Nitride-based light-emitting devices

Abstract

The nitride-based light-emitting device (semiconductor laser device (51a)) comprises: a nitride-based semiconductor light-emitting element (semiconductor laser element (11)) which is formed on an Al x Ga 1‑x N (0≤x≤1) substrate (GaN substrate (101)) has Al x Ga 1‑x The N substrate side is stacked with a multilayer structure of a first cladding layer (103), a first optical guide layer (105), a quantum well active layer (106), a second optical guide layer (107) and a second cladding layer (109) in sequence; and a base substrate (122) for mounting a nitride-based semiconductor light-emitting element. The nitride-based semiconductor light-emitting element is mounted on the base substrate (122) so that the multilayer structure and the base substrate (122) are opposite. The base substrate (122) is formed of diamond. In the nitride-based semiconductor light-emitting element, the Al x Ga 1‑x A concave warp is formed on the N substrate side.

Description

[0001] This application is a divisional application of the invention patent application with the application date of April 12, 2018, application number 201880027686.X (international application number PCT / JP2018 / 015319), and invention name “Nitride-based light-emitting device”. Technical Field

[0002] The present disclosure relates to a nitride-based light-emitting device. Background Art

[0003] Currently, as light sources for vehicle headlights, halogen lamps, HID (High Intensity Discharge) headlights, and LED (Light Emitting Diode) lamps are widely used.

[0004] Halogen lamps, which use a trace amount of halogen gas added to an inert gas like nitrogen or argon enclosed within the bulb, then energize the filament, generating light when it incandescent. Unlike halogen lamps, HID lamps lack a filament, meaning the bulb never burns out; it continues to emit light as long as it can discharge. While generally more expensive than halogen lamps, HID lamps offer advantages such as low power consumption, high brightness, and a long lifespan. LED lamps have a longer lifespan, requiring only replacement of the tube, resulting in lower power consumption and heat generation than HID lamps. However, LED lamps are less bright than HID lamps, so HID lamps are currently the primary headlight option, with LEDs being used in fog lamps and other decorative lighting applications.

[0005] Recently, laser headlight light sources, which utilize LDs (laser diodes) to enhance luminous intensity, have attracted attention as light-emitting elements with higher luminous intensity than LEDs. For example, ultra-high-output blue semiconductor lasers are desired as light-emitting elements for headlight light sources. These ultra-high-output blue semiconductor lasers operate for several thousand hours or more, even at high temperatures of 85°C, while operating at a watt-class output within the 450nm wavelength range.

[0006] In order to realize such a light-emitting element, it is necessary to suppress as much as possible the temperature rise of the light-emitting element due to self-heating during laser oscillation operation.

[0007] In order to suppress the temperature rise caused by self-heating, it is important to reduce the thermal resistance of the semiconductor laser element.

[0008] In the semiconductor laser device described in Patent Document 1, Figure 53 As shown in FIG, in order to reduce the thermal resistance of a semiconductor laser element, the semiconductor laser element is mounted in a junction-down manner on a diamond base substrate having high thermal conductivity (see Patent Document 1).

[0009] In addition, from the perspective of extending the operating life of components, such as Figure 54 As shown in FIG, a technique is disclosed in which unevenness is formed on a base substrate on which a semiconductor laser element is mounted, and the shape after mounting is controlled so that the substrate side of the semiconductor laser element becomes convex (see Patent Document 2).

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: International Publication No. 2013 / 175697

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-31895 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] In order to obtain laser oscillation in the 450 nm wavelength range in a blue laser, the In composition of the InGaN layer used in the quantum well layer serving as the light emitting layer needs to be increased to approximately 0.18 (18%).

[0016] Generally, the nitride material used in nitride-based semiconductor lasers is formed by mixing at least two of InN, GaN, and AlN. Here, the lattice constants of InN, GaN, and AlN are respectively and InGaN, formed by mixing InN and GaN, has a larger lattice constant than GaN, resulting in a lattice mismatch with GaN. Specifically, the lattice mismatch between the InGaN quantum well layer with an In composition of 0.19 used in the blue laser light-emitting layer and the GaN substrate is as high as 2.1%.

[0017] In contrast, in conventional blue-violet lasers with a wavelength of 405nm, used in Blu-ray (registered trademark) optical disc systems, the In composition of the InGaN used in the quantum well is approximately 0.07 (7%). In this case, the lattice mismatch with the GaN substrate is 0.74%. Therefore, in blue lasers with a wavelength of 450nm, the stress generated in the quantum well layer increases several times compared to conventional blue-violet lasers with a wavelength of 405nm. This increase in stress not only creates lattice defects, but also causes an electric field to be generated due to the piezoelectric effect within the crystal in crystals with a wurtzite (WZ) crystal structure, such as nitride materials. This electric field generated by the piezoelectric effect hinders the injection of current into the active layer. As a result, phenomena such as an increase in operating voltage and a decrease in luminous efficiency may occur.

[0018] To achieve high-temperature, high-output operation, a bonded-down mounting method is used, where the quantum well active layer, which will serve as the light-emitting layer, is mounted on the side closest to the base substrate on which the semiconductor laser element is mounted. This is effective in reducing thermal resistance and suppressing temperature rise in the semiconductor laser element. In this case, the distance between the quantum well active layer and the base substrate is close, resulting in greater stress in the quantum well active layer caused by the difference in thermal expansion coefficient between the base material and the semiconductor laser element.

[0019] Furthermore, in nitride-based semiconductor laser elements designed for watt-level operation, it is necessary to form a current non-injection window region in the quantum well active layer near the resonator end facets to suppress the reduction in the band gap energy of the active layer caused by heat generated by non-luminescent recoupling at the resonator end facets, thereby suppressing the occurrence of COD (Catastrophic Optical Damage), in which the resonator end facets are destroyed by their own light.

[0020] Here, when the piezoelectric field generated by stress in the quantum well active layer is generated in an orientation where current injected into the semiconductor laser element tends to flow toward the resonator facets, the current is more likely to leak into the current non-injection window region described above, thereby easily causing non-luminescent recoupling. Consequently, this deteriorates the COD level of the semiconductor laser element.

[0021] Therefore, in order to guarantee long-term operation for thousands of hours or more while operating at high output power in the 450nm wavelength range at a high temperature of 85°C, simply suppressing the temperature rise of the semiconductor laser device by reducing thermal resistance is not necessarily sufficient. Specifically, in addition to suppressing the temperature rise of the semiconductor laser device, it is necessary to control the stress generated in the quantum well active layer, which serves as the light-emitting layer, to suppress the diffusion of current into the current non-injection window region near the cavity end facets, thereby improving the current injection efficiency into the quantum well active layer, where current is injected.

[0022] Therefore, an object of the present disclosure is to provide a nitride-based light-emitting device capable of simultaneously achieving a reduction in the temperature rise of a quantum well active layer and an improvement in the current injection efficiency into the quantum well active layer.

[0023] Means for solving problems

[0024] A nitride-based light-emitting device according to one embodiment of the present disclosure comprises: a nitride-based semiconductor light-emitting element, wherein the nitride-based semiconductor light-emitting element is a nitride-based semiconductor light-emitting element; x Ga 1- x N (0≤x≤1) substrate has the Al x Ga 1-xThe N substrate has a multilayer structure in which a first cladding layer of a first conductive type, a first optical guide layer, a quantum well active layer, a second optical guide layer, and a second cladding layer of a second conductive type are sequentially stacked on the N substrate side; and a base substrate for mounting the nitride-based semiconductor light-emitting element. The nitride-based semiconductor light-emitting element is mounted on the base substrate so that the multilayer structure and the base substrate are opposite to each other. The base substrate is formed of diamond. x Ga 1-x A concave warp is formed on the N substrate side.

[0025] Effects of the Invention

[0026] According to the present disclosure, it is possible to provide a nitride-based light-emitting device that can simultaneously achieve reduction in temperature rise of a quantum well active layer and improvement in current injection efficiency into the quantum well active layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A This is a schematic cross-sectional view showing the structure of the semiconductor laser element according to the first embodiment.

[0028] Figure 1B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device according to the first embodiment.

[0029] Figure 1C This is a schematic cross-sectional view showing the structure near the cavity end of the semiconductor laser element according to the first embodiment.

[0030] Figure 2 It is a diagram showing the energy band structure of the quantum well active layer.

[0031] Figure 3A This is a schematic side view showing the appearance of an example of the semiconductor laser device according to the first embodiment.

[0032] Figure 3B This is a schematic side view showing the appearance of another example of the semiconductor laser device according to the first embodiment.

[0033] Figure 4 Graphs showing the distribution of shear stress and piezoelectric field in the resonator length direction when the base substrate is formed of diamond.

[0034] Figure 5 Graphs showing the distribution of shear stress and piezoelectric field in the resonator length direction when the base substrate is formed of diamond.

[0035] Figure 6 This is a graph showing the distribution of shear stress and piezoelectric field in the resonator length direction when the base substrate is formed of AlN (aluminum nitride).

[0036] Figure 7A This is a schematic diagram explaining the definition of warpage ΔR.

[0037] Figure 7B Graph showing the relationship between the average strain and the warpage ΔR of the multilayer structure.

[0038] Figure 8A This is a graph showing an example of distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of the first embodiment.

[0039] Figure 8B yes Figure 8A An enlarged view of the quantum well active layer in the CMOS process.

[0040] Figure 8C is an average strain ε in the growth layer direction of the multilayer structure of the first embodiment. tave A graph showing an example of the distribution of .

[0041] Figure 9A This is a graph showing calculation results of the wavelength and carrier concentration dependence of the gain obtained in the quantum well active layer when the piezoelectric effect is taken into account.

[0042] Figure 9B This is a graph showing calculation results of the wavelength and carrier concentration dependence of the gain obtained in the quantum well active layer when the piezoelectric effect is not taken into account.

[0043] Figure 9C This is a graph showing the calculation results of the carrier concentration dependence of the injected gain into the quantum well active layer.

[0044] Figure 10 This is a graph showing the dependence of the piezoelectric field generated in the quantum well layer on the In composition of the barrier layer.

[0045] Figure 11 This is a graph showing the calculation results of the dependence of the operating voltage of the semiconductor laser element when operating at 100 mA on the In composition of the barrier layer.

[0046] Figure 12 This is a diagram showing the relationship between the piezoelectric field and the gain of the semiconductor laser element according to the first embodiment.

[0047] Figure 13 This is a graph showing the carrier concentration dependence of the gain of the semiconductor laser element according to the first embodiment.

[0048] Figure 14A This is a graph showing the relationship between the Fermi level (Fermi energy) and the conduction band energy in the region near the quantum well active layer 106 in the semiconductor laser device according to the first embodiment.

[0049] Figure 14B This is a graph showing the relationship between the Fermi level and the valence electron band energy in the vicinity of the quantum well active layer 106 in the semiconductor laser device according to the first embodiment.

[0050] Figure 14C This is a graph showing the electron and hole concentration distributions determined by the relationship between the Fermi level and the conduction band energy in the region near the quantum well active layer 106 in the semiconductor laser device according to the first embodiment.

[0051] Figure 15 This is a diagram showing the relationship between the carrier concentration in each optical guiding layer and the In composition of the barrier layer and each optical guiding layer in the semiconductor laser element according to the first embodiment.

[0052] Figure 16A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a second embodiment.

[0053] Figure 16B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device according to the second embodiment.

[0054] Figure 16C This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a modified example of the second embodiment.

[0055] Figure 16D This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a modification of the first embodiment.

[0056] Figure 17A This is a graph showing another example of the distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of the first embodiment.

[0057] Figure 17B This is a graph showing another example of the distribution of average strain in the growth layer direction of the multilayer structure according to the first embodiment.

[0058] Figure 18A This is a graph showing another example of the distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of the second embodiment.

[0059] Figure 18B This is a graph showing another example of the distribution of average strain in the growth layer direction of the multilayer structure of the second embodiment.

[0060] Figure 19A is the average strain ε of the multilayer structure of the comparative example. tave A graph showing the relationship between the total thickness of the first light guiding layer and the second light guiding layer.

[0061] Figure 19B The average strain ε of the multilayer structure of the second embodiment is shown.tave A graph showing an example of the relationship with the total thickness of the first light guiding layer and the second light guiding layer.

[0062] Figure 19C The average strain ε of the multilayer structure of the second embodiment is shown. tave A graph showing another example of the relationship with the total thickness of the first light guiding layer and the second light guiding layer.

[0063] Figure 20 is the average strain ε of the entire multilayer structure of the second embodiment. tave A graph showing the relationship between the thickness of the InGaN layer and the AlGaN layer constituting the buffer layer 102.

[0064] Figure 21A This figure shows the shear stress distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0065] Figure 21B This figure shows the piezoelectric field distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0066] Figure 21C This figure shows the piezoelectric potential distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0067] Figure 22A This figure shows the shear stress distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the semiconductor laser element bonded upward.

[0068] Figure 22B This figure shows the piezoelectric field distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the semiconductor laser element bonded upward.

[0069] Figure 22C This figure shows the piezoelectric potential distribution in the x-axis direction at 25° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the semiconductor laser element bonded upward.

[0070] Figure 23A This figure shows the shear stress distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0071] Figure 23BThis figure shows the piezoelectric field distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0072] Figure 23C This figure shows the piezoelectric potential distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0073] Figure 24A This figure shows the shear stress distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the semiconductor laser element bonded upward.

[0074] Figure 24B This figure shows the piezoelectric field distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the junction facing upward.

[0075] Figure 24C This figure shows the piezoelectric potential distribution in the x-axis direction at 150° C. in the quantum well layer when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the junction facing upward.

[0076] Figure 25A This is a graph showing the measurement results of the current-light output characteristics at 25° C. and 85° C. when the semiconductor laser element according to the second embodiment is mounted on a base substrate formed of diamond.

[0077] Figure 25B This is a graph showing the measurement results of the current-light output characteristics at 25° C. and 85° C. when the semiconductor laser element according to the second embodiment is mounted on a base substrate made of SiC.

[0078] Figure 26A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a third embodiment.

[0079] Figure 26B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device according to the third embodiment.

[0080] Figure 27A This is a graph showing the x-axis direction distribution of the shear stress at 25° C. in the quantum well layer in the quantum well active layer when the In composition of the third optical guiding layer is changed to 0%.

[0081] Figure 27B This is a graph showing the x-axis direction distribution of the shear stress at 25° C. in the quantum well layer in the quantum well active layer when the In composition of the third optical guiding layer is changed by 1%.

[0082] Figure 27C This is a graph showing the x-axis direction distribution of the shear stress at 25° C. in the quantum well layer in the quantum well active layer when the In composition of the third optical guiding layer is changed by 2%.

[0083] Figure 28 This is a graph showing the relationship between the piezoelectric potential generated in the quantum well active layer and the position in the x-axis direction in Embodiment 3.

[0084] Figure 29A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a fourth embodiment.

[0085] Figure 29B This is a schematic cross-sectional view showing the structure of a quantum well active layer in a semiconductor laser device according to a fourth embodiment.

[0086] Figure 30A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a fifth embodiment.

[0087] Figure 30B This is a schematic cross-sectional view showing the structure of a quantum well active layer in a semiconductor laser device according to a fifth embodiment.

[0088] Figure 31A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a sixth embodiment.

[0089] Figure 31B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device according to the sixth embodiment.

[0090] Figure 32A This figure shows the calculation results of the shear stress generated in the quantum well layer at 25° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0091] Figure 32B This figure shows the calculation results of the piezoelectric field generated in the quantum well layer at 25° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0092] Figure 32C This figure shows the calculation results of the piezoelectric potential generated in the quantum well layer at 25° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0093] Figure 33AThis figure shows the calculation results of the shear stress generated in the quantum well layer at 150° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0094] Figure 33B This figure shows the calculation results of the piezoelectric field generated in the quantum well layer at 150° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0095] Figure 33C This figure shows the calculation results of the piezoelectric potential generated in the quantum well layer at 150° C. when the isolation groove width D of the semiconductor laser element according to the third embodiment is changed from 2 μm to 24 μm.

[0096] Figure 34 This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a seventh embodiment.

[0097] Figure 35 This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a modified example of the seventh embodiment.

[0098] Figure 36 This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to an eighth embodiment.

[0099] Figure 37 This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a modified example of the eighth embodiment.

[0100] Figure 38A This diagram shows the energy band structure near the quantum well active layer when a multilayer structure including a first cladding layer and a second cladding layer having an Al composition of 0 is formed on a GaN substrate having a C-plane primary surface.

[0101] Figure 38B This diagram shows the energy band structure near the quantum well active layer when a multilayer structure including a first cladding layer and a second cladding layer having an Al composition of 0 is formed on a GaN substrate having a semipolar primary surface.

[0102] Figure 38C This diagram shows the energy band structure near the quantum well active layer when a multilayer structure including a first cladding layer and a second cladding layer having an Al composition of 0 is formed on a GaN substrate having a non-polar primary surface.

[0103] Figure 39A This is a graph showing the dependence of the operating voltage of a semiconductor laser element having a multilayer structure formed on a C-plane on the Al composition of each cladding layer when operating at 100 mA.

[0104] Figure 39BThis is a graph showing the dependence of the operating voltage of a semiconductor laser element having a multilayer structure formed on a semipolar plane on the Al composition of each cladding layer when operating at 100 mA.

[0105] Figure 39C This is a graph showing the dependence of the operating voltage of a semiconductor laser element having a multilayer structure formed on a non-polar surface upon the Al composition of each cladding layer when operating at 100 mA.

[0106] Figure 40 is the average deformation ε of the multilayer structure tave Graph showing the Al composition dependence of each cladding layer.

[0107] Figure 41 This is a diagram showing overflow of solder material formed on the side wall near the center of the laser element.

[0108] Figure 42 This is a schematic cross-sectional view showing a state in which the semiconductor laser element according to Embodiment 1 is mounted on the immediately front surface of a base substrate with the semiconductor laser element facing downward.

[0109] Figure 43 This is a schematic cross-sectional view showing a state in which the semiconductor laser element according to the ninth embodiment is mounted face-down on the immediately front surface of a base substrate by bonding.

[0110] Figure 44 This is a schematic cross-sectional view showing the structure of a semiconductor laser device according to a ninth embodiment.

[0111] Figure 45A This is a schematic cross-sectional view showing the structure of a semiconductor laser element according to a modified example of the ninth embodiment.

[0112] Figure 45B This is a schematic plan view showing an example of the shape of the P-side multilayer electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0113] Figure 45C This is a schematic plan view showing another example of the shape of the P-side multilayer electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0114] Figure 45D This is a schematic plan view showing still another example of the shape of the P-side multilayer electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0115] Figure 45EThis is a schematic plan view showing an example of the shape of the N-side electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0116] Figure 45F This is a schematic plan view showing another example of the shape of the N-side electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0117] Figure 45G This is a schematic plan view showing still another example of the shape of the N-side electrode of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0118] Figure 46 This is a perspective view showing the shape of a base substrate according to the tenth embodiment.

[0119] Figure 47 This is a diagram showing the structure of electrodes mounted on a base substrate in accordance with a tenth embodiment.

[0120] Figure 48A This is a schematic cross-sectional view showing the structure of a semiconductor laser device in which a semiconductor laser element is mounted on a base substrate in which a bonding layer is not formed on an inclined portion.

[0121] Figure 48B This is a schematic cross-sectional view showing the structure of a semiconductor laser device in which a semiconductor laser element is mounted on a base substrate in which a bonding layer is formed on an inclined portion.

[0122] Figure 49A This is a schematic cross-sectional view showing the structure of a semiconductor laser device in which a semiconductor laser element having a current non-injection window region is mounted on a base substrate in which a bonding layer is not formed on an inclined portion.

[0123] Figure 49B This is a schematic cross-sectional view showing the structure of a semiconductor laser device in which a semiconductor laser element having a current non-injection window region is mounted on a base substrate in which a bonding layer is formed on an inclined portion.

[0124] Figure 50 This is a diagram showing the structure of an example of an optical module according to the eleventh embodiment.

[0125] Figure 51 This is a cross-sectional view showing the structure of an example of an optical module according to the twelfth embodiment.

[0126] Figure 52 This is a cross-sectional view showing an example of the structure of a light source according to Embodiment 13.

[0127] Figure 53This is a cross-sectional view showing an example of the structure of a conventional semiconductor light-emitting device.

[0128] Figure 54 This is a cross-sectional view showing another example of the structure of a conventional semiconductor light-emitting device. DETAILED DESCRIPTION

[0129] (Insights that form the basis of this disclosure)

[0130] Before describing the embodiments of the present disclosure, the knowledge that is the basis of the present disclosure will be described.

[0131] As mentioned above, ultra-high-output blue semiconductor laser devices are desired as light-emitting elements used in headlamp light sources. These ultra-high-output blue semiconductor laser devices are capable of long-term operation for several thousand hours or more, even when operating at high output power of watts at temperatures of 85°C in the 450nm wavelength range. If such an ultra-high-output blue semiconductor laser can be used to excite a phosphor to produce yellow light, a white ultra-high-output light source can be obtained as the overall irradiation light.

[0132] To achieve such a highly reliable, ultra-high-output blue semiconductor laser device, it is necessary to minimize the temperature rise of the semiconductor laser element during laser oscillation. To this end, it is very effective to mount the semiconductor laser element face-down on a high-heat-dissipating mount to reduce its thermal resistance. The following describes the structure of a conventional semiconductor light-emitting device using the accompanying drawings. Figure 53 This is a cross-sectional view showing an example of the structure of a conventional semiconductor light-emitting device. Figure 54 This is a cross-sectional view showing another example of the structure of a conventional semiconductor light-emitting device. Figure 53 and Figure 54 The structures of semiconductor light-emitting devices disclosed in Patent Document 1 and Patent Document 2 are shown respectively.

[0133] For example, in the semiconductor light emitting device 300 of Patent Document 1, Figure 53 As shown in FIG, a method for reducing the thermal resistance of a nitride light-emitting element 310 by bonding it face-down to a diamond base substrate 311 is disclosed. Diamond has a thermal conductivity of approximately 1000 W / m·K or higher, significantly higher than other base materials such as SiC (approximately 200 W / m·K) and AlN (approximately 150 W / m·K), making it suitable for achieving high heat dissipation.

[0134] However, when using a GaN substrate with the (0001) plane (C-plane) of GaN crystal as the main surface, it is known that GaN has piezoelectricity (piezoelectric effect) as a physical property due to its atomic arrangement, since GaN has a wurtzite (WZ) crystal structure. In this case, when stress is applied to the crystal, a piezoelectric field is generated in the crystal due to polarization corresponding to the stress.

[0135] Furthermore, as mentioned above, in nitride-based semiconductor laser devices designed for Watt-level operation, it is necessary to form a current non-injection window region in the quantum well active layer near the cavity facets to suppress the reduction in the band gap energy of the quantum well active layer caused by heat generated by non-luminescent recoupling at the cavity facets. This can thereby suppress the occurrence of COD.

[0136] However, the piezoelectric field generated by stress in the quantum well active layer can sometimes be generated in an orientation that favors current injected into the semiconductor laser device toward the resonator facets. In this case, current leaks easily into the non-injection window region, making non-luminescent recoupling more likely. This results in heat generation and a decrease in the COD level of the semiconductor laser device.

