Manufacturing method for laser diode bars

Abstract

To provide a method for manufacturing a laser diode bar capable of improving oscillation performance of a wavelength beam coupling system.SOLUTION: A method for manufacturing a laser diode bar includes the steps of: preparing a nitride semiconductor substrate 10 having a substrate surface provided with an off angle larger than 0° from a (0001) plane to at least one of an m-axis and an a-axis; forming a laminate structure body composed of a first conduction type cladding layer 21, an active layer 22, and a second conduction type cladding layer 23 on a nitride semiconductor substrate 10; forming a plurality of emitters 13 arranged in a stripe shape in a laminate structure body so that a primary axis direction of an off angle of the nitride semiconductor substrate 10 and a waveguide direction of an emitter 13 coincide with each other; and cutting out a laser diode bar 20 having a plurality of emitters 13 from the nitride semiconductor substrate 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing laser diode bars. [Background technology]

[0002] In recent years, expectations for laser processing have been rising for various materials such as copper, gold, and resin. For example, in the automotive industry, there is a demand for electrification, miniaturization, high rigidity, improved design freedom, and improved productivity, and expectations for laser processing are very high. In particular, in copper processing for motors and batteries for electric vehicles, a blue-violet to blue (wavelength 350 to 450 nm) laser light source with high light absorption efficiency is required, and in order to achieve highly productive processing, a laser light source with high output and highly focused beam quality is required.

[0003] A wavelength beam combining (WBC) system is known as a system that can collect multiple laser beams to obtain high-output, high-beam-quality laser beams. The wavelength beam combining system is described in, for example, Patent Document 1.

[0004] The wavelength beam combining system includes a laser diode bar, a beam twister unit, a transmission or reflection type diffraction grating, and an external resonator mirror. An emitter for emitting light is arranged in the laser diode bar, and multiple beams of light are emitted from one end face of the emitter. The beam twister unit rotates each of the multiple beams of light emitted from the laser diode bar by 90 degrees to prevent individual beams of light having close wavelengths from interfering with each other. When the diffraction grating is a transmission type, the diffraction grating diffracts the incident beam of light at a diffraction angle determined by its wavelength and emits it. The beam of light emitted from the diffraction grating is incident on the external resonator mirror, and a part of the beam of light is perpendicularly reflected in the direction of the diffraction grating by the external resonator mirror, which is a partially transmission type mirror. As a result, laser light of a wavelength (sometimes called the locking wavelength) that is uniquely determined by the positional relationship between the individual emitters, diffraction grating, and external resonator mirror of the laser diode bar causes external resonance of light between the external resonator mirror and a reflective film provided on the side opposite the side from which the laser light of the laser diode bar is emitted, and the laser light is output.

[0005] Since each emitter of the laser diode bar has a different relative position from the diffraction grating, it causes external resonance at different wavelengths and emits laser light, but they are combined at one point by the external resonance mirror. Therefore, in the wavelength beam combining system, it is possible to obtain high-power, high-quality laser light by adding up the output of the individual emitters. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-106707 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in a wavelength beam combining system, due to the structure of the laser diode bar, a difference may occur between the wavelength at which the laser diode bar can oscillate most strongly (sometimes called the gain peak wavelength) and the lock wavelength that is uniquely determined by the configuration of the wavelength beam combining system. If this difference becomes large, there is a risk that laser oscillation will not be possible, resulting in a problem of reduced oscillation performance.

[0008] An object of the present disclosure is to provide a wavelength beam combining system with improved oscillation performance, and a manufacturing method for a laser diode bar and a laser diode bar capable of improving the oscillation performance of a wavelength beam combining system. [Means for solving the problem]

[0009] The present disclosure, which solves the above-mentioned problems, is 1. A method for manufacturing a laser diode bar for use in a wavelength beam combining system, comprising: preparing a nitride semiconductor substrate having a substrate surface oriented in the (0001) plane and having an off-angle of greater than 0° from the (0001) plane to at least one of the m-axis and the a-axis; determining the size of the laser diode bar required for the wavelength beam combining system, and setting a layout related to the planned formation position of the laser diode bar in the nitride semiconductor substrate so that the principal axis direction of the off-angle coincides with the waveguide direction; forming a laminated structure including a first conductive type cladding layer, an active layer, and a second conductive type cladding layer on the nitride semiconductor substrate; estimating a distribution of gain peak wavelengths of the laser diode bars to be formed in the nitride semiconductor substrate; forming a plurality of emitters arranged in a stripe pattern in the laminated structure such that a principal axis direction of the off-angle coincides with a waveguide direction; cutting the laser diode bar having the plurality of emitters from the nitride semiconductor substrate; determining a position of the laser diode bar in the wavelength beam combining system based on a distribution of gain peak wavelengths of the laser diode bar and a lock wavelength determined by a configuration of the wavelength beam combining system; The method for producing a laser diode bar includes the steps of: Effect of the Invention

[0010] The method for manufacturing a laser diode bar according to the present disclosure can improve the oscillation performance of a wavelength beam combining system. [Brief description of the drawings]

