Semiconductor laser device and manufacturing method thereof

Abstract

To provide a semiconductor laser device which contributes to an improvement in visibility or image quality.SOLUTION: In a semiconductor laser device LD0, a substrate 1, a first clad layer 2 of a first conductivity type, a light-emitting layer EL and a second clad layer 3 of a second conductivity type are successively laminated and the light-emitting layer EL includes at least two, first and second light-emitting parts EM01 and EM02 radiating laser beams. The semiconductor laser device also comprises first and second ridges R01 and R02 corresponding to the respective first and second light-emitting parts EM01 and EM02. Further, the thickness ET01 of a first light-emitting layer EL01 corresponding to the first light-emitting part EM01 is different from the thickness ET02 of a second light-emitting layer EL02 corresponding to the second light-emitting part EM02, and the width RW01 of the first ridge R01 is different from the width RW02 of the second ridge R02.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser device. [Background technology]

[0002] BACKGROUND ART In recent years, the market for display devices such as projectors that use semiconductor laser devices (hereinafter simply referred to as "semiconductor LD" or "LD") has been expanding.

[0003] Furthermore, reality technologies such as augmented reality (AR), virtual reality (VR), mixed reality (MR), and substitutional reality (SR) have been put to practical use in various fields, and display devices using these technologies, such as head-mounted displays (HMDs), head-up displays, and AR glasses, have been commercialized.

[0004] For example, a head-mounted display (HMD) uses three laser colors (red, green, and blue) as the light source, creates an image using a microelectromechanical system (MEMS), a spatial modulation element for image display, and projects it onto the retina or other surfaces through a waveguide. This MEMS-based system is said to offer advantages such as a wide color gamut, high resolution, and a wide viewing angle. Meanwhile, to further improve image quality, such as a wide color gamut, high resolution, and a wide viewing angle, multi-beam laser diodes (multiple semiconductor laser devices) have been used for each of the RGB colors, but the wavelengths of each color are identical. If all the beams have the same wavelength (i.e., the same wavelength), image quality will be degraded due to the coherence of the laser light.

[0005] Patent Document 1 discloses a multi-wavelength semiconductor laser capable of emitting laser light at multiple wavelengths within the same device. Patent Document 1 does not disclose the specific wavelength of the laser light, but because it is an AlGaAs-based quantum well laser, it describes laser light in the infrared region and in color regions other than RGB. In addition, the first and second quantum well active layers emitting different wavelengths have different well widths (physical film thicknesses). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 05-082894 Summary of the Invention [Problem to be solved by the invention]

[0007] In addition to the technical background described above, there is a demand for monolithic single-mode transverse laser diodes that independently drive multi-emitters (multiple light-emitting elements) at narrow pitches in order to improve image quality (resolution and frame rate).However, the transverse single-mode laser has a narrow wavelength spectrum and high coherence, which causes image quality degradation.

[0008] Furthermore, in order to improve the performance of display devices, there is a demand for suppressing interference of laser light and further improving visibility and image quality, such as a wide color gamut, high resolution, and wide viewing angle. To further improve visibility and image quality, for example, a semiconductor laser device capable of emitting multiple laser beams with different oscillation wavelengths for each color of a light source using three RGB laser beams is preferable from the viewpoint of suppressing degradation of image quality due to the above-mentioned coherence of laser light.

[0009] However, to emit laser beams with different oscillation wavelengths, it is necessary to change the band gap energy of the light-emitting layer (active layer) of each light-emitting unit that emits the laser beam. The inventors discovered that, for example, by changing the thickness of the light-emitting layer or the composition of the light-emitting layer without changing the thickness of the light-emitting layer for each light-emitting unit, laser beams with different wavelengths can be obtained. On the other hand, they also discovered that if the thickness of the light-emitting layer differs for each light-emitting unit, differences in the beam shape of the laser beam emitted from each light-emitting unit will occur even if the wavelength of each laser beam is the same. Such differences in beam shape can be one cause of deterioration in luminosity and image quality. Furthermore, if the beam shape and beam divergence angle of the laser beam emitted from the light-emitting end face of the LD differ for each laser beam, problems resulting from differences in beam shape can be corrected to some extent by designing and adjusting the optical system, such as the lens onto which the laser beam is incident, for each beam. However, this is not only extremely time-consuming but also increases costs.

[0010] The above-mentioned Patent Document 1 does not mention at all the beam shapes of the respective laser beams due to the difference in film thickness of the active layer described above, and the problems due to the influence of the difference.

[0011] An object of the present invention is to provide a semiconductor laser device that contributes to improving visibility and image quality. Other objects and novel features will become apparent from the description of this specification and the drawings. [Means for solving the problem]

[0012] A semiconductor laser device according to one embodiment includes a substrate, a first cladding layer of a first conductivity type, a light-emitting layer, and a second cladding layer of a second conductivity type stacked in that order, and the light-emitting layer has at least two first and second light-emitting portions that emit laser light. The light-emitting layer also has first and second ridges corresponding to the first and second light-emitting portions, respectively. Furthermore, the thickness of the first light-emitting layer corresponding to the first light-emitting portion is different from the thickness of the second light-emitting layer corresponding to the second light-emitting portion, and the width of the first ridge is different from the width of the second ridge. [Effects of the Invention]

[0013] The semiconductor laser device according to one embodiment can provide a semiconductor laser device that contributes to improving visibility and image quality. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing an example of the configuration of a semiconductor laser device according to a preferred embodiment. [Figure 2] 1 is a perspective view showing an example of the configuration of a semiconductor laser device according to a first embodiment. [Figure 3] 1A and 1B are a side view and a top view showing the configuration of a semiconductor laser device according to a first embodiment. [Figure 4] 2 is a cross-sectional view of a main part showing an example of the configuration of light-emitting layers EL11 to EL13 in the semiconductor laser device according to the first embodiment. FIG. [Figure 5] FIG. 1 is an explanatory diagram (1) relating to the beam shape (NFP / FFP) of laser light. [Figure 6] FIG. 2 is an explanatory diagram (2) relating to the beam shape (NFP / FFP) of the laser light. [Figure 7] 10 is an explanatory diagram showing the relationship between the beam shape of laser light and the thickness of a light-emitting layer. FIG. [Figure 8] FIG. 1 is an explanatory diagram (1) showing the relationship between the beam shape of laser light and the ridge width. [Figure 9] FIG. 2 is an explanatory diagram (2) showing the relationship between the beam shape of laser light and the ridge width. [Figure 10] FIG. 3 is an explanatory diagram (3) showing the relationship between the beam shape of laser light and the ridge width. [Figure 11] 4 is a graph showing an improvement result of the beam shape (NFP) of the laser light in the semiconductor laser device according to the first embodiment. [Figure 12] 1 is a graph (1) showing an improvement result of the beam shape (FFP) of the laser light in the semiconductor laser device according to the first embodiment. [Figure 13]10 is a graph (2) showing the results of improving the beam shape (FFP) of the laser light in the semiconductor laser device according to the first embodiment. [Figure 14] 3 is a cross-sectional view of a main part illustrating an example of a step included in a manufacturing method of the semiconductor laser device according to the first embodiment. FIG. [Figure 15] 3 is a cross-sectional view of a main part illustrating an example of a step included in a manufacturing method of the semiconductor laser device according to the first embodiment. FIG. [Figure 16] 3 is a cross-sectional view of a main part illustrating an example of a step included in a manufacturing method of the semiconductor laser device according to the first embodiment. FIG. [Figure 17] 3 is a cross-sectional view of a main part illustrating an example of a step included in a manufacturing method of the semiconductor laser device according to the first embodiment. FIG. [Figure 18] 3 is a cross-sectional view of a main part illustrating an example of a step included in a manufacturing method of the semiconductor laser device according to the first embodiment. FIG. [Figure 19] 10A and 10B are a side view and a top view showing the configuration of a semiconductor laser device according to a second embodiment. [Figure 20] 10 is a graph showing an improvement result of the beam shape (NFP) of the laser light in the semiconductor laser device according to the second embodiment. [Figure 21] 10 is a graph showing an improvement result of the beam shape (FFP) of the laser light in the semiconductor laser device according to the second embodiment. [Figure 22] 10 is an explanatory diagram showing the relationship between the beam shape of laser light and the ridge width in the semiconductor laser device according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Semiconductor laser devices according to the embodiments will be described in detail below with reference to the drawings. In the specification and drawings, identical or corresponding components are designated by the same reference numerals, and redundant description will be omitted. For ease of description, the drawings may omit or simplify configurations. At least some of the embodiments and modifications may be combined with each other in any manner. When individual descriptions are required due to differences in the locations where components are formed, for example, different reference numerals will be used for the light-emitting units EM11, EM12, and EM13. However, when describing the functions inherent to the components, the light-emitting units may be referred to as, for example, the light-emitting unit EM.