[0137] In semiconductor laser devices operating at high output power levels of watts at temperatures as high as 85°C, the magnitude of injected current exceeds several amperes. Therefore, the direction of the piezoelectric field generated in the quantum well active layer must be controlled to prevent the current injected into the semiconductor laser device from flowing toward the resonator facets. Therefore, if leakage current toward the resonator facets is not minimized, even if a current non-injection window region is formed near the resonator facets, the semiconductor laser device may degrade with a reduced COD level.

[0138] Patent Document 1 does not disclose any method of controlling the direction of the piezoelectric field so that the current injected into the semiconductor laser element is less likely to flow toward the cavity end face.

[0139] In addition, in the semiconductor light emitting device 400 of Patent Document 2, as shown in FIG. Figure 54 As shown in FIG. 4 , a structure is disclosed in which a light-emitting element 402 on a GaN substrate 401 is mounted face-down on a convex base substrate 410, with the GaN substrate 401 side of the element convex. This suppresses stress generated in the active layer and inhibits degradation of the active layer.

[0140] However, Patent Document 2 does not disclose any method for controlling stress in the resonator direction or for controlling the direction of the piezoelectric field generated in the active layer so that the current injected into the element is less likely to flow toward the resonator end face.

[0141] Furthermore, when diamond is used as the base substrate, since diamond is extremely hard, forming a convex, smoothly curved shape on the diamond base as disclosed in Patent Document 2 is extremely difficult in terms of processing, resulting in increased costs. Furthermore, if the mounting position of the component on the base is not controlled with high precision, the light-emitting surface may tilt.

[0142] As described above, in order to suppress the decrease in COD levels, a major cause of degradation in watt-class semiconductor laser devices, it is effective to form a current non-injection window region near the resonator facets, where no current is injected. In this case, to reduce current leakage from the current-injection region into the current non-injection window region, it is necessary not only to minimize the operating device temperature to suppress the increase in the operating current itself, but also to control the direction of the piezoelectric field generated in the active layer so that current is less likely to flow toward the resonator facets.

[0143] Therefore, the purpose of the present disclosure is to provide a low-power-consumption, Watt-class ultra-high-output semiconductor laser device that minimizes the temperature rise of the semiconductor laser element even during high-temperature operation at 85°C, reduces leakage current into the current non-injection window region, and enables long-term high-output operation.

[0144] A nitride-based light-emitting device according to one embodiment of the present disclosure includes: a nitride-based semiconductor light-emitting element having an Al x Ga 1-x N (0≤x≤1) substrate has the Al x Ga 1-x The N substrate has a multilayer structure in which a first cladding layer of a first conductive type, a first optical guide layer, a quantum well active layer, a second optical guide layer, and a second cladding layer of a second conductive type are sequentially stacked on the N substrate side; and a base substrate for mounting the nitride-based semiconductor light-emitting element. The nitride-based semiconductor light-emitting element is mounted on the base substrate so that the multilayer structure and the base substrate are opposite to each other. The base substrate is formed of diamond. x Ga 1-x A concave warp is formed on the N substrate side.

[0145] In addition, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the Al x Ga 1-x The N substrate is a GaN substrate.

[0146] In addition, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the multilayer structure may be x Ga 1-x The N substrate has a compressive average deformation.

[0147] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, at least one of the first optical guiding layer and the second optical guiding layer may include In.

[0148] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the first optical guiding layer and the second optical guiding layer may each have an In composition of 6% or less.

[0149] In addition, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the Al x Ga 1-x A buffer layer is further provided between the N substrate and the first cladding layer, the buffer layer comprising x Ga 1-x The N substrate has a compressive average strain nitride semiconductor layer.

[0150] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the buffer layer may include In.

[0151] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the buffer layer may further include an AlGaN layer.

[0152] In the nitride-based light-emitting device according to one embodiment of the present disclosure, the quantum well active layer may include a quantum well layer and a barrier layer, and the In composition of the barrier layer may be equal to or greater than the In composition of the first and second optical guiding layers.

[0153] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, a ridge may be formed on the second cladding layer.

[0154] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, a layer including In or a layer composed of GaN may be provided on the second optical guiding layer side of the ridge.

[0155] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the GaN substrate may have a nonpolar or semipolar plane orientation, and the Al composition in the multilayer structure may be 1% or less.

[0156] Furthermore, in the nitride-based light-emitting device according to one embodiment of the present disclosure, the multilayer structure may not include Al.

[0157] In addition, in one embodiment of the nitride-based light-emitting device of the present disclosure, a first barrier layer, a first pad electrode layer, a second barrier layer and a bonding layer may be provided in sequence from the second cladding side between the multilayer structure and the base substrate, and the width of the second barrier layer in the short side direction may be narrower than the width of the first barrier layer in the short side direction.

[0158] In addition, in one embodiment of the nitride-based light-emitting device disclosed herein, a first barrier layer, a first pad electrode layer, a second barrier layer, and a bonding layer may be provided between the multilayer structure and the base substrate from the second cladding side, and the bonding layer may extend between the second barrier layer and the first barrier layer to a position closer to the inside than the end of the second barrier layer.

[0159] Furthermore, a nitride-based light-emitting device according to one embodiment of the present disclosure includes:

[0160] Nitride-based semiconductor light-emitting device, which is based on Al x Ga 1-x The N substrate has the Al x Ga 1-x The N substrate has a multilayer structure in which a first cladding layer of a first conductivity type, a first optical guide layer, a quantum well active layer, a second optical guide layer, and a second cladding layer of a second conductivity type are sequentially stacked; and a base substrate for mounting the nitride-based semiconductor light-emitting element. The multilayer structure is opposite to the Al x Ga 1-x The N substrate has a compressive average strain, the nitride-based semiconductor light-emitting element is mounted on the base substrate so that the multilayer structure faces the base substrate, and the base substrate is formed of diamond.

[0161] Furthermore, a nitride-based light-emitting device according to one embodiment of the present disclosure includes:

[0162] Nitride-based semiconductor light-emitting device, which is based on Al x Ga 1-x The N substrate has the Al x Ga 1-x The N substrate has a multilayer structure in which a first cladding layer of a first conductivity type, a first optical guide layer, a quantum well active layer, a second optical guide layer, and a second cladding layer of a second conductivity type are sequentially stacked; and a base substrate for mounting the nitride-based semiconductor light-emitting element. The multilayer structure is opposite to the Al x Ga 1-x The N substrate has a 5.2×10 -4 Following the average deformation of tension or compression, the Al x Ga 1-x The thickness of the N substrate is 75 μm or more and 95 μm or less. The nitride-based semiconductor light-emitting element is mounted on the base substrate so that the multilayer structure faces the base substrate. The base substrate is formed of diamond.

[0163] Hereinafter, the embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the embodiments described below each illustrate a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, constituent elements, configuration positions and connection methods of the constituent elements, as well as processes and the order of the processes shown in the following embodiments are examples and are not intended to limit the present disclosure. Therefore, the constituent elements in the following embodiments that are not recorded in the independent claims showing the highest concept of the present disclosure are described as arbitrary structural elements.

[0164] In addition, each figure is a schematic diagram and is not a strict illustration. It should be noted that in each figure, the same reference numerals are given to substantially the same structures, and repeated descriptions are omitted or simplified.

[0165] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0166] (Implementation 1)

[0167] A description will be given of the nitride-based light-emitting device according to Embodiment 1. First, a semiconductor laser element 11 as an example of a nitride-based semiconductor light-emitting element used in the nitride-based light-emitting device according to Embodiment 1 will be described with reference to the drawings.

[0168] Figure 1A This is a schematic cross-sectional view showing the structure of the semiconductor laser element 11 according to the first embodiment. Figure 1A A cross section perpendicular to the cavity length direction of the semiconductor laser element 11 is shown. Figure 1B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 11 according to the first embodiment. Figure 1C : is a schematic cross-sectional view showing the structure of the semiconductor laser element 11 in the vicinity of the cavity end according to the first embodiment. Figure 1C , a cross section of a portion where a current non-injection window region is formed is shown.

[0169] like Figure 1A As shown, semiconductor laser device 11 is a nitride-based semiconductor light-emitting device having a multilayer structure comprising a first cladding layer 103 of a first conductivity type, a first optical guiding layer 105, a quantum well active layer 106, a second optical guiding layer 107, and a second cladding layer 109 of a second conductivity type stacked in this order from the GaN substrate 101 side. In Embodiment 1, semiconductor laser device 11 further includes an N-type GaN layer 104, an electron barrier layer 108, a contact layer 110, a current blocking layer 112, a P-side ohmic electrode 113, a P-side first adhesion layer 114, a first barrier layer 115, a pad electrode 116, and an N-side electrode 117.

[0170] The GaN substrate 101 is an Al substrate that serves as the base of the semiconductor laser element 11. x Ga 1-x An example of an N (0≤x≤1) substrate.

[0171] The first cladding layer 103 is a first conductivity type cladding layer disposed above the GaN substrate 101. In this embodiment, the first cladding layer 103 is formed of N-type AlGaN. The film thickness of the first cladding layer 103 is not particularly limited, but is 1.2 μm in the first embodiment.

[0172] The N-type GaN layer 104 is an example of a first-conductivity-type optical guiding layer disposed above the first cladding layer 103 and guiding light generated in the quantum well active layer 106. In this embodiment, the N-type GaN layer 104 is formed of N-type GaN. The thickness of the N-type GaN layer 104 is not particularly limited, but is 100 nm in Embodiment 1.

[0173] The first optical guiding layer 105 is disposed between the first cladding layer 103 and the quantum well active layer 106 and guides light generated in the quantum well active layer 106. In this embodiment, the first optical guiding layer 105 is formed of undoped InGaN. The thickness of the first optical guiding layer 105 is not particularly limited, but is 200 nm in Embodiment 1.

[0174] The quantum well active layer 106 is an undoped multiple quantum well active layer that generates light in the semiconductor laser element 11. The structure of the quantum well active layer 106 will be described later.

[0175] The second optical guiding layer 107 is disposed between the second cladding layer 109 and the quantum well active layer 106 and guides light generated in the quantum well active layer 106. In this embodiment, the second optical guiding layer 107 is formed of undoped InGaN. The thickness of the second optical guiding layer 107 is not particularly limited, but is 180 nm in Embodiment 1.

[0176] The electron barrier layer 108 is a layer that suppresses the leakage of electrons injected into the quantum well active layer 106. This layer prevents the leakage of carriers caused by the thermal excitation of the second cladding layer 109 by electrons injected into the quantum well active layer 106, thereby improving the temperature characteristics. In this embodiment, the electron barrier layer 108 is composed of AlGaN with an Al composition of 0.3 (30%) and a film thickness of 5 nm.

[0177] The second cladding layer 109 is a second conductivity type cladding layer disposed above the quantum well active layer 106. In this embodiment, the second cladding layer 109 is formed of P-type AlGaN. The thickness of the second cladding layer 109 is not particularly limited, but is 660 nm in the first embodiment.

[0178] The contact layer 110 is a layer that forms an ohmic contact. In this embodiment, the contact layer 110 is formed of P-type GaN. The film thickness of the contact layer 110 is not particularly limited, but is 0.1 μm in the first embodiment.

[0179] The current blocking layer 112 is a layer that limits the path of the current. It is formed from a material that is transparent with respect to the light distribution, that is, a transparent material that substantially does not absorb the light generated in the quantum well active layer 106. In the first embodiment, the current blocking layer 112 is formed from SiO2. The thickness of the current blocking layer 112 is not particularly limited, but in the first embodiment, it is 0.2 μm.

[0180] The P-side ohmic electrode 113 is a layer that forms an ohmic contact and includes, for example, a Pd layer with a thickness of 40 nm and a Pt layer with a thickness of 35 nm.

[0181] The P-side first adhesion layer 114 is a layer disposed between the P-side ohmic electrode 113 and the first barrier layer 115. The P-side first adhesion layer 114 is formed of, for example, Ti having a film thickness of 10 nm.

[0182] The first barrier layer 115 is a layer disposed between the P-side first adhesion layer 114 and the pad electrode 116. The first barrier layer 115 is formed of, for example, Pt with a film thickness of 10 nm.

[0183] The pad electrode 116 is a pad-shaped electrode disposed above the first barrier layer 115. The pad electrode 116 is formed of, for example, Au with a film thickness of 0.6 μm, Pt with a film thickness of 35 nm, and Au with a film thickness of 1 μm.

[0184] The N-side electrode 117 is formed on the lower surface of the GaN substrate 101, that is, on the surface opposite to the principal surface where the first cladding layer 103 is formed. The N-side electrode 117 is formed of, for example, 10 nm thick Ti, 35 nm thick Pt, and 2 μm thick Au.

[0185] In addition, if Figure 1A As shown, a ridge having a width W is formed on the second cladding layer 109 of the semiconductor laser element 11. The width W of the ridge is not particularly limited, but is 30 μm in the first embodiment.

[0186] At this time, the distance dp between the lower end of the ridge and the quantum well active layer 106 was set to 0.2 μm.

[0187] In order to obtain a light output of several watts even when operating at a high temperature of 85°C or above, the resonator length of the semiconductor laser element 11 is 1200 μm. Figure 1CAs shown, an insulating film (0.2 μm thick) made of SiO2 is formed on the P-type GaN contact layer 110 on the ridge near the resonator end facets on the front and back sides of the resonator, forming a current non-injection window region within a region less than 30 μm from the resonator end. If the semiconductor laser element 11 does not have a current non-injection window region, when the action carrier density in the quantum well active layer 106 increases, heat is generated due to non-luminescent recoupling, and the band gap energy decreases. At this time, light absorption also increases, light output further decreases, and heat generation in the semiconductor laser element increases, eventually damaging the resonator end facet and causing COD. On the other hand, by forming a current non-injection window region near the resonator end facet of the semiconductor laser element 11, current injection into the laser resonator end facet is suppressed, thereby suppressing the increase in action carrier density in the quantum well active layer near the end facet. Consequently, the temperature rise in the quantum well active layer of the semiconductor laser element 11 is suppressed, thereby suppressing the occurrence of COD.

[0188] Here, increasing the Al composition of the first cladding layer 103 composed of N-type AlGaN and the second cladding layer 109 composed of P-type AlGaN can increase the refractive index difference between the quantum well active layer 106 and each cladding layer. This allows for stronger light confinement in the quantum well active layer in the direction perpendicular to the substrate (normal to the substrate), thereby reducing the oscillation threshold current value. However, due to the difference in thermal expansion coefficient between each cladding layer composed of AlGaN layers and the GaN substrate 101, excessively increasing the Al composition of each cladding layer composed of AlGaN can cause lattice defects, cracks, etc., leading to a decrease in reliability.

[0189] Furthermore, since the band gap energy of each cladding layer composed of AlGaN increases with the increase in Al composition, increasing the Al composition leads to an increase in the operating voltage. Therefore, it is necessary to set the Al composition of each cladding layer composed of AlGaN to 0.05 (5%) or less in order to manufacture the semiconductor laser device 11.

[0190] In the first embodiment, the Al composition of each cladding layer composed of AlGaN is set to 3.5% in order to increase the light confinement coefficient in the vertical direction of the active layer, reduce the occurrence of lattice defects and cracks, and suppress the operating voltage.

[0191] In addition, in order to obtain laser oscillation with a wavelength of 450nm, the quantum well active layer 106 in the first embodiment has a DQW (Double Quantum Well) structure. Figure 1B The structure of the quantum well active layer 106 will be described. Figure 1B As shown, the quantum well active layer 106 has a DQW structure, which has two layers with a thickness of Quantum well layers 106b and 106d are composed of InGaN with an indium composition of 0.18 (18%). The quantum well active layer 106 further includes barrier layers 106a, 106c, and 106e composed of InGaN. The thicknesses of barrier layers 106a, 106c, and 106e are, for example, 3 nm, 7 nm, and 3 nm, respectively. The thicker the barrier layer 106c between quantum well layers 106b and 106d, the more it suppresses the coupling of wave functions between quantum well layers 106b and 106d. In order to suppress the coupling of wave functions to a certain extent, the film thickness of the barrier layer between the quantum well layers can be above 5 nm. The combination of the thicknesses of the barrier layers 106a, 106c and 106e can be, for example, 7 nm, 7 nm and 5 nm, 5 nm, 5 nm and 3 nm, 5 nm, 7 nm and 5 nm, 10 nm, 10 nm and 8 nm, 15 nm, 15 nm and 13 nm, etc.

[0192] Figure 2 is a diagram showing the energy band structure of the quantum well active layer. Figure 2 ] shows the energy band structure when the In composition of the quantum well layer is 0.145 (14.5%) and the In composition of the barrier layer is 0.008 (0.8%). Figure 2 Graph (a) shows the energy band structure of the conduction band and the wave function of the electrons confined in the quantum well layer when the piezoelectric effect is neglected. Figure 2 Graph (b) shows the energy band structure of the valence electron band and the wave function of the holes enclosed in the quantum well layer when the piezoelectric effect is neglected. Figure 2 Graph (c) shows the energy band structure of the conduction band and the wave function of the electrons confined in the quantum well layer when the piezoelectric effect is taken into account. Figure 2 Graph (d) shows the energy band structure of the valence band and the wave function of holes confined in the quantum well layer when the piezoelectric effect is taken into account.

[0193] In the quantum well layer, a piezoelectric field is generated due to the piezoelectric effect, and the energy band structure of the quantum well layers 106b and 106d has a slope that causes the potential to decrease toward the second cladding layer 109, which is composed of p-type AlGaN. In this case, the wave function of electrons diffuses toward the second cladding layer 109, which is composed of p-type AlGaN. Conversely, the wave function of holes diffuses toward the first cladding layer 103, which is composed of n-type AlGaN.

[0194] As a result, the overlap integral of the distributions of the electron wave function and the hole wave function becomes smaller, which leads to a decrease in the interaction between electrons and holes, a decrease in the gain of the quantum well, and thus an increase in the oscillation threshold.

[0195] To suppress the diffusion of electron wave functions toward the second cladding layer 109 composed of p-type AlGaN, if the band gap energy of the second optical guiding layer 107 is greater than that of the barrier layer 106e, the thickness of the barrier layer 106e can be reduced, bringing the second optical guiding layer 107 closer to the quantum well active layer. This increases the difference between the energy of the electron's quantum energy level and the conduction band energy of the second optical guiding layer 107, thereby increasing the attenuation of the electron wave function toward the second cladding layer 109 composed of p-type AlGaN.

[0196] Furthermore, in the region of barrier layer 106a closest to first cladding layer 103 composed of an N-type AlGaN layer, the wave function of holes tends to diffuse toward first cladding layer 103, resulting in a decrease in the overlap integral of the distributions of the wave functions of electrons and holes. To suppress the diffusion of the wave function of holes toward first cladding layer 103, if the band gap energy of first optical guiding layer 105 is greater than that of barrier layer 106a, the thickness of barrier layer 106a can be reduced, thereby bringing first optical guiding layer 105 closer to the quantum well active layer.

[0197] Here, the effective masses of heavy holes and light holes in the quantum well layers 106b and 106d are about 8 times and 1.6 times larger than the effective mass of electrons, respectively. Therefore, the diffusion of the wave function of heavy holes toward the first cladding 103 side is smaller than the diffusion of the wave function of electrons in the blocking layer 106e toward the second cladding side.

[0198] Furthermore, in the barrier layer 106c between the quantum well layers, there are wave functions for electrons diffusing from the quantum well layer 106b toward the second cladding layer 109 composed of p-type AlGaN, and for heavy and light holes diffusing from the quantum well layer 106d toward the first cladding layer 103 composed of n-type AlGaN. As a result, a decrease in the interaction between electrons and holes in the barrier layer 106c between the quantum well layers is suppressed.

[0199] Therefore, regardless of the influence of wave function coupling between quantum well layers, when the band gap energies of the first and second optical guiding layers 105 and 107 are greater than the band gap energies of the barrier layers 106a and 106e, if at least the thickness of the barrier layer closest to the second cladding layer 109 composed of p-type AlGaN is made thinner than the thickness of the barrier layers between the quantum well layers, the decrease in quantum well gain due to a decrease in the interaction between the electron and hole wave functions can be suppressed, thereby lowering the oscillation threshold. Furthermore, if the thickness of the barrier layer closest to the first cladding layer 103 composed of n-type AlGaN is made thinner than the thickness of the barrier layers between the quantum well layers, the decrease in quantum well gain due to a decrease in the interaction between the electron and hole wave functions can be further suppressed, thereby lowering the oscillation threshold.

[0200] When the thickness of the barrier layer between quantum well layers is less than 5 nm, the influence of the coupling of the wave function between the quantum well layers becomes greater. In this case, as described above, in the region between the quantum well layers, there are wave functions of electrons that diffuse toward the second cladding layer 109, and wave functions of heavy holes and light holes that diffuse from the quantum well layer 106 d toward the first cladding layer 103, which suppress the decrease in the interaction between electrons and holes in the barrier layer 106 c between the quantum well layers. Therefore, even when the thickness of the barrier layer between the quantum well layers is less than 5 nm, if the combination of the thicknesses of the barrier layers 106 a, 106 c, and 106 e is set to, for example, 3 nm, 3 nm, and 1 nm, or 5 nm, 5 nm, and 3 nm, the diffusion of the wave function of electrons toward the second cladding layer 109 becomes smaller, which can reduce the increase in the oscillation threshold associated with the decrease in gain caused by coupling between quantum wells.

[0201] Furthermore, by setting the thickness of the barrier layers 106a, 106c, and 106e to, for example, 1 nm, 3 nm, and 1 nm, or 3 nm, 5 nm, and 3 nm, it is possible to suppress the diffusion of the wave function of holes toward the first cladding layer 103 and the diffusion of the wave function of electrons toward the second cladding layer 109. As a result, the increase in the oscillation threshold associated with the decrease in gain due to coupling between quantum wells can be further reduced.

[0202] Even when there are three or more quantum well layers, and the band gap energies of the first and second optical guiding layers 105 and 107 are greater than those of the barrier layers, if at least the thickness of the barrier layer closest to the second cladding layer 109 composed of p-type AlGaN is made thinner than the thickness of the barrier layers between the quantum well layers, the decrease in quantum well gain due to a decrease in the interaction between the wave functions of electrons and holes can be suppressed, thereby lowering the oscillation threshold. Furthermore, if the thickness of the barrier layer closest to the first cladding layer 103 composed of n-type AlGaN is made thinner than the thickness of the barrier layers between the quantum well layers, the decrease in quantum well gain due to a decrease in the interaction between the wave functions of electrons and holes can be further suppressed, thereby lowering the oscillation threshold.

[0203] In order to obtain laser oscillation light in the 450nm segment, the In composition of the quantum well layer needs to be about 15%. In this case, the lattice mismatch with GaN becomes more than 1.7%. When the film thickness is too thick, lattice defects are generated. On the contrary, when the film thickness is too thin, the light confinement coefficient in the vertical direction to the quantum well layer becomes smaller, and the oscillation threshold and the action carrier density become higher, thereby leading to an increase in leakage current during high-temperature operation. Therefore, in order to fully increase the vertical direction (stacked direction, i.e., the direction of the quantum well layer) to the quantum well layer while suppressing the generation of lattice defects, the In composition of the quantum well layer needs to be about 15%. In this case, the lattice mismatch with GaN becomes more than 1.7%. When the film thickness is too thick, lattice defects are generated. On the contrary, when the film thickness is too thin, the light confinement coefficient in the vertical direction to the quantum well layer becomes smaller, and the oscillation threshold and the action carrier density become higher, thereby leading to an increase in leakage current during high-temperature operation. Figure 1A The light confinement coefficient in the y-axis direction) of the quantum well layer can also be Above and In the first embodiment, the thickness of the quantum well layer is set to

[0204] Furthermore, when the indium content of the first and second optical guiding layers 105 and 107 is low, light confinement in the direction perpendicular to the quantum well active layer 106 decreases, increasing the oscillation threshold and the operating carrier density. Consequently, leakage current increases during high-temperature operation. Therefore, at least one of the first and second optical guiding layers 105 and 107 may contain indium. This can suppress leakage current.