[0011] [Figure 1] Illustrates the manufacturing method of laser diode bars. [Diagram 2] Perspective view of a laser diode bar [Diagram 3] Schematic of a wavelength beam combining system using transmission gratings [Figure 4] Schematic of a wavelength beam combining system using a reflective grating [Diagram 5] Diagram showing the relationship between the laser diode bar and the diffraction grating [Figure 6] A diagram showing the relationship between the lock wavelength of each emitter in Table 2 and the emitter position. [Figure 7] Diagram showing the wavelength range of the emitters of laser diode bars [Figure 8] A diagram showing the range in which laser oscillation is possible within the emitter of a laser diode bar. [Figure 9] A diagram showing the range in which laser oscillation is possible within the emitter of a laser diode bar. [Figure 10] A diagram showing the range in which laser oscillation is possible within the emitter of a laser diode bar. [Figure 11] Graph showing the distribution of off-angles in a gallium nitride substrate whose main axis of off-angle is in the +m-axis direction and in a gallium nitride substrate whose main axis of off-angle is in the +a-axis direction. [Figure 12]FIG. 1 shows the off-angle distribution of gallium nitride substrates according to an embodiment and a comparative example. [Figure 13] Layout of laser diode bars on a gallium nitride substrate [Figure 14] 13 is a graph showing the distribution of gain wavelengths in the gallium nitride substrate of FIG. 12. [Figure 15] FIG. 1 shows the λg_CENTER of a laser diode bar according to an embodiment. [Figure 16] FIG. 1 shows the difference between λg on the left side and λg on the right side for a laser diode bar according to an embodiment of the present invention. [Figure 17] FIG. 13 is a diagram showing Δλg_BAR when the transmissive film and the reflective film are interchanged in the laser diode bar of the embodiment. [Figure 18] FIG. 1 shows the position and number of laser diode bars in an embodiment. [Figure 19] FIG. 1 shows the position and number of laser diode bars in a comparative example. [Figure 20] A diagram comparing the number of laser diode bars and the value of λg_CENTER in the examples and comparative examples. [Figure 21] A graph showing the relationship between the longitudinal length of a laser diode bar and Δλg_BAR. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First, the configuration of the wavelength beam combining system, the configuration of the laser diode bar, the locking wavelength of the laser diode bar, and the range of wavelengths that the laser diode bar can oscillate will be described based on a specific example.

[0013] <Wavelength Beam Combining System> Fig. 3 shows a transmissive wavelength beam combining system 30. An actual wavelength beam combining system may have elements such as optical components in addition to the elements shown in Fig. 3, but these elements are omitted.

[0014] The wavelength beam combining system 30 includes a laser diode bar array 20T including a plurality of laser diode bars 20a-20e, a transmission type diffraction grating 37, and an external resonator mirror 38. Note that in practice, an optical component such as a beam twister unit (not shown) may be provided between the laser diode bars 20a-20e and the diffraction grating 37.

[0015] 4 shows a reflective wavelength beam combining system 40. The wavelength beam combining system 40 has a similar configuration to the transmissive wavelength beam combining system 30, except that a reflective diffraction grating 39 is used.

[0016] In the wavelength beam combining system 30, the light emitted from the laser diode bars 20a-20e is diffracted by the diffraction gratings 37, 39, and then a part of the light is vertically reflected in the direction of the diffraction grating by the external resonator mirror 38. As a result, external resonance of the light occurs between the reflective film 17 of the laser diode bars 20a-20e and the external resonator mirror, and laser light is output. The multiple laser diode bars 20a-20e may be arranged in order from the laser diode bar 20a with a short wavelength to the laser diode bar 20e with a long wavelength.

[0017] <Laser diode bar> 2 shows a laser diode bar 20. The laser diode bar 20 has a plurality of emitters 13 formed at intervals from one another. The plurality of emitters 13 are arranged in a line along the longitudinal direction of the laser diode bar 20 in a stripe shape.

[0018] Specifically, the emitter 13 of the laser diode bar 20 is formed in a laminated structure 12 of a first conductive cladding layer 21, an active layer 22, and a second conductive cladding layer 23 on a nitride semiconductor substrate 10. The laser diode bar 20 has a P-side electrode 15 on its upper surface and an N-side electrode 24 on its lower surface. A transmission film 16 is provided on the entire end face of the laser diode bar 20 on the side from which light is emitted, and a reflection film 17 is provided on the entire end face opposite the transmission film 16 on the side from which light is not emitted. The laser diode bar 20 shown in FIG. 2 can be used as the laser diode bars 20a to 20e in the wavelength beam combining system 30 shown in FIGS. 3 to 5.

[0019] The longitudinal direction of the laser diode bar 20 is designated as W, and the waveguide direction is designated as D. The white arrow in FIG.

[0020] The P-side electrode 15 is a current injection region that injects current into a plurality of emitters 13 formed at intervals on an end face of the laser diode bar 20. The P-side electrodes 15 are arranged in a stripe shape along the longitudinal direction of the laser diode bar 20. When a current is injected in parallel from a power supply unit (not shown) into the P-side electrodes 15 of the laser diode bar 20, laser light 25 is simultaneously emitted in the waveguide direction (i.e., the external resonance direction) from the plurality of emitters 13 corresponding to each P-side electrode 15.

