Surface-emitting laser device

Abstract

The present invention comprises a surface-emitting laser element, a mounting board onto which the surface-emitting laser element is bonded by means of an element bonding member, and a stress adjustment member provided between the element bonding member and the mounting board. The surface-emitting laser element has a translucent 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, a vacancy layer with vacancies which is included in the first semiconductor layer or the second semiconductor layer and which is disposed to have two-dimensional periodicity in a plane parallel to the active layer, a first electrode electrically connected to the first semiconductor layer, and a second electrode provided in ohmic contact with the second semiconductor layer and having a light-reflecting surface.

Description

Surface-emitting laser device

[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.

[0002] 2. Description of the Related Art In recent years, development of a photonic-crystal surface-emitting laser using a photonic crystal (PC) has been progressing.

[0003] In order to obtain a high resonance effect in a photonic crystal surface-emitting laser, it is necessary to enhance the diffraction effect in the photonic crystal layer, and to enhance the diffraction effect, it is necessary for the two-dimensional refractive index period in the photonic crystal to be uniform.

[0004] For example, Patent Document 1 discloses a surface-emitting laser having a photonic crystal with a uniform refractive index period and a high diffraction effect.

[0005] Patent No. 7101370

[0006] However, when a photonic crystal surface-emitting laser element is mounted on a circuit board or a heat sink, stress and distortion occur in the photonic crystal surface-emitting laser element, which increases the oscillation threshold current, reduces the light-emitting efficiency, and causes the oscillation mode to become unstable.

[0007] 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.

[0008] The present invention aims 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, which has a stable oscillation mode and excellent beam quality.

[0009] a mounting substrate to which the surface-emitting laser element is bonded with an element bonding member and electrically connected to the surface-emitting laser element; and a stress adjusting member which is a conductive layer provided between the element bonding member and the mounting substrate, wherein the surface-emitting laser element comprises: 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 hole layer which is included in the first semiconductor layer or the second semiconductor layer and is a photonic crystal layer having holes arranged with two-dimensional periodicity in a plane parallel to the active layer; a first electrode electrically connected to the first semiconductor layer; and a second electrode provided on the second semiconductor layer in ohmic contact with the second semiconductor layer and having a light reflecting surface.

[0010] 1 is a cross-sectional view showing a cross section of a surface-emitting laser device of a first embodiment; FIG. 2 is a cross-sectional view showing a schematic example of the structure of a photonic crystal surface-emitting laser element (PCSEL element) of the surface-emitting laser device of this embodiment; FIG. 3 is a plan view showing a schematic top surface of the PCSEL element shown in FIG. 2; FIG. 4 is a cross-sectional view showing a schematic cross section of a plane parallel to an n-side guide layer of a photonic crystal layer; and FIG. 5 is a plan view showing a schematic bottom surface of a PCSEL element. center <ε edge 1 is a diagram showing the photonic bands at ε of a PCSEL element. center >ε edge FIG. 1 is a diagram showing the photonic band in . FIG. 2 is a diagram showing the calculation results for the dependency of strain distribution on the thickness of the bonding material. center , the strain at the edge (periphery) is ε edge The difference in strain relative to the thickness of the bonded material when center -ε edge1 is a diagram showing a comparison of the IL characteristics before and after mounting (before and after bonding) of a PCSEL element in a surface-emitting laser device of the present embodiment. FIG. 2 is a diagram showing an example of a comparison of the IL characteristics before and after mounting of a PCSEL element in a surface-emitting laser device of a comparative example (CMP). FIG. 3 is a diagram showing a comparison of the IL characteristics before and after mounting when the film thickness FT of the stress adjusting member is 7 μm. FIG. 4 is a diagram showing a comparison of the IL characteristics before and after mounting when the film thickness FT of the stress adjusting member is 9 μm.

[0011] In the following, preferred embodiments of the present invention will be described, but these 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.

[0012] 1 is a cross-sectional view showing a cross section of a surface-emitting laser device 5 according to this embodiment. The surface-emitting laser device 5 includes a photonic-crystal surface-emitting laser (PCSEL) element 10, an element bonding member 31, a stress adjusting member 32, a mounting substrate 33, a substrate bonding member 34, a heat sink 35, and a housing 38.

