, and 40 on the diagram indicate the ranges of the resonator 30, the transparent electrode 36, and the second reflecting mirror 40, respectively. The light intensity on the vertical axis indicates the light intensity of the standing wave. The refractive index on the vertical axis indicates the refractive index of each material. Each material is the material shown in specific example 1.

[0037] 5(a), an electric field node in the standing wave is located at the center of the transparent electrode 36. This suppresses absorption of the standing wave by the transparent electrode 36. In the central portion 50, the wavelength of the standing wave is 445.022 nm.

[0038] 5(b), the total thicknesses T30A and T30B of the resonator 30 and the transparent electrode 36 are the same in the central portion 50 and the peripheral portion 52. However, because the refractive index of the transparent electrode 36 is lower than that of the resonator 30, the resonance wavelength in the peripheral portion 52 is shorter than that in the central portion 50. In the peripheral portion 52, the wavelength of the standing wave is 444.86 nm.

[0039] As shown by the dashed circle in Figure 5(b), the thickness T36B of the transparent electrode 36 is greater than T36A, so that the portion of the transparent electrode 36 where the optical intensity of the standing wave is high is located near the resonator 30. As a result, the oscillating light is absorbed by the transparent electrode 36, and the threshold carrier density increases. Therefore, oscillation becomes difficult in the outer peripheral portion 52, and the generation of higher-order transverse modes is suppressed.

[0040] (Modification 1 of the first embodiment) 6 is a cross-sectional view of a main part of a surface-emitting laser according to Modification 1 of the first embodiment of the present invention. As shown in FIG. 6, in a surface-emitting laser 102 according to Modification 1 of the first embodiment, the semiconductor layer 32 includes a semiconductor layer 32a and a contact layer 32b. The contact layer 32b has a higher dopant concentration than the semiconductor layer 32a. For example, the dopant concentration of the contact layer 32b is 1×10 20 cm -3 That is, the dopant concentration is at least twice the dopant concentration of the semiconductor layer 32a. As a result, the contact resistance between the transparent electrode 36 and the semiconductor layer 32 in the central portion 50 is lower than the contact resistance between the transparent electrode 36 and the semiconductor layer 32 in the peripheral portion 52. Therefore, the current flowing from the transparent electrode 36 is limited to the central portion 50. The other configurations are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0041] (Modification 2 of the first embodiment) FIG. 7 is a cross-sectional view of a main portion of a surface-emitting laser according to Modification 2 of the first embodiment of the present invention. As shown in FIG. 7, the surface-emitting laser 104 according to Modification 2 of the first embodiment includes an insulating layer 38. The insulating layer 38 has a thickness T38. The insulating layer 38 is provided between the semiconductor layer 32 and the transparent electrode 36 in the peripheral portion 52. The insulating layer 38 is not provided in the central portion 50. The insulating layer 38 is an inorganic insulator layer, such as a silicon oxide layer or a silicon nitride film. In the central portion 50, the transparent electrode 36 is in electrical contact with the semiconductor layer 32. Therefore, the current flowing from the transparent electrode 36 is confined to the central portion 50. The other configurations are the same as those of Modification 1 of the first embodiment, and therefore a description thereof will be omitted.

[0042] (Modification 3 of the first embodiment) Fig. 8 is a cross-sectional view of the main parts of a surface-emitting laser according to Modification 3 of the first embodiment of the present invention. As shown in Fig. 8, in a surface-emitting laser 106 according to Modification 1 of the first embodiment, the transparent electrode 36 has a convex portion 56 such that a central portion 50 on the surface facing the second reflecting mirror 40 protrudes relative to an outer peripheral portion 52. A thickness T36A of the transparent electrode 36 at the central portion 50 is smaller than a thickness T36B of the transparent electrode 36 at the outer peripheral portion 52. If the thickness T36A is smaller than T36B, the convex portion 56 may be provided. The other configuration is the same as that of Modification 1 of the first embodiment, and a description thereof will be omitted.

