JP7680711B2 - Semiconductor laser device and its manufacturing method - Google Patents

Description

The present invention relates to a semiconductor laser device.

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

In addition, reality technologies such as augmented reality (AR), virtual reality (VR), mixed reality (MR), and substitution reality (SR) have been put to practical use in various fields, and display devices using these technologies, such as head mounted displays (HMD), head-up displays, and AR glasses, have been commercialized.

For example, in a head mounted display (HMD), a technology is known in which three colors of laser light, RGB (red, green, and blue), are used as the light source, an image is created by a MEMS (Micro Electro Mechanical Systems), which is a spatial modulation element for image display, and the image is projected onto the retina or the like through a waveguide. This system using MEMS is said to have advantages such as a wide color gamut, high resolution, and wide viewing angle. On the other hand, in order to further improve image quality such as a wide color gamut, high resolution, and wide viewing angle, multi-beam LDs (multiple semiconductor laser devices) have been used for each color of RGB, but the wavelengths of each color are the same. If the wavelengths of all the beams are the same (i.e., the wavelengths are the same), image quality will deteriorate due to the coherence of the laser light.

Patent Document 1 discloses a multi-wavelength semiconductor laser capable of oscillating lasers of multiple wavelengths within the same element. Patent Document 1 does not state the specific wavelength of the laser light, but since 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 that oscillate different wavelengths have different well widths (physical film thicknesses).

Japanese Patent Application Publication No. 05-082894

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

In addition, 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, it is preferable to use a semiconductor laser device that can emit multiple laser beams with different oscillation wavelengths for each color of a light source using three colors of laser light, RGB, from the viewpoint of suppressing the deterioration of image quality due to the coherence of the laser light mentioned above.

However, the inventors have found the following. In order to emit laser light of multiple wavelengths with different oscillation wavelengths, it is possible to change the band gap energy of the light emitting layer (active layer) of each light emitting unit that emits the laser light. For example, the thickness of the light emitting layer, or the composition of the light emitting layer without changing the thickness of the light emitting layer, can be changed for each light emitting unit to obtain laser light of multiple different wavelengths. However, as a result of the intensive research of the inventors, it has been found that if the wavelength of the laser light differs for each light emitting unit, the beam shape of the laser light emitted from each light emitting unit will differ. This is because, when the wavelength of the laser light differs, the equivalent refractive index felt by each laser light propagating in the optical waveguide changes, and as a result, the beam shape of each laser light will differ. And when such a difference in beam shape occurs (or when the deviation of each beam shape becomes large), it can be one of the causes of deterioration of visibility and image quality. Furthermore, if the beam shape and beam spread angle of the laser light emitted from the light-emitting end face of the LD differ for each laser light, problems arising from differences in beam shape can be corrected to some extent by designing and adjusting the optical system, such as the lenses that receive the beam, for each beam. However, this is not only extremely time-consuming, but also leads to increased costs.

The aforementioned Patent Document 1 makes no mention of the beam shapes of the laser beams and the differences therebetween due to differences in emission wavelength.

The objective of the present invention is to provide a semiconductor laser device that contributes to improving visibility and image quality. Other objectives and novel features will become apparent from the description of this specification and the drawings.

A semiconductor laser device according to one embodiment includes a substrate, a first cladding layer of a first conductivity type and a second cladding layer of a second conductivity type stacked on a main surface of the substrate, and a light-emitting layer formed between the first cladding layer and the second cladding layer and formed on a first surface parallel to the main surface of the substrate. The semiconductor laser device also includes at least two first and second light-emitting sections formed in the light-emitting layer and emitting laser light, an optical waveguide formed of the light-emitting layer, the first cladding layer, and a part of the second cladding layer and extending in the resonator direction, and an adjustment region for adjusting the beam shape of the laser light emitted from the first and second light-emitting sections. Furthermore, the adjustment region is formed at least on the light-emitting end surface side of the optical waveguide, and includes a first adjustment region formed in the first light-emitting section and a second adjustment region formed in the second light-emitting section. Furthermore, the first and second adjustment regions are formed in the light-emitting layer corresponding to at least the first and second light-emitting units, respectively, and the first wavelength of the first laser light emitted from the first light-emitting unit is different from the second wavelength of the second laser light emitted from the second light-emitting unit, and the lengths of the first and second adjustment regions in the resonator direction are different.

The semiconductor laser device according to one embodiment can provide a semiconductor laser device that contributes to improving visibility and image quality.

1 is a perspective view showing a main part of an example of a configuration of a semiconductor laser device according to a preferred embodiment. 1 is a perspective view showing a main part of an example of a configuration of a semiconductor laser device according to a first embodiment; 1 is a top view of a main portion showing a configuration of a semiconductor laser device according to a first embodiment; 2 is a cross-sectional view showing an example of a configuration of a main portion of light-emitting layers EL11 to EL13 in a semiconductor laser device according to a first embodiment. FIG. 1 is an explanatory diagram (1) relating to the beam shape (NFP/FFP) of laser light. FIG. 2 is an explanatory diagram (2) relating to the beam shape (NFP/FFP) of laser light. 1 is an explanatory diagram showing an improvement result of the beam shape (NFP) of the laser light in the semiconductor laser device according to the first embodiment. FIG. 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. 4 is a graph showing an improvement result of the beam shape (FFP) of the laser light in the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 4 is a cross-sectional view of a main part illustrating an example of a process included in a manufacturing method of the semiconductor laser device according to the first embodiment. 11A and 11B are a top view and a cross-sectional view of a main portion showing a configuration of a semiconductor laser device according to a second embodiment. 11 is an explanatory diagram showing the distribution of laser light near an optical waveguide in a semiconductor laser device according to a second embodiment. FIG. 11A and 11B are a top view and a cross-sectional view of a main portion showing a configuration of a semiconductor laser device according to a third embodiment. FIG. 13 is a top view of a main portion showing a configuration of a semiconductor laser device according to a fourth embodiment. 13 is an explanatory diagram showing the operation of a semiconductor laser device according to a fourth embodiment. FIG.

The semiconductor laser device according to the embodiment will be described in detail below with reference to the drawings. In the specification and drawings, the same or corresponding components are given the same reference numerals, and duplicated explanations are omitted. In the drawings, the configuration may be omitted or simplified for convenience of explanation. At least some of the embodiments and modifications may be combined with each other in any way. In addition, when it is necessary to explain the components individually because they are formed in different locations, for example, different reference numerals are used for each component, but when explaining the functions that the components originally have, it may be expressed as the light emitting unit EM, for example.

[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.

Note that with regard to the x-axis, y-axis, and z-axis shown in Figure 1, x means the horizontal direction/width direction/lateral direction, y means the resonator direction/depth direction/vertical direction, and z means the vertical direction/thickness direction/height direction. The definitions of these directions are the same in other figures.

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. In addition, 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 with different wavelengths are emitted from the light-emitting portions EM01 and EM02, respectively.

In the light emitting sections EM01 and EM02, optical waveguides OW01 and OW02, each of which is composed of a light emitting layer EL and a part of the first cladding layer 2 and the second cladding layer 3, are formed in the resonator direction (y direction).

In addition, at least on the light emitting end surface side of the optical waveguide OW, an adjustment region AR is provided that adjusts (corrects) the beam shape of the laser light λ01, λ02 emitted from the first and second light emitting units EM01, EM02. The adjustment region AR includes a first adjustment region AR01 formed in the first light emitting unit EM01 and a second adjustment region AR02 formed in the second light emitting unit EM02. The first and second adjustment regions AR01, AR02 may be formed at least in the light emitting layers EL01, EL02 of the optical waveguides OW01, OW02. The lengths ARL01, ARL02 in the resonator direction of the first and second adjustment regions AR01, AR02 are formed differently. In FIG. 1, the adjustment region AR is formed within the region of the light emitting unit EM in the x direction, but the formation range in the x direction is not particularly limited to this and can be formed in any range that produces an effect.