[0013] The photonic crystal surface-emitting laser element (hereinafter also referred to as a PCSEL element) 10 has a photonic crystal layer 14P therein. The PCSEL element 10 also has an n-electrode 25K (first electrode) and a p-electrode 25A (second electrode).

[0014] The PCSEL device 10 is mounted on a mounting substrate 33 (submount) by being bonded to a stress adjusting member 32 by an element bonding member 31. More specifically, the p-electrode 25A of the PCSEL device 10 is bonded to the stress adjusting member 32, which is a conductive layer on the mounting substrate 33, by the element bonding member 31, and is electrically connected. That is, the PCSEL device 10 is bonded junction-down to the mounting substrate 33. Note that, in the following, a case will be described in which the mounting substrate 33 is a so-called submount made of a uniform material. However, it may also be a substrate in which multiple materials are laminated, or a mixed substrate in which multiple materials are mixed. However, it is preferable that the substrate be made of a material in which the thermal expansion coefficient and elastic modulus (Young's modulus) are not anisotropic in-plane.

[0015] The mounting substrate 33 is joined to a heat sink 35 by a substrate joining member 34. The stress adjusting member 32 is electrically connected to an anode terminal 37A (bonding pad) on the conductive heat sink 35 by a bonding wire W2.

[0016] In this embodiment, the heat sink 35 is a conductor (e.g., Cu or Al) and functions as an anode electrode of the surface-emitting laser device 5. However, the connection configuration is not limited to this. For example, the mounting substrate 33 may be configured to be connected to the anode terminal 37A of the surface-emitting laser device 5.

[0017] Furthermore, the n-electrode 25K of the PCSEL element 10 is electrically connected by a bonding wire W1 to a cathode terminal 37K (first terminal) of the surface-emitting laser device 5. Therefore, when a voltage is applied between the anode terminal 37A and the cathode terminal 37K, the PCSEL element 10 emits light.

[0018] The above-mentioned components are housed in a housing 38 to form the surface-emitting laser device 5. The emitted light LE emitted from the rear surface of the element substrate 12 of the PCSEL element 10 is radiated to the outside through a window in the housing 38. The housing 38 can have various shapes.

[0019] 2. Structure of Photonic Crystal Surface-Emitting Laser Element A photonic crystal surface-emitting laser element (PCSEL element) 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.

[0020] 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).

[0021] FIG. 2 is a cross-sectional view schematically showing an example of the structure of a photonic crystal surface-emitting laser element (PCSEL element) 10 of the surface-emitting laser device 5 of this embodiment.

[0022] 2, a semiconductor structure layer 11 is formed on a light-transmitting element substrate 12. The semiconductor layers are stacked perpendicularly to the central axis CZ of the semiconductor structure layer 11.

[0023] 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. However, the semiconductor structure layer 11 is not limited to a hexagonal nitride semiconductor. For example, a cubic semiconductor such as a GaAs-based semiconductor or an InP-based semiconductor may also be used. More specifically, the semiconductor structure layer 11 is made of a plurality of semiconductor layers on the element substrate 12, namely, 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, 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 blocking layer (EBL) 17, a p-clad layer (second clad layer of a second conductivity type) 18, and a p-contact layer 19 are formed in this order.

[0024] Although the case where the first conductivity type is n-type and the second conductivity type opposite to the first conductivity type is p-type will be described, the first conductivity type and the second conductivity type may be p-type and n-type, respectively.

[0025] The element substrate 12 is a hexagonal GaN single crystal substrate with 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 at the outermost surface. The substrate surface (back surface, light emitting surface) on which the light emitting region 25L ( FIG. 3C ) is provided, facing the main surface, is a −c plane, which is a (000-1) plane in which N atoms are arranged at the outermost surface. The −c plane is suitable as a light emitting surface because it is resistant to oxidation and the like.

[0026] Although the element substrate 12 is not limited to this, 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 whose main surface is 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.

[0027] The composition, thickness, and other configurations of each semiconductor layer of the semiconductor structure layer 11 will be described below, but these are merely examples and can be modified as appropriate within the scope of the present invention.

[0028] The n-clad layer 13 is, for example, n-Al having an Al composition of 4%. ０．０４ Ga ０．９６ 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 (i.e., the n-side guide layer 14).

