Patent Application
20220209507
The present invention relates to a semiconductor laser device and a method of manufacturing the semiconductor laser device.
In recent years, a market of display apparatuses including projectors using semiconductor laser devices (hereinafter simply refers to semiconductor LD or LD) has been expanding.
Moreover, in recent years, reality technologies such as augmented reality (AR), virtual reality (VR), mixed reality (MR) and substitutional reality (SR) have found practical application in various fields. These technologies have been used to commercialize display apparatuses such as head mount display (HMD), head-up display (HMD) and AR glasses.
For example, a head mounted display (HMD) is known to involve the technologies including a light source having three colors of laser beams (red, green and blue), MEMS (Micro Electro Mechanical Systems) that creates an image as a spatial modulator element for image display and a waveguide that transmits the image to project it onto, for example, retinas. This system using MEMS is noted for its advantages in wide color gamut, high resolution and wide viewing angle. Meanwhile, in order to achieve high performance images with a wide color gamut, high resolution and a wide viewing angle, multi-beam LDs (multiple semiconductor laser devices) are used for each RGB color; however, each of the colors has the same wavelength. If all the beams constituting each color emit light having the same wavelength, the image quality is degraded due to the interference of the laser beams.
Patent reference 1 discloses a multi-wavelength semiconductor laser device that is capable of oscillating laser with multiple wavelengths in the device. The Patent Document 1 does not describe the specific wavelength of the laser beam; however, it describes the laser beam in the infrared range, which is other than RGB color region because the laser device is an AlGaAs-based quantum well laser. It also describes that the first and second quantum well active layers, which oscillate at different wavelengths, have the same composition and different well widths (physical thickness).
Patent reference 1: JP-A-1993-082894
In order to improve image quality (resolution and a frame rate), transverse single-mode LDs with a monolithic structure that independently drives multi-emitters (multiple light-emitting sections) at a narrow pitch are requested. Unfortunately, transverse single-mode lasers have a narrow wavelength spectrum and high interference, posing a problem of image quality degradation.
In addition, for high performance display devices, it is necessary to suppress the interference of laser beam and further improve visual sensitivity and image quality such as a wide color gamut, high resolution and a wide viewing angle. For the further improvement of the visual sensitivity and image quality, for example, the light source using laser beams of RGB three colors is desirably a semiconductor laser device that can emit multiple laser beams with different oscillation wavelengths in each color from the viewpoint of suppressing the image quality degradation caused by the interference of laser beams as described above.
In Patent reference 1, in order to oscillate lasers of multiple wavelengths in the same device (the same chip), crystal layers having different thicknesses are selectively grown for each of the different wavelengths of laser to be oscillated. Specifically, the crystal layers that oscillate the respective lasers include an upper n-type cladding layer, a quantum well active layer, a p-type cladding layer and a cap layer, which are selectively grown in sequence to form a stripe-patterned crystal structure. This configuration results in not only different oscillated laser positions due to different heights of the quantum well active layer, but also large differences in the thickness (height) of the striped-patterned crystal layer. Since the cladding layer is usually formed in the order of several microns, the difference in thickness (height) of the striped-patterned crystal layer is more pronounced. In addition to the different heights of the light-emitting points, the large differences in the heights of the striped-patterned crystal layers pose practical problems, such as the complexity of the structure for supplying power to the laser chip.
One method of mounting a laser chip includes a junction down (J-down) mounting method in which the active layer side (i.e., stripe or ridge side) is bonded to the stem or other base, instead of the substrate side of the device being bonded thereto. Semiconductor laser devices in the red wavelength band have a larger temperature dependence on the characteristics such as threshold and efficiency due to their physical properties of the material than semiconductor laser devices in the infrared wavelength band. Hence, heat dissipation is important to achieve stability of the characteristics and high optical output, thereby the J-down mounting method, which enables heat dissipation from the active layer side to the submount, is often adopted for semiconductor laser devices in the red wavelength band. However, if the stripe heights differ greatly in the laser regions of the respective wavelengths, the cladding layer will be distorted during the J-down mounting, resulting in problems such as reduced device reliability. Furthermore, during the J-down mounting, problems may arise such as tilting of the device due to differences in stripe (ridge) height, variation in solder wetting and poor bonding at the lower height ridges. In addition, the different height of each stripe (ridge) may cause a problem in the formation of openings for contacts between the electrodes to be formed on the ridge and the p-type cladding layer. In this way, the significant difference in the height of the stripes (ridges) causes practical problems including those during mounting.