[0043] In the second modification of the first embodiment, the transparent electrode 36 also has the protrusions 56, and the thickness T36A may be smaller than the thickness T36B.

[0044] Δn / nA was calculated for structures including the first embodiment and its modified examples. Fig. 9 is a diagram showing Δn / nA for each sample. In all samples, the thickness T36A of the transparent electrode 36 at the central portion 50 was set to 20 nm. The height T54 of the convex portion 54 was set to 0 nm, 10 nm, and 20 nm. T54 = 0 nm indicates that the convex portion 54 is not provided. The shaded areas indicate that the convex portion 54 is provided.

[0045] The thickness T38 of the insulating layer 38 in FIG. 7 was set to 0 nm, 10 nm, and 20 nm. T38=0 nm indicates that the insulating layer 38 was not provided. The shaded areas indicate that the insulating layer 38 was provided. The thickness T36B of the transparent electrode 36 in the peripheral portion 52 was set to 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm. T36A-T36B is the difference between the thicknesses T36A and T36B. The shaded areas indicate that the thickness T36A is smaller than T36B.

[0046] The height T56 of the convex portion 56 was calculated from the height T54 and the thicknesses T38 and T36B. A positive height T56 indicates that a convex portion 56 is provided, where the upper surface of the transparent electrode 36 in the central portion 50 is convex relative to the outer peripheral portion 52. A height T26 of 0 nm indicates that the upper surface of the transparent electrode 36 in the central portion 50 is flat. A negative height T26 indicates that the upper surface of the transparent electrode 36 in the central portion 50 is concave relative to the outer peripheral portion 52. The shaded areas indicate that the height T56 is 0 nm or more.

[0047] The examples indicate that each sample corresponds to a reference example, a reference example, or a modified example. No. 2 does not have a protrusion 54, and the thickness of the transparent electrode 36 is the same in the central portion 50 and the peripheral portion 52, and corresponds to the reference example. Δn / nA indicates the amount of change in Δn / nA relative to the reference example, with the reference example being set to 0%. A positive Δn / nA indicates that Δn / nA is larger than that of the reference example.

[0048] Nos. 4 and 9, where T36A-T36B=0 nm, correspond to Reference Examples. Nos. 5 and 11 correspond to Modified Example 1. No. 14 corresponds to Modified Example 2. No. 10 corresponds to Modified Example 3.

[0049] As in No. 2, No. 4, and No. 9, when T36A-T36B=0 nm and T54 is increased, Δn / nA increases. Therefore, the oscillating light is more likely to be confined to the central portion 50. However, the thickness of the transparent electrode 36 in the central portion 50 is the same as that in the peripheral portion 52. Therefore, the effect of the transparent electrode 36 on absorbing light in the peripheral portion 52 is small.

[0050] As seen in the comparison between Nos. 5 and 6, and the comparison between Nos. 10, 11, and 12, when the height T54 of the convex portion 54 is kept the same and the thickness T36B of the transparent electrode 36 in the peripheral portion 52 is increased, the height T56 of the convex portion 56 decreases. Accordingly, Δn / nA decreases. When T56 becomes negative, Δn / nA also becomes negative. This indicates that the light confinement is smaller than in the reference example.

[0051] As can be seen from the comparison between No. 14 and No. 15, even when the insulating layer 38 is provided, if T56 is negative, Δn / nA becomes negative. Thus, it is preferable that the height T56 is 0 or positive.

[0052] To summarize the above, the surface of the semiconductor layer 32 facing the transparent electrode 36 protrudes at the central portion 50 relative to the peripheral portion 52. This increases Δn / nA, and oscillating light can be confined within the central portion 50. Furthermore, the thickness T36A of the transparent electrode 36 at the central portion 50 is smaller than the thickness T36A of the transparent electrode 36 at the peripheral portion 52. This makes it possible to suppress the occurrence of higher-order transverse modes in the peripheral portion 52 that would increase light intensity.