In this way, by making the lengths of the first and second adjustment regions AR01 and AR02 in the resonator direction different, the difference in the beam shapes of the laser beams λ01 and λ02 caused by the different wavelengths can be corrected, and the variation in the beam shapes can be suppressed.

The adjustment region AR for adjusting (correcting) the beam shape of the laser light means a region where the degree of light confinement is relatively weak, and is a region where the difference in refractive index between the first cladding layer 2, the second cladding layer 3, and the light emitting layer EL constituting the optical waveguide is small. As an example, it is a region selected from the following.
(1) A region in the light-emitting layer EL where the band gap energy of the light-emitting layer EL in a specific region is wider than that of the light-emitting layer EL in other regions. (2) A region in the light-emitting layer EL where the band gap energy of the light-emitting layer EL in a specific region is closer to the band gap energy of the cladding layers 2 and 3. (3) A region in the optical waveguide where the equivalent refractive index of the optical waveguide OW in a specific region is relatively lower than that of the waveguide OW in other regions. (4) A region in the light-emitting layer EL where the thickness of the light-emitting layer EL in a specific region is relatively thinner than that of the light-emitting layer EL in other regions. (5) A region in the light-emitting layer EL where the composition of the light-emitting layer EL in a specific region is made different from that of the light-emitting layer EL in other regions so as to widen the band gap energy or reduce the equivalent refractive index. As an example of a different composition, it is possible to mix more zinc (Zn) as an impurity than in other regions. (6) A region where the above-mentioned (1) to (5) are appropriately combined.

[First embodiment]
In the semiconductor laser device LD1 according to the first embodiment, three light emitting portions EM11, EM12, and EM13 that emit laser light are formed, and the light emitting portions EM emit laser light λ11, λ12, and λ13 with different wavelengths. In the light emitting portions EM11, EM12, and EM13, optical waveguides OW11, OW12, and OW13 that are constituted by the light emitting layer EL and a part of the first cladding layer 2 and the second cladding layer 3 are formed in the resonator direction (y direction). Furthermore, an adjustment region AR that adjusts (corrects) the beam shapes of the laser light λ11, λ12, and λ13 emitted from the light emitting portions EM11, EM12, and EM13 is provided in the region on the light emitting end surface side of the semiconductor laser device LD1 including the optical waveguides OW11, OW12, and OW13. The adjustment region AR includes adjustment regions AR11, AR12, and AR13 corresponding to the light emitting portions EM11, EM12, and EM13, respectively. The adjustment regions AR11, AR12, and AR13 have lengths ARL11, ARL12, and ARL13 in the resonator direction, respectively, and the lengths ARL are different from each other.

In this embodiment, the adjustment region AR is a region in which the band gap energy of the light-emitting layer EL on the light-emitting end surface side is widened and the equivalent refractive index of the optical waveguide is relatively small.

(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 top view of a 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 the light emitting layers EL11 to EL13 in the semiconductor laser device LD1 according to the embodiment 1.

2, the semiconductor laser device LD1 has an n-type cladding layer 2 (thickness 2 μm), light emitting layers EL11, EL12, EL13, and a p-type cladding layer 3 (thickness 1.7 μm) formed on a GaAs substrate 1. 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), where x=1 and y=0.5.

The semiconductor laser device LD1 is formed with three light emitting portions EM11, EM12, and EM13, and in order to emit laser light of different wavelengths λ, the thicknesses (ET11, ET12, ET13) of the light emitting layers EL11, EL12, and EL13 in each light emitting portion EM are made different. In other words, 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, so that the respective thicknesses ET can be made different.

The wavelengths λ emitted from the three light-emitting elements EM11, EM12, and EM13 have the following relationship: light-emitting element EM11 > light-emitting element EM12 > light-emitting element EM13. As an example, light-emitting region ER11 emits laser light with a wavelength of 642 nm (λ11), light-emitting region ER12 emits laser light with a wavelength of 639 nm (λ12), and light-emitting region ER13 emits laser light with a wavelength of 636 nm (λ13). In this way, the wavelength of the laser light varies depending on the thickness ET of the light-emitting layer EL, and the thicker the thickness ET of the light-emitting layer EL, the larger the value of the wavelength λ.

In the above example, the wavelengths are set with a difference of 3 nm, but the difference in wavelengths can be appropriately selected between 1 nm and 30 nm. For example, if the difference in wavelengths is 1 nm, then light-emitting region ER11 emits laser light with a wavelength of 622 nm, light-emitting region ER12 emits laser light with a wavelength of 621 nm, and light-emitting region ER13 emits laser light with a wavelength of 620 nm. If the difference in wavelengths is 30 nm, then light-emitting region ER11 emits laser light with a wavelength of 690 nm, light-emitting region ER12 emits laser light with a wavelength of 660 nm, and light-emitting region ER13 emits laser light with a wavelength of 630 nm.

In each of the light emitting sections EM11, EM12, and EM13, a ridge groove RG is formed by etching a part of the p-type cladding layer 3, and ridges R11, R12, and R13 are formed as a current confinement structure (current injection structure) and a structure for lateral (x-direction) light confinement. In this way, the ridge R has a ridge structure formed along the resonator direction (y-direction) so that it is sandwiched on both sides by air (refractive index = 1), which has a lower refractive index than the p-type cladding layer 3.

In the light emitting sections EM11, EM12, and EM13, optical waveguides OW11, OW12, and OW13, each of which is composed of a light emitting layer EL and a part of the first cladding layer 2 and the second cladding layer 3, are formed in the resonator direction (y direction).

In addition, an adjustment area AR is provided in the region of the light-emitting end face side of the semiconductor laser device LD1 including the optical waveguides OW11, OW12, and OW13, which adjusts (corrects) the beam shapes of the laser beams λ11, λ12, and λ13 emitted from the light-emitting portions EM11, EM12, and EM13. That is, the adjustment area AR is formed in a part of the first cladding layer 2, the light-emitting layer EL, and the second cladding layer 3 on the light-emitting end face side.

The adjustment region AR is a region in which the band gap energy of the light emitting layer EL on the light emitting end surface side is widened and the equivalent refractive index of the optical waveguide is relatively small. In the present embodiment, as an example, it is a region in which zinc (Zn) is mixed by a method such as thermal diffusion. By mixing zinc (Zn), the light emitting layer EL and the clad layers 2 and 3 are mixed, and the band gap energy of the light emitting layer EL is widened. As a result, the refractive index of the light emitting layer EL is reduced, and the equivalent refractive index of the optical waveguide is lowered. Although details will be described later, the region with a small equivalent refractive index has a small degree of light confinement and can act in the direction of widening the beam shape of the laser light in the optical waveguide.

In the semiconductor laser device LD1 according to this embodiment, the adjustment region AR is formed continuously in the x direction on the light emitting end face, but has different lengths in the resonator direction (y direction). That is, the adjustment region AR includes adjustment regions AR11, AR12, and AR13 corresponding to the light emitting portions EM11, EM12, and EM13, respectively. The adjustment regions AR11, AR12, and AR13 also have lengths ARL11, ARL12, and ARL13 in the resonator direction, and the lengths ARL are different. In this embodiment, as an example, the lengths ARL are ARL11 (20 μm), ARL12 (15 μm), and ARL13 (10 μm).