It is an object of the present invention that provides a semiconductor laser device to suppress a practical problem caused by the difference in the height in the chip thereof. The other problems or new features will be described in the present specification and drawings.
The semiconductor laser device includes:
a substrate having a main surface;
a first cladding layer with a first conductive type and a second cladding layer with a second conductive type different from the first conductive type, which are stacked over the main surface of the substrate; and
a light-emitting layer that is formed between the first cladding layer and the second cladding layer, and is formed on a first surface parallel to the main surface of the substrate;
wherein the light-emitting layer has a plurality of light-emitting regions emitting laser beams in a red range; and
values of peak wavelengths in an optical spectrum of the laser beams emitted from the light-emitting regions, are different in accordance with the thickness of the light-emitting layer from the first surface.
The semiconductor laser device in accordance with one embodiment of the present invention is capable of providing a semiconductor laser device that suppresses a practical problem caused by a difference in the height in the chip thereof.
The semiconductor laser device according to the present embodiment will be described with reference to the drawings. In the specifications and drawings, the same components or the corresponding components are assigned to the same sign, and duplicate explanations are omitted. In the drawings, some configuration may be omitted or simplified for convenience of explanation. In addition, at least part of each embodiment and each variation may be suitably combined with each other. It is noted that different signs are assigned to the components when they are necessary to be described individually due to the reason including different their formed locations or the like, for example, the light-emitting sections EM11, EM12, EM13; however, the single sign may be assigned to the component when it is described as a function the component inherently has, for example, the light-emitting section EM.
As shown in
The light-emitting section EM emits laser beam in the red range (wavelength λ=600 nm to 700 nm). The light-emitting sections EM001, EM002, EM003 and EM004 preferably emit laser beam having wavelengths of λ001 to λ004 respectively, which are different from each other in a range of the red range. It is noted that all of the wavelengths λ of the laser beam emitted from the light-emitting section EM does not have to be different from each other; however, at least one wavelength needs to be different from the others. The wavelength λ shown here refers to the value of the peak wavelength in the optical spectrum of the laser beam emitted from the light-emitting section EM. The same also applies to the other embodiments 1, 2 shown below.
The light-emitting layers EL001, EL002, EL003 and EL004, which are located in the light-emitting sections EM001, EM002, EM003 and EM004 respectively, are constituted by a crystal layer of (AlxGa1-x)1-yInyP (0≤x<1, 0<y<1) formed on the same main surface. The light-emitting layers EL001, EL002, EL003 and EL004 have different thicknesses EH of the crystal layer. It is noted that all of the thicknesses EH of the light-emitting layers EL do not have to be different from each other; however, at least one thickness EH of the light-emitting layer EL needs to be different from the others. Here, the thickness EH of the crystal layer is expressed by the relationship EH001<EH002<EH003<EH004. In this way, the value of the wavelength λ of the emitted laser beam also differs in accordance with the thickness of the light-emitting layer EL.
In
The semiconductor laser device LD01 according to another embodiment 1 includes four light-emitting sections EM01, EM02, EM03 and EM04, which emit laser beam. Each of the light-emitting sections EM01, EM02, EM03 and EM04 has the respective width (EW01, EW02, EW03, EW04) of the light-emitting layers EL, the width being different in size each other. In addition, the light-emitting layers EL01, EL02, EL03 and EL04 have different thicknesses EH of the crystal layers in the respective light-emitting sections EM01, EM02, EM03 and EM04. The light emitting sections EM01, EM02, EM03 and EM04 emit laser beam having different wavelengths 2
As shown in
The semiconductor laser device LD01 includes four light-emitting sections EM01, EM02, EM03 and EM04. Each light-emitting section EM has the respective width EW (corresponding to the size in the x direction (horizontal direction) in
Each of the light-emitting sections EM01, EM02, EM03, EM04 includes a ridge 4 as a current narrowing structure (current injection structure) that is formed by removing a portion of the p-type cladding layer 3 with etching, and as a structure for confining light in the transverse direction (the x direction in
Applying a current between the n-side electrode 7N and A-side electrode 7P causes laser beams (wavelength: 600 nm to 700 nm) in the red range to be emitted from the light-emitting regions ER01, ER02, ER03 and ER04, which are formed in the four light-emitting sections EM01, EM02, EM03 and EM04, respectively. The laser beams emitted from the light-emitting regions ER have different wavelengths in the respective light-emitting sections EM. Specifically, the wavelength 2, is expressed by the relationship EM01<EM02<EM03<EM04. For example, laser beam having a wavelength of 640 nm is emitted from EM01, 643 nm from EM02, 646 nm from EM03, and 649 nm from EM04, respectively. In this way, the value of wavelength 2, increases, as the thickness EH of the light-emitting layer EL increases.