[0053] The surface of the transparent electrode 36 on the second reflecting mirror 40 side has a central portion 50 that protrudes relative to the outer peripheral portion 52, or is flat between the outer peripheral portion 52 and the central portion 50. This increases Δn / nA and allows the oscillating light to be confined by the central portion 50.

[0054] In the central portion 50, the semiconductor layer 32 and the transparent electrode 36 are in contact with each other. This allows current to flow through the central portion 50. As in the second modification, in the peripheral portion 52, an insulating layer 38 is provided between the semiconductor layer 32 and the transparent electrode 36. This allows current in the peripheral portion 52 to be further suppressed.

[0055] The absorption coefficient of the transparent electrode 36 for the oscillating light is greater than the absorption coefficient of the semiconductor layer 32. This makes it possible to increase the threshold carrier density in the thick outer peripheral portion 52 of the transparent electrode 26. The absorption coefficient of the transparent electrode 36 for the oscillating light is preferably at least twice the absorption coefficient of the semiconductor layer 32, and more preferably at least five times.

[0056] The semiconductor layers 31, 32 and the active layer 34 are nitride semiconductor layers. In this case, to provide an electrode 14 on the second reflecting mirror 40, the second reflecting mirror 40 must be a nitride semiconductor layer and have low electrical resistance. However, if the second reflecting mirror 40 is made of a nitride semiconductor layer, it is difficult to reduce electrical resistance. Therefore, the second reflecting mirror 40 is made of a dielectric layer. A transparent electrode 36 is provided between the resonator 30 and the second reflecting mirror 40, and an intra-cavity structure is adopted in which current is injected from the transparent electrode 36 into the resonator 30. Therefore, a structure like that of the first embodiment and its modifications is preferable.

[0057] In the first embodiment and its modifications, the first conductivity type is n-type and the second conductivity type is p-type, but the first conductivity type may be p-type and the second conductivity type may be n-type.

[0058] (Specific example 1 of modified example 1 of first embodiment) As specific example 1, an example of a surface-emitting laser with an oscillation wavelength of 445 nm will be described. The substrate 10 is a GaN substrate. In the first reflecting mirror 20, the high-refractive-index layers 24 are InGaN layers. The low-refractive-index layers 22 are superlattice layers of AlGaN and GaN. The number of pairs of the high-refractive-index layers 24 and the low-refractive-index layers 22 is 55 pairs.

[0059] In the resonator 30, the semiconductor layer 31 is an n-type GaN layer. The dopant of the semiconductor layer 31 is Si or Ge. The active layer 34 is a multi-quantum well (MQW) having an InGaN layer and a GaN layer. The semiconductor layer 32 is a p-type GaN layer, and has a semiconductor layer 32a and a contact layer 32b as in the first modification. The dopant of the semiconductor layer 32 is Mg. The dopant concentration of the contact layer 32b is 1 to 2×10 20 cm -3 The contact layer 32b has a thickness of 10 nm. The dopant concentration of the semiconductor layer 32a is 2 to 3×10 19 cm -3 is.

[0060] The height T54 of the protrusion 54 is 10 nm. The transparent electrode 36 is an ITO film. The thicknesses T36A and T36B are 20 nm and 30 nm, respectively. This makes the upper surface of the transparent electrode 36 flat between the central portion 50 and the outer peripheral portion 52.

[0061] In the second reflecting mirror 40, the high refractive index layer 44 is a tantalum oxide layer. The low refractive index layer 42 is a silicon oxide layer. The number of pairs of the high refractive index layer 44 and the low refractive index layer 42 is 10.5 pairs. In the central portion 50, the active layer 34 is located at the antinode of the standing wave, and the transparent electrode 36 is located at the node of the standing wave. The electrode 12 is a Ti film and an Al film from the semiconductor layer 31 side. The electrode 14 is a Ni film and an Au film from the transparent electrode 36 side.

[0062] A current is injected from the electrode 14 into the transparent electrode 36, flows laterally within the transparent electrode 36 from the outer periphery 52 to the central portion 50, and then flows vertically in the outer periphery 52 from the semiconductor layer 32 to the active layer 34. This causes oscillation light to be generated in the active layer 34, resulting in the emission of laser light.