[0021] The laser diode bar 20 shown in FIG. 2 has a structure having a current injection region in which protrusions called ridge stripes are formed in a stripe shape, but the laser diode bar 20 may have a buried structure, in which case the current injection region may be selectively formed.

[0022] <Lock wavelength> 2, 3 and 5, a method for calculating the locking wavelength of the laser diode bars 20 required for the wavelength beam combining system 30 will be described.

[0023] Fig. 5 is a diagram for explaining the method of calculating the lock wavelength and each emitter of the laser diode bars 20a to 20e. Fig. 6 is a diagram showing the relationship between the emitter 13 of each laser diode bar 20a to 20e and the lock wavelength.

[0024] Of the laser light 25 emitted from each emitter 13 of the laser diode bar 20, only the lock wavelength that satisfies the diffraction conditions of the diffraction grating 37 and is vertically reflected by the external resonator mirror 38 returns to the original emitter 13, causing external resonance between the end face (reflective film 17) of the laser diode bar 20 from which light is not emitted and the external resonator mirror 38, resulting in laser oscillation.

[0025] The lock wavelength of each emitter 13 corresponding to the laser diode bar 20 and the injection region shown in FIG. L , the period of the diffraction grating 37 is d, the angle of incidence is α, the angle of emergence is β, and the order is m, then the lock wavelength λ L can be calculated using the following formula (1). d(sinα+sinβ)=mλ L ...(1)

[0026] In this case, it is common to select a diffraction grating arrangement with order m=1.

[0027] For example, in the case where the laser wavelength beam combining system 30 is configured by arranging five laser diode bars 20a to 20e as shown in FIG. 3 so that the incidence angle α increases by 0.8 deg from 21.6 deg, the lock wavelength λ of the emitter 13 located at the center of each of the laser diode bars 20a to 20e is L_CENTER (Hereinafter, the lock wavelength λ at the longitudinal center position of the laser diode bar 20 is L_CENTER As shown in Table 1, the laser diode bars 20a and 20b have wavelengths of 435.9 nm and 440.3 nm, respectively, and the laser diode bar 20e has wavelengths of 453.0 nm, which are longer by approximately 4.3 nm each.

[0028] [Table 1]

[0029] Next, λ in the laser diode bars 20a to 20e L This will be explained using the laser diode bar 20 as an example.

[0030] 5, 25 emitters 13 are formed on the laser diode bar 20. The length W of the laser diode bar 20 in the longitudinal direction is 10 mm.

[0031] Here, a diffraction grating (d=0.333 μm) 37 with a groove period of 3,000 lines / mm is used, and light with a wavelength of approximately 400 to 500 nm is arranged so that the incident angle α is 21.6°, the length W of the laser diode bar 20 is 10 mm, and the distance L from the laser diode bar 20 to the diffraction grating 37 is 2.6 m.

[0032] At this time, as shown in Table 2, the lock wavelength λ of the first emitter from the right side of the laser diode bar 20 is L is 435.37 nm, and the lock wavelength λ of each emitter of the laser diode bar 20 is L The lock wavelength of the 25th emitter, λ, is approximately 0.05 nm longer for each emitter. L is 420T.51 nm, and the lock wavelength λ of the emitters at both ends of the laser diode bar 20 is L Difference Δλ L_BAR (Hereinafter, the difference in lock wavelength between both ends of the laser diode bar 20, Δλ L_BAR ") is approximately 1.1 nm (see Figure 6).

[0033] [Table 2]

[0034] Similarly, when the distance L from the laser diode bar 20 to the diffraction grating 37 is 1.3 m, as shown in Table 3, the lock wavelength difference Δλ L_BAR is 2.3 nm.

[0035] [Table 3]

[0036] As described above, the locking wavelength λ of the longitudinal center position of the laser diode bar 20 can be determined by the layout and component design of the wavelength beam combining system 30. L_CENTER , and the lock wavelength difference Δλ between both ends of the laser diode bar 20 L_BAR Although there is a difference in the amount of change in the lock wavelength, when W is 10 mm, the lock wavelength difference Δλ L_BAR In the above description, the transmission type wavelength beam combining system 30 is used as the basis for explanation. However, the reflection type wavelength beam combining system 40 also requires the lock wavelength λ at the center position in the longitudinal direction of the laser diode bar 20 to be 1.0 to 2.5 nm. L_CENTER , and the lock wavelength difference Δλ between both ends of the laser diode bar 20 L_BAR The amount of change can be calculated.

