Surface-emitting laser device

Abstract

To provide a photonic crystal surface-emitting laser device in which a rise in oscillation threshold current and drive current of a photonic crystal surface-emitting laser element is suppressed, and which has a stable oscillation mode and excellent beam quality.SOLUTION: A surface-emitting laser device includes: a surface-emitting laser element; a mounting substrate on which the surface-emitting laser element is mounted and which is connected to the element; and an electrically conductive element-bonding member that bonds the surface-emitting laser element and the mounting substrate and that mitigates the distortion of the surface-emitting element due to the mounting substrate. The surface-emitting laser element includes: a translucent element substrate; a first semiconductor layer on the element substrate; an active layer on the first semiconductor layer; a second semiconductor layer of the opposite electrically conductive type to the first semiconductor layer, the second semiconductor layer provided on the active layer; a void layer provided with voids arranged in a two-dimensional periodic manner within a plane, the void layer included in the first semiconductor layer or the second semiconductor layer; and a light reflective layer having a reflective surface and provided on the second semiconductor layer. A light emission surface is provided on the side opposite to the first semiconductor layer side of the element substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art In recent years, the development of photonic-crystal surface-emitting lasers using photonic crystals (PC) has progressed.

[0003] For example, Patent Document 1 discloses that a photonic crystal layer having a uniform size and a uniform refractive index periodicity is formed by forming holes having two-dimensional periodicity in a guide layer, forming recesses having facets of a predetermined plane orientation above the openings of the holes, and flattening the recesses by mass transport.

[0004] Non-Patent Document 1 also discloses a formulation of diffracted light from a photonic crystal surface emitting laser, and a profile of diffracted radiation waves diffracted in a photonic crystal layer and emitted in a direction perpendicular to the photonic crystal layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7101370 [Non-patent literature]

[0006] [Non-Patent Document 1] Y. Liang et al.: Phys.Rev. B vol.84, 195119 (2011) Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a photonic crystal surface-emitting laser element is mounted on a circuit board or a heat sink, stress is generated in the photonic crystal surface-emitting laser element, causing an increase in the oscillation threshold current, decreasing the luminous efficiency, and also causing an unstable oscillation mode.

[0008] In particular, when driven by continuous current (CW drive), the drive current increases due to the distortion inherent in the photonic crystal surface-emitting laser element, reducing the power conversion efficiency and increasing the amount of heat generated, making it impossible to obtain sufficient output and causing the oscillation mode to become unstable.

[0009] An object of the present invention is to provide a photonic crystal surface-emitting laser device in which increases in the oscillation threshold current and drive current of the photonic crystal surface-emitting laser element are suppressed, the photonic crystal surface-emitting laser device has a stable oscillation mode, and has excellent beam quality. [Means for solving the problem]

[0010] A surface emitting laser device according to one embodiment of the present invention comprises: A surface emitting laser element; a mounting substrate on which the surface-emitting laser element is mounted and which is electrically connected to the surface-emitting laser element; an element bonding member made of a conductive bonding material that bonds the surface-emitting laser element and the mounting substrate and relieves distortion of the surface-emitting laser element caused by the mounting substrate; The surface emitting laser element is A light-transmitting element substrate; A first semiconductor layer provided on the element substrate; an active layer provided on the first semiconductor layer; a second semiconductor layer provided on the active layer and having an opposite conductivity type to the first semiconductor layer; a hole layer which is a photonic crystal layer included in the first semiconductor layer or the second semiconductor layer and has holes arranged with two-dimensional periodicity in a plane parallel to the active layer; a light reflective layer provided on the second semiconductor layer and having a reflective surface; The element substrate has a light emitting surface on the side opposite to the surface on which the first semiconductor layer is provided. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a cross section of a surface-emitting laser device according to a first embodiment. [Figure 2A] 1 is a cross-sectional view illustrating an example of the structure of a PCSEL element according to a first embodiment. [Figure 2B] 2B is an enlarged cross-sectional view showing a schematic diagram of hole pairs arranged in the photonic crystal layer shown in FIG. 2A. FIG. [Figure 3A] FIG. 2B is a plan view showing a schematic top surface of the PCSEL device shown in FIG. 2A. [Figure 3B] 3 is a cross-sectional view that illustrates a schematic cross section of a photonic crystal layer in a plane parallel to an n-side guide layer. FIG. [Figure 3C] FIG. 2 is a plan view showing a schematic view of the bottom surface of a PCSEL element. [Figure 4] FIG. 2 is a schematic diagram showing a cross section of a formed photonic crystal layer, the cross section being perpendicular to the crystal layer. [Figure 5A] 1 is a surface SEM image showing a main hole 14H1 and a sub-hole 14H2 that have been dug in a GaN layer (n-side guide layer) when forming a photonic crystal layer. [Figure 5B] FIG. 13 is a view showing a surface SEM image of the formed main void 14K1 and sub-void 14K2. [Figure 6] 1 is a cross-sectional view showing a schematic cross section of the arrangement of main holes 14K1 and sub-holes 14K2 in the depth direction of a double lattice structure. [Figure 7] FIG. 7 shows the current-output characteristics of the PCSEL element before and after mounting in the surface-emitting laser device 5 of Example 1 (EMB1). [Figure 8] 1 is a graph showing the oscillation spectra before and after mounting a PCSEL element in the surface-emitting laser device of Example 1 when a current of 3.0 A is applied to the PCSEL element. [Figure 9A]FIG. 1 shows the photonic bands of a PCSEL device. [Figure 9B] FIG. 13 is a diagram showing the Γ-point spectrum before oscillation (lower part) and the spectrum immediately after oscillation (upper part). [Figure 10A] FIG. 13 is a diagram showing the FFP before mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Example 1. [Figure 10B] FIG. 13 is a diagram showing the FFP after mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Example 1. [Figure 11] FIG. 13 is a diagram showing current-output characteristics before and after mounting a PCSEL element in the surface-emitting laser device of Comparative Example 1 (CMP1). [Figure 12] 1 shows the oscillation spectra before and after mounting the PCSEL element in the surface-emitting laser device of Comparative Example 1 when a current of 3.0 A is applied to the PCSEL element. [Figure 13A] 13 is a diagram showing the FFP before mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Comparative Example 1. FIG. [Figure 13B] 13 is a diagram showing the FFP after mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Comparative Example 1. FIG. [Figure 14] FIG. 1 shows a substrate that is a graphite laminate. [Figure 15] 13 is a graph showing current-output characteristics before and after mounting a PCSEL element in the surface-emitting laser device of Example 2 (EMB2). [Figure 16] 13 shows the oscillation spectra before and after mounting the PCSEL element in the surface emitting laser device of Example 2 when a current of 3.0 A is applied to the PCSEL element. [Figure 17A] FIG. 13 is a diagram showing the FFP before mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Example 2. [Figure 17B] FIG. 13 is a diagram showing the FFP after mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Example 2. [Figure 18A]1 is a table showing base materials and bonding conditions of a mounting substrate of a surface-emitting laser device in Example 1, and oscillation characteristics before and after mounting a PCSEL element.