[0205] Conversely, when the In composition of the first and second optical guiding layers 105 and 107 is high, lattice defects are more likely to form due to the increased lattice mismatch with GaN. Therefore, to increase the light confinement coefficient perpendicular to the quantum well layer without generating lattice defects, the In composition of the first and second optical guiding layers 105 and 107 can be set to 0.025 (2.5%) or higher and 0.07 (7%) or lower. In Embodiment 1, the In composition of the first and second optical guiding layers 105 and 107 is set to 0.03 (3%), achieving a balance between suppressing the generation of lattice defects and increasing the light confinement coefficient perpendicular to the quantum well layer.

[0206] In addition, if Figure 1A As shown in FIG. 1 , a current blocking layer 112 made of a dielectric material of SiO2 is formed on the side surface of the ridge of the semiconductor laser element 11. In this structure, the current injected from the contact layer 110 made of P-type GaN is narrowed only to the ridge through the current blocking layer 112 and injected into the quantum well active layer 106 located below the bottom of the ridge. As a result, the inverted distribution state of the carriers required for laser oscillation is achieved by the injection current of about 100 mA. The light emitted by the recombination of the carriers composed of the electrons and positive holes injected into the quantum well active layer 106 is in the direction perpendicular to the quantum well active layer 106 ( Figure 1A In the y-axis direction of the quantum well active layer 106, the first optical waveguide layer 105, the second optical waveguide layer 107, the first cladding layer 103 and the second cladding layer 109 are enclosed. Figure 1A In the direction perpendicular to the y-axis (hereinafter referred to as the horizontal direction), the refractive index of the current blocking layer 112 is lower than that of each cladding layer, so light is confined. In addition, since the current blocking layer 112 is transparent to the laser oscillation light, there is no light absorption, and a low-loss waveguide can be realized. In addition, the light distribution propagating in the waveguide can penetrate the current blocking layer to a large extent, so it is easy to obtain a 1×10 -3Furthermore, by adjusting the distance dp between the current blocking layer 112 and the quantum well active layer 106, the ΔN (the difference in the effective refractive index in the vertical direction between the inside and outside of the ridge) can be reduced to 10 -3 The size of the light distribution is precisely controlled. Therefore, it is possible to obtain a semiconductor laser element 11 with a low operating current and high output while precisely controlling the light distribution. In the first embodiment, by setting ΔN to 5×10 -3 This confines light in the horizontal direction.

[0207] Furthermore, in the structure of the semiconductor laser element 11 described above, by varying the In composition of the first optical waveguide layer 105, the second optical waveguide layer 107, and the barrier layers 106a, 106c, and 106e, it is possible to control the average value of the stress generated by the entire multilayer structure formed on the GaN substrate 101, thereby controlling the direction of warping of the GaN substrate 101 after crystal growth.

[0208] Specifically, for example, when the In composition of the first optical guiding layer 105 and the second optical guiding layer 107 is increased, the lattice constant of the InGaN layer becomes greater than the lattice constant of the GaN substrate 101. Consequently, the average lattice constant of the multilayer structure becomes greater than the lattice constant of the GaN substrate 101. Consequently, when the multilayer structure is averaged as a whole, it is compressed by the GaN substrate 101. In other words, the multilayer structure is subjected to compressive stress by the GaN substrate 101. In other words, the multilayer structure experiences an average compressive deformation relative to the GaN substrate 101. As a result, the warpage that occurs in the GaN substrate 101 after crystal growth is described using the accompanying drawings.

[0209] Figure 3A and Figure 3B Each of them is a schematic side view showing the appearance of semiconductor laser devices 51 a and 51 b according to the first embodiment.

[0210] Figure 3A The semiconductor laser device 51a shown is an example of a nitride-based light-emitting device including a nitride-based semiconductor light-emitting element and a base substrate 122 for mounting the nitride-based semiconductor light-emitting element. The semiconductor laser device 51a includes a semiconductor laser element 11 as a nitride-based semiconductor light-emitting element. In the semiconductor laser device 51a, the semiconductor laser element 11 is mounted on the base substrate 122 so that the multilayer structure is opposite to the base substrate 122. In addition, the base substrate 122 is formed of diamond. It should be noted that in embodiment 1, the semiconductor laser element 11 is mounted on the base substrate 122 via a bonding layer 121 composed of AuSn solder or the like. Here, the multilayer structure of the semiconductor laser element 11 has a compressive average deformation relative to the GaN substrate 101. On the other hand, Figure 3BThe semiconductor laser device 51b shown is different from the semiconductor laser device 11 in that the multilayer structure of the semiconductor laser element 11 has an average tensile deformation with respect to the GaN substrate 101. Figure 3A The semiconductor laser device 51a shown is different, but the other aspects are the same.

[0211] When the multilayer structure of the semiconductor laser element 11 has a compressive average deformation relative to the GaN substrate 101, as shown in FIG. Figure 3A As shown in FIG. 1 , the semiconductor laser element 11 is warped concavely toward the GaN substrate 101. Figure 3A In the Figure 1A The semiconductor laser element 11 shown is mounted downwardly on a base substrate, with the upper surface (outer side) of the GaN substrate 101 concave relative to the resonator direction (z-axis direction). Here, ΔR represents the magnitude (distance) of the warpage of the semiconductor laser element 11 at the center of the resonator direction. ΔR is negative when the upper surface of the GaN substrate 101 is concave, and positive when the upper surface is convex.

[0212] On the other hand, when the In composition of the first optical guiding layer 105 and the second optical guiding layer 107 is reduced, the lattice constants of the first cladding layer 103 composed of N-type AlGaN and the second cladding layer 109 composed of P-type AlGaN are smaller than the lattice constant of the GaN substrate 101. Therefore, the multilayer structure has a tensile average deformation with respect to the GaN substrate 101. As a result, Figure 3B As shown, the warpage of the GaN substrate 101 after crystal growth becomes convex when the GaN substrate 101 faces upward. Figure 3B Show Figure 1A The semiconductor laser element 11 shown is mounted facing downward on a base substrate so that the GaN substrate 101 side becomes a convex shape with respect to the cavity direction.

[0213] When a nitride layer is formed on the C-plane of the GaN substrate 101, piezoelectric charges are generated at the interface where the lattice mismatch occurs due to the deformation caused by the lattice mismatch. As a result, the piezoelectric charges are generated in the normal direction ( Figure 3A and Figure 3B In the y-axis direction, a piezoelectric field is generated, and the band structure in the growth layer direction changes. In addition, when shear stress, which is a rotational (torsion) stress, is generated in the element structure, due to the shear stress ( Figure 3A and Figure 3B The rotational stress in the zy plane) and in the direction parallel to the growth layer ( Figure 3A and Figure 3BA piezoelectric field is also generated in the z-direction (in the z-direction). The piezoelectric field in the direction parallel to the growth layer (z-direction) caused by this shear stress changes the band structure in the z-axis direction, thereby affecting the distribution of the ease of current injection in the resonator direction.

[0214] Here, when shear stress occurs in the cavity direction of the semiconductor laser element 11 , warping occurs in the semiconductor laser element 11 . There is a close relationship in which the warping in the cavity direction of the semiconductor laser element 11 and the shear stress are proportional to each other.

[0215] Therefore, simulation is used to estimate the Figure 1A The following describes the magnitude of shear stress generated in the quantum well layers 106b and 106d of the quantum well active layer 106 when a device having the structure shown is mounted face-down on various base substrate materials and the warpage (ΔR) is varied from -1 μm to 1 μm at 0.5 μm intervals. The results are described using the accompanying drawings.

[0216] Figure 4 、 Figure 5 and Figure 6 The graphs show the distribution of shear stress and piezoelectric field along the resonator length direction for base substrate 122 formed of diamond, SiC (silicon carbide), and AlN (aluminum nitride), respectively. SiC and AlN have high heat dissipation properties when mounting semiconductor laser elements and are widely used as base substrate materials with high thermal conductivity.

[0217] exist Figures 4 to 6 Graphs (a), (b), and (c) show the distribution of shear stress in the resonator direction, the piezoelectric field, and the piezoelectric potential (piezoelectric voltage) generated by the piezoelectric field, respectively, at a temperature of 25°C. The resonator length of the semiconductor laser element 11 is assumed to be 1200 μm, and the coordinates of the center portion in the resonator direction are assumed to be 0 μm.

[0218] Likewise, in Figures 4 to 6 Graphs (d), (e), and (f) show the distribution of the shear stress relative to the resonator direction, the piezoelectric field, and the magnitude of the piezoelectric potential generated by the piezoelectric field at a temperature of 150°C, respectively.

[0219] Likewise, in Figures 4 to 6 Graphs (g), (h), and (i) show the distribution of the shear stress relative to the resonator direction, the piezoelectric field, and the magnitude of the piezoelectric potential generated by the piezoelectric field at a temperature of 200°C, respectively.

[0220] Regarding the magnitude of the piezoelectric potential, the piezoelectric potential at the center of the resonator is set to 0 V. In a watt-class ultra-high output semiconductor laser device made of nitride-based materials, for example, when operating at 3 W, the optical density in the quantum well active layer at the resonator end facet is several tens of MW / cm 2 Therefore, to prevent the occurrence of COD at the end face, a current non-injection window region is formed at the end face to suppress non-luminescent recoupling in the area near the end face, thereby suppressing the decrease in COD level. Therefore, it is necessary to suppress the leakage of injected current into the current non-injection window region. However, in the piezoelectric potential distribution in the direction of the resonator, the area near the end face of the resonator may be lower than the central part in the direction of the resonator. In this case, current is likely to leak into the current non-injection window region, easily causing non-luminescent recoupling, resulting in heat generation and a decrease in COD level.

[0221] Therefore, in semiconductor laser devices operating at high output power levels of watts at a high temperature of 85°C, the magnitude of the injected current becomes large, exceeding several amperes. Therefore, the direction of the piezoelectric field generated in the quantum well active layer is controlled to prevent the current injected into the semiconductor laser device from flowing toward the resonator facets. Therefore, unless leakage current toward the resonator facets is minimized, device degradation will occur due to a decrease in the COD level, even if a current non-injection window region is formed at the resonator facets.

[0222] Furthermore, when operating a semiconductor laser device at an ambient temperature of 85°C, the temperature of the quantum well active layer of the semiconductor laser device rises to a high temperature of approximately 150°C due to heat generation associated with power consumption in the semiconductor laser device. Therefore, the piezoelectric potential must be set to prevent current leakage into the current non-injection window region not only at room temperature but also at temperatures exceeding 150°C.

[0223] Here, when diamond is used for the base substrate 122, as shown in FIG. Figure 4 As shown in FIG. 1 , it can be seen that the piezoelectric potential near the end face of the resonator is higher than the piezoelectric potential in the center portion in the resonator direction. On the other hand, when SiC and AlN are used as the base, as shown in FIG. Figure 5 and Figure 6 As shown, the piezoelectric potential near the end surface of the resonator is lower than the piezoelectric potential in the center portion in the resonator direction.

[0224] This is believed to be because the thermal expansion coefficient of SiC is 6.6×10 -6 , the thermal expansion coefficient of AlN is 4.15×10 -6 In contrast, the thermal expansion coefficient of diamond is 1.1×10 -6 , with the thermal expansion coefficient of GaN being 5.59×10-6 Thus, the thermal residual stress generated when the semiconductor laser element 11 is mounted on the base substrate 122 formed of diamond having a small thermal expansion coefficient will be described.

[0225] When AuSn solder is used as the bonding layer 121 and the semiconductor laser element 11 is mounted on the base substrate 122 at a high temperature of approximately 300°C, the effect of thermal residual stress caused by the difference in thermal expansion coefficients between the diamond-formed base substrate 122 and the semiconductor laser element 11 becomes greater than when a base substrate formed of SiC or AlN is used. Consequently, when the semiconductor laser element 11 is mounted on the diamond-formed base substrate 122, the tensile stress in the resonator direction (z-axis direction) of the semiconductor laser element 11 becomes greater than when the semiconductor laser element 11 is mounted on a SiC or AlN-formed base substrate. At this time, shear stress in the yz plane is generated in a direction where the piezoelectric potential at the resonator end facets is relatively higher than that at the center of the resonator direction. Therefore, when the diamond-formed base substrate 122 is used, the effect of increasing the piezoelectric potential near the resonator end facets relative to that at the center of the resonator direction is greatest at high temperatures ranging from 25°C to 150°C. The inventors' analysis has shown that this effect is particularly pronounced when the GaN substrate 101 of the semiconductor laser element 11 is oriented upward relative to the multilayer structure, and the warpage in the cavity direction is concave. Furthermore, when using a diamond-formed base substrate 122, if the warpage ΔR of the GaN substrate 101 is 0.5 μm or less, the piezoelectric potential in the region near the cavity end facets is increased relative to the center region in the cavity direction, even at a high temperature of 200°C.

[0226] Therefore, if diamond is used for the base substrate 122 and the semiconductor laser element 11 is mounted so that ΔR is less than 0.5 μm when the GaN substrate 101 is facing upward, the piezoelectric potential in the region near the cavity end facets can be increased relative to the center portion in the cavity direction. Furthermore, if diamond is used for the base substrate 122 and the semiconductor laser element 11 is mounted so that ΔR is less than 0 μm when the GaN substrate 101 is facing upward (concave shape), the piezoelectric potential in the region near the cavity end facets can be further increased relative to the center portion in the cavity direction.

[0227] On the other hand, when SiC is used for the base substrate, as Figure 5 As shown in the graphs (c), (f), and (i), it can be seen that it is difficult to increase the piezoelectric potential in the vicinity of the resonator end face relative to the central portion in the resonator direction.

[0228] In addition, when AlN is used for the base substrate, as Figure 6As shown in the graphs (c), (f) and (i), it can be seen that in order to increase the piezoelectric potential of the region near the end face of the resonator relative to the center portion in the resonator direction, ΔR needs to be controlled to a range of less than -1 μm.

[0229] In order to control the warp ΔR of the semiconductor laser element 11 to -1 μm or less for a device with a cavity length of 1200 μm, the InGaN layers (e.g., the first optical guiding layer 105 and the second optical guiding layer 107) used in the multilayer structure of the semiconductor laser element must have a very high In composition or a very thick film thickness. In this case, lattice defects due to lattice mismatch are likely to occur in the first optical guiding layer 105 and the second optical guiding layer 107. Therefore, from the perspective of the reliability of the semiconductor laser element 11, it is not preferable to reduce the warp ΔR in the negative direction beyond what is necessary.

[0230] Furthermore, diamond has a thermal conductivity of approximately 1000 W / m·K, which is significantly higher than the thermal conductivity of SiC (approximately 200 W / m·K) or AlN (approximately 150 W / m·K). Thus, when mounted on a diamond-formed base substrate 122 with the bonding facing downward and ΔR being less than 0.5 μm, preferably less than 0 μm, high heat dissipation can be achieved, and the piezoelectric potential near the resonator facets can be increased relative to the center portion in the resonator direction. This mounting method is considered highly suitable for mounting nitride-based blue semiconductor laser devices that can ensure long-term reliability during high-temperature, high-output operation.

[0231] Next, a method for setting ΔR to 0.5 μm or less and preferably to a negative state (forming a concave shape when the GaN substrate 101 faces upward) as described above will be described.

[0232] Since the lattice constant of InN is larger than that of GaN, the compressive strain increases as the In composition in the InGaN layer increases. Figure 1A In the structure shown, increasing the In composition of the first and second InGaN optical guiding layers 105 and 107 increases the compressive strain within the average strain of the multilayer structure formed on the GaN substrate 101, and tends to form a concave shape when the substrate is turned upward. Therefore, increasing the In composition of the In-containing layers as much as possible can reduce ΔR, resulting in a negative state.

[0233] Here, the average deformation (ε ave ) is defined by the following formula 1.

[0234] [Formula 1]

[0235]

[0236] Here, ε(y) is the lattice mismatch (strain) of each layer in the growth layer direction (position y) relative to the GaN substrate 101, and T is the distance from the GaN substrate 101 in the growth layer direction in the multilayer structure formed on the GaN substrate 101 (i.e., the film thickness of the multilayer structure). In addition, when the lattice constant of GaN is set to L s , let the lattice constant at each position in the growth layer direction be L v When , the quality mismatch is given by the following formula 2.

[0237] (L s -L y ) / L s Formula 2

[0238] At this time, ε ave (T) represents the average strain from the GaN substrate 101 to the position of the film thickness T in the multilayer structure on the GaN substrate 101. Therefore, when T is the film thickness of the entire multilayer structure, ε ave (T) refers to the average lattice mismatch of the entire multilayer structure (the average strain of the entire multilayer structure: ε tave ). In addition, according to Formula 2, in a layer subjected to compressive deformation, the deformation takes a negative value.

[0239] Here, the warpage ΔR and the average deformation ε are compared using the figure. tave The relationship between . Figure 7A This is a schematic diagram explaining the definition of warpage ΔR. Figure 7B This is a graph showing the relationship between the average strain and the warpage ΔR of the multilayer structure. Figure 7B Calculation results of the average strain dependence of the warpage ΔR of the entire multilayer structure when the thickness of the GaN substrate 101 is changed from 65 μm to 105 μm at 10 μm intervals are shown in FIG.

[0240] like Figure 7A As shown, when the GaN substrate 101 is arranged above the crystal growth layer constituting the multilayer structure, when the upper surface of the GaN substrate 101 is in a concave state, the warpage ΔR is defined as negative.

[0241] like Figure 7B As shown in FIG. 1 , it can be seen that the warpage ΔR of the semiconductor laser element 11 is almost independent of the thickness of the GaN substrate 101. tave -1.5×10 -4 When the GaN substrate 101 is facing upward, the warpage becomes negative (concave shape when the GaN substrate 101 is facing upward). In addition, it can be seen that when the thickness of the GaN substrate 101 is thin, the degree of change in the warpage relative to the average deformation ε taveThis is because when the thickness of the GaN substrate 101 is thin, the warping of the semiconductor laser element 11 as a whole is easily affected by the average deformation ε of the multilayer structure. tave Here, when the thickness of the GaN substrate 101 is thin, it is easy to break during the processing in the wafer state after crystal growth. When the thickness of the GaN substrate 101 is too thick, it is difficult to split the wafer used to make the resonator end face of the laser element. Therefore, in order to facilitate splitting and prevent the damage of the wafer during the processing of other semiconductor laser elements 11, the thickness of the GaN substrate 101 is greater than 75μm and less than 95μm, preferably in the range of 85μm±5μm. In this case, if the size is controlled to be less than 0 so that the average deformation ε of the entire multilayer structure is tave If the compressibility is achieved, ΔR also becomes less than 0.1 μm. tave Set to -1.5×10 -4 When ΔR is less than 0.1 μm, ΔR becomes a negative value (concave shape when the GaN substrate 101 side faces upward). Figure 4 The results show that even when the quantum well active layer 106 reaches a high temperature of 200° C. or higher, the piezoelectric potential at the resonator end portion is stably increased relative to the piezoelectric potential at the center portion in the resonator direction, thereby reducing current leakage into the current non-injection window region.

[0242] Here, the accompanying drawings are used Figure 1A The average strain ε of the multilayer structure of the embodiment 1 shown is tave Provide explanation. Figure 8A This is a graph showing an example of the distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of Embodiment_1. Figure 8B yes Figure 8A An enlarged view of the quantum well active layer 106 in FIG. Figure 8C is an average strain ε in the growth layer direction of the multilayer structure of the first embodiment. tave A graph showing an example of the distribution of . Figures 8A to 8C Figure 2 shows the strain when the In composition of the barrier layers 106a, 106c, and 106e in the multilayer structure is set to 0.8%, the thickness of the first light guiding layer 105 composed of InGaN and the second light guiding layer 107 composed of InGaN are set to 185nm and 100nm respectively, and the In composition is set to 0.03 (3%). In this multilayer structure, the overall average strain ε is tave The size becomes 1.9×10 -4, becoming an average strain of tensile properties. Therefore, in this multilayer structure, the average strain of the entire layer becomes tensile, and the warpage ΔR of the element after crystal growth becomes positive. Therefore, in order to make the average strain of the entire multilayer structure compressive, it is necessary to increase the In composition of the layer containing In composition or increase its film thickness. Here, Figure 1A In the structure shown, as layers containing In, the first optical guiding layer 105 , the second optical guiding layer 107 , and the barrier layers 106 a , 106 c , and 106 e were the subjects of investigation of In composition.

[0243] However, when the In composition of the layer containing In is increased, the lattice mismatch with the GaN substrate 101 becomes larger, so lattice defects are easily generated. In addition, since the piezoelectric polarization charge at the heterojunction becomes larger, the band structure changes, and this leads to a problem of increasing the operating voltage. Therefore, it is necessary to pay attention to the setting of the In composition. Figure 2 Let's explain in detail.

[0244] like Figure 2 As shown in Figure 1, the piezoelectric effect biases the wave function toward the end of the quantum well layer. The larger the overlap integral of the wave functions of electrons and holes injected into the quantum well layer, the greater the interaction between the electrons and holes. Therefore, when a bias is introduced into the wave functions of electrons and holes, the interaction decreases, and the amplification gain (hereinafter referred to as "gain") in the quantum well active layer 106 obtained for the same injected current decreases. This, in turn, increases the oscillation threshold current value.

[0245] Next, the gain obtained in the quantum well active layer will be described using the drawings. Figure 9A This is a graph showing calculation results of the wavelength and carrier concentration dependence of the gain obtained in the quantum well active layer when the piezoelectric effect is taken into account. Figure 9B This is a graph showing calculation results of the wavelength and carrier concentration dependence of the gain obtained in the quantum well active layer when the piezoelectric effect is not taken into account. Figure 9C This is a graph showing the calculation results of the carrier concentration dependence of the injected gain into the quantum well active layer. Figure 9C The gains are shown in the figure when the piezoelectric effect is taken into account (with a piezoelectric field) and when the piezoelectric effect is not taken into account (without a piezoelectric field). Figures 9A to 9C As shown, it can be seen that the gain becomes smaller due to the piezoelectric effect.

[0246] The reason is that, Figure 2 As shown in the graph (c) of , the band structure of the quantum well layer is tilted due to the piezoelectric effect, and the wave function is biased within the quantum well layer. Therefore, to suppress this wave function bias, the absolute value of the piezoelectric field generated in the quantum well layer can be reduced.

[0247] Here, the relationship between the piezoelectric field in the quantum well layer and the In composition of the barrier layer will be described using the drawings. Figure 10 Graph showing the dependence of the piezoelectric field generated in the quantum well layer on the In composition of the barrier layer. Figure 10 Calculation results of the In composition dependence of the piezoelectric field blocking layer are shown in the case of using a plurality of first and second optical guiding layers each having an In composition of 2% to 7%.