As the detail will be described later, the dashed line A (
Furthermore, the p-side electrode 7P formed on the top face of the ridge 4 may be formed with a different thickness for each of the light-emitting sections EM to compensate for the difference in the height of each of the light-emitting sections EM. This compensation allows the top face positions of the A-side electrodes 7P to be flush with each other in the light-emitting sections EM, as shown by the dashed line B. This makes it possible to achieve uniform solder wettability during the J-down mounting, preventing the chips from tilting. In addition, it can easily focus on the electrode positions corresponding to the respective light-emitting sections when the chip is mounted by mounting equipment through the image recognition of the chip.
The pitch interval between the center positions of the multiple light-emitting regions ER (or between the center positions of the ridges 4) in the transverse direction (x-direction in
As shown in
Upon the reference to the light-emitting layer EL in the present embodiment, the light-emitting layer EL is defined to be any one of the followings: the light-emitting layer EL includes all of the lower n-side guide layer nGL, the quantum well layer QW, the barrier layer BL and the upper p-side guide layer pGL described above; the light-emitting layer EL includes the quantum well layer QW and the barrier layer BL; or the light-emitting layer EL includes at least part of one of the p-type cladding layer 3 and the n-type cladding layer 2 in addition to the quantum well layer QW and the barrier layer BL.
Next, an example of the manufacturing method of the semiconductor laser device LD01 according to the other embodiment 1 will be described.
The manufacturing method of the semiconductor laser device LD01 according to another embodiment 1 mainly includes the steps of:
(1) forming an n-type cladding layer 2 on a GaAs substrate 1;
(2) forming a mask layer MK;
(3) forming light-emitting layers EL01, EL02, EL03 and EL04 by the selective growth method;
(4) forming a p-type cladding layer 3 and a cap layer 5 (including the step of removing the mask layer MK); and
(5) forming ridges and electrodes and then separating into a piece.
(1) Step to Form the n-Type Cladding Layer 2 on the GaAs Substrate 1
First, as shown in
Next, as shown in
After the SiO2 film being formed, multiple striped-patterned openings (four openings in the present embodiment) are formed in the SiO2 film using the lithography method, as shown in
Next, as shown in
The crystal grown by the selective growth method is (AlxGa1-x)1-yInyP (0≤x<1, 0<y<1). The raw material gases used include trimethylaluminum (TMA), trimethylgallium (TMG) and trimethylindium (TMI).
By the selective growth method, deposited are the lower n-side guide layer nGL, the quantum well layer QW, the barrier layer BL, the quantum well layer QW and the upper p-side guide layer pGL in sequence on the region through the openings of the mask layer MK as shown in
The step of forming the light-emitting layer EL includes forming (AlxGa1-x)1-yInyP by the selective growth method. The value of x and y, which indicate the composition ratio of elements is determined on the followings. The guide layer GL may be referred to a separated confinement hetero-structure (SCH) 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. Hence, the feed ratio of the raw material is adjusted such that the Al composition ratio (x) of the guide layer GL becomes smaller than that of the cladding layer 2 (3). For example, the feed amount of the raw material is adjusted such that the Al composition ratio (x) is highest in the cladding layer 2 (3), and lowers in the order of the guide layer GL, the barrier layer BL and the quantum well layer QW.
In the present embodiment, the composition ratio of the guide layer GL and the barrier layer BL is determined to be x=0.7 and y=0.5. In the growth of the quantum well layer QW, TMA of the raw material gas is not fed, thus the quantum well layer QW is made of GaInP, which contain no Al (i.e., x=0). The quantum well layer QW has a thickness in the range of 5 nm to 6 nm.