[0012] [Figure 18B] 13 is a table showing the base material and bonding conditions of the mounting substrate of the surface emitting laser device in Example 2, and the oscillation characteristics before and after mounting the PCSEL element. [Figure 18C] 1 is a table showing the base material and bonding conditions of the mounting substrate of the surface-emitting laser device in Comparative Example 1, and the oscillation characteristics before and after mounting a PCSEL element. [Figure 19] 1 is a table showing physical property values ​​of materials used in Examples 1 and 2 and Comparative Example 1. [Figure 20] 1 is a graph plotting the rate of change in threshold current versus the amount of strain ε applied to a PCSEL element by mounting it on a mounting substrate (base material). [Figure 21] FIG. 13 is a diagram showing the stress σ applied to GaN when mounted on a mounting substrate, in cases where GaN, diamond, and three-layer graphite are used as the base material of the mounting substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following, preferred embodiments of the present invention will be described, which may be modified and combined as appropriate. In the following description and accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0014] [First embodiment] 1. Structure of photonic crystal surface-emitting laser device 1 is a cross-sectional view showing a surface-emitting laser device 5 of this embodiment. The surface-emitting laser device 5 has a photonic-crystal surface-emitting laser (PCSEL: Photonic-Crystal Surface-Emitting Laser) element 10, an element bonding member 31, a mounting substrate 32, a substrate bonding member 34, a heat sink 35, and a housing 38.

[0015] Photonic crystal surface-emitting laser device (hereinafter also referred to as PCSEL device) 10 has a photonic crystal layer 14P therein. PCSEL device 10 also has a first electrode 20A (n-electrode) and a second electrode 20B (p-electrode).

[0016] The PCSEL device 10 is mounted on the mounting substrate 32 by being bonded to the mounting substrate 32 by the device bonding member 31. More specifically, the second electrode 20B of the PCSEL device 10 is bonded by the device bonding member 31 to a wiring electrode 33, which is a conductive layer on the mounting substrate 32, and is electrically connected thereto.

[0017] The mounting board 32 is joined to the heat sink 35 by a board joining member 34. Furthermore, the wiring electrodes 33 of the mounting board 32 are electrically connected to the heat sink 35 by bonding wires W2.

[0018] In this embodiment, the heat sink 35 is a conductor and functions as an anode electrode of the surface-emitting laser device 5. However, the connection form is not limited to this. For example, the wiring electrode 33 may be configured to be connected to the anode electrode (second terminal, not shown) of the surface-emitting laser device 5.

[0019] Moreover, the first electrode 20A of the PCSEL element 10 is electrically connected to a first terminal 37 (cathode electrode) of the surface-emitting laser device 5 by a bonding wire W2. Therefore, the PCSEL element 10 emits light when a voltage is applied between the first terminal 37 and the second terminal.

[0020] The above-mentioned components are accommodated in a housing 38 to form the surface-emitting laser device 5.

[0021] (Mounting board) A diamond substrate having a thickness of 500 μm and excellent heat dissipation properties was used as the base material 32A of the mounting substrate 32 (submount). Other materials that may be used as the base material 32A of the mounting substrate 32 include aluminum nitride (AlN), silicon carbide (SiC), alumina (Al2O3), copper-aluminum nitride-copper (Cu-AlN-Cu), copper-tungsten (CuW), GaN, and graphite.

[0022] In this embodiment, the wiring electrodes 33 of the mounting substrate 32 are formed using a metal film coating layer made of nickel / palladium / gold (Ni / Pd / Au).

[0023] (Element joining material) A paste material (MAX102, manufactured by Nippon Handa) in which silver particles (silver nanoparticles) are mixed in an organic solvent, or a paste material (AuRoFUSE, manufactured by Tanaka Kikinzoku Kogyo) in which gold particles (gold nanoparticles) are mixed, was used for the element bonding member 31. This paste material can be sintered at 200°C, which is sufficiently low temperature to bond the PCSEL element 10 and the mounting substrate 32 compared to the sintering temperature of 320°C of gold-tin alloy (AuSn), which has been used as a bonding material in the past. In other words, the PCSEL element 10 can be bonded while suppressing thermal distortion.

[0024] Specifically, after the bonding material is applied to the mounting substrate 32, the PCSEL element 10 is subjected to a pressure of approximately 1.5 kfg / cm 2 The mounting substrate 32 on which the PCSEL device 10 was mounted under a load was placed in a sintering oven, heated to 200° C. in an N2 atmosphere, and sintered for 1 hour.

[0025] The sintering temperature may be in the range of 80 to 320°C. If the temperature is too low, the metal particles will not be sintered, and if the temperature is too high, the element characteristics will deteriorate, for example, the IV characteristics will be impaired. Furthermore, the sintering time may be long enough to vaporize the organic solvent contained in the element bonding material 31 during sintering, and may be, for example, 2 minutes to 8 hours.

[0026] Although a paste material containing silver nanoparticles or gold nanoparticles was used in this embodiment, any paste material containing at least one type of metal fine particles (nanoparticles) such as gold (Au), silver (Ag), copper (Cu), etc. The use of nanometer-order metal fine particles for the element bonding member 31 is preferable in that the bonding temperature between the PCSEL element 10 and the mounting substrate 32 can be reduced.

[0027] As described above, fine particles other than the metal nanoparticles described above can be used as long as the contact areas between particles are bonded (necked) by sintering at low temperatures and the fine metal particles have high electrical conductivity and heat dissipation properties.

[0028] Furthermore, it is preferable that the element bonding member 31 has a Young's modulus smaller than that of the mounting substrate 32. The Young's modulus of the element bonding member 31 is more preferably 100 or less, and further preferably 70 or less.

[0029] Furthermore, a bonding process at room temperature may be used when mounting the PCSEL device 10 on the mounting substrate 32. For example, the bonding surfaces of the second electrode 20B and the wiring electrode 33 of the PCSEL device 10 are activated by Ar and H2 plasma, and then the second electrode 20B and the wiring electrode 33 are pressurized at room temperature. This allows the PCSEL device 10 and the mounting substrate 32 to be bonded together.

[0030] (Bonding material for circuit boards) An indium alloy (content ratio: In0.52-Sn0.48) was used for the substrate bonding member 34. Specifically, after the substrate bonding material was applied to the heat sink 35, the heat sink 35 was heated to 120° C. to soften the bonding material, and the mounting substrate 32 on which the PCSEL device 10 was mounted was pressurized, thereby bonding the heat sink 35 and the mounting substrate 32.

[0031] (heat sink) The heat sink 35 is made of copper (Cu), which has excellent electrical and thermal conductivity. A Peltier cooling device is disposed on the back surface of the heat sink 35 (the surface opposite to the bonding surface with the mounting substrate 32), and the back surface is kept at a predetermined constant temperature.

[0032] (filled gas) The surface emitting laser device 5 is sealed in a housing 38, and dry nitrogen is used as the gas filled inside. Other gases that can be used as the gas filled include nitrogen-oxygen mixed gas and dry air.

[0033] When the wavelength of the emitted light from the PCSEL device 10 is shorter than 420 nm, the generation of charcoal derived from residual organic matter can be suppressed by mixing a few percent of oxygen.

[0034] 2. Structure of photonic crystal surface-emitting laser element A photonic crystal surface-emitting laser element (PCSEL element) is an element that has a resonator layer in a direction 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 perpendicular to the resonator layer.

