Surface emitting laser element

Abstract

The present invention is provided with: a translucent substrate; a first semiconductor layer formed on the substrate and having an air hole layer as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a current constriction layer formed on the second semiconductor layer, the current constriction layer having a contact opening of a circular shape or a rotationally symmetrical shape; a contact electrode formed by filling the contact opening of the current constriction layer; and a pad electrode formed on the contact electrode in which a thermal conductivity adjustment layer having a lower thermal conductivity than the effective thermal conductivity of the second semiconductor layer is embedded, the thermal conductivity adjustment layer having a thermal conductivity adjustment opening having a central axis coaxial with the contact opening, and the thermal conductivity adjustment opening having an opening diameter (W2) smaller than an opening diameter (W1) of the contact opening.

Description

Technical Field

[0001] The present invention relates to a surface-emitting laser element, and more particularly, to a surface-emitting laser element having a photonic crystal. Background Art

[0002] In recent years, development of photonic crystal surface-emitting lasers (PCSEL: Photonic-Crystal Surface-Emitting Laser) using photonic crystals (PC: Photonic Crystal) has been underway.

[0003] The resonant wavelength of a photonic crystal laser is determined by the lattice constant of the photonic crystal and the effective refractive index of the waveguide mode. It is known that during continuous wave (CW) oscillation of a photonic crystal laser, a temperature distribution is generated in the current injection region due to heat generation. This temperature distribution causes an in-plane distribution in the resonant wavelength, adversely affecting the laser characteristics.

[0004] Furthermore, in particular, in nitride (GaN)-based semiconductor photonic crystal lasers, the influence of this heat generation is significant due to the high driving voltage and resistance of the semiconductor material.

[0005] For example, Patent Document 1 discloses an invention in which the size of air holes in a photonic crystal is adjusted according to temperature distribution.

[0006] Furthermore, Patent Document 1 describes adjusting the size of air holes and the lattice constant of a photonic crystal according to temperature distribution.

[0007] Prior art literature

[0008] Patent Literature

[0009] [Patent Document 1] Japanese Patent Application No. 2017 / 038595

[0010] Non-patent literature

[0011] [Non-patent document 1] S. Katsuno, T. Inoue, M. Yoshida, M.D. Zoysa, K. Ishizaki, and S. Noda, “Self-consistent analysis of photonic-crystal surface-emitting lasers under continuous-wave operation,” Opt. Express Vol. 29, No. 16, 25118-25132 (2021).

[0012] [Non-Patent Document 2] Koizumi et al., “Continuous Operation of Blue Photonic Crystal Lasers,” 69th Spring Symposium of the Japanese Society of Applied Physics [25p-E303-13] Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, adjusting the size and lattice constant of a photonic crystal based on the temperature distribution requires extremely high precision control, down to nanometers. This extremely high precision adjustment is extremely difficult, as is verification during manufacturing. Furthermore, manufacturing reproducibility is difficult, and the manufacturing yield is low.

[0015] The present invention has been made with the above-mentioned points in mind, and its object is to provide a photonic crystal surface emitting laser that can simply flatten the temperature distribution of the photonic crystal during continuous wave (CW) driving, thereby improving luminous efficiency and excelling in oscillation stability.

[0016] Means for solving problems

[0017] According to one embodiment of the present invention, a surface-emitting laser element is provided, which comprises: a light-transmitting substrate; a first semiconductor layer formed on the substrate and having an air hole layer serving as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a current constriction layer formed on the second semiconductor layer and having a circular or rotationally symmetrical contact opening; a contact electrode formed by filling the contact opening of the current constriction layer; and a pad electrode having a thermal conductivity adjustment layer embedded therein and formed on the contact electrode, wherein the thermal conductivity of the thermal conductivity adjustment layer is smaller than the effective thermal conductivity of the second semiconductor layer, the thermal conductivity adjustment layer has a thermal conductivity adjustment opening whose central axis is coaxial with the contact opening, and the thermal conductivity adjustment opening has an opening diameter (W2) smaller than the opening diameter (W1) of the contact opening.

[0018] According to another embodiment of the present invention, there is provided a surface-emitting laser element having a photonic crystal, the surface-emitting laser element comprising: a light-transmitting substrate; a first semiconductor layer formed on the substrate and having an air hole layer serving as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a contact electrode partially formed on the second semiconductor layer and in ohmic contact with the second semiconductor layer; a thermal conductivity adjustment layer formed on the second semiconductor layer and having a thermal conductivity adjustment opening, the thermal conductivity adjustment opening extending to the upper portion of the peripheral portion of the contact electrode and formed in a manner partially covering the upper surface of the peripheral portion to expose the second semiconductor layer, the thermal conductivity adjustment layer being composed of a layer including at least one of an insulator and a semiconductor having a thermal conductivity less than the effective thermal conductivity of the second semiconductor layer; and a metal electrode formed to fill the thermal conductivity adjustment opening of the thermal conductivity adjustment layer and to cover at least the entire contact electrode when viewed from above.

[0019] According to another embodiment of the present invention, a surface-emitting laser element is provided, which has a photonic crystal, and the surface-emitting laser element has: a light-transmitting substrate; a first semiconductor layer, which is formed on the substrate and has an air hole layer serving as a photonic crystal layer; an active layer, which is formed on the first semiconductor layer; a second semiconductor layer, which is formed on the active layer; a current constriction layer, which is formed on the second semiconductor layer and has a contact opening; a contact electrode, which is formed by filling the contact opening of the current constriction layer; a metal electrode, which is formed on the contact electrode; a bonding metal, which is formed on the metal electrode; a heat dissipation substrate, which is bonded to the bonding metal via the bonding metal; and a thermal conductivity adjustment layer, which is arranged inside any one of the metal electrode, the bonding metal and the heat dissipation substrate, the thermal conductivity adjustment layer including at least one of an insulator and a semiconductor material having a thermal conductivity lower than that of at least any one of the bonding metal and the heat dissipation substrate, the thermal conductivity adjustment layer having a thermal conductivity adjustment opening, and the thermal conductivity adjustment opening has a size and configuration so as to be included in the contact opening when viewed from above. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A It is a cross-sectional view schematically showing an example of the structure of the PCSEL element according to the first embodiment of the present invention.

[0021] Figure 1B It is schematically represented Figure 1A A partially enlarged cross-sectional view of an air hole layer and air holes arranged in the air hole layer.

[0022] Figure 2AIt is a plan view schematically showing the upper surface of the PCSEL element (with the pad electrode removed).

[0023] Figure 2B It is a cross-sectional view schematically showing a cross section of the air hole layer taken along a plane parallel to the n-side guide layer.

[0024] Figure 2C It is a plan view schematically showing the bottom surface of the PCSEL element.

[0025] Figure 3 This is a diagram schematically showing an example of the arrangement of air holes in a plane parallel to the air hole layer.

[0026] Figure 4 This is a cross-sectional view showing a surface-emitting laser device composed of a PCSEL element mounted on a submount.

[0027] Figure 5 This figure shows the results of calculation using the finite element method of the temperature distribution of the air hole layer in the PCSEL element without a temperature adjustment layer.

[0028] Figure 6 It is a diagram showing the calculation results of the temperature distribution of the air hole layer of the PCSEL element (EMB1) according to the first embodiment.

[0029] Figure 7A It is a cross-sectional view schematically showing an example of the structure of the PCSEL element (EMB2) according to the second embodiment.

[0030] Figure 7B It is schematically represented Figure 7A A top view of the upper surface of the thermal conductivity adjustment layer of the PCSEL element is shown.

[0031] Figure 8 This is a diagram showing the calculation results of the temperature distribution of the air hole layer of the PCSEL element (EMB2).

[0032] Figure 9A It is a cross-sectional view schematically showing an example of the structure of a PCSEL element (EMB3) according to the third embodiment.

[0033] Figure 9B It is schematically represented Figure 9A A top view of the upper surface of the thermal conductivity adjustment layer of the PCSEL element is shown.

[0034] Figure 10 It is a cross-sectional view schematically showing an example of the structure of a PCSEL element (EMB4) according to the fourth embodiment.

[0035] Figure 11AIt is a cross-sectional view schematically showing an example of the structure of a PCSEL element (EMB5) according to the fifth embodiment.

[0036] Figure 11B It is a cross-sectional view schematically showing an example of the structure of a PCSEL element as a modified example of the fifth embodiment.

[0037] Figure 12 It is a cross-sectional view schematically showing an example of the structure of a PCSEL element (EMB6) according to the sixth embodiment.

[0038] Figure 13A It is a plan view schematically showing Modification 1 of the thermal conductivity adjusting layer.

[0039] Figure 13B It is a plan view schematically showing Modification 2 of the thermal conductivity adjusting layer.

[0040] Figure 13C It is a plan view schematically showing Modification 3 of the thermal conductivity adjusting layer.

[0041] Figure 13D It is a plan view schematically showing Modification 4 of the thermal conductivity adjusting layer.

[0042] Figure 14A It is a cross-sectional view schematically showing the structure of a PCSEL element according to the seventh embodiment.

[0043] Figure 14B It is a plan view schematically showing the upper surface of the PCSEL element.

[0044] Figure 15A This is a graph showing calculation results of the temperature distribution of the air hole layer of the PCSEL element according to the seventh embodiment.

[0045] Figure 15B This is a graph showing the calculation results of the temperature distribution of the air hole layer of a comparative example PCSEL element in which no thermal conductivity adjustment layer is provided.

[0046] Figure 16A It is a cross-sectional view schematically showing the structure of a PCSEL element according to the eighth embodiment.

[0047] Figure 16B It is a plan view schematically showing the upper surface of the PCSEL element.

[0048] Figure 17 Graphs comparing calculation results of temperature distributions of air hole layers in PCSEL elements according to the eighth embodiment and a comparative example.

[0049] Figure 18It is a cross-sectional view schematically showing the structure of a PCSEL element according to Modification 1 of the eighth embodiment.

[0050] Figure 19 1 is a cross-sectional view schematically showing the structure of a PCSEL element according to Modification Example 2.

[0051] Figure 20 1 is a cross-sectional view schematically showing the structure of a PCSEL element according to Modification Example 3.

[0052] Figure 21 It is a cross-sectional view schematically showing the structure of a PCSEL element according to Modification 4.

[0053] Figure 22 It is a cross-sectional view schematically showing the structure of a PCSEL element according to a ninth embodiment.