[0037] <Wavelength range that laser diode bars can oscillate in> The range of wavelengths at which the laser diode bar 20 can oscillate will be described with reference to FIG. 7. The curve in FIG. 7 shows an example of the gain wavelength spectrum of the laser diode bar 20. The laser diode bar 20 can oscillate only at wavelengths where the gain wavelength intensity is equal to or greater than a predetermined value. In other words, the gain peak wavelength λ of the laser diode bar 20 g Therefore, the laser oscillates at a lock wavelength within a predetermined range, and does not oscillate at a lock wavelength outside the predetermined range. In the example of Fig. 7, when the lock wavelength is wavelength 1, the laser oscillates because it is within the range of wavelengths that can be oscillated due to the configuration of the wavelength beam combining system 30, but when the lock wavelength is wavelength 2, the laser oscillates because it is outside the range of wavelengths that can be oscillated.

[0038] 8 to 10 show the gain peak wavelength λ of each emitter 13 arranged in one laser diode bar 20. g and the lock wavelength λ determined by the configuration of the wavelength beam combining system 30. L The relationship between the lock wavelength λ L has a unique value and slope corresponding to the change in the angle of incidence on the diffraction grating 37. g As shown in FIG. 7, there is a certain range in which laser oscillation can occur.

[0039] Lock wavelength λ L and the gain peak wavelength λ g If the relationship is as shown in the example of FIG. 8, the gain peak wavelength λ g The lock wavelength difference Δλ between both ends of the laser diode bar 20 is L_BAR Since the wavelength is within the range of 100 nm, all the emitters 13 of the laser diode bar 20 can oscillate.

[0040] In the case of FIG. 9, all the emitters 13 can oscillate. g The direction of the lock wavelength λ L When the angle is different from the gain peak wavelength λ g The upper and lower limits of the lock wavelength difference Δλ L_BAR In this state, laser oscillation cannot be achieved with all the emitters 13. However, if the emission surface and the non-emission surface of the laser diode bar 20 in FIG. 3 are interchanged and a reflective film 17 and a transmissive film 16 are formed, the gain peak wavelength λ g The distribution of λ can be inverted and the slope can be inverted. Therefore, the configuration is the same as that of FIG. 8, and the gain peak wavelength λ g Either of the upper and lower limits of the range is the lock wavelength difference Δλ L_BARSince the wavelength is within the range of 100 nm, all the emitters of the laser diode bar 20 can oscillate.

[0041] In contrast, as shown in FIG. 10, the gain peak wavelength λ g The magnitude of the slope of the gain peak wavelength difference Δλ g_BAR ) is the locking wavelength λ at each position along the longitudinal direction of the laser diode bar 20. L The magnitude of the inclination of the laser diode bar 20 (i.e., the lock wavelength difference Δλ L_BAR ), the gain peak wavelength λ g The upper and lower limits of oscillation are determined by the difference in lock wavelength Δλ between the two ends of the laser diode bar 20. L_BAR Therefore, laser oscillation by external resonance cannot be obtained.

[0042] The laser diode bar 20 of the present disclosure has a gain peak wavelength difference Δλ between both ends of the laser diode bar 20 due to the ingenuity used during the manufacturing process of the laser diode bar 20. g_BAR This reduces the number of emitters 13 that cannot oscillate among the multiple emitters 13 formed in the laser diode bar 20.

[0043] Next, a method for manufacturing the laser diode bar 20, a method for calculating the gain peak wavelength of the laser diode bar 20, and characteristics of the distribution shape will be described.

[0044] <Laser Diode Bar Manufacturing Method> FIG. 1 is a diagram showing a method for manufacturing a laser diode bar 20. As shown in FIG.

[0045] The method for manufacturing the laser diode bar 20 includes the steps of forming a first-conductivity-type cladding layer 21, an active layer 22, and a second-conductivity-type cladding layer 23 on a nitride semiconductor substrate 10, forming an emitter 13, and forming a P-side electrode and an N-side electrode. The first-conductivity-type cladding layer 21, the active layer 22, and the second-conductivity-type cladding layer 23 can be formed by epitaxial growth. The emitter 13 may be formed as a ridge stripe structure.

[0046] The manufacturing method of the laser diode bar 20 further includes a step of cutting out a plurality of laser diode bars 20 each having a plurality of emitters 13, and a step of forming a transmission film 16 on the light-emitting end face of the laser diode bar 20 and forming a reflective film 17 on the end face opposite to the face on which the transmission film 16 is formed. Furthermore, a laser diode bar array 20T used in the wavelength beam combining system 30 is manufactured by combining a plurality of the cut out laser diode bars 20.

[0047] <Calculation method of gain peak wavelength and characteristics of distribution shape> Gain peak wavelength λ g can be calculated with a certain degree of accuracy after epitaxial growth by performing a known Photo Luminescence Spectroscopy measurement (hereinafter referred to as PL measurement) after the process of stacking a first conductivity type cladding layer 21, an active layer 22, and a second conductivity type cladding layer 23 on a nitride semiconductor substrate 10 (hereinafter referred to as epitaxial growth).