[0029] 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. The photonic crystal layer 14P has a thickness d ＰＣ For example, the thickness d ＰＣ is 40 to 180 nm.

[0030] In this specification, the photonic crystal layer 14P refers to the layer portion extending from the upper end to the lower end of the holes in the n-side guide layer 14. Therefore, the layer thickness d ＰＣ is equal to the height of the hole 14K.

[0031] Lower guide layer 14A is made of n-GaN and has a thickness of 100 to 400 nm, for example. Photonic crystal layer 14P is made of n-GaN and has a thickness (or the height of holes 14K) of 40 to 180 nm.

[0032] 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 of the buried layer 14B is, for example, 50 to 150 nm.

[0033] The n-side semiconductor layer including the n-cladding layer 13 and the n-side guide layer 14 is also referred to as a first semiconductor layer 13A (FIG. 1).

[0034] The active layer 15, which is a light-emitting layer, is a multiple quantum well (MQW) layer having, for example, two quantum well layers. The barrier layer and quantum well layer of the MQW are made of 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.

[0035] It is preferable that active layer 15 is located within 180 nm (that is, within empty period PC) of photonic crystal layer 14P, in which case a high resonance effect can be obtained by photonic crystal layer 14P.

[0036] The p-side guide layer 16 is an undoped In ０．０２ Ga ０．９８ N layer (70 nm thick) and undoped In ０．０２ Ga ０．９８ The p-side guide layer 16 is made of In. ｘ Ga １－ｘ It may be composed of a single layer of N layers (0≦x<1), or may be composed of three or more layers.

[0037] The p-side guide layer 16 is an undoped layer in consideration of light absorption by a dopant (Mg: magnesium, etc.), but may be doped to obtain good electrical conductivity. The In composition and layer thickness of the InGaN layer of the p-side guide layer 16 can be appropriately selected to adjust the electric field distribution in the oscillation operation mode.

[0038] The electron barrier layer (EBL) 17 is a p-type Al doped with magnesium (Mg). ０．２ G a ０．８ The N layer has a thickness of, for example, 15 nm.

[0039] The p-cladding layer 18 is made of Mg-doped p-Al ０．０６ Ga ０．９４ 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.

[0040] The p-contact layer 19 is an 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 for ohmic contact with the transparent electrode 21, 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.

[0041] 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 20 .

[0042] In this specification, the terms "n-side" and "p-side" do not necessarily mean that the conductivity types are n-type and p-type, respectively. 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 i-layer).

[0043] The n-cladding layer 13 may be composed of multiple layers instead of a single layer, and in that case, not all layers 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.

[0044] 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.

[0045] Furthermore, in this embodiment, the case where the photonic crystal layer 14P (hole layer) is provided in the first semiconductor layer (n-type semiconductor layer) has been described, but the photonic crystal layer may also be provided in the second semiconductor layer (p-type semiconductor layer).

[0046] A transparent electrode 21 is provided on the p-contact layer 19 and is in ohmic contact with the p-contact layer 19. The film thickness of the transparent electrode 21 is 130 nm. The region where the transparent electrode 21 is in ohmic contact is a current injection region RA.

[0047] The transparent electrode 21 has a circular shape with a diameter RA centered on the central axis CZ of the semiconductor structure layer 11. The diameter of the current injection region RA will also be described using the same reference symbol RA. Specifically, the transparent electrode 21 has a diameter RA of, for example, 300 μm in top view (i.e., when viewed from a direction perpendicular to the semiconductor structure layer 11).

[0048] The transparent electrode 21 is formed of a transparent conductor, such as indium tin oxide (ITO). Note that the transparent electrode 21 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.

[0049] The transparent electrode 21 can be formed by sputtering, vacuum deposition, or the like. The thickness of the transparent electrode 21 is preferably not thick enough to cause light absorption, specifically, preferably 500 nm or less, and more preferably 300 nm or less. Therefore, the thickness of the transparent electrode 21 is sufficiently thin compared with the bonding material, so that the stress that the transparent electrode 21 applies to the element can be almost negligible.