[0016] [Configuration of a semiconductor laser device according to a preferred embodiment] FIG. 1 is a perspective view of a main part showing an example of the configuration of a semiconductor laser device according to a preferred embodiment.

[0017] In addition, with regard to the x-axis, y-axis, and z-axis shown in Fig. 1, x means the horizontal direction / width direction / lateral direction, y means the resonator direction / depth direction / longitudinal direction, and z means the vertical direction / thickness direction / height direction. The definitions of these directions are the same in other figures.

[0018] As shown in Fig. 1, the semiconductor laser device LD0 according to the preferred embodiment has an n-type cladding layer 2, an emission layer EL, and a p-type cladding layer 3 formed on a GaAs substrate 1. At least two light-emitting portions EM01 and EM02 that emit laser light are formed at a predetermined interval in the x direction. Laser light λ01 and λ02 are emitted from the light-emitting portions EM01 and EM02, respectively. The wavelengths of the laser light λ01 and λ02 may be the same or different.

[0019] Furthermore, the thicknesses of the light-emitting layers EL01 and EL02 in the light-emitting portions EM01 and EM02 are different, and the thickness ET01 of the light-emitting layer EL01 is greater than the thickness ET02 of the light-emitting layer EL02.

[0020] Ridges R01 and R02 are formed on the upper portions of the light emitting portions EM01 and EM02, respectively. The ridges R01 and R02 are formed in the cavity direction so as to be sandwiched on both sides between regions having a refractive index different from or lower than that of the p-type cladding layer 3, so as to function as optical waveguides.

[0021] The ridges R01 and R02 have widths RW01 and RW02, respectively, with RW01 being wider than RW02. That is, the width RW01 of the ridge R01 provided on the light-emitting layer EL01 is wider than the width RW02 of the ridge R02 provided on the light-emitting layer EL02. By making the ridge widths RW different in this way, it is possible to correct the beam shape of the laser light caused by differences in the thickness of the light-emitting layer EL.

[0022] [Embodiment 1] The semiconductor laser device LD1 according to the first embodiment is formed with three light-emitting portions EM11, EM12, and EM13 that emit laser light, and each light-emitting portion EM emits laser light of a different wavelength. The thicknesses (ET11, ET12, ET13) of the light-emitting layers EL11, EL12, and EL13 in the light-emitting portions EM11, EM12, and EM13 are different, with a relationship of ET11>ET12>ET13. Furthermore, ridges R11, R12, and R13 are formed on the tops of the light-emitting portions EM11, EM12, and EM13, and the widths (RW11, RW12, RW13) of the ridges R are different, with a relationship of RW11>RW12>RW13.

[0023] (Configuration of semiconductor laser device) Fig. 2 is a perspective view of a main part showing an example of the configuration of the semiconductor laser device LD1 according to the embodiment 1. Fig. 3 is (a) a side view and (b) a top view of the main part showing the configuration of the semiconductor laser device LD1 according to the embodiment 1. Fig. 4 is a cross-sectional view of a main part showing an example of the configuration of light-emitting layers EL11 to EL13 in the semiconductor laser device LD1 according to the embodiment 1.

[0024] As shown in Figures 2 and 3, the semiconductor laser device LD1 has an n-type cladding layer 2 (thickness 2 µm), light-emitting layers EL11, EL12, and EL13 (thickness about 100 nm) formed on a GaAs substrate 1, and a p-type cladding layer 3 (thickness 1.7 µm) formed thereon. The composition of the n-type cladding layer 2 and the p-type cladding layer 3 is (Al x Ga 1-x ) 1-y In y P(0 <x≦1、0<y<1)であり、ここではx=1、y=0.5とした。

[0025] The semiconductor laser device LD1 is formed with three light-emitting portions EM11, EM12, and EM13, and the thicknesses (ET11, ET12, ET13) of the light-emitting layers EL11, EL12, and EL13 in each light-emitting portion EM are different. That is, the thicknesses have the relationship ET11>ET12>ET13. In this embodiment, the respective thicknesses ET are ET11 (104 nm), ET12 (92 nm), and ET13 (80 nm). As will be described in detail later, the light-emitting layers EL11, EL12, and EL13 are formed by selective growth, and therefore have different thicknesses ET.

[0026] In each of the light-emitting portions EM11, EM12, and EM13, a ridge groove RG is formed by etching a portion of the p-type cladding layer 3, forming a ridge R as a current confinement structure (current injection structure) and a structure for lateral (x-direction) light confinement. The ridge R is thus formed in the cavity direction (y-direction) so as to be sandwiched on both sides by air (refractive index = 1), which has a lower refractive index than the p-type cladding layer 3, to function as an optical waveguide. The ridge R has a predetermined width in the lateral direction, and each ridge width (RW11, RW12, RW13) is different. That is, for reasons to be described later, the relationship is RW11 > RW12 > RW13. In this embodiment, the ridge widths RW are RW11 (1.7 μm), RW12 (1.5 μm), and RW13 (1.3 μm).

[0027] Note that because the ridges R11, R12, and R13 are simultaneously formed by etching a portion of the p-type cladding layer 3 (i.e., the amount of p-type cladding layer 3 removed by etching is the same on the top surface of each of the light-emitting layers EL11, EL12, and EL13), the distances from the top surface of each of the light-emitting layers EL11, EL12, and EL13 to the bottom surface of each of the ridge grooves RG11, RG12, and RG13 are approximately the same. However, the thicknesses (ET11, ET12, and ET13) of the light-emitting layers EL11, EL12, and EL13 are different because they are formed by a selective growth method described later. Therefore, the distance ED from the center position in the thickness direction of the light-emitting layer EL to the bottom surface of the ridge groove RG differs for each light-emitting layer EL. That is, the relationship of the distances ED is ED11>ED12>ED13. In this embodiment, the distances ED are ED11 (52 nm), ED12 (46 nm), and ED13 (40 nm).

[0028] Furthermore, an n-side electrode and a p-side electrode (not shown) are formed on the rear surface of the GaAs substrate 1 and the upper surface of the ridge R.

[0029] By applying current to the n-side electrode and the p-side electrode, laser light in the red region (wavelength: 600 nm to 700 nm) is emitted from the light-emitting regions ER11, ER12, and ER13 formed in the three light-emitting units EM11, EM12, and EM13. The wavelength λ of the emitted light is in the order light-emitting unit EM11 > light-emitting unit EM12 > light-emitting unit EM13. As an example, light-emitting unit ER11 emits laser light with a wavelength of 645 nm (λ11), light-emitting unit ER12 emits laser light with a wavelength of 641 nm (λ12), and light-emitting region ER13 emits laser light with a wavelength of 637 nm (λ13). Thus, the wavelength of the laser light varies depending on the thickness ET of the light-emitting layer EL, and the thinner the thickness ET of the light-emitting layer EL, the smaller the value of the wavelength λ.