[0248] like Figure 10 As shown in the figure, the piezoelectric field generated in the quantum well layer is independent of the In composition of each InGaN optical guide layer. On the other hand, increasing the In composition of the barrier layer decreases the absolute value of the piezoelectric field generated in the quantum well layer. Therefore, it is found that increasing the In composition of the barrier layer is best to suppress the decrease in gain of the active layer due to the piezoelectric effect.

[0249] However, when the In composition of the barrier layer is increased, the piezoelectric polarization charge generated at the interface with the photoconductive layer increases, resulting in an increase in the operating voltage. Figure 11 This is a graph showing the calculation results of the dependence of the operating voltage of the semiconductor laser element when operating at 100 mA on the In composition of the barrier layer. Figure 11 The results of calculating the dependence of the operating voltage on the In composition of the barrier layer in the case of using a plurality of first and second optical guiding layers with an In composition of 2% to 7% are shown in FIG. Figure 11 The results show that when the In composition of each InGaN optical guide layer is set to 0.06 (6%) or higher, the operating voltage increases, and when the In composition of the barrier layer is set to 0.06 (6%) or higher, the increase in operating voltage becomes significant. Therefore, it is found that to suppress the increase in operating voltage, the In composition of each optical guide layer should be set to 0.06 (6%) or lower, more preferably 0.05 (5%) or lower, and the In composition of the barrier layer should be set to 0.06 (6%) or lower. Furthermore, it is found that when the In composition of the barrier layer is set to 0.01 (1%) or higher, the operating voltage is minimized when the In composition of the guide layer is 0.03 (3%). An increase in operating voltage leads to an increase in self-heating during operation of the semiconductor laser element, so the operating voltage needs to be kept as low as possible.

[0250] Next, the relationship between the piezoelectric field and the gain will be described using the drawings.

[0251] Figure 12 : is a diagram showing the relationship between the piezoelectric field and the gain of the semiconductor laser element 11 according to the first embodiment. Figure 12The graphs (a) and (b) show the energy band structure of the conduction band when the In composition of the barrier layer is set to 0.8% and 4%, respectively. Figure 12 The electron wave function and energy level are also shown in the graphs (a) and (b). Figure 12 Graphs (c) and (d) show the wavelength dependence of the gain when the In composition of the barrier layer is set to 0.8% and 4%, respectively. Figure 12 Graphs (c) and (d) show the wavelength dependence of the gain for various cases where the carrier density injected into the quantum well active layer is varied as a parameter. It can be seen that when the In composition of the barrier layer is set to 4%, the piezoelectric field generated in the quantum well layer is smaller, and the gain for the same number of injected carriers is also larger. As a result, the oscillation threshold current can be reduced, thereby reducing the power consumption of the semiconductor laser device.

[0252] Next, the carrier concentration dependence of gain will be described using the drawings. Figure 13 Graph showing the carrier concentration dependence of the gain of the semiconductor laser element 11 according to the first embodiment. Figure 13 The calculation results of the gain at a wavelength of 450 nm are shown in the figure for the case where the In composition of the barrier layer is set to 0%, 3%, and 6%. In Embodiment 1, the resonator length is 1200 μm, and the front and rear end faces are coated so that the reflectivity is 16% and 95%, respectively. The mirror loss of the resonator in this case is 7.8 cm -1 , when the waveguide loss is about 5cm -1 When the total loss of the resonator becomes about 12.8cm -1 In the semiconductor laser device of embodiment 1, the thickness of the quantum well active layer is Since the DQW active layer is very thin, the light confinement coefficient is usually as low as 1% to 2%. In this case, the gain required for laser oscillation is 640 cm -1 to 1280cm -1 It should be noted that Figure 13 In the middle, the dotted line is at 800cm -1 The gain required for laser oscillation is shown in FIG.

[0253] like Figure 13 As shown in the figure, it can be seen that the gain of the quantum well active layer required for laser oscillation is at 640 cm -1 to 1280cm -1When the In composition of the barrier layer is increased from 0% to 6%, laser oscillation can be achieved with a lower injected carrier density. However, as mentioned above, increasing the In composition of the barrier layer tends to increase the operating voltage. Therefore, in order to reduce the oscillation threshold and increase the average strain ε of the multilayer structure without causing a significant increase in the operating voltage, tave In order to improve the compressibility, in Embodiment 1, the In composition of the barrier layer is set to 4%.

[0254] Next, the influence of the In composition of the first optical guiding layer 105 and the second optical guiding layer 107 composed of InGaN on the waveguide loss will be described using the drawings. Figure 14A Graph showing the relationship between the Fermi level (Fermi energy) and the conduction band energy in the vicinity of the quantum well active layer 106 in the semiconductor laser device 11 according to the first embodiment. Figure 14B Graph showing the relationship between the Fermi level and the valence electron band energy in the vicinity of the quantum well active layer 106 in the semiconductor laser device 11 according to the first embodiment. Figure 14C This is a graph showing the electron and hole concentration distributions determined by the relationship between the Fermi level and the conduction band energy in the region near the quantum well active layer 106 in the semiconductor laser device 11 according to the first embodiment.

[0255] exist Figures 14A to 14C Calculation results of the distributions in the growth layer direction during 100 mA operation are shown when the In composition of the first optical guiding layer 105 and the second optical guiding layer 107 is 3% and the In composition of the barrier layer is 5%. Figure 14A ΔEc and Figure 14B ΔEv represents the difference between the conduction band energy and the Fermi energy (conduction band energy - Fermi energy) and the difference between the valence band energy and the Fermi energy (Fermi energy - valence band energy). A smaller ΔEc indicates the presence of electrons with higher average energy in the conduction band, indicating a higher electron concentration in the conduction band. Similarly, a smaller ΔEv indicates an increase in the concentration of holes in the conduction band.

[0256] As described above, when the In composition of each optical guide layer increases, the average deformation ε of the multilayer structure tave The compressibility in the optical waveguide is improved, and ΔR can be controlled in the negative direction. However, as the In content of each optical waveguide layer increases, its band gap energy decreases. During the operation of the semiconductor laser device, the number of free carriers (electrons and holes) generated in each optical waveguide layer increases, resulting in increased waveguide loss.

[0257] exist Figure 14C In the state shown, it is shown that an average of 1.2×10 17 cm -3 of electrons and 6×1016 cm -3 There are an average of 9×10 holes in the second optical guide layer 107. 16 cm -3 of holes and 1.8×10 17 cm -3 In this operating state, free carrier loss occurs in an amount corresponding to the carrier concentration. The concentrations of electrons and holes in each photoconductive layer are affected by the band gap of each photoconductive layer and barrier layer. Therefore, care must be taken in setting the band gap of the photoconductive layer and barrier layer, that is, in setting the In composition.

[0258] Here, the relationship between the carrier concentration in each optical guiding layer and the In composition of the barrier layer and each optical guiding layer will be described using the drawings. Figure 15 : is a graph showing the relationship between the carrier concentration in each optical guiding layer and the In composition of the barrier layer and each optical guiding layer of the semiconductor laser element according to the first embodiment. Figure 15 Graphs (a) and (b) show the dependence of the electron concentration and hole concentration in the first optical guiding layer 105 on the In composition of the blocking layer when operating at 100 mA. Figure 15 Graphs (c) and (d) of FIG. 1 show the dependence of the electron concentration and hole concentration in the second optical guiding layer 107 on the In composition of the barrier layer during 100 mA operation. Each graph shows the dependence of the carrier concentration on the In composition of the barrier layer calculated for multiple cases in which the In composition of each optical guiding layer was varied. The first optical guiding layer 105 and the second optical guiding layer 107 have the same In composition.

[0259] In addition, Figure 15 Each graph shows the average value of the electron and hole concentrations present in each photoconductive layer.

[0260] like Figure 15 As shown in the figure, it can be seen that as the In composition of each optical guide layer increases, the concentration of electrons and holes in each optical guide layer increases. This is believed to be because as the In composition increases, the band gap energy of each optical guide layer decreases, thereby reducing ΔEc and ΔEv. In particular, when the In composition of each optical guide layer is set to 6% or more, the concentration of electrons and holes in the optical guide layer approaches 1×10 18 cm -3 As a free carrier loss, it increases by 0.5 cm compared to the state where the In composition of the optical guide layer is 2% or more. -1 Therefore, the slope efficiency (AP / ΔI) in the current-light output characteristic decreases. Here, ΔP is the change in light output, and ΔI is the change in the amount of injected current. Therefore, in order to control the electron and hole concentrations in each photoconductive layer to 1×10 18 cm -3The In composition of each photoconductive layer should be set to 6% or less, and more preferably to 5% or less. If the In composition of each photoconductive layer is set to 5% or less, the electron and hole concentrations in each photoconductive layer can be more stably suppressed to 1×10 18 cm -3 the following.

[0261] In addition, according to Figure 15 The calculation results shown in the figure show that when the In composition of the barrier layer increases, the concentration of electrons and holes in each photoconductive layer decreases. This is because when the In composition of the barrier layer is increased, the piezoelectric polarization charge generated between each photoconductive layer and the quantum well layer is easily dispersed to the interface between each photoconductive layer and the barrier layer and the interface between the barrier layer and the quantum well layer. Figure 12 Graphs (a) and (b) and Figure 14A As shown in FIG. 1 , the piezoelectric field generated at the interface of the barrier layers 106a and 106e between the optical guiding layers and the quantum well layer decreases. As a result, as the In composition of the barrier layers increases, ΔEc and ΔEv increase, which is believed to reduce the concentration of electrons and holes in the optical guiding layers.

[0262] Therefore, it can be seen that in order to simultaneously achieve the three goals of (1) suppressing the occurrence of free carrier loss in the photoconductive layer, (2) preventing an increase in the operating voltage, and (3) suppressing the piezoelectric field generated in the quantum well active layer, increasing the gain of the quantum well layer, and lowering the oscillation threshold, it is sufficient to set the In composition of the photoconductive layer and the barrier layer to 6% or less, more preferably 5% or less, and to set the In composition of the barrier layer to be greater than the In composition of the photoconductive layer. Furthermore, in order to increase the confinement coefficient in the perpendicular direction of the light distribution, it is necessary to set the In composition of each photoconductive layer to 2.5% or more. Furthermore, if the In composition of each photoconductive layer is set to 3% or more, the occurrence of carrier overflow can be suppressed even during high-temperature, high-output operation.

[0263] Therefore, in Figure 1A In the multilayer structure of the first embodiment shown, the first optical waveguide layer has an In composition of 3% and a thickness of 200 nm, the second optical waveguide layer has an In composition of 3% and a thickness of 180 nm, and the barrier layers 106a, 106c, and 106e have an In composition of 4%. The average strain ε of the entire multilayer structure is thus tave =1×10 -5 And it becomes compressibility.

[0264] In this case, when a base substrate formed of diamond is used, ΔR becomes 0.1 μm or less. Figure 4The results show that even when the quantum well active layer 106 reaches a high temperature of 200° C. or higher, the piezoelectric potential at the resonator end portion is stably increased relative to the piezoelectric potential at the center portion in the resonator direction, thereby preventing current leakage to the current non-injection window region.

[0265] Furthermore, when the In composition of the first optical waveguide layer is set to 3% and the film thickness is set to 175 nm, the In composition of the second optical waveguide layer is set to 3% and the film thickness is set to 98 nm, and the In composition of the barrier layers 106a, 106c, and 106e is set to 4%, the average strain ε of the entire multilayer structure is tave becomes 2.5×10 -4 .

[0266] according to Figure 4 The results shown in graph (i) show that when the quantum well active layer 106 is in a high-temperature state of 200°C, the piezoelectric potential distribution in the quantum well active layer in the resonator direction is substantially constant when ΔR is 0.5 μm or greater, and the effect of preventing current leakage into the current non-injection window region disappears. Therefore, if ΔR is set to 0.25 μm or less, current leakage prevention into the current non-injection window region can be ensured even at a high temperature of 200°C.

[0267] In this case, according to Figure 7B The results shown in FIG. 1 show that, when the thickness of the GaN substrate 101 is 105 μm, the average strain ε of the entire multilayer structure is tave Set to 6.2×10 -4 In the following, the average strain ε of the entire multilayer structure is calculated when the thickness of the GaN substrate 101 is 95 μm. tave Set to 5.2×10 -4 In the following, the average strain ε of the entire multilayer structure is calculated when the thickness of the GaN substrate 101 is 85 μm. tave Set to 4.2×10 -4 In the following, the average strain ε of the entire multilayer structure is calculated when the thickness of the GaN substrate 101 is 75 μm. tave Set to 3.2×10 -4 In the following, the average strain ε of the entire multilayer structure is calculated when the thickness of the GaN substrate 101 is 65 μm. tave Set to 2.2×10 -4 Below, ΔR can be set to 0.25 μm or less.

[0268] Therefore, when the thickness of the GaN substrate 101 is 95 μm or less, the average strain ε of the entire multilayer structure is tave Set to 5.2×10 -4Below, even at a high temperature of 200° C. or higher, it is possible to ensure prevention of current leakage to the current non-injection window region.

[0269] In addition, according to Figure 4 The results shown in graph (i) show that when ΔR is less than 0.25 μm, even at a high temperature of 200°C, the piezoelectric potential in the quantum well active layer 106 in the resonator direction gradually begins to form a higher potential than that in the center of the resonator at a distance of 300 μm from the center position in the resonator direction. The potential difference in the resonator direction is the magnitude of the piezoelectric field formed in the resonator direction integrated with respect to the resonator direction. Therefore, the longer the distance in the resonator direction, the greater the influence of the piezoelectric field formed in the resonator direction.

[0270] Therefore, when the resonator length is 600 μm or more and the thickness of the GaN substrate 101 is 95 μm or less, the average strain ε of the entire multilayer structure is tave Set to 5.2×10 -4 Even at a high temperature of 200° C. or higher, the piezoelectric potential in the current non-injection window region can be increased compared to the resonator center portion, thereby ensuring the effect of preventing current leakage to the current non-injection window region.

[0271] When the semiconductor laser element is operated at high output, the light density at the cavity end face increases, and COD (Catastrophic Optical Damage) in which the cavity end face is destroyed by the laser light of the semiconductor laser element itself is likely to occur, thereby reducing the reliability of the semiconductor laser element.

[0272] In contrast, according to this embodiment, the resonator lengthening not only reduces the thermal resistance of the semiconductor laser element but also enhances the effect of preventing leakage current into the current non-injection window region. As a result, even when the optical output of the semiconductor laser element is increased, the occurrence of COD can be further suppressed.

[0273] Therefore, in the structure shown in this embodiment, increasing the resonator length can not only improve the heat dissipation performance but also enhance the effect of suppressing the occurrence of COD.

[0274] On the other hand, if the resonator is made longer, the size of the semiconductor laser element will increase, which will lead to an increase in production cost. Therefore, the resonator length is preferably as short as possible relative to the desired high output.

[0275] For example, when the resonator length is set to 1200 μm, 1500 μm, and 2000 μm, semiconductor laser devices capable of long-term reliable operation at high outputs of 3 W or more, 3.5 W or more and 4 W or less, and 4 W or more and 4.5 W or less at 85°C, respectively, can be obtained. When the resonator length is set to 2000 μm or more, semiconductor laser devices capable of long-term reliable operation at high outputs of 4.5 W or more at 85°C can be obtained.

[0276] In the structure of embodiment 1, the electron barrier layer 108 is constructed as an AlGaN layer with an Al composition of 0.3 (30%) and a thickness of 5 nm. However, as the Al composition increases, the band gap energy increases, and thus the energy barrier for electrons in the conduction band increases, which can suppress the occurrence of leakage current. However, if the Al composition of the electron barrier layer 108 is excessively increased or the thickness is excessively thickened, the tensile strain increases in the average strain of the multilayer structure as a whole, and ε tave Therefore, in order to increase the energy barrier to electrons while suppressing the increase in tensile strain, the electron barrier layer 108 may be configured such that the maximum Al composition is 30% or greater. Within a region of the electron barrier layer 108 having the maximum Al composition within ±1 nm from position X in the film thickness direction, the Al composition is substantially the same as the maximum Al composition. In regions outside this region, the Al composition decreases with distance from position X. Alternatively, the thickness of the electron barrier layer 108 may be set to 7 nm or less.

[0277] Specifically, the electron barrier layer 108 can be constructed by sequentially forming a first region with a thickness of 2 nm and an Al composition of 0.02 (2%), a second region with a thickness of 3 nm and an Al composition increasing from 0.02 (2%) to 0.36 (36%), and a third region with a thickness ranging from 0 nm to 2 nm and a constant Al composition of 0.36 (36%). This structure can form a potential barrier to electrons with a maximum Al composition of 0.36 (36%), while also reducing the average Al composition of the electron barrier layer 108 and suppressing the increase in tensile strain.

[0278] By forming a first region with a relatively low and constant Al composition in the structure of electron barrier layer 108, the controllability of the Al composition distribution in the second region of the electron barrier layer formed later is improved. In other words, by forming the first region, it is easier to control the Al composition distribution in the second region to a desired distribution.

[0279] In the structure of the electron barrier layer 108, similar effects can be achieved if the maximum Al composition is 0.3 (30%) or greater. However, when the maximum Al composition is 0.4 (40%) or greater, the potential barrier to holes increases, leading to an increase in the operating voltage. Therefore, the maximum Al composition of the electron barrier layer is preferably 0.3 (30%) or greater and 0.4 (40%) or less.

[0280] Furthermore, when the Al composition of the first region is increased, the average Al composition of the electron barrier layer 108 as a whole increases. However, if the Al composition of the first region is 0.1 (10%) or less, the average Al composition of the electron barrier layer can be reduced to less than about half of the maximum Al composition.

[0281] In this case, ΔR becomes 0.2 μm or less, according to Figure 4 The results show that even when the quantum well active layer 106 reaches a high temperature of 200° C. or higher, the piezoelectric potential at the resonator end portion is stably increased relative to the piezoelectric potential at the center portion in the resonator direction, thereby preventing current leakage to the current non-injection window region.

[0282] In addition, if the average deformation ε of the multilayer structure is further increased tave To improve the compressibility, for example, the first optical waveguide layer can have an In composition of 4% and a thickness of 200 nm, the second optical waveguide layer can have an In composition of 4% and a thickness of 180 nm, and the barrier layers 106a, 106c, and 106e can have an In composition of 5%. This can reduce the average strain ε of the entire multilayer structure to tave becomes -1.8×10 -4 , therefore, the compressibility can be improved so that ΔR becomes negative.

[0283] Furthermore, by using an AlGaN substrate instead of the GaN substrate 101, the substrate's lattice constant can be reduced. Consequently, the compressibility of the average lattice strain of the multilayer structure stacked on the substrate can be improved. As a result, compared to a multilayer structure formed on a GaN substrate, ΔR can be more easily controlled to a smaller range of 0.25 μm or less, enhancing the effect of preventing current leakage into the current non-injection window region.

[0284] (Implementation Method 2)

[0285] A semiconductor laser device according to a second embodiment will be described. The semiconductor laser device according to the second embodiment differs from the semiconductor laser device 11 according to the first embodiment in that a buffer layer is provided between the GaN substrate 101 and the first cladding layer 103. The semiconductor laser device according to the second embodiment is identical to the semiconductor laser device 11 according to the first embodiment in all other respects. The following description of the semiconductor laser device according to the second embodiment will focus on the differences from the semiconductor laser device 11 according to the first embodiment, using the accompanying drawings.

[0286] Figure 16A This is a schematic cross-sectional view showing the structure of a semiconductor laser element 12 according to the second embodiment. Figure 16A A cross section perpendicular to the cavity length direction of the semiconductor laser element 12 is shown. Figure 16B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 12 according to the second embodiment.

[0287] like Figure 16A As shown, the semiconductor laser element 12 of the second embodiment is similar to the semiconductor laser element 11 of the first embodiment, and is a nitride-based semiconductor light-emitting element having a multilayer structure in which a first cladding layer 103 of a first conductivity type, a first optical guiding layer 105, a quantum well active layer 106, a second optical guiding layer 107, and a second cladding layer 109 of a second conductivity type are stacked in this order from the GaN substrate 101 side. Figure 16B As shown, the quantum well active layer 106 includes quantum well layers 106 b and 106 d and barrier layers 106 a , 106 c , and 106 e , similarly to the quantum well active layer 106 in the first embodiment.

[0288] The semiconductor laser element 12 further includes a buffer layer 102 on the GaN substrate 101 . That is, the semiconductor laser element 12 includes the buffer layer 102 between the GaN substrate 101 and the first cladding layer 103 .

[0289] The semiconductor laser element 12, like the semiconductor laser element 11 of embodiment 1, also includes an N-type GaN layer 104, an electron barrier layer 108, a contact layer 110, a current blocking layer 112, a P-side ohmic electrode 113, a P-side first adhesion layer 114, a first blocking layer 115, a pad electrode 116 and an N-side electrode 117.

[0290] In this embodiment, the first cladding layer 103 has a thickness of 1.5 μm. Furthermore, the N-side electrode 117 is formed of 40 nm thick Pd, 35 nm thick Pt, and 1 μm thick Au, and the pad electrode 116 is formed of 1 μm thick Au. The ridge width W is 30 μm, similar to the semiconductor laser device 11 in Embodiment 1, and the distance dp between the lower end of the ridge and the quantum well active layer 106 is 0.2 μm.

[0291] The cavity length of the semiconductor laser element 12 is 1200 μm, similarly to the semiconductor laser element 11 of the first embodiment, and current non-injection window regions are formed near the cavity end faces at the front and rear surfaces of the cavity.

[0292] In the second embodiment, similarly to the first embodiment, the Al composition of each cladding layer composed of AlGaN is set to 3.5% in order to increase the light confinement factor perpendicular to the active layer and prevent the generation of lattice defects and cracks and an increase in operating voltage.

[0293] In addition, the quantum well active layer 106 in the second embodiment is the same as that in the first embodiment. Figure 16B The DQW structure is shown, which has two layers of thickness The quantum well layers 106b and 106d are made of InGaN with an In composition of 0.18 (18%). The quantum well active layer 106 further includes barrier layers 106a, 106c, and 106e made of InGaN. The thicknesses of the barrier layers 106a, 106c, and 106e are 3 nm, 7 nm, and 3 nm, respectively.

[0294] In addition, similar to embodiment 1, by setting the In composition of the first optical waveguide layer 105 and the second optical waveguide layer 107 to 3% and the In composition of the blocking layers 106a, 106c and 106e to 4%, it is possible to simultaneously achieve an increase in the confinement coefficient in the vertical direction of the light distribution, suppression of the free carrier loss generated in the optical waveguide layer, suppression of the increase in the operating voltage, suppression of the piezoelectric field generated in the quantum well active layer, and an increase in the gain in the quantum well active layer.