[0050] On the translucent electrode 21, an Ag / Au layer consisting of a silver (Ag) layer and a gold (Au) layer formed on the Ag layer was formed as the reflective electrode 23. The thicknesses of the Ag and Au were 50 nm and 300 nm, respectively. That is, the reflective electrode 23 functions as a light-reflecting layer, and the interface between the translucent electrode 21 and the Ag layer of the reflective electrode 23 is the reflective surface. The reflective surface is arranged parallel to the photonic crystal layer 14P. Pd, Al, Al alloys, etc. may also be used for the reflective electrode 23. A pad electrode, etc. may also be provided on the reflective electrode 23.

[0051] The periphery of the semiconductor structure layer 11, i.e., the side and top surfaces of the semiconductor structure layer 11 and the side surfaces of the p-electrode 25A are made of SiO ２ The p-electrode 25A is covered with a protective film 28 made of an insulating material such as a SiO 2 film or the like. The protective film 28 is formed so as to overlap the p-electrode 25A and cover the edge of the upper surface of the p-electrode 25A.

[0052] The protective film 28 protects 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 deposits or solder creeping up during mounting, contributing to improved reliability and yield. The material of the protective film 28 is SiO ２ Not limited to ZrO ２ , HfO ２ , TiO ２ , Al ２ O ３ , SiNx, etc. can be selected.

[0053] A circular n-electrode 25K (see FIG. 3C) is formed on the rear surface of the element substrate 12. An anti-reflection (AR) coating layer 27 is formed on the inner surface of the n-electrode 25K.

[0054] The n-electrode 25K is made of Ti / Au and is in ohmic contact with the element substrate 12. In addition to Ti / Au, the electrode material can be selected from Ti / Al, Ti / Rh, Ti / Al / Pt / Au, Ti / Pt / Au, and the like.

[0055] The light emitted from the active layer 15 is diffracted by the photonic crystal layer (PC layer) 14P. The light diffracted by the photonic crystal layer 14P and directly emitted from the photonic crystal layer 14P (direct diffracted light Ld: first diffracted light) and the light emitted by the photonic crystal layer 14P and reflected by the reflective electrode 23 (reflected diffracted light Lr: second diffracted light) are emitted to the outside as output light LE from a light output region 25L ( FIG. 3C ) on the rear surface (output surface) 12R of the element substrate 12.

[0056] Fig. 3A is a plan view schematically showing the upper surface of the PCSEL device 10. Fig. 3B is a cross-sectional view schematically showing a 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 schematically showing the lower surface of the PCSEL device 10.

[0057] 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 periodically arranged.

[0058] As shown in FIG. 3C, the region of the p-electrode 25A (that is, the current injection region RA) is formed so as to be included within the void formation region 14R in top view.

[0059] Furthermore, n-electrode 25K is provided as a ring-shaped electrode outside p-electrode 25A so as not to overlap p-electrode 25A when viewed from a direction perpendicular to photonic crystal layer 14P (when viewed from above).

[0060] The region inside the n-electrode 25K is the light emitting region 25L. Also provided is a bonding pad 25C that is electrically connected to the n-electrode 25K and to which a wire for power supply from the outside is connected.

[0061] 3. Manufacturing of a Photonic Crystal Surface-Emitting Laser Device (Mounting Substrate) A diamond substrate with a thickness of 300 μm, which has excellent heat dissipation properties, was used as the mounting substrate 33 (submount). Other materials that may be used for the mounting substrate 33 include aluminum nitride (AlN), silicon carbide (SiC), alumina (Al2O3), copper-aluminum nitride-copper (Cu-AlN-Cu), copper-tungsten (CuW), GaN, and graphite.

[0062] (Stress adjustment member) The diamond surface of the mounting substrate 33 is metallized with a thin Au film (layer thickness: 700 nm). After degreasing and cleaning the diamond substrate, a gold (Au) film was formed as the stress adjustment member 32. The film thickness of the stress adjustment member 32, including the metallized film, was approximately 4 μm. Considering that the thickness of the element bonding member 31 is 1 to 2 μm, it is preferable that the film thickness of the stress adjustment member 32 be 3 μm or more.

[0063] On the other hand, a thick stress adjusting member increases thermal resistance, so it is preferable not to make it thicker than necessary. For example, when the resonator size (the size of the p-electrode 25A) is 300 μmφ or 300 μm square, if the stress adjusting member 32 exceeds 25 μm, the thermal resistance increases by about twice as much as when there is no stress adjusting member 32. Therefore, it is preferable that the stress adjusting member 32 be at least 25 μm thick. Furthermore, since the stress adjusting member 32 has the function of alleviating distortion (strain) that occurs when the mounting substrate 33 and the PCSEL device 10 are bonded, it is preferable that the stress adjusting member 32 be made of a material that is softer and more easily deformed than either of them, i.e., has a small Young's modulus.