[0054] Figure 23A Graphs showing the comparison of calculation results of the temperature distribution of the air hole layer of the PCSEL element according to the ninth embodiment and the comparative example.

[0055] Figure 23B Graph showing the comparison of calculation results of the resonance center wavelengths of the PCSEL elements according to the ninth embodiment and the comparative example.

[0056] Figure 24 It is a cross-sectional view showing another example of the PCSEL element according to the ninth embodiment. DETAILED DESCRIPTION

[0057] Hereinafter, preferred embodiments of the present invention will be described, but they may be appropriately modified and combined. In the following description and drawings, substantially the same or equivalent parts are denoted by the same reference numerals for description.

[0058] [First embodiment]

[0059] 1. Structure of Photonic Crystal Surface-Emitting Laser

[0060] (a) Component structure

[0061] A photonic crystal surface emitting laser (hereinafter also referred to as a PCSEL) is an element that has a resonator layer parallel to the semiconductor light-emitting structure layers (n-side guide layer, light-emitting layer, p-side guide layer) that constitute the light-emitting element, and emits coherent light in a direction orthogonal to the resonator layer.

[0062] Specifically, in a photonic crystal surface emitting laser (PCSEL), light waves propagating in a plane parallel to the photonic crystal layer (air hole layer) are diffracted by the diffraction effect of the photonic crystal, forming a two-dimensional resonance mode. Furthermore, light waves are also diffracted in a direction perpendicular to this parallel plane. In other words, in a PCSEL, the light extraction direction is perpendicular to the resonance direction (in the plane parallel to the air hole layer).

[0063] Figure 1A 1 is a cross-sectional view of an example of the structure of a photonic crystal surface emitting laser element (hereinafter referred to as a PCSEL element) 10 according to the first embodiment of the present invention. Figure 1B It is schematically shown Figure 1A FIG. 1 is an enlarged cross-sectional view of an air hole layer 14P and a pair of air holes 14K arranged in the air hole layer 14P.

[0064] like Figure 1A As shown, the semiconductor structure layer 11 is formed on a light-transmitting substrate 12. The semiconductor structure layer 11 is composed of a hexagonal nitride semiconductor. In this embodiment, the semiconductor structure layer 11 is composed of, for example, a gallium nitride (GaN)-based semiconductor.

[0065] More specifically, a semiconductor structure layer 11 composed of multiple semiconductor layers is formed in sequence on the substrate 12, namely, an n-cladding layer (a first cladding layer of a first conductivity type) 13, an n-side guide layer (a first guide layer) 14 as a guide layer arranged on the n side, an active layer (ACT) 15, a p-side guide layer (a second guide layer) 16 as a guide layer arranged on the p side, an electron blocking layer (EBL: Electron Blocking Layer) 17, a p-cladding layer (a second cladding layer of a second conductivity type) 18, and a p-contact layer 19.

[0066] In addition, hereinafter, the semiconductor layers provided on the active layer 15 , that is, in the case of this embodiment, the p-side guide layer 16 , the electron blocking layer 17 , the p-cladding layer 18 and the p-contact layer 19 are collectively referred to as the second semiconductor layer (p semiconductor layer) 11A.

[0067] Furthermore, the description is given of a case where the first conductivity type is n-type and the second conductivity type, which is the opposite conductivity type of the first conductivity type, is p-type. However, the first conductivity type and the second conductivity type may be p-type and n-type, respectively.

[0068] Substrate 12 is a hexagonal GaN single crystal substrate having high transmittance for light emitted from active layer 15. More specifically, substrate 12 is a hexagonal GaN single crystal substrate whose principal surface (crystal growth surface) is the {0001} plane, i.e., the +c plane, where Ga atoms are arranged on the outermost surface.

[0069] The back surface opposite to the main surface (the light emitting surface having the light emitting region 20L) is a -c plane, which is a (000-1) plane with N atoms arranged on the outermost surface. The -c plane is resistant to oxidation and is therefore suitable as a light emitting surface.

[0070] The substrate 12 is not limited thereto, but is preferably a so-called positive substrate, or a substrate whose principal surface is offset by about 1° in the m-axis direction or the a-axis direction. For example, a substrate offset by about 1° in the m-axis direction can achieve mirror growth under a wide range of growth conditions.

[0071] The following describes the structure of each semiconductor layer, such as the composition and thickness, but these are merely examples and can be appropriately modified for application.

[0072] The n-cladding layer 13 is, for example, n-Al with an Al composition of 4%. 0.04 Ga 0.96 The N layer has a thickness of 2 μm. The composition ratio of aluminum (Al) is smaller than the composition ratio of the layer having a refractive index adjacent to the active layer 15 (ie, the n-side guide layer 14).

[0073] The n-side guide layer 14 is composed of a lower guide layer 14A, an air-hole layer 14P as a photonic crystal layer, and a buried layer 14B. Figure 1B As shown, the air hole layer 14P has a layer thickness (depth) d PC , the buried layer 14B has a thickness d EMB .

[0074] The lower guide layer 14A is made of n-GaN with a thickness of, for example, 300 nm. The air hole layer 14P is made of n-GaN with a thickness (or the depth of the air holes 14K) of, for example, 90 nm.

[0075] The buried layer 14B is composed of n-GaN, n-InGaN, undoped GaN, or undoped InGaN. Alternatively, it may be a stack of these semiconductor layers. The buried layer 14B has a thickness of, for example, 120 nm.

[0076] The active layer 15, serving as a light-emitting layer, is, for example, a multi-quantum well (MQW) layer having two quantum well layers. The barrier layer and quantum well layer of the MQW are GaN (3.0 nm thick) and InGaN (3.0 nm thick), respectively. The oscillation wavelength of the active layer 15 is, for example, 432 nm.

[0077] In addition, the active layer 15 is preferably disposed within 180 nm from the air hole layer 14P. In this case, a high resonance effect of the air hole layer 14P can be obtained.

[0078] The p-side guide layer 16 is composed of, for example, undoped GaN or undoped InGaN and has a thickness of 250 nm. The p-side guide layer 16 is undoped to account for light absorption by the dopant, but may be doped with magnesium (Mg) or the like to improve conductivity.

[0079] The electron blocking layer (EBL) 17 is a p-type Al doped with magnesium (Mg). 0.2 Ga 0.8 The N layer has a thickness of 15 nm, for example.

[0080] The p-cladding layer 18 is Mg-doped p-Al 0.06 Ga 0.94 The N layer has a thickness of 300 nm, for example. Preferably, the Al composition of the p-cladding layer 18 is selected so as to have a refractive index smaller than that of the p-side guide layer 16 .

[0081] The p-contact layer 19 is a Mg-doped p-GaN layer having a thickness of, for example, 25 nm. The carrier density of the p-contact layer 19 is set to a concentration that enables ohmic contact with the p-electrode 23 provided on its surface. Instead of p-type GaN, p-type InGaN can be used. Alternatively, a layer composed of a stack of GaN and InGaN layers can be used.

[0082] It should be noted that, in this specification, "n-side" and "p-side" do not necessarily mean n-type or p-type. For example, an n-side guide layer refers to a guide layer disposed on the n-side relative to the active layer, and may also be an undoped layer (or i-layer).

[0083] Furthermore, the n-cladding layer 13 may be composed of multiple layers instead of a single layer. In this case, not all layers need to be n-layers (n-doped layers) but may include undoped layers (i-layers). The same applies to the guide layer 16 and the p-cladding layer 18.

[0084] In addition, it is not necessary to provide all of the above-mentioned semiconductor layers, and a structure having a first semiconductor layer of the first conductivity type including an air hole layer, a second semiconductor layer of the second conductivity type, and an active layer (light-emitting layer) sandwiched between these layers is sufficient.

[0085] The side and top surfaces of the semiconductor structure layer 11 are covered with an insulating film 21 made of SiO2 or the like. Furthermore, an opening OP (also referred to as a "contact opening") having a diameter W1 is provided in the insulating film 21, exposing the top surface of the semiconductor structure layer 11 (i.e., the top surface of the p-contact layer 19). More specifically, a circular (cylindrical) opening OP is provided, having a central axis CZ and extending through the insulating film 21. Furthermore, the insulating film 21 functions as a current constriction layer.

[0086] The insulating film 21 also serves as a protective film, protecting the aluminum (Al) crystal layer that makes up the PCSEL element 10 from corrosive gases and other factors. Furthermore, it prevents short circuits caused by deposits or solder runoff during mounting, contributing to improved reliability and yield. The material of the insulating film 21 is not limited to SiO2; other materials can include ZrO2, HfO2, TiO2, Al2O3, SiNx, and Si.

[0087] A p-electrode 23 (also referred to as “contact electrode”) is provided on the p-contact layer 19 exposed from the contact opening OP and is in ohmic contact with the p-contact layer 19 .

[0088] More specifically, the p-electrode 23 is formed to fill the circular opening OP serving as the current injection region 23R. That is, the p-electrode 23 has a circular shape with a central axis CZ passing through the center of the p-electrode 23 and perpendicular to the air hole layer 14P (z direction) in a plan view.

[0089] The p-electrode 23 is filled so that its upper surface is flat and parallel to the air hole layer 14P. Figure 1A As shown, it is preferably formed so as to fill the opening OP and extend over the insulating film 21, with a flat upper surface. This allows for more accurate formation of a flat light-reflecting layer 24, enabling the reflected diffracted light Lr to be emitted as light substantially parallel to the direct diffracted light Lr. Alternatively, the upper surface of the p-electrode 23 may be formed flush with the upper surface of the insulating layer 21. In other words, simply by filling the opening OP with the p-electrode 23, the upper surface of the p-electrode 23 and the upper surface of the insulating layer 21 are flush.

[0090] The p-electrode 23 is preferably formed of a light-transmitting conductor, such as indium tin oxide (ITO), and has a layer thickness of 135 nm.

[0091] Furthermore, the p-electrode 23 is not limited to ITO, and may be made of a light-transmitting conductor such as zinc tin oxide (ZTO), GZO (ZnO:Ga), or AZO (ZnO:Al).

[0092] The diameter W1 of the formation region of the p-electrode 23 (ie, the current injection region 23R) is 300 μm. The thickness of the p-electrode 23 can be appropriately selected within the range of 20 nm to 300 nm. In the embodiment, the thickness is 135 nm.