Furthermore, as shown in Figures 2 and 3, in the semiconductor laser device LD1 according to this embodiment, a rear region ARR having a similar configuration to the adjustment region AR is also formed on the light reflecting end face side. In the plan view (a) of Figures 2 and 3, the rear region ARR is formed continuously in the x direction on the light reflecting end face, and the length of the rear region ARR in the resonator direction is the same. Note that, from the viewpoint of suppressing the variation in the beam shape of the laser light, it is not necessarily required to form the rear region ARR, but it may be formed for other reasons (described later in embodiment 4), from the viewpoint of end face protection, or for manufacturing convenience.

As a modification of the rear region ARR, as shown in the plan view (b) of FIG. 3, the rear region ARR formed on the light reflecting end face side may be similar in shape to the adjustment region AR formed on the light emitting end face side. That is, the lengths ARL11 and ARRL111 of the adjustment region AR11 and rear region ARR111 in the resonator direction in the light emitting unit EM11 are formed to be the same. Similarly, the lengths ARL12 and ARRL121 of the adjustment region AR12 and rear region ARR121 in the resonator direction in the light emitting unit EM12 are formed to be the same. Also, the lengths ARL13 and ARRL131 of the adjustment region AR13 and rear region ARR131 in the resonator direction in the light emitting unit EM13 are formed to be the same.

When the thickness of the light-emitting layer EL is large, the degree of light confinement increases, and the light density at the end face increases. For example, the thickness of the light-emitting layer EL11 is formed to be thicker than the thicknesses of the other light-emitting layers EL12 and EL13. Therefore, by making the rear region ARR111 formed on the light-reflecting end face side of the thick light-emitting layer EL11 longer, it is possible to further improve protection of the rear end face (light-reflecting end face).
In addition, an n-side electrode and a p-side electrode (not shown) are formed on the back surface of the GaAs substrate 1 and the upper surface of the ridge R. By applying a current to the n-side electrode and the p-side electrode, laser light (wavelength: 600 nm to 700 nm) in the red region is emitted from light emitting regions ER11, ER12, and ER13 formed in the three light emitting portions EM11, EM12, and EM13.

The configuration 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 in the optical waveguide. As shown in FIG. 4, the light-emitting layer EL is composed of, from the bottom, 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. 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 about 50 nm to about 500 nm for red lasers, and is about 100 nm in this embodiment. The light-emitting regions ER11, ER12, and ER13 shown in FIG. 2 mainly correspond to the desired regions of the quantum well layer QW. In FIG. 4, the quantum well layer QW is shown as a single quantum well layer (SQW), but may be a multiple quantum well layer (MQW).

In the semiconductor laser device LD1 according to the present 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 the bottom, the lower n-side guide layer nGL (40 nm), the barrier layer BL (9 nm), the quantum well layer QW (6 nm), the barrier layer BL (9 nm) and the upper p-side guide layer pGL (40 nm), and the total thickness ET11 is 104 nm. The light-emitting layer EL12 is composed of, from the bottom, the lower n-side guide layer nGL (35 nm), the barrier layer BL (8.25) nm), the quantum well layer QW (5.5 nm), the barrier layer BL (8.25 nm) and the upper p-side guide layer pGL (35 nm), and the total thickness ET12 is 92 nm. The light-emitting layer EL13 is composed of, from the bottom up, 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 ET13 of 80 nm.

Thus, the thickness ET of the light-emitting layer EL is ET11 (104 nm), ET12 (92 nm), and ET13 (80 nm), with the thickness varying in increments of 12 nm.

The crystal layers of the light-emitting layers EL11, EL12, and EL13 are composed of ( _{AlxGa1 -x} ) _{1- yInyP} (0≦x<1, 0<y<1). The quantum well layer QW is (Ga1 _{- yInyP} (x=0, y=0.55), and the guide layer GL and the barrier layer BL are ( _{AlxGa1 -x} ) _{1-yInyP (} x=0.7, y=0.5). In the quantum well layer QW, the Al composition (x) is set to x=0, but it can be appropriately selected so that the Al composition (x) of the quantum well layer QW is the smallest in the light-emitting layer EL. However, if the Al composition (x) of the quantum well layer QW is larger than about 0.5, it becomes an indirect transition type, so that the Al composition (x) of the quantum well layer QW is preferably 0.5 or less.

In addition, in the semiconductor laser device according to this embodiment, by changing the thickness ET of the light-emitting layer EL, it is possible to emit laser beams of different wavelengths from one chip. However, even without changing the thickness of the light-emitting layer EL, it is also possible to change the energy band gap by changing the composition ratio of In (indium) among the compositions constituting the crystal layer of the light-emitting layer EL, and to emit multiple laser beams of different wavelengths from one chip. In this case, as an example, if the In composition ratio (y) of the light-emitting layer EL11 is 0.59, the In composition ratio (y) of the light-emitting layer EL12 is 0.55, and the In composition ratio (y) of the light-emitting layer EL13 is 0.51, it is possible to emit laser beams of different wavelengths from one chip. Note that this In composition ratio (y) is preferably selected from the range of 0.35 to 0.65.

In the present embodiment, the expression "light emitting layer EL" means that the light emitting layer EL includes all of the lower n-side guide layer nGL, quantum well layer QW, barrier layer BL, and upper p-side guide layer pGL described above, and may also mean that the light emitting layer EL includes the quantum well layer QW and the barrier layer BL, or may also mean that the light emitting layer EL includes at least a part of either the p-type cladding layer 3 or the n-type cladding layer 2.

In addition, 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 other embodiments described below.

(Laser light beam shape (NFP/FFP))
Next, NFP (Near Field Pattern) and FFP (Far Field Pattern) used to evaluate the beam shape and characteristics of laser light will be described with reference to Figs. 5 and 6. Note that NFP and FFP have shapes in the horizontal direction (slow axis) corresponding to the x direction and the vertical direction (fast axis) corresponding to the z direction. In evaluating the characteristics of the beam shape, evaluation and consideration are required in both the horizontal and vertical directions, but in this embodiment, the beam shape in the vertical direction will be described unless otherwise specified.

First, the definitions of NFP and FFP will be explained using Figure 5. In Figure 5, (a) is a schematic side view of the light-emitting end face of a semiconductor laser device, and (b) is a schematic top view of the semiconductor laser device as seen from above. Also, (c) and (d) are diagrams showing distribution examples showing NFP and FFP, respectively.

As shown in (b), the laser light propagates through the optical waveguide OW and is emitted from the light exit surface to the outside. NFP indicates the characteristics of the beam shape at the light exit surface, and as shown in (c), the horizontal axis is expressed as the vertical position (μm) corresponding to the z direction, and the vertical axis is expressed as the light intensity. FFP indicates the characteristics of the beam shape at a position (approximately 10 mm) away from the light exit surface, and as shown in (d), the horizontal axis is expressed as the angle (deg) indicating the beam spread angle in the z direction, and the vertical axis is expressed as the light intensity. In other words, when it comes to the beam shape of laser light, it is important to evaluate the beam shape after it is emitted from the light exit surface that is directly visible to humans, that is, the beam shape indicated by FFP.

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 long, and the dashed line shows the characteristics when the wavelength λ is short. When the laser light has a narrow vertical beam shape in NFP, the vertical beam spread angle is wider in FFP. On the other hand, when the laser light has a wide vertical beam shape in NFP, the vertical beam spread angle is narrower in FFP. This can be explained by the wave diffraction phenomenon, but the explanation will be omitted here. Thus, it can be said that in order to adjust the beam spread angle in FFP, it is necessary to improve the beam characteristics in NFP.

Here, the 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. As described above, the semiconductor laser device LD1 according to this embodiment employs a ridge structure, and therefore a medium with a low refractive index, such as _SiO2 or air, exists around the ridge R.