[0030] In the above example, the wavelengths are set to differ by 4 nm, but the difference in wavelength can be appropriately selected between 1 nm and 30 nm. For example, if the difference in wavelength is 1 nm, light-emitting region ER11 will emit laser light with a wavelength of 622 nm, light-emitting region ER12 will emit laser light with a wavelength of 621 nm, and light-emitting region ER13 will emit laser light with a wavelength of 620 nm. If the difference in wavelength is 30 nm, light-emitting region ER11 will emit laser light with a wavelength of 690 nm, light-emitting region ER12 will emit laser light with a wavelength of 660 nm, and light-emitting region ER13 will emit laser light with a wavelength of 630 nm.

[0031] The structure of the light-emitting layers EL11, EL12, and EL13 will be described with reference to FIG. 4. The light-emitting layer EL functions as a core layer of an optical waveguide. As shown in FIG. 4, the light-emitting layer EL is composed of, from bottom to top, a lower n-side guide layer nGL, a barrier layer BL, a quantum well layer QW, another barrier layer BL, and an upper p-side guide layer pGL. The thickness of the light-emitting layer EL depends on the wavelength and the refractive index of each layer, but is selected from the range of approximately 50 nm to approximately 500 nm for red lasers. In this embodiment, the thickness is approximately 100 nm. The light-emitting regions ER11, ER12, and ER13 shown in FIG. 2 mainly correspond to the desired regions of the quantum well layer QW. Note that, although the quantum well layer QW is shown as a single quantum well layer (SQW) in FIG. 4, it may also be a multiple quantum well layer (MQW).

[0032] In the semiconductor laser device LD1 according to this embodiment, the thicknesses of the layers constituting the light-emitting layer EL are set as follows: The light-emitting layer EL11 is composed of, from bottom to top, a lower n-side guide layer nGL (40 nm), a barrier layer BL (9 nm), a quantum well layer QW (6 nm), a barrier layer BL (9 nm), and an upper p-side guide layer pGL (40 nm), with a total thickness ET11 of 104 nm. The light-emitting layer EL12 is composed of, from bottom to top, a lower n-side guide layer nGL (35 nm), a barrier layer BL (8.25 nm), a quantum well layer QW (5.5 nm), a barrier layer BL (8.25 nm), and an upper p-side guide layer pGL (35 nm), with a total thickness ET12 of 92 nm. The light-emitting layer EL13 is composed of, from bottom to top, a lower n-side guide layer nGL (30 nm), a barrier layer BL (7.5 nm), a quantum well layer QW (5 nm), a barrier layer BL (7.5 nm), and an upper p-side guide layer pGL (30 nm), with a total thickness ET11 of 80 nm.

[0033] Thus, the thicknesses ET of the emitting layers EL are ET11 (104 nm), ET12 (92 nm), and ET13 (80 nm), varying in 12 nm increments. Furthermore, half the thicknesses EHT of the emitting layers EL (i.e., the distance from the center of the emitting layer EL in the thickness direction to the surface of the emitting layer EL) are EHT11 (52 nm), EHT12 (46 nm), and EHT13 (40 nm), varying by 6 nm. As mentioned above, the distances from the top surfaces of the emitting layers EL11, EL12, and EL13 to the bottom surfaces of the ridge grooves RG11, RG12, and RG13 are approximately the same, so the distances ED (see FIG. 3 ) from the center of the emitting layer EL in the thickness direction to the ridge groove RG are affected by the thicknesses of the emitting layers EL. That is, as mentioned above, the half thickness EHT of the emitting layer EL is EHT11 (52 nm), EHT12 (46 nm), and EHT13 (40 nm), so there is a difference of 6 nm between adjacent emitting layers EL. Therefore, there is also a difference of 6 nm in the distance ED between adjacent emitting layers EL. The relationship between the difference in distance ED and the pattern shape of the laser light will be described later.

[0034] The crystal layers of the light-emitting layers EL11, EL12, and EL13 are (Al x Ga 1-x ) 1-y In y P (0 ≦ x < 1, 0 < y < 1). The quantum well layer QW is (Ga 1-y In y P (x = 0, y = 0.55), and the guide layer GL and the barrier layer BL are (Al x Ga 1-x ) 1-y In y P (x = 0.7, y = 0.5). In the quantum well layer QW, the Al composition (x) is set to x = 0, but it can also be appropriately selected so that the Al composition (x) in the light-emitting layer EL is the smallest in the quantum well layer QW. However, when the Al composition (x) of the quantum well layer QW becomes larger than about 0.5, it becomes an indirect transition type, so the Al composition (x) of the quantum well layer QW is preferably 0.5 or less.

[0035] In the semiconductor laser device according to the present embodiment, by changing the thickness ET of the light-emitting layer EL, it is possible to emit laser light of different wavelengths from one chip. However, among the compositions constituting the crystal layer of the light-emitting layer EL, by changing the composition ratio of In (indium) in particular, it is also possible to change the energy band gap and emit a plurality of laser lights of different wavelengths from one chip. In this case, as an example, the In composition ratio (y) of the light-emitting layer EL11 can be 0.59, the In composition ratio (y) of the light-emitting layer EL12 can be 0.55, and the In composition ratio (y) of the light-emitting layer EL13 can be 0.51. The In composition ratio (y) is preferably selected from the range of 0.35 to 0.65.

[0036] When referring to the light-emitting layer EL in the present embodiment, it means including all of the above-mentioned lower n-side guide layer nGL, quantum well layer QW, barrier layer BL, and upper p-side guide layer pGL in the light-emitting layer EL. In addition, it may mean including the quantum well layer QW and the barrier layer BL, or including at least a part of either one of the p-type clad layer 3 and the n-type clad layer 2.

[0037] Furthermore, unless otherwise specified, the configuration of the light-emitting layer EL shown in FIG. 4 is the same as that of the light-emitting layer EL in the second embodiment described later.

[0038] (Laser beam shape (NFP / FFP)) Next, the near field pattern (NFP) and far field pattern (FFP) used to evaluate the beam shape and characteristics of laser light will be described with reference to Figures 5 and 6. Note that the NFP and FFP have shapes in the horizontal direction (slow axis) corresponding to the x direction and in the vertical direction (fast axis) corresponding to the z direction. When evaluating the characteristics of the beam shape, evaluation and consideration are required in both the horizontal and vertical directions, but in this embodiment, unless otherwise specified, the beam shape in the horizontal direction will be described.

[0039] First, the definitions of NFP and FFP will be explained using Fig. 5. In Fig. 5, (a) is a schematic side view of the light-emitting end face of the semiconductor laser device, (b) is a schematic top view of the upper surface of the semiconductor laser device, and (c) and (d) are diagrams showing distribution examples of NFP and FFP, respectively.

[0040] As shown schematically in (b), laser light propagates through the ridge R, an optical waveguide, and is emitted externally from the light-emitting surface. NFP indicates the characteristics of the beam shape at the light-emitting surface, and as shown in (c), the horizontal axis represents the horizontal position (μm) corresponding to the x-direction, and the vertical axis represents the light intensity. FFP indicates the characteristics of the beam shape at a distance (approximately 10 mm) from the light-emitting surface, and as shown in (d), the horizontal axis represents the beam divergence angle (deg), and the vertical axis represents the light intensity. In other words, when evaluating the laser beam shape, it is important to evaluate the beam shape after it is emitted from the light-emitting surface, which is the surface that is directly visible to humans, i.e., the beam shape indicated by FFP.

[0041] Figure 6 is an explanatory diagram showing the relationship between NFP and FFP. In Figure 6, the solid line shows the characteristics when the wavelength λ is short, and the dashed line shows the characteristics when the wavelength λ is long. When a laser beam has a narrow horizontal beam shape in NFP, the horizontal beam divergence angle in FFP widens. On the other hand, when a laser beam has a wide horizontal beam shape in NFP, the horizontal beam divergence angle in FFP narrows. Therefore, to adjust the beam divergence angle in FFP, it can be said that it is necessary to improve the beam characteristics in NFP.