The light-emitting layer EL formed by the selective growth method functions as a core layer in the optical waveguide. The thickness of the light-emitting layer EL, which is dependent on the wavelength of each laser beam and the refractive index of each layer, is selected in the range between approximately 50 nm and approximately 500 nm for a red laser; in the present embodiment, the thickness thereof is approximately 100 nm in total.
Each of the light-emitting layers EL formed by the selective growth method has the different thickness EH. In other words, the size of the openings of the mask layer MK causes the thickness of the light-emitting layer EL to vary during the selective growth, making the thickness of the light-emitting layer EL thicker as the widths of the light-emitting layer EL is narrower. Specifically, the thickness EH is expressed by the relationship EH01<EH02<EH03<EH04.
As described above, depositing the light-emitting layer EL by the selective growth method on the region through the openings of the mask layer MK, which are different in size, causes the thickness of the light-emitting layer EL to vary. The mechanism is not clearly understood; however, it is inferred as described in the following (i)-(iv).
(i) In the selective growth method, layer growth does not occur on the surface of the mask layer MK; thereby the raw material gas fed to the surface of the mask layer MK migrates on the surface of the mask layer MK and moves to the region of the openings of the mask layer MK.
(ii) The amount of the migrating raw material gas increases as the surface area of the mask layer MK is larger.
(iii) A larger amount of raw material gas migrates to the region of the openings of the mask layer MK adjacent to the mask layer MK having a larger surface area, thus the concentration of the raw material gas in the openings becomes high. Furthermore, if the opening of the mask layer MK is smaller, the concentration of the raw material gas will be higher.
(iv) As a result, more raw materials are fed to the light-emitting layer EL04, which is formed on the region through the narrowest opening of the mask layer MK.
(4) Step of Forming the p-Type Cladding Layer 3 and the Cap Layer 5 (Including the Step of Removing the Mask Layer MK)
Next, as shown in
(5) Step of Forming Ridges and Electrodes and then Separating into a Piece
Next, as shown in
In this way, the layer deposited by the selective growth method in accordance with the present embodiment 1 is the light-emitting layer EL, which is a relatively thin layer and formed in the step (3). In contrast, the n-type cladding layer 2 and the p-type cladding layer 3, which are formed in the step (1) and the step (4), are formed without using the selective growth method.
Here, the thickest light-emitting layer EL04 is approximately 1.2 to 1.3 times as thick as the thinnest light-emitting layer EL01. This corresponds to a difference in thickness of approximately 20 to 30 nm, which is a negligible thickness compared with the total thickness (several micrometers (several thousand nanometers)) including the GaAs substrate 1. When a thickness from the bottom face of the n-type cladding layer 2 to the top face of the cap layer 5 is, for example, 4 to 5 μm (4000 to 5000 nm), the difference in thickness (20 to 30 nm) between the thickest light-emitting layer EL04 and the thinnest light-emitting layer EL01 is less than 1% of the thickness.
The value of the peak wavelength in the optical spectrum of the laser beam varies in accordance with the thickness of the light-emitting layers EL01, EL02, EL03 and EL04 formed on the same surface. In addition, since only the light-emitting layer EL is formed by the selective growth method in the manufacturing process of the semiconductor laser device (the n-type cladding layer and p-type cladding layer are not formed by the selective growth method), the level difference with respect to the overall chip height is reduced. In this way, performing separately the crystal growth three times to the layers (n-type cladding layer, light-emitting layer EL and p-type cladding layer) allows the n-type cladding layer and the p-type cladding layer (approximately 4 μm in thickness) to have no difference in thickness, exhibiting the difference in thickness only in the light-emitting layer (about 100 nm), which is formed relatively thin. Hence, this makes it possible to suppress the difference in height of the beam position from which the light-emitting section EM emits the beam, thereby eliminating defects even in the J-down mounting. In other words, the embodiment 1 provides a semiconductor laser device that suppresses a practical problem caused by the difference in height in a chip. This configuration makes it possible to suppress the image quality degradation due to the interference of laser beam, further improving visual sensitivity and image quality such as a wide color gamut, high resolution and a wide viewing angle.