[0093] A silver alloy (Ag alloy) layer is provided on the p-electrode 23 as a light reflecting layer 24. The light reflecting layer 24 is provided to cover at least the entire opening OP in a plan view. The light reflecting layer 24 has a flat surface parallel to the air hole layer 14P.

[0094] The light reflecting layer 24 is made of a silver alloy (Ag alloy) and has a thickness of, for example, 150 nm. In addition to the Ag alloy, the light reflecting layer 24 may also be made of Al, an Al alloy, a dielectric DBR (Distributed Bragg Reflector), or the like.

[0095] A thermal conductivity adjustment layer 31 is formed on the light reflecting layer 24. The thermal conductivity adjustment layer 31 includes a layer made of at least one material having a thermal conductivity lower than the effective thermal conductivity of at least the semiconductor layer provided on the active layer 15, that is, the semiconductor layer between the active layer 15 and the p-electrode 23 (that is, the second semiconductor layer 11A).

[0096] When the second semiconductor layer 11A is composed of a gallium nitride (GaN)-based semiconductor, the thermal conductivity adjustment layer 31 is preferably formed of a material having a lower thermal conductivity than GaN. In this embodiment, the thermal conductivity adjustment layer 31 is formed of a material having a lower thermal conductivity than GaN.

[0097] For example, the thermal conductivity adjustment layer 31 can be made of oxides such as SiO2, Al2O3, Ta2O5, ZrO2, and HfO2, nitrides such as SiNx, oxynitrides such as SiON and AlON, conductive oxide films such as ITO, AZO, and GZO, or metals such as Ti, V, and Pt.

[0098] The pad electrode 32 covering the entire thermal conductivity adjustment layer 31 and embedding the thermal conductivity adjustment layer 31 is provided on the light reflection layer 24. As described above, the thermal conductivity adjustment layer 31 and the light reflection layer 24 are provided in contact with each other.

[0099] The pad electrode 32 is composed of, for example, a Ni / Pd / Au layer formed by sequentially depositing nickel (layer thickness: 10 nm), palladium (layer thickness: 200 nm), and gold (layer thickness: 800 nm).

[0100] In addition, the pad electrode 32 can also use Ni / Au, platinum / gold (Pt / Au), Pt / Pd / Au, titanium / gold (Ti / Au), Ti / Pt / Au, tungsten / palladium / gold (W / Pd / Au), W / Au, W / Pt / Au, etc.

[0101] A circular opening ( Figure 2C , the n-electrode 25 (cathode) of the light emitting region 20L. In addition, an anti-reflection (AR) coating 27 is formed in the region inside the n-electrode 25.

[0102] The n electrode 25 is composed of Ti / Pt / Au and is in ohmic contact with the substrate 12. In addition to Ti / Pu / Au, the electrode materials can also be selected from Ti / Al, Ti / Rh, Ti / Al / Pt / Au, Ti / Au, vanadium / aluminum (V / Al), V / Rh, V / Al / Pt / Au, V / Pt / Au, etc.

[0103] The emitted light from the active layer 15 is diffracted by the air hole layer (PC layer) 14P. The light diffracted by the air hole layer 14P and directly emitted from the air hole layer 14P (direct diffracted light Ld: the first diffracted light) and the light diffracted by the air hole layer 14P and reflected by the light reflection layer 24 (reflected diffracted light Lr: the second diffracted light) are emitted from the light emission region 20L ( Figure 2C [[ID=|5]]) of the back surface (emission surface) 12R of the substrate 12 to the outside.

[0104] Figure 2A is a top view schematically showing the upper surface of the PCSEL element 10. In addition, for the clarity of the figure and ease of understanding, the upper surface in a state where the pad electrode 32 is removed is schematically shown.

[0105] In addition, Figure 2B is a cross-sectional view schematically showing a cross-section in a plane parallel to the n-side guiding layer 14 of the air hole layer 14P, Figure 2C is a top view schematically showing the lower surface of the PCSEL element 10.

[0106] As Figure 2A shown, the thermal conductivity adjustment layer 31 has an annular plate shape centered on the central axis of the p electrode 23, that is, the central axis CZ of the current injection region 23R (coaxial). More specifically, the thermal conductivity adjustment layer 31 has a circular opening 31W (also referred to as "thermal conductivity adjustment opening") in a top view. The opening diameter (diameter) W2 of the opening 31W is smaller than the diameter W1 of the p electrode 23 (current injection region 23R) (W2 < W1). That is, the thermal conductivity adjustment opening 31W has a similar shape with a smaller diameter than the contact opening OP. In terms of being able to two-dimensionally and uniformly adjust the heat generation distribution, the thermal conductivity adjustment opening 31W is preferably set to a similar shape to the contact opening OP. In addition, the thermal conductivity adjustment layer 31 has an outer diameter W5.

[0107] As Figure 2BAs shown, in the air hole layer 14P, air holes 14K are periodically arranged within an air hole forming region 14R, which has a circular cross-section, for example. When viewed in a direction perpendicular to the air hole layer 14P (z direction) (in a top view), the diameter W3 of the air hole forming region 14R is greater than or equal to the diameter W1 of the current injection region 23R (W1 ≤ W3). The shape of the air hole forming region 14R is not limited to a circular shape. It can be any shape as long as it is large enough to encompass at least the current injection region 23R when viewed in a top view.

[0108] like Figure 2C As shown, the n-electrode 25 (cathode) is formed to have a circular opening outside the air hole forming region 14R so that the n-electrode 25 does not overlap the air hole forming region 14R when viewed from a direction perpendicular to the air hole layer 14P.

[0109] The opening of the n-electrode 25 has a diameter W4 , and the diameter W4 of the opening is larger than the diameter W1 of the current injection region 23R ( W1 < W4 ).

[0110] Furthermore, a pad 25C to which a power supply cable is connected is provided on the n-electrode 25 .

[0111] (b) Photonic crystal layer (air hole layer)

[0112] like Figure 1A and Figure 1B As shown, the air hole layer 14P includes regularly arranged air holes that allow light emitted from the active layer 15 to resonate in a horizontal plane.

[0113] Figure 3 This diagram schematically illustrates an example of the arrangement of air holes in a plane parallel to the air hole layer 14P. Specifically, it is a top view of an air hole pair 14K (sometimes simply referred to as air hole 14K) consisting of a main air hole 14K1 and a secondary air hole 14K2 arranged in a square lattice within the plane of the air hole layer 14P.

[0114] That is, the air hole layer 14P has a double lattice structure. In order to clarify the drawings, the main air holes 14K1 and the auxiliary air holes 14K2 (air holes 14K) are shown with hatching.

[0115] More specifically, the centers of gravity CD1 of the main air holes 14K1 are arranged in two orthogonal directions (x and y) at a period (lattice constant) of PK on a square lattice. Similarly, the centers of gravity CD2 of the auxiliary air holes 14K2 are arranged in two orthogonal directions at a period of PK on a square lattice. Furthermore, the period PK of the air holes 14K can be adjusted according to the desired oscillation wavelength.

[0116] The main air holes 14K1 have a long hexagonal shape surrounded by m-planes, which are {10-10} planes, in a plan view (ie, when the air hole layer 14P is viewed from a vertical direction). The auxiliary air holes 14K2 also have a shape surrounded by m-planes.

[0117] The x and y directions are directions tilted 45° relative to the major axis (<11-20> direction) and minor axis (<1-100> direction) of the main air hole 14K1, respectively.

[0118] Furthermore, the center of gravity CD2 of the auxiliary air hole 14K2 is spaced apart from the center of gravity CD1 of the main air hole 14K1 by Δx in the x-direction and by Δy in the y-direction. Here, Δx = Δy = 0.46PK. That is, the center of gravity CD2 of the auxiliary air hole 14K2 is spaced apart from the center of gravity CD1 of the main air hole 14K1 in the <1-100> direction.

[0119] Here, the distance Δx between the centers of gravity in the x direction and the distance Δy between the centers of gravity in the y direction can be appropriately adjusted according to laser characteristics such as the current value required by the device to which the laser element is applied and the slope efficiency of the laser emission intensity.

[0120] It should be noted that, here, the case where the air hole layer 14P has a double lattice structure is described as an example, but the invention is not limited thereto and the air hole layer 14P may also have a single lattice structure or a polylattice structure.

[0121] 2. Manufacturing method of PCSEL element

[0122] Next, manufacturing steps S1 to S9 of the method for manufacturing the PCSEL element 10 will be described in order.

[0123] (S1) Crystal Growth

[0124] Using a MOVPE (Metalorganic Vapor Phase Epitaxy) device, an n-Al layer as the n-cladding layer 13 was grown on the +c-plane GaN substrate 12 with a thickness of 2 μm. 0.04 Ga 0.96 Next, an n-GaN layer with a thickness of 500 nm is grown on the n-cladding layer 13 .

[0125] (S2) Forming a hole

[0126] A SiNx film of approximately 100 nm is formed on the grown n-GaN layer using plasma CVD. Next, a resist for electron beam lithography (EB) is applied to the SiNx film by spin coating and placed in an electron beam lithography (EB) apparatus to form a two-dimensional periodic pattern corresponding to the aforementioned two-dimensional photonic crystal structure.

[0127] After developing the patterned resist, the SiNx layer is selectively dry-etched using an ICP-RIE (Inductively Coupled Plasma Reactive Ion Etching) device, thereby forming openings arranged in a square lattice pattern that penetrate the SiNx film.

[0128] The resist was then removed, and the n-GaN layer was dry-etched using an ICP-RIE apparatus with Cl₂, BCl₃, and Ar gases, using SiNx as a hard mask. This formed holes arranged in a square lattice pattern in the n-GaN layer. The etching depth was approximately 190 nm. The SiNx hard mask was then removed using buffered hydrofluoric acid (BHF).

[0129] (S3) Re-crystallization

[0130] The substrate with the photonic crystal formed was placed back into the MOVPE apparatus, where embedded growth was performed with residual holes to form air holes 14K. Specifically, undoped GaN was grown to a thickness of 70 nm, and undoped InGaN was grown to a thickness of 50 nm to form buried layer 14B. Thus, n-side guide layer 14 including air hole layer 14P was formed.

[0131] It should be noted that, due to embedded growth, the main air holes 14K1 and the secondary air holes 14K2 in the air hole layer 14P have a hexagonal shape surrounded by m-planes, which are {10-10} planes, when viewed from above. Furthermore, the main air holes 14K1 in the air hole layer 14P have a depth of 90 nm, and the secondary air holes 14K2 have a depth of 70 nm.