The beam shape of laser light varies depending on the equivalent refractive index weighted by the distribution of light (i.e., what the light feels). The light distribution includes three elements: the refractive index of the material through which the laser light passes, the film thickness, and the wavelength (the wavelength of light in a vacuum). For example, when the wavelength λ of the laser light changes, the equivalent refractive index felt by the light propagating in the optical waveguide changes, and as a result, the beam shape (NFP) of the laser light changes. Similarly, when the film thickness of the light-emitting layer EL increases, the equivalent refractive index felt by the light propagating in the optical waveguide increases, and as a result, the beam shape (NFP) of the laser light changes.

In the structure of this embodiment, when the equivalent refractive index increases due to an increase in the thickness of the light-emitting layer EL, the degree of light confinement in the optical waveguide becomes relatively stronger, and the beam shape (NFP) of the laser light becomes narrower. In other words, the beam shape of a laser light with a long wavelength becomes relatively narrower than the beam shape of a laser light with a short wavelength.

Therefore, when emitting multiple laser beams with different wavelengths, in order to align the beam divergence angle (FFP), it is important to consider the beam shape (NFP) of the laser beam as it propagates through the optical waveguide. In this way, by controlling the equivalent refractive index of each optical waveguide of laser beams with different wavelengths, it is possible to adjust (correct) the beam shape of each laser beam, and as a result, it is possible to suppress the differences in the beam shapes of each emitted laser beam.

(Improved beam shape)
Next, the improvement results of NFP and FFP by forming the adjustment region AR will be described. Fig. 7A is an explanatory diagram 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. 7B 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. 7C 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.
In FIG. 7A, (A) is a diagram showing a schematic diagram of the process in which the laser light λ11 to λ13 in the light emitting units EM11 to EM13 propagates through the optical waveguide. The right side is the direction of the light emitting end face on the front side, and the left side is the direction of the light reflecting end face on the rear side. In addition, in the figure, the vertical beam shape (NFP) at each position ((a) to (e)) in the optical waveguide is shown. The dotted line (P) is the boundary between the adjustment area AR and the gain area (also called the non-adjusted area non-AR) formed in the optical waveguide, and the right side of the dotted line (P) is the adjustment area AR, and the left side is the gain area (non-adjusted area non-AR). In addition, in FIG. 7A, (B) is a graph showing qualitatively the degree of spread of the beam shape (NFP) in the vertical direction of the laser light in the process in which the laser light λ11 to λ13 propagates through the optical waveguide. The horizontal axis indicates the propagation length (μm), and the vertical axis indicates the full width at half maximum of the vertical beam shape (NFP). As described above, the wavelengths of the laser beams are λ11 (642 nm), λ12 (639 nm), and λ13 (636 nm).

As shown in (A) of FIG. 7A, at position (a) in the optical waveguide, the beam shapes of the laser beams λ11, λ12, and λ13 are different. This is because the quantum well of EM11 is thick and the degree of optical confinement is relatively strong, so the vertical beam shape (NFP) is narrow and the NFP value is small. In addition, in EM13, the quantum well is thin and the degree of optical confinement is relatively weak, so the equivalent refractive index in the optical waveguide is relatively low. Therefore, the vertical beam shape (NFP) spreads and the NFP value increases. The vertical NFP at position (a) varies greatly, as shown in (B) of FIG. 7A near the propagation length of 0 μm. If the adjustment region AR is not provided, each laser beam will be emitted from the light emitting end face with the beam shape at position (a), resulting in laser beams with uneven spread angles of the vertical beam shape (FFP).

In this embodiment, an adjustment area AR is provided to adjust (correct) the vertical beam shape (NFP) of each laser light. The adjustment area AR is formed up to a position 20 μm (ARL11) from the light emitting end face in EM11, 15 μm (ARL12) from the light emitting end face in EM12, and 10 μm (ARL13) from the light emitting end face in EM13.

Here, as described above, the adjustment region AR is a region in which the band gap energy of the light emitting layer EL on the light emitting end surface side is widened and the equivalent refractive index of the optical waveguide is relatively small. Therefore, in the laser light λ11 having a narrow vertical beam shape (NFP), the vertical beam shape (NFP) can be corrected in the widening direction by propagating the optical waveguide with a relatively small equivalent refractive index over a long distance. As shown in (A) of FIG. 7, the beam shape of the laser light λ11 in EM11 can be widened from position (a) to position (e). In addition, in the laser light λ13 having a wide vertical beam shape (NFP), the width of the widening of the vertical beam shape (NFP) can be reduced by propagating the optical waveguide with a relatively small equivalent refractive index over a short distance.

In this way, by adjusting the length ARL of the adjustment region AR in the resonator direction for each light emitting portion EM, as shown in (B), it is possible to suppress the variation in the vertical beam shape (NFP) near the propagation length of 20 μm (light emitting end face) corresponding to position (e). Therefore, by adjusting the propagation distance through the adjustment region AR according to the beam shape of each laser light (i.e., according to the wavelength of the laser light), it is possible to align the spread angle of the beam shape (FFP) of the laser light emitted from the light emitting end face.

7B and 7C show the results of improving the beam shape (NEP, FFP) of the laser light. In each figure, (a) shows the NFP characteristic and FFP characteristic when the adjustment region AR is not formed as a comparative example. (b) shows the NFP characteristic and FFP characteristic of the semiconductor laser device LD1 according to the first embodiment. The solid line shows the NFP characteristic and FFP characteristic corresponding to the light emitting unit EM13 (wavelength λ13 = 636 nm), and the dotted line shows the NFP characteristic and FFP characteristic corresponding to the light emitting unit EM11 (wavelength λ = 642 nm). Note that, for the sake of comparison, the NFP characteristic and FFP characteristic of the light emitting unit EM12 (wavelength λ12 = 639 nm) that emits an intermediate wavelength are omitted in FIGS. 7B and 7C.

As can be seen from FIG. 7B, in the comparative example (a), the difference in the full width at half maximum of the NFP was 0.15 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 0.03 μm. In this way, the variation in the characteristics of the NFP shape in the vertical direction has been improved.

Also, as can be seen from FIG. 7C, in the comparative example (a), the difference in the full width at half maximum of the FFP was 1.9°, whereas 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 0.3°. In this way, the variation in the characteristics of the FFP shape in the vertical direction has been improved.

In this way, by making the length ARL of the adjustment region AR in the resonator direction different for each light-emitting section EM, the NFP of the laser light propagating through the optical waveguide is improved, and as a result, the FFP (spread angle of the beam shape) is improved, making it possible to suppress the variation in the vertical spread angle of each beam shape.

The degree of difference in the divergence angle of the beam shape in a plurality of laser beams depends on the design of the semiconductor laser device, but since the refractive index difference between the light emitting layer and the cladding layer of an (Al _x Ga _1-x ) _1-y In _y P-based red laser is larger than that of a GaN-based blue laser, the influence of the difference in structure such as film thickness tends to be large. Therefore, the method of adjusting the equivalent refractive index in the optical waveguide as in this embodiment can be more significantly effective when applied to a red laser.

(Relationship between Beam Shape Adjustment Region AR and Window Structure)
As the output of semiconductor laser devices increases, facet damage (catastrophic optical damage (COD)) occurs, and as a countermeasure to this, a method called an end face window structure that reduces the light absorption of the light emitting end face is known. Next, the relationship between the adjustment region AR and the window structure in this embodiment will be described.

The window structure is a technology that aims to reduce heat generation near the light-emitting end face by expanding the band gap energy near the light-emitting end face and suppressing light absorption. Such a window structure is formed by diffusing impurities into the light-emitting end face and intermixing the cladding layer with the light-emitting layer and guide layer.

The adjustment region AR in this embodiment is a region for eliminating the difference in refractive index between the entire light-emitting layer EL and the cladding layers 2 and 3. As described above, the light-emitting layer EL is composed of the quantum well layer QW, the barrier layer BL, and the guide layer GL, and even if the refractive index of at least the guide layer GL is reduced, this has the effect of adjusting (correcting) the beam shape.

