JP7635619B2 - Semiconductor light emitting device - Google Patents

Description

The present invention relates to a semiconductor light-emitting device.

In recent years, the market for display devices such as projectors using semiconductor lasers has expanded.
Furthermore, in recent years, reality technologies such as Augmented Reality (AR), Virtual Reality (VR), Mixed Reality (MR), and Substitutional Reality (SR) have been put to practical use in various fields, and display devices using these technologies, such as Head Mount Displays (HMDs), Head-up Displays, and AR glasses, have been commercialized.

For example, a known technology for head mounted displays is to use three colors of laser light, RGB (red, green, and blue), as the light source, create an image using a MEMS (Micro Electro Mechanical Systems), which is a spatial modulation element for image display, and project the image onto the retina or the like through a waveguide. This MEMS-based system can achieve a wide color gamut, high resolution, and a wide viewing angle for images, and multiple semiconductor lasers are used to create multiple beams for each of the RGB colors.

Patent document 1 discloses a multi-wavelength semiconductor laser capable of oscillating lasers of multiple wavelengths within the same element. In the technology of Patent document 1, in an AlGaAs-based quantum well laser, the well width (physical film thickness) of the first and second quantum well active layers is made different to achieve multi-wavelength.

Patent Document 2 also discloses a monolithic laser diode that mounts a CD laser diode (emission wavelength 780 nm) and a DVD laser diode LD2 (emission wavelength 650 nm) on a single chip.

Japanese Patent Application Publication No. 05-082894 JP 2009-016881 A

Journal of the Society of Applied Physics, Vol. 61, No. 8, 1992, pp. 806-812, "Electronic states of natural superlattice structures in compound semiconductors", Hiroshi Yoshida

When a semiconductor laser is used in a display device, a monolithic lateral single mode semiconductor laser that independently drives multiple light emitting layers (plurality of light emitting layers) at a narrow pitch is required to improve image quality such as resolution and frame rate.
However, a transverse single mode laser has a narrow wavelength width and is highly coherent, so if the wavelengths of the RGB colors are made the same and the wavelengths of the colors are aligned, the image quality will deteriorate due to the coherence of the laser light.

The object of the present invention is to provide a semiconductor light-emitting element that can reduce the coherence of laser light.

A semiconductor light-emitting device according to one aspect of the present invention includes a semiconductor substrate having inclined surfaces with different inclination angles, and a plurality of light-emitting layers stacked on the inclined surfaces and emitting laser light with a wavelength according to the inclination angle.

By this, by forming a light-emitting layer on a semiconductor substrate having an inclined surface with a different inclination angle, it is possible to form a plurality of light-emitting layers that emit laser light of a plurality of wavelengths. Therefore, in order to form a plurality of light-emitting layers that emit laser light of a plurality of wavelengths, it is no longer necessary to repeatedly form a light-emitting layer for each light-emitting layer that emits laser light of a different wavelength. In addition, since the light-emitting layers that emit laser light of different wavelengths are formed in one step, it is no longer necessary to form insulating layers with different aperture ratios on the semiconductor substrate as a selective growth mask as in the conventional technology (Patent Document 1). In addition, it is possible to prevent polycrystals from accumulating on the selective growth mask, a crystal structure different from the desired layer configuration due to composition deviation of the light-emitting layer, and crystal defects from occurring. Therefore, it is possible to form a plurality of light-emitting layers that emit laser light of a plurality of wavelengths while suppressing deterioration of crystal quality and an increase in the number of processes.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the inclined surface is provided with a crystal plane on which the elements of the semiconductor substrate are likely to form a natural superlattice as a reference plane. In the present invention, the crystal plane on which a natural superlattice is likely to form refers to a surface having an orientation that can realize a lattice arrangement that realizes an energetically stable state, for example, in an InGaP crystal, a lattice plane with a large number of In atoms and a lattice plane with a large number of Ga atoms are regularly arranged on the group III crystal plane.

As a result, by changing the inclination angle with respect to the reference plane, the band gap of the light-emitting layer can be changed, and the oscillation wavelength can be changed. Therefore, by depositing a light-emitting layer on a semiconductor substrate having inclined surfaces with different inclination angles, multiple light-emitting layers that emit laser light of multiple wavelengths can be formed.

In a semiconductor light-emitting device according to one aspect of the present invention, the inclined surface includes a growth surface that is not a specific crystal surface of the semiconductor substrate. The "specific crystal surface" here refers to a crystal surface defined by simple Miller indices such as the (001) surface, the (111) surface, or the (0001) surface.

This makes it possible to change the angle of the inclined surface of the semiconductor substrate in steps of several degrees, and to change the wavelength of the laser light while maintaining the same color. This makes it possible to reduce the coherence of the laser light based on laser light of different wavelengths, and suppress degradation of image quality due to the coherence of the laser light.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the reference surface is set horizontally relative to the rear surface of the semiconductor substrate, and the average value of the inclination angle of the multiple inclined surfaces is equal to the inclination angle of the reference surface relative to the semiconductor substrate.

This reduces the step between the locations where the semiconductor light-emitting elements are formed that occurs when the inclined surface is formed during the manufacturing process of the semiconductor light-emitting elements, and prevents a decrease in processing accuracy during processes such as photolithography and dry etching.

In addition, according to one aspect of the present invention, a semiconductor light-emitting device has multiple light-emitting layers stacked at positions where the inclination of the tangent line of the curved surface formed on the semiconductor substrate is different.

This makes it possible to form a light-emitting layer that emits laser light with different emission wavelengths at positions with different tilt angles.