[0132] Next, an active layer 15 (MQW layer) consisting of two pairs of InGaN / GaN quantum wells is grown on buried layer 14B (i.e., on n-side guide layer 14). Subsequently, undoped InGaN with a thickness of 70 nm and undoped GaN with a thickness of 180 nm are grown on active layer 15 to form p-side guide layer 16.

[0133] Next, an electron blocking layer 17 composed of p-AlGaN is grown to a thickness of 15 nm, and a p-cladding layer 18 composed of a p-AlGaN layer is grown to a thickness of 300 nm on the electron blocking layer 17. Subsequently, a p-contact layer 19 composed of a p-GaN / p-InGaN layer is grown to a thickness of 25 nm.

[0134] (S4) Formation of electrodes and light reflecting layer

[0135] First, using a dry etching apparatus, separation grooves for separating the individual PCSEL elements 10 are formed on the grown wafer. The separation grooves are formed to a depth that reaches the inside of the substrate 12.

[0136] Next, a 100 nm thick SiO2 film was deposited on the wafer by sputtering. After deposition, the SiO2 film was removed using BHF by photolithography and patterned. This resulted in the formation of an insulating film 21 having an opening OP with a diameter of 300 μm corresponding to the current injection region 23R.

[0137] Next, an ITO film (thickness: 135 nm) is formed to form the p-electrode 23 filling the opening OP. The p-electrode 23 is formed to fill the opening OP and cover the insulating film 21 .

[0138] Thereafter, a Ag alloy film was formed to a thickness of 150 nm on the p-electrode 23 to form the light reflecting layer 24 .

[0139] (S5) Formation of Thermal Conductivity Adjusting Layer

[0140] Next, a ring-shaped thermal conductivity adjustment layer 31 made of SiO2 film and having a circular opening 31W was formed on the light reflection layer 24. The thermal conductivity adjustment layer 31 had a thickness of 25 nm and an opening diameter W2 of 160 nm.

[0141] (S6) Formation of pad electrodes

[0142] On the thermal conductivity adjustment layer 31 , Ni / Pd / Au films were sequentially formed with thicknesses of 10 nm / 200 nm / 800 nm to form a pad electrode 32 that buried the thermal conductivity adjustment layer 31 .

[0143] (S7) Formation of back electrode

[0144] Next, the back surface of the substrate 12 was polished and then mirror-finished by chemical mechanical polishing (CMP) to obtain a wafer with a thickness of 170 nm. Next, Ti / Pt / Au films (layer thickness: 50 nm / 50 nm / 500 nm) were deposited on the polished surface to form the n-electrode 25 (cathode electrode).

[0145] Furthermore, a non-reflective coating 27 serving as an anti-reflection layer is formed on the back surface of the substrate in the opening region of the n-electrode 25 (ie, the light emitting region 20L) by forming SiNx / SiO2 (layer thickness: 32nm / 53nm).

[0146] (S9) Single Chip

[0147] Finally, the wafer is diced using a laser scribing device or a diamond scribing device, and then cleaved using a cleaving device to separate the wafer into individual pieces, thereby obtaining PCSEL elements 10 .

[0148] 3. Installation of PCSEL components

[0149] Figure 4 1 is a cross-sectional view showing a surface emitting laser device 50 composed of the PCSEL element 10 mounted on a submount 50M. In addition, a cross section including the central axis CZ of the p-electrode 23 (current injection region 23R) is shown.

[0150] In the surface emitting laser device 50 , the PCSEL element 10 is mounted on a submount 50M by solder bonding. The submount 50M includes a base 51 , an anode wiring 53 and a cathode wiring 54 provided on the base 51 .

[0151] Specifically, in PCSEL element 10, pad electrode 32 is bonded and electrically connected to anode wiring 53 by junction-down bonding (epitaxial-down bonding). In addition, n-electrode 25 (pad 25C) of PCSEL element 10 and cathode wiring 54 are connected using bonding wire BW, which is a gold wire.

[0152] In the embodiment, a submount 50M is used whose base material 51 is diamond. Suitable materials for the base material of the submount 50M include, in addition to diamond, aluminum nitride (AlN), silicon carbide (SiC), graphite, copper tungsten (CuW), Cu, and Ag diamond, which have high thermal conductivity.

[0153] Furthermore, a heat sink is mounted on the back surface of the submount 50M on which the PCSEL element 10 is mounted.

[0154] Light from the PCSEL element 10 is emitted from the back surface side of the substrate 12 (in the figure, emitted light LE).

[0155] 4. PCSEL component characteristic evaluation

[0156] (a) Temperature distribution of the air pore layer

[0157] First, the influence of the temperature distribution of the air hole layer is investigated. Figure 5 The graph shows the calculation results of the temperature distribution of the air hole layer using the finite element method. More specifically, the graph shows the temperature distribution of the air hole layer in a PCSEL element without the thermal conductivity adjustment layer 31 as a comparative example (CMP).

[0158] The PCSEL element of the comparative example (CMP) differs from the PCSEL element 10 of the first embodiment in that the thermal conductivity adjustment layer 31 is not provided, but the other structures are the same. Figure 5 FIG. 4 shows the temperature distribution of the air hole layer in a surface emitting laser device in which the PCSEL element of the comparative example is mounted.

[0159] Figure 5The calculation results are shown when a power of 24 W is injected. The dotted line in the figure indicates the current injection region (W1 = 300 μm). In the comparative example without the thermal conductivity adjustment layer 31, the temperature distribution is convex upward with the center of the current injection region as the peak.

[0160] The peak temperature at the center is 68.2° C., and at the periphery of the current injection region is 51.2° C. Since the refractive index varies according to the temperature distribution, the resonance wavelength also varies according to the shape of the temperature distribution.

[0161] According to the inventors' research, even with a temperature distribution similar to that of the comparative example, CW oscillation is possible (see Non-Patent Document 2). However, the region (resonator length) in which coherent resonance is possible is narrowed, resulting in reduced laser efficiency. This reduction in efficiency is due to in-plane light leakage caused by an increase in the area not contributing to oscillation and a reduction in the resonator length.

[0162] When applying 24 W of power, the effective oscillation region (i.e., the resonator length for coherent operation) is approximately 195 μm, relative to the current injection region of 300 μm. Converting this resonator length (region) to a temperature difference indicates a temperature difference of approximately 4°C for coherent oscillation.

[0163] (b) Temperature distribution of the air hole layer in the first embodiment

[0164] The calculation results of the temperature distribution of the air hole layer 14P of the PCSEL element 10 (EMB1) of the first embodiment are shown in FIG. Figure 6 In addition, similarly to the case of the comparative example, a surface emitting laser device 50 ( Figure 4 ) is the temperature distribution of the air hole layer 14P of the PCSEL element 10. The calculation result when the power of 24W is applied is the same in this respect.

[0165] As described above, in the PCSEL element 10 (EMB1), the thermal conductivity adjustment layer 31 has the opening 31W whose opening diameter W2 is smaller than the diameter W1 of the current injection region 23R.

[0166] like Figure 6 As shown, the temperature distribution of the air hole layer 14P of the PCSEL element 10 (EMB1) is flatter than that of the comparative example. Specifically, based on a 4°C temperature difference, which allows for coherent oscillation, the diameter of the effective oscillation region is 256 μm relative to the current injection region of 300 μm. This indicates that the effective oscillation region has increased in diameter by 31% and in area by 72% compared to the comparative example.

[0167] This effect is achieved when the opening diameter W2 of the opening 31W in the thermal conductivity adjustment layer 31 is smaller than the diameter W1 of the current injection region 23R (W2 < W1). This is because, when the p-semiconductor side is junction-down with the heat sink to improve heat dissipation, the distance between the active layer and the heat sink is very short, and most of the heat is dissipated toward the heat sink.

[0168] Therefore, the luminous efficiency during continuous wave (CW) driving is improved. In addition, a surface emitting laser having excellent oscillation stability, such as single-mode stability, can be provided.

[0169] [Second embodiment]

[0170] Figure 7A : is a cross-sectional view schematically showing an example of the structure of the PCSEL element 60 (EMB2) of the second embodiment. In addition, a cross section including the central axis CZ of the p-electrode 23 (current injection region 23R) is shown. Figure 7B 1 is a plan view schematically showing the upper surface of the PCSEL element 60. In addition, the upper surface is schematically shown in a state where the pad electrode 32 is removed.

[0171] (a) Component structure

[0172] The PCSEL element 60 (EMB2) is different from the PCSEL element 10 of the first embodiment in that it includes a thermal conductivity adjustment layer 33 having a double-layer structure, but the other structures are the same.

[0173] In more detail, Figure 7B As shown, the thermal conductivity adjustment layer 33 has a two-layer structure including a first low thermal conductivity layer 33A and a second low thermal conductivity layer 33B. The first low thermal conductivity layer 33A has a circular opening 33W1 in an annular shape with an opening diameter W2, and the second low thermal conductivity layer 33B has a circular opening 33W2 in an annular shape with an opening diameter W2B (>W2).

[0174] That is, the two-layered thermal conductivity adjustment layer 33 has an opening 33W1 with an opening diameter W2, and the diameter W1 of the current injection region 23R (p-electrode 23) and the opening diameters W2 and W2B of the first and second low thermal conductivity layers 33A and 33B satisfy W2<W2B<W1.

[0175] The first and second low thermal conductive layers 33A and 33B overlap with each other with their central axes being coaxial. The central axes of the first and second low thermal conductive layers 33A and 33B are coaxial with the central axis CZ of the p-electrode 23 (current injection region 23R).

[0176] The first low thermal conductive layer 33A and the second low thermal conductive layer 33B are formed of SiO 2 films. For example, the first low thermal conductive layer 33A has a thickness of 20 nm, and the second low thermal conductive layer 33B has a thickness of 100 nm.

[0177] (b) Temperature distribution of the air pore layer

[0178] Figure 8 Calculation results of the temperature distribution of the air hole layer 14P of the PCSEL element 60 (EMB2) are shown. In addition, similarly to the case of the PCSEL element 10 (EMB1) of the first embodiment, a surface emitting laser device in which the PCSEL element 60 is mounted on the submount 50M is shown (see Figure 4 ) The temperature distribution of the air hole layer 14P in FIG. Calculation results when a power of 24 W is applied are also the same in this respect.