[0063] A method for manufacturing the surface-emitting laser of Example 1 will be described. The nitride semiconductor layers of the first reflecting mirror 20 and the resonator 30 are formed on a wafer-shaped substrate 10 using MOCVD. The substrate 10 is then heat-treated in a nitrogen atmosphere to activate the dopants in the p-type GaN layer of the semiconductor layer 32. Next, a mesa 58 is formed using photolithography and dry etching. A silicon oxide layer is then formed as an insulating layer over the entire surface of the wafer. Next, the insulating layer on the top surface of the mesa 58 and in the region where the electrode 12 is to be formed is removed using photolithography and wet etching.

[0064] Next, protrusions 54 are formed on the upper surface of the semiconductor layer 32 using photolithography and dry etching. In Example 1, although not limited thereto, etching is performed so that the semiconductor layer 32 has a flat portion in a portion corresponding to the outer periphery 52 around the protrusions 54. Next, a portion of the transparent electrode 36 is formed on the semiconductor layer 32. Next, the remaining portion of the transparent electrode 36 is formed in the outer periphery 52. ​​The upper surface of the transparent electrode 36 is flat between the central portion 50 and the outer periphery 52.

[0065] Next, the electrode 12 is formed on the semiconductor layer 31, and the electrode 14 is formed on the transparent electrode 36. Next, the second reflecting mirror 40 is formed on the transparent electrode 36. In this way, the surface-emitting laser of Example 1 is manufactured.

[0066] (Specific example 2 of modified example 2 of first embodiment) As specific example 2, a surface-emitting laser with an oscillation wavelength of 515 nm will be described. The substrate 10 is a GaN substrate. In the first reflecting mirror 20, the number of pairs of high-refractive-index layers 24 and low-refractive-index layers 22 is 60. In the resonator 30, the composition and film thickness of each layer of the active layer 34 are set to generate oscillation light of 515 nm.

[0067] The height T54 of the convex portion 54 is 20 nm. A silicon oxide layer is provided as the insulating layer 38 on the semiconductor layer 32 in the outer circumferential portion 52. The thickness T38 of the insulating layer 38 is 10 nm. The transparent electrode 36 is an ITO film. The thicknesses T36A and T36B are 20 nm and 30 nm, respectively. In the second reflecting mirror 40, the number of pairs of the high refractive index layer 44 and the low refractive index layer 42 is 11.5 pairs. The other configurations are the same as in specific example 1, and therefore description thereof will be omitted.

[0068] A method for manufacturing the surface-emitting laser of Example 2 will now be described. Using photolithography and dry etching, protrusions 54 are formed on the upper surface of the semiconductor layer 32. Using the mask layer used at this time as a mask, an insulating layer 38 is formed on the semiconductor layer 32 in the outer periphery 52. ​​In this way, the protrusions 54 and the insulating layer 38 can be formed using a self-aligned process.

[0069] The transparent electrode 36 in the central portion 50 is formed on the semiconductor layer 32, and the transparent electrode 36 in the peripheral portion 52 is formed on the insulating layer 38. As a result, the crystallinity of the transparent electrode 36 differs between the central portion 50 and the peripheral portion 52. When the transparent electrode 36 is etched, the etching rate in the central portion 50 is faster than the etching rate in the peripheral portion 52. This allows the thickness T36A of the central portion 50 to be smaller than the thickness T26B of the peripheral portion 52, even without forming the transparent electrode 36 in two separate steps as in Example 1. The remaining manufacturing methods are the same as in Example 1, and therefore will not be described again.

[0070] (Specific example 3 of modified example 3 of first embodiment) As specific example 3, an example of a surface-emitting laser with an oscillation wavelength of 445 nm will be described. The height T54 of the convex portion 54 is set to 20 nm. The thicknesses T36A and T36B of the transparent electrode 36 are set to 20 nm and 30 nm, respectively. As a result, the convex portion 56 is formed on the upper surface of the transparent electrode 36, and the height T56 is 10 nm. The other configurations are the same as in specific example 1, so further description will be omitted.