In addition, a semiconductor light-emitting device according to one aspect of the present invention includes a ridge stripe structure formed on the semiconductor substrate, and the inclined surface extends along the ridge stripe structure at a certain angle relative to the semiconductor substrate and is inclined in a direction perpendicular to the ridge stripe structure.

This allows the laser light to be amplified for each wavelength while confining the light along the guided direction of the laser light, improving the light emission efficiency and producing multi-wavelength multi-beams.

In addition, according to one aspect of the present invention, the semiconductor light-emitting device is provided with electrodes that are arranged at the same height on the ridge stripe structure.

This allows the multi-wavelength, multi-beam semiconductor laser to be mounted by junction-down bonding on a submount on which electrodes are arranged. This improves the heat dissipation of the multi-wavelength, multi-beam semiconductor laser, and improves the reliability of the multi-wavelength, multi-beam semiconductor laser.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the semiconductor substrate is a GaAs substrate, and the active layer included in the light-emitting layer includes at least one of an AlGaInP crystal layer or a GaInAsP crystal layer (including the case where the Al or As composition is zero).

This makes it possible to realize a multi-wavelength, multi-beam semiconductor laser in the red to near-infrared range.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the semiconductor substrate is a GaN substrate, and the active layer included in the light-emitting layer includes at least one of an InGaN crystal layer or an AlGaInN crystal layer.

This makes it possible to realize a multi-wavelength, multi-beam semiconductor laser in the blue-violet to green range.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the semiconductor substrate is formed on a support substrate made of a semiconductor or dielectric material of a different type, and the semiconductor substrate is made of the same material as the light-emitting layer.

This allows the semiconductor substrate to be made thinner, reducing the cost of the semiconductor substrate, and also allows the semiconductor substrate to be handled stably even if it is prone to cracking.

In addition, according to one aspect of the semiconductor light-emitting device of the present invention, the laser light has different wavelengths within the same color region.

This makes it possible to reduce the coherence of the laser light based on laser light of multiple wavelengths, thereby suppressing degradation of image quality due to the coherence of the laser light.

In one aspect of the present invention, the coherence of laser light can be reduced.

1 is a cross-sectional view showing a configuration of a semiconductor light emitting element according to a first embodiment, cut perpendicularly to an optical waveguide direction. 2 is an enlarged cross-sectional view showing one ridge stripe structure of the semiconductor light emitting device of FIG. 1. 4 is a diagram showing the relationship between the wavelength and the substrate tilt angle of the semiconductor light emitting device according to the first embodiment. 3A to 3C are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment. 3A to 3C are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment. 3A to 3C are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment. 3A to 3C are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment. 3A to 3C are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment. 5A to 5C are cross-sectional views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 5A to 5C are perspective views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment. 6 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a second embodiment, cut perpendicularly to the optical waveguide direction. FIG. 11 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a third embodiment, cut perpendicularly to the optical waveguide direction. FIG. 11 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to a fourth embodiment, cut perpendicularly to the optical waveguide direction. FIG. FIG. 13 is a perspective view showing a configuration of a semiconductor light emitting device according to a fifth embodiment.

Below, the embodiments of the present invention will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the configuration of the present invention. The configuration of the embodiments may be modified or changed as appropriate depending on the specifications of the device to which the present invention is applied and various conditions (conditions of use, environment of use, etc.). The technical scope of the present invention is determined by the claims, and is not limited by the individual embodiments below. Also, the drawings used in the following description may differ in scale and shape from the actual structure in order to make each configuration easier to understand.

Figure 1 is a cross-sectional view showing the configuration of the semiconductor light-emitting device according to the first embodiment cut perpendicularly to the optical waveguide direction, and Figure 2 is a cross-sectional view showing an enlarged ridge stripe structure of one of the semiconductor light-emitting devices of Figure 1. Note that Figure 2 shows an enlarged view of region R in Figure 1. In addition, the following description will take as an example a configuration in which four light-emitting layers are stacked on a semiconductor substrate and laser light of four different wavelengths is emitted, but a configuration in which m (m is an integer of 2 or more) light-emitting layers are stacked on a semiconductor substrate and laser light of m different wavelengths is also possible. In addition, the following description will take as an example a semiconductor laser with multiple wavelengths in the red range.

In Fig. 1 and Fig. 2, the semiconductor laser LA has m (m = 4 in the example of Fig. 1) light-emitting layers stacked on an n-type semiconductor substrate 11. The n-type semiconductor substrate 11 has m inclined surfaces MA1 to MAm with different inclination angles θ1 to θm. The m light-emitting layers are stacked on the m inclined surfaces MA1 to MAm, respectively, and emit laser light of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined surfaces MA1 to MAm can be provided using a crystal plane on which the elements of the n-type semiconductor substrate 11 are likely to form a natural superlattice as a reference plane. It is preferable that the inclined surfaces MA1 to MAm include a growth surface of the n-type semiconductor substrate 11 that is not a specific crystal plane. The "specific crystal plane" referred to here refers to a crystal plane defined by simple Miller indices such as the (001) plane, the (111) plane, or the (0001) plane. This reference plane is set horizontally relative to the rear surface of the n-type semiconductor substrate 11, and the average value of the inclination angles θ1 to θm is preferably equal to the inclination angle of the reference plane relative to the n-type semiconductor substrate 11.