[0064] Furthermore, the stress adjusting member 32 and the element bonding member 31 are preferably made of a material with high electrical conductivity, since current is injected through the stress adjusting member 32. Here, Au is used as the material for the stress adjusting member 32, from the viewpoint that Au has high electrical conductivity and thermal conductivity, and a Young's modulus smaller than those of GaN and diamond.

[0065] It is preferable that the stress adjusting member 32 and the element bonding member 31 have high electrical conductivity and a Young's modulus smaller than that of the material (GaN-based semiconductor) of the PCSEL element 10 and the mounting substrate 33. The Young's modulus of the stress adjusting member 32 is preferably 100 GPa or less, and more preferably 40 GPa or less. Here, electrolytic plating, which can more easily form a film on the order of several micrometers, is used as the film-forming method for the stress adjusting member 32, but other film-forming methods may also be used. However, it is preferable that the film-forming method be one that can obtain sufficiently high adhesion strength even when forming a film with a thickness of several micrometers or more. Examples of such methods include sputtering, ion plating, and plasma CVD.

[0066] (Element Bonding Material) After degreasing and cleaning the mounting substrate 33 on which the stress adjusting member 32 was formed, the surface coating was removed using Ar plasma. A 100 μm-thick element bonding material was applied to the center of the mounting substrate 33 by printing. A paste material (Nihon Solder: MAX102) containing silver particles mixed in an organic solvent was used as the element bonding material. This paste material can be sintered at 200°C, which is significantly lower than the sintering temperature of 320°C for gold-tin alloy (AuSn), a conventional bonding material, and can bond the PCSEL element 10 to the mounting substrate 33. In other words, the PCSEL element 10 can be bonded while suppressing thermal distortion. Specifically, immediately after applying the bonding material to the mounting substrate 33, the PCSEL element 10 was sintered at a temperature of approximately 1.5 kfg / cm. 2 The mounting substrate 33 on which the PCSEL element 10 was mounted under pressure was introduced into a sintering oven, and N ２ The temperature was raised to 200° C. in the atmosphere, and sintering was carried out for 1 hour.

[0067] The sintering temperature may be in the range of 80 to 320°C. A low temperature prevents the metal particles from sintering, while a high temperature deteriorates the device characteristics. For example, the I-V characteristics may be impaired. Furthermore, the sintering time may be set to a value sufficient for the organic solvent contained in the device bonding member 31 to evaporate during sintering, such as 2 minutes to 8 hours. While a paste material containing silver nanoparticles is used for the device bonding member 31 in this embodiment, any paste material containing at least one type of metal particles (nanoparticles) such as gold (Au), silver (Ag), or copper (Cu) may be used. Using nanometer-order metal particles for the device bonding member 31 is preferable because it allows for a lower temperature for bonding the PCSEL device 10 to the mounting substrate 33. As described above, metal particles other than the aforementioned metal nanoparticles may also be used as long as they bond (neck) at the contact points between particles during low-temperature sintering and have high conductivity and heat dissipation properties.

[0068] Furthermore, it is preferable that the element bonding member 31 has a Young's modulus smaller than that of the mounting substrate 33. The Young's modulus of the element bonding member 31 is more preferably 100 GPa or less, and even more preferably 70 GPa or less. Furthermore, when mounting the PCSEL element 10 on the mounting substrate 33, a bonding process at room temperature may be used. For example, the bonding surfaces of the p-electrode 25A (second electrode) of the PCSEL element 10 and the stress adjusting member 32 are activated with Ar and H2 plasma, and then the p-electrode 25A and the stress adjusting member 32 are pressurized at room temperature. This allows the PCSEL element 10 and the mounting substrate 33 to be bonded together.