[0071] (Second embodiment) The second embodiment is an example of an array light source that uses the surface-emitting lasers according to the first embodiment and its modifications. Fig. 10 is a plan view showing an array light source according to the second embodiment of the present invention. As shown in Fig. 10, the array light source 200 includes a substrate 201, a surface-emitting laser 202, and common electrodes 203a to 203d.

[0072] The substrate 201 is a semiconductor substrate corresponding to, for example, the substrate 10. The surface-emitting laser 202 is a surface-emitting laser according to the first embodiment and its modified examples. The surface-emitting laser 202 is provided on the substrate 201. Common electrodes 203a to 203d are electrodes provided in common by the electrode 14 among the plurality of surface-emitting lasers 202.

[0073] By selecting a common electrode to which a voltage is applied from among the plurality of common electrodes 203a to 203d, the surface-emitting lasers 202 sharing the selected common electrode 203a to 203d can emit light. A single common electrode may be used. In this case, all of the plurality of surface-emitting lasers 202 emit light simultaneously. Thousands to tens of thousands of surface-emitting lasers 202 may be provided in a two-dimensional array on the substrate 201. The arrangement of the surface-emitting lasers 202 and the arrangement of the common electrodes 203a to 203d can be appropriately selected depending on the purpose.

[0074] (Third embodiment) The third embodiment is an example of a projection device that uses the surface-emitting laser according to the first embodiment and its modifications, or the array light source according to the second embodiment, and is, for example, an example of a laser scanning projector. Fig. 11 is a diagram showing a projection device according to the third embodiment of the present invention.

[0075] 11, the projection device 210 includes a light source 212 and an optical scanning unit 214. The light source 212 is the surface-emitting laser 100, 102, 104, or 106 according to the first embodiment and its modifications, or the array light source 200 according to the first embodiment.

[0076] When the light source 212 is monochromatic, the projection device 210 projects a monochromatic image onto the object 216. When the light source 212 has surface-emitting lasers of multiple colors, the projection device 210 can project images of multiple colors onto the object 216. In this case, the optical axes of the surface-emitting lasers are aligned coaxially and emitted from the emission surfaces, and the oscillation wavelengths of the surface-emitting lasers are different.

[0077] The optical scanning unit 214 is an example of an optical element onto which light emitted from the surface-emitting laser is incident, and includes an element for scanning the laser light emitted from the light source 212 and projecting an image onto the object 216. As such an element, a MEMS (micro electro mechanical systems) mirror that is movable in two axial directions or an element combining two MEMS mirrors that are movable in one axial direction can be used. The optical scanning unit 214 is an example of an optical element that adjusts the traveling direction of the laser light emitted from the light source 212.

[0078] When generating an image, the intensity of the laser light is modulated in accordance with the scanning of the optical scanning unit 214, and the laser light is irradiated onto the object 216. In this way, an image can be generated directly on the object 216.

[0079] When a surface-emitting laser is used as the light source 212, the surface-emitting laser outputs laser light of the order of μW to several mW, and can draw an image in a very small area. Such a projection device 210 can be used, for example, as a retinal display that draws an image directly on the retina with laser light. By using a surface-emitting laser, which consumes less power than an edge-emitting laser, as the light source 212, it is possible to reduce the battery capacity, thereby realizing a small and lightweight retinal display.

[0080] When an array light source is used for the light source 212, laser light of the order of mW to kW can be output, and an image can be drawn over a large area. Such a projection device can be used, for example, as a projector. A densely integrated two-dimensional array light source simplifies the optical system, making it possible to realize a compact projector.

[0081] (Fourth embodiment) The fourth embodiment is an example of a display device such as a head-mounted display, and is a retinal display that draws images directly on the retina with laser light. Fig. 12 is a perspective view showing a head-mounted display according to the fourth embodiment of the present invention.