A semiconductor laminated structure 12 including a light emitting layer is formed on an n-type semiconductor substrate 11. The semiconductor laminated structure 12 includes m ridge stripe structures SA1 to SAm. A protective film 13 is formed on the n-type semiconductor substrate 11 so that the top surfaces of the ridge stripe structures SA1 to SAm are exposed. The protective film 13 is, for example, an insulating film such as a _SiO2 film or a SiN film. A p-side electrode 14 is formed on each of the ridge stripe structures SA1 to SAm in contact with the top surface of the ridge stripe structures SA1 to SAm.

2, in the semiconductor laminate structure 12, for example, an n-type buffer layer 21, an n-type cladding layer 22, an active layer 23, a p-type first cladding layer 24, a p-type etching stop layer 25, a p-type second cladding layer 26, a p-type interface layer 27, and a p-type cap layer 28 are sequentially laminated on an n-type semiconductor substrate 11. Here, in the semiconductor laminate structure 12, the p-type second cladding layer 26, the p-type interface layer 27, and the p-type cap layer 28 are patterned into a ridge stripe shape. At this time, the p-type etching stop layer 25 can be used to stop etching when the p-type second cladding layer 26, the p-type interface layer 27, and the p-type cap layer 28 are patterned into a ridge stripe shape.

When the semiconductor laser LA is multi-wavelength in the red region, the semiconductor laminate structure 12 can be, for example, a laminate structure of an n-type GaAs buffer layer, an n-type AlGaInP cladding layer (Al composition X=0.7), an AlGaInP/GaInP multi-quantum well (MQW: Multi Quantum Well) active layer, a p-type AlGaInP first cladding layer (Al composition X=0.7), a p-type GaInP etching stop layer, a p-type AlGaInP second cladding layer, a p-type GaInP interface layer, and a p-type GaAs cap layer.

In order to provide the inclined surfaces MA1 to MAm on the n-type semiconductor substrate 11, for example, the chip width can be set to 300 to 400 um, and a curved surface KMA that is periodically curved convexly at a pitch of this chip width can be formed on the n-type semiconductor substrate 11. The shape of this curved surface KMA may be semi-cylindrical or arched. By arranging m inclined surfaces MA1 to MAm at positions where the inclination of the tangent of the curved surface KMA formed on the n-type semiconductor substrate 11 is different, the inclination angles θ1 to θm of the m inclined surfaces MA1 to MAm can be made different from one another. By stacking m light-emitting layers on each of the inclined surfaces MA1 to MAm, it is possible to emit laser light of a different wavelength for each light-emitting layer.

For example, m light-emitting layers can be arranged at intervals of 50 μm on the curved surface KMA, and the inclination angles θ1 to θm can be changed from -5 degrees to +4 degrees in 3-degree steps. In this case, the inclination angles θ1 to θm of each inclined surface MA1 to MAm can be set to 5 degrees, 8 degrees, 11 degrees, and 14 degrees off, with the surface where the elements of the n-type semiconductor substrate 11 form a natural superlattice as the reference surface. When the characteristics were evaluated after the semiconductor laser LA was assembled, laser oscillation at different wavelengths was confirmed for each light-emitting layer of the four-beam laser. At this time, a wavelength difference of 15 nm was obtained, from the shortest wavelength of 636 nm to the longest wavelength of 651 nm. In this embodiment, the number of light-emitting layers integrated in the semiconductor laser LA was set to four, but there is no particular restriction on the number of light-emitting layers as long as they can be arranged on the chip.

When GaInP crystals grown on a GaAs substrate are used for the active layer 23, the band gap of the GaInP layer can be controlled by controlling the natural superlattice structure. For example, as described in "Laser Research, Vol. 18, No. 8, PP592-595, August 1990, Isao Hino, Crystal Structure and Device Characteristics of Visible Light Semiconductor Laser Material AlGaInP," the band gap can be changed by about 1.85 to 1.91 eV (corresponding to a range of 649 to 670 nm in terms of light wavelength) by adjusting the growth temperature, V/III ratio, and off-angle of the substrate during crystal growth. In GaInP crystals, a crystal lattice is formed by the III group elements Ga and In and the V group element P, and in the disordered state, Ga and In are arranged irregularly. In contrast, when grown on a crystal with specific crystal growth conditions and substrate surface, an ordered state (ordered) may occur in which Ga and In are regularly arranged and Ga and In planes are alternately arranged. This ordered state is called a natural superlattice because it is a state in which a GaP-type InP superlattice is formed spontaneously. In this state in which the natural superlattice is formed, the forbidden band width is reduced and the forbidden band width of the GaInP layer changes. Then, when the inclination is changed from the plane in which the natural superlattice is formed, the regularity of the natural superlattice is gradually disturbed and the forbidden band width gradually increases according to the inclination, so that the wavelength of the laser light can be gradually changed. The formation of a natural superlattice is a phenomenon specific to growth on a crystal plane close to the (001) plane when the n-type semiconductor substrate 11 is an n-type GaAs semiconductor substrate 11.

In addition, by changing the crystal growth conditions such as the V/III ratio of the raw material gas and the growth temperature, the formation of a natural superlattice may be spontaneously suppressed, and the variation in the forbidden band width may be almost eliminated regardless of the crystal plane orientation of the substrate surface. For this reason, it is necessary to select crystal growth conditions that can obtain the desired wavelength difference according to the wavelength range of the multi-wavelength semiconductor laser LA. However, even if crystal growth conditions that cause such a large wavelength change are set, there is no adverse effect such as a decrease in the quality of the grown (Al)GaInP crystal or a decrease in the characteristics and performance of the semiconductor laser LA produced. Therefore, crystal growth conditions that can obtain the desired wavelength difference can be selected within the range of crystal growth conditions that can realize a semiconductor laser LA with the desired performance.