[0179] Note that the calculation was performed under the assumption that W2 = 160 μm, W2B = 260 μm, and W1 = 300 μm.

[0180] like Figure 8 As shown, it can be seen that the temperature distribution is flatter than that of PCSEL element 10 (EMB1). Specifically, when the temperature difference that allows coherent oscillation is 4°C, the diameter of the effective oscillation region is 290 μm relative to the current injection region of 300 μm.

[0181] That is, it can be seen that the diameter of the effective oscillation region is increased by 49% and the area is increased by 121% compared to the comparative example (CMP) in which the diameter of the effective oscillation region is 195 μm.

[0182] Therefore, compared with the comparative example (CMP) and the PCSEL element 10 (EMB1) of the first embodiment, the luminous efficiency during continuous (CW) driving is significantly improved, and a surface emitting laser having excellent oscillation stability such as single mode stability can be provided.

[0183] In addition, the thermal conductivity adjusting layer 33 has been described as having a two-layer structure. However, the thermal conductivity adjusting layer 33 may also be formed as a stepped thermal conductivity adjusting layer having an outer peripheral portion (corresponding to the second low thermal conductivity layer 33B) and an annular inner peripheral portion having a thickness smaller than that of the outer peripheral portion.

[0184] [Third embodiment]

[0185] Figure 9A This is a cross-sectional view schematically showing an example of the structure of the PCSEL element 70 (EMB3) according to the third embodiment. Figure 1A and Figure 7A The same figure is shown. Figure 9B1 is a plan view schematically showing the upper surface of the PCSEL element 70. In addition, the upper surface is schematically shown in a state where the pad electrode 32 is removed.

[0186] The PCSEL element 70 of this embodiment differs from the PCSEL element 10 of the first embodiment in that the thermal conductivity adjustment layer 35 has an inclined annular inner peripheral portion 35T whose thickness decreases in a tapered manner toward the center of the thermal conductivity adjustment opening 35W. The remaining structure is the same as that of the PCSEL element 10 of the first embodiment.

[0187] More specifically, the thermal conductivity adjustment layer 33 has an annular shape and includes a circular opening 35W with an opening diameter W2. Furthermore, the annular inner peripheral portion 35T has an outer diameter W2T. Furthermore, the diameter W1 of the current injection region 23R and the thermal conductivity adjustment opening 35W of the thermal conductivity adjustment layer 33 satisfy the relationship W2 < W1.

[0188] The outer diameter W2T of the inner peripheral portion 35T preferably satisfies W2T<W1, but is not limited thereto. That is, as long as the layer thickness decreases toward the center within the diameter W1 of the current injection region 23R, W2T≥W1 may also be satisfied.

[0189] [Fourth embodiment]

[0190] Figure 10 It is a cross-sectional view schematically showing an example of the structure of a PCSEL element 80 (EMB4) according to the fourth embodiment.

[0191] In the PCSEL element 10 of the first embodiment, the thermal conductivity adjustment layer 31 is provided on the light reflecting layer 24 . However, in the PCSEL element 80 of this embodiment, the thermal conductivity adjustment layer 31 is entirely embedded in the pad electrode 32 and formed separately from the p-electrode.

[0192] That is, the thermal conductivity adjustment layer 31 may be formed separately from the p-electrode 23 (contact electrode). The heat uniformity effect can be adjusted by selecting the separation distance.

[0193] [Fifth embodiment]

[0194] Figure 11A It is a cross-sectional view schematically showing an example of the structure of a PCSEL element 90 (EMB5) according to the fifth embodiment. Figure 11B 1 is a cross-sectional view schematically showing an example of the structure of a PCSEL element 95 as a modified example of the fifth embodiment.

[0195] In the PCSEL element 90 of the present embodiment, the thermal conductivity adjustment layer 31 is in contact with the light reflecting layer 24 and is arranged below the light reflecting layer 24. In more detail, the thermal conductivity adjustment layer 31 has an opening portion of the thermal conductivity adjustment layer 31 on the central axis CZ and is arranged on the p-electrode 23. The opening portion is filled with the translucent conductor 91, and the upper surfaces of the thermal conductivity adjustment layer 31 and the translucent conductor 91 become flat surfaces. At this time, the upper surfaces of the thermal conductivity adjustment layer 31 and the translucent conductor 91 are preferably the same continuously flat surface. The light reflecting layer 24 is provided on the thermal conductivity adjustment layer 31 and the translucent conductor 91, and a pad electrode 32 is formed on the upper surface of the light reflecting layer 24. At this time, it is preferred to use a material with a small refractive index difference between the translucent conductor 91 and the thermal conductivity adjustment layer 31. For example, ITO can be used for the translucent conductor 91, and SiN can be used for the thermal conductivity adjustment layer 31. In addition, as Figure 11B As shown, the opening can also be filled with the light-reflecting layer 24. In this case, the upper surface of the light-reflecting layer 24 becomes a flat surface. Specifically, a structure can be adopted in which the light-transmitting conductor 91 is not formed in the opening. Instead, the light-reflecting layer 24 is formed on the upper surface of the opening and the thermal conductivity adjusting layer 31 in place of the light-transmitting conductor 91, and the upper surface of the light-reflecting layer 24 is flat.

[0196] In the PCSEL element 90 , since the thermal conductivity adjustment layer 31 is provided in contact with the p-electrode 23 (contact electrode), a higher heat distribution effect can be obtained.

[0197] [Sixth embodiment]

[0198] Figure 12 It is a cross-sectional view schematically showing an example of the structure of the PCSEL element 100 (EMB6) according to the sixth embodiment.

[0199] In the PCSEL element 100 of this embodiment, the thermal conductivity adjustment layer 31 is composed of a layer formed with a dot pattern 31D. The dot pattern 31D is formed from the same material as the thermal conductivity adjustment layer 31, for example, a layer of SiO2 formed into dots. The dot pattern 31D can be either a periodic or aperiodic pattern, but preferably has a shape in which the spacing between dots decreases as the distance from the central axis CZ increases. This structure, in which the spacing between dots decreases as the distance from the central axis CZ increases, achieves a higher heat distribution effect.

[0200] [Change example]

[0201] Figure 13A This is a plan view schematically showing Modification 1 of the thermal conductivity adjusting layer of the first to fifth embodiments. The thermal conductivity adjusting layer 37 of Modification 1 has polygonal openings 37W (thermal conductivity adjusting openings).

[0202] In Modification 1, the aperture diameter of the opening 37W is defined as the diameter (or major axis) of a circle (including an ellipse) that circumscribes the opening 37W, and has an aperture diameter W2. The aperture diameter W2 of the current injection region 23R (p electrode 23) and the diameter W1 (i.e., the aperture diameter of the contact opening) satisfy W2 < W1. Additionally, the opening 37W preferably has a regular polygon shape.

[0203] Figure 13B FIG. is a top view schematically showing Modification 2 of the thermal conductivity adjustment layer of the above-described embodiment. The thermal conductivity adjustment layer 37 of Modification 2 has an opening 37W in the shape of a gear.

[0204] In Modification 2, the aperture diameter of the opening 37W is defined as the diameter of a circle that circumscribes the opening 37W, and has an aperture diameter W2. The aperture diameter W2 of the current injection region 23R and the diameter W1 satisfy W2 < W1.

[0205] Figure 13C FIG. is a top view schematically showing Modification 3 of the thermal conductivity adjustment layer of the above-described embodiment. The thermal conductivity adjustment layer 37 of Modification 2 has a double-ring shape. More specifically, the thermal conductivity adjustment layer 37 has a first thermal conductivity adjustment layer 37M and a ring-shaped second thermal conductivity adjustment layer 37S provided inside the first thermal conductivity adjustment layer 37M.

[0206] In Modification 3, the first thermal conductivity adjustment layer 37M has a circular opening 37W, and the opening 37W has an aperture diameter W2. The aperture diameter W2 of the current injection region 23R and the diameter W1 satisfy W2 < W1.

[0207] Figure 13D FIG. is a top view schematically showing Modification 4 of the thermal conductivity adjustment layer of the above-described embodiment. In Modification 4, the thermal conductivity adjustment layer 37 has a rectangular outer shape, which is different from the thermal conductivity adjustment layer of the above-described embodiment, but other structures are the same as those of the thermal conductivity adjustment layer of the above-described embodiment.

[0208] In Modification 4, the thermal conductivity adjustment layer 37 has a circular opening 37W, and the opening 37W has an aperture diameter W2. The aperture diameter W2 of the current injection region 23R and the diameter W1 satisfy W2 < W1.

[0209] As described above, the embodiments of the present invention have been described in detail. In addition, in the above-described embodiments, it is preferable that the shapes of the contact opening and the thermal conductivity adjustment opening are circular, but it is not limited thereto. It may have an elliptical, polygonal, gear-shaped, etc., but a shape that is rotationally symmetric about the central axis is preferred. In these cases, the aperture diameter is defined by the diameter (or major axis) of a circle (including an ellipse) that circumscribes the shape of the opening.

[0210] Additionally, it is preferable that the thermal conductivity adjustment opening has a shape similar to that of the contact opening.

[0211] As described above, the present invention can provide a photonic crystal surface emitting laser that can easily flatten the temperature distribution of a photonic crystal during continuous wave (CW) driving, improves luminous efficiency, and exhibits excellent oscillation stability.

[0212] [Seventh embodiment]

[0213] (1) Component structure

[0214] Figure 14A : is a cross-sectional view schematically showing the structure of the PCSEL element 210 of the seventh embodiment. In addition, a cross section including the central axis CZ of the p-electrode 213 is shown. Figure 14B 2 is a plan view schematically showing the upper surface of the PCSEL element 210. The upper surface is schematically shown with the pad electrode 215 and the light reflecting layer 214 removed.

[0215] Furthermore, although the case where the air hole layer 14P has a single-crystalline structure is described, it may also have a polycrystalline structure.

[0216] In the PCSEL element 210 according to this embodiment, a light-transmitting p-electrode 213 (p-contact electrode) is formed in ohmic contact with the p-contact layer 19. That is, the region where the p-electrode 213 contacts the p-contact layer 19 is a contact region, ie, a current injection region 213R.