[0048] Gain peak wavelength λ in nitride semiconductor substrate 10 g The distribution of the gain peak wavelength λ varies with various characteristics depending on the gas flow rate for epitaxial growth, the equipment conditions, and the quality of the substrate. For example, when the temperature distribution in the substrate surface during epitaxial growth is concentric, the in-plane distribution is also concentric. In addition, when the deviation amount (called the off-angle in this invention) from the normal (crystal axis) of the crystal plane (0001) of the substrate 10 to the normal of the substrate surface differs in the upper and lower directions of the nitride semiconductor substrate 10, the gain peak wavelength λ varies with the distribution of the off-angle.g are distributed in the vertical direction of the nitride semiconductor substrate 10.

[0049] In particular, when the nitride semiconductor active layer contains 3% or more, more specifically 7% or more, of indium (In) in the composition of the entire layer, the gain peak wavelength λ due to the off-angle distribution of the nitride semiconductor substrate 10 g The distribution of the above in the substrate is clearly evident.

[0050] When manufacturing a blue-violet to blue semiconductor laser with an oscillation wavelength of about 350 nm to 450 nm, a gallium nitride substrate (hereinafter referred to as a GaN substrate) whose wavelength calculated from the band gap is close to the oscillation wavelength is preferably used as the base material.

[0051] Usually, GaN substrates are tilted at a certain off angle (greater than 0°, about 0.3° to 0.7°) with respect to a certain axis in order to improve the crystal quality of the active layer. The main axis of the off direction within the substrate plane is uniquely determined, and the main axis direction of the off angle (represents the inclination direction of the sliced ​​surface with respect to the crystal plane with an off angle of 0°; the same applies below) is generally uniaxial along the ±m-axis or ±a-axis directions.

[0052] In addition, since GaN substrates are formed by crystal growth using heterogeneous substrates with different thermal expansion coefficients, crystal warpage is generally more likely to occur in the GaN substrate than in Si or GaAs. Therefore, according to the findings of the inventors of the present application, when a GaN substrate is sliced ​​from an ingot with an off-angle provided on the (0001) plane of the GaN substrate, the off-angle gradually increases from one side to the other side in the principal axis direction of the off-angle within the substrate plane of the GaN substrate, as shown in FIG.

[0053] According to the findings of the present inventors, for example, when an InGaN layer is used for the active layer, the In composition of the InGaN layer is affected by the off-angle distribution in the GaN substrate plane, and the In composition tends to become small in regions with large off-angles, and the oscillation wavelength tends to become short (see FIG. 14). Specifically, in a semiconductor laser formed by epitaxially growing an InGaN layer on a GaN substrate, the emission wavelength of the semiconductor laser changes at a rate of 30 nm / ° in response to changes in the off-angle of the GaN substrate.

[0054] This means that when the laser diode bar 20 is formed on the GaN substrate, if the waveguide direction of the laser diode bar 20 (emitter 13) coincides with the main axis direction of the off-angle of the GaN substrate, the difference in the off-angle of the GaN substrate at both ends in the longitudinal direction of the laser diode bar 20 becomes small. In other words, by forming the laser diode bar 20 so that the waveguide direction of the laser diode bar 20 (emitter 13) coincides with the main axis direction of the off-angle of the GaN substrate, the gain peak wavelength difference Δλ at both ends of the laser diode bar 20 can be reduced. g_BAR Based on this knowledge, the inventors of the present application have devised a method for manufacturing the laser diode bar 20.

[0055] A method for manufacturing the laser diode bar 20 according to the embodiment of the present invention will now be described in detail.

[0056] <Preparation of the substrate> In the manufacturing method of the laser diode bar 20 of the present disclosure, the nitride semiconductor substrate 10 has a primary surface (0001) and has an off-angle greater than 0° along at least one of the m-axis or a-axis. In this embodiment, a GaN substrate is used as the nitride semiconductor substrate 10. The GaN substrate 10 has a major off-axis direction in the +m-axis direction, and an off-angle of 0.5° is imparted to the center of the GaN substrate 10. The distribution of the off-angle in the GaN substrate 10 is +0.3 to +0.7° in the +m-axis direction and -0.1 to 0.1° in the +a-axis direction.

[0057] <Laser diode bar layout> The size of the laser diode bars 20 required for the wavelength beam combining system 30 is determined, and the positions and number of the laser diode bars 20 to be disposed within the GaN substrate 10 are determined.

[0058] <Epitaxial growth> A first conductive type cladding layer 21, an active layer 22 containing 7% In with respect to the composition of the entire active layer, and a second conductive type cladding layer 23 are formed by epitaxial growth on a GaN substrate 10. g In order to avoid any temperature distribution, the substrate temperatures during epitaxial growth are preferably 900 to 1,150° C. for the first conductivity type cladding layer 21 and the second cladding layer 23, and 800 to 850° C. for the active layer 22. More preferably, temperature control is performed by shaping a member for heating the GaN substrate 10 so that the temperature distribution within the plane of the GaN substrate 10 falls within ±2° C.

[0059] <Calculation of gain peak wavelength> A PL measurement is performed at room temperature on the surface of the GaN substrate 10 on which epitaxial growth has been performed, using a He—Cd laser with an excitation wavelength of 325 nm as excitation light. This causes light to be excited from the active layer 22, and the gain peak wavelength λ of the laser diode bar 20 laid out in the GaN substrate 10 is measured. g The value of can be known with a certain degree of accuracy.