[0069] (Substrate Bonding Member) An indium alloy (content ratio: In0.52-Sn0.48) was used for the substrate bonding member 34. Specifically, after applying the substrate bonding material to the heat sink 35, the heat sink 35 was heated to 120°C to soften the bonding material, and the mounting substrate 33 on which the PCSEL device 10 was mounted was pressed, thereby bonding the heat sink 35 and the mounting substrate 33. (Heat Sink) The heat sink 35 was made of copper (Cu), which has excellent electrical and thermal conductivity. A Peltier cooling device was placed on the back surface of the heat sink 35 (the surface opposite to the surface bonded to the mounting substrate 33), and the back surface was maintained at a predetermined constant temperature.

[0070] 4. In-plane strain distribution and threshold current of photonic crystal layer (1) Spatial distribution of in-plane strain and resonance frequency Fig. 4A is a diagram showing the photonic bands of the band edges A and B at the Γ point of the photonic band of the PCSEL element. More specifically, with respect to the in-plane strain ε in the current injection region RA, the strain ε at the edge of the current injection region RA edge is the strain at the center, ε center If it is greater than (ε center <ε edge ) is shown.

[0071] In this case, the edges are subjected to stronger tensile strain than the center. That is, in the current injection region RA, the hole spacing PK increases slightly from the center to the edges. Here, since the resonant wavelength λ of a PCSEL element is expressed as "λ = n × PK" (n is the refractive index), the resonant wavelength λ increases from the center to the edges.

[0072] For example, in the case of a PCSEL element having a square lattice photonic crystal, the resonance effect at band edges A and B, which have a mode frequency lower than the photonic band gap at the Γ point, is utilized, but if the resonance wavelength λ has the distribution described above within the element, the spatial distribution of the resonance frequencies at band edges A and B will be as shown in Figure 4A. That is, in this case, due to the presence of a photonic band gap at the edge of the current injection region RA, photons cannot exist and are localized in the center of the current injection region RA (white arrow in the figure). Therefore, ε center <ε edge In this case, the effective resonator size becomes smaller and the oscillation threshold current increases.

[0073] 4B is a diagram showing the photonic bands at the band edges A and B of the PCSEL element. More specifically, the strain ε center is the strain at the edge ε edge If it is greater than (ε center >ε edge ) is shown.

[0074] In this case, the center portion is subjected to a stronger tensile strain than the edges. That is, in the current injection region RA, the hole spacing PK decreases slightly from the center to the edges. Therefore, the resonant wavelength λ becomes shorter from the center to the edges.

[0075] For example, in the case of a PCSEL element having a square lattice photonic crystal, if the resonant wavelength λ has the distribution described above within the element, the spatial distribution of the resonant frequencies at the band edges A and B will be as shown in FIG. center <ε edge In contrast to the case of , the photons spread over the entire surface.

[0076] (2) Simulation of In-Plane Strain Distribution Consideration was given to the in-plane distribution of strain generated in the photonic crystal layer 14P due to the mounting (bonding) of the PCSEL device 10 and the increase in threshold current due to the in-plane distribution of strain.

[0077] The magnitude of strain generated in the photonic crystal layer 14P of the PCSEL device 10 due to mounting was calculated using the numerical analysis software COMSOL. Specifically, we assumed that a 150 μm thick, 0.8 mm × 0.8 mm PCSEL device 10 was bonded to a 300 μm thick, 3 mm × 3 mm diamond heat dissipation substrate. The thickness of the sintered (200°C) bonding material (Ag fine particle paste) was varied, and the strain distribution generated in the photonic crystal layer 14P was calculated.

[0078] That is, when the bonding material is viewed as the element bonding member 31 and the stress adjusting member 32 in the PCSEL element 10, a simulation was performed to see how the strain distribution in the photonic crystal layer 14P changes depending on the total film thickness of the element bonding member 31 and the stress adjusting member 32.

[0079] In this simulation, Ag fine particle paste was used as the bonding material. The Young's modulus of the sintered Ag used in the calculation was approximately 14.8 GPa, which is almost the same as the Young's modulus (9.5 GPa) of a plated Au film. Therefore, the results of this simulation can be applied to stress adjustment members 32 using Au films. Figure 5A shows the calculation results of the dependency of strain distribution on bonding material thickness when the bonding material thickness is 1, 3, 5, 10, and 20 μm. The horizontal axis represents the horizontal position (x direction in Figure 2) of the cross section passing through the center of the void formation region 14R of the photonic crystal layer 14P, and the vertical axis represents the strain amount (%). The dashed line indicates the region of the p-electrode 25A (i.e., the current injection region RA) in a top view.