[0295] As described above, in the semiconductor laser element 12 of embodiment 2, a buffer layer 102 is provided between the GaN substrate 101 and the first cladding layer. The buffer layer 102 is a deformation control layer including a nitride semiconductor layer that has compressive deformation relative to the GaN substrate 101. By providing the semiconductor laser element 12 with the buffer layer 102, the average deformation of the entire multilayer structure grown on the GaN substrate 101 can be made more compressive, and when the GaN substrate 101 is facing upward, the warping of the GaN substrate 101 can be controlled to be a concave shape (ΔR<0). The structure of the buffer layer 102 is not particularly limited as long as it has compressive deformation. The buffer layer 102 may also include In. Thus, the buffer layer 102 has compressive deformation relative to the GaN substrate 101. In addition, the buffer layer 102 may also include an AlGaN layer. In the second embodiment, the buffer layer 102 is a stacked film of a 300 nm thick AlGaN layer containing 1% Al and a 200 nm thick InGaN layer containing 4% In and a 200 nm thick InGaN layer formed in this order.

[0296] In the semiconductor laser element 12 of the second embodiment, the electrode structure is not limited to Figure 16A Hereinafter, a modification of the electrode structure of the semiconductor laser element according to the second embodiment will be described with reference to the drawings.

[0297] Figure 16C This is a schematic cross-sectional view showing the structure of a semiconductor laser element 12a according to a modified example of the second embodiment. Figure 16D This is a schematic cross-sectional view showing the structure of a semiconductor laser element 11 a according to a modification of the first embodiment.

[0298] As the structure of the electrode, Figure 16C As shown, the P-side first adhesion layer 114 composed of Ti may not be formed on the ridge. By adopting such a structure, the resistance of the semiconductor laser element 12a can be reduced, and a semiconductor laser element 12a operating at a low voltage can be obtained. Figure 16C The electrode structure shown can also be Figure 16D The semiconductor laser element 11a shown in FIG. 1 is applied to the semiconductor laser element 11 of Embodiment 1. Thus, similarly to the semiconductor laser element 12a, the semiconductor laser element 11a can be obtained which operates at a lower voltage than the semiconductor laser element 11.

[0299] Here, the average strain of the multilayer structure of Embodiment 2 will be described with reference to the drawings. Before describing the average strain of the multilayer structure of Embodiment 2, another example of the average strain of the multilayer structure of Embodiment 1 will be described with reference to the drawings.

[0300] Figure 17A This is a graph showing another example of the distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of the first embodiment. Figure 17B This is a graph showing another example of the distribution of the average strain in the growth layer direction of the multilayer structure of the first embodiment. Figure 17A and Figure 17B In, as used in Figure 1A The average deformation ε of the multilayer structure as a whole is estimated in the multilayer structure shown tave As an example, the strain and average strain are shown when the In composition of the barrier layer is set to 4%, the thickness of the first light guide layer 105 and the second light guide layer are both set to 200 nm, and the In composition is set to 0.05 (5%). In this case, the average strain ε in the entire multilayer structure is tave The size becomes -2.4×10 -4 , which becomes a compressive average strain. Therefore, with this multilayer structure, the direction of the element warping becomes the direction of negative ΔR.

[0301] Next, the average strain of the multilayer structure of the second embodiment will be described using the drawings. Figure 18A This is a graph showing another example of the distribution of lattice mismatch (strain) in the film thickness direction in the multilayer structure of the second embodiment. Figure 18BThis is a graph showing another example of the distribution of the average strain in the growth layer direction of the multilayer structure of Embodiment 2. Specifically, Figure 18A and Figure 18B The multilayer structure shown in Figure 17A and Figure 17B The buffer layer 102 is an additional structure in addition to the multilayer structure used in the calculation. The buffer layer 102 includes an AlGaN layer 102b with an Al composition of 1% and a film thickness of 300nm, and an InGaN layer 102a with an In composition of 4% and a film thickness of 200nm, in order from the GaN substrate 101 side. Figure 16A As shown, the buffer layer 102 is positioned between the GaN substrate 101 and the first cladding layer 103. Placing the buffer layer 102 between the GaN substrate 101 and the first cladding layer 103 increases the distance between the buffer layer 102 and the quantum well active layer 106, thereby substantially suppressing the light intensity within the buffer layer 102. Consequently, the effect of the buffer layer 102 on the light distribution can be substantially minimized. Furthermore, by positioning the buffer layer 102 in this manner, the average strain of the entire multilayer structure can be controlled to be compressive.

[0302] Here, an example in which the buffer layer 102 is formed of two layers is shown. However, the buffer layer 102 only needs to be a layer disposed between the GaN substrate 101 and the first cladding layer 103 and having an average compressive deformation. The buffer layer 102 may be composed of three or more layers or a single layer.

[0303] like Figure 18A As shown, the buffer layer 102, especially the InGaN layer 102a, has compressive deformation. Figure 18B As shown, the average deformation ε of the multilayer structure as a whole tave The size becomes -4.6×10 -4 ,exist Figure 18B In the example shown, it can be seen that the average deformation ε tave compared to Figure 17B The example shown is more compressible. Therefore, by providing the buffer layer 102, the direction of warpage of the semiconductor laser element can be controlled to be a negative direction with a smaller ΔR.

[0304] Furthermore, by using the buffer layer 102, even if the In composition of the first optical guide layer 105 and the second optical guide layer 107 is about 3%, the average strain ε of the entire multilayer structure is reduced. tave To become compressible, preferably -1.5×10 -4 The warpage of the semiconductor laser element can also be controlled so that the GaN substrate 101 side is concave. In this case, by setting the In composition of the first optical guiding layer 105 and the second optical guiding layer 107 to approximately 3%, the generation of lattice defects and the occurrence of free carrier loss in each optical guiding layer can be further suppressed.

[0305] Next, the relationship between the total film thickness of the first optical guiding layer 105 and the second optical guiding layer 107 (hereinafter also referred to as the total thickness) and the In composition of each optical guiding layer and the average strain will be described using the drawings.

[0306] Figure 19A is the average strain ε of the multilayer structure of the comparative example. tave The graph shows the relationship between the total thickness of the first light guiding layer 105 and the second light guiding layer 107. Figure 19A In the figure, it is shown that Figure 16A The multilayer structure of the semiconductor laser element 12 of the second embodiment shown here does not include the average strain ε in the multilayer structure of the buffer layer 102. tave The calculation results of .

[0307] Figure 19B The average strain ε of the multilayer structure of the second embodiment is shown. tave A graph showing an example of the relationship between the total thickness of the first light guiding layer 105 and the second light guiding layer 107. Figure 19B In the Figure 16A The calculation results are for the case where an InGaN layer 102a having an In composition of 4% and a thickness of 200 nm is formed as the buffer layer 102 on an AlGaN layer 102b having an Al composition of 1% and a thickness of 300 nm in the multilayer structure of the semiconductor laser element 12 according to the second embodiment.

[0308] In the strain-compensating buffer layer 102 in which tensile and compressive layers are alternately formed as described above, directions in which displacement tends to occur in two adjacent layers are opposite to each other, and thus the generation of lattice defects can be suppressed.

[0309] Figure 19C The average strain ε of the multilayer structure of the second embodiment is shown. tave A graph showing another example of the relationship between the total thickness of the first light guiding layer 105 and the second light guiding layer 107. Figure 19C In the Figure 16A In the multilayer structure of the semiconductor laser element 12 of the second embodiment shown, the average strain ε is obtained when an InGaN layer having an In composition of 4% and a film thickness of 200 nm is formed as the buffer layer 102. tave The calculation results of .

[0310] In addition, Figures 19A to 19C The figure shows the average strain ε when the In composition of each optical guide layer is changed from 1% to 7%. tave .

[0311] like Figure 19AAs shown in the figure, in the multilayer structure without the buffer layer 102, in order to make the average deformation ε of the multilayer structure as a whole tave becomes less than 0 or -1.5×10 -4 Hereinafter, when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 3%, the total thickness of each optical guide layer needs to be 460 nm. Above or 610nm Similarly, when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 4%, the total thickness of each of them needs to be 350 nm. Above or 460nm In addition, it can be seen that when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 5%, the total thickness of each of them needs to be 280 nm. Above or 360nm above.

[0312] Here, when the In composition of the InGaN layer used in each optical guide layer is set to 3% or more and the total thickness is grown to 500nm or more, lattice defects and pits are likely to occur during crystal growth, which may cause degradation of the characteristics of the semiconductor laser element. Figure 19B In the example shown, it can be seen that in order to make the average deformation ε of the multilayer structure as a whole tave becomes less than 0 or -1.5×10 -4 Hereinafter, when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 3%, the total thickness thereof is 220 nm. Above or 380nm Similarly, when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 4%, the total thickness of each is 200 nm. Above or 280nm In addition, it can be seen that when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 5%, the total thickness of each is 130 nm. Above or 220nm That’s all.

[0313] As a result, even when using the first and second optical guiding layers having an In composition of 3% or more, the required total thickness of the optical guiding layers can be reduced, thereby stably obtaining a good crystal with reduced lattice defects and pits.

[0314] In contrast, in Figure 19C In the example shown, it can be seen that in order to make the average deformation ε of the entire multilayer structure tavebecomes less than 0 or -1.5×10 -4 In the following, when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is 3%, the total thickness thereof is 200 nm. Above or 340nm As a result, good crystals can be stably obtained even in the optical waveguide layer with an In composition of 3%. Similarly, it can be seen that when the In composition of the first optical waveguide layer 105 and the second optical waveguide layer 107 is 4%, their total thickness is 160nm. Above or 250nm In addition, it can be seen that when the In composition of the first optical waveguide layer 105 and the second optical waveguide layer 107 is 5%, the total thickness of each of them needs to be 120 nm. Above or 200nm That’s all.

[0315] From these results, the use of the buffer layer 102 can reduce the total thickness of the optical guiding layer required when an optical guiding layer having an In composition of 3% or more is used, thereby stably obtaining a good crystal.

[0316] As described above, if the buffer layer 102 is used as a compressive strain control layer, the average strain ε can be reduced. tave becomes less than 0 or -1.5×10 -4 The film thickness of each optical guide layer required as follows can suppress the generation of lattice defects and pits during crystal growth.

[0317] Next, the average strain ε is calculated when the In composition of the first optical guide layer 105 and the second optical guide layer 107 is set to 3% and the total thickness thereof is set to 250 nm. tave becomes less than 0 or -1.5×10 -4 The structure of the buffer layer 102 required for this purpose was studied as follows.

[0318] To achieve good temperature characteristics, the quantum well active layer requires a light confinement coefficient of 1.2% or greater. To achieve this coefficient, the waveguide structure requires that the indium content of both the first and second optical guiding layers 105 and 107 be set to 3% or greater, and their combined thickness be set to 250 nm or greater. Further increasing the indium content or combined thickness of each optical guiding layer can increase the light confinement coefficient of the quantum well active layer. Furthermore, increasing the indium content improves the compressibility of each optical guiding layer, thereby increasing the compressive strain.

[0319] As mentioned above, in Figure 19BIn the example shown in

[15] , a strain-compensating buffer layer 102 is employed, in which an InGaN layer 102a is formed on an AlGaN layer 102b having an Al composition of 1%. By setting the compositions and thicknesses of the AlGaN and InGaN layers 102b and 102a so that the average strain of the two layers becomes compressive, a compressible buffer layer 102 is formed. If the Al composition is too low, the strain-compensating effect is reduced. Conversely, if the Al composition is too high, lattice defects are likely to occur due to lattice mismatch with the GaN substrate 101. In the multilayer structure of embodiment 2, by setting the Al composition of the AlGaN layer 102b to between 0.5% and 1%, both the strain-compensating effect and the suppression of lattice defects can be achieved. In the multilayer structure of embodiment 2, the Al composition of the AlGaN layer 102b in the buffer layer 102 is set to 1%. With an AlGaN layer having an Al composition of less than 1%, the generation of lattice defects can be suppressed even when the layer is grown to a thickness of approximately 2μm.

[0320] Next, the film thickness and average strain ε of each layer constituting the buffer layer 102 are compared using the drawings. tave The relationship between . Figure 20 is the average strain ε of the entire multilayer structure of the second embodiment. tave The graph shows the relationship between the thickness of the InGaN layer 102a and the AlGaN layer 102b constituting the buffer layer 102. Figure 20 Graphs (a), (b), (c), and (d) show the average strain ε of the multilayer structure as a whole calculated for various AlGaN layer thicknesses, with the In composition of the InGaN layer 102a constituting the buffer layer 102 set to 2%, 3%, 4%, and 5%, respectively. tave The results are obtained based on the dependence of the InGaN layer thickness. Figure 20 The graphs show calculation results for each case where the AlGaN layer thickness is changed from 0 nm to 200 nm in increments of 50 nm.

[0321] like Figure 20 As shown in the graph (a), in order to make the average strain ε of the whole multilayer structure of the InGaN layer 102a with an In composition of 2% tave To achieve a value below 0, when the AlGaN layer thickness is 0 nm (i.e., when there is no AlGaN layer), the InGaN layer thickness needs to be 320 nm or more. Similarly, when the AlGaN layer thickness is 500 nm, the InGaN layer thickness needs to be 350 nm or more, when the AlGaN layer thickness is 1000 nm, the InGaN layer thickness needs to be 420 nm or more, when the AlGaN layer thickness is 1500 nm, the InGaN layer thickness needs to be 480 nm or more, and when the AlGaN layer thickness is 2000 nm, the InGaN layer thickness needs to be 500 nm or more.

[0322] In addition, it can be seen that in order to make the average deformation ε of the multilayer structure as a whole tave becomes -1.5×10 -4 Hereinafter, when the AlGaN layer thickness is 0 nm, the InGaN layer thickness also needs to be 500 nm or more.

[0323] like Figure 20 As shown in the graph (b), in order to make the average deformation ε of the whole multilayer structure of the InGaN layer 102a with an In composition of 3% tave To achieve a value below 0, when the AlGaN layer thickness is 0 nm, the InGaN layer thickness needs to be 220 nm or greater. Similarly, when the AlGaN layer thickness is 500 nm, the InGaN layer thickness needs to be 260 nm or greater. When the AlGaN layer thickness is 1000 nm, the InGaN layer thickness needs to be 280 nm or greater. When the AlGaN layer thickness is 1500 nm, the InGaN layer thickness needs to be 320 nm or greater. When the AlGaN layer thickness is 2000 nm, the InGaN layer thickness needs to be 340 nm or greater.

[0324] In addition, it can be seen that in order to make the average deformation ε of the multilayer structure as a whole tave becomes -1.5×10 -4 Hereinafter, when the AlGaN layer thickness is 0 nm, the InGaN layer thickness needs to be greater than 370 nm; when the AlGaN layer thickness is 500 nm, the InGaN layer thickness needs to be greater than 430 nm; and when the AlGaN layer thickness is 1000 nm, the InGaN layer thickness needs to be greater than 490 nm.

[0325] like Figure 20 As shown in the graph (c), in order to make the average deformation ε of the whole multilayer structure of the InGaN layer 102a with an In composition of 4% tave To achieve a value below 0, when the AlGaN layer thickness is 0 nm, the InGaN layer thickness must be at least 160 nm. Similarly, when the AlGaN layer thickness is 500 nm, the InGaN layer thickness must be at least 180 nm. When the AlGaN layer thickness is 1000 nm, the InGaN layer thickness must be at least 200 nm. When the AlGaN layer thickness is 1500 nm, the InGaN layer thickness must be at least 230 nm. When the AlGaN layer thickness is 2000 nm, the InGaN layer thickness must be at least 260 nm.

[0326] In addition, in order to make the average strain ε of the multilayer structure as a whole tave becomes -1.5×10 -4Below, when the AlGaN layer thickness is 0nm, the InGaN layer thickness needs to be at least 260nm. Similarly, when the AlGaN layer thickness is 500nm, the InGaN layer thickness needs to be at least 300nm, and when the AlGaN layer thickness is 1000nm, the InGaN layer thickness needs to be at least 350nm. It can be seen that when the AlGaN layer thickness is 1500nm, the InGaN layer thickness needs to be at least 395nm, and when the AlGaN layer thickness is 2000nm, the InGaN layer thickness needs to be at least 440nm.

[0327] like Figure 20 As shown in the graph (d), in order to make the average deformation of the multilayer structure ε tave To achieve a thickness of 0 or less, when the AlGaN layer thickness is 0 nm, the InGaN layer thickness must be 130 nm or more. Similarly, when the AlGaN layer thickness is 500 nm, the InGaN layer thickness must be 160 nm or more; when the AlGaN layer thickness is 1000 nm, the InGaN layer thickness must be 180 nm or more; when the AlGaN layer thickness is 1500 nm, the InGaN layer thickness must be 195 nm or more; and when the AlGaN layer thickness is 2000 nm, the InGaN layer thickness must be 210 nm or more.

[0328] In addition, in order to make the average strain ε of the multilayer structure as a whole tave becomes -1.5×10 -4 Below, when the AlGaN layer thickness is 0nm, the InGaN layer thickness needs to be at least 220nm. Similarly, when the AlGaN layer thickness is 500nm, the InGaN layer thickness needs to be at least 260nm, and when the AlGaN layer thickness is 1000nm, the InGaN layer thickness needs to be at least 300nm. Furthermore, when the AlGaN layer thickness is 1500nm, the InGaN layer thickness needs to be at least 330nm, and when the AlGaN layer thickness is 2000nm, the InGaN layer thickness needs to be at least 360nm.

[0329] exist Figure 20 The calculation results shown in the various graphs show that by setting the InGaN layer thickness to 500 nm or less, the generation of pits and lattice defects in the InGaN layer can be suppressed. Setting the InGaN layer thickness to 400 nm or less further suppresses the generation of lattice defects and pits.

[0330] Furthermore, if the thickness of the AlGaN layer is set to 1 μm or less, the Al composition is set to 1% or less, and the thickness of the InGaN layer is set to 490 nm or less, and the In composition is set to 3% or more and 5% or less, the average strain ε of the entire multilayer structure can be reduced to 1 μm or less.tave becomes -1.5×10 -4 the following.

[0331] exist Figure 16A In the multilayer structure of the second embodiment shown, the first optical guide layer 105 has an In composition of 3% and a thickness of 185 nm, the second optical guide layer 107 has an In composition of 3% and a thickness of 100 nm, the barrier layer has an In composition of 4%, and the buffer layer 102 has an InGaN layer having an In composition of 4% and a thickness of 350 nm formed on an AlGaN layer having an Al composition of 1% and a thickness of 1000 nm. The average strain ε of the entire multilayer structure is reduced to 1. tave becomes -1.8×10 -4 .

[0332] In this multilayer structure, the In composition in each optical waveguide layer is 3%, so all of the following six tasks can be achieved: (1) suppressing the occurrence of free carrier loss generated in the optical waveguide layer; (2) not causing an increase in the operating voltage; (3) suppressing the piezoelectric field generated in the quantum well active layer, thereby increasing the gain in the quantum well active layer; (4) making the light confinement coefficient in the vertical direction greater than 1.2%; (5) reducing the oscillation threshold; and (6) suppressing the leakage of current into the current non-injection window area at the end face of the resonator due to the influence of the piezoelectric potential generated by the piezoelectric field in the resonator direction, thereby suppressing the decrease in the COD level.

[0333] Furthermore, the AlGaN layer 102b and the InGaN layer 102a in the buffer layer 102 can each be divided into multiple layers, forming a multilayer structure or a superlattice structure, so that their total thickness reaches the appropriate total thickness obtained based on the above calculation results. For example, the compressive strain of a buffer layer having an InGaN layer having an In composition of 4% and a thickness of 350nm formed on an AlGaN layer having an Al composition of 1% and a thickness of 1000nm is equivalent to the compressive strain of a buffer layer having a multilayer structure formed by stacking a pair of 100nm AlGaN layers and a 35nm InGaN layer ten times.

[0334] In addition, Figure 16A In the multilayer structure of the second embodiment shown, the first optical guide layer 105 has an In composition of 3% and a thickness of 175 nm, the second optical guide layer 107 has an In composition of 3% and a thickness of 98 nm, the barrier layer has an In composition of 4%, and the buffer layer 102 has an InGaN layer having an In composition of 3% and a thickness of 100 nm formed on an AlGaN layer having an Al composition of 1% and a thickness of 400 nm. Thus, the average strain ε of the entire multilayer structure can be reduced to 1. tavebecomes 1.3×10 -4 .

[0335] In this case, when a base substrate formed of diamond is used, ΔR becomes 0.2 μm or less. Figure 4 The results show that even when the quantum well active layer 106 reaches a high temperature of 200° C. or higher, the piezoelectric potential at the resonator end portion is stably higher than the piezoelectric potential at the center portion in the resonator direction, thereby suppressing current leakage to the current non-injection window region.

[0336] The above describes a method for suppressing the leakage of current into the current non-injection window region of the resonator end face due to the influence of the piezoelectric potential generated by the piezoelectric field in the resonator direction. The formation of piezoelectric potential based on the piezoelectric effect exists not only in the resonator direction, but also in the horizontal direction ( Figure 16A This is because in Figure 1A 、 Figure 16A In the structure shown, a ridge is formed in the second cladding layer 109, and a material having a thermal expansion coefficient of 4.2×10 -6 Therefore, when the semiconductor laser element is mounted face-down on a base substrate, stress is also generated in the x-direction due to the difference in thermal expansion coefficients between the Au and GaN materials, generating shear stress in the plane perpendicular to the resonator direction (in the xy plane).

[0337] This shear stress in the xy plane generates a piezoelectric field and piezoelectric potential in the x direction, affecting the band structure in the x-axis direction of the quantum well active layer 106. The shear stress and the like generated in a plane perpendicular to the cavity direction of the semiconductor laser device according to Embodiment 2 will be described below using the accompanying drawings.

[0338] Figure 21A 、 Figure 21B and Figure 21C These diagrams respectively show the shear stress distribution in the x-axis direction, the piezoelectric field distribution, and the piezoelectric potential distribution at 25° C. in the quantum well layers 106 b and 106 d when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding face downward.

[0339] Figure 22A 、 Figure 22B and Figure 22C These diagrams respectively show the shear stress distribution in the x-axis direction, the piezoelectric field distribution, and the piezoelectric potential distribution at 25° C. in the quantum well layers 106 b and 106 d when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding facing upward.

[0340] Figure 23A 、 Figure 23B and Figure 23CThese are the shear stress distribution in the x-axis direction, the piezoelectric field distribution, and the piezoelectric potential distribution in the quantum well layers 106 b and 106 d at 150° C. when the semiconductor laser element according to the second embodiment is mounted face-down on a base substrate.

[0341] Figure 24A 、 Figure 24B and Figure 24C These are the shear stress distribution in the x-axis direction, the piezoelectric field distribution, and the piezoelectric potential distribution at 150° C. in the quantum well layers 106 b and 106 d when the semiconductor laser element according to the second embodiment is mounted on a base substrate with the bonding facing upward.

[0342] exist Figures 21A to 24C The figures show the calculation results when using base substrates made of diamond, AlN, and SiC, respectively. The center of the ridge in the x-axis direction is set to a center distance of 0 μm.