[0042] Here, laser light propagates through the optical waveguide and is emitted to the outside. The optical waveguide is composed of the ridge R (part of the p-type cladding 3), the light-emitting layer EL, and part of the n-type cladding 2. Note that the semiconductor laser device LD1 according to this embodiment employs an air ridge structure, so air (with a refractive index of n = 1) surrounds the ridge R. The beam shape of laser light is affected by three factors: the refractive index of the material through which the laser light passes, the film thickness, and the wavelength (wavelength of light in a vacuum). For example, as the film thickness of the light-emitting layer EL increases, the equivalent refractive index experienced by the light propagating within the optical waveguide increases, resulting in a change in the beam shape (NFP) of the laser light. Furthermore, as the wavelength increases, the equivalent refractive index experienced by the light propagating within the optical waveguide changes, resulting in a change in the beam shape of the laser light.

[0043] Therefore, in order to align the beam divergence angle (FFP) of multiple laser beams, it is important to consider the laser beam shape (NFP) as the laser beam propagates through the optical waveguide. Details will be explained later.

[0044] (Relationship between light-emitting layer thickness and beam shape) 7 is an explanatory diagram illustrating the relationship between the beam shape of laser light and the thickness of the light-emitting layer EL. Two light-emitting portions EM are shown in FIG. 7, with the left side corresponding to the light-emitting portion EM11 in this embodiment and the right side corresponding to the light-emitting portion EM13 in this embodiment. In FIG. 7, in order to explain the relationship between the beam shape and the thickness of the light-emitting layer EL, the ridge widths RW of the two light-emitting portions EM are set to the same dimension (1.5 μm).

[0045] First, let's consider the equivalent refractive index in the vertical direction for the ridge R portion (center) and the ridge groove RG portion (side). The equivalent refractive index in the vertical direction is the equivalent refractive index in each region enclosed by the dotted-line box in the upper part of Figure 7. As mentioned above, the equivalent refractive index is determined by three factors: the refractive index of the material through which the laser light propagates, the film thickness, and the wavelength (wavelength of light in a vacuum). Therefore, the relationship between the equivalent refractive index (n_center) of the ridge R portion and the equivalent refractive index (n_side) of the ridge groove RG portion in the light-emitting portions EM11 and EM13 is as follows: Note that in the following, we assume that the refractive index n of each material is 3.2 for the light-emitting layer EL, 3.1 for the cladding layer 2(3), and 1 for air, and the relationship between the equivalent refractive index in the vertical direction is qualitatively shown.

[0046] In the ridge R portion, the equivalent refractive indexes have the relationship "n11_center > n13_center." This is because the thickness ET11 (104 nm) of the light-emitting layer EL11 in the light-emitting portion EM11 is thicker than the thickness ET13 (80 nm) of the light-emitting layer EL13 in the light-emitting portion EM13. That is, the thickness EHT from the center position in the film thickness direction of the light-emitting layer EL to the surface of the light-emitting layer EL is 52 nm in the light-emitting layer EL11 and 40 nm in the light-emitting layer EL13. This is because the proportion of layers with a high refractive index n is higher in the light-emitting portion EM11 (12 nm thicker). As mentioned above, the distance from the top surface of the light-emitting layer EL to the bottom surface of the ridge groove RG is approximately the same in this embodiment, so only the thickness of the light-emitting layer EL is mentioned here.

[0047] Furthermore, in the portion (side) of the ridge groove RG, the equivalent refractive index has the relationship "n11_side >> n13_side." This is because, as in the case of the portion of the ridge R, the thickness EHT from the center position in the film thickness direction of the light-emitting layer EL to the surface of the light-emitting layer EL is 52 nm for the light-emitting layer EL11 and 40 nm for the light-emitting layer EL13, and the proportion of layers with a high refractive index n is high in the light-emitting portion EM11 (12 nm thick). In other words, in the light-emitting portion EM11, the center position in the film thickness direction of the light-emitting layer EL is far from the air layer (which has a very low refractive index), and the influence of the refractive index of air is smaller than in the light-emitting portion EM13.

[0048] Comparing the difference in equivalent refractive index in the horizontal direction based on the relationship between the vertical equivalent refractive index of the ridge R portion (center) and the ridge groove RG portion (side) described above, the relationship shown in the lower part of Figure 7 is obtained. In the diagram shown in the lower part of Figure 7, the vertical axis represents the equivalent refractive index, and the horizontal axis represents the horizontal (x-direction) position (which also corresponds to the ridge width RW). The diagram shown in the middle part of Figure 7 also shows a schematic diagram of the beam shape (NFP) of the laser light emitted from the light-emitting portions EM11 and EM13, with the vertical axis representing the light intensity and the horizontal axis representing the horizontal position. As can be seen from the diagram, the difference in equivalent refractive index between the ridge R11 portion (n11_center) and the ridge groove RG portion (n11_side) in the light-emitting portion EM11 is small, resulting in a relatively weak degree of light confinement in the horizontal direction. On the other hand, the difference in equivalent refractive index between the ridge R13 portion (n13_center) and the ridge groove RG portion (n13_side) in the light-emitting portion EM13 is large, resulting in a relatively strong degree of light confinement in the horizontal direction. That is, a difference in the equivalent refractive index in the horizontal direction causes a difference in the shape of the NFP in the horizontal direction.

[0049] In this way, the difference in thickness of the light-emitting layers EL causes the beam shapes of the laser light emitted from each light-emitting layer EL to differ.

[0050] (Relationship between ridge width and beam shape) FIG. 8 is an explanatory diagram showing the relationship between the beam shape of laser light and the ridge width RW. FIG. 8 illustrates the relationship between the ridge width and the horizontal NFP width for three horizontal equivalent refractive index differences (A, B, C). Curve A corresponds to the light-emitting unit EM12 in this embodiment, where the horizontal equivalent refractive index difference is 0.002. Curves B and C correspond to light-emitting units in any configuration in which the distance from the center of the light-emitting layer to the bottom of the ridge groove is changed from that of the light-emitting unit EM12. The horizontal equivalent refractive index differences are 0.005 (curve B) and 0.01 (curve C), respectively. The distance from the center of the light-emitting layer to the bottom of the ridge groove has the following relationship: Curve A > Curve B > Curve C.

[0051] The difference in equivalent refractive index in the horizontal direction in FIG. 8 is calculated in the same manner as explained in FIG. 7, and the relationship between the equivalent refractive index in the vertical direction is calculated assuming that the refractive index n of each material is 3.2 for the light-emitting layer EL, 3.1 for the cladding layer 2(3), and 1 for air. For example, in the light-emitting portion EM12 of curve A, the equivalent refractive index in the vertical direction of the ridge R12 portion (n12_center) is calculated to be 3.175, and the equivalent refractive index in the vertical direction of the ridge groove RG portion (n12_side) is calculated to be 3.173. The difference between 3.175 and 3.173 (0.002) is calculated as the difference in equivalent refractive index in the horizontal direction in the light-emitting portion EM12. Curves B and C are also calculated in the same manner, but their explanation will be omitted here. The curve shown in FIG. 8 (the relationship between the NFP width and the ridge width in the horizontal direction) is calculated for red laser light (Al x Ga 1-x ) 1-y In y The calculation was carried out by simulation, taking into account factors such as the refractive index of the P-based material, the air ridge structure, and the transverse single mode laser.

[0052] The results in Figure 8 show that adjusting the ridge width allows us to adjust the horizontal NFP width, and therefore the beam shape. The relationship between ridge width and NFP width is divided by the dashed-dotted line. Region P to the right of the dashed-dotted line is the region where the ridge width and NFP width are proportional. In other words, increasing the ridge width also increases the NFP width. On the other hand, region IP to the left is the region where the ridge width and NFP width are inversely proportional. In other words, increasing the ridge width decreases the NFP width. The boundary between regions P and IP occurs when the ridge width is 1.2 μm for curve C, 1.5 μm for curve B, and 1.9 μm for curve A.