On the other hand, the minimum requirement for a window structure to be used as a COD countermeasure is that the band gap energy of the quantum well layer must be wide. Even if the band gap energy of the guide layer or barrier layer changes, if the band gap energy of the quantum well layer does not change, there will be little effect as a COD countermeasure.

In addition, the adjustment region AR in this embodiment is a region where the band gap energy is expanded. As an example of the adjustment region AR, when the band gap wavelength is 10 nm shorter than the emission wavelength, it is insufficient as a window structure for COD countermeasures, but can be considered as a region that has the effect of changing the beam shape. For example, in the case of a light emitting section with an emission wavelength of 630 nm, if the band gap wavelength of the emission layer or guide layer in the vicinity of the region near the light emitting end face is 620 nm or less, the effect of expanding the beam shape can be obtained. On the other hand, the region where the current is injected and emits light (gain region) and the region where the band gap wavelength does not change even if no current is injected are not the adjustment region AR in this embodiment, but are non-adjusted regions. In addition, as an example of a method for confirming the band gap wavelength of the adjustment region AR, there is photoluminescence measurement. This is a method of measuring the light generated in the process of relaxing a material in an excited state to a stable state by applying light with energy higher than the band gap energy from the outer surface. If the photoluminescence wavelength near the end face is 10 nm or more shorter than the emission wavelength, or if the photoluminescence intensity decreases due to increased intermixing, it can be assumed that the material has the characteristics of the adjustment region AR in this embodiment.

(Method of manufacturing a semiconductor laser device)
Next, a description will be given of an example of a method for manufacturing the semiconductor laser device LD1 according to the first embodiment. Figures 8 to 13 are cross-sectional views of a main part showing an example of steps included in the method for manufacturing the semiconductor laser device LD1.

The method for manufacturing the semiconductor laser device LD1 according to the first embodiment mainly includes the steps of (1) forming an n-type cladding layer 2 on a GaAs substrate 1, (2) forming a mask MK, (3) forming the light-emitting layers EL11, EL12, and EL13 by selective growth, (4) forming a p-type cladding layer 3 and a cap layer 4 (including a step of removing the mask MK), (5) forming an adjustment region AR, and (6) forming a ridge R and electrodes and singulating the device.

(1) Step of forming n-type cladding layer 2 on GaAs substrate 1 First, as shown in FIG. 8, an n-type cladding layer 2 having a thickness of about 2 μm is epitaxially grown on a GaAs substrate 1 by MOCVD. The raw material gas used is trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), or the like. 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), where x=1 and y=0.5. In this embodiment, the In composition y is adjusted to 0.5 in consideration of lattice matching with the GaAs substrate 1. In addition, it is preferable that the composition ratio (x:1-x) of Al and Ga is larger than x, and (x:1-x)=1:0 may be used.

(2) Step of Forming Mask MK Next, after forming the n-type cladding layer 2, a silicon oxide ( _SiO2 ) film functioning as a mask MK is formed by CVD on the surface of the n-type cladding layer 2. This _SiO2 film is a film that inhibits crystal growth, and for example, a silicon _nitride ( _Si3N4 ) film may be used.

After forming the _SiO2 film, as shown in Fig. 9, a plurality of stripe-shaped openings (three openings in this embodiment) are formed in the _SiO2 film by using a lithography method. The widths of the three openings (corresponding to the size in the x direction (horizontal direction)) are different from each other, and are formed so as to become wider from the left side in Fig. 9. That is, the widths of the openings are, for example, EW11 (20 μm), EW12 (30 μm), and EW13 (40 μm). Also, the mask widths are, for example, MK1 (50 μm), MK2 (25 μm), MK3 (15 μm), and MK4 (5 μm).

(3) Step of forming light-emitting layers EL11, EL12, EL13 by selective growth Next, as shown in Fig. 10, light-emitting layers EL11, EL12, EL13 consisting 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 opening region of the mask MK. These layers are formed by a method called selective growth. The selective growth method utilizes the fact that no crystals are formed on the upper surface of the mask MK, and forms a desired film only in the opening region of the mask MK.

The crystal grown by the selective growth method is (Al _x Ga _1-x ) _1-y In _y P (0≦x<1, 0<y<1), and the source gas used is trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), or the like.

By selective growth, the lower n-side guide layer nGL, barrier layer BL, quantum well layer QW, barrier layer BL, and upper p-side guide layer pGL are deposited in the order shown in FIG. 4 in each region of the opening of the mask MK. In the region (EW11) of the mask MK shown in FIG. 9 where the opening is the narrowest, the light-emitting layer EL11 is formed as shown in FIG. 10, and in the region (EW13) of the mask MK where the opening is the widest, the light-emitting layer EL13 is formed. When the light-emitting layer EL is formed by selective growth, a gentle slope is formed on the side of the light-emitting layer EL, but this is omitted in the drawing. Also, FIG. 4 shows the case of a single quantum well layer QW, but a multiple quantum well layer having multiple quantum wells may be used.

In the process of forming the light emitting layer EL, (Al _x Ga _1-x ) _1-y In _y P is formed by selective growth, with the values of x and y indicating the composition ratio of each element being set as follows. That is, in this embodiment, the guide layer GL and the barrier layer BL have x=0.7 and y=0.5. In addition, the quantum well layer QW is grown without supplying the source gas TMA, and is made of GaInP that does not contain Al (i.e., x=0).

The guide layer GL is sometimes called an SCH (Separated Confinement Heterostructure) layer or a confinement layer, and 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.

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 about 50 nm to about 500 nm for red lasers, and in this embodiment, the total thickness is about 100 nm.

The thickness ET of the light-emitting layer EL formed by selective growth differs for each light-emitting layer EL. That is, the size of the opening in the mask MK causes differences in the thickness of the selectively grown light-emitting layer EL, 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 (see Figure 2): ET11 (104 nm) > ET12 (92 nm) > ET13 (80 nm).

As described above, when the light-emitting layer EL is deposited by selective growth in different opening regions of the mask MK, 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 (i) to (iv).

(i) In the selective growth method, since no film growth occurs on the surface of the mask MK, the source gas supplied to the surface of the mask MK migrates 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) In the opening region of the mask MK adjacent to the mask MK with a large surface area, a larger amount of source gas moves to the opening, and the concentration of the source gas at the opening becomes higher. Also, if the opening of the mask MK is smaller, the concentration of the source gas becomes higher. (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.

In addition, the above embodiment is not limited to this, and a portion of the lower n-side guide layer nGL may be formed on 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 selective growth of the lower n-side guide layer nGL. In addition, 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.

(4) Step of forming p-type cladding layer 3 and cap layer 4 (including step of removing mask MK)
Next, as shown in Fig. 11, the mask MK is removed. Then, as shown in Fig. 12, a p-type cladding layer 3 having a thickness of about 1.7 µm is epitaxially grown by MOCVD, and the source gas used is trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), or the like. The composition of the p-type cladding layer 3 is (Al _x Ga _1-x ) _1-y In _y P (0<x≦1, 0<y<1), where x=1 and y=0.5. Next, GaAs is formed on the upper surface of the p-type cladding layer 3 as a cap layer 4 having a thickness of 300 nm.

The process of forming the p-type cladding layer 3 may include a step of forming an etch stop layer (not shown). The etch stop layer functions as an etch stop layer when the p-type cladding layer 3 is etched to form the ridge R in the subsequent step (6).