[0082] As shown in Fig. 12, the head mounted display (HMD) 220 includes a front 221 and temples 222. The front 221 and temples 222 are provided in pairs on the left and right, approximately symmetrically. The front 221 includes, for example, a light guide plate 223. The temples 222 house, for example, an optical system, a control device, etc. The HMD 60 is an example of a head-mounted display device that can be worn on a human head, and can have a shape similar to that of glasses, for example.

[0083] Fig. 13 is a cross-sectional view of the inside of a front and temples in a head mounted display according to a fourth embodiment of the present invention. Fig. 13 illustrates a front 221 and temple 222 for the left eye, but the front 221 and temple 222 for the right eye also have the same configuration as those in Fig. 13.

[0084] The HMD 220 includes a control device 224, a light source unit 225, a light amount adjustment unit 226, and a movable device 227 in a temple 222. The HMD 220 includes a light guide plate 223 and a half mirror 229 in a front 221. The light amount adjustment unit 226, the movable device 227, the light guide plate 223, and the half mirror 229 are examples of optical elements onto which light emitted from the surface-emitting laser is incident.

[0085] The light source unit 225 includes one or more surface-emitting lasers as laser light sources, a collimating lens, and a dichroic mirror inside an optical housing. When the light source unit 225 includes multiple surface-emitting lasers with different wavelengths, the light source unit 225 can emit, for example, RGB laser light. The light source unit 225 emits collimated light. When the laser light is composed of multiple wavelengths, the parallel light is formed by combining multiple laser lights.

[0086] The light intensity adjusting unit 226 adjusts the intensity of the laser light emitted from the light source unit 225. The movable device 227 has a reflecting surface 228. The movable device 227 moves the reflecting surface 228 in the X and Y directions based on a signal from the control device 224. This causes the laser light, the intensity of which has been adjusted, to perform two-dimensional scanning. The drive control of the movable device 227 is performed in synchronization with the emission timing of the laser light source.

[0087] The light guide plate 223 reflects the laser light scanned by the movable device 227 on its inner wall surface and guides the light to the half mirror 229. The light guide plate 223 is made of a resin or the like that is transparent to the wavelength of the laser light.

[0088] The half mirror 229 reflects the light from the light guide plate 223 towards the back side of the HMD 220 and emits the light in the direction of the eyes of the wearer 250 wearing the HMD 220. The half mirror 229 has, for example, a free-form surface shape. An image formed by the scanning light is formed on the retina of the wearer 250 by reflection on the half mirror 229. Alternatively, an image formed by the scanning light is formed on the retina of the wearer 250 by reflection on the half mirror 229 and the lens effect of the crystalline lens in the eyeball. Furthermore, spatial distortion of the image is corrected by reflection on the half mirror 229. The wearer 250 can view the image formed by the light scanned in the X and Y directions.

[0089] Because the half mirror 229 is used, an image based on light from the outside world and an image based on the scanning light are superimposed and visible to the wearer 250. By providing a mirror instead of the half mirror 229, it is possible to eliminate light from the outside world and configure the wearer 250 to be able to see only the image based on the scanning light.

[0090] By using a surface-emitting laser for the light source unit 225, the number of parts such as ND filters can be reduced and power consumption is also reduced compared to when an edge-emitting laser is used, making it possible to realize a compact and lightweight HDM.

[0091] (Fifth embodiment) The fifth embodiment is an example of a biometric information acquisition device that uses a human pupil response. Fig. 14 is a diagram showing a biometric authentication device according to the fifth embodiment of the present invention. The biometric authentication device 230 includes a light source 231, a light scanning unit 232, a first optical element 233, a second optical element 234, and an image sensor 235.

[0092] The light source 231 includes one or more surface-emitting lasers. The optical scanning unit 232 two-dimensionally scans the laser light emitted from the light source 231. The first optical element 233 is a waveguide that guides the laser light scanned by the optical scanning unit 232 to the second optical element 234. The second optical element 234 is, for example, a mirror, and changes the path of the laser light emitted from the first optical element 233 to irradiate the pupil 252. In the fifth embodiment, the first optical element 233 and the second optical element 234 are described separately, but any other optical element may be used as long as it emits the scanned laser light to the pupil 252. The optical scanning unit 232, the first optical element 233, and the second optical element 234 are examples of optical elements onto which the light emitted from the surface-emitting laser is incident.