[0217] The p-electrode 213 has a thin cylindrical shape (central axis CZ), and the thermal conductivity adjustment layer 211 extends to the outer periphery of the p-electrode 213 and is formed so as to partially cover the upper surface of the outer periphery.

[0218] More specifically, the p-electrode 213 is formed of translucent indium tin oxide (ITO). The p-electrode 213 is preferably a translucent conductor. In this case, the p-electrode 213 is not limited to ITO; translucent conductors such as zinc tin oxide (ZTO), GZO (ZnO:Ga), and AZO (ZnO:Al) may also be used.

[0219] The diameter W1 of the p-electrode 213 is 300 μm, and the thickness is 135 nm. The thickness of the p-electrode 213 can be appropriately selected within the range of 20 to 300 nm.

[0220] The thermal conductivity adjustment layer 211 is formed of a SiO2 film having a thickness of 25 nm on the p-electrode 213. Figure 14BAs shown, the thermal conductivity adjustment layer 211 has a circular shape, i.e., a thin cylindrical shape, with its central axis coaxial with the p-electrode 213 (central axis CZ) when viewed from above, and has an opening 211R (thermal conductivity adjustment opening) whose diameter W2 is smaller than the diameter W1 of the p-electrode 213 (W2 < W1). In addition, when viewed from above, the current injection region 213R is included in the air hole formation region 14R. Specifically, the diameter W1 of the current injection region 213R is smaller than the diameter W3 of the air hole formation region 14R (W1 < W1). <W3)。

[0221] As in the above-described embodiment, the thermal conductivity adjustment layer 211 is composed of a layer containing at least one of an insulator and a semiconductor having a thermal conductivity at least lower than the effective thermal conductivity of the semiconductor layer (second semiconductor layer) provided on the active layer 15. Furthermore, as in the above-described embodiment, when the second semiconductor layer 11A is composed of a gallium nitride (GaN)-based semiconductor, the thermal conductivity adjustment layer 211 is preferably formed of a material having a thermal conductivity lower than that of GaN.

[0222] In addition, the thermal conductivity adjustment layer 211 can be made of oxides such as SiO 2 , Al 2 O 3 , Ta 2 O 5 , ZrO 2 , and HfO 2 , nitrides such as SiN x , oxynitrides such as SiON and AlON , or metals such as Ti, V, and Pt.

[0223] The p-electrode 213 is exposed from the opening 211R of the thermal conductivity adjusting layer 211. A metal electrode 215A is provided on the p-electrode 213 exposed from the thermal conductivity adjusting layer 211. The metal electrode 215A is formed to cover at least the entire p-electrode 213 in a plan view.

[0224] Metal electrode 215A is composed of light-reflecting layer 214 and pad electrode 215. Light-reflecting layer 214 is made of a silver alloy (Ag alloy) and has a thickness of, for example, 150 nm. In addition to Ag alloy, light-reflecting layer 214 can also be made of Al, Al alloy, Rh, Ru, or a dielectric DBR.

[0225] A pad electrode 215 is provided on the light reflecting layer 214. The pad electrode 215 is formed of Ni, Pd, and Au with thicknesses of 10 nm, 200 nm, and 800 nm, respectively. The pad electrode 215 is preferably provided to cover the entire upper surface of the light reflecting layer 214.

[0226] The p-electrode 213 and the thermal conductivity adjustment layer 211 can be selected to have any shape such as a circle, a polygon, a gear shape, or a multiple ring shape when viewed from above (for example, see Figures 13A to 13D . ), preferably having a rotationally symmetrical shape about the central axis CZ perpendicular to the air hole layer 14P. In addition, in terms of uniformly adjusting the temperature distribution in two dimensions, a circular shape is further preferred.

[0227] After the PCSEL element 210 is bonded to the submount made of diamond using solder, it is mounted on a heat sink. In addition, as the submount, a material with high thermal conductivity can be used, such as AlN, SiC, graphite, CuW, Cu diamond, Ag diamond, etc.

[0228] (2) Evaluation of the element

[0229] Figure 15A It is a graph showing the calculation result of the temperature distribution of the air hole layer of the PCSEL element 210 (EMB7) of the present embodiment using the finite element method. In addition, Figure 15B It is a graph showing the temperature distribution of the air hole layer in the PCSEL element without the thermal conductivity adjustment layer 211 as a comparative example (CMP7).

[0230] In addition, the horizontal axis represents the position within the air hole layer 14P when the center position of the current injection region 213R (diameter W1) is 400 μm (element size: 800 μm), and the vertical axis represents the temperature of the air hole layer 14P.

[0231] As Figure 15A and Figure 15B shown, it can be seen that the temperature distribution of the air hole layer 14P of the PCSEL element 210 (EMB7) has become flatter compared to the comparative example (CMP7). Specifically, as discussed in the first embodiment above, based on the case where the temperature difference ΔT for coherent oscillation is 4 °C, with respect to the current injection region 213R (W1 = 300 μm), the diameter of the effective oscillation region is 256 μm (ΔT ≤ 4 °C). That is, it can be seen that compared to the diameter of the effective oscillation region of 195 μm (ΔT ≤ 4 °C) in the comparative example (CMP7), the diameter of the effective oscillation region has increased by 31%, and the area has increased by 72%.

[0232] This effect occurs only when the diameter W2 of the opening 211R (thermal conductivity adjustment opening) of the thermal conductivity adjustment layer 211 is smaller than the diameter W1 of the current injection region 213R (W2 < W1). This is because, in the case of downward bonding where the p semiconductor side is bonded to the submount (or support substrate) to improve heat dissipation, the distance between the active layer and the submount is very short, and most of the heat dissipation is achieved by heat dissipation to the submount side. In other words, in the outer peripheral part of the current injection region where the temperature of the air hole layer is significantly reduced (refer to Figure 15B ), by compensating the temperature distribution, the in-plane distribution of the resonance wavelength can be flattened.

[0233] The deterioration of the oscillation characteristics caused by such a temperature distribution is a unique problem of the PCSEL element in which light resonates in the in-plane direction of the air hole layer and diffracted waves are emitted in the direction perpendicular to the air hole layer.

[0234] Therefore, providing a thermal conductivity adjustment layer can prevent an increase in threshold current during continuous wave (CW) driving, thereby improving luminous efficiency. Furthermore, it is possible to provide a surface emitting laser with excellent oscillation stability, such as single-mode stability.

[0235] Furthermore, the PCSEL element of this embodiment includes a thermal conductivity adjustment layer 211 extending upward to the outer periphery of the p-electrode 213 (p-contact electrode) and partially covering the upper surface of this outer periphery. This reduces current (electric field) concentration at the ends of the p-electrode 213 and the active layer 15. While current concentration at the ends can cause device failure and degradation, the PCSEL element of this embodiment improves device reliability and lifetime.

[0236] [Eighth Embodiment]

[0237] (1) Component structure

[0238] Figure 16A : is a cross-sectional view schematically showing the structure of the PCSEL element 220 of the eighth embodiment. Figure 16B 2 is a plan view schematically showing the upper surface of the PCSEL element 220. In addition, the top surface of the thermal conductivity adjustment layer 221 is schematically shown.

[0239] In the PCSEL element 220, the insulating film 21 formed on the upper surface of the semiconductor structure layer 11 is provided with an opening (contact opening) OP having a diameter W1, which exposes the upper surface of the p-contact layer 19. The p-electrode 23 makes ohmic contact with the p-contact layer 19 exposed from the contact opening OP and fills the contact opening OP.

[0240] The p-electrode 23 is formed of a light-transmitting conductor, such as indium tin oxide (ITO). The diameter of the contact opening OP, ie, the diameter W1 of the current injection region 23R, is 500 μm, and the thickness of the p-electrode 23 is 135 nm.

[0241] A silver alloy (Ag alloy) layer is provided on the p-electrode 23 as a light-reflecting layer 24. The light-reflecting layer 24 is provided so as to cover at least the entire contact opening OP when viewed from above. The light-reflecting layer 24 has a flat surface parallel to the air hole layer 14P. The light-reflecting layer 24 has a thickness of, for example, 150 nm.

[0242] A pad electrode 32 is provided on the light reflecting layer 24. The pad electrode 32 is bonded to the heat dissipation substrate 225 (submount) made of diamond via a wiring electrode 224P on the heat dissipation substrate 225 through a bonding metal 224.

[0243] A thermal conductivity adjustment layer 221 is provided on the bonding surface (lower surface) of the heat dissipation substrate 225. The thermal conductivity adjustment layer 221 includes a first layer 221A and a second layer 221B. The first layer 221A has an opening coaxial with the central axis CZ of the p-electrode 23 and having a diameter of W2 (W2 < W1). The second layer 221B is provided on the lower surface side of the first layer 221A and has an opening coaxial with the central axis CZ and having a diameter of W4 (W2 < W4 < W1). That is, the first layer 221A and the second layer 221B are formed as layers having circular openings in a cross section parallel to the air hole layer 14P (that is, the semiconductor structure layer 11). That is, the diameter W2 of the first layer 221A as the opening diameter of the thermal conductivity adjustment layer 221 is smaller than the diameter W1 (contact opening diameter) (W2) of the current injection region 23R. <W1)。

[0244] The first layer 221A and the second layer 221B (hereinafter sometimes collectively referred to as the thermal conductivity adjustment layer 221) are composed of SiO2. The thickness of the first layer 221A is 20 nm, and the thickness of the second layer 221B is 120 nm. Furthermore, the diameter W2 of the opening in the first layer 221A is, for example, 240 μm, and the diameter W4 of the opening in the second layer 221B is, for example, 400 μm.

[0245] The thermal conductivity adjustment layer 221 can be made of at least one of an insulator or semiconductor material having a thermal conductivity at least lower than that of the heat dissipation substrate 225 or the bonding metal 224. For example, oxides (such as SiO2, Al2O3, Ta2O5, ZrO2, and HfO2), nitrides (such as SiNx), and oxynitrides (such as SiON and AlON) can be used. In the thermal conductivity adjustment layer 221, oxide insulators such as SiO2 are preferred due to their low thermal conductivity and high electrical resistance.

[0246] The thermal conductivity adjusting layer 221 is in close contact with the heat dissipation substrate 225 via an adhesion layer 222A provided between the thermal conductivity adjusting layer 221 and the first layer 221A, and is in close contact with the bonding metal 224 via an adhesion layer 222B provided between the thermal conductivity adjusting layer 221 and the second layer 221B.