13, a silicon oxide ( _SiO2 ) film functioning as a mask MK is formed by CVD on the surface of the cap layer _4. Instead of this SiO2 film, a material capable of protecting the semiconductor surface in a heat treatment process, such as a silicon _nitride ( _Si3N4 ) film, may be used.

After forming the mask MK, as shown in FIG. 13, an opening is formed in the mask MK using lithography. This opening is formed so as to open the region corresponding to the light emitting end face. In the figure, the dashed line P indicates the cleavage position of the wafer when forming the element, and is the position that becomes the resonator end face when the element is separated. Then, in this embodiment, zinc (Zn) is mixed in up to the p-type cladding layer 3 and the light emitting layer EL using a method such as thermal diffusion or ion implantation at about 600° C. Alternatively, zinc (Zn) may reach the n-type cladding layer 2. The region where zinc (Zn) is mixed is the region that functions as the adjustment region AR.

At this time, by changing the size of the opening of the mask MK for each of the light-emitting portions EM11, EM12, and EM13, the lengths ARL11, ARL12, and ARL13 of the adjustment region AR in the resonator direction can be made different for each of the light-emitting portions EM11, EM12, and EM13.

The vertical dashed line P shown in FIG. 13 corresponds to the location that will be divided by cleavage during the subsequent singulation process in step (6).

(6) Step of forming ridge R and electrodes and dividing Next, the p-type cladding layer 3 is etched to form the ridge groove RG shown in FIG. 2, to form ridges R extending in the cavity direction for each of the light-emitting layers EL11, EL12, and EL13.

Then, although not shown in Fig. 2 for simplicity, a passivation oxide film such as _SiO2 is formed, and an opening is provided in the oxide film on the top of the ridge using photolithography and etching techniques, and an electrode is formed on the opening. After that, the GaAs substrate is cleaved, and an end face coating is formed on the cleaved surface. Through these steps, the semiconductor laser device LD1 shown in Fig. 2 and Fig. 3 is formed.

In this manner, 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.

(effect)
In the region on the light emitting end face side, an adjustment region AR is provided for adjusting (correcting) the beam shapes of the laser beams λ11, λ12, and λ13 emitted from the light emitting units EM11, EM12, and EM13, and the length ARL of the adjustment region AR in the resonator direction is adjusted for each light emitting unit EM, thereby suppressing the variation in the vertical beam shape (NFP) of each laser beam propagating in the optical waveguide. Furthermore, it becomes possible to align the spread angle of the beam shape (FFP) of the laser beam emitted from the light emitting end face.

This enables further improvements in visibility and image quality, such as a wide color gamut, high resolution, and wide viewing angle. In other words, in the first embodiment, a semiconductor laser device that contributes to improving visibility and image quality can be provided.

[Embodiment 2]
(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 concentration distribution of zinc (Zn) in the adjustment region AR2 is different. Therefore, unless otherwise specified, the following mainly describes the differences from the first embodiment, and the same description will be omitted.

Figure 14 shows (a) a top view and (b) a cross-sectional view of the essential parts of the configuration of a semiconductor laser device LD2 according to embodiment 2. In (b) the cross-sectional view of the essential parts, a cross-sectional view in the resonator direction (y direction) of three light-emitting layers EL21, EL22, and EL23 is shown.

In the second embodiment, as in the first embodiment, the adjustment region AR2 is a region in which the band gap energy of the light-emitting layer EL on the light-emitting end surface side is widened and the equivalent refractive index of the optical waveguide is relatively small. In other words, zinc (Zn) is mixed into the adjustment region AR2 to widen the band gap energy of the light-emitting layer EL and relatively reduce the equivalent refractive index of the optical waveguide.

In this embodiment, as shown in FIG. 14, the lengths ARL21, ARL22, and ARL23 of the adjustment regions AR21, AR22, and AR23 in the resonator direction are different from one another, and the adjustment region AR2 in this embodiment has a gradient in the concentration of zinc (Zn) mixed into the adjustment region AR2. The zinc (Zn) concentration is formed so that it gradually increases from the gain region on the light reflecting end face side toward the light emitting end face in the resonator direction. In other words, the band gap energy is gradually expanded from the gain region toward the light emitting end face. This allows the equivalent refractive index of the optical waveguide to be gradually reduced.

15 is an explanatory diagram for explaining the distribution of laser light near the optical waveguide in the semiconductor laser device LD2 according to the second embodiment. In FIG. 15, the upper part shows the equivalent refractive index and zinc (Zn) concentration distribution in the resonator direction, and the lower part shows the simulation results showing the distribution of laser light. Also, (a) shows the case where there is no gradient in the zinc (Zn) concentration in the adjustment region AR, and (b) shows the case where there is a gradient in the zinc (Zn) concentration in the adjustment region AR2 according to the second embodiment. In the lower part of FIG. 15, the white region between the black regions corresponds to the region of the light emitting layer EL, and indicates that the light intensity is strong. Also, the black region corresponds to the optical waveguide OW, including a part of the cladding layers 2 and 3. In both FIG. 15(a) and (b), the right side of the figure is the light emitting end surface side.

As can be seen from FIG. 15(a), when there is no gradient in the zinc (Zn) concentration and the equivalent refractive index changes sharply at the boundary of the adjustment region AR (i.e., the equivalent refractive index drops sharply), light is scattered near the boundary (dotted line area). On the other hand, as shown in FIG. 15(b), if the zinc (Zn) concentration is gradient and the concentration is gradually increased toward the light-emitting end face, the equivalent refractive index can also be gradually decreased. As a result, the scattering of light seen in FIG. 15(a) is suppressed, and it is possible to suppress the loss of light propagating through the optical waveguide OW. This can increase the output efficiency of the semiconductor laser device.

(Method of manufacturing a semiconductor laser device)
The concentration distribution of zinc (Zn) in the adjustment region AR2 as described above can be formed in the step (5) (FIG. 13) of forming the adjustment region AR described in the embodiment 1. That is, when zinc (Zn) is diffused by a method such as thermal diffusion, the desired concentration distribution can be obtained by adjusting the temperature and time.

The other steps are the same as those in the manufacturing process shown in embodiment 1, so their explanation will be omitted.

(effect)
The semiconductor laser device LD2 according to the second embodiment also has the same effects as the semiconductor laser device LD1 according to the first embodiment. In the semiconductor laser device LD2 according to the second embodiment, the change rate of the equivalent refractive index in the adjustment region AR2 is gradually changed, so that in addition to being able to suppress the variation in the beam shape of the laser light, it is also possible to suppress the loss of the light propagating through the optical waveguide OW.

[Embodiment 3]
(Configuration of Semiconductor Laser Device)
The semiconductor laser device LD3 according to the third embodiment has the same configuration as the semiconductor laser device LD1 according to the first embodiment, except for the difference in the configuration of the adjustment region AR3. Therefore, unless otherwise specified, the following mainly describes the differences from the first embodiment, and the same description will be omitted.

Figure 16 shows (a) a top view of the essential parts and (b) a cross-sectional view of the essential parts, illustrating the configuration of a semiconductor laser device LD3 according to embodiment 3. In (b) the cross-sectional view of the essential parts, a cross-sectional view in the resonator direction (y direction) of three light-emitting layers EL31, EL32, and EL33 is shown.

In the adjustment region AR3 in the third embodiment, the film thicknesses Et31, Et32, and Et33 of the light-emitting layer EL in the adjustment region AR3 are thinner than the film thicknesses ET31, ET32, and ET33 of the light-emitting layer EL in the gain region. In other words, by making the film thickness Et of the light-emitting layer EL in the adjustment region AR3 thinner, the band gap energy of the light-emitting layer EL is widened and the equivalent refractive index of the optical waveguide is relatively small.