A modified example 1 of the manufacturing method for the semiconductor laser device LD01 according to another embodiment will be described.
As shown in
As described above, the laser device of the red range is constituted by a crystal layer of (AlxGa1-x)1-yInyP, which contains Al; however, Al is highly susceptible to be oxidized. Hence, the buffer layer BAL is formed as an oxidation prevention layer to prevent the oxidation of the crystal growth interface between the processes. The oxidation of Al causes an increase in the rate of non-light-emitting recombination of carriers, leading to performance degradation such as a decrease in the light-emitting efficiency, which in undesirable. The buffer layer BAL uses a material selected from materials containing no Al or having a low mixed ratio of Al; for example, GaInP or GaAs is selected. When GaAs is selected as a material for the buffer layer BAL, the buffer layer may be removed by etching immediately before the subsequent step after the step of having formed the buffer layer BAL. As long as GaAs serves to suppress the oxidation of Al between the processes, GaAs is not necessarily present in the finished product, because it absorbs light.
A modified example 2 of the manufacturing method for the semiconductor laser device LD01 according to another embodiment will be described.
In the modified example 2 of another embodiment 1, the buffer layer BAL is formed in the middle of the step (1) and the step (4) as shown in
The modified example 1 and 2 described above is also applicable to another embodiment 2 that will be described below.
The semiconductor laser device LD1 (See
The semiconductor laser device LD1 according to another embodiment 2 has the same configuration of the semiconductor laser device LD01 according to another embodiment 1 except the fact that each of the light-emitting sections EM11, EM12, EM13 has a different composition ratio in the crystal layer thereof. Thus, unless otherwise mentioned, the following description will focus on the points that differ from those of another embodiment 1, and the repetition of the same description will be omitted. In another embodiment 2, it is noted that the configuration is opposite to that of another embodiment 1 with respect to the left and right sides, also the numbers of the light-emitting layers and the etch-stop layers 6, which are shown in another embodiment 1, are omitted from the configuration for convenience of explanation.
For the red range laser beam, Al (aluminum) and In (indium) are doped in the crystal layer of the semiconductor laser device, as described in detail below. The semiconductor laser device according to embodiment 2 is capable of emitting multiple laser beams having different wavelengths from a single chip by particularly varying the composition ratio of In (indium) among the compositions constituting the crystal layers.
As shown in
Each of the light-emitting sections EM01, EM02, EM03 includes a ridge 4 that acts as a current narrowing structure (current injection structure) that has been formed by removing a portion of the p-type cladding layer 3 with etching, and also acts as a structure for confining light in the transverse direction (the x direction in
Applying a current between the p-type electrodes 7P and the n-type electrodes 7N allows the light-emitting regions ER11, ER12, ER13 formed in the three light-emitting sections EM11, EM12, EM13 respectively, to emit laser beams having the red range (wavelength: 600 nm to 700 nm). The wavelength 2 of the laser beams emitted is expressed by the relationship EM13>EM12>EM11. As an example, the light-emitting region ER11 emits the laser beam having a wavelength of 654 nm, ER12 of 658 nm, and ER13 of 662 nm, respectively.
In the example described above, every adjacent wavelength is set to have a difference of 4 nm; however, the wavelength difference can be set in the range of 1 nm to 30 nm. For example, when the wavelength difference is set to 1 nm, the light-emitting region ER11 emits the laser beam having a wavelength of 620 nm, ER12 of 621 nm, and ER13 of 622 nm, respectively. In addition, when the wavelength difference is set to 30 nm, the light-emitting region ER11 emits the laser beam having a wavelength of 630 nm, ER12 of 660 nm, and ER13 of 690 nm, respectively.
The light-emitting layers EL11, EL12, EL13 are constituted by the crystal layer of (AlxGa1-x)1-yInyP (0≤x<1, 0<y<1), each of the light-emitting layers EL includes the crystal layer having a different In composition ratio (y). As an example, the In composition ratio (y) of the light-emitting layer EL11 is 0.51, 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 0.59. The In composition ratio (y) is preferably selected from a range of 0.35 to 0.65, the detail of which will be described later. As the detail will be described later, the light-emitting layers EL are constituted by multiple layers; the quantum well layer QW has a smallest Al composition ratio (x). It is noted that an indirect transition occurs when the Al composition ratio (x) exceeds approximately 0.5, thus the Al composition ratio (x) of the quantum well layer QW is 0.5 or less.