As described above, according to the above-mentioned embodiment, the inclined surfaces MA1 to MAm are formed in a direction perpendicular to the resonator direction in which the stripe-shaped waveguide structure extends at the position where each light-emitting layer is arranged on the n-type semiconductor substrate 11, and the inclination angles θ1 to θm with respect to the substrate surface are controlled for each light-emitting layer, thereby adjusting the emission wavelength for each light-emitting layer, and a semiconductor laser LA that operates at a different wavelength for each light-emitting layer can be configured by a simple manufacturing process. When an AlGaInP crystal or GaInP crystal material is used for the active layer 23, the degree of regularity of the natural superlattice structure in the active layer 23 changes depending on the inclination angles θ1 to θm. As a result, the forbidden band width of the active layer 23 can be changed depending on the inclination angles θ1 to θm, and the oscillation wavelength can be changed for each of the m light-emitting layers. In addition, although an example in which the inclination angles θ1 to θm change stepwise is shown, it is not necessary to change the inclination angles θ1 to θm at equal intervals, and as long as at least two or more types of inclination angles are included, it is not necessary for the inclination angles θ1 to θm to all be different.

In addition, in the semiconductor laser LA, the inclination angles θ1 to θm of the inclined surfaces MA1 to MAm provided on the n-type semiconductor substrate 11 are adjusted for each light-emitting layer, thereby realizing wavelength control of each light-emitting layer. Therefore, the semiconductor laser LA can be manufactured without repeating the multilayer crystal growth for forming the semiconductor laminated structure 12 multiple times, and the increase in cost can be suppressed. In addition, since it is possible to prevent exposure to multiple heat histories without repeating the multilayer crystal growth multiple times, it is possible to prevent the diffusion of dopants in the crystal, the deterioration of the quality of the crystal due to the detachment, substitution, and oxidation of the constituent elements near the crystal surface, and the contamination of impurities from the outside. Furthermore, in order to complete the film formation of the light-emitting layers that emit laser light of different wavelengths in one go, it is no longer necessary to form insulating layers with different aperture ratios as selective growth masks on the n-type semiconductor substrate 11, and it is possible to prevent polycrystals from accumulating on the selective growth mask, the crystal structure from becoming different from the desired layer configuration due to the composition deviation of the light-emitting layer, and the occurrence of crystal defects. As a result, it is possible to suppress the deterioration of the quality of the semiconductor laser LA while achieving wavelength multi-beam generation.

Figure 3 is a diagram showing the relationship between the PL (Photoluminescence) wavelength and the substrate tilt angle of the semiconductor light-emitting device according to the first embodiment. Note that Figure 3 shows an example of the relationship between the tilt angle of the GaAs substrate from the (001) plane and the emission wavelength due to photoluminescence of the GaInP crystal grown thereon.

As shown in Fig. 3, by adjusting the inclination of the inclined surface, for example by adjusting the inclination angle of the substrate surface in the range of 0 to 15° for each light-emitting layer, it is possible to easily fabricate a multi-wavelength multi-beam laser in which the wavelength difference between the light-emitting layers is about 20 nm. In the figure, the emission wavelength of a GaInP layer formed on a GaAs substrate is shown, but even when a GaInP layer or an AlGaInP layer is used for the well layer of the multiple quantum well structure, the change in the forbidden band width of the multiple quantum well layer appears as a difference in the emission wavelength.

Regarding the tilt angle at the position of the light-emitting layer, if the tilt angle of the substrate surface is set to vary between 0 and 15 degrees, the wavelength difference between the light-emitting layers can be maximized, and a wavelength difference of 20 nm or more can be achieved. This wavelength difference is sufficient to improve image quality. Therefore, it is sufficient to configure the tilt angle of the substrate surface at the position of each light-emitting layer to be changeable from a maximum of 0 to 15 degrees, and the tilt angle of each light-emitting layer can be changed by the amount necessary to obtain the required wavelength difference according to the requirements of the system in which the semiconductor laser is actually used. For example, to obtain a wavelength difference of 10 nm, the tilt angle of the light-emitting layer can be changed in the range of 7 to 12 degrees.

The original substrate tilt angle of the semiconductor substrate may be selected in the same way as when fabricating a single-wavelength semiconductor laser, but it is preferable to take it as an approximate average value of the range of the tilt angle at the position of the light-emitting layer selected to achieve the desired wavelength difference. In the above-mentioned embodiment, the ridge structure formed on a surface that is more inclined than the original surface of the semiconductor substrate is inclined, and the light-emitting layers (particularly the two outer light-emitting layers in Figure 1) are also inclined obliquely. In order not to significantly affect the fabrication process and performance of the semiconductor laser, this tilt angle is preferably 15 degrees or less.

In the configuration of FIG. 1, in order to provide multiple inclination angles on the n-type GaAs semiconductor substrate, the n-type GaAs semiconductor substrate (substrate off by 10 degrees from (001)) is processed to form a semi-cylindrical slope extending in the direction of the laser resonator. In this case, the method of processing the substrate surface can be, for example, a method of processing a microlens on the surface of a semiconductor material or a glass material.

However, as shown in Figure 1, when forming a large, semi-cylindrical slope, the step becomes large at the top of the curved surface KMA and the position inclined at 15 degrees. For this reason, it is necessary to adjust the photoresist application conditions and etching conditions when performing various processing and pattern formation in the wafer process. Therefore, by setting the substrate inclination angle of the semiconductor substrate itself to approximately the average value of the inclination angle of the position of the light-emitting layer, the inclination angle of the position of the light-emitting layer can be reduced, and the likelihood of the process surface can be improved.