[0035] That is, in a PCSEL element, light waves propagating in a plane parallel to the photonic crystal layer are diffracted by the diffraction effect of the photonic crystal to form a two-dimensional resonance mode, and are also diffracted in a direction perpendicular to the parallel plane. That is, in a PCSEL element, the light extraction direction is perpendicular to the resonance direction (in the plane parallel to the photonic crystal layer).

[0036] Fig. 2A is a cross-sectional view showing an example of the structure of a photonic crystal surface-emitting laser device (PCSEL device) 10 according to an embodiment of the present invention, and Fig. 2B is an enlarged cross-sectional view showing a photonic crystal layer 14P and air hole pairs 14K arranged in the photonic crystal layer 14P in Fig. 2A.

[0037] 2A, a semiconductor structure layer 11 is formed on a light-transmitting element substrate 12. Note that semiconductor layers are stacked perpendicularly to the central axis CX of the semiconductor structure layer 11.

[0038] The semiconductor structure layer 11 is made of a hexagonal nitride semiconductor. In this embodiment, the semiconductor structure layer 11 is made of, for example, a GaN-based semiconductor.

[0039] More specifically, a semiconductor structure layer 11 consisting of a plurality of semiconductor layers is formed on an element substrate 12, in this order: an n-clad layer (first clad layer of a first conductivity type) 13, an n-side guide layer (first guide layer) 14 which is a guide layer provided on the n-side, a light distribution adjustment layer 23, an active layer (ACT) 15, a p-side guide layer (second guide layer) 16 which is a guide layer provided on the p-side, an electron barrier layer (EBL: Electron Blocking Layer) 17, a p-clad layer (second clad layer of a second conductivity type) 18, and a p-contact layer 19.

[0040] Although the case will be described where the first conductivity type is n-type and the second conductivity type opposite to the first conductivity type is p-type, the first conductivity type and the second conductivity type may be p-type and n-type, respectively.

[0041] The element substrate 12 is a hexagonal GaN single crystal substrate having a high transmittance for light emitted from the active layer 15. More specifically, the element substrate 12 is a hexagonal GaN single crystal substrate whose main surface (crystal growth surface) is a +c plane, which is a {0001} plane in which Ga atoms are arranged on the outermost surface. The back surface (light emission surface) is a -c plane, which is a (000-1) plane in which N atoms are arranged on the outermost surface. The -c plane is suitable as a light emission surface because it is resistant to oxidation and the like.

[0042] Although the element substrate 12 is not limited thereto, a so-called just substrate or, for example, a substrate whose main surface is offset by about 1° in the m-axis direction is preferable. For example, a substrate offset by about 0.3 to 0.7° in the m-axis direction can obtain mirror-finish growth under a wide range of growth conditions.

[0043] The substrate surface (back surface, light emission surface) on which the light emission region 20L (FIG. 3C) facing the main surface is provided is the "-c" surface, which is the (000-1) surface on which N atoms are arranged. The -c surface is resistant to oxidation and the like, making it suitable as a light extraction surface.

[0044] The composition, thickness, and other configurations of each semiconductor layer will be described below, but these are merely examples and can be modified as appropriate.

[0045] The n-clad layer 13 is, for example, n-Al 0.04 Ga 0.96 The N layer has a thickness of 2 μm. The aluminum (Al) composition ratio is set so that the refractive index is smaller than that of the layer adjacent to the active layer 15 side (that is, the n-side guide layer 14).

[0046] The n-side guide layer 14 is composed of a lower guide layer 14A, a photonic crystal layer (PC layer) 14P which is an air-hole layer, and a buried layer 14B. As shown in FIG. 2B, the photonic crystal layer 14P has a layer thickness d PC The buried layer 14B has a thickness d EMB For example, the thickness d PC is 40 to 180 nm.

[0047] In this specification, photonic crystal layer 14P refers to the layer portion from the upper end to the lower end of the holes in n-side guide layer 14 (see FIG. 2B). PC is equal to the height of the hole.

[0048] Lower guide layer 14A is, for example, n-GaN with a layer thickness of 100 to 400 nm. Photonic crystal layer 14P is n-GaN with a layer thickness (or the depth of holes 14K) of 40 to 180 nm.

[0049] The buried layer 14B is made of n-GaN, n-InGaN, undoped GaN, or undoped InGaN. Alternatively, it may be a layer in which these semiconductor layers are stacked. The thickness d of the buried layer 14B is EMBThe thickness is, for example, 50 to 150 nm. The buried layer 14B is made up of a first buried layer 14B1 and a second buried layer 14B2.

[0050] The light distribution adjustment layer 23 formed on the buried layer 14B is an undoped In 0.03 Ga 0.97 It is an N layer, and the layer thickness is, for example, 50 nm.

[0051] The n-side semiconductor layer including the n-side guide layer 14 and the light distribution adjustment layer 23 is also referred to as a first semiconductor layer, but the light distribution adjustment layer 23 does not necessarily have to be provided.

[0052] The active layer 15, which is a light emitting layer, is, for example, a multiple quantum well (MQW) layer having two quantum well layers. The barrier layer and quantum well layer of the MQW are GaN (layer thickness 6.0 nm) and InGaN (layer thickness 4.0 nm), respectively. The central emission wavelength of the active layer 15 is 440 nm.

[0053] Active layer 15 is preferably disposed within 180 nm (ie, within the period PC of the holes) from photonic crystal layer 14P, in which case a high resonance effect is obtained by photonic crystal layer 14P.

[0054] The p-side guide layer 16 is an undoped In 0.02 Ga 0.98 It is composed of a p-side guide layer (1) 16A which is an N layer (layer thickness 70 nm) and a p-side guide layer (2) 16B which is an undoped GaN layer (layer thickness 180 nm).

[0055] The p-side guide layer 16 is an undoped layer in consideration of light absorption by dopants (Mg: magnesium, etc.), but may be doped to obtain good electrical conductivity. In addition, the In composition and layer thickness of the p-side guide layer (1) 16A can be appropriately selected to adjust the electric field distribution in the oscillation operation mode.

[0056] The electron barrier layer (EBL) 17 is a magnesium (Mg) doped p-type Al 0.2 Ga 0.8N layers, for example, having a layer thickness of 15 nm.

[0057] The p-cladding layer 18 is made of Mg-doped p-Al 0.06 Ga 0.94 The p-cladding layer 18 is an N layer having a thickness of, for example, 600 nm. The Al composition of the p-cladding layer 18 is preferably selected so that the refractive index is smaller than that of the p-side guide layer 16. The p-cladding layer 18 functions as a first p-cladding layer.

[0058] The p-contact layer 19 is a Mg-doped p-GaN layer having a thickness of, for example, 20 nm. The carrier density of the p-contact layer 19 is set to a concentration that allows ohmic junction with the transparent electrode 29, which is a transparent conductive layer provided on the surface of the p-contact layer 19. Instead of p-type GaN, p-type or undoped InGaN may be used. Alternatively, a layer in which a GaN layer and an InGaN layer are stacked may be used.

[0059] The layer consisting of the p-side guide layer 16, the electron barrier layer 17, the p-cladding layer 18 and the p-contact layer 19 is also referred to as a second semiconductor layer.