[0093] The image capturing element 235 is an example of a light receiving element that receives light incident from the outside, and captures an image of light emitted from the pupil 252 by the laser light that the second optical element 234 irradiates onto the pupil 252. In this way, the image capturing element 235 acquires iris information of the pupil 252. By controlling the intensity of the laser light that the second optical element 234 irradiates onto the pupil 252, it is also possible to control the size of the pupil.

[0094] When the light source 231 includes a plurality of surface-emitting lasers, the light source 231 may emit laser light of four wavelengths, for example, red, blue, green, and infrared, on the same optical axis. Since the pupillary response to blue and green wavelengths is more sensitive than to other wavelengths, it is possible to obtain more detailed iris information by narrowing the pupil. Furthermore, by using multiple wavelengths, biometric information for each wavelength of the iris can be obtained, thereby increasing the accuracy of authentication.

[0095] (Sixth embodiment) 15 is a diagram showing a light-emitting device according to the sixth embodiment of the present invention. A light-emitting device 240 includes a light source 242, a fluorescent member 244, and a light-emitting member 246.

[0096] The light source 242 is, for example, the array light source 200 of the second embodiment. The fluorescent member 244 is an example of an optical element into which light emitted from a surface-emitting laser is incident, and is excited by the laser light emitted from the light source 242 to emit fluorescence. For example, if the laser light emitted from the light source 242 is blue light, the fluorescent member 244 emits yellow light. If the light emitted from the light source 242 is ultraviolet light, the fluorescent member 244 emits white light. The fluorescent member 244 may be any optical element that adjusts the wavelength of the laser light emitted from the light source 242.

[0097] The light projecting member 246 projects the laser light emitted by the light source 242 and the fluorescence emitted by the fluorescent member 244. The light projecting member 246 is, for example, a reflecting mirror. The light projecting member 246 may be any optical element that adjusts the traveling direction of the laser light that is emitted from the light source 242 and whose wavelength has been adjusted by the fluorescent member 244.

[0098] When the array light source 200 of the second embodiment is used as the light source 242, a common electrode is selected and a voltage is applied. This allows the floodlight device 240 to project light into any location or space. For example, when the floodlight device 240 is used as an in-vehicle headlight module, providing multiple upper common electrodes in the array light source 200 allows it to be used as a high-output, compact, variable light distribution headlamp. Furthermore, by selecting a surface-emitting laser to emit light, it is possible to irradiate a laser beam at a targeted position.

[0099] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0100] The above-disclosed embodiments include, for example, the following aspects. (1) 1. A surface-emitting laser comprising, in order, a first reflecting mirror, a first conductivity type semiconductor layer, an active layer, a second conductivity type semiconductor layer, a transparent electrode, and a second reflecting mirror, wherein a surface of the second conductivity type semiconductor layer facing the transparent electrode has a central portion that protrudes relative to an outer periphery, and the thickness of the transparent electrode at the central portion is smaller than the thickness of the transparent electrode at the outer periphery. (2) The surface-emitting laser according to (1), wherein the surface of the transparent electrode facing the second reflector has the central portion protruding relative to the outer periphery, or the outer periphery and the central portion are flat. (3) The surface-emitting laser according to (1) or (2), wherein the second conductivity type semiconductor layer and the transparent electrode are in contact with each other in the central portion. (4) The surface-emitting laser according to (3), further comprising an insulating layer provided in the outer periphery between the second conductivity type semiconductor layer and the transparent electrode. (5) The surface-emitting laser according to any one of (1) to (4), wherein an electrode is disposed on the transparent electrode in the outer periphery, the electrode being in electrical contact with the transparent electrode. (6) A surface-emitting laser according to any one of (1) to (5), wherein in the peripheral portion, the surface of the second conductivity type semiconductor layer on the transparent electrode side includes a flat portion, and the thickness of the transparent electrode on the flat portion is greater than the thickness of the transparent electrode in the central portion. (7) 7. The surface-emitting laser according to claim 1, wherein the first conductive type semiconductor layer, the active layer, and the second conductive type semiconductor layer are nitride semiconductor layers, and the first reflector is a dielectric layer. (8) The surface-emitting laser according to any one of (1) to (7), wherein the absorption coefficient of the transparent electrode is greater than the absorption coefficient of the second conductivity type semiconductor layer. (9) An array light source comprising a plurality of surface-emitting lasers according to any one of (1) to (8). (10) A projection device comprising: a surface-emitting laser according to any one of (1) to (8); and an optical element onto which light emitted from the surface-emitting laser is incident, and which projects the light. (11) The display device according to (10), wherein the optical element includes a light guide plate that guides the light while reflecting it. (12) The light projecting device according to (10) or (11), further comprising a light receiving element that receives light incident from outside. [Explanation of symbols]