4A to 4E are perspective views showing an example of a method for manufacturing the semiconductor light emitting device according to the first embodiment.
4A, a photoresist is applied by a method such as spin coating onto the surface of the semiconductor wafer W. Next, the photoresist is exposed to light through a photomask on which a striped pattern is formed, and developed to form a resist pattern 31 extending in a striped shape in the cavity length direction on the semiconductor wafer W.

Next, the semiconductor wafer W on which the resist pattern 31 is formed is heated at about 200°C for several minutes to 20 minutes. At this time, the pattern shape of the resist pattern 31 is deformed due to the thermoplasticity of the resist pattern 31, and a semi-cylindrical resist pattern 32 is formed on the semiconductor wafer W. (Figure 4B)

Next, the resist pattern 32 is thinned by dry etching from the top surface of the semiconductor wafer W. At this time, the surface of the semiconductor wafer W exposed from the resist pattern 32 is also etched, and the resist pattern 32 is thinned. Therefore, in the parts where the resist pattern 32 is thin, the amount of etching in the thickness direction of the semiconductor wafer W increases, and curved surfaces KMA periodically arranged in a direction perpendicular to the resonator direction are formed on the surface of the semiconductor wafer W. (Figure 4C)

In this embodiment, an example in which the curved surfaces KMA are periodically arranged on the semiconductor wafer W is shown, but the curved surfaces KMA are not limited to being periodically arranged. Depending on the method of changing the wavelength for each light-emitting layer or the convenience of the chip arrangement on the semiconductor wafer W, a non-periodic pattern arrangement or a structure in which the period changes partially may be used. In addition, in this process step, a method of directly processing the semiconductor wafer W using the resist pattern 32 as an etching mask is shown, but depending on the type of etching device, etching gas, and substrate material, it may be difficult to adjust the etching selectivity between the resist pattern 32 and the semiconductor wafer W. In this case, an intermediate layer such as a hard mask made of SiO ₂ or the like may be sandwiched between the resist pattern 32 and the semiconductor wafer W, and the resist pattern 32 may be transferred to the hard mask once, and then the semiconductor wafer W may be processed using this hard mask as an etching mask.

In addition, when the shape of a resist pattern is transferred to a semiconductor substrate to form an inclined surface on the semiconductor substrate using a microlens processing method, the height of the shape formed on the semiconductor substrate is determined by the etching selectivity of the resist pattern and the material of the semiconductor substrate. The etching selectivity can be adjusted to some extent by adjusting the etching gas and dry etching conditions or using an intermediate layer such as a _SiO2 film.

However, due to process variations during processing of the semiconductor substrate, the inclination angle of the semiconductor substrate surface at the position of each light-emitting layer may vary. For example, even if the inclination angle of the semiconductor surface at the position of each light-emitting layer or a specific light-emitting layer deviates by ±1 degree, the wavelength difference for each light-emitting layer can be sufficiently guaranteed based on the relationship between the substrate inclination angle and the wavelength change in Figure 3.

The angular deviation of the inclined surface of the semi-cylindrical curved surface KMA relative to the resonator direction need only ensure the pattern alignment accuracy when manufacturing the single-wavelength laser. For example, the pattern shape of the inclined surface for one laser chip may be arranged to be inclined by 1 to 2 degrees relative to the resonator direction. In the single-wavelength semiconductor laser manufacturing process, the angular deviation of the pattern is suppressed to within about ±0.03° to prevent deviation in the cleavage position in the bar-shaped cleavage when performing end face coating. In the multi-wavelength semiconductor laser manufacturing process, the pattern can be formed with the same accuracy as the alignment accuracy of the single-wavelength semiconductor laser manufacturing process.

When the curved surface KMA is formed on the semiconductor wafer W, a multi-wavelength multi-beam semiconductor laser can be produced by carrying out a semiconductor lamination process similar to the semiconductor lamination process for a single-wavelength semiconductor laser. At this time, as shown in FIG. 4D, a semiconductor lamination structure 12 is formed on the semiconductor wafer W by performing multi-layer crystal growth on the semiconductor wafer W on which the curved surface KMA is formed.

Next, the semiconductor laminated structure 12 is dry-etched using a hard mask such as a _SiO2 film as an etching mask to form ridge stripe structures SA1-SAm for each of the element regions RA1-RA4, as shown in Fig. 4E. Detailed manufacturing process steps are shown in Fig. 5A to Fig. 5J, and Fig. 4E further shows that after removing the hard mask from the semiconductor wafer W, a protective film 13 such as a _SiO2 film is formed on the semiconductor wafer W so as to cover the ridge stripe structures SA1-SAm.
Next, openings for passing a current through the ridge stripe structures SA1 to SAm are formed in the protective film 13.
Next, a p-side electrode 14 that comes into contact with the top surface of the ridge stripe structures SA1 to SAm through the openings formed in the protective film 13 is formed for each of the ridge stripe structures SA1 to SAm in the element regions RA1 to RA4.

In the above-described embodiment, the ridge stripe structures SA1 to SAm protected by an insulating film are shown, but a laser structure in which embedding growth is performed using GaAs, AlInP, or the like instead of the insulating film may also be used.
In this embodiment, the structure in which each light-emitting layer is formed on a portion having a step of 1 to several microns is shown. In this case, the height of the top of each light-emitting layer may be adjusted by plating the p-type electrode 14 with Au, and the chip surface may be flattened.