[0343] like Figure 21A and Figure 23A As shown in the figure, when the bonding is mounted downward, the directions of the shear stress in the x-direction and the piezoelectric field in the x-direction caused by the shear stress are reversed when mounted on a diamond base and when mounted on an AlN or SiC base substrate. This is believed to be because, as mentioned above, the thermal expansion coefficient of SiC is 6.6×10 -6 , the thermal expansion coefficient of AlN is 4.15×10 -6 In contrast, the thermal expansion coefficient of diamond is 1.1×10 -6 , with the thermal expansion coefficient of GaN being 5.59×10 -6 It is also relatively small in comparison. In this case, when AuSn solder is used as the bonding layer 121 and is mounted on a base substrate at a high temperature of about 300°C, the thermal expansion coefficient of the base substrate formed of diamond is small. Therefore, when the temperature is lowered to 25°C, the influence of the thermal residual stress caused by the difference in thermal expansion coefficient with the semiconductor laser element becomes larger than when a base substrate formed of SiC or AlN is used. Therefore, when a semiconductor laser element is mounted on a base substrate formed of diamond, the tensile stress in the x-axis direction of the semiconductor laser element becomes larger than when a semiconductor laser element is mounted on a base substrate formed of SiC or AlN. At this time, the shear stress in the xy plane is formed in the direction where the piezoelectric potential on the outside of the ridge becomes relatively higher than that on the ridge. Therefore, in the case of using a base substrate formed of diamond, from a high temperature state of 25°C to 150°C, as Figure 21C and Figure 23CAs shown, it can be seen that a potential barrier based on the piezoelectric effect is formed outside the ridge, which has the effect of suppressing the leakage of current outside the ridge. When SiC or AlN is used for the base substrate, when the semiconductor laser element reaches a high temperature state of 150°C, the piezoelectric potential that suppresses the injected current from leaking outside the ridge almost disappears, and it can be seen that this leads to an increase in leakage current compared to the case of using a diamond base substrate. When the semiconductor laser element is used at an ambient temperature of 85°C, the waveguide of the semiconductor laser element, including the quantum well active layer, reaches a high temperature state of more than 150°C due to the influence of self-heating. Therefore, even in a high temperature state of more than 150°C, by forming a piezoelectric potential for suppressing the leakage of current outside the ridge, not only can the increase in the operating current value and the thermal saturation of the light output be suppressed, but the operating current itself can also be reduced, thereby reducing the leakage of current to the current non-injection window area near the end face of the resonator.

[0344] Regarding the formation of a piezoelectric potential that suppresses the leakage of current out of the ridge, as Figure 22C and Figure 24C As shown, even when diamond is used for the base substrate, no difference in thermal expansion coefficient is observed in the bond-up mounting method. This is believed to be because the gap between the quantum well active layer 106 and the base substrate is large in the bond-up mounting method, making it difficult for the base substrate material to have a difference in thermal expansion coefficient.

[0345] Thus, it can be seen that when the ridge-type semiconductor laser element is mounted with the joint facing downward, the effect of suppressing the leakage of current outside the ridge is newly added, and compared with SiC and AlN, the effect of low operating current can be obtained in addition to the high heat dissipation effect caused by the high thermal conductivity.

[0346] Furthermore, the piezoelectric potential that suppresses current leakage outside the ridge is generated by the difference in thermal expansion coefficients between the diamond-based base substrate and the nitride material (primarily Au) used as the structural material of the semiconductor laser element. Therefore, the material of the current blocking layer 112 is not limited to SiO2. It can also be an insulator transparent to laser light, such as ZrO2, Al2O3, Ta2O5, TiO2, SiN, or a semiconductor material such as AlN. The thermal conductivity of AlN is approximately 150 W / m·K, which is lower than that of diamond, but higher than that of oxide materials such as SiO2 (approximately 1.38 W / m·K), ZrO2 (approximately 4 W / m·K), and Al2O3 (approximately 20 W / m·K), as well as silicon nitride (SiN; thermal conductivity approximately 20 W / m·K). Therefore, using a current blocking layer 112 composed of AlN is effective for achieving high heat dissipation.

[0347] Here, the effects of using a base substrate formed of diamond will be described using the drawings. Figure 25A and Figure 25B These are graphs showing measurement results of current-light output characteristics at 25° C. and 85° C. when the semiconductor laser element according to the second embodiment is mounted on base substrates made of diamond and SiC, respectively.

[0348] according to Figure 25A and Figure 25B It can be seen that the case of using a diamond base substrate has a lower oscillation threshold current and higher slope efficiency than the case of using a SiC base substrate. In particular, the case of using a diamond base substrate shows little tendency towards thermal saturation in the current-light output characteristics, even when a high current of 3A is injected at a high temperature of 85°C. This is believed to be due to the high heat dissipation effect of the diamond base substrate as described above, as well as the effect of suppressing the generation of ineffective current accompanied by the formation of piezoelectric potential to prevent current leakage outside the ridges.

[0349] (Implementation 3)

[0350] A semiconductor laser device according to a third embodiment will be described. The semiconductor laser device according to the third embodiment differs from the semiconductor laser device 11 according to the first embodiment in that it includes a third optical guide layer and a third cladding layer; otherwise, the semiconductor laser device is identical to the semiconductor laser device 11 according to the first embodiment. The following description of the semiconductor laser device according to the third embodiment will focus on the differences from the semiconductor laser device 11 according to the first embodiment, using the accompanying drawings.

[0351] Figure 26A This is a schematic cross-sectional view showing the structure of a semiconductor laser element 13 according to the third embodiment. Figure 26A A cross section perpendicular to the cavity length direction of the semiconductor laser element 13 is shown. Figure 26B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 13 according to the third embodiment.

[0352] like Figure 26A As shown, the semiconductor laser element 13 of the third embodiment is similar to the semiconductor laser element 11 of the first embodiment, and is a nitride-based semiconductor light-emitting element having a multilayer structure in which a first cladding layer 103 of a first conductivity type, a first optical guiding layer 105, a quantum well active layer 106, a second optical guiding layer 107, and a second cladding layer 109 of a second conductivity type are stacked in this order from the GaN substrate 101 side on a GaN substrate 101. Figure 26B As shown, the quantum well active layer 106 includes quantum well layers 106 b and 106 d and barrier layers 106 a , 106 c , and 106 e , similarly to the quantum well active layer 106 in the first embodiment.

[0353] The semiconductor laser element 13, like the semiconductor laser element 11 of embodiment 1, also includes an N-type GaN layer 104, an electron barrier layer 108, a contact layer 110, a current blocking layer 112, a P-side ohmic electrode 113, a P-side first adhesion layer 114, a first blocking layer 115, a pad electrode 116 and an N-side electrode 117.

[0354] like Figure 26A As shown, the semiconductor laser element 13 further includes a third optical guiding layer 130 and a third cladding layer 131 on the second cladding layer 109. In the semiconductor laser element 13, the second cladding layer 109 is formed of P-type AlGaN and has a film thickness of 0.2 μm.

[0355] The third optical guiding layer 130 is a layer formed of P-type InGaN with a film thickness of 0.2 μm.

[0356] The third cladding layer 131 is a layer made of P-type AlGaN with a thickness of 0.2 μm. The Al composition of the third cladding layer 131 is 0.035 (3.5) similarly to the second cladding layer 109 .

[0357] The semiconductor laser element 13 also has a ridge formed therein similarly to the semiconductor laser element 11 of the first embodiment. However, in the semiconductor laser element 13, as shown in FIG. Figure 26A As shown, the ridge is formed on the third optical guide layer 130 and the third cladding layer 131. The lower end of the ridge is arranged on the upper surface of the second cladding layer 109.

[0358] In the semiconductor laser element 13, by including the third optical guide layer 130, the direction parallel to the active layer ( Figure 26A The shear stress in the quantum well active layer 106 (in the x-direction) increases. Because the lattice constant of InGaN is larger than that of GaN, the third optical guiding layer 130 applies stress in the region near the ridge, which causes the ridge to stretch horizontally. This influences the shear stress distribution in the quantum well active layer 106, increasing the shear stress. The shear stress in the quantum well active layer 106 will be described below using the accompanying drawings.

[0359] Figure 27A 、 Figure 27B and Figure 27C The graphs show the x-axis distribution of shear stress at 25°C in the quantum well layers 106b and 106d in the quantum well active layer 106 when the In composition of the third optical guiding layer 130 is changed to 0% (i.e., the third optical guiding layer 130 is formed of GaN), 1%, and 2%. The position where the distance becomes 0 μm is the center of the ridge in the x-axis direction. Figure 27A 、 Figure 27B and Figure 27CAs shown in the figure, increasing the In composition of the third optical guiding layer 130 to 0%, 1%, and 2% increases the absolute value of the peak shear stress, and the shear stress becomes stronger. This is because increasing the In composition increases the lattice mismatch of the third optical guiding layer 130, increasing the stress that spreads horizontally from the lower end of the ridge toward the outside of the ridge. As a result, the rotational stress component in the xy plane of the stress generated in the quantum well active layer 106 becomes stronger, increasing the absolute value of the peak shear stress. The piezoelectric potential generated in the quantum well active layer 106 by this shear stress will be described using the accompanying figures.

[0360] Figure 28 Graph showing the relationship between the piezoelectric potential generated in the quantum well active layer 106 and the position in the x-axis direction in Embodiment 3. Figure 28 : The piezoelectric potentials when the In composition of the third optical guide layer 130 is changed to 0%, 1% and 2% are shown in FIG. Figure 28 As shown, the potential barrier generated by the piezoelectric potential inside and outside the ridge increases with the increase in the In content, which can enhance the effect of suppressing the leakage of the injected current outside the ridge. As a result, a semiconductor laser element 13 that is more excellent in high-temperature and high-output operation can be obtained.

[0361] By forming a piezoelectric potential to suppress current leakage outside the ridge, not only can the increase in the operating current value and the thermal saturation of the light output be suppressed, but the operating current itself can also be reduced, thereby reducing the leakage of current into the current non-injection window area near the end face of the resonator.

[0362] Here, the shear stress generated in the ridge waveguide is generated at the boundary between materials with different thermal expansion coefficients or lattice constants. Therefore, in the vicinity of the current blocking layer 112 at the lower end of the ridge ( Figure 26A Shear stress is maximized in regions A1 and A2 (in the middle). Therefore, by forming the third optical guiding layer 130 at the lower end of the ridge and adding stress due to the lattice mismatch of the InGaN layer to this region, the shear stress can be further enhanced. On the other hand, if the thickness of the third optical guiding layer 130 is excessively increased, the refractive index of the third optical guiding layer 130 becomes higher than that of the second cladding layer 109 and the third cladding layer 131. This reduces the confinement effect of light distribution perpendicular to the quantum well active layer 106, resulting in a decrease in the light confinement coefficient. In the semiconductor laser device of Embodiment 3, by having the thickness of the third optical guiding layer 130 be between 0.1 μm and 0.2 μm, it is possible to achieve both an increase in the piezoelectric potential and a good light confinement effect.

[0363] Furthermore, even when the third optical guiding layer 130 is made of GaN, the tensile stress generated in this region is reduced compared to when it is an AlGaN layer, thus also having the effect of increasing the piezoelectric potential. Therefore, if the indium content of the third optical guiding layer 130 is set to 0% to 2%, the effect of suppressing leakage of injected current outside the ridge can be improved compared to when the p-type layer in the ridge is formed entirely of AlGaN. In Embodiment 3, the indium content of the third optical guiding layer 130 is set to 1%, and the film thickness is set to 0.2 μm.

[0364] (Implementation 4)

[0365] A semiconductor laser device according to a fourth embodiment will be described. The semiconductor laser device according to the fourth embodiment differs from the semiconductor laser device 13 according to the third embodiment in that the lower end of the ridge is positioned within the growth thickness direction of the third optical guiding layer; otherwise, the device is identical to the semiconductor laser device 13 according to the third embodiment. The following description of the semiconductor laser device according to the fourth embodiment will focus on the differences from the semiconductor laser device 13 according to the third embodiment, using the accompanying drawings.

[0366] Figure 29A This is a schematic cross-sectional view showing the structure of a semiconductor laser element 14 according to a fourth embodiment. Figure 29A A cross section perpendicular to the cavity length direction of the semiconductor laser element 14 is shown. Figure 29B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 14 according to the fourth embodiment.

[0367] like Figure 29A As shown, the semiconductor laser element 14 of the fourth embodiment is a nitride-based semiconductor light-emitting element having a multilayer structure in which a first cladding layer 103 of a first conductivity type, a first optical guiding layer 105, a quantum well active layer 106, a second optical guiding layer 107, and a second cladding layer 109 of a second conductivity type are stacked on a GaN substrate 101 in this order from the GaN substrate 101 side. Figure 29B As shown, the quantum well active layer 106 includes quantum well layers 106 b and 106 d and barrier layers 106 a , 106 c , and 106 e , similarly to the quantum well active layer 106 in the first embodiment.

[0368] The semiconductor laser element 14, like the semiconductor laser element 13 of embodiment 3, also includes an N-type GaN layer 104, an electron barrier layer 108, a contact layer 110, a current blocking layer 112, a P-side ohmic electrode 113, a P-side first adhesion layer 114, a first blocking layer 115, a pad electrode 116 and an N-side electrode 117.

[0369] The semiconductor laser element 14 further includes a third optical guiding layer 130 and a third cladding layer 131 on the second cladding layer 109 .

[0370] like Figure 29A As shown, the multilayer structure of embodiment 4 is Figure 26A In the multilayer structure of the third embodiment shown, the ridge bottom end is arranged in the growth thickness direction of the third optical guide layer 130 composed of P-type InGaN with a film thickness of 0.2 μm. In other words, the ridge bottom end is arranged in the film thickness direction of the third optical guide layer 130 ( Figure 29A The other structures of the multilayer structure of the fourth embodiment are the same as those of the multilayer structure of the third embodiment.

[0371] In such a semiconductor laser element 14 , if the thickness of the third optical guiding layer 130 in the ridge region at the lower end of the ridge is 0.1 μm to 0.2 μm, the same effects as those of the semiconductor laser element 13 described in the third embodiment can be obtained.

[0372] (Implementation 5)

[0373] A semiconductor laser element according to a fifth embodiment will be described. The semiconductor laser element according to the fifth embodiment differs from the semiconductor laser element 13 according to the third embodiment in that it includes a buffer layer; otherwise, the semiconductor laser element is identical to the semiconductor laser element 13 according to the third embodiment. The following description of the semiconductor laser element according to the fifth embodiment will focus on the differences from the semiconductor laser element 13 according to the third embodiment, using the accompanying drawings.

[0374] Figure 30A This is a schematic cross-sectional view showing the structure of a semiconductor laser element 15 according to the fifth embodiment. Figure 30A A cross section perpendicular to the cavity length direction of the semiconductor laser element 15 is shown. Figure 30B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 15 according to the fifth embodiment.

[0375] like Figure 30A As shown in FIG. 1 , the semiconductor laser element 15 of the fifth embodiment further includes a buffer layer 102 in addition to the semiconductor laser element 13 of the third embodiment. Figure 30B As shown, the quantum well active layer 106 of the semiconductor laser element 15 includes quantum well layers 106 b and 106 d and barrier layers 106 a , 106 c , and 106 e , similarly to the semiconductor laser element 13 .

[0376] In this structure, if the thickness of the third optical guiding layer 130 is 0.1 μm to 0.2 μm, the same effects as those of the semiconductor laser element 13 of the third embodiment can be obtained. In addition, the same effects as those of the semiconductor laser element 12 of the second embodiment can be obtained.

[0377] (Implementation 6)

[0378] A semiconductor laser device according to a sixth embodiment will be described. The semiconductor laser device according to the sixth embodiment differs from the semiconductor laser device 14 according to the fourth embodiment in that it includes a buffer layer; otherwise, the semiconductor laser device is identical to the semiconductor laser device 14 according to the fourth embodiment. The following description of the semiconductor laser device according to the sixth embodiment will focus on the differences from the semiconductor laser device 14 according to the fourth embodiment, using the accompanying drawings.

[0379] Figure 31A This is a schematic cross-sectional view showing the structure of a semiconductor laser element 16 according to the sixth embodiment. Figure 31A A cross section perpendicular to the cavity length direction of the semiconductor laser element 16 is shown. Figure 31B This is a schematic cross-sectional view showing the structure of the quantum well active layer 106 in the semiconductor laser device 16 according to the sixth embodiment.

[0380] like Figure 31A As shown in FIG. 1 , the semiconductor laser element 16 of the sixth embodiment further includes a buffer layer 102 in addition to the semiconductor laser element 14 of the fourth embodiment. Figure 31B As shown, the quantum well active layer 106 of the semiconductor laser element 16 includes quantum well layers 106 b and 106 d and barrier layers 106 a , 106 c , and 106 e , similarly to the semiconductor laser element 13 .

[0381] In this structure, if the thickness of the third optical guiding layer 130 is 0.1 μm to 0.2 μm, the same effects as those of the semiconductor laser element 14 of the fourth embodiment can be obtained. In addition, the same effects as those of the semiconductor laser element 12 of the second embodiment can be obtained.

[0382] In the semiconductor laser devices of the third to sixth embodiments described above, the shear stress generated in the ridge waveguide is generated at the boundary between materials having different thermal expansion coefficients or lattice constants. Therefore, in the vicinity of the current blocking layer 112 at the lower end of the ridge ( Figure 26A In regions A1 and A2), the shear stress is maximum.

[0383] In the case of ridge-type lasers, the shear stress is Figure 26A The shear stress generated in the regions B1 and B2 also affects the x-direction shear stress distribution in the quantum well active layer 106. The shear stress generated in the region B1 and the shear stress generated in the region A1 rotate in opposite directions. In addition, the shear stress generated in the region B2 and the shear stress generated in the region A2 rotate in opposite directions. Therefore, when the separation groove width D on both sides of the ridge is Figure 26A) is narrow, the shear stress in regions B1 and B2 cancels out the shear stress in regions A1 and A2, reducing the absolute value of the shear stress generated in the quantum well active layer. Consequently, when the semiconductor laser element is mounted face-down on a diamond base substrate, the piezoelectric potential generated along the x-axis direction decreases.

[0384] Here, the relationship between the shear stress and the separation groove width D will be described using the drawings. Figure 32A 、 Figure 32B and Figure 32C The graphs show the calculation results of shear stress, piezoelectric field and piezoelectric potential generated in the quantum well layers 106b and 106d at 25°C when the separation groove width D of the semiconductor laser element 13 of the third embodiment is changed from 2 μm to 24 μm. Figure 32C In FIG, the piezoelectric potential when the separation groove region reaches both ends of the chip, that is, when the separation groove width is the largest, is shown by the dotted line. Figure 32C As shown in the figure, it can be seen that when the separation groove width D is small, the piezoelectric potential becomes smaller, and above 6μm, the end of the ridge ( Figure 32C The piezoelectric potential at the positions (with a distance of -15μm and +15μm) is approximately constant. Furthermore, the width of the potential barrier formed within the separation trench narrows as the separation trench width decreases. Therefore, in order to form a potential barrier width of 5μm or more, the separation trench width is set to 6μm or more.

[0385] Figure 33A 、 Figure 33B and Figure 33C The graphs show the calculation results of shear stress, piezoelectric field, and piezoelectric potential generated in the quantum well layers 106b and 106d at 150°C when the separation groove width D of the semiconductor laser element 13 of the third embodiment is changed from 2 μm to 24 μm. As in the case of 25°C, it can be seen that as the separation groove width D is reduced, the piezoelectric potential decreases, and at 6 μm or more, the ridge end ( Figure 33C The piezoelectric potential at the positions (with a distance of -15μm and +15μm) is approximately constant. Furthermore, the width of the potential barrier formed within the separation trench narrows as the separation trench width decreases. Therefore, in order to form a potential barrier width of 5μm or more, the separation trench width is set to 6μm or more.

[0386] According to the results, when a semiconductor laser element is mounted face down on a base substrate formed of diamond, if the separation groove width is not formed to be greater than 6 μm, the piezoelectric potential formed along the x-axis direction becomes smaller, and the leakage suppression effect of suppressing the current injected into the ridge from leaking out of the ridge becomes smaller.

[0387] Furthermore, if the separation groove width D is too wide, the mounting load during face-down bonding will concentrate on the ridge, potentially damaging the ridge region. Furthermore, lattice defects may form in the quantum well active layer directly below the ridge. In the semiconductor laser devices of Embodiments 3 to 6, by setting the separation groove width D to within 15 μm, such ridge damage can be reduced.

[0388] Therefore, by setting the separation groove width D to be greater than 6 μm and less than 15 μm, it is possible to suppress damage to the ridge and the generation of lattice defects in the ridge region when the semiconductor laser element is mounted face down on a base substrate formed of diamond, while achieving a leakage suppression effect of suppressing the current injected into the ridge from leaking out of the ridge.

[0389] In each embodiment of the present disclosure, the separation groove width D is set to 7μm to suppress the damage of the ridge and the generation of lattice defects in the ridge area when the bonding is downwardly mounted on a base substrate formed of diamond, while at the same time obtaining a leakage suppression effect of suppressing the current injected into the ridge from leaking out of the ridge.

[0390] (Implementation 7)

[0391] The semiconductor laser device of embodiment 7 is described below. In the semiconductor laser devices of each embodiment described above, a multilayer structure is formed on a (0001) C-plane GaN substrate. When a nitride layer is formed on the C-plane in this way, piezoelectric polarization charges are generated at the heterojunction where there is a lattice mismatch. For example, in the normal direction relative to the main surface of the GaN substrate, Figure 2 As shown in graph (c) of FIG, a piezoelectric field in the c-axis direction ((0001) direction) is generated, causing an increase in the operating voltage. To suppress the generation of this c-axis piezoelectric field and reduce the operating voltage, the semiconductor laser device of embodiment 7 has a multilayer structure formed on a semipolar plane composed of GaN {11-22} planes. The semiconductor laser device of embodiment 7 is described below using the accompanying drawings.

[0392] Figure 34 This is a schematic cross-sectional view showing the structure of a semiconductor laser element 17 according to the seventh embodiment.

[0393] like Figure 34 As shown, the semiconductor laser device 17 of the seventh embodiment differs from the semiconductor laser device 11 of the first embodiment in terms of the GaN substrate 140, but is identical in other respects. As described above, the primary surface of the GaN substrate 140 of the seventh embodiment is a semipolar surface composed of a {11-22} plane.

[0394] Here, the C-plane of the GaN substrate 101 of each of the above-mentioned embodiments is called a polar plane, which is the plane most affected by piezoelectric polarization. However, planes perpendicular to the C-plane, such as the {10-10} plane (M plane) and the {11-20} plane (A plane), do not undergo polarization and are called non-polar planes. By using a GaN substrate having such a plane, it is possible to suppress the decrease in luminous efficiency caused by piezoelectric polarization in semiconductor laser elements. In addition, planes other than the C-plane and inclined from the non-polar plane, such as the {20-21} plane or the {11-22} plane, are called semi-polar planes, which can reduce piezoelectric polarization.

[0395] The multilayer structure formed on the GaN substrate 140 is different from the multilayer structure shown in Embodiment 1 in terms of the first cladding layer 163 , the electron barrier layer 168 , and the second cladding layer 169 , but is identical in other respects.

[0396] Semiconductor laser element 17 includes electron barrier layer 168, but it is not necessary to include electron barrier layer 168. Furthermore, the Al composition of first cladding layer 163 composed of N-type AlGaN and second cladding layer 169 composed of P-type AlGaN can be approximately 1% or less, or 0% (GaN). In other words, the Al composition in the multilayer structure can be 1% or less. The reason for this is described in Embodiment 8.

[0397] Furthermore, the semiconductor laser element 17 of the seventh embodiment may further include a compressible buffer layer 102 . Figure 35 : is a schematic cross-sectional view showing the structure of a semiconductor laser element 17a according to a modification of the seventh embodiment. Figure 35 As shown, the semiconductor laser element 17 a includes a compressible buffer layer 102 .