[0060] In this specification, "n-side" and "p-side" do not necessarily mean n-type and p-type. For example, the n-side guide layer means a guide layer provided on the n-side of the active layer, and may be an undoped layer (or an i-layer).

[0061] In addition, the n-cladding layer 13 may be composed of multiple layers instead of a single layer, and in that case, all layers do not need to be n layers (n-doped layers) and may include an undoped layer (i layer). The same applies to the guide layer 16 and the p-cladding layer 18.

[0062] Furthermore, it is not necessary to provide all of the semiconductor layers described above, and it is sufficient to have a configuration having a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and an active layer (light-emitting layer) sandwiched between these layers.

[0063] Furthermore, in this embodiment, a case has been described in which the photonic crystal layer 14P (hole layer) is provided in the first semiconductor layer (n-type semiconductor layer), but the photonic crystal layer may also be provided in the second semiconductor layer (p-type semiconductor layer).

[0064] A transparent electrode 29 (anode) is provided on the p-contact layer 19 and is in ohmic contact with the p-contact layer 19. The transparent electrode 29 functions not only as an electrode layer but also as a second p-clad layer.

[0065] The translucent electrode 29 has a circular shape with a diameter RA centered on the central axis CX of the semiconductor structure layer 11. Specifically, the translucent electrode 29 has a diameter of, for example, RA=300 μm in top view (i.e., when viewed from a direction perpendicular to the semiconductor structure layer 11).

[0066] The transparent electrode 29 is formed of a transparent conductor, for example, indium tin oxide (ITO). Note that the transparent electrode 29 is not limited to ITO, and other transparent conductors such as zinc tin oxide (ZTO), GZO (ZnO:Ga), and AZO (ZnO:Al) can be used.

[0067] On translucent electrode 29, an Ag / Au layer consisting of a silver (Ag) layer and a gold (Au) layer formed on the Ag layer is formed as p-electrode 20B (second electrode). That is, p-electrode 20B functions as a light reflecting layer, and the interface between translucent electrode 29 and the Ag layer of p-electrode 20B is reflecting surface SR. Reflecting surface SR is provided parallel to photonic crystal layer 14P.

[0068] The p-electrode 20B may be made of Pd, Al, an Al alloy, a dielectric DBR (Distributed Bragg Reflector), etc. A pad electrode or the like may be provided on the p-electrode 20B.

[0069] The side and upper surface of the semiconductor structure layer 11 and the side surfaces of the light-transmitting electrode 29 and the p-electrode 20B are covered with an insulating film 21 such as SiO2. The insulating film 21 is formed so as to climb up onto the p-electrode 20B and cover the edge of the upper surface of the p-electrode 20B.

[0070] The insulating film 21 also functions as a protective film, protecting the aluminum (Al)-containing crystal layer that constitutes the PCSEL element 10 from corrosive gases and the like. It also prevents short circuits caused by adhesions or solder creeping up during mounting, contributing to improved reliability and yield. The material for the insulating film 21 is not limited to SiO2, but may be ZrO2, HfO2, TiO2, Al2O3, SiNx, Si, or the like.

[0071] A circular cathode electrode 20A (first electrode) (see FIG. 3C) is formed on the back surface of the element substrate 12. In addition, an anti-reflection (AR) coating layer 27 is formed on the inner side of the cathode electrode 20A.

[0072] The cathode electrode 20A is made of Ti / Au and is in ohmic contact with the element substrate 12. In addition to Ti / Au, the electrode material may be selected from Ti / Al, Ti / Rh, Ti / Al / Pt / Au, Ti / Pt / Au, and the like.

[0073] The light emitted from active layer 15 is diffracted by photonic crystal layer (PC layer) 14P. Light diffracted by photonic crystal layer 14P and directly emitted from photonic crystal layer 14P (direct diffracted light Ld: first diffracted light) and light emitted by diffraction of photonic crystal layer 14P and reflected by light reflecting layer 32 (reflected diffracted light Lr: second diffracted light) are emitted to the outside from light emission region 20L ( FIG. 3C ) of rear surface (emission surface) 12R of element substrate 12.

[0074] Fig. 3A is a plan view diagrammatically illustrating the upper surface of the PCSEL device 10. Fig. 3B is a cross-sectional view diagrammatically illustrating the cross section of the photonic crystal layer 14P in a plane parallel to the n-side guide layer 14, and Fig. 3C is a plan view diagrammatically illustrating the lower surface of the PCSEL device 10.

[0075] As shown in FIG. 3B, in photonic crystal layer 14P, holes 14K are provided, for example, in a rectangular hole formation region 14R, and are arranged periodically.

[0076] As shown in FIG. 3C, the anode region RA is formed so as to be contained within the hole-forming region 14R.

[0077] Cathode electrode 20A is provided as a ring-shaped electrode on the outside of p-electrode 20B so as not to overlap p-electrode 20B when viewed from a direction perpendicular to photonic crystal layer 14P.

[0078] The region inside the cathode electrode 20A is the light emission region 20L. Also provided is a bonding pad 20C that is electrically connected to the cathode electrode 20 and for connecting a wire for power supply from the outside.

[0079] (Photonic crystal layer structure) 4 is a schematic diagram showing a cross section perpendicular to the crystal layer of the formed photonic crystal layer 14P. Photonic crystal layer 14P of this embodiment is a double lattice photonic crystal layer in which hole pairs 14K, each consisting of a main hole 14K1 and a sub-hole 14K2, are arranged at each of the square lattice points. When there is no particular distinction between main hole 14K1 and sub-hole 14K2, they may be collectively referred to as hole 14K.

[0080] More specifically, the main holes 14K1 have their centers of gravity CD1 arranged in a square lattice pattern with a period PC in two mutually perpendicular directions (x direction and y direction). Similarly, the sub-holes 14K2 have their centers of gravity CD2 arranged in a square lattice pattern with a hole period PC in the x direction and y direction.

[0081] The major axes of the main void 14K1 and the sub-void 14K2 are parallel to the <11-20> crystal orientation, and the minor axes of the main void 14K1 and the sub-void 14K2 are parallel to the <1-100> crystal orientation.

[0082] The center of gravity CD2 of the subhole 14K2 is spaced apart from the center of gravity CD1 of the main hole 14K1 by Δx and Δy (Δx=Δy here). That is, the center of gravity CD2 of the subhole 14K2 is spaced apart from the center of gravity CD1 of the main hole 14K1 in the <1-100> direction.

[0083] Specifically, the period P c =176.8 nm, and the distances Δx, Δy between the centers of gravity of the main hole 14K1 and the subhole 14K2 are set to Δx=Δy=0.46 P c .

[0084] FIG. 5A is a surface SEM (Scanning Electron Microscope) image showing main hole 14H1 and sub-hole 14H2 dug in a GaN layer (n-side guide layer 14) when forming photonic crystal layer 14P.

[0085] The main hole 14H1 and the sub-hole 14H2 have an elongated cylindrical shape with a central axis perpendicular to the crystal layer. When there is no need to distinguish between the main hole 14H1 and the sub-hole 14H2, they may be collectively referred to as the hole 14H.

[0086] The main hole 14H1 and the sub-hole 14H2 are filled and blocked by mass transport to form a first buried layer 14B1, and then filled with a second buried layer 14B2 to form a main hole 14K1 and a sub-hole 14K2.