[0053] FIG. 9, like FIG. 8, is an explanatory diagram showing the relationship between the beam shape of laser light and the ridge width RW. In FIG. 9, in addition to the curve A12 (corresponding to the curve A in FIG. 8) corresponding to the light-emitting portion EM12 in this embodiment, curves for the light-emitting portions EM11 (curve A11) and EM13 (curve A13) in this embodiment are added. The difference in the equivalent refractive index in the horizontal direction for the light-emitting portions EM11 and EM13 was calculated in the same way as for the light-emitting portion EM12 described above, and the curves A11 and A13 were calculated. The difference in the equivalent refractive index in the horizontal direction for the light-emitting portion EM11 (curve A11) is 0.0018, and the difference in the equivalent refractive index in the horizontal direction for the light-emitting portion EM13 (curve A13) is 0.0025. The wavelengths of the laser light emitted from the respective light-emitting portions EM are the light-emitting portion EM11 (645 nm), the light-emitting portion EM12 (641 nm), and the light-emitting portion EM13 (637 nm).

[0054] In Figure 9, the plots marked with "■" and "○" indicate the case where the ridge width RW of each light-emitting portion EM is set to 1.5 μm as the initial value. Both belong to the region IP side. Here, it can be seen that when the ridge width RW11 of light-emitting portion EM11 is widened from 1.5 μm, the horizontal NFP width narrows (shifts from "○" to "●"). Furthermore, when the ridge width RW13 of light-emitting portion EM13 is narrowed from 1.5 μm, the horizontal NFP width widens (shifts from "○" to "●"). As a result, as shown by the plots marked with "■" and "●," it can be seen that the horizontal NFP width can be improved so that it is uniform across the three light-emitting portions EM.

[0055] This will be further explained using the simulation results in Figure 10. In Figure 10, the left side shows the horizontal NFP shape of the light-emitting portion EM11, and the right side shows the horizontal NFP shape of the light-emitting portion EM13. Also, (a) in the upper row shows the NFP shape when the ridge width RW is the initial value of 1.5 μm, and (b) in the lower row shows the NFP shape when the ridge width RW is changed. As can be seen from the figure, when the ridge width RW11 of the light-emitting portion EM11 is increased by 0.2 μm from 1.5 μm to 1.7 μm, the horizontal NFP width narrows from NFP(a11) to NFP(b11). Also, when the ridge width RW13 of the light-emitting portion EM13 is narrowed by 0.2 μm from 1.5 μm (upper row) to 1.3 μm (lower row), the horizontal NFP width expands from NFP(a13) to NFP(b13). In this way, by adjusting the ridge width RW, the NFP shape in the horizontal direction can be made uniform.

[0056] The relationship between the ridge width and the beam shape described above will be briefly summarized. (1) If the film thickness of the light-emitting layer EL differs for each light-emitting portion EM, the distance ED (the distance from the center position in the film thickness direction of the light-emitting layer EL to the bottom surface of the ridge groove RG) will differ for each light-emitting portion EM. (2) The difference in the equivalent refractive index in the horizontal direction in the light-emitting portion EM will differ for each light-emitting portion EM, resulting in a difference in the degree of light confinement in the horizontal direction for each light-emitting portion EM. (3) If the ridge width RW is the same for each light-emitting portion EM, the NFP width will vary in the horizontal direction. (4) The NFP width can be made uniform by changing the ridge width RW for each light-emitting portion EM. (5) Generally, the ridge width RW and the NFP width are proportional to each other (i.e., widening the ridge width RW also widens the NFP width). However, in the semiconductor laser device according to this embodiment, the ridge width RW and the NFP width are adjusted in a range where they are inversely proportional to each other (i.e., widening the ridge width RW narrows the NFP width).

[0057] Note that the shape of the emitted beam is mainly determined by the ridge shape near the light-emitting end facet, so the ridge width RW does not need to be limited to the above relationship at all points in the cavity direction. For example, it is also possible to make the ridge width RW uniform from the rear end facet to the center of the cavity.

[0058] (Improved beam shape) Next, the improvement results of NFP and FFP by adjusting the ridge width RW will be described. Fig. 11 is a graph showing the improvement results of the beam shape (NFP) of the laser light in the semiconductor laser device LD1 according to the first embodiment. Fig. 12 is a graph showing the improvement results of the beam shape (FFP) of the laser light in the semiconductor laser device LD1 according to the first embodiment.

[0059] In each figure, (a) shows the NFP and FFP characteristics for a comparative example in which the ridge width RW is the same (1.5 μm). (b) shows the NFP and FFP characteristics of the semiconductor laser device LD1 according to the first embodiment. The solid lines show the NFP and FFP characteristics corresponding to the light-emitting element EM13 (wavelength λ=637 nm), and the dotted lines show the NFP and FFP characteristics corresponding to the light-emitting element EM11 (wavelength λ=645 nm). For ease of comparison, the NFP and FFP characteristics of the light-emitting element EM12 (wavelength λ=641 nm), which emits an intermediate wavelength, are omitted in FIGS. 11 and 12.

[0060] 11, in the comparative example where the ridge width RW is constant (a), the difference in the full width at half maximum of the NFP was 0.46 μm, but in the semiconductor laser device LD1 according to the first embodiment (b), the difference in the full width at half maximum of the NFP could be reduced to 0.16 μm. In this way, the variation in the characteristics of the NFP shape is improved.

[0061] As can be seen from FIG. 12, in the comparative example in which the ridge width RW is constant (a), the difference in full width at half maximum of the FFP is 2.6°, but in the semiconductor laser device LD1 according to the first embodiment (b), FFP The difference in full width at half maximum (FWHM) between the two was reduced to 0.48°, which is less than 1.0°. In this way, the variation in FFP shape characteristics has been improved. 13 shows the full width at half maximum values ​​of the FFP shown in FIG. 12 for the light emitting portions EM11, EM12, and EM13. (a) shows the full width at half maximum of the FFP when the ridge width RW is the same (1.5 μm) as a comparative example, and (b) shows the full width at half maximum of the FFP in the semiconductor laser device LD1 according to the first embodiment. In the comparative example of (a), the variation in the full width at half maximum was about 25%, but it can be seen that by adjusting the ridge width RW in (b), the variation in the full width at half maximum is reduced to about 5%.

[0062] In this way, by adjusting the ridge width RW for each light-emitting element EM, the NFP was improved, and as a result, the FFP (beam shape divergence angle) was also improved, and the variation in the horizontal divergence angle of each beam shape was reduced.

[0063] (Method for manufacturing a semiconductor laser device) Next, an example of the method for manufacturing the semiconductor laser device LD1 according to Embodiment 1 will be described. FIGS. 14 to 18 are cross-sectional views of main parts showing an example of the steps included in the method for manufacturing the semiconductor laser device LD1.

[0064] The method for manufacturing the semiconductor laser device LD1 according to Embodiment 1 mainly includes: (1) a step of forming an n-type cladding layer 2 on a GaAs substrate 1; (2) a step of forming a mask MK; (3) a step of selectively growing light-emitting layers EL11, EL12, and EL13; (4) a step of forming a p-type cladding layer 3 and a cap layer 4 (including the step of removing the mask MK); and (5) a step of forming a ridge R and electrodes and separating them into individual pieces.

[0065] (1) Step of forming an n-type cladding layer 2 on a GaAs substrate 1 First, as shown in FIG. 14, an n-type cladding layer 2 with a thickness of about 2 μm is epitaxially grown on the GaAs substrate 1 by MOCVD. The source gases used are trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), etc. The composition of the n-type cladding layer 2 is (Al x Ga 1-x ) 1-y In y P (0 < x ≦ 1, 0 < y < 1), and here x = 1 and y = 0.5. In this embodiment, considering the lattice matching with the GaAs substrate 1, the In composition y is adjusted to 0.5. Also, the composition ratio of Al to Ga (x:1 - x) is preferably such that x is larger, and (x:1 - x) = 1:0 is also acceptable.