An exemplary configuration of the light-emitting layer EL11, EL12, EL13 will be described in
It is noted that upon the reference to the light-emitting layer EL of the present embodiment, the light-emitting layer EL is defined to be any one of the followings: the light-emitting layer includes all of the lower n-side guide layer nGL, the quantum well layers QW, the barrier layer BL and the upper p-side guide layer pGL, which are described above; the light-emitting layer EL includes the quantum well layers QW and the barrier layer BL; or the light-emitting layer EL includes part of the p-type cladding layer 3 in addition to the quantum well layers QW and the barrier layer BL.
An exemplary method of manufacturing the semiconductor laser device LD1 according to another embodiment 2 will be described.
The method of manufacturing the semiconductor laser device LD1 according to another embodiment 2 mainly includes the step of (1) forming the n-type cladding layer 2 on the GaAs substrate 1, (2) forming the mask layer MK, (3) forming the light-emitting layer EL11, EL12, EL13 by the selective growth method, (4) forming the p-type cladding layer 3 and the cap layer 5 (including a process of removing the mask layer MK), (5) forming ridges and electrodes and then separating into a piece.
(1) Step of Forming the n-Type Cladding Layer 2 on the GaAs Substrate 1
First, as shown in
Next, as shown in
After forming the SiO2 film, multiple stripe-shaped openings (three openings in the present embodiment) are formed in the SiO2 film by the lithography method, as shown in
Next, as shown in
The crystals grown by the selective growth method is (AlxGa1-x)1-yInyP (0≤x<1, 0<y<1). The raw material gases used include trimethylaluminum (TMA), trimethylgallium (TMG) and trimethylindium (TMI).
By the selective growth method, deposited are the lower n-side guide layer nGL, the quantum well layer QW, the barrier layer BL, the quantum well layer QW and the upper p-side guide layer pGL in sequence on the regions through the openings of the mask layer MK. The light-emitting layer EL11 is formed in the region having the widest opening (EW11) of the mask layer MK, and the light-emitting layer EL13 is formed in the region having the narrowest opening (EW13). The light-emitting layer EL12 is formed in the region having the intermediate opening (EW12) of the mask layer MK.
The step of forming the light-emitting layers EL uses the selective growth method to form (AlxGa1-x)1-yInyP; the values of x and y representing the composition ratio of elements are determined on the followings.
The guide layer GL is referred to a 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. Hence, the feed ratio of the raw material is adjusted to make the Al composition ratio (x) lower compared to that of the cladding layer 2 (3). For example, the feed amount of the raw material gas is adjusted such that the Al composition ratio (x) is highest in the cladding layer 2 (3), and becomes lower in the guide layer GL or the barrier layer BL, and the quantity well layer QW in that order.
According to the present embodiment, the guide layers GL and the barrier layers BL are constituted by the composition of (AlxGa1-x)1-yInyP, where the composition ratio is x=0.7 and y=0.5, and have a thickness of, for example, 50 nm to 60 nm. TMA as a raw material is not supplied for growing the quantum well layer QW, thus the quantum well layer QW contains no Al (i.e., x=0) and has the composition of GaInP. The quantum well layer QW has a thickness of 5 nm to 6 nm.
The light-emitting layer EL formed by the selective growth method functions as a core layer of an optical waveguide. In a laser beam in red range, the thickness of the light-emitting layer EL is selected in the range of approximately 50 nm and 500 nm although depending on the wavelength of the laser and the refractive indexes of the respective layers; the light-emitting layer EL of the present embodiment has a total thickness of approximately 100 nm.
In the step of forming the light-emitting layer EL, the growth rate by the selective growth method is set to be higher than the normal rate. For example, in the case in which the normal growth rate is 1 to 2 μm/h, the growth rate according to the present embodiment is increased approximately by 20 to 80 percent by increasing the feed amount of the raw material gas. Increasing the growth rate enables the In composition in the light-emitting layer EL11, EL12, E113 to be controlled. Specifically, the In composition ratio is highest in the light-emitting layer EL13, which is formed on the region through the narrowest opening (EW13) in the mask layer MK; and the In composition ratio becomes lower in the light-emitting layer EL12 and the light-emitting layer EL11 in order. In this way, the condition that higher In composition ratio is deposited on the region through the stripe having the narrower opening in the mask layer MK is used.