[0060] The PL measurement results in the GaN substrate 10 are obtained, and the gain peak wavelength λ g The distribution of the PL peak wavelength and the gain peak wavelength λ g However, depending on the structure of the active layer 22, for example, the number of well layers in the active layer 22, the values ​​are not necessarily the same, and it is possible that there is an offset of about several nm. Therefore, it is necessary to determine the gain peak wavelength λ g It is desirable to know the offset value between the PL peak wavelength and the

[0061] With reference to the PL measurement and offset value, the reference value λ of the gain peak wavelength of each laser diode bar 20 when the laser diode bar 20 is arranged in the GaN substrate 10 is determined. g_CENTER (meaning the gain peak wavelength of the emitter 13 located at the middle position among the multiple emitters 13 arranged in the longitudinal direction of the laser diode bar 20; the same applies below) is determined.

[0062] In addition, the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 when the +m-axis direction of the GaN substrate 10 is upward. g_BAR Calculate.

[0063] <Laser diode bar emitter formation, cutting, light emission surface selection, and film formation> The emitter 13 is formed by aligning the main axis direction 11 of the off-angle of the GaN substrate 10 on which epitaxial growth has been performed, i.e., the m-axis direction, with the waveguide direction D of the laser diode bar 20. Next, a P-side electrode 15 and an N-side electrode 24 are formed, and the laser diode bar 20 is cut out from the GaN substrate 10 on which the emitter 13 has been formed. The gain peak wavelength λ of the left-end emitter 13 of the laser diode bar 20 is measured. g The gain peak wavelength λ of emitter 13 on the right g In the laser diode bar 20 where the value obtained by subtracting m is positive, a transmission film 16 is formed in the -m-axis direction and a reflection film 17 is formed in the +m-axis direction. g The gain peak wavelength λ of emitter 13 on the right g For the laser diode bar 20 having a negative value obtained by subtracting m, a reflective film 17 is formed in the -m-axis direction, and a transmissive film 16 is formed in the +m-axis direction.

[0064] The difference in gain peak wavelength Δλ between both ends of the laser diode bar 20 as viewed from the emission surface of the laser diode bar 20 g_BAR As described above, the λ of the leftmost emitter 13 is calculated. g The gain peak wavelength λ of emitter 13 on the right g If the subtraction result is negative, the value is converted to positive.

[0065] <Laser diode bar selection> First, for each of the multiple laser diode bars 20 formed in the GaN substrate 10, the gain peak wavelength λ of the laser diode bar 20 that enables all the emitters 13 to oscillate is determined. g (i.e., the gain peak wavelength difference Δλ between both ends of the laser diode bar 20) g_BAR ) is calculated.

[0066] Next, from the configuration of the wavelength beam combining system 30 (such as the lock wavelength at each position along the longitudinal direction of the laser diode bar 20 shown in FIG. 6), the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 depending on the arrangement position of the laser diode bar 20 is calculated. g_BAR Calculate.

[0067] In this way, the positions of the laser diode bars 20 that can be applied to the wavelength beam combining system 30 can be identified, and selection can be performed. The selected laser diode bars 20 are then mounted on the actual wavelength beam combining system 30, and confirmation is made as to whether or not all of the emitters 13 are oscillating. If all of the emitters 13 of each of the mounted laser diode bars 20 are oscillating, the wavelength beam combining system 30 is treated as a completed product.

[0068] A method for manufacturing the laser diode bar 20 according to an embodiment of the present disclosure and a method for manufacturing a comparative laser diode bar will be described below.

[0069] [Example] <Preparation of the substrate> As shown in FIG. 12, a 2-inch GaN substrate 10 was prepared, which has a primary surface (0001), the +m-axis direction is the main axis of the off angle, the m-axis direction has an off angle of +0.55° from the substrate center, the off angle distribution within the substrate is +0.28 to +0.68° at a distance of 20 mm from the substrate center, the center of the off angle in the +a-axis direction is 0.02°, and the distribution at a distance 20 mm from the substrate center is -0.08° to +0.14°.

[0070] <Laser diode bar layout> The length of the laser diode bar 20 in the waveguide direction was 2.0 mm and the length in the longitudinal direction was 10.0 mm. The main axis direction of the off-angle of the GaN substrate 10 was aligned with the waveguide direction of the laser diode bar 20, and 60 laser diode bars 20 were arranged within the GaN substrate 10, as shown in FIG. 13.

[0071] <Epitaxial growth> A first conductive type cladding layer 21, an active layer 22 of a nitride semiconductor containing 7.0% In with respect to the composition of the entire active layer, and a second conductive type cladding layer 23 were formed by epitaxial growth on a GaN substrate 10. The temperatures of the GaN substrate 10 during epitaxial growth were 980°C for the first conductive type cladding layer 21 and the second cladding layer 23, and 820°C for the active layer 22. The carbon heat equalizer plate for heating the GaN substrate 10 was curved with a difference of 30 μm, so that the surface temperature of the GaN substrate 10 during epitaxial growth was controlled to be within a range of 978 to 982°C during growth of the first conductive type cladding layer 21 and the second cladding layer 23, and 818 to 822°C during growth of the active layer 22, to perform the epitaxial growth.