[0101] 10 Substrate 12, 14 electrodes 20 1st reflector 22, 42 Low refractive index layer 24, 44 High refractive index layer 30 resonator 31, 32, 32a Semiconductor layers 32b Contact layer 34 Active layer 36 Transparent electrode 38 Insulating layer 40 Second reflector 50 central part 52 Outer periphery 54, 56 Convex parts 58 Mesa 100. Surface-emitting laser 200 Array Light Source 210 Projection device 220 HMD 230 Biometric authentication device 240 Floodlight [Prior art documents] [Patent documents]

[0102] [Patent Document 1] Japanese Patent Publication No. 2022-23686

Claims

1. a first reflector, a first conductivity type semiconductor layer, an active layer, a second conductivity type semiconductor layer, a transparent electrode, and a second reflector, in that order; a surface of the second conductive type semiconductor layer on the transparent electrode side has a central portion protruding relative to an outer periphery thereof; the thickness of the transparent electrode at the central portion is smaller than the thickness of the transparent electrode at the peripheral portion; Surface-emitting laser.

2. 2. The surface-emitting laser according to claim 1, wherein the surface of the transparent electrode facing the second reflector has the central portion protruding relative to the outer periphery, or the outer periphery and the central portion are flat.

3. 3. The surface-emitting laser according to claim 1, wherein the second conductivity type semiconductor layer and the transparent electrode are in contact with each other at the central portion.

4. 4. The surface-emitting laser according to claim 3, further comprising an insulating layer provided in the outer periphery between the second conductivity type semiconductor layer and the transparent electrode.

5. 3. The surface-emitting laser according to claim 1, wherein an electrode is disposed on the transparent electrode in the outer periphery, the electrode being in electrical contact with the transparent electrode.

6. 3. The surface-emitting laser according to claim 1, wherein in the outer peripheral portion, a surface of the second conductivity type semiconductor layer facing the transparent electrode includes a flat portion, and a thickness of the transparent electrode on the flat portion is greater than a thickness of the transparent electrode in the central portion.

7. the first conductive type semiconductor layer, the active layer, and the second conductive type semiconductor layer are nitride semiconductor layers; 3. The surface-emitting laser according to claim 1, wherein the first reflector is a dielectric layer.

8. 3. The surface-emitting laser according to claim 1, wherein the absorption coefficient of the transparent electrode is greater than the absorption coefficient of the second conductivity type semiconductor layer.

9. An array light source comprising a plurality of surface-emitting lasers according to claim 1 or 2.

10. a surface-emitting laser according to claim 1 or 2; an optical element onto which light emitted from the surface-emitting laser is incident; Equipped with a light projecting device that projects the light;

11. The light projecting device according to claim 10 , wherein the optical element includes a light guide plate that guides the light while reflecting it.

12. The light projecting device according to claim 10 , further comprising a light receiving element that receives light incident from outside.

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