[0066] (2) Step of forming a mask MK Next, after forming the n-type cladding layer 2, a silicon oxide (SiO2) film that functions as a mask MK is formed on the surface of the n-type cladding layer 2 by CVD. This SiO2 film is a film that inhibits crystal growth, and for example, a silicon nitride (Si3N4) film may be used instead.

[0067] After forming the SiO2 film, as shown in Fig. 15, a plurality of stripe-shaped openings (three openings in this embodiment) are formed in the SiO2 film by a lithography method. The widths of the three openings (corresponding to the sizes in the x-direction (horizontal direction)) are different from each other and are formed so as to become wider in order from the left side of Fig. 15. That is, as an example, the widths of the openings are EW11 (20 μm), EW12 (30 μm), and EW13 (40 μm). Also, as an example, the respective mask widths are MK1 (50 μm), MK2 (25 μm), MK3 (15 μm), and MK4 (5 μm).

[0068] (3) Step of forming the light-emitting layers EL11, EL12, and EL13 by a selective growth method Next, as shown in Fig. 16, light-emitting layers EL11, EL12, and EL13, which are composed of a lower n-side guide layer nGL, a barrier layer BL, a quantum well layer QW, a barrier layer BL, and an upper p-side guide layer pGL, are formed in the region of the openings of the mask MK. The formation of these layers is carried out by a method called selective growth. The selective growth method utilizes the fact that crystals are not formed on the upper surface of the mask MK and forms a desired film only in the region of the openings of the mask MK.

[0069] The crystals grown by the selective growth method are (Al x Ga 1-x ) 1-y In y P (0 ≦ x < 1, 0 < y < 1), and the source gases used are trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), etc.

[0070] By selective growth, a lower n-side guide layer nGL, a barrier layer BL, a quantum well layer QW, a barrier layer BL, a quantum well layer QW, and an upper p-side guide layer pGL are formed in this order in each region of the opening of the mask MK, as shown in Fig. 4. The light-emitting layer EL11 is formed in the region (EW11) where the opening of the mask MK is narrowest, and the light-emitting layer EL13 is formed in the region (EW13) where the opening of the mask MK is widest. When the light-emitting layer EL is formed by selective growth, gently sloping surfaces are formed on the side surfaces of the light-emitting layer EL, but these are omitted in the drawing.

[0071] In the process of forming this light-emitting layer EL, (Al x Ga 1-x ) 1-y In y The layer made of P is formed by selective growth, and the values ​​of x and y, which indicate the composition ratio of each element, are set as follows: In this embodiment, the guide layer GL and the barrier layer BL have x=0.7 and y=0.5. Furthermore, the quantum well layer QW is grown without supplying TMA as a source gas, and the quantum well layer QW is made of GaInP that does not contain Al (i.e., x=0).

[0072] The guide layer GL, sometimes called an SCH (Separated Confinement Heterostructure) layer or confinement layer, preferably has a higher refractive index than the cladding layer 2(3) and a lower refractive index than the quantum well layer QW. Therefore, the supply ratio of the raw material is adjusted so that the Al composition ratio x is smaller than that of the cladding layer 2(3). For example, the supply amount of the raw material gas is adjusted so that the Al composition ratio x is highest in the cladding layer 2(3), and decreases in the order of the guide layer GL or barrier layer BL, and the quantum well layer QW.

[0073] As mentioned above, the quantum well layer QW is formed to a thickness in the range of 5 nm to 6 nm. The light-emitting layer EL formed by selective growth functions as a core layer in the optical waveguide. The thickness of the light-emitting layer EL depends on the wavelength and the refractive index of each layer, but is selected from the range of approximately 50 nm to approximately 500 nm for red lasers, and in this embodiment, the total thickness is approximately 100 nm.

[0074] Furthermore, the thickness ET of each light-emitting layer EL formed by selective growth differs for each light-emitting layer EL. That is, the thickness of the selectively grown light-emitting layer EL differs depending on the size of the opening in the mask MK, and the narrower the width EW of the light-emitting layer EL, the thicker the thickness ET of the light-emitting layer EL. Specifically, the thicknesses ET have the following relationship: ET11 (104 nm) > ET12 (92 nm) > ET13 (80 nm).

[0075] As described above, when the light-emitting layer EL is deposited in different opening regions of the mask MK by selective growth, the film thickness of the light-emitting layer EL differs. The mechanism behind this is not clear, but it can be assumed to be due to the following reasons (i) to (iv).

[0076] (i) In the selective growth method, film growth does not occur on the surface of the mask MK, so the source gas supplied to the surface of the mask MK moves over the surface of the mask MK and moves to the opening region of the mask MK. (ii) The larger the surface area of ​​the mask MK, the greater the amount of source gas that moves. (iii) A larger amount of source gas moves to the opening region of the mask MK adjacent to the mask MK with a larger surface area, and the source gas concentration at the opening becomes higher. Also, the smaller the opening of the mask MK, the higher the source gas concentration. (iv) As a result, more source material is supplied to the light-emitting layer EL11 formed in the region where the opening of the mask MK is narrowest.

[0077] The present invention is not limited to the above-described configuration, and a portion of the lower n-side guide layer nGL may be formed immediately after the n-type cladding layer 2 before the formation of the mask MK. Alternatively, after forming an opening in the mask MK, a portion of the n-type cladding layer 2 may be selectively grown, followed by the selective growth of the lower n-side guide layer nGL. Furthermore, after the formation of the upper p-side guide layer pGL, a portion of the p-type cladding layer 3 to be formed in the next step (4) may be selectively grown.

[0078] (4) Step of forming p-type cladding layer 3 and cap layer 4 (including step of removing mask MK) Next, as shown in FIG. 17, the mask MK is removed. Then, as shown in FIG. 18, a p-type clad layer 3 with a thickness of about 1.7 μm is epitaxially grown by the MOCVD method. The source gases used are trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), etc. The composition of the p-type clad layer 3 is (Al x Ga 1-x ) 1-y In y P (0 < x ≤ 1, 0 < y < 1), and here x = 1, y = 0.5. Subsequently, a 300-nm cap layer 4 (p-type GaAs) is formed on the upper surface of the p-type clad layer 3. Here, in FIG. 18, the surfaces of the p-type clad layer 3 and the cap layer 4 are depicted as flat, but in reality, steps are generated due to the difference in the thickness of the light-emitting layer EL as described above.

[0079] Note that, during the formation of the p-type clad layer 3, a process of forming an etch stop layer (not shown) may be included. The etch stop layer functions as an etching stop layer when etching the p-type clad layer 3 to form the ridge R in the next step (5).

[0080] (5) Process of forming the ridge R and electrodes and dicing Next, the p-type clad layer 3 is etched to form a ridge groove RG, and a ridge R extending in the resonator direction is formed for each of the light-emitting layers EL11, EL12, and EL13. At this time, the width RW of each ridge R is formed so as to satisfy the relationship RW11 > RW12 > RW13. In this embodiment, RW11 is 1.7 μm, RW12 is 1.5 μm, and RW13 is 1.3 μm.

[0081] Then, a passivation oxide film such as SiO2 (not shown) is formed, an opening of the oxide film is provided on the ridge using photolithography and etching techniques, and a p-side electrode (not shown) is formed thereon. Thereafter, the GaAs substrate is cleaved, and an end face coating or the like is formed on the cleavage surface. Through such processes, the semiconductor laser device LD1 as shown in FIGS. 2 and 3 is formed.

[0082] As described above, in the present embodiment 1, the layer deposited by selective growth is the relatively thin light-emitting layer EL formed in step (3). On the other hand, the thick n-type cladding layer 2 and p-type cladding layer 3 formed in steps (1) and (4) are formed without using selective growth.

[0083] (effect) By changing the ridge width RW of each of the light-emitting layers EL11, EL12, and EL13 according to the thickness ET, it is possible to suppress variations in the horizontal beam shape of the laser light emitted from the three light-emitting portions EM11, EM12, and EM13. This makes it possible to suppress degradation of image quality due to interference of the laser light, and further improve luminosity and image quality, such as a wide color gamut, high resolution, and wide viewing angle. In other words, the first embodiment can provide a semiconductor laser device that contributes to improving luminosity and image quality.