[0087] 5B is a diagram showing a surface SEM image of the formed main void 14K1 and sub-void 14K2. When filling the hole 14H in the group III nitride, the shape of the hole 14H is deformed by mass transport into a shape composed of thermally stable surfaces, and the void 14K is formed.

[0088] That is, in the +c-plane substrate, the inner side surface of the hole 14H changes shape to a (1-100) plane (i.e., an m-plane), that is, changes shape from an oval cylindrical shape to an oval hexagonal prism-shaped hole 14K whose side surface is formed of an m-plane.

[0089] The formed primary void 14K1 had a long hexagonal prism shape with a long diameter of 72.5 nm, a short diameter of 43.5 nm, and a long diameter / short diameter ratio of 1.67. The secondary void 14K2 had a long diameter of 44.6 nm, a short diameter of 38.3 nm, and a long diameter / short diameter ratio of 1.16, and had a long hexagonal prism shape closer to a regular hexagonal prism than the primary void 14K1.

[0090] It was also confirmed that the distances Δx and Δy between the centers of gravity of the main hole 14K1 and the subhole 14K2 were 81.6 nm (Δx=Δy=0.46PC), which was unchanged from before filling. It was also confirmed that the major axes of the main hole 14K1 and the subhole 14K2 were parallel to the <11-20> axis (i.e., the a-axis).

[0091] Furthermore, the hole filling factors FF1 and FF2 of the main holes 14K1 and the sub-holes 14K2 were calculated to be FF1 = 8.8% and FF2 = 4.2%. Here, the hole filling factor is the ratio of the area occupied by each hole per unit area in a two-dimensional regular array. Specifically, when the areas of the main holes 14K1 and the sub-holes 14K2 in the photonic crystal layer 14P are S1 and S2, respectively, the hole filling factors FF1 and FF2 of the main holes 14K1 and the sub-holes 14K2 are given by the following equations.

[0092] FF1=S1 / PC 2 , FF2=S2 / PC 2

[0093] (Distance between diffractive and reflective surfaces) In the PCSEL device 10 of this embodiment, the distance dr from the diffractive surface WS to the reflective surface SR is adjusted (see FIG. 2A ), thereby controlling the interference between the direct diffracted light Ld that is directly emitted from the diffractive surface WS and the reflected diffracted light Lr that is diffracted in the +z direction and reflected by the reflective surface SR and emitted, thereby suppressing loss due to diffraction in the direction perpendicular to the photonic crystal layer 14P.

[0094] For example, from Non-Patent Document 1, the position of the diffraction surface WS (or the wave source), which is the diffraction position of the diffracted wave by the photonic crystal layer 14P, and the radiated wave that is diffracted and radiated in the vertical direction of the photonic crystal layer 14P can be calculated using the coupled wave theory. Therefore, the position of the diffraction surface WS can be used to calculate the separation distance dr between the diffraction surface WS and the reflection surface SR.

[0095] The position of the diffraction plane WS in the photonic crystal layer 14P in the PCSEL device 10 of this embodiment was estimated using the technique described in Non-Patent Document 1. That is, the diffraction plane WS was estimated to be located about 7 nm closer to the active layer 15 than the center of the photonic crystal layer 14P.

[0096] When the phase difference between the first diffracted light (direct diffracted light Ld) diffracted by the diffractive surface WS and the second diffracted light (reflected diffracted light Lr) diffracted by the diffractive surface WS and reflected by the reflecting surface SR is θ (deg), the wavelength of the first diffracted light is λ, the average refractive index of the crystal layer from the diffractive surface WS to the reflecting surface SR is nave, and m is an integer greater than or equal to 0, the separation distance dr is expressed by the following equation (1).

number

[0097] Moreover, when the phase difference θ satisfies the following formula (2), the light intensity of the interference light between the direct diffracted light Ld and the reflected diffracted light Lr becomes smaller than the light intensity of the direct diffracted light Ld.

number

[0098] In other words, the emitted light is weakened by the interference between the direct diffracted light Ld and the reflected diffracted light Lr, and the radiation loss (loss in the vertical direction) is reduced.

[0099] In order to prevent interference (mutual weakening) from occurring inside the photonic crystal layer 14P, the photonic crystal layer 14P has a thickness (d PC) is preferably used.

[0100] Therefore, a two-dimensional photonic crystal surface-emitting laser device (PCSEL device) that can be driven with a low current can be obtained.

[0101] (Arrangement of main and sub-holes in double lattice structure) 6 is a cross-sectional view showing a cross section of the main hole 14K1 and the sub-hole 14K2 in the depth direction of the double lattice structure. Here, the hole height (depth) of the main hole 14K1 and the sub-hole 14K2 is different. That is, the height of the main hole 14K1 is h K1 and is equal to the thickness of the photonic crystal layer 14P (h K1 =d PC ) The height of the subvoid 14K2 is h K2 It is.

[0102] More specifically, the lower end of the main hole 14K1 is located deeper than the lower end of the sub-hole 14K2, i.e., in the -z direction. The difference between the lower ends of the main hole 14K1 and the sub-hole 14K2 is h DOWN The upper end of the sub-hole 14K2 is deeper than the upper end of the main hole 14K1, and the difference is h UP It is.

[0103] Here, the difference in the upper end h UP is the difference between the lower ends h DOWN is smaller than the center C of the subvoid 14K2 in the depth direction (-z direction). PC (=C K2 ) is the center C of the main hole 14K1 K1 It is located closer to the active layer 15 than the other.

[0104] In a nitride-based PCSEL element, when holes of different sizes are simultaneously formed by a method such as dry etching and then filled to form main holes 14K1 and sub-holes 14K2, the main holes 14K1 and sub-holes 14K2 have a hexagonal columnar structure with m-plane sides, and therefore the size relationship between the main holes 14K1 and sub-holes 14K2 at any z-direction position in the photonic crystal layer 14P is the same as the size relationship between the holes before filling.

[0105] In photonic crystal layer 14P of the nitride-based PCSEL device, the lower ends of main holes 14K1, which have a large hole filling factor FF, are located closer to the lower end of photonic crystal layer 14P than subholes 14K2, i.e., main holes 14K1 are deeper than subholes 14K2. Also, by burying growth, the upper ends of subholes 14K2 are formed deeper than the upper ends of main holes 14K1.

[0106] Furthermore, when the active layer 15 is formed after the photonic crystal layer 14P is formed, i.e., when the photonic crystal layer 14P is provided on the -z direction side of the active layer 15, the relationship FF1>FF2 is always satisfied. That is, in a nitride-based PCSEL device, even in the case of a double lattice structure, the wave source (diffraction plane) WS is always located at the center C in the z direction of the photonic crystal layer 14P. PC (that is, it is present at a position away from the center of the main hole 14K1) on the active layer 15 side, for example, about 1 to 10 nm.

[0107] Therefore, in the depth direction (−z direction), there is a region (h UP and h DOWN ) and the region where both the main void 14K1 and the sub-void 14K2 exist (h K2 However, the propagating light component diffracted in the vertical direction is larger in the region where both the main air holes 14K1 and the sub-air holes 14K2 exist. PC It is located at a position shifted further in the +z direction (towards the active layer 15) than the above.

