JP2022162707A - Semiconductor light emitting element - Google Patents

Abstract

To reduce heat generation in a semiconductor light-emitting element and improve slope efficiency.SOLUTION: According to one aspect of a semiconductor light emitting element, it has a semiconductor substrate having a tilted surface with different tilting angles and a plurality of light emitting layers stacked on the tilted surface and emitting laser light with wavelengths corresponding to the tilting angles.SELECTED DRAWING: Figure 1

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 is expanding.
In recent years, in various fields, reality technology such as augmented reality (AR), virtual reality (VR), mixed reality (MR) and alternative reality (SR) has been introduced. It has been put to practical use, and display devices such as head-mounted displays (HMDs), head-up displays, and AR glasses using these technologies have been commercialized.

For example, in a head-mounted display, three colors of RGB (red, green, blue) laser light is used as a light source, an image is created by MEMS (Micro Electro Mechanical Systems), which are spatial modulation elements for image display, and a waveguide is used. A technique for projecting onto the retina or the like through a waveguide is known. A system using this MEMS is capable of widening the color gamut, high resolution, and widening the viewing angle of images, and achieves multi-beams using a plurality of semiconductor lasers for each color of RGB.

Patent Document 1 discloses a multi-wavelength semiconductor laser capable of oscillating lasers of a plurality of wavelengths within the same device. In the technique 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 multiple wavelengths.

Patent document 2 discloses a monolithic laser diode in which a laser diode for CD (light emission wavelength 780 nm) and a laser diode LD2 for DVD (light emission wavelength 650 nm) are mounted on one chip.

JP-A-05-082894 JP 2009-016881 A

Journal of the Japan Society of Applied Physics, Applied Physics 1992, Vol. 61, No. 8, PP806-PP812, "Electronic States of Natural Superlattice Structures of Compound Semiconductors", Hiroshi Yoshida

When a semiconductor laser is used in a display device, a lateral single-mode semiconductor laser with a monolithic structure that independently drives multiple light-emitting layers (multiple light-emitting layers) with a narrow pitch is required in order to improve image quality such as resolution and frame rate.
However, the transverse single mode laser has a narrow wavelength width and high coherence. Therefore, if the wavelengths of the respective colors of RGB are the same and the wavelengths of the respective colors are uniform, the image quality is deteriorated due to the coherence of the laser light.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor light emitting device capable of reducing the coherence of laser light.

According to a semiconductor light emitting device according to an aspect of the present invention, a semiconductor substrate having inclined surfaces with different inclination angles, and a plurality of light emitters laminated on the inclined surfaces and emitting laser beams having wavelengths corresponding to the inclination angles. a layer;

Thus, by forming light-emitting layers on a semiconductor substrate having inclined surfaces with different inclination angles, 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 different wavelengths, it is not necessary to repeat deposition of light-emitting layers for each light-emitting layer that emits laser light of different wavelengths. In addition, since the light-emitting layers that emit laser light of different wavelengths can be formed in one step, it is not necessary to form insulating layers with different aperture ratios on the semiconductor substrate as selective growth masks as in the prior art (Patent Document 1). . In addition, it is possible to prevent the deposition of polycrystals on the selective growth mask, the crystal structure different from the desired layer structure due to the compositional deviation of the light-emitting layer, and the occurrence of crystal defects. Therefore, it is possible to form a plurality of light-emitting layers that emit laser beams of a plurality of wavelengths while suppressing deterioration in crystal quality and an increase in the number of steps.

Further, according to the semiconductor light emitting device according to one aspect of the present invention, the inclined plane is provided with a crystal plane in which elements of the semiconductor substrate tend to form a natural superlattice as a reference plane. In the present invention, the crystal planes that are likely to form a natural superlattice are, for example, lattice planes in which many In atoms are present and lattice planes in which many Ga atoms are present in the group III crystal planes of an InGaP crystal. By doing so, it becomes a lattice arrangement that realizes an energetically stable state.