[0080] In this simulation, when the thickness of the bonding material (i.e., the total film thickness of the element bonding member 31 and the stress adjusting member 32) is thin (1 to 3 μm), it can be seen that the distortion has a downward convex in-plane distribution within the current injection region RA of 300 μmφ.

[0081] FIG. 5B shows the strain at the center of the current injection area RA as εcenter , the strain at the edge (periphery) is ε edge The difference in strain relative to the thickness of the bonded material when center -ε edge (%) is shown.

[0082] 5A and 5B, when the total thickness of the bonding material, i.e., the element bonding member 31 and the stress adjusting member 32, is about 4 μm or more, the central strain ε center is larger than the strain at the edge (ε center -ε edge ≧0).

[0083] That is, the effective resonator area is approximately equal to the current injection area RA, and the oscillation threshold does not increase. center ≧ε edge In other words, the strain ε center is the strain ε at the end of the corresponding region. edge is greater than (ε center >ε edge ) is preferred.

[0084] That is, when a PCSEL element is bonded junction-down, the distance between the photonic crystal layer and the bonding portion of the mounting substrate is short, and stress is applied to the photonic crystal layer, causing distortion and distortion distribution, which may make the oscillation mode unstable.

[0085] As described above, the degradation and instability of the emission mode caused by the strain distribution generated when stress is applied to the photonic crystal layer 14P is a problem specific to PCSEL elements that use a photonic crystal layer.

[0086] 5. Evaluation of Photonic Crystal Surface-Emitting Laser Device (1) Study of Stress Adjustment Member The surface-emitting laser device 5 of this embodiment was evaluated. Figure 6A shows a comparison of the current-light output characteristics (IL characteristics) before and after mounting (before and after bonding) the PCSEL element 10 on the mounting substrate 33 in the surface-emitting laser device 5. Here, to eliminate the influence of heat dissipation, the current-light output characteristics were evaluated under short pulse conditions (1 kHz, 100 nsec, room temperature (RT)). The film thickness FT of the stress adjustment member 32 was 4 μm.

[0087] As shown in FIG. 6A, the threshold current I ｔｈ０ and slope efficiency η ｓｅ０ are 1.48 A and 0.44 W / A, respectively, and the threshold current I ｔｈ１ and slope efficiency η ｓｅ１ are 1.46 A and 0.47 W / A, respectively, and the threshold current I ｔｈ and slope efficiency η ｓｅ No significant changes were observed in either case. Therefore, it was confirmed that the IL characteristics before mounting were maintained.

[0088] Furthermore, the effect of increasing the thickness FT of the stress adjusting member 32 beyond 4 μm in the above example was examined. Here, the PCSEL element 10 was mounted on the stress adjusting member 32 when the thickness FT was set to 7 μm and 9 μm, and the IL characteristics of each element were evaluated before and after mounting.

[0089] 6B shows an example of a comparison of the IL characteristics before and after mounting (before and after bonding) a PCSEL element in a surface-emitting laser device of the comparative example (CMP). In the surface-emitting laser device of the comparative example (CMP), the PCSEL element 10 was mounted on a high-heat-dissipation substrate (diamond) onto which a bonding material made of Ag nanoparticle solder had been printed. The thickness of the bonding material after bonding was 1 to 2 μm due to pressure bonding.

[0090] As shown in FIG. 6B, the threshold current I ｔｈ increases, and the slope efficiency η ｓｅ１Specifically, the threshold current I in the IL characteristics before mounting decreased. ｔｈ０ and slope efficiency η ｓｅ０ are 2.04 A and 0.36 W / A, respectively, and the threshold current I ｔｈ１ and slope efficiency η ｓｅ１ are 2.39 A and 0.33 W / A, respectively, and the threshold current I ｔｈ and slope efficiency η ｓｅ 7A and 7B show the IL characteristics before and after mounting when the film thickness FT of the stress adjusting member 32 is 7 μm and 9 μm. As shown in FIG. 7A, before mounting, the threshold current I ｔｈ０ = 1.61 A, slope efficiency η ｓｅ０ = 0.44 W / A, and after mounting, the threshold current I ｔｈ１ = 1.58A, slope efficiency η ｓｅ１ = 0.44 W / A.