[0247] The adhesion layer 222A and the adhesion layer 222B (hereinafter, sometimes collectively referred to as the adhesion layer 222 ) may be made of, for example, a Ti / Pu / Au layer, but are not limited thereto.

[0248] The bonding metal 224 covers the entire thermal conductivity adjustment layer 221 to embed the thermal conductivity adjustment layer 221 , and is bonded to the heat dissipation substrate 225 .

[0249] Furthermore, the heat dissipation substrate 225 is not limited to diamond, and AlN, SiC, graphite, CuW, Cu diamond, Ag diamond, or the like can be used.

[0250] (2) Component evaluation

[0251] Figure 17 This graph compares the calculated results of the temperature distribution of the air hole layer for the PCSEL element 220 (EMB8) of this embodiment and the PCSEL element (CMP8) of the comparative example. The comparative example (CMP8) differs from the PCSEL element 220 (EMB8) of this embodiment only in that it lacks the thermal conductivity adjustment layer 221 and the adhesion layer 222.

[0252] like Figure 17 As shown, the temperature distribution of the air hole layer 14P of PCSEL element 220 (EMB8) is flatter than that of the comparative example (CMP8). Specifically, the diameter of the region capable of effective oscillation is 467 μm (based on the aforementioned ΔT ≤ 4°C). Compared to the 318 μm diameter of the region capable of oscillation in the comparative example (CMP8A), this indicates a larger oscillation area and improved efficiency.

[0253] This effect is achieved by making the diameter W2 of the opening 221R (thermal conductivity adjustment opening) of the thermal conductivity adjustment layer 221 smaller than the diameter W1 of the current injection region 23R (contact region) (W2 < W1). In other words, the PCSEL element of this embodiment can resolve the unique issue of PCSEL elements, namely, degradation of oscillation characteristics caused by the temperature distribution of the air hole layer (photonic crystal layer).

[0254] Therefore, providing a thermal conductivity adjustment layer can prevent an increase in threshold current during continuous wave (CW) driving, thereby improving luminous efficiency. Furthermore, it is possible to provide a surface emitting laser with excellent oscillation stability, such as single-mode stability.

[0255] Furthermore, in the PCSEL element 220 of this embodiment, the thermal conductivity adjustment layer 221 is provided separately from the p-electrode 23 (contact electrode) on the side of the heat dissipation substrate 225. Specifically, compared to a case where the thermal conductivity adjustment layer is provided near the p-electrode 23, the current injected from the wiring electrode 224P on the heat dissipation substrate 225 connected to the bonding metal 224 is not hindered by the thermal conductivity adjustment layer 221, allowing for uniform current injection.

[0256] In-plane non-uniformity in current injection can lead to degradation of device characteristics and reliability. Therefore, the PCSEL element of this embodiment can improve these characteristics.

[0257] In this embodiment, the thermal conductivity adjustment layer 221 is described as being composed of two layers with different opening diameters, but it may also be composed of a single layer having an opening of diameter W2 or a tapered layer with a thickness decreasing toward the center of the opening.

[0258] (3) Modification Example 1

[0259] Figure 18 1 is a cross-sectional view schematically showing the structure of a PCSEL element 230 according to Modification 1 of Embodiment 8. In addition, a cross section including the central axis CZ of the p-electrode 23 is shown.

[0260] In the PCSEL element 230 of Modification 1, the thermal conductivity adjustment layer 226 is formed as a cavity (air layer) provided in the heat dissipation substrate 225. The heat dissipation substrate 225 is made of, for example, AlN (aluminum nitride).

[0261] More specifically, the thermal conductivity adjustment layer 226 includes a recessed portion recessed from the lower surface of the heat dissipation substrate 225 (i.e., the bonding surface with the bonding metal 224). Furthermore, the inner wall surface of the thermal conductivity adjustment layer 226 has a cylindrical shape. Specifically, the heat dissipation substrate 225 includes a cylindrical protrusion 225C coaxial with the central axis CZ of the p-electrode 23 and having a diameter of W2 (W2 < W1).

[0262] By bonding the lower surface of the heat dissipation substrate 225 having the recessed portion to the pad electrode 32 , a thermal conductivity adjustment layer 226 is formed between the heat dissipation substrate 225 and the pad electrode 32 , forming a cavity (air layer) formed in the heat dissipation substrate 225 .

[0263] Such a cavity-shaped thermal conductivity adjustment layer 226 can be formed, for example, as follows. First, dry etching is performed on an AlN substrate using an ICP-RIE apparatus to form a cylindrical protrusion 225C and a recessed portion surrounding the protrusion 225C and recessed from the peripheral surface of the heat dissipation substrate 225. This recessed portion is formed, for example, in a circular ring shape when viewed from above.

[0264] Next, in order to suppress the spread of melted metal during bonding with the pad electrode 32 , a bonding metal film 224 composed of Ti / Pt / Au is patterned and formed only on the bonding region of the heat dissipation substrate 225 .

[0265] Next, the pad electrode 32 is bonded to the bonding region of the heat dissipation substrate 225. Since solder such as AuSn is difficult to melt and spread, and thus difficult to form a cavity, it is preferable to use a bond that is difficult to melt and spread, such as Au-Au bonding.

[0266] (4) Modification Example 2

[0267] Figure 19This is a cross-sectional view schematically illustrating the structure of a PCSEL element 240 according to Modification 2 of the eighth embodiment. In PCSEL element 240 according to Modification 2, a thermal conductivity adjustment layer 221 is provided so as to be entirely embedded within a bonding metal 224. The thermal conductivity adjustment layer 221 has an opening coaxial with the central axis CZ of the p-electrode 23 and having a diameter W2. This opening is smaller than the opening diameter W1 of the contact opening OP (W2 < W1), similar to the PCSEL element of the above-described embodiment.

[0268] (5) Modification Example 3

[0269] Figure 20 This is a cross-sectional view schematically illustrating the structure of a PCSEL element 250 according to Modification 3 of the eighth embodiment. In PCSEL element 250 according to Modification 3, a thermal conductivity adjustment layer 221 is provided on the upper surface of the pad electrode 32 in contact with the bonding metal 224. Similar to PCSEL element 240 according to Modification 2, the thermal conductivity adjustment layer 221 has an opening coaxial with the central axis CZ of the p-electrode 23 and having a diameter of W2 (W2 < W1).

[0270] (6) Modification Example 4

[0271] Figure 21 This is a cross-sectional view schematically illustrating the structure of a PCSEL element 260 according to Modification 4 of the eighth embodiment. In PCSEL element 260 according to Modification 4, a thermal conductivity adjustment layer 221 is provided in contact with the pad electrode 32 and embedded in the bonding metal 224. Similar to the PCSEL element of the above embodiment, the thermal conductivity adjustment layer 221 has an opening coaxial with the central axis CZ of the p-electrode 23 and having a diameter of W2 (W2 < W1).

[0272] Therefore, the PCSEL element of this embodiment, by providing a thermal conductivity adjustment layer, can prevent an increase in threshold current during continuous (CW) driving, thereby improving luminous efficiency. Furthermore, it can provide a surface emitting laser with excellent oscillation stability, such as single-mode stability.

[0273] [Ninth embodiment]

[0274] (1) Component structure

[0275] Figure 22 1 is a cross-sectional view schematically showing the structure of a PCSEL element 280 according to a ninth embodiment. The PCSEL element 280 according to this embodiment includes the same thermal conductivity adjustment layer 31 as the PCSEL element 10 according to the first embodiment.

[0276] In addition, the PCSEL element 280 further includes a refractive index adjustment layer 288 embedded in the second semiconductor layer. More specifically, the refractive index adjustment layer 288 is embedded in the p-cladding layer 18 and the p-contact layer 19.

[0277] In the PCSEL element 280 , the refractive index adjustment layer 288 is formed, for example, of an AlxInyGa1-x-yN layer (0≤x≤1, 0≤y≤1, 0≤x+y≤1) (semiconductor heterostructure), and is formed as a layer extending from a position shallower than the lower surface of the p-cladding layer 18 to the upper surface of the p-contact layer 19.

[0278] A p-electrode 283 (p-contact electrode) is formed on the p-contact layer 19 and the refractive index adjustment layer 288. Similar to the PCSEL element 10 of the first embodiment, a light reflecting layer 24 is formed on the p-electrode 283, which is made of a light-transmitting conductor, and a pad electrode 32 in which a thermal conductivity adjustment layer 31 is embedded is provided on the light reflecting layer 24.

[0279] More specifically, the refractive index adjustment layer 288 has a cylindrical opening coaxial with the central axis CZ of the opening of the thermal conductivity adjustment layer 31, and the diameter WR of this cylindrical opening is 500 μm. Specifically, the refractive index adjustment layer 288 is formed so that a portion of the p-cladding layer 18 and the p-contact layer 19 fill the cylindrical opening of the refractive index adjustment layer 288. Here, the refractive index adjustment layer 288 has a refractive index higher than the effective refractive index of the p-cladding layer 18 and the p-contact layer 19 contained within the cylindrical opening.

[0280] Furthermore, the refractive index adjustment layer 288 also functions as a current confinement layer. That is, the cylindrical region functions as a current injection region. Therefore, the diameter (opening diameter) WR of the cylindrical opening is larger than the opening diameter (diameter) W2 of the thermal conductivity adjustment layer 31 ( W2 < WR).

[0281] The refractive index adjustment layer 288 (AlInGaN) is formed by, for example, dry etching the p-contact layer 19 and p-cladding layer 18, then performing embedding growth on the etched portion using MOVPE. The refractive index adjustment layer 288 is not limited to MOVPE; it can also be formed using MBE or sputtering. In the PCSEL element 280, the refractive index adjustment layer 288 is formed to a depth of approximately 320 nm. Alternatively, ZrO2, TiO2, Ta2O5, Nb2O5, SiNx, or the like can be used for the refractive index adjustment layer 288.

[0282] (2) Component evaluation

[0283] Figure 23AThis graph compares the calculated results of the temperature distribution of the air hole layer for PCSEL element 280 (EMB9) of this embodiment and PCSEL element (CMP9) of a comparative example. The PCSEL element of the comparative example differs from PCSEL element 280 only in that it lacks a refractive index adjustment layer 288. Here, it is assumed that the applied voltage to the element is 6 V and the injected current is 7 A.