Accordingly, by changing the tilt angle with respect to the reference plane, it is possible to change the forbidden band width of the light-emitting layer and change the oscillation wavelength. Therefore, by forming light-emitting layers on a semiconductor substrate having inclined surfaces with different inclination angles, it is possible to form a plurality of light-emitting layers that emit laser light of a plurality of wavelengths.

According to the semiconductor light emitting device according to one aspect of the present invention, the inclined plane includes a growth plane that is not a specific crystal plane of the semiconductor substrate. The term "specific crystal plane" as used herein refers to a crystal plane defined by a simple Miller index, such as the (001) plane, the (111) plane, or the (0001) plane.

As a result, the angle of the inclined surface of the semiconductor substrate can be changed in steps of several degrees, and the wavelength of the laser light can be changed while maintaining the same color. Therefore, the coherence of the laser beams can be reduced based on the laser beams of different wavelengths, and the deterioration of image quality due to the coherence of the laser beams can be suppressed.

Further, according to the semiconductor light emitting device according to one aspect of the present invention, the reference plane is set horizontally with respect to the back surface of the semiconductor substrate, and the average value of the inclination angles of the plurality of inclined planes is equal to the semiconductor substrate. is equal to the angle of inclination of the reference plane with respect to

As a result, it is possible to reduce the difference in level with each semiconductor light emitting element forming part due to the formation of the inclined surface in the manufacturing process of the semiconductor light emitting element, and it is possible to suppress the deterioration of the processing accuracy in processes such as photolithography and dry etching. .

Further, according to the semiconductor light emitting device according to one aspect of the present invention, a plurality of light emitting layers are stacked at positions where the tangent lines of the curved surface formed on the semiconductor substrate have different inclinations.

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

Further, according to a semiconductor light emitting device according to an aspect of the present invention, a ridge stripe structure formed on the semiconductor substrate is provided, and the inclined surface has a constant angle along the ridge stripe structure with respect to the semiconductor substrate. and is inclined in a direction perpendicular to the ridge stripe structure.

As a result, laser light can be amplified for each wavelength while confining light along the waveguide direction of the laser light, and multi-wavelength multi-beam can be achieved while improving light emission efficiency.

Further, according to the semiconductor light emitting device according to one aspect of the present invention, the electrodes are provided on the ridge stripe structure so as to have the same height.

As a result, the multi-wavelength multi-beam semiconductor laser can be junction-down-bonded mounted on the submount on which the electrodes are arranged. Therefore, the heat dissipation of the multi-wavelength multi-beam semiconductor laser can be improved, and the reliability of the multi-wavelength multi-beam semiconductor laser can be improved.

Further, according to the 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 is an AlGaInP crystal layer or a GaInAsP crystal layer (with an Al or As composition of zero). including the case) at least one of.

As a result, a multi-wavelength multi-beam semiconductor laser can be realized in the red to near-infrared region.

Further, according to the 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 and an AlGaInN crystal layer. .

As a result, a multi-wavelength multi-beam semiconductor laser can be realized in the blue-violet to green region.

Further, according to the 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 of a different material, and the semiconductor substrate is made of the same material as the light emitting layer. consists of

As a result, the thickness of the semiconductor substrate can be reduced, the cost of the semiconductor substrate can be reduced, and the semiconductor substrate can be stably handled even when the semiconductor substrate is easily cracked.

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

As a result, the coherence of the laser light can be reduced based on the laser light of a plurality of wavelengths, and the deterioration of the image quality due to the coherence of the laser light can be suppressed.

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

FIG. 2 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; 2 is an enlarged cross-sectional view showing one ridge stripe structure of the semiconductor light emitting device of FIG. 1; FIG. FIG. 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; It is a perspective view which shows an example of the manufacturing method of the semiconductor light-emitting device which concerns on 1st Embodiment. It is a perspective view which shows an example of the manufacturing method of the semiconductor light-emitting device which concerns on 1st Embodiment. It is a perspective view which shows an example of the manufacturing method of the semiconductor light-emitting device which concerns on 1st Embodiment. It is a perspective view which shows an example of the manufacturing method of the semiconductor light-emitting device which concerns on 1st Embodiment. It is a perspective view which shows an example of the manufacturing method of the semiconductor light-emitting device which concerns on 1st Embodiment. FIG. 4 is a cross-sectional view showing an example of a method for manufacturing the ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 4 is a perspective view showing an example of a method for manufacturing a ridge stripe structure of the semiconductor light emitting device according to the first embodiment; FIG. 5 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to a second embodiment, cut perpendicularly to the optical waveguide direction; FIG. 10 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to a third embodiment, cut perpendicularly to the optical waveguide direction; FIG. 10 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. 11 is a perspective view showing the configuration of a semiconductor light emitting device according to a fifth embodiment;