[0072] < λ of each laser diode bar g_CENTER , Δλ g_BAR Calculation of > The GaN substrate 10 on which the epitaxial growth had been performed was subjected to PL measurement at room temperature using a He-Cd laser with an excitation wavelength of 325 nm as excitation light.

[0073] Figure 14 shows the gain peak wavelength λ calculated from the PL measurement. g As shown in FIG. 14, the gain peak wavelength λ g It can be seen that the distribution of the gain peak wavelength λ depends on the distribution of the off-angle in the GaN substrate 10. The gain peak wavelength λ is calculated by adding 4.0 nm to the peak top wavelength of the PL measurement. g It was confirmed in advance that this was the case.

[0074] Gain peak wavelength λ g 13, and the reference value λ of the gain peak wavelength of each of the 60 laser diode bars 20 is determined. g_CENTER The reference value λ of the gain peak wavelength of each laser diode bar 20 in the GaN substrate 10 is shown in FIG. g_CENTER Indicates the value of.

[0075] Next, the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 of each of the 60 laser diode bars when the +m-axis direction of the GaN substrate 10 is placed upward. g_BAR was calculated as shown in FIG.

[0076] <Laser diode bar emitter formation, cutting, light emission surface selection and film formation> The emitter 13 was formed by aligning the main axis direction of the off-angle of the GaN substrate 10 on which epitaxial growth was performed, i.e., the m-axis direction, with the waveguide direction of the laser diode bar 20. The crystal orientation was based on the orientation flat 18 provided on the GaN substrate 10. Next, a P-side electrode 15 and an N-side electrode 24 were formed, and a laser diode bar 20 was cut out from the GaN substrate 10 on which the emitter 13 was formed, and the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 was measured. g_BAR The laser diode bar 20 with a positive m-axis has a transmission film formed in the -m-axis direction and a reflection film formed in the +m-axis direction. g_BAR For the laser diode bar 20 with a negative value, a reflective film 17 was formed in the -m-axis direction, and a transmissive film 16 was formed in the +m-axis direction.

[0077] FIG. 17 shows the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 as viewed from the emission surface of the laser diode bar 20. g_BAR The gain peak wavelength difference Δλ between both ends of the laser diode bar 20 in FIG. g_BAR is a negative value, that is, the laser diode bar 20 colored in FIG. 17 has an inverted emission surface, and the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 with a negative value isg_BAR is inverted to a positive value. This makes it possible to obtain a laser diode bar 20 having opposite transmissive and reflective films.

[0078] <Laser diode bar selection> The wavelength beam combining system 30 is configured with a diffraction grating period d=0.33 μm and L=2.6 m. In this wavelength beam combining system 30, the lock wavelength difference Δλ between both ends of the laser diode bar 20 required for the laser diode bar 20 is L_BAR The gain peak wavelength difference Δλ between both ends of the laser diode bar 20 was 1.1 nm. g_BAR A plurality of laser diode bars 20 having different gain peak wavelengths are mounted on a wavelength combining system 30, and the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 at which all emitters can oscillate is g_BAR was confirmed to be 1.1±1.0 nm.

[0079] The gain peak wavelength difference Δλ between both ends of the laser diode bar 20 in the 60 laser diode bars 20 in the GaN substrate 10 g_BAR The laser diode bars 20 that satisfy the condition of 1.1±1.0 nm are the laser diode bars 20 in the positions not painted in color shown in FIG. 18, and 53 of the 60 laser diode bars 20 were present. These 53 laser diode bars 20 were compared with the reference value λ g_CENTER When the positions of the emitters 13 were changed and the laser diode bars 20 were mounted on the wavelength beam combining system 30, it was confirmed that all the emitters 13 oscillated in all the laser diode bars 20 when the positions of the emitters 13 were different.

[0080] [Comparative Example] In the comparative example, a GaN substrate 10 with almost the same properties as in the example was used, except that the emitter 13 was formed by aligning the crystal axis other than the principal axis direction of the off-angle, i.e., the a-axis direction, with the waveguide direction of the laser diode bar 20. The laser diode bar 20 was produced under the same other conditions as in the example. In the comparative example, as shown in FIG. 19, the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 wasg_BAR Of the 60 laser diode bars 20 laid out on the GaN substrate 10, 22 satisfied the 1.1±1.0 nm threshold.

[0081] When 22 laser diode bars 20 were mounted on the wavelength beam combining system 30, oscillation was not confirmed in all emitters 13 of two of the laser diode bars 20.