[0398] (Implementation 8)

[0399] A semiconductor laser device according to an eighth embodiment will be described. In order to suppress the generation of the piezoelectric field in the C-axis direction described in the seventh embodiment and achieve a reduction in operating voltage, the semiconductor laser device according to the eighth embodiment differs from the semiconductor laser devices according to the aforementioned embodiments in that a multilayer structure is formed on a nonpolar plane composed of GaN {10-10} planes (M planes). The following description of the semiconductor laser device according to the eighth embodiment will focus on the differences from the semiconductor laser devices according to the aforementioned embodiments, using the accompanying drawings.

[0400] Figure 36 This is a schematic cross-sectional view showing the structure of a semiconductor laser element 18 according to the eighth embodiment. Figure 37 This is a schematic cross-sectional view showing the structure of a semiconductor laser element 18a according to a modification of the eighth embodiment.

[0401] like Figure 36As shown, the semiconductor laser element 18 of the eighth embodiment includes a GaN substrate 141 whose principal surface is a {10-10} plane (M-plane). The multilayer structure formed on the GaN substrate 141 differs from the multilayer structure shown in the first embodiment in terms of the first cladding layer 163, the electron barrier layer 168, and the second cladding layer 169, but is identical in all other respects.

[0402] In addition, the semiconductor laser element 18 may also include a compressible buffer layer 102. Figure 37 As shown, a semiconductor laser element 18 a according to a modification of the eighth embodiment includes a buffer layer 102 .

[0403] Semiconductor laser element 18 includes electron barrier layer 168, but it is not necessary. Furthermore, the Al composition of first cladding layer 163 and second cladding layer 169 can be approximately 1% or less, or 0% (GaN). In other words, the Al composition in the multilayer structure can be 1% or less. The reason for this will be described later.

[0404] By forming a multilayer structure on a semi-polar surface or a non-polar GaN substrate, the piezoelectric field generated in the normal direction relative to the GaN substrate can be reduced or eliminated, and the operating voltage can be reduced. This is because the lattice constants of AlGaN and InGaN are different from those of GaN. Therefore, although piezoelectric polarization charges are generated at the heterogeneous interface due to lattice mismatch, their generation is suppressed or prevented. Therefore, the deformation of the band structure generated in the normal direction relative to the GaN substrate when formed on the C surface is suppressed, and low voltage can be achieved. Therefore, the Figure 2 The piezoelectric field in the C-axis direction ((0001) direction) shown in the graph (c) is suppressed or disappears, so the band structure becomes Figure 2 As a result, in the quantum well active layer, as shown in the diagram (a) Figure 9B As shown, a higher gain can be obtained with a lower injected carrier density, and the oscillation threshold current value and the action carrier density during operation can be reduced. Therefore, the action carrier density during high-temperature and high-output operation becomes smaller, and the occurrence of carrier overflow in which thermally excited carriers leak from the quantum well active layer to each cladding layer is suppressed. As a result, there is no need to use AlGaN in each cladding layer to increase the light confinement into the quantum well active layer, and there is no need to use the electron barrier layer 168 to suppress the occurrence of carrier overflow. Therefore, as described above, the semiconductor laser element 18 can also be without the electron barrier layer 168, and the Al composition of the first cladding layer 163 and the second cladding layer 169 can also be less than about 1% or 0% (GaN). That is, the Al composition in the multilayer structure can also be less than 1%.

[0405] In addition, when a semi-polar or non-polar GaN substrate is used, the piezoelectric polarization charge generated at the interface between the quantum well layer and the barrier layer becomes smaller or disappears. Therefore, even if the number of quantum well layers in the quantum well active layer is increased from a DQW structure to four layers, for example, it will not lead to an increase in the operating voltage, and the vertical light confinement coefficient of the entire quantum well layer can be increased.

[0406] As a result, if the number of quantum well layers is increased, the density of action carriers in the quantum well layers decreases, and the occurrence of carrier overflow can be further suppressed.

[0407] When an AlGaN layer is used in a multilayer structure as described above, the AlGaN layer undergoes tensile deformation relative to the GaN substrate. Therefore, the average strain ε of the entire multilayer structure is tave The Al content in the GaN layer is increased, which acts to enhance the tensile strength. Consequently, the warping of the semiconductor laser device tends to be convex (ΔR>0) when the substrate is facing upward. Therefore, to achieve a concave warping shape (ΔR<0) when the GaN substrate is facing upward, it is best to reduce or eliminate the Al content in the Al-containing layer.

[0408] Here, the relationship between the band structure in the multilayer structure and the polarity of the primary surface of the GaN substrate will be described using the drawings. Figure 38A This diagram shows the energy band structure near the quantum well active layer 166 when a multilayer structure including a first cladding layer 163 and a second cladding layer 169 having an Al composition of 0 is formed on a GaN substrate having a C-plane primary surface.

[0409] in addition, Figure 38B This diagram shows the energy band structure near the quantum well active layer 166 when a multilayer structure including a first cladding layer 163 and a second cladding layer 169 having an Al composition of 0 is formed on a GaN substrate having a semipolar primary surface.

[0410] in addition, Figure 38C This diagram shows the energy band structure near the quantum well active layer 166 when a multilayer structure including a first cladding layer 163 and a second cladding layer 169 having an Al composition of 0 is formed on a GaN substrate having a non-polar primary surface.

[0411] Here, the quantum well active layer 166 has four quantum well layers. The In composition of each quantum well layer is 18%, and the film thickness is The thickness of each barrier layer is 3 nm, 7 nm, 7 nm, 7 nm, and 3 nm in order from the end. The Al composition of the electron barrier layer 168 is also 0 (ie, GaN).

[0412] like Figure 38AAs shown, when a multilayer structure is formed on the C-plane, a large piezoelectric field is generated in the quantum well layer of the quantum well active layer 166. This increases the operating voltage and reduces the gain due to the bias of the wave function.

[0413] In contrast, Figure 38B As shown, when a multilayer structure is formed on a semipolar surface, the magnitude of the piezoelectric field generated in the quantum well layer of the quantum well active layer 166 decreases, thereby suppressing an increase in operating voltage and a decrease in gain due to a wave function bias.

[0414] In addition, if Figure 38C As shown, when a multilayer structure is formed on a non-polar surface, the piezoelectric field generated in the quantum well layer of the quantum well active layer disappears. This suppresses the increase in operating voltage and prevents the gain reduction caused by the offset of the wave function.

[0415] Therefore, if a multilayer structure is formed on a GaN substrate whose primary surface is a semipolar surface or a nonpolar surface, a higher gain can be obtained from each quantum well layer with a smaller injection current, thereby obtaining a semiconductor laser element with a low voltage and a low operating current.

[0416] Furthermore, when a semiconductor laser element, which has a concave shape when the GaN substrate faces upward, is mounted face-down on a base substrate using AuSn solder as a bonding layer, the element is mounted at a high temperature of approximately 300°C. When the temperature is lowered to 25°C, the solder layer and the P-side electrode contract in accordance with the thermal expansion coefficient. Consequently, ΔR, which indicates the concave shape of the semiconductor laser element, decreases compared to before mounting.

[0417] To prevent this, when AuSn solder is used to bond a laser element, which has a convex shape when the GaN substrate is facing upward, to a base substrate and then mounted face-down, the element is also mounted at a high temperature of approximately 300°C. When the temperature is lowered from this state to 25°C, the solder layer and the electrodes on the P-type layer side contract in accordance with the thermal expansion coefficient, causing ΔR, which indicates the convex shape of the element, to increase compared to before mounting.

[0418] Here, the quantum well active layer generates Figure 3A and Figure 3B When the compressive strain in the z-axis direction is concave, the quantum well active layer is further stretched, and thus the compressive strain is reduced. Therefore, when the GaN substrate is facing upward and the shape is concave, the compressive stress generated in the quantum well active layer tends to be reduced, which is beneficial for suppressing the generation of lattice defects.

[0419] When a semi-polar substrate or a non-polar substrate is used, even without an AlGaN layer, a high gain can be obtained from each quantum well layer with a small injection current, thereby achieving a laser element with a low voltage and a low operating current. In addition, in a multilayer structure, if Al is not used in the AlGaN cladding layer, the average strain ε of the entire multilayer structure is reduced even without a compressive buffer layer in the multilayer structure. tave It is also easy to become compressible and can become concave (ΔR<0) when the GaN substrate is facing upward. In this case, if the number of quantum well layers in the quantum well active layer is increased, the effect becomes greater. Therefore, the average deformation ε of the multilayer structure is tave While achieving compressibility, the compressive strain generated in the quantum well can be reduced, and the generation of lattice defects can be suppressed. Therefore, a highly reliable semiconductor laser device suitable for long-term operation can be realized.

[0420] Here, the relationship between the operating voltage of a semiconductor laser element and the Al composition of each cladding layer and the number of quantum well layers will be described using the drawings.

[0421] Figure 39A 、 Figure 39B and Figure 39C The graphs show the dependence of the operating voltage of a semiconductor laser element having a multilayer structure formed on a C-plane, a semipolar plane, and a nonpolar plane on the Al composition of each cladding layer when operating at 100 mA. Figures 39A to 39C In the figure, it is shown that Figure 34 The operating voltage of the semiconductor laser element with the same structure as the semiconductor laser element shown in FIG. Figures 39A to 39C Calculation results are shown for varying the number of quantum well layers from two to four. The Al composition of the electron barrier layer is the same as that of the cladding layers in each calculation. For a three-quantum well configuration, the barrier layer thicknesses are 3 nm, 7 nm, 7 nm, and 3 nm, respectively, from the GaN substrate side.

[0422] like Figure 39A As shown, it can be seen that when a multilayer structure is formed on the C-plane, as the number of quantum well layers increases, the operating voltage increases significantly due to the piezoelectric field in the substrate normal direction.

[0423] In contrast, Figure 39B and Figure 39CAs shown, when forming a multilayer structure on a semipolar or nonpolar substrate, even if the number of quantum well layers is increased, the increase in the operating voltage is suppressed. In particular, it is found that even if the number of quantum well layers is increased from two to three, the increase in the operating voltage is substantially suppressed. In the case of three quantum well layers, the confinement factor in the direction perpendicular to the quantum well active layer can be increased by approximately 1.5 times compared to the case of three quantum well layers, thereby reducing the operating carrier density in the quantum well active layer.

[0424] Furthermore, it was found that when using a semipolar or nonpolar substrate, even when the Al composition of each cladding layer was increased to 1%, the increase in the operating voltage was suppressed. Therefore, it was found that even when the Al composition of each cladding layer was set to 0% (GaN) or higher and 1% or lower on a semipolar or nonpolar substrate, the operating voltage hardly increased.

[0425] Next, the average deformation ε of the multilayer structure is analyzed using the accompanying drawings. tave The relationship between the Al composition of each cladding layer and the number of quantum well layers will be described. Figure 40 is the average deformation ε of the multilayer structure tave Graph showing the Al composition dependence of each cladding layer. Figure 40 In the Figure 34 In the structure shown, the average strain ε of the entire multilayer structure is calculated when the In composition of the barrier layer is 4%, the In composition of the first light guiding layer 105 and the second light guiding layer 107 is 3%, and the total thickness of the first light guiding layer 105 and the second light guiding layer 107 is 300 nm. tave The calculation results of . Figure 40 Calculation results for quantum well layers ranging from one to five are shown in FIG. In the calculation, the Al composition of the first cladding layer 163 and the second cladding layer 169 composed of AlGaN is the same as the Al composition of the electron barrier layer 168 .

[0426] like Figure 40 As shown in the figure, it can be seen that when the number of quantum well layers increases from one to five, the average deformation ε tave The compressibility is improved. In particular, it is known that when the Al composition is less than 1%, the average deformation ε tave Become -2×10 -4 Thereafter, a state in which ΔR is negative is obtained.

[0427] Therefore, when using a semipolar substrate or a nonpolar substrate, even when using a cladding layer with an Al composition of 1% or less or a layer containing no Al, high gain can be obtained from each quantum well layer with a small amount of injection current. Therefore, a laser element with low voltage and low operating current can be obtained. In addition, in a multilayer structure, if the Al composition of each cladding layer is set to 1% or less, the average deformation ε of the entire multilayer structure can be reduced to 1%.tave The GaN substrate is compressible, so it can be concave (ΔR<0) when the GaN substrate is facing upward. In this case, if the number of quantum well layers in the quantum well active layer is increased, the effect becomes greater. Therefore, it is possible to make the average deformation ε of the multilayer structure tave While becoming compressible, the compressive strain generated in the quantum well layer is reduced, and the generation of lattice defects can be suppressed. Therefore, a highly reliable laser element suitable for long-term operation can be realized.

[0428] (Implementation 9)

[0429] Embodiment 9 will be described. In Embodiment 9, a method of mounting the semiconductor laser element 11 of Embodiment 1 on a base substrate 122 will be described.

[0430] When the semiconductor laser element 11, which has a concave shape when the substrate side is facing upward, is mounted on the base substrate facing downward, the center portion in the resonator direction is concave. Therefore, the end portion of the base substrate side of the multilayer structure is convex in the center portion in the resonator direction. Therefore, during mounting, the load is concentrated first on the portion of the base substrate corresponding to the vicinity of the center portion in the resonator direction. Figure 41 As shown, the solder forming the bonding layer easily overflows on the side wall near the center of the laser element.

[0431] This state will be described in detail using the drawings. Figure 42 1 is a schematic cross-sectional view showing a state where the semiconductor laser element 11 of the first embodiment is mounted on the immediately front surface of the base substrate 122 with the semiconductor laser element 11 facing downward. Figure 42 , a cross section perpendicular to the cavity direction of the semiconductor laser element 11 is shown. Figure 42 1 and 2 show a cross-sectional view of the semiconductor laser element 11 according to the first embodiment in conjunction with the state of the mounting. Figure 42 The cross-sectional view of the semiconductor laser element 11 shown is relative to Figure 1A The cross-sectional view shown is reversed in the vertical direction.

[0432] like Figure 42 As shown, pad electrode 116 formed on first barrier layer 115 of semiconductor laser element 11 includes first pad electrode 201 composed of 0.6 μm-thick Au, second barrier layer 202 composed of 35 nm-thick Pt, and second pad electrode 203 composed of 1.0 μm-thick Au. Furthermore, P-side first adhesion layer 114, first barrier layer 115, first pad electrode 201, second barrier layer 202, and second pad electrode 203 form P-side multilayer electrode 118.

[0433] In addition, Figure 421 shows the structure of a base substrate 122 formed of diamond and a bonding layer 121 formed on the base substrate 122. In addition, a lower contact metal layer 207 composed of Ti, Pt, and Au is formed under the base substrate 122.

[0434] On the base substrate 122 , an upper adhesion metal layer 206 composed of Ti, Pt, and Au, a base barrier layer 205 composed of Pt, and a bonding layer 121 composed of AuSn are formed in this order from the base substrate 122 side.

[0435] In this state, the bonding layer 121 made of AuSn is kept at a high temperature of 300° C., which is the melting temperature, and a load is applied to the semiconductor laser element 11 to bring the semiconductor laser element 11 into close contact with the base substrate 122 .

[0436] After mounting, the second pad electrode 203, composed of Au, chemically reacts with the bonding layer 121, composed of AuSn, and substantially the entire second pad electrode 203 becomes an AuSn layer. Furthermore, the second barrier layer 202, composed of Pt, functions as a barrier, preventing the first pad electrode 201, composed of Au, from chemically reacting with the bonding layer 121, composed of AuSn. The first pad electrode 201 also remains in the Au state after mounting.

[0437] As described above, when the semiconductor laser element 11, which has a concave shape when the GaN substrate 101 faces upward, is mounted face-down on the base substrate by bonding it, the concave shape of the center portion in the resonator direction causes the load to concentrate first near the center portion of the base substrate in the resonator direction during mounting. Consequently, the material of the AuSn bonding layer 121, which forms the center portion in the resonator direction, can easily overflow along the sidewalls of the semiconductor laser element 11 and cover them. In this case, the AuSn short-circuit between the first cladding layer 103 and the second cladding layer 109 occurs. Consequently, when power is applied to the semiconductor laser element 11, leakage current flows that does not pass through the PN junction of the semiconductor laser element 11. This leakage current increases the oscillation threshold current and operating current.

[0438] Therefore, in order to prevent the side walls of the semiconductor laser element 11 from being covered with AuSn in this manner, the structure of the semiconductor laser element will be described with reference to the drawings. Figure 43 1 is a schematic cross-sectional view showing a state where the semiconductor laser element 11a of the ninth embodiment is mounted on the immediately front surface of the base substrate 122 with the semiconductor laser element 11a facing downward. Figure 43 ] shows a cross section perpendicular to the cavity direction of the semiconductor laser element 11a.

[0439] like Figure 43As shown, the semiconductor laser element 11a of the ninth embodiment differs from the semiconductor laser element 11 of the first embodiment in the structure of the second barrier layer 202a of the pad electrode 116a, but is identical in all other respects. The width of the second barrier layer 202a in the short-side direction is narrower than the width of the first barrier layer 115 in the short-side direction. In other words, the second barrier layer 202a has a smaller width in the direction perpendicular to the cavity direction and the stacking direction than the first barrier layer 115. The structure of a semiconductor laser device formed by bonding such a semiconductor laser element 11a to a base substrate 122 with the device facing downward will be described using the accompanying drawings.

[0440] Figure 44 : is a schematic cross-sectional view showing the structure of a semiconductor laser device 59 according to Embodiment 9. Figure 44 3 shows a cross section perpendicular to the cavity direction of the semiconductor laser device 59 .

[0441] Figure 44 The semiconductor laser device 59 shown is an example of a nitride-based light-emitting device including a semiconductor laser element 11a and a base substrate 122. In the semiconductor laser device 59, the semiconductor laser element 11a is mounted on the base substrate 122 in a multilayer structure so as to face the base substrate 122.

[0442] like Figure 44 As shown, the bonding layer 121 composed of AuSn chemically reacts with the first pad electrode 201 in the area not covered by the second barrier layer 202a, and a portion of the first pad electrode 201 becomes AuSn, which is directed toward the center of the laser element (ie, Figure 44 The bonding layer 121 diffuses from the center of the bonding layer 121 in the horizontal direction. As a result, the bonding layer surface at the bonding portion between the bonding layer 121 and the first pad electrode 201 is curved toward the center at the outer edge of the first pad electrode 201. That is, the bonding layer 121 extends between the second barrier layer 202a and the first barrier layer, to a position further inboard than the end of the second barrier layer 202a. In other words, a portion of the bonding layer 121 is positioned between the second barrier layer 202a and the first barrier layer 115, further inboard than the end of the second barrier layer 202a.

[0443] Therefore, diffusion of the bonding layer 121 to the side walls of the semiconductor laser element 11 a is suppressed, and generation of leakage current due to short circuit on the side walls can be suppressed.

[0444] In addition, the structure of the electrode of the semiconductor laser element is not limited to Figure 43 Hereinafter, modifications of the structure of the electrode of the semiconductor laser element will be described with reference to the drawings. Figure 45A : is a schematic cross-sectional view showing the structure of a semiconductor laser element 11b according to a modification of the ninth embodiment. Figure 45A As shown, the semiconductor laser element 11b of this modification differs from the semiconductor laser element 11a in the structure of the P-side first adhesion layer 114a in the electrode, but is identical to the semiconductor laser element 11a in other respects. Figure 45A As shown, the P-side first adhesion layer 114a made of Ti is not formed on the ridge. With such a structure, the resistance of the semiconductor laser element 11b can be reduced, and a semiconductor laser element operating at a low voltage can be obtained.

[0445] In the semiconductor laser device 59 of Embodiment 9, the total thickness of the pad electrode 116, comprising the first pad electrode 201 made of Au with a thickness of 0.6 μm, the second barrier layer 202a made of Pt with a thickness of 35 nm, and the second pad electrode 203 made of Au with a thickness of 1.0 μm, is approximately 1.6 μm. The thickness of the bonding layer 121 made of AuSn is 1.6 μm. If the total thickness is too thick, the distance between the base substrate 122 and the semiconductor laser element 11a increases, thereby suppressing the formation of piezoelectric potential caused by the base substrate 122 having a lower thermal expansion coefficient than the nitride-based light-emitting element and metal materials such as Au. Furthermore, if the total thickness is too thin, the bonding strength between the semiconductor laser element 11a and the base substrate 122 decreases. Therefore, the total thickness of the first pad electrode 201, the second barrier layer 202a, the second pad electrode 203, and the bonding layer 121 may be between 3 μm and 5 μm. Furthermore, the combined thickness of the first pad electrode 201, the second barrier layer 202a, and the second pad electrode 203 may be substantially the same as the thickness of the bonding layer 121. This is because, when the combined thickness of the first pad electrode 201, the second barrier layer 202a, the second pad electrode 203, and the bonding layer 121 is set to 3 μm or greater and 5 μm or less, if the bonding layer 121 is too thick, the bonding layer material may easily overflow onto the sidewalls of the semiconductor laser element 11a during assembly. Conversely, if the bonding layer 121 is too thin, the adhesive strength decreases. Therefore, in Embodiment 9, the thickness of the bonding layer 121 is 1.6 μm.

[0446] In this way, the combined thickness of the first pad electrode 201, the second barrier layer 202a, and the second pad electrode 203, as well as the thickness of the bonding layer 121, can all be set to 1.5 μm or more and 2.5 μm or less. This allows for simultaneous suppression of a decrease in adhesive strength, suppression of overflow of the bonding layer onto the element sidewalls, suppression of leakage current into the current non-injection window region near the resonator end facets caused by downward bonding to the diamond base substrate, and suppression of leakage current outside the ridge.

[0447] The above-described effects can be obtained not only in the semiconductor laser elements according to the first and ninth embodiments described so far, but also in the semiconductor laser elements according to the second to eighth embodiments.

[0448] Furthermore, due to the high thermal conductivity of the diamond-based base substrate, the solder composed of AuSn, a bonding layer material that easily conducts heat during mounting, tends to melt quickly and overflow toward the sidewalls. As a result, compared to the case of using a base substrate composed of SiC or AlN, even for semiconductor laser elements with a flat or convex shape when the GaN substrate side is facing upward, or for the average deformation ε of the entire multilayer structure, the average deformation ε is significantly reduced. tave Even for semiconductor laser elements with zero or tensile strength, solder can easily overflow along the sidewalls of the semiconductor laser element during mounting. In this case, as described above, solder can coat the sidewalls of the semiconductor laser element, causing leakage current. To address this issue, the structure using the second barrier layer provided in semiconductor laser element 11a of Embodiment 9 is effective.

[0449] In addition, when the direction from the GaN substrate 101 to the quantum well active layer 106 on the current blocking layer 112 is set as the upward direction, as shown in FIG. Figure 45A As shown, a P-side multilayer electrode 118 a including a P-side first adhesion layer 114 a , a first pad electrode 201 , a second barrier layer 202 a , and a second pad electrode 203 is formed.

[0450] Here, the shapes of the P-side multilayer electrodes 118 and 118 a will be described using the drawings. Figures 45B to 45D 1 is a schematic top view showing an example of the shape of the P-side multilayer electrode 118 of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction. Figures 45B to 45D 1 and 2. The P-side multilayer electrode 118 is shown in FIG. 1 , but the P-side multilayer electrode 118a also has the same shape.