[0108] In the above, the hole shape is a hexagonal column shape and the cross-sectional area does not change in the depth direction. When either the main hole 14K1 or the subhole 14K2 has a shape in which the cross-sectional area changes in the depth direction, it is preferable that the center of gravity of the subhole 14K2 is located closer to the active layer 15 than the center of gravity of the main hole 14K1.

[0109] 2. Operating Characteristics (1) Example 1 To evaluate the effect that mounting on mounting board 32 has on the laser characteristics, the current-output characteristics of PCSEL device 10 were measured before and after mounting. To eliminate thermal effects during evaluation, the characteristics were evaluated by pulse driving with a pulse width of 100 ns and a repetition frequency of 1 kHz (i.e., a duty of 0.01%). In both cases, the evaluation was performed at room temperature. That is, in evaluating the current-output characteristics, PCSEL device 10 was driven under pulse conditions that had no or negligible thermal effects.

[0110] The current-output characteristics of the PCSEL element 10 before and after mounting in the surface-emitting laser device 5 of Example 1 (EMB1) having the above-described structure are shown in Fig. 7. As shown in Fig. 7, in this example, there was no increase in the threshold current of the PCSEL element 10 due to mounting on the mounting substrate 32, and no change was observed in the current-output characteristics, indicating that there was no degradation of the characteristics.

[0111] 8 shows the oscillation spectra before and after mounting when a current of 3.0 A was applied to the PCSEL element 10 in the surface-emitting laser device of Example 1. The oscillation wavelength λ was 436.24 nm before mounting and 436.32 nm after mounting.

[0112] Here, the oscillation wavelength λ is expressed as m, an integer of 1 or more, and the effective refractive index is n eff Then, it is given by the following equation (3).

[0113] λ=m×n eff ×PC (3) Considering that the duty is an extremely small pulse drive and that there is no thermal effect, the effective refractive index n eff Therefore, it can be seen from equation (3) that the amount of change in the oscillation wavelength λ before and after mounting is proportional to the amount of change in the hole period PC of the photonic crystal layer.

[0114] In this embodiment, since the oscillation wavelength λ becomes longer before and after mounting, it is believed that the hole period PC becomes larger and that mounting applies tensile strain to the PCSEL device 10. The amount of strain ε is given by the following equation (4).

[0115] ε=ΔPC / PC=Δλ / λ (4) The amount of distortion ε in this example was calculated to be ε=0.0018%.

[0116] 9A is a diagram showing the photonic band of a PCSEL device. A PCSEL device lases by utilizing the effect of zero group velocity at the Γ point of the photonic band (i.e., the resonance effect).

[0117] In the case of a square lattice photonic crystal, there are four oscillation modes (A, B, C, and D from the low frequency side) at the Γ point, and the laser oscillates in one of these modes. Each mode can be evaluated by measuring the spectrum at the Γ point before oscillation, that is, the emission spectrum in the direction perpendicular to the substrate (normal direction).

[0118] 9B shows the Γ-point spectrum before oscillation (lower row) and the spectrum immediately after oscillation (upper row). That is, by comparing the Γ-point spectrum before oscillation with the spectrum after laser oscillation, it is possible to know in which mode the PCSEL element is oscillating. In this embodiment, oscillation occurs in mode B. Note that modes C and D are degenerate in the spectrum before oscillation.

[0119] 10A and 10B show the beam emission patterns (FFP: Far Field Pattern) before and after mounting the PCSEL element 10 in the surface emitting laser device of Example 1 when a current of 3.0 A is applied to the PCSEL element 10. FIG.

[0120] By measuring the spectrum before and after oscillation, we obtained information about the spectrum in Figure 9B, which shows that oscillation occurs in the band-edge B mode both before and after mounting. A difference is seen in the appearance level of the higher-order mode of the band-edge B mode before and after mounting, which is thought to be due to the effect of distortion induced in the PCSEL element by mounting.

[0121] (2) Comparative Example 1 The surface-emitting laser device of Comparative Example 1 (CMP1) differs from the surface-emitting laser device 5 of Example 1 described above in the following points, but is otherwise the same as Example 1.

[0122] In the surface-emitting laser device of Comparative Example 1, a fluxless gold-tin alloy (AuSn) was used as the element bonding material instead of the element bonding material 31 of Example 1. The melting point of the gold-tin alloy (AuSn) is approximately 280°C, and a temperature higher than this must be applied in order to sinter-mount the device.

[0123] Specifically, after the element bonding material (AuSn) is applied to the mounting substrate 32, the mounting substrate 32 is heated to 340° C., and the surface emitting laser element is bonded to the mounting substrate 32 at a temperature of about 1.5 kfg / cm 2 . 2 The load was maintained for 10 seconds and then immediately cooled.

[0124] The surface-emitting laser element (PCSEL element) was the same as the PCSEL element 10 in the surface-emitting laser device of Example 1 described above, except that the hole period PC of the photonic crystal layer 14P was 177.5 nm.

[0125] (Characteristics evaluation) In order to evaluate the influence of mounting on a mounting board using an element bonding material (AuSn) on the laser characteristics, the current-output characteristics of the surface-emitting laser element were measured before and after mounting. As in Example 1, in order to eliminate the thermal influence during evaluation, the characteristics were evaluated by pulse driving with a pulse width of 100 ns and a repetition frequency of 1 kHz (i.e., a duty of 0.01%). In both cases, the evaluation was performed at room temperature.

[0126] 11 shows the current-output characteristics before and after mounting the PCSEL element 10 in the surface-emitting laser device of Comparative Example 1 (CMP1) having the above-mentioned structure. In Comparative Example 1, the current-output characteristics before mounting were almost the same as those of the surface-emitting laser device 5 of Example 1. However, after mounting, the threshold current increased, the slope efficiency decreased, and the current-output characteristics were significantly deteriorated.

[0127] 12 shows the oscillation spectra before and after mounting when a current of 3.0 A was applied to the PCSEL element in the surface-emitting laser device of Comparative Example 1. As described above, the oscillation wavelength λ of Example 1 was 436.24 nm before mounting and 436.32 nm after mounting.

[0128] In contrast, the oscillation wavelength λ of Comparative Example 1 was 438.48 nm before mounting and 438.83 nm after mounting. The strain amount ε estimated from formula (4) was 0.079%. In other words, it was found that a large stress (tensile strain) was applied to the PCSEL element compared to Example 1.

[0129] 13A and 13B show the beam emission patterns (FFP) before and after mounting when a current of 3.0 A is applied to the PCSEL element in the surface-emitting laser device of Comparative Example 1. From this FFP, it can be seen that before mounting, the oscillation was in the band edge B mode, whereas after mounting, the oscillation changed to the flat band mode. Here, the flat band mode is a mode extending in the Γ-X direction from the mode B of the photonic band shown in FIG. 9A, and refers to an unintended oscillation mode in which laser oscillation occurs from a region other than the Γ point.

[0130] 12, it is considered that the distortion amount ε is large in the surface-emitting laser device of Comparative Example 1, which weakens the two-dimensional optical resonance effect in the photonic crystal layer and causes the flat band mode, which is a one-dimensional oscillation mode, to appear. Oscillation in the flat band mode is not preferable even for applications requiring high light focusing, because the beam quality is significantly deteriorated.