[0082] Normally, all emitters 13 of the 22 laser diode bars 20 should oscillate. However, there is a certain conversion error when calculating the gain wavelength from the peak wavelength of the PL measurement, and the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 is g_BAR It is possible that the difference in the length of the laser diode bar 20 when cut out in the working example was large. Alternatively, since the longitudinal direction when the laser diode bar 20 was cut out coincided with the cleavage plane of the GaN crystal 10, the emission surface was uniform at the atomic level, but since the longitudinal direction did not coincide with the cleavage plane in the comparative example, it is possible that the emission surface was not uniform, and laser oscillation was inhibited. It is considered that the comparative example included laser diode bars 20 in which all of the emitters 13 did not oscillate due to a combination of either or both of the above possibilities.

[0083] As described above, according to the manufacturing method of the laser diode bar 20 of the present disclosure, the emitter 13 is configured so that the principal axis direction (preferably the m-axis) of the off-angle of the nitride semiconductor substrate (preferably the GaN substrate 10) coincides with the waveguide direction of the laser diode bar 20. As a result, even if there is a distribution of gain peak wavelengths caused by the off-angle of the nitride semiconductor substrate 10, the gain peak wavelength difference Δλ between both ends of the laser diode bar 20 is smaller in more laser diode bars 20 out of the multiple laser diode bars 20 configured in the nitride semiconductor substrate 10. g_BAR 8, it is possible to reduce the wavelength of the laser beam and place it within the range of the lock wavelength of the wavelength beam combining system 30. This makes it possible to improve the performance of the oscillation output of the wavelength beam combining system 30.

[0084] As shown in FIG. 20, in the embodiment, the reference value λ of the gain peak wavelength arranged in the wavelength beam combining system 30 is smaller than that of the comparative example. g_CENTER Therefore, a large number of laser diode bars 20 having different characteristics can be obtained, thereby improving the production efficiency of the laser diode bars 20.

[0085] From the standpoint of reducing the number of components in the optical system of the wavelength beam combining system 30, improving stability, and reducing the labor required for adjusting the optical system, it is preferable that the longitudinal length of the laser diode bar 20 is long.

[0086] FIG. 21 shows the relationship between Δλ and the laser diode length of the laser diode bar 20 when the length of the laser diode bar 20 is changed in the example and the comparative example. g_BAR 1 is a graph showing the ratio of the length of the laser diode bar 20 that satisfies the range required for realizing the wavelength beam combining system 30. The longer the length of the laser diode bar 20, the greater the difference in conformance rate between the embodiment and the comparative example. It was found that when the length of the laser diode bar 20 is 6.0 mm or more, the embodiment can obtain a conformance rate that is 40% or higher than that of the comparative example.

[0087] The above-mentioned embodiment and examples are merely examples of the embodiment of the present disclosure, and the technical scope of the present disclosure is not limited to the above-mentioned embodiment and examples. In other words, the present disclosure can be implemented in various forms without departing from the gist of the present disclosure. [Industrial Applicability]

[0088] The present disclosure is suitable for a method of manufacturing laser diode bars for use in wavelength beam combining systems. [Explanation of symbols]

[0089] 10. Nitride Semiconductor Substrate 11 Offset angle of the main axis 12 Laminated structure 13 Emitter 15 P side electrode 16 Permeable membrane 17 Reflective film 18 Orifura 20 Laser Diode Bars 21 First conductive type cladding layer 22 Active layer 23 Second conductive type cladding layer 24 N side electrode 25 Laser Light 30 Transmissive Wavelength Beam Combining System 31~35 Laser Diode Bars 20T Laser Diode Bar Array 37 Transmission type diffraction grating 38 External cavity mirror 39 Reflective diffraction grating 40 Reflective Wavelength Beam Combining System

Claims

[Claim 1] 1. A method for manufacturing a laser diode bar for use in a wavelength beam combining system, comprising: preparing a nitride semiconductor substrate having a substrate surface oriented in the (0001) plane and having an off-angle of greater than 0° from the (0001) plane toward at least one of the m-axis and the a-axis; determining the size of the laser diode bar required for the wavelength beam combining system, and setting a layout related to the planned formation position of the laser diode bar in the nitride semiconductor substrate so that the principal axis direction of the off-angle coincides with the waveguide direction; forming a laminated structure including a first conductive type cladding layer, an active layer, and a second conductive type cladding layer on the nitride semiconductor substrate; estimating a distribution of gain peak wavelengths of the laser diode bars to be formed in the nitride semiconductor substrate; forming a plurality of emitters arranged in a stripe pattern in the laminated structure such that a principal axis direction of the off-angle coincides with a waveguide direction; cutting the laser diode bar having the plurality of emitters from the nitride semiconductor substrate; determining a position of the laser diode bar in the wavelength beam combining system based on a distribution of gain peak wavelengths of the laser diode bar and a lock wavelength determined by a configuration of the wavelength beam combining system; Including, the nitride semiconductor substrate is a single crystal gallium nitride substrate; a principal axis direction of the off-angle is an m-axis direction of the gallium nitride substrate, the off-angle at the center position of the substrate surface is greater than 0°, an off angle in the substrate is in a range of +0.3 to +0.7° in the m-axis direction and gradually increases from one side to the other side in the m-axis direction in the substrate; The active layer contains In. A method for manufacturing laser diode bars.

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