The mechanism of controlling the In composition in each of the light-emitting layers EL11, EL12, EL13 is not clearly understood; however, it is inferred as described in the following (i)-(iv).
(i) In the selective growth method, layer growth does not occur on the surface of the mask layer MK; thereby the raw material gas fed to the surface of the mask layer MK migrates on the surface of the mask layer MK and moves to the region of the openings of the mask layer MK.
(ii) The amount of the migrating raw material gas increases as the surface area of the mask layer MK is larger.
(iii) A larger amount of raw material gas migrates to the region of the openings of the mask layer MK adjacent to the mask layer MK having a larger surface area, thus the concentration of the raw material gas in the openings becomes high. Furthermore, if the opening of the mask layer MK is smaller, the concentration of the raw material gas will be higher.
(iv) As a result, higher In (indium) is incorporated into the light-emitting layer EL13, which is formed on the region through the narrowest opening of the mask layer MK. In this way, the composition ratio on the region through each opening is adjusted by facilitating the diffusion of the raw material gas in the lateral direction on the surface of the mask layer MK, and by especially using the phenomenon that the region through the narrower opening has the higher composition of the raw material (for example, TMI including In) that tends to be influenced by diffusion in the lateral direction.
The thickness of the light-emitting layer EL is expressed by the relationship EL11<EL12<EL13.
(4) Step of Forming the p-Type Cladding Layer 3 and the Cap Layer 5 (Including the Step of Removing the Mask Layer MK)
Next, the mask layer MK is removed as shown in
(5) Step of Forming Ridges and Electrodes and then Separating into a Piece
Next, as shown in
The relation between the oscillation wavelength and the composition ratio (In composition ratio) will now be explained with reference to
For the purpose of indicating the fundamental relation between the oscillation wavelength and the composition ratio (In composition ratio), the data in
Next, in another embodiment 2, explained is the background that the present inventors have reached the idea that the oscillation wavelength is adjusted (controlled) by varying the composition ratio of the crystal of the light-emitting layer EL, in addition to by varying the thickness of the light-emitting layer.
The present inventors acknowledged that methods of varying the wavelength included varying the thickness of the light-emitting layer and varying the composition of the light-emitting layer. Moreover, the present inventors, through their consideration, found that the laser beam having a shorter wavelength allows the amount of wavelength to vary less with respect to the thickness of the light-emitting layer. For example, the present inventors concluded that in the case that the quantum well layer QW having a thickness of around 5 nm for emitting a wavelength band of the red range, adjusting only the thickness of the layer has a limit on the amount of variation in the wavelength (adjustment range), thereby adjusting only the thickness of the layer may not sufficiently secure the wavelength difference. Hence, the present inventors focus on varying the energy band gap using the difference in the composition of the light-emitting layer to control the wavelength, in addition to varying the thickness of the light-emitting layer.
The active layer of (AlxGa1-x)1-yInyP for emitting a red wavelength band involves a cladding layer having a mixed crystal of (AlxGa1-x)1-yInyP constituted by at least Al and In. Increasing Al composition ratio (doping amount) enables variation of the energy band; however, the technical difficulties on the process may arise shown on the following (1) and (2). (1) Al is highly susceptible to be oxidized, making it difficult to treat the interface in selective growth process. (2) Al easily forms poly deposits on the mask layer during the selective growth, making it difficult to control the composition of the crystals to be grown. Thereby, the present inventors have found that adjusting the composition ratio of the crystal, especially the In composition ratio thereof, is effective in varying the energy band gap in terms of both the control of the amount of wavelength variation and the process availability. Therefore, varying the In composition ratio in the composition constituting the crystal layer enables the single laser device to readily emit multiple laser beams having different wavelengths.
The semiconductor laser device LD1 according to another embodiment 2 also exhibits the advantages similar to that of the semiconductor laser device LD01 according to another embodiment 1. In the semiconductor laser device LD1 according to another embodiment 2, the three light-emitting sections EM11, EM12, EM13 emit laser beams having different wavelengths by forming the light-emitting layers with different composition ratios in accordance with the widths of the light-emitting layers EL11, E112, EL13. This configuration makes it possible to suppress the image quality degradation due to the interference of laser beam and further improve visual sensitivity and image quality such as a wide color gamut, high resolution and a wide viewing angle.