[0131] (3) Example 2 In the surface-emitting laser device 5 of Example 2 (EMB2), a graphite laminate was used as the base material 32A of the mounting substrate 32 (submount). A gold-tin alloy (AuSn) was used for the element bonding member 34 (same as in Comparative Example 1). The other points were the same as those of Example 1.

[0132] 14 is a diagram showing a substrate 32A which is a graphite laminated plate. The substrate 32A is a graphite laminated plate having a three-layer structure formed by laminating three graphite plates GL1, GL2, and GL3 in this order.

[0133] The graphite plate GL1 has a thermal conductivity of 7 W / mK in one direction (x direction) within the plane, and a thermal conductivity of 1700 W / mK in directions perpendicular to the x direction (y direction and z direction). In other words, the graphite plate GL1 is a heat-conducting plate with high thermal conductivity in a specific direction and high anisotropy of thermal conductivity. Specifically, any material may be used as long as it has high thermal conductivity in the a- and b-axis directions (y direction and z direction) relative to the c-axis direction (x direction) in the graphite crystal lattice, and for example, boron nitride (BN) may be used.

[0134] Graphite plates GL2 and GL3 are the same thermally conductive plates as graphite plate GL1, but graphite plate GL2 is rotated 90 degrees and graphite plate GL3 is stacked in the same orientation as graphite plate GL1 (FIG. 14, right side).

[0135] The substrate 32A, which is a graphite laminate, is an isotropic heat diffusion material having high thermal conductivity, and has a thermal conductivity comparable to that of diamond.

[0136] Although the graphite laminate has been described as having a three-layer structure, the present invention is not limited to this. It is preferable that a plurality of graphite plates are laminated in different directions according to the in-plane anisotropy of the thermal conductivity.

[0137] 15 is a graph showing the current-output characteristics before and after mounting the PCSEL element 10 in the surface-emitting laser device 5 of Example 2 (EMB2). Note that, like Example 1 and Comparative Example 1, the characteristics were evaluated by pulse driving with a pulse width of 100 ns and a repetition frequency of 1 kHz (duty cycle of 0.01%).

[0138] Even in Example 2, in which a gold-tin alloy (AuSn) was used as the bonding material, there was no increase in the threshold current of the PCSEL device 10 due to mounting on the mounting substrate 32, and no change was observed in the current-output characteristics, indicating that there was no degradation of the characteristics. Therefore, by also using the device bonding member 31, which relieves the stress applied to the PCSEL device 10, it is possible to significantly suppress degradation of the characteristics of the PCSEL device 10, particularly during CW operation.

[0139] Fig. 16 shows the oscillation spectra before and after mounting when a current of 3.0 A is applied to the PCSEL element 10 in the surface-emitting laser device 5 of Example 2. Fig. 17A and Fig. 17B show the beam emission patterns (FFP) before and after mounting when a current of 3.0 A is applied to the PCSEL element 10.

[0140] From the spectra and beam emission pattern FFP before and after oscillation, it was confirmed that oscillation occurred in the band edge B mode both before and after mounting.

[0141] 3. Theoretical analysis and considerations (Changes in threshold current and oscillation mode with respect to strain) In order to estimate the amount of distortion that does not deteriorate the laser characteristics, multiple samples were fabricated and elements were mounted. Figures 18A, 18B, and 18C show the base material and bonding conditions of the mounting substrate of the surface-emitting laser device in Example 1 (EMB1), Example 2 (EMB2), and Comparative Example 1 (CMP1), and the oscillation characteristics before and after mounting the PCSEL element.

[0142] The mounting temperature (bonding temperature) is Tm, the oscillation wavelengths before and after mounting are λ1 and λ2, the oscillation thresholds before and after mounting are Ith1 and Ith2, and the oscillation modes before and after mounting are OM1 and OM2. In the oscillation modes OM1 and OM2 in Figures 18A to 18C, B represents the oscillation mode B, and Flat represents the flat band mode.

[0143] FIG. 19 shows the physical properties of the materials used in Examples 1 and 2 and Comparative Example 1. The three-layer graphite is based on the technical documentation of Thermographics, and the Ag nanoparticles are based on the technical documentation of Nihon Handa's "MAX102." Since there are no thermal property values ​​for the Au nanoparticles, the thermal property values ​​of Au were used. The element bonding material (Nano Ag) in Example 1 was a submicron Au nanoparticle bonding material (AuRoFUSE, manufactured by Tanaka Kikinzoku). Since the bonding material made of nanoparticles is porous, the Young's modulus of the submicron Au nanoparticle bonding material is smaller than that of Au.

[0144] 20 shows a graph plotting the rate of change in threshold current versus the strain ε applied to the PCSEL element by mounting on a mounting substrate (base material). Here, the strain ε was estimated from the change in the oscillation wavelength λ before and after mounting (ε = ΔPC / PC = Δλ / λ: Equation (4)).

[0145] In detail, plots are shown for the case where the substrate 32A of the mounting substrate 32 is diamond and the element bonding member 34 is Au nanoparticles (Example 1), the case where the substrate 32A is diamond and the element bonding member 34 is Ag nanoparticles (Example 1), the case where the substrate 32A is a graphite laminate and the element bonding member 34 is AuSn (Example 2), and the case where the substrate of the mounting substrate is diamond and the element bonding member is AuSn (Comparative Example 1).

[0146] 20, it can be seen that when the strain ε in the PCSEL element exceeds 0.04%, the threshold current increases. This is believed to be because the tensile stress generated in the PCSEL element changes the lattice constant (hole period PC) of the photonic crystal layer, resulting in an increase in cavity loss.

[0147] Furthermore, when the strain ε exceeds 0.05%, the oscillation mode changes from the band edge mode (band B) to the flat band mode. This is thought to be because the application of a strong tensile stress to the photonic crystal layer weakens the two-dimensional coupling of light propagating through the photonic crystal layer, and resonance via linear coupling becomes the main oscillation mode.

[0148] When the strain ε is increased from 0.05%, the threshold current also increases in the flat band mode, and the beam quality, i.e., the focusing ability of the beam, is significantly deteriorated in the flat band mode.

[0149] Considering both positive and negative strain ε (tensile strain and compressive strain), the strain ε is preferably within 0.05%, more preferably within 0.04%, and more preferably within 0.03% when considering the variation in threshold current (FIG. 20).

[0150] (Stress applied to PCSEL element) FIG. 21 shows the stress σ applied to GaN (ie, the base material or device substrate of the PCSEL device) during mounting on a mounting substrate when GaN, diamond, and three-layer graphite are used as the base material for the mounting substrate.

[0151] The stress σ applied to GaN is given by the following formula (5) using the physical property values ​​shown in FIG.

number

[0152] Here, the thermal expansion coefficients of GaN and the substrate are αa and αb, the Young's moduli are Ea and Eb, and the thicknesses are ta and tb, respectively.

[0153] As shown in FIG. 20, if the stress during mounting is 100 MPa or less, mounting can be performed without increasing the oscillation threshold value. (Diffraction and distortion of the photonic crystal layer) In a two-dimensional photonic crystal surface-emitting laser (PCSEL), the resonant action is achieved by utilizing the effect that the group velocity becomes zero at the Γ point of the two-dimensional photonic crystal. In other words, the resonator of a two-dimensional PCSEL is a two-dimensional photonic crystal layer. Light diffracted by the photonic crystal to the outside of the resonator is always diffracted in a direction perpendicular to the photonic crystal layer.