[0284] like Figure 23A As shown, it can be seen that there is no significant difference in temperature distribution between the PCSEL element 280 (EMB9) of the present embodiment and the PCSEL element (CMP9) of the comparative example (overlapping in the figure), and the temperature distribution in the current injection region (diameter WR) is flat.

[0285] Figure 23B This graph compares the results of calculating the resonance center wavelength (nm) for the PCSEL element 280 (EMB9) of this embodiment and the PCSEL element (CMP9) of the comparative example. In this calculation, the wavelength of Bragg reflection is calculated based on the effective refractive index and the lattice constant of the photonic crystal, taking temperature into account.

[0286] It can be seen that in the comparative example without a refractive index adjustment layer, the resonant wavelength shifts inside and outside the current injection region. However, in the PCSEL element 280 of this embodiment, this shift in the resonant wavelength is mitigated. Therefore, light diffraction can be obtained even outside the current injection region, reducing in-plane light leakage and losses. In other words, the efficiency of the PCSEL element can be improved.

[0287] In addition, the refractive index adjustment layer 288 is formed by embedding in the second semiconductor layer, preferably as shown in FIG. Figure 24 As shown, the refractive index adjusting layer 288 is formed as a layer provided between the lower surface of the p-cladding layer 18 and the upper surface of the p-electrode 23. In this case, the refractive index adjusting layer 288 may have a refractive index higher than the effective refractive index of the entirety of the p-cladding layer 18, the p-contact layer 19, and the p-electrode 23 included in the cylindrical region of the refractive index adjusting layer 288.

[0288] The above describes the embodiments of the present invention in detail. Furthermore, in the above embodiments, the contact openings (current injection regions) and thermal conductivity adjustment openings of the p-electrode (contact electrode) and thermal conductivity adjustment layer, respectively, are preferably circular in plan view, but are not limited thereto. Alternatively, they may have elliptical shapes, polygonal shapes, roughly circular shapes with periodic irregularities on the periphery (including gear shapes), or multiple ring shapes. Therefore, in this specification, the term "circular shape" encompasses elliptical shapes, roughly circular shapes with periodic irregularities on the periphery, and multiple ring shapes.

[0289] When the contact opening (current injection region) and the thermal conductivity adjustment opening are non-circular in shape, they are preferably rotationally symmetric about the central axis. In these cases, the opening diameter is defined by the diameter (or major axis) of a circle (including an ellipse) circumscribing the opening shape.

[0290] In order to uniformly adjust the temperature distribution two-dimensionally, the contact opening (current injection region) and the thermal conductivity adjustment opening preferably have a circular shape or a regular n-sided shape (n is an integer greater than or equal to 4) in a plan view, and more preferably a circular shape.

[0291] Furthermore, the thermal conductivity adjustment opening preferably has a similar shape, with its central axis coaxial with the contact opening. In short, the shapes of the p-electrode (contact electrode) and the thermal conductivity adjustment layer can be determined so that their dimensions ensure that the thermal conductivity adjustment opening region is included in the current injection region when viewed from above, and that the temperature of the outer periphery of the current injection region is uniform with the temperature of the central portion of the current injection region, resulting in a flat temperature distribution. Furthermore, the various embodiments described above can be appropriately modified or combined within the scope of the present invention.

[0292] As described above, the present invention can provide a photonic crystal surface emitting laser that can easily flatten the temperature distribution of a photonic crystal during continuous wave (CW) driving, improves luminous efficiency, and exhibits excellent oscillation stability.

[0293] Explanation of symbols

[0294] 10, 60, 70, 80, 90, 210, 220, 230, 240, 250, 260, 280: PCSEL components

[0295] 11: Semiconductor structure layer

[0296] 11A: Second semiconductor layer

[0297] 14: First guide layer

[0298] 14P: air hole layer

[0299] 14K: Air holes

[0300] 15: Active layer

[0301] 19: Contact layer

[0302] 23, 213: p-electrode (contact electrode)

[0303] 23R, 213R: Current injection area

[0304] 24, 214: Light reflection layer

[0305] 31, 33, 35, 211, 221: Thermal conductivity adjustment layer

[0306] 32, 215: pad electrode

[0307] 226: Thermal conductivity adjustment layer (cavity)

[0308] 31W, 35W, 37W, 211R, 221R: Thermal conductivity adjustment opening

[0309] 215A: Metal electrode

[0310] 224: Joining Metals

[0311] 225: Heat dissipation substrate

[0312] 288: Refractive Index Adjustment Layer

[0313] OP: contact opening

Claims

1. A surface-emitting laser element comprising a photonic crystal, The surface-emitting laser element has: a light-transmitting substrate; a first semiconductor layer formed on the substrate and having an air hole layer as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a current constriction layer formed on the second semiconductor layer and having a circular or rotationally symmetrical contact opening; a contact electrode formed by filling the contact opening of the current constriction layer; and a pad electrode having a thermal conductivity adjustment layer embedded therein and formed on the contact electrode, wherein the thermal conductivity of the thermal conductivity adjustment layer is smaller than the effective thermal conductivity of the second semiconductor layer; The thermal conductivity adjustment layer has a thermal conductivity adjustment opening whose central axis is coaxial with the contact opening. The thermal conductivity adjustment opening has an opening diameter (W2) smaller than an opening diameter (W1) of the contact opening.

2. The surface-emitting laser element according to claim 1, wherein The thermal conductivity adjustment opening has a similar shape with a central axis being coaxial with a central axis of the contact opening.

3. The surface-emitting laser element according to claim 2, wherein The thermal conductivity adjustment opening has a circular shape, The thermal conductivity adjusting layer includes an outer peripheral portion and an annular inner peripheral portion having a thickness smaller than that of the outer peripheral portion.

4. The surface-emitting laser element according to claim 1, wherein The thermal conductivity adjusting layer has a layer thickness that decreases in a tapered shape toward the center of the thermal conductivity adjusting opening, and has an inner peripheral portion that is annular similar to the contact opening.

5. The surface-emitting laser element according to claim 1, wherein The surface-emitting laser element has a light reflecting layer provided between the pad electrode and the contact electrode.

6. The surface-emitting laser element according to claim 1, wherein The second semiconductor layer is made of gallium nitride, ie, a GaN-based semiconductor, and the thermal conductivity adjustment layer is formed of a material having a lower thermal conductivity than GaN.

7. The surface-emitting laser element according to claim 1, wherein The thermal conductivity adjusting layer is formed in a dot pattern.

8. A surface-emitting laser element comprising a photonic crystal, The surface-emitting laser element has: a light-transmitting substrate; a first semiconductor layer formed on the substrate and having an air hole layer as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a contact electrode partially formed on the second semiconductor layer and in ohmic contact with the second semiconductor layer; a thermal conductivity adjustment layer formed on the second semiconductor layer and having a thermal conductivity adjustment opening, the thermal conductivity adjustment opening extending upward to the outer periphery of the contact electrode and formed so as to partially cover the upper surface of the outer periphery to expose the second semiconductor layer, the thermal conductivity adjustment layer being composed of a layer including at least one of an insulator and a semiconductor having a thermal conductivity less than an effective thermal conductivity of the second semiconductor layer; and The metal electrode is formed to fill the thermal conductivity adjustment opening of the thermal conductivity adjustment layer and to cover at least the entire contact electrode in a plan view.

9. The surface-emitting laser element according to claim 8, wherein The contact electrode and the opening of the thermal conductivity adjustment layer may have either a circular shape or a rotationally symmetrical shape that are coaxial with each other in a plan view.

10. The surface-emitting laser element according to claim 8, wherein The contact electrode is a light-transmitting conductor, and the metal electrode is composed of a light-reflecting layer formed on the contact electrode and a pad electrode formed on the light-reflecting layer.

11. A surface-emitting laser element comprising a photonic crystal. The surface-emitting laser element has: a light-transmitting substrate; a first semiconductor layer formed on the substrate and having an air hole layer as a photonic crystal layer; an active layer formed on the first semiconductor layer; a second semiconductor layer formed on the active layer; a current constriction layer formed on the second semiconductor layer and having a contact opening; a contact electrode formed by filling the contact opening of the current constriction layer; a metal electrode formed on the contact electrode; a bonding metal formed on the metal electrode; a heat dissipation substrate bonded to the bonding metal via the bonding metal; and a thermal conductivity adjustment layer provided inside any one of the metal electrode, the bonding metal, and the heat dissipation substrate; The thermal conductivity adjustment layer includes at least one of an insulator and a semiconductor material having a thermal conductivity lower than that of at least one of the bonding metal and the heat dissipation substrate. The thermal conductivity adjustment layer has a thermal conductivity adjustment opening, and the thermal conductivity adjustment opening has a size and a configuration included in the contact opening in a plan view.

12. The surface-emitting laser element according to claim 11, wherein The contact opening and the opening of the thermal conductivity adjustment layer may have either a circular shape or a rotationally symmetrical shape that are coaxial with each other in a plan view.

13. The surface-emitting laser element according to claim 12, wherein The thermal conductivity adjustment layer is disposed on the lower surface of the heat dissipation substrate.

14. The surface-emitting laser element according to claim 12, wherein The thermal conductivity adjustment layer is a cavity formed in the heat dissipation substrate between the heat dissipation substrate and the bonding metal.

15. The surface-emitting laser element according to claim 12, wherein The thermal conductivity adjusting layer is provided inside the bonding metal.

16. The surface-emitting laser element according to claim 12, wherein The thermal conductivity adjusting layer is provided within the metal electrode at an interface between the metal electrode and the bonding metal.

17. The surface-emitting laser element according to any one of claims 1 to 16, wherein The surface-emitting laser element has a refractive index adjusting layer embedded in the second semiconductor layer. The refractive index adjustment layer is formed so as to be embedded in a cylindrical opening region coaxial with the central axis of the contact electrode so as to fill a portion of the second semiconductor layer. The opening diameter of the thermal conductivity adjustment opening is smaller than the opening diameter of the cylindrical opening of the refractive index adjustment layer.

18. The surface-emitting laser element according to claim 17, wherein The second semiconductor layer has a p-side guide layer formed on the active layer, an electron blocking layer formed on the p-side guide layer, a p-cladding layer formed on the electron blocking layer, and a p-contact layer formed on the p-cladding layer. The refractive index adjustment layer is formed as a layer extending from a position shallower than the lower surface of the p-cladding layer to the upper surface of the p-contact layer.

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