In this embodiment, a red laser is shown using GaAs for the semiconductor substrate and AlGaInP-based semiconductor materials for the semiconductor laser, but the semiconductor substrate and semiconductor laser are not limited to these materials. For example, the present invention may be applied to a red to near-infrared semiconductor laser using GaAs for the semiconductor substrate and InGaAsP for the semiconductor material of the active layer, or to a GaN-based blue-violet to green semiconductor laser using GaN for the semiconductor substrate and nitride semiconductors such as AlGaN and InGaN for the semiconductor laser.

For example, when manufacturing a blue semiconductor laser with an oscillation wavelength of 450 to 460 nm, the well layers of the multiple quantum well active layer are made of In _x Ga _1-x N (0.18≦x≦0.2) with an In composition of about 0.18 to 0.2. To obtain a wavelength difference of 10 nm between the light-emitting layers, a composition difference of about 0.015 to 0.02 In may be sufficient, and for example, light-emitting layers may be provided on the (0001) c-plane and on a plane tilted about 10 degrees from the c-plane toward the a-axis.

5A to 5J are cross-sectional views showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment.
In FIG. 5A, a semiconductor laminated structure 12 is formed over the entire surface of an n-type semiconductor substrate 11 on which a curved surface KMA is formed by multi-layer crystal growth.

Next, as shown in FIG. 5B, a SiO ₂ film 33 is formed on the entire surface of the semiconductor laminate structure 12 by a method such as CVD or sputtering.

5C, a resist film is coated on the entire surface of the SiO ₂ film 33 by a method such as spin coating. Then, the resist film is patterned by photolithography to form a striped resist pattern 34 on the SiO ₂ film 33.

Next, as shown in FIG. 5D, the SiO ₂ film 33 is dry-etched using the resist pattern 34 as an etching mask, thereby patterning the SiO ₂ film 33 into stripes.

Next, as shown in FIG. 5E, the SiO ₂ film 33 patterned in stripes is used as an etching mask to remove part of the p-type cladding layer of the semiconductor laminate structure 12 by dry etching, thereby forming ridge stripe structures SA1 to SAm.

5F, the SiO ₂ film 33 is removed by a method such as dry etching. Then, the protective film 13 made of a SiO ₂ film or the like is formed on the entire surface of the semiconductor laminate structure 12 by a method such as CVD.

Next, as shown in FIG. 5G, the protective film 13 is patterned using photolithography and dry etching techniques to form an opening 15 in the protective film 13 for injecting a current into the light-emitting layer.

Next, as shown in FIG. 5H, in order to drive each light-emitting layer independently, a p-side electrode 14 connected to the top surface of the semiconductor laminate structure 12 via an opening 15 is formed on each of the ridge stripe structures SA1 to SAm. At this time, the height of the p-type electrodes 14 may be made uniform by plating the p-type electrodes 14 with Au. In this case, the plating thickness can be adjusted for each of the ridge stripe structures SA1 to SAm by adjusting the current flow time for electrolytic plating of the p-side electrodes 14 for each of the ridge stripe structures SA1 to SAm.

Next, as shown in FIG. 5I, the back side of the n-type semiconductor substrate 11 is thinned by a method such as CMP (Chemical Mechanical Polishing) or etch-back. At this time, the thickness of the n-type semiconductor substrate 11 can be set to about 100 μm. Next, as shown in FIG. 5J, an n-side electrode 35 is formed on the back side of the semiconductor wafer W.

FIG. 6 is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the second embodiment, cut perpendicularly to the optical waveguide direction.
In FIG. 6, the semiconductor laser LB includes m (m=4 in the example of FIG. 6) light-emitting layers stacked on an n-type semiconductor substrate 41. The n-type semiconductor substrate 41 has m inclined surfaces MB1 to MBm with different inclination angles θ1 to θm. The m light-emitting layers are stacked on the m inclined surfaces MB1 to MBm, respectively, and emit laser light of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined surfaces MB1 to MBm can be provided with a surface where the elements of the n-type semiconductor substrate 41 form a natural superlattice as a reference surface. Here, the inclined surfaces MB1 to MBm are set with inclination angles θ1 to θm individually for each light-emitting layer formed thereon. At this time, the heights of the inclined surfaces MB1 to MBm can be made equal to each other on the n-type semiconductor substrate 41, and unevenness and steps on the chip surface can be suppressed to be small.

A semiconductor laminate structure 42 including a light emitting layer is formed on an n-type semiconductor substrate 41. The semiconductor laminate structure 42 has m ridge stripe structures SB1 to SBm. A protective film 43 is formed on the n-type semiconductor substrate 41 so that the top surfaces of the ridge stripe structures SB1 to SBm are exposed. A p-side electrode 44 is formed on each of the ridge stripe structures SB1 to SBm, in contact with the top surface of the ridge stripe structures SB1 to SBm.

The inclined surfaces MB1 to MBm on the n-type semiconductor substrate 41 can be formed by wet etching. When wet etching the GaAs substrate, a resist mask with a certain degree of solubility in the etching solution is used as an etching mask to form the inclined surfaces MB1 to MBm. When such an etching mask is used, the resist mask dissolves during etching of the GaAs substrate, causing the pattern boundary to gradually recede, making it possible to control the inclination angles θ1 to θm of the inclined surfaces MB1 to MBm. The inclination angles θ1 to θm of the inclined surfaces MB1 to MBm can be adjusted, for example, by adjusting the mixture ratio of the etching solution used, specifically the mixture ratio of sulfuric acid and hydrogen peroxide.