[0154] As described above, the distortion in the photonic crystal layer (hole layer) changes the hole period and also the position of the diffraction plane WS, thereby inhibiting the interference between the direct diffracted light Ld and the reflected diffracted light Lr. Therefore, it is important to keep the distortion amount ε to an extremely small value.

[0155] The photonic crystal layer 14P has a double lattice structure in which a hole set including a main hole and a subhole having a size (including the hole diameter) and a depth smaller than those of the main hole is arranged at a lattice point. The center of gravity of the subhole in the depth direction of the photonic crystal layer 14P is located closer to the active layer than the center of gravity of the main hole.

[0156] The strain in the photonic crystal layer (hole layer) changes the hole period, but the spacing between the main hole and the subhole (the distance between the centers of gravity Δx, Δy) also changes due to the strain, so the effect on the threshold current and the oscillation mode is also large. Therefore, the effect of suppressing the strain amount ε is greater than that in the case of a single lattice.

[0157] As described above in detail, according to the present invention, it is possible to provide a photonic crystal surface emitting laser device in which increases in the oscillation threshold current and drive current of the mounted PCSEL element are suppressed, the oscillation mode is stable, and the beam quality is excellent.

[0158] The numerical values ​​in the above-described embodiments are merely examples and may be modified as appropriate. In addition, although a double-lattice PCSEL element has been illustrated, the present invention can be applied to a single-lattice PCSEL element and generally to a multiple-lattice PCSEL element.

[0159] Furthermore, although the present invention has been exemplified with respect to a photonic crystal layer in which the holes have a hexagonal columnar shape, the present invention can also be applied to photonic crystal layers in which the holes have an irregular columnar shape, such as a cylindrical, rectangular, polygonal, or teardrop shape.

[0160] In this embodiment, one PCSEL element 10 is mounted on one mounting substrate 32, but a plurality of PCSEL elements 10 can be mounted on one mounting substrate 32 according to the present invention. For example, a plurality of PCSRL elements 10 can be arranged in a 3×3 matrix and mounted on one mounting substrate. Also, a single PCSEL element mounted on a single mounting substrate 32 can be arranged in a matrix and used as one emitter.

[0161] A diamond substrate or a graphite laminate was used as the mounting substrate 32, but a composite substrate in which the a- and b-axes of the graphite crystal lattice are arranged vertically or inclined on the surface of the diamond substrate on which the elements are mounted can also be used. [Explanation of symbols]

[0162] 5: Surface emitting laser device 10: PCSEL element, 12: Element substrate 13: First cladding layer 14: First guide layer 14A: Lower guide layer 14B: Buried layer 14K: Hole / hole pair 14K1 / 14K2: Main / secondary hole 14P: Photonic crystal layer (hole layer) 15:Active layer 16: Second guide layer 17: Electron barrier layer 18: Second cladding layer 19: Contact layer 20A: First electrode 20B: Second electrode 20L: Light output area 27: Anti-reflection film 29: Transparent conductor layer 31: Element bonding material 32: Mounting board 33: Wiring electrode (coating layer) 34: Substrate bonding material 35: Heat sink 38: Housing CD1,CD2: Center of gravity dr: separation distance Ld: Direct diffraction light Lr: Reflected and diffracted light SR: Reflective surface

Claims

1. a surface-emitting laser element; a mounting substrate on which the surface-emitting laser element is mounted and which is electrically connected to the surface-emitting laser element; an element bonding member made of a conductive bonding material that bonds the surface-emitting laser element and the mounting substrate and relieves distortion of the surface-emitting laser element caused by the mounting substrate, The surface-emitting laser element is a light-transmitting element substrate; a first semiconductor layer provided on the element substrate; an active layer provided on the first semiconductor layer; a second semiconductor layer provided on the active layer and having an opposite conductivity type to that of the first semiconductor layer; a transparent conductor provided on the second semiconductor layer; a hole layer that is a photonic crystal layer included in the first semiconductor layer or the second semiconductor layer and has holes that are arranged with two-dimensional periodicity in a plane parallel to the active layer; a light reflective layer provided on the second semiconductor layer and having a reflective surface, the first semiconductor layer, the active layer, and the second semiconductor layer are Group III nitride-based semiconductor layers; a surface-emitting laser device having a light-emitting surface on the surface of the element substrate opposite to the surface on which the first semiconductor layer is provided;

2. The hole period of the hole layer of the surface-emitting laser element is PC ２ The hole period of the hole layer before the surface-emitting laser element is bonded to the mounting substrate by the element bonding member is PC １ When this is the case, the change in the hole period ΔPC = PC ２ -PC １ 2. The surface-emitting laser device according to claim 1, wherein the difference is within 0.04%.

3. 2. The surface-emitting laser device according to claim 1, wherein a thermal stress σ acting between the surface-emitting element and the mounting substrate satisfies σ≦100 (MPa).

4. 2. The surface-emitting laser device according to claim 1, wherein the mounting substrate has a base material and a conductive layer provided on the base material, the base material being diamond, and the element bonding material including metal nanoparticles.

5. 2. The surface-emitting laser device according to claim 1, wherein the mounting substrate has a base material and a conductive layer provided on the base material, and the base material is a graphite laminate.

6. 6. The surface-emitting laser device according to claim 5, wherein the graphite laminate is a graphite laminate in which a plurality of graphite plates are laminated in different directions according to in-plane anisotropy of thermal conductivity.

7. the hole layer has a diffraction surface that diffracts light standing in the hole layer in a direction perpendicular to the hole layer; The phase difference between the first diffracted light diffracted by the diffracting surface and the second diffracted light diffracted by the diffracting surface and reflected by the reflecting surface is defined as θ (deg), the wavelength of the first diffracted light is defined as λ, and the average refractive index of the crystal layer from the diffracting surface to the reflecting surface is defined as n ａｖｅ , where m is an integer equal to or greater than 0, the separation distance dr between the diffractive surface and the reflecting surface is expressed by the following formula: [Equation 1] The phase difference θ is [Equation 2] 2. The surface-emitting laser device according to claim 1, wherein the following is satisfied:

8. 2. The surface-emitting laser device according to claim 1, wherein the hole layer has a multi-lattice structure in which a hole set including a main hole and a sub-hole having a size and depth smaller than that of the main hole is arranged at each lattice point.

9. 9. The surface-emitting laser device according to claim 1, wherein the hole layer has a thickness such that the optical path length of the hole layer is less than one wavelength.

10. the hole layer has a multi-lattice structure in which a hole set including a main hole and a sub-hole having a size and a depth smaller than those of the main hole is arranged at each lattice point, 9. The surface-emitting laser device according to claim 1, wherein the center of gravity of the sub-holes in the depth direction of the hole layer is closer to the active layer than the center of gravity of the main hole.

11. A surface-emitting laser device as described in claim 1, wherein when the hole period of the hole layer of the surface-emitting laser element is PC 2 and the hole period of the hole layer before the surface-emitting laser element is joined to the mounting substrate by the element joining member is PC 1, the change in the hole period ΔPC = PC 2 - PC 1 is 0.02% or more and 0.05% or less.

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