[0091] Furthermore, as shown in FIG. 7B, before mounting, the threshold current I ｔｈ０ = 1.51 A, slope efficiency η ｓｅ０ = 0.46 W / A, and after mounting, the threshold current I ｔｈ１ = 1.58A, slope efficiency η ｓｅ１ = 0.47 W / A.

[0092] When the film thickness FT of the stress adjusting member 32 is 7 μm or 9 μm, the threshold current I ｔｈ and slope efficiency η ｓｅ It was found that if the film thickness FT of the stress adjusting member 32 is greater than a predetermined film thickness, an effect of suppressing an increase in the threshold value and a decrease in the slope efficiency can be obtained.

[0093] (2) Thickness of Element Bonding Member The stress adjusting member 32 functions effectively as long as the thickness FT of the element bonding member 31 and the stress adjusting member 32 are such that the total thickness of the element bonding member 31 and the stress adjusting member 32 is 4 μm or more. Here, the thickness FT of the element bonding member 31 is preferably in the range of 1 μm to 2 μm. If the thickness is too thin, the bonding strength decreases. Furthermore, the thickness of the element bonding member 31 also affects the stress applied to the photonic crystal layer 14P. If the thickness is too thick, the density of the element bonding material (solder, etc.) decreases, and it becomes difficult to achieve uniformity in density and thickness. As described above, the thickness GT of the stress adjusting member 32 is preferably 3 μm or more. Furthermore, the total thickness of the element bonding member 31 and the stress adjusting member 32 is preferably 4 μm or more and 25 μm or less.

[0094] As described above, according to the present invention, it is possible to provide a photonic crystal surface-emitting laser device that suppresses increases in the oscillation threshold current and drive current of the photonic crystal surface-emitting laser element, has a stable oscillation mode, and has excellent beam quality.

[0095] 10: PCSEL element 11: Semiconductor structure layer 12: Element substrate 13: n-clad layer (first clad layer) 13A: First semiconductor layer 14: n-side guide layer (first guide layer) 14P: Photonic crystal layer (hole layer) 15: Active layer (ACT) 16: p-side guide layer (second guide layer) 17: Electron barrier layer 18: p-clad layer (second clad layer) 19: p-contact layer 20: Second semiconductor layer 21: Light-transmitting electrode 23: Reflecting electrode 25A: p-electrode (second electrode) 25K: n-electrode (first electrode) 31: Element bonding member 32: Stress adjusting member 33: Mounting substrate 33

Claims

1. A surface-emitting laser device comprising: a surface-emitting laser element; a mounting substrate to which the surface-emitting laser element is bonded with an element bonding member and electrically connected to the surface-emitting laser element; and a stress adjustment member which is a conductive layer provided between the element bonding member and the mounting substrate, wherein the surface-emitting laser element comprises: 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 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 first electrode electrically connected to the first semiconductor layer; and a second electrode provided on the second semiconductor layer in ohmic contact with the second semiconductor layer and having a light-reflecting surface.

2. The surface-emitting laser device according to claim 1, wherein the total thickness of the element bonding member and the stress adjusting member is 4 μm or more.

3. The surface-emitting laser device according to claim 2, wherein the thickness of said element bonding member is within the range of 1 to 2 μm, and the thickness of said stress adjusting member is 3 μm or more.

4. The surface-emitting laser device according to claim 2, wherein the film thickness of said stress adjusting member is 25 μm or less.

5. The surface-emitting laser device according to claim 1, wherein the element substrate is made of a GaN-based semiconductor, and the Young's modulus of the stress adjusting member is smaller than the Young's modulus of the element substrate.

6. The surface-emitting laser device according to claim 5, wherein the Young's modulus of said stress adjusting member is smaller than the Young's modulus of said mounting substrate.

7. The surface-emitting laser device according to claim 1, wherein the Young's modulus of said stress adjusting member is 100 GPa or less.

8. The surface-emitting laser device according to claim 1, wherein the element bonding member is made of metal nanoparticles, and the stress adjusting member is made of Au.

9. Strain ε at the center of the hole layer corresponding to the current injection region, which is the ohmic contact region of the second semiconductor layer center is the strain at the edge ε edge is greater than (ε center >ε edge 9. The surface-emitting laser device according to claim 1.

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