As mentioned above, the invention made by the present inventors have been specifically described in accordance with the embodiment; however, the present invention is not limited to the above-mentioned embodiments, and may be modified in various ways without departing from the gist thereof. For example, the semiconductor laser device of the red range is described in the above-mentioned embodiments; however, the description can also be applied to semiconductor laser devices of other color regions as long as the color regions are a visible light region other than red. In addition, a semiconductor laser device of GaAs (substrate)/AlGaInP (crystal layer) is described in the above-mentioned embodiment; however, the description can also be applied to semiconductor laser devices of GaAs/AlGaAs, GaAs/InGaAsP and GaN/AlGaN. Moreover, described is the case in which the single semiconductor laser device emits three or four laser beams with different wavelengths in the above embodiment; however, the single semiconductor laser device may emit five or more laser beams.
In addition, even when the exemplary specific numerical value is described, a numerical value may exceed the specific numerical value or fall short of the specific numerical value, unless it is clearly limited by the theory. In addition, with respect to a component in a layer/film or a structure, it may mean “B containing A as a major component” and so on, and does not exclude the inclusion of other components.
The above-mentioned embodiments include the following aspects.
The semiconductor laser device includes:
a substrate having a main surface;
a first cladding layer with a first conductive type and a second cladding layer with a second conductive type different from the first conductive type, which are stacked over the main surface of the substrate; and
a light-emitting layer that is formed between the first cladding layer and the second cladding layer, and is formed on a first surface parallel to the main surface of the substrate;
the light-emitting layer has a plurality of light-emitting sections emitting laser beams in a red range, and
values of peak wavelengths in an optical spectrum of the laser beams emitted from the light-emitting sections, are different in accordance with the thickness of the light-emitting layer from the first surface.
The semiconductor laser device according to Aspect 1, the value of the peak wavelength in the optical spectrum of the laser beam emitted from the light-emitting section, is longer when the thickness of the respective light-emitting layer from the first surface is thicker.
The semiconductor laser device according to Aspect 1, the light-emitting layer is separately formed on the first surface so as to separate the light-emitting sections, the second cladding layer formed over the light-emitting layer has a substantially same thickness over the respective light-emitting sections.
The semiconductor laser device according to Aspect 1, further including a buffer layer that is formed each of between the first cladding layer and the light-emitting layer, and between the light-emitting layer and the second cladding layer.
The semiconductor laser device according to Aspect 1, further including a buffer layer that is formed each of in the first cladding layer and in the second cladding layer as an intervening layer.
The semiconductor laser device according to Aspect 4, the light-emitting layer includes a quantum well layer, and the buffer layer is thinner than the quantum well layer.
The semiconductor laser device according to Aspect 1, further including a ridge that is formed over the light-emitting layer,
the light-emitting layer has a side face extending in a longitudinal direction of the ridge, and the side face inclines inward as the thickness of the light-emitting layer increases.
The semiconductor laser device according to Aspect 1, the light-emitting sections adjacent each other have an interval of 5 μm or more and 100 μm or less.
The semiconductor laser device according to Aspect 1, further including ridges formed over the light-emitting layer so as to correspond to the light-emitting sections; and electrodes formed over the ridges, the electrodes having different thicknesses,
the ridges corresponding to the light-emitting sections have a substantially same height from the main surface of the substrate to an upper surface of the electrodes in a thickness direction.
The semiconductor laser device according to Aspect 1, further including ridges formed over the light-emitting layer so as to correspond to the light-emitting sections;
a submount that is bonded to the ridges at the electrode via junction material; and
a heat-dissipating component that is connected to the submount.
A method of manufacturing a semiconductor laser device, includes:
The method of manufacturing the semiconductor laser device according to Aspect 11, further including (G) forming a buffer layer after each of (A) and (C).
The method of manufacturing the semiconductor laser device according to Aspect 11, further including (G) forming a buffer layer in the middle of each of (A) and (E).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-215676 | Dec 2020 | JP | national |