In addition, by utilizing the effect of increasing the etching rate of semiconductor crystals due to photochemical reactions and proceeding with chemical etching while projecting an etching pattern, inclined surfaces MB1 to MBm having desired inclination angles θ1 to θm may be formed on the n-type semiconductor substrate 41. After the inclined surfaces MB1 to MBm are formed on the n-type semiconductor substrate 41, a multi-wavelength multi-beam laser can be manufactured by a process similar to that of the first embodiment.

In this embodiment, the height of each light-emitting layer is almost uniform, so the additional Au plating required for height adjustment as in the first embodiment can be omitted.

FIG. 7 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to the third embodiment, cut perpendicularly to the optical waveguide direction.
In FIG. 7, the semiconductor laser LC includes m (m=4 in the example of FIG. 7) light-emitting layers stacked on an n-type semiconductor substrate 51. The n-type semiconductor substrate 51 has m inclined surfaces MC1 to MCm with different inclination angles θ1 to θm. The m light-emitting layers are stacked on the m inclined surfaces MC1 to MCm, respectively, and emit laser light of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined surfaces MC1 to MCm can be provided with a surface where the elements of the n-type semiconductor substrate 51 form a natural superlattice as a reference surface. Here, a curved surface KMC on which the inclined surfaces MC1 to MCm are set is formed on the n-type semiconductor substrate 51. The cross section of this curved surface KMC can have a periodically undulating shape. The inclination angles θ1 to θm are set individually for each period of the undulations of this curved surface KMC. In this case, compared to the configuration in which inclined surfaces MA1 to MAm are provided on a single semi-cylindrical curved surface KMA in Figure 1, the difference in height between the inclined surfaces MC1 to MCm on the n-type semiconductor substrate 51 can be made smaller, and unevenness and steps on the chip surface can be kept small.

A semiconductor laminate structure 52 including a light emitting layer is formed on an n-type semiconductor substrate 51. The semiconductor laminate structure 52 has m ridge stripe structures SC1 to SCm. A protective film 53 is formed on the n-type semiconductor substrate 51 so that the top surfaces of the ridge stripe structures SC1 to SCm are exposed. A p-side electrode 54 is formed on each of the ridge stripe structures SC1 to SCm, in contact with the top surface of the ridge stripe structures SC1 to SCm.

When forming a curved surface KMC on an n-type semiconductor substrate 51, a microlens processing method can be used, as shown in Figures 4A to 4C. At this time, if a pattern that is too small is formed, the processing accuracy decreases. Therefore, in order to increase the processing accuracy and reduce the steps on the chip, a single semi-cylindrical curved surface KMA may be formed as in the first embodiment, and then the curved surface KMA may be partially dry-etched through a hard mask to adjust the height position for each light-emitting layer.

FIG. 8 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to the fourth embodiment, cut perpendicularly to the optical waveguide direction.
8, the semiconductor laser LD includes m (m=4 in the example of FIG. 8) light emitting layers stacked on an n-type semiconductor substrate 61. The n-type semiconductor substrate 61 is formed on a sapphire substrate 60. The support substrate for the n-type semiconductor substrate 61 is not limited to the sapphire substrate 60, and may be made of a semiconductor or dielectric material different from that of the n-type semiconductor substrate 61. However, the n-type semiconductor substrate 61 may be made of the same material as the light emitting layers.

The n-type semiconductor substrate 61 has m inclined surfaces MD1 to MDm with different inclination angles θ1 to θm. The m light-emitting layers are stacked on the m inclined surfaces MD1 to MDm, respectively, and emit laser light of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined surfaces MD1 to MDm can be provided using a surface where the elements of the n-type semiconductor substrate 61 form a natural superlattice as a reference surface. Here, in order to provide the inclined surfaces MD1 to MDm on the n-type semiconductor substrate 61, a single semi-cylindrical curved surface KMD is formed on the n-type semiconductor substrate 51. The inclined surfaces formed on the n-type semiconductor substrate 61 may have the configuration shown in FIG. 6 or the configuration shown in FIG. 7.

A semiconductor laminate structure 62 including a light emitting layer is formed on an n-type semiconductor substrate 61. The semiconductor laminate structure 62 has m ridge stripe structures SD1 to SDm. A protective film 63 is formed on the n-type semiconductor substrate 61 so that the top surfaces of the ridge stripe structures SD1 to SDm are exposed. A p-side electrode 64 is formed on each of the ridge stripe structures SD1 to SDm in contact with the top surface of the ridge stripe structures SD1 to SDm. An n-side electrode 65 is formed on the n-type semiconductor substrate 61 in contact with the surface of the n-type semiconductor substrate 61.

An n-type GaN layer may be used as the n-type semiconductor substrate 61. In this case, an n-type GaN layer may be grown on the sapphire substrate 60 to a thickness of about 10 to 20 μm, and inclined surfaces MD1 to MDm may be provided on the surface of the n-type GaN layer. For example, an n-type GaN buffer layer, an n-type AlGaN cladding layer, an InGaN multiple quantum well active layer, a p-type AlGaN cladding layer, a p-type GaN contact layer, and the like may be crystal-grown in sequence on the n-type semiconductor substrate 61 to form the semiconductor laminate structure 62.

When an insulating substrate is used as a support substrate for the n-type semiconductor substrate 61, such as when a sapphire substrate 60 is used, providing an n-side electrode on the back surface of the n-type semiconductor substrate 61 will not provide electrical continuity to the element. For this reason, the n-side electrode 65 can be formed after removing a portion of the semiconductor laminate structure 62 on the front surface side of the n-type semiconductor substrate 61, and both the p-side electrode 64 and the n-side electrode 65 can be provided on the front surface side of the n-type semiconductor substrate 61. Alternatively, a GaN layer or GaAs layer may be formed on a Si substrate to be used as a semiconductor substrate.