[0451] like Figure 45B As shown, when the P-side multilayer electrode 118 is rectangular, stress is likely to concentrate at corners Ra through Rd of the P-side multilayer electrode 118, making it susceptible to electrode peeling. Peeling at the corners of the P-side multilayer electrode 118 not only hinders uniform current injection but also reduces heat dissipation, thereby degrading the operating characteristics and reliability of the semiconductor laser device.

[0452] Therefore, in order to suppress the occurrence of electrode peeling, Figure 45C and Figure 45DThe P-side multilayer electrode 118 shown has a rectangular shape with the four corners cut off. In other words, the outer periphery of the P-side multilayer electrode 118, at corners Ra through Rd, is formed to be located inward of the intersection of the extensions of the P-side multilayer electrode 118's sides parallel to the resonator and the extensions of the sides parallel to the resonator end faces. In this embodiment, corners Re through Rh, where no electrodes are formed, are provided at a distance of approximately 10 μm to 30 μm in both the long and short directions from the apex of the rectangle. The apex of the rectangle is formed by the P-side multilayer electrode 118's side parallel to the resonator and its extension (long side) and the side parallel to the resonator end face and its extension (short side).

[0453] As a result, it is possible to suppress the formation of stress concentration areas in the P-side multilayer electrode 118 and suppress the occurrence of electrode peeling. Figure 45C and Figure 45D In the illustrated P-side multilayer electrode 118, no electrode is formed at a distance of 20 μm from the vertices of the rectangle in both the resonator direction and the width direction of the semiconductor laser element. In other words, the P-side multilayer electrode 118 has a shape obtained by cutting out triangular regions from the four corners Re to Rh of the rectangular electrode.

[0454] like Figure 45C As shown, the position of the P-side multilayer electrode 118 end on the resonator end face side may be the same as the resonator end face, but it may also be as shown in FIG. Figure 45D In other words, a gap may be formed between the end of the P-side multilayer electrode 118 and the end of the resonator.

[0455] When the gap is too small, the cleavage is not affected by the P-side multilayer electrode 118, and the processing accuracy of the cleavage process becomes difficult. A portion of the end of the P-side multilayer electrode 118 may be included at the cleavage position. In this case, the end of the P-side multilayer electrode 118 may affect the direction of cleavage. That is, the cleavage direction deviates from the desired direction in the middle of the cleavage process. On the contrary, when the above-mentioned gap is too large, the heat dissipation in the area near the end face of the resonator decreases. Therefore, it is best to form a gap of about 1μm or more and 20μm or less between the end face of the resonator and the end of the P-side multilayer electrode 118. Figure 45D In the example shown, a gap of 10 μm is formed.

[0456] Furthermore, the shape of the N-side electrode 117 when viewed from the substrate normal direction can be said to be the same as that of the P-side multilayer electrode 118 . Figures 45E to 45GThis is a schematic plan view showing an example of the shape of the N-side electrode 117 of the semiconductor laser element according to the first embodiment, the ninth embodiment, or a modification of the ninth embodiment, as viewed in the substrate normal direction.

[0457] like Figure 45E As shown, when the N-side electrode 117 is rectangular, stress tends to concentrate at corners Ra through Rd, which can easily become starting points for electrode peeling. Peeling off the corners of the N-side electrode 117 not only hinders uniform current injection but also reduces heat dissipation, thereby degrading the operating characteristics and reliability of the semiconductor laser device.

[0458] Therefore, in order to suppress the occurrence of electrode peeling, Figure 45F 、 Figure 45G The N-side electrode 117 shown has a shape formed by cutting off the four corners of a rectangle. In other words, at the corners Ra to Rd of the N-side electrode 117, the periphery of the N-side electrode 117 is formed to be located inside the intersection of the extension line of the side of the N-side electrode 117 parallel to the resonator and the extension line of the side parallel to the end face of the resonator. In this embodiment, corners Re to Rh where no electrodes are formed are provided at a distance of about 10 μm or more and 30 μm or less from the vertex of the rectangle in the long side direction and the short side direction, respectively. The vertex of the rectangle is formed by the side of the N-side electrode 117 parallel to the resonator direction and its extension line (long side) and the side parallel to the end face of the resonator and its extension line (short side). In Figure 45F and Figure 45G In the N-side electrode 117 shown, no electrode is formed at a distance of 20 μm from the vertices of the rectangle in both the cavity direction and the width direction of the semiconductor laser element. In other words, N-side electrode 117 has a shape obtained by cutting out triangular regions from the rectangular electrode at the four corners Re to Rh.

[0459] As a result, it is possible to suppress the formation of a stress concentration region in the N-side electrode 117 , and to suppress the occurrence of electrode peeling.

[0460] like Figure 45F As shown, the position of the N-side electrode 117 end at the resonator end face may be the same as that of the resonator end face, but may also be as shown in FIG. Figure 45G In other words, a gap may be formed between the end of the N-side electrode 117 and the end face of the resonator.

[0461] When the gap is too small, cleavage is not affected by the N-side electrode 117, and the processing accuracy of the cleavage process becomes difficult. A portion of the end of the N-side electrode 117 may be included at the cleavage position. In this case, the end of the N-side electrode 117 may affect the direction of cleavage. That is, the cleavage direction may deviate from the desired direction in the middle of the cleavage process. On the contrary, when the above-mentioned gap is too large, the heat dissipation in the area near the end face of the resonator decreases. Therefore, it is best to form a gap of about 1μm or more and 20μm or less between the end face of the resonator and the end of the N-side electrode 117. Figure 45G In the example shown, a gap of 10 μm is formed.

[0462] In addition, Figure 45F and Figure 45G In the structure shown, the N-side electrode 117 is also formed in a region inside the end of the semiconductor laser element in the width direction of the semiconductor laser element. This is to facilitate separation in the element separation process of separating the semiconductor laser device along the resonator direction. In this case, the distance between the N-side electrode 117 and the end of the semiconductor laser element in the width direction of the semiconductor laser element can be greater than 1μm and less than 20μm. Figure 45F and Figure 45G In the example shown, a gap of 10 μm is formed.

[0463] In addition, when mounting with the bonding face downward, thermal residual stress is applied to the P-side multilayer electrode 118 due to the difference in thermal expansion coefficient with the base material. Therefore, in order to prevent the electrode from peeling off due to the stress during mounting of the P-side multilayer electrode 118, a Figure 45C and Figure 45D The electrode pattern having a shape in which the corners of the electrode where stress is likely to concentrate are cut off is effective.

[0464] (Implementation 10)

[0465] A semiconductor laser device according to a tenth embodiment will be described.

[0466] First, the shape of the diamond-formed base substrate described above will be described. Since the base substrate itself is relatively hard, it is difficult to separate the diamond wafer. Therefore, in order to form the base substrate, it is necessary to melt the wafer-shaped diamond by irradiating it with a laser. In this case, when a relatively strong laser is irradiated from the upper surface of the wafer and the laser melts it to near the lower surface of the wafer, it is easy to cleave the wafer. However, the melted portion of the wafer degenerates into conductive carbon, so when the melted portion is used for the sidewalls of the base substrate, the insulation of the base substrate cannot be ensured. Therefore, when the wafer is irradiated with a laser to melt it, it is melted to a depth of about half its film thickness. This allows the carbonized portion of the wafer's split surface to be suppressed to about half its film thickness.

[0467] When laser light is irradiated onto a wafer, the laser intensity is higher in the center of the wafer. Therefore, the portion of the wafer irradiated by the laser light near the center melts more deeply, while the portion near the outer edge melts less deeply. Consequently, the sidewalls of the base substrate formed by the above method are inclined to a depth of approximately half the thickness.

[0468] By forming the base substrate as described above, it is possible to achieve both the separability of the base substrate from the wafer state and the insulation properties of the base substrate.

[0469] Figure 46 1 is a perspective view showing the shape of the base substrate 122 of the tenth embodiment. Figure 46 As shown, the base substrate 122 of Embodiment 10 is not in the shape of a rectangular parallelepiped, but has an inclined portion with a thickness of H1 and a vertical portion with a thickness of H2 on the sidewall (surface other than the main surface). The inclined portion of the sidewall is formed by a surface inclined at an angle θ relative to the normal to the main surface of the base substrate 122, while the vertical portion of the sidewall is formed by a surface parallel to the normal.

[0470] The thickness H1 of the inclined portion may be approximately half the thickness of the base substrate, for example, within a range of ±50 μm from half the thickness of the entire base substrate.

[0471] The sidewall inclination angle θ may also be within a range of 2.5° to 15°, centered at 8°. This is because if the inclination angle θ is too large, the heat dissipation path of the base substrate 122 becomes too small. Conversely, if the inclination angle θ is too small, it becomes difficult to form an electrode on the inclined portion of the sidewall, as will be described later.

[0472] Next, the electrodes formed on the base substrate 122 will be described with reference to the drawings. Figure 47 1 is a diagram showing the structure of electrodes formed on the base substrate 122 of the tenth embodiment. Figure 47 , cross-sectional views (a) and (c) and a top view (b) of the base substrate 122 on which electrodes are formed are shown. The cross-sectional views (a) and (c) respectively show the AA cross-sectional view and the CC cross-sectional view shown in the top view (b).

[0473] like Figure 47 As shown in the cross-sectional view (c), an upper contact metal layer 206, a base barrier layer 205 and a bonding layer 121 are formed on the upper surface of the base substrate 122 in a manner covering the inclined portion of the side wall. Figure 47 As shown in the top view (b), the pedestal barrier layer 205 is formed in an area inward of the upper contact metal layer 206, and the bonding layer 121 is formed slightly inward. This patterning allows for identification of the mounting position of the semiconductor laser element during mounting. It also prevents the bonding layer 121 from significantly spreading outside the pedestal barrier layer 205.

[0474] Furthermore, when mounted with the bonding face downward, the emission pattern of light emitted from the front facet (the emission-side facet of the resonator) of the semiconductor laser element may be disturbed by the bonding layer material, such as AuSn, that overflows from the base substrate toward the front facet. To prevent this disturbance in the laser emission pattern, it is effective to mount the semiconductor laser element with the front facet protruding from the end of the base substrate.

[0475] like Figure 47 As shown in the cross-sectional view (c), by also forming the upper close-fitting metal layer 206 and the bonding layer 121 on the inclined portion of the base substrate 122, when the front end face of the laser is mounted so as to protrude from the end of the base substrate, the bonding layer 121 can be fixedly formed to cover the pad electrode of the protruding portion. This improves the heat dissipation of the protruding portion. This mounting method is described below using the accompanying drawings.

[0476] Figure 48A 1 is a schematic cross-sectional view showing the structure of a semiconductor laser device 60 a in which a semiconductor laser element is mounted on a base substrate 122 in which a bonding layer 121 is not formed on an inclined portion. Figure 48B 1 is a schematic cross-sectional view showing the structure of a semiconductor laser device 60b in which a semiconductor laser element is mounted on a base substrate 122 in which a bonding layer 121 is formed on an inclined portion. Figure 48A and Figure 48B : shows a cross section parallel to the cavity direction of the semiconductor laser device and the stacking direction of the multilayer structure.

[0477] like Figure 48AAs shown, when the base barrier layer 205, the upper contact metal layer 206 and the bonding layer 121 are not formed on the side wall of the base substrate 122, the front end surface side ( Figure 48A The protruding portion (on the left side) is not covered by the bonding layer 121.

[0478] On the other hand, Figure 48B As shown, by forming a base barrier layer 205, an upper close-fitting metal layer 206 and a bonding layer 121 on the side wall of the base substrate 122, the front end surface side ( Figure 48B The bonding layer 121 is fixed by the protruding portion of the left side of the semiconductor laser element. This can improve the heat dissipation of the front end of the semiconductor laser element. Since the optical density of the front end of the semiconductor laser element is very high, it is most likely to cause heat. Therefore, Figure 48B As shown, fixing the bonding layer 121 to the pad electrode 116 is very effective in preventing the COD level from decreasing.

[0479] In particular, this effect can be further improved in preventing a decrease in the COD level when the current non-injection window region is formed near the cavity facet.

[0480] Figure 49A 1 is a schematic cross-sectional view showing the structure of a semiconductor laser device 60 c in which a semiconductor laser element having a current non-injection window region 210 is mounted on a base substrate 122 in which a bonding layer 121 is not formed on an inclined portion. Figure 49B 1 is a schematic cross-sectional view showing the structure of a semiconductor laser device 60 c in which a semiconductor laser element having a current non-injection window region 210 is mounted on a base substrate 122 in which a bonding layer 121 is formed on an inclined portion.

[0481] The current non-injection window region 210 is a region where an insulating film made of SiO2 is formed on the contact layer near the end face of the semiconductor laser element to prevent current injection. By having such a current non-injection window region 210, the action carrier density in the quantum well active layer 106 near the end face of the semiconductor laser element is reduced, thereby suppressing the heat generated by the Auger non-luminescence recoupling. In this state, by Figure 49B As shown in the semiconductor laser device 60d, the front end surface side ( Figure 49B By fixing the bonding layer in the manner of the protruding portion (on the left side of the ) , it is possible to further improve the heat dissipation in the current non-injection window region 210. Therefore, it is possible to suppress a decrease in the COD level of the semiconductor laser device 60d.

[0482] In addition, even in a semiconductor laser device with a flat or convex shape when the GaN substrate 101 is facing upward, or in a multilayer structure with an average strain ε tave Even for a laser device with zero or tensile properties, the heat dissipation performance of the front end portion of the semiconductor laser device can be improved by using the structure shown in Embodiment 10. As a result, the COD level of the semiconductor laser device can be suppressed from decreasing.

[0483] (Implementation 11)

[0484] An optical module according to the eleventh embodiment will be described.

[0485] The semiconductor laser element disclosed above is mounted on a base substrate formed of diamond, thereby achieving a leakage current suppression effect, which suppresses current leakage into the current non-injection window region. In addition, in the case of a ridge laser, it also suppresses current leakage outside the ridge. In addition, since the thermal expansion coefficient of the base substrate formed of diamond is smaller than that of nitride materials and metal materials such as Au, such as Figure 4 、 Figure 21C and Figure 23C As shown, these effects are enhanced when used in a room temperature environment of 25°C compared to when used at a high temperature of 150°C.

[0486] Therefore, if the semiconductor laser element is used under environmental conditions close to room temperature, the effect of suppressing degradation of the semiconductor laser element and the effect of suppressing the operating current value can be improved compared to a semiconductor laser element mounted on a base substrate formed of SiC, AlN, etc.

[0487] Hereinafter, embodiments that can enhance the effects of the semiconductor laser element of the present disclosure will be described with reference to the drawings.

[0488] Figure 50 : is a diagram showing a structure of an example of an optical module 240 according to Embodiment 11. Figure 50 1 shows a rear view (a), a front view (b), and a cross-sectional view (c) of an optical module 240 according to Embodiment 11. The rear view (a) shows the appearance of the back side of the light-emitting side of the optical module 240. The front view (b) shows the appearance of the light-emitting side of the optical module 240. The cross-sectional view (c) shows a cross section passing through the optical axis of the optical module 240.

[0489] The optical module 240 includes a CAN package 221 on which the semiconductor laser element and the base substrate according to the above-described embodiments are mounted, and a metal base 220 having a built-in water cooling mechanism.

[0490] A pipe 224 for circulating a refrigerant for cooling the metal base 220 is built into the metal base 220. This structure allows the metal base 220 to be maintained at a temperature equivalent to or close to room temperature. As a result, the semiconductor laser device can be operated in an environment close to room temperature, improving the ability to suppress semiconductor laser device degradation and operating current compared to semiconductor laser devices mounted on a base substrate made of SiC, AlN, or the like.

[0491] (Implementation 12)

[0492] The optical module of embodiment 12 is described. The optical module of embodiment 12 differs from the optical module 240 of embodiment 11 in that it includes an optical fiber, but is identical in other respects. The optical module of embodiment 12 is described below using the drawings.

[0493] Figure 51 1 is a cross-sectional view showing the structure of an example of an optical module according to Embodiment 12. Figure 51 , a cross section passing through the optical axis of the optical module according to the twelfth embodiment is shown.

[0494] The optical module of Embodiment 12 integrates optical fiber 226 in addition to optical module 240 of Embodiment 11. This structure enables the semiconductor laser element to operate in an environment close to room temperature, similar to Embodiment 11, while also facilitating the delivery of watt-class 450nm blue laser light to locations where it is needed. The optical module of Embodiment 12 can be used, for example, as a processing laser source.

[0495] Furthermore, by disposing a fluorescent substance that generates yellow light, or a fluorescent substance that generates red light or green light, for example, near the emission portion of the optical fiber 226 , a white light source can be realized.

[0496] (Implementation 13)

[0497] A light source according to Embodiment 13 will be described. The light source according to Embodiment 13 converts blue laser light emitted from a semiconductor laser element into white light and emits the converted light. The light source according to Embodiment 13 will be described below using the accompanying drawings.

[0498] Figure 52 This is a cross-sectional view showing an example of the structure of the light source 250 according to the thirteenth embodiment.

[0499] like Figure 52As shown, light source 250 of embodiment 13 includes the CAN package 221 and metal base 220 of optical module 240 of embodiment 11. Light source 250 also includes a lens 227, a reflector 228, a base 229, and a phosphor 230. These components are integrated into light source 250. This structure enables the semiconductor laser element of light source 250 to operate in an environment close to room temperature, and lens 227 can be used to focus watt-class 450nm blue laser light on phosphor 230.

[0500] In this structure, the phosphor can be excited by irradiating it with a blue laser beam in the 450nm band. Therefore, the phosphor generates yellow light, red light, and green light, and can be used as a light source that emits white light as a whole.

[0501] In this case, not only is the degradation of the semiconductor laser element suppressed by using a face-down mounting pattern on a diamond-formed base substrate, but also, since the phosphor is used at an ambient temperature close to room temperature, degradation of the phosphor due to heat can be suppressed. Consequently, a white light source with excellent long-term reliability can be achieved.

[0502] As mentioned above, the nitride-based light-emitting device of the present disclosure has been described based on the respective embodiments, but the present disclosure is not limited to the aforementioned embodiments.

[0503] For example, embodiments obtained by applying various modifications that can be conceived by those skilled in the art to the embodiments, or embodiments achieved by arbitrarily combining constituent elements and functions in the embodiments and modifications without departing from the spirit of the present disclosure are also included in the present disclosure.

[0504] In the various embodiments, examples of substrates for fabricating semiconductor laser elements are shown in which the principal surface of the substrate is a (0001) C-plane, a semipolar plane, or a nonpolar plane. However, an offset substrate (offset substrate) in which the principal surface of the substrate is tilted from the (0001) C-plane may also be used. By using an offset substrate, the piezoelectric effect in the C-axis direction generated in the quantum well active layer can be reduced, thereby reducing the operating voltage.

[0505] Industrial applicability

[0506] The nitride-based light-emitting device disclosed herein can be used as a light source for a vehicle headlamp having excellent temperature characteristics and long-term reliability even when operating at an ultra-high output of 3 watts or more in an environment of 85°C, for example.

[0507] Description of reference numerals:

[0508] 11, 11a, 11b, 12, 12a, 13, 14, 15, 16, 17, 17a, 18, 18a semiconductor laser elements;

[0509] 51a, 51b, 59, 60a, 60b, 60c, 60d semiconductor laser devices;

[0510] 101, 140, 141, 401 GaN substrate;

[0511] 102 buffer layer;

[0512] 102a InGaN layer;

[0513] 102b AlGaN layer;

[0514] 103, 163 first cladding;

[0515] 104 N-type GaN layer;

[0516] 105 first light guide layer;

[0517] 106, 166 quantum well active layer;

[0518] 106a, 106c, 106e barrier layer;

[0519] 106b, 106d quantum well layer;

[0520] 107 second light guide layer;

[0521] 108, 168 electron barrier layer;

[0522] 109, 169 second cladding;

[0523] 110 contact layer;

[0524] 112 current blocking layer;

[0525] 113 P-side ohmic electrode;

[0526] 114, 114a P-side first close-fitting layer;

[0527] 115 first barrier layer;

[0528] 116, 116a pad electrode;

[0529] 117 N-side electrode;

[0530] 118, 118a P-side multilayer electrode;

[0531] 121 bonding layer;

[0532] 122, 311, 410 base substrate;

[0533] 130 third light guide layer;

[0534] 131 Third cladding;

[0535] 201 first pad electrode;

[0536] 202, 202a second barrier layer;

[0537] 203 second pad electrode;

[0538] 205 base barrier;

[0539] 206 The upper portion is in close contact with the metal layer;

[0540] 207 The lower part is in close contact with the metal layer;

[0541] 210 current non-injection window region;

[0542] 220 metal abutment;

[0543] 221 CAN package;

[0544] 224 tubes;

[0545] 226 optical fiber;

[0546] 227 lens;

[0547] 228 reflector;

[0548] 229 pedestal;

[0549] 230 phosphor;

[0550] 240 optical modules;

[0551] 250 light sources;

[0552] 300, 400 semiconductor light emitting devices;

[0553] 310 Nitride light emitting element;

[0554] 402 light-emitting element.

Claims

1. A nitride-based light-emitting device comprising: A nitride-based semiconductor light-emitting element having a multilayer structure disposed on a GaN substrate; a base substrate for mounting the nitride-based semiconductor light-emitting element; and a bonding layer for bonding the nitride-based semiconductor light-emitting element and the base substrate; The multilayer structure includes a first cladding layer of a first conductivity type, a first optical guide layer, a quantum well active layer, a second optical guide layer, and a second cladding layer of a second conductivity type stacked in order from the GaN substrate side. The multilayer structure has a 5.2×10 -4 The average deformation of the following tensile or compressive The nitride-based semiconductor light-emitting element is mounted on the base substrate so that the multilayer structure faces the base substrate. The nitride-based semiconductor light-emitting element includes an electrode disposed between the multilayer structure and the base substrate. The nitride-based semiconductor light-emitting element is mounted on the base substrate in a state where the emission-side end face thereof protrudes from the side wall of the base substrate. The base substrate is flat and formed of diamond, At least one of the first optical waveguide layer and the second optical waveguide layer includes In, The side wall of the base substrate has an inclined portion that is inclined with respect to a normal direction of a main surface of the base substrate.

2. The nitride-based light-emitting device according to claim 1, wherein: The nitride-based semiconductor light-emitting element includes a resonator. A current non-injection window region is provided near the end face of the resonator.

3. The nitride-based light-emitting device according to claim 2, wherein: The length of the resonator is greater than 600 μm.

4. The nitride-based light-emitting device according to any one of claims 1 to 3, wherein: A ridge is formed on the second cladding layer.

5. The nitride-based light-emitting device according to any one of claims 1 to 3, wherein: The GaN substrate has a thickness of 75 μm or more and 95 μm or less.

6. The nitride-based light-emitting device according to any one of claims 1 to 3, wherein: The first cladding layer is composed of AlGaN with an Al composition of less than 0.05, The second cladding layer is composed of AlGaN having an Al composition of 0.05 or less.

7. The nitride-based light-emitting device according to any one of claims 1 to 3, wherein: The bonding layer is fixedly formed to cover a portion of the electrode protruding from the side wall of the base substrate.

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