[0084] [Embodiment 2] The semiconductor laser device LD2 according to the second embodiment has three light-emitting portions EM21, EM22, and EM23 that emit laser light, and each light-emitting portion EM emits laser light of a different wavelength. The thicknesses (ET21, ET22, and ET23) of the light-emitting layers EL21, EL22, and EL23 in the light-emitting portions EM21, EM22, and EM23 are different, with a relationship of ET21>ET22>ET23. Ridges R21, R22, and R23 are formed on the upper portions of the light-emitting portions EM21, EM22, and EM23, and the widths (RW21, RW22, and RW23) of the ridges R are different, with a relationship of RW21>RW22>RW23. Furthermore, the depths RT (RT21, RT22, and RT23) of the ridges R are different, with a relationship of RT21>RT22>RT23.

[0085] (Configuration of semiconductor laser device) The semiconductor laser device LD2 according to the second embodiment has the same configuration as the semiconductor laser device LD1 according to the first embodiment, except that the ridge depth RT and the ridge groove width RGW of each of the light-emitting portions EM21, EM22, and EM23 are different. Therefore, unless otherwise specified, the following description will mainly focus on the differences from the first embodiment, and the same description will not be repeated.

[0086] FIG. 19 shows the configuration of a semiconductor laser device LD2 according to the second embodiment, with (a) a side view of a main part and (b) a top view of a main part.

[0087] 19, in the semiconductor laser device LD2, not only are the ridge widths RW different in the light-emitting portions EM21, EM22, and EM23, but the ridge groove widths RGW and ridge depths RT are also different in the light-emitting portions EM. By adjusting the ridge depths RT and ridge groove widths RGW in the light-emitting portions EM, it is possible to further reduce the variation in the beam shape of the laser light.

[0088] That is, in the second embodiment, the ridge depth RT is made different for each light-emitting portion EM. This suppresses the variation in the equivalent refractive index in the vertical direction between the ridge R portion (center) and the ridge groove RG portion (side) in each light-emitting portion EM, which is caused by the difference in thickness ET of the light-emitting layer EL, as explained in FIG. 7. That is, the distance from the top surface of the light-emitting layer EL (or from the center position in the film thickness direction of the light-emitting layer EL) to the bottom surface of the ridge groove RG is made different for each light-emitting portion EM. As a result, this makes it possible to further suppress the difference in equivalent refractive index in the horizontal direction for each light-emitting portion EM, and ultimately to further suppress the variation in the beam shape of the laser light.

[0089] In the second embodiment, as an example, the ridge depth RT21 of the light emitting portion EM21 is 1414 nm, the ridge depth RT22 of the light emitting portion EM22 is 1407 nm, and the ridge depth RT23 of the light emitting portion EM23 is 1400 nm. As a result, a p-type cladding layer 3 thicker than the other light emitting layers EM21 and EM22 remains on the upper surface of the thin light emitting layer EL23. This makes it possible to suppress variations in the equivalent refractive index in the vertical direction in each light emitting portion EM. As a result, it is possible to further suppress the difference in equivalent refractive index in the horizontal direction in each light emitting portion EM, and to suppress variations in the degree of light confinement in the horizontal direction.

[0090] Next, we will explain the improvement results of NFP and FFP in the semiconductor laser device LD2 according to the second embodiment. Fig. 20 is a graph showing the improvement results of the beam shape (NFP) of the laser light in the semiconductor laser device LD2 according to the first embodiment. Fig. 21 is a graph showing the improvement results of the beam shape (FFP) of the laser light in the semiconductor laser device LD2 according to the first embodiment.

[0091] In each figure, (a) shows the NFP and FFP characteristics for a comparative example in which the ridge width RW is the same (1.5 μm). (b) shows the NFP and FFP characteristics of the semiconductor laser device LD2 according to the second embodiment. The solid lines show the NFP and FFP characteristics corresponding to the light-emitting element EM23 (wavelength λ=637 nm), and the dotted lines show the NFP and FFP characteristics corresponding to the light-emitting element EM21 (wavelength λ=645 nm). For ease of comparison, the NFP and FFP characteristics of the light-emitting element EM22 (wavelength λ=641 nm), which emits an intermediate wavelength, are omitted in FIGS. 20 and 21.

[0092] 20 and 21, it is apparent that the semiconductor laser device LD2 according to the second embodiment has improved variations in both NFP and FFP. That is, the difference in the beam shapes of the laser beams emitted from the light-emitting elements EM21 and EM23 is suppressed.

[0093] FIG. 22, like FIG. 9, is an explanatory diagram showing the relationship between the beam shape of laser light and the ridge width RW. In FIG. 22, the plots of "■" and "◯" indicate the cases where the ridge width RW of each light-emitting portion EM is set to 1.5 μm as the initial value. Both belong to the region IP side. Here, it can be seen that when the ridge width RW21 of the light-emitting portion EM21 is widened from 1.5 μm to 1.7 μm, the NFP width in the horizontal direction narrows (shifts from "◯" to "◎"). Note that "◎" corresponds to the light-emitting portion EM11 according to the first embodiment. It can also be seen that when the ridge width RW23 of the light-emitting portion EM23 is narrowed from 1.5 μm to 1.3 μm, the NFP width in the horizontal direction widens (shifts from "◯" to "◎"). Note that "◎" corresponds to the light-emitting portion EM13 according to the first embodiment. Furthermore, by deepening the ridge depth RT21 of the light-emitting portion 21 from 1407 nm to 1414 nm, the horizontal NFP width can be further narrowed (shifted from "◎" to "●"). Also, by shallowing the ridge depth RT23 of the light-emitting portion 23 from 1407 nm to 1400 nm, the horizontal NFP width can be widened (shifted from "◎" to "●"). As a result, as shown by the plots of "■" and "●", the horizontal NFP width can be improved so that it is more uniform across the three light-emitting portions EM.

[0094] In the semiconductor laser device LD2 according to the second embodiment, both the ridge depth RT and the ridge groove width RGW are made different in each of the light-emitting portions EM21, EM22, and EM23, but an improvement effect can also be obtained by simply making the ridge depth RT different without changing the ridge groove width RGW.

[0095] (Method of manufacturing a semiconductor laser device) Next, an example of a method for manufacturing the semiconductor laser device LD2 according to the second embodiment will be described.

[0096] The manufacturing method of the semiconductor laser device LD2 according to the second embodiment mainly includes the steps of (1) forming an n-type cladding layer 2 on a GaAs substrate 1 (FIG. 14), (2) forming a mask MK (FIG. 15), (3) forming an emission layer EL (FIG. 16), (4) forming a p-type cladding layer 3 and a cap layer 4 (FIGS. 17 and 18), and (5) forming a ridge R and electrodes and singulating the device.

[0097] Here, steps (1) to (4) are the same as those in the manufacturing method shown in the first embodiment, so the differences between step (5) and the manufacturing method shown in the first embodiment will be mainly explained.

[0098] (5) Forming ridges and electrodes and separating them into individual pieces The process of forming the ridge R includes the following steps, which differ from those in the first embodiment. After the ridge R is formed, the process is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0099] First, a mask layer (not shown) that functions as a mask during etching is formed by a CVD method on the surface of the cap layer 4 shown in Fig. 18. The mask layer is selected from a photoresist film, a silicon oxide (SiO2) film, a silicon nitride (Si3N4) film, or the like.

[0100] Next, a plurality of stripe-shaped openings (six openings in this embodiment) are formed in the mask layer using lithography. The opening widths of the mask layer are set so that the ridge groove widths RGW are RGW21 (7 μm), RGW22 (6 μm), and RGW23 (5 μm), as shown in FIG. 19. A dry etching method is used to form the ridge R. The etching conditions used were such that the etching rate decreases by approximately 0.5% for every 1 μm narrowing of the groove width.

[0101] In this way, by etching with different openings in the mask layer, different ridge depths RT can be formed for each light-emitting portion EM in a single etching process. As an example, the etching depths were set to 1414 nm for ridge R21, 1407 nm for ridge R22, and 1400 nm for ridge R23.

[0102] It is also possible to perform etching for each ridge R without changing the openings in the mask layer and keeping the ridge groove width RGW constant (that is, perform etching three times).

[0103] (effect) The semiconductor laser device LD2 according to the second embodiment also achieves the same effects as the semiconductor laser device LD1 according to the first embodiment. Note that in the semiconductor laser device LD2 according to the second embodiment, the ridge groove widths RGW of the light-emitting portions EM21, EM22, and EM23 are made different from each other, and in addition, the ridge depths RT are also made different from each other, so that the variation in the beam shape of the laser light can be further suppressed.

[0104] The present invention has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention. For example, although the above embodiments have been described with respect to a semiconductor laser device in the red region, the present invention can also be applied to semiconductor laser devices in other color regions as long as they are fabricated using the same material system and have a visible light region other than red.

[0105] Furthermore, in the above embodiment, the case where three or four laser beams with different wavelengths are emitted from one semiconductor laser device has been described, but the number of laser beams emitted may be five or more.

[0106] Furthermore, even when a specific numerical example is described, unless there is a clear theoretical limitation to that numerical value, the numerical value may be greater than or less than that specific numerical value. Furthermore, the component means "B containing A as a main component," etc., and does not exclude embodiments containing other components.

[0107] The above embodiment also includes the following configurations.

[0108] (Appendix 1) A substrate; a first clad layer of a first conductivity type and a second clad layer of a second conductivity type stacked on a main surface of the substrate; a light-emitting layer formed on a first surface parallel to the substrate main surface, the light-emitting layer being sandwiched between the first cladding layer and the second cladding layer; At least two light emitting sections, first and second, formed in the light emitting layer and emitting laser light; a ridge having a predetermined width, formed in the second cladding layer and sandwiched from both sides by regions having a refractive index different from or lower than that of the second cladding layer so as to function as an optical waveguide; the ridge includes first and second ridges corresponding to the first and second light emitting portions, respectively; the light-emitting layer includes a first light-emitting layer corresponding to the first light-emitting portion and a second light-emitting layer corresponding to the second light-emitting portion; a semiconductor laser device in which the first light emitting layer and the second light emitting layer have different thicknesses, and the first ridge and the second ridge have different widths.

[0109] (Appendix 2) 10. The semiconductor laser device according to claim 1, the first and second ridges have an air ridge structure in which the regions on the side surfaces of the ridges are formed as grooves, A semiconductor laser device in which a first distance from a center position in a film thickness direction of the first light-emitting layer to a bottom surface of the groove formed on a side surface side of the first ridge is different from a second distance from a center position in a film thickness direction of the second light-emitting layer to the bottom surface of the groove formed on a side surface side of the second ridge.

[0110] (Appendix 3) In the semiconductor laser device according to Appendix 2, A semiconductor laser device in which the first distance is greater than the second distance and a width of the first ridge is wider than a width of the second ridge.

[0111] (Appendix 4) In the semiconductor laser device according to Appendix 1 or Appendix 2, A semiconductor laser device in which a first wavelength of laser light emitted from the first light-emitting portion is longer than a second wavelength of laser light emitted from the second light-emitting portion and a width of the first ridge is wider than a width of the second ridge.

[0112] (Appendix 5) In the semiconductor laser device according to Appendix 1 or Appendix 2, A semiconductor laser device in which a difference in full width at half maximum of beam divergence angles of two laser lights emitted from the first and second light-emitting portions is 1.0° or less or 5% or less.

[0113] (Appendix 6) In the semiconductor laser device according to Appendix 1 or Appendix 2, The light-emitting layer is composed of a crystal layer of (Al x Ga 1-x ) 1-y In y P (0 ≦ x < 1, 0 < y < 1), and the laser light is laser light in a red region. (Appendix 7) In the semiconductor laser device according to Appendix 1 or Appendix 2, A thickness of the first light-emitting layer is thicker than a thickness of the second light-emitting layer, a depth dimension of the groove formed on the side surface of the first ridge is greater than a depth dimension of the groove formed on the side surface of the second ridge;

[0114] (Appendix 8) In the semiconductor laser device according to Supplementary Note 1 or Supplementary Note 2, the thickness of the first light-emitting layer is greater than the thickness of the second light-emitting layer; a width dimension of the groove formed on the side surface of the first ridge is wider than a width dimension of the groove formed on the side surface of the second ridge; [Explanation of symbols]

[0115] BL Barrier Layer EM light emitting part EL light-emitting layer ER light-emitting region EW: width of the light-emitting layer ET emitting layer thickness EHT Half the thickness of the light-emitting layer ED: Distance from the center of the light-emitting layer to the bottom of the ridge groove R Ridge RW ridge width RG Ridge Groove LD semiconductor laser device QW quantum well layer MK Mask nGL Lower n-side guide layer pGL Upper p-side guide layer 1 GaAs substrate 2 n-type cladding layer 3 p-type cladding layer 4 Cap Layer

Claims

1. A substrate; a first clad layer of a first conductivity type, a light emitting layer, and a second clad layer of a second conductivity type are sequentially stacked; the light-emitting layer has at least two light-emitting portions, namely, first and second light-emitting portions, which emit laser light of a single transverse mode in a red region, and the wavelength difference between the laser light emitted from the first light-emitting portion and the second light-emitting portion is 1 nm to 30 nm; a first ridge and a second ridge corresponding to the first and second light emitting portions, respectively; a thickness of the first light-emitting layer corresponding to the first light-emitting portion is greater than a thickness of the second light-emitting layer corresponding to the second light-emitting portion; a first wavelength of the laser light emitted from the first light-emitting portion is longer than a second wavelength of the laser light emitted from the second light-emitting portion, and a width of the first ridge is wider than a width of the second ridge; The light-emitting layer is ｘ Ga １－ｘ ) １－ｙ In ｙ P (0≦x<1, 0<y<1) crystalline layers, the first and second ridges have grooves formed on the side surfaces of the ridges; a first distance from a center position in a thickness direction of the first light-emitting layer to a bottom surface of the groove formed on a side surface of the first ridge is different from a second distance from a center position in a thickness direction of the second light-emitting layer to a bottom surface of the groove formed on a side surface of the second ridge, and the first distance is greater than the second distance; the refractive indexes of the light-emitting layer, the ridge, and the groove portion satisfy the relationship of light-emitting layer>ridge>groove portion, a difference in full width at half maximum of horizontal divergence angles in the beam shapes of the two laser beams emitted from the first and second light-emitting units in FFP (Far Field Pattern) is set to 1.0° or less; Semiconductor laser device.

2. 2. The semiconductor laser device according to claim 1, wherein the depth of the groove formed on the side surface of said first ridge is deeper than the depth of the groove formed on the side surface of said second ridge.

3. 2. The semiconductor laser device according to claim 1, wherein the width of the groove formed on the side surface of said first ridge is wider than the width of the groove formed on the side surface of said second ridge.

4. 2. The semiconductor laser device according to claim 1, wherein the distance from the lower surface of the light emitting layer to the upper surface of the substrate is the same in the first light emitting portion and the second light emitting portion.

5. 2. A method for manufacturing a semiconductor laser device according to claim 1, comprising: a step (1) of forming an n-type cladding layer as the first cladding layer on the substrate; (2) forming a mask on the n-type cladding layer; a step (3) of forming the light-emitting layer by selective growth; a step (4) of forming a p-type cladding layer as the second cladding layer and a cap layer; and (5) forming the first and second ridges and electrodes and dividing the resultant into individual pieces, The step (4) further includes a step of removing the mask. A method for manufacturing a semiconductor laser device.

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