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention, and not all combinations of features described in the embodiments are essential for the configuration of the present invention. The configuration of the embodiment can be appropriately modified or changed according to the specifications of the device to which the present invention is applied and various conditions (use conditions, use environment, etc.). The technical scope of the present invention is defined by the claims and is not limited by the following individual embodiments. In addition, the drawings used in the following description may differ from the actual structure in terms of scale, shape, etc., in order to make each configuration easier to understand.

FIG. 1 is a cross-sectional view showing the structure of the semiconductor light emitting device according to the first embodiment cut perpendicularly to the optical waveguide direction, and FIG. 2 is an enlarged view of one ridge stripe structure of the semiconductor light emitting device of FIG. It is a sectional view. In addition, in FIG. 2, the area|region R of FIG. 1 was expanded and shown. In the following description, four light-emitting layers are stacked on a semiconductor substrate, and four laser beams with different wavelengths are emitted. may be stacked to emit m laser beams of different wavelengths. In the following description, a semiconductor laser with multiple wavelengths in the red region will be taken as an example.

In FIGS. 1 and 2, the semiconductor laser LA includes 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 planes 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 beams of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined planes MA1 to MAm can be provided using a crystal plane in which the elements of the n-type semiconductor substrate 11 easily form a natural superlattice as a reference plane. The inclined planes MA1 to MAm preferably include growth planes that are not specific crystal planes of the n-type semiconductor substrate 11 . The term "specific crystal plane" as used herein refers to a crystal plane defined by a simple Miller index, such as the (001) plane, the (111) plane, or the (0001) plane. It is preferable that this reference plane is set horizontally with respect to the back surface of the n-type semiconductor substrate 11 and that the average value of the inclination angles θ1 to θm is equal to the inclination angle of the reference plane with respect 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 SiO ₂ film or a SiN film. A p-side electrode 14 is formed on each of the ridge stripe structures SA1-SAm so as to be in contact with the top surfaces of the ridge stripe structures SA1-SAm.

As shown in FIG. 2, in the semiconductor laminated 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 A cladding layer 26 , a p-type interface layer 27 and a p-type cap layer 28 are sequentially laminated on the n-type semiconductor substrate 11 . Here, the p-type second cladding layer 26, the p-type interface layer 27 and the p-type cap layer 28 of the semiconductor laminated structure 12 are patterned into a ridge stripe. At this time, the p-type etching stop layer 25 can be used to stop etching when patterning the p-type second cladding layer 26, the p-type interface layer 27 and the p-type cap layer 28 into a ridge stripe.

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

In order to provide the inclined surfaces MA1 to MAm on the n-type semiconductor substrate 11, the chip width is set to, for example, 300 to 400 μm, and the curved surface KMA periodically convexly curved at the pitch of the chip width is formed on the n-type semiconductor substrate 11. can be formed on. The shape of this curved surface KMA may be semicylindrical or arch-shaped. By arranging the m inclined surfaces MA1 to MAm at positions where the tangents of the curved surface KMA formed on the n-type semiconductor substrate 11 have different inclinations, the inclination angles θ1 to θm of the m inclined surfaces MA1 to MAm are determined. can be different from each other. By stacking m light-emitting layers on each of the inclined surfaces MA1 to MAm, laser light with different wavelengths can be emitted from each light-emitting layer.

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

When a GaInP crystal grown on a GaAs substrate is used for the active layer 23, the forbidden band width 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", growth during crystal growth By adjusting the temperature, the V/III ratio, and the off-angle of the substrate, the bandgap can be changed by about