Figure 9 is a perspective view showing the configuration of a semiconductor light-emitting device according to the fifth embodiment. Note that, while the above-described embodiments use edge-emitting semiconductor lasers as examples, this embodiment uses a vertical cavity semiconductor laser as an example.

In FIG. 9, the semiconductor laser LE has m (m=4 in the example of FIG. 9) light-emitting layers stacked on an n-type semiconductor substrate 71. The n-type semiconductor substrate 71 has m inclined surfaces ME1 to MEm with different inclination angles θ1 to θm. The m light-emitting layers are stacked on the m inclined surfaces ME1 to MEm, respectively, and emit laser light of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined surfaces ME1 to MEm can be provided with the surface on which the elements of the n-type semiconductor substrate 71 form a natural superlattice as a reference surface. Here, in order to provide the inclined surfaces ME1 to MEm on the n-type semiconductor substrate 71, one semi-cylindrical curved surface KME is formed on the n-type semiconductor substrate 71. The inclined surfaces formed on the n-type semiconductor substrate 71 may have the configuration shown in FIG. 6 or the configuration shown in FIG. 7. Also, as shown in FIG. 8, the n-type semiconductor substrate 71 may be provided on a sapphire substrate.

A semiconductor laminate structure 72 including a light-emitting layer is formed on an n-type semiconductor substrate 71. The semiconductor laminate structure 72 has m cylindrical ridge structures SE1 to SEm. Furthermore, a light-emitting portion 73 that emits laser light is provided on the top surface of each of the cylindrical ridge structures SE1 to SEm. Furthermore, an electrode that injects current into the light-emitting layer is provided on the top surface of each of the cylindrical ridge structures SE1 to SEm so as to surround the light-emitting portion 73, and is connected to a pad electrode 74.

As the semiconductor laminate structure 72, for example, a laminate structure of an n-type GaAs buffer layer, a GaInP/AlInP DBR layer (Distributed Bragg Reflector), an n-type AlGaInP layer, an MQW active layer, a p-type AlGaInP layer, a p-type AlAs layer, a p-type GaInP/AlInP DBR layer, and a GaAs contact layer can be used. In this case, a current confinement layer is formed by oxidizing the AlAs layer, and the current carrying region and the transverse mode can be controlled.

The wavelength change for each light-emitting layer depends on the inclination angles θ1 to θm of the light-emitting layer's position, and the emission wavelength changes based on the forbidden band width of the MQW active layer crystal-grown in that area. This makes it possible to achieve multi-wavelength, multi-beam generation for vertical cavity semiconductor lasers LE as well.

In this embodiment, a one-dimensional arrangement in which the light-emitting layers are arranged in a row in the horizontal direction is illustrated, but the light-emitting layers may be arranged two-dimensionally, or the arrangement positions of multiple light-emitting layers may be adjusted depending on the application.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments and includes various modified examples. For example, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

LA semiconductor laser 11 n-type semiconductor substrate 12 semiconductor laminate structure 13 protective film 14 electrodes SA1 to SAm ridge stripe structure 21 n-type buffer layer 22 n-type cladding layer 23 active layer 24 p-type first cladding layer 25 p-type etching stop layer 26 p-type second cladding layer 27 p-type interface layer 28 p-type cap layer

Claims (9)

A semiconductor substrate having inclined surfaces with different inclination angles;
a plurality of light-emitting layers stacked on the inclined surface and configured to emit laser light having a wavelength corresponding to the inclination angle ,
the inclined surface is provided with respect to a crystal plane in which elements of the semiconductor substrate tend to form a natural superlattice as a reference plane;
A semiconductor light-emitting device , comprising: a semiconductor substrate having a convex curved surface; a plurality of light-emitting layers laminated at positions where the inclinations of the tangents to the curved surface differ ; The semiconductor light-emitting device according to claim 1, characterized in that the inclined surface includes a growth surface that is not a specific crystal plane of the semiconductor substrate. the reference surface is set parallel to the rear surface of the semiconductor substrate;
2 . The semiconductor light emitting device according to claim 1 , wherein an average value of the inclination angle of the inclined surface is equal to an inclination angle of the reference surface with respect to the semiconductor substrate. a ridge stripe structure formed on the semiconductor substrate,
2 . The semiconductor light emitting device according to claim 1 , wherein the inclined surface extends along the ridge stripe structure at a constant angle with respect to the semiconductor substrate and is inclined in a direction perpendicular to the ridge stripe structure. 5. The semiconductor light emitting device according to claim 4 , further comprising an electrode provided on the ridge stripe structure so as to be uniform in height. the semiconductor substrate is a GaAs-based substrate,
2. The semiconductor light emitting device according to claim 1, wherein the active layer included in the light emitting layer includes at least one of an AlGaInP crystal layer or a GaInAsP crystal layer (including a case where the Al or As composition is zero). the semiconductor substrate is a GaN-based substrate,
2. The semiconductor light emitting device according to claim 1, wherein the active layer included in the light emitting layer includes at least one of an InGaN crystal layer or an AlGaInN crystal layer. The semiconductor substrate is formed on a support substrate made of a different material, such as a semiconductor or a dielectric;
The semiconductor light-emitting device according to claim 1 , wherein the semiconductor substrate is made of the same material as the light-emitting layer. The semiconductor light-emitting element according to claim 1, characterized in that the laser light has different wavelengths within the same color region.