In other words, because the thickness of the quantum well layer in the light-emitting layer EL in the adjustment region AR3 is thinner than the thickness of the quantum well layer in the gain region, the quantum level of the carriers in the quantum well layer becomes higher, and the band gap energy relatively expands. In addition, by reducing the thickness of the quantum well layer and the guide layer, the equivalent refractive index of the optical waveguide decreases, and the degree of light confinement can be relatively weakened.

Also in this embodiment, as shown in FIG. 16, the lengths ARL31, ARL32, and ARL33 of the adjustment regions AR31, AR32, and AR33 in the resonator direction are different from each other.

It is also possible to gradually reduce the film thickness Et of the light-emitting layer EL in the adjustment region AR3 in the resonator direction toward the light-reflecting end face. By forming a gradient in the film thickness Et of the light-emitting layer EL in the resonator direction, it is possible to suppress the abrupt change in the equivalent refractive index at the boundary between the adjustment region AR3 and the gain region, as described in embodiment 2. In this way, by providing a gradient in the film thickness, it is possible to suppress losses due to light scattering, as in embodiment 2.

(Method of manufacturing a semiconductor laser device)
The adjustment region AR3 in the third embodiment can be formed in the manufacturing process in the first embodiment, in the process (2) of forming a mask MK (FIG. 9) and the process (3) of forming the light-emitting layers EL11, EL12, and EL13 by selective growth (FIG. 10). In addition, the manufacturing process in the first embodiment, in which the adjustment region AR is formed (FIG. 13), is omitted in the third embodiment. Unless otherwise specified, the following mainly describes the points that are different from the first embodiment, and the same description will be omitted. In addition, the other steps are the same as the manufacturing process shown in the first embodiment, and therefore the description thereof will be omitted.

(2) Step of forming mask MK In the first embodiment, stripe-shaped openings extending in the y direction are formed on the mask MK so that openings are formed in the region where the light-emitting layer EL is formed (see FIG. 9), but in the third embodiment, continuous openings are provided in the mask MK along the x direction on both the light-emitting end face side and the light-reflecting end face side (for example, the portion of the adjustment region AR shown in FIG. 3 corresponds to the opening where the mask MK is not provided). That is, in addition to the stripe-shaped openings, large continuous openings including regions corresponding to the adjustment region AR3 and the rear region ARR3 are provided along the x direction on both the light-emitting end face side and the light-reflecting end face side.

(3) Step of forming the light-emitting layer EL by selective growth The openings of the mask MK on the light-emitting end face side and the light-reflecting end face side formed in step (2) are wide openings that are continuous in the x direction. That is, the light-emitting layer EL is formed as a film that is continuous in the x direction on the light-emitting end face side and the light-reflecting end face side. Therefore, when the light-emitting layer EL is selectively grown, the film thickness Et of the light-emitting layer EL in the region corresponding to the adjustment region AR3 and the rear region ARR3 can be formed thin. The reason why different film thicknesses are formed depending on the size of the opening of the mask MK has been explained in the first embodiment, so it will not be repeated here.

In this way, the thickness Et of the light-emitting layer EL in the adjustment region AR3 can be made thinner than the thickness ET of the light-emitting layer EL in the gain region.

In the manufacturing process described above, the light-emitting layer EL of the gain region and the light-emitting layer of the adjustment region AR are formed simultaneously, but the light-emitting layer EL of the gain region and the light-emitting layer of the adjustment region AR may be formed separately in separate processes.

(effect)
The semiconductor laser device LD3 according to the third embodiment has the same effects as the semiconductor laser device LD1 according to the first embodiment.

[Fourth embodiment]
(Configuration of Semiconductor Laser Device)
The semiconductor laser device LD4 according to the fourth embodiment has the same configuration as the semiconductor laser device LD1 according to the first embodiment, except that a rear region ARR4 is provided on the light reflecting end face side with a configuration similar to the adjustment region AR formed on the light emitting end face side, and the length ARRL of the rear region ARR4 in the resonator direction is made different for each light emitting portion EM. Therefore, unless otherwise specified, the following mainly describes the differences from the first embodiment, and the same description will be omitted.

Figure 17 is a top view of the essential parts showing the configuration of the semiconductor laser device LD4 according to the fourth embodiment. Figure 18 is an explanatory diagram showing the operation of the semiconductor laser device according to the fourth embodiment.

In the fourth embodiment, as in the first, second and third embodiments described above, an adjustment region AR4 is formed on the light emitting end surface side. The adjustment region AR4 can be selected from the configurations of the adjustment region AR described in the first, second and third embodiments described above. The adjustment region AR4 formed on the light emitting end surface side includes adjustment regions AR41, AR42 and AR43 formed for each light emitting portion EM. As in the other embodiments described above, the lengths ARL of the adjustment regions AR41, AR42 and AR43 in the resonator direction are different from one another, and have the relationship ARL41>ARL42>ARL43.

The rear region ARR4 formed on the light reflecting end surface side includes rear regions ARR41, ARR42, and ARR43 formed for each light emitting portion EM. The lengths ARRL of the rear regions ARR41, ARR42, and ARR43 in the resonator direction are different from one another, and have the relationship ARRL41<ARRL42<ARRL43.

As in the other embodiments, differences in beam shape due to differences in the wavelength of the laser light can be adjusted (corrected) by the adjustment region AR4 formed on the light-emitting end face side, thereby suppressing the differences in beam shape. However, the output characteristics of the laser light shown in FIG. 18 vary depending on the length of the gain region in which the adjustment region AR is not formed, and if the length of the gain region differs, variations will occur in the threshold value at which the laser light oscillates and the output efficiency.

Therefore, in this embodiment, in order to suppress the variation in the output characteristics in each light-emitting unit EM, the length of the gain region is made uniform. That is, the length ARRL of the rear regions ARR41, ARR42, and ARR43 in the resonator direction is changed to make the length of the gain region uniform. In other words, the difference in the length of the gain region that occurs based on the length ARL of each of the adjustment regions AR4 formed on the light-emitting end face side is adjusted by the rear region ARR4. Therefore, in each light-emitting unit EM, the length ARL of the adjustment region AR4 on the light-emitting end face side and the length ARRL of the rear region ARR4 on the light-reflecting end face side are formed to be different.

(Method of manufacturing a semiconductor laser device)
The rear region ARR41 can be formed, for example, in the step (5) (FIG. 13) of forming the adjustment region AR described in the first embodiment. That is, this can be realized by adding openings for forming the rear regions ARR41, ARR42, and ARR43 to a mask MK used when diffusing zinc (Zn) by a method such as thermal diffusion. The other steps are the same as the manufacturing steps described in the first embodiment, and therefore the description thereof will be omitted.

(effect)
The semiconductor laser device LD4 according to the fourth embodiment also has the same effects as the semiconductor laser device LD1 according to the first embodiment. In the semiconductor laser device LD4 according to the fourth embodiment, the length ARRL of the rear region ARR4 on the light reflecting end face side is made different for each light-emitting portion EM, so that the length of the gain region can be made uniform for each light-emitting portion EM, and it is possible to suppress the variation in output characteristics between the beams of laser light.

The invention made by the present inventors 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 gist of the invention. For example, the above embodiments have been described with respect to a semiconductor laser device in the red region, but the present invention can also be applied to semiconductor laser devices in other color regions as long as they are in the visible light region other than red and can be fabricated using the same material system. Furthermore, the above embodiments have been described based on a ridge structure as the optical waveguide structure, but other optical waveguide structures may also be used, such as embedded type, high mesa type, channel type, and other structures. Furthermore, the respective embodiments may be combined as appropriate.

In addition, in the above embodiment, a case has been described in which three or four laser beams with different wavelengths are emitted from one semiconductor laser device, but the number of emitted laser beams may be five or more.

Even if a specific numerical example is stated, the numerical value may be greater than or less than the specific numerical value, unless it is theoretically clearly limited to that numerical value. In addition, when referring to components, it means "B containing A as a main component," etc., and does not exclude embodiments containing other components.

Also, the light-emitting unit EM that emits one wavelength may not be provided with an adjustment area AR, and the light-emitting unit EM that emits the other wavelengths may be provided with an adjustment area AR to suppress variation in output characteristics between beams of laser light. Furthermore, the above embodiment includes the following forms.

(Appendix 1)
A substrate;
a first clad layer of a first conductivity type and a second clad layer of a second conductivity type laminated on a main surface of the substrate;
a light emitting layer formed on a first surface parallel to the main surface of the substrate, the light emitting layer being sandwiched between the first cladding layer and the second cladding layer;
At least two first and second light emitting sections formed in the light emitting layer and emitting laser light;
an optical waveguide including the light emitting layer, the first cladding layer, and a part of the second cladding layer, the optical waveguide extending in a resonator direction;
an adjustment region that adjusts the beam shape of the laser light emitted from the first and second light-emitting units;
the adjustment region is formed at least on the light emitting end surface side of the optical waveguide, and includes a first adjustment region formed in the first light emitting portion and a second adjustment region formed in the second light emitting portion, the first and second adjustment regions being formed in the light emitting layer corresponding at least to the first and second light emitting portions, respectively;
a first wavelength of the first laser light emitted from the first light-emitting unit is different from a second wavelength of the second laser light emitted from the second light-emitting unit;
A semiconductor laser device, wherein the first and second adjustment regions have different lengths in the resonator direction.

(Appendix 2)
In the semiconductor laser device according to claim 1,
the first wavelength is longer than the second wavelength;
A semiconductor laser device, wherein a length of the first adjustment region in the resonator direction is longer than a length of the second adjustment region in the resonator direction.

(Appendix 3)
In the semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the band gap energy of each of the first and second adjustment regions is wider than the band gap energy of each of the light emitting layers located at a central portion in the resonator direction.

(Appendix 4)
In the semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the equivalent refractive index of each of the first and second adjustment regions is lower than the equivalent refractive index in each of the waveguides located at the center in the resonator direction.

(Appendix 5)
In the semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the thicknesses of the light-emitting layers in the first and second adjustment regions are different from the thicknesses of the light-emitting layers located in a central portion in the resonator direction.

(Appendix 6)
In the semiconductor laser device according to claim 5,
a thickness of each of the light-emitting layers in the first and second adjustment regions is thinner than a thickness of each of the light-emitting layers located in a central portion in the resonator direction.

(Appendix 7)
In the semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the composition of each of the light emitting layers in the first and second adjustment regions is different from the composition of each of the light emitting layers located in a central portion in the resonator direction.

(Appendix 8)
8. The semiconductor laser device according to claim 7,
The first and second adjustment regions are regions in which zinc (Zn) is mixed at a higher concentration than the central portion in the resonator direction,
The concentration of the zinc is gradually decreased from the light emitting end face toward the resonator.

(Appendix 9)
In the semiconductor laser device according to claim 1,
a light reflecting end face formed on the opposite side of the light emitting end face in the resonator direction, and on the light reflecting end face side, regions having the same configuration as the first and second adjustment regions are formed with different lengths in the resonator direction.

(Appendix 10)
In the semiconductor laser device according to claim 1,
a gain region disposed in a central portion of the waveguide has a length in a resonator direction that is the same in the first and second light emitting portions.

(Appendix 11)
In the semiconductor laser device according to claim 1,
The light emitting layer is made of a crystal layer of ( _{AlxGa1 -x} ) _{1- yInyP} (0≦x<1, 0<y<1), and the laser light is a laser light in the red region.

AR Beam shape adjustment region ARL Length of the adjustment region in the cavity direction ARR Rear region ARRL Length of the rear region in the cavity direction BL Barrier layer EM Light emitting portion EL Light emitting layer ER Light emitting region EW Width of the light emitting layer ET Thickness of the light emitting layer OW Optical waveguide region R Ridge 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 (11)

A substrate;
a first clad layer of a first conductivity type and a second clad layer of a second conductivity type laminated on a main surface of the substrate;
a light emitting layer formed on a first surface parallel to the main surface of the substrate, the light emitting layer being sandwiched between the first cladding layer and the second cladding layer;
At least two light emitting sections, a first light emitting section and a second light emitting section, are formed in the light emitting layer and emit a laser beam in a single transverse mode ;
an optical waveguide including the light emitting layer, the first cladding layer, and a part of the second cladding layer, the optical waveguide extending in a resonator direction;
an adjustment region that adjusts a variation in a vertical divergence angle in a beam shape of the laser light emitted from the first and second light emitting units;
having
a beam wavelength difference between the first light-emitting unit and the second light-emitting unit is 1 to 30 nm;
the adjustment region is formed at least on the light emitting end surface side of the optical waveguide, and includes a first adjustment region formed in the first light emitting portion and a second adjustment region formed in the second light emitting portion, the first and second adjustment regions being formed in the light emitting layer corresponding at least to the first and second light emitting portions, respectively;
a first wavelength of the first laser light emitted from the first light-emitting unit is longer than a second wavelength of the second laser light emitted from the second light-emitting unit;
a length of the first adjustment region in the resonator direction is longer than a length of the second adjustment region in the resonator direction;
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), the laser light is a red laser light having a wavelength λ of 600≦λ≦700 nm,
In the first and second light emitting sections, the thickness of the light emitting layer is thicker and the length of the adjustment region is longer as the wavelength of the laser light is larger.
Semiconductor laser device. The semiconductor laser device according to claim 1, wherein the band gap energy of each of the first and second adjustment regions is wider than the band gap energy of each of the light-emitting layers located at the center in the resonator direction. The semiconductor laser device according to claim 1, wherein the equivalent refractive index of each of the first and second adjustment regions is lower than the equivalent refractive index in each of the waveguides located at the center in the resonator direction. The semiconductor laser device according to claim 1, wherein the thickness of each of the light-emitting layers in the first and second adjustment regions is different from the thickness of each of the light-emitting layers located in the center in the resonator direction. 5. The semiconductor laser device according to claim 4 , wherein the thickness of each of the light emitting layers in the first and second adjustment regions is thinner than the thickness of each of the light emitting layers located at a central portion in the resonator direction. The semiconductor laser device of claim 1, wherein the composition of each of the light-emitting layers in the first and second adjustment regions is different from the composition of each of the light-emitting layers located in the center in the resonator direction. The first and second adjustment regions are regions mixed with zinc (Zn),
7. The semiconductor laser device according to claim 6 , wherein the concentration of said zinc is gradually decreased from said light emitting end face toward said resonator. The semiconductor laser device according to claim 1, further comprising a light reflecting end face formed on the opposite side of the light emitting end face in the resonator direction, and regions having the same configuration as the first and second adjustment regions are formed on the light reflecting end face side, each with a different length in the resonator direction. 2. The semiconductor laser device according to claim 1, wherein a length in the resonator direction of a gain region disposed in a central portion of said optical waveguide is the same in said first and second light emission portions. 2. The semiconductor laser device according to claim 1, wherein the first light emitting portion and the second light emitting portion have the same distance from a lower surface of each light emitting layer to an upper surface of the substrate. 2. A method for manufacturing a semiconductor laser device according to claim 1, comprising the steps of:
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;
(3) forming the light emitting layer by selective growth;
(4) forming a p-type cladding layer as the second cladding layer and a capping layer;
and (5) forming a ridge and an electrode as a part of the optical waveguide and dividing the optical waveguide into individual pieces.
The step (4) further includes a step of removing the mask.
A method for manufacturing a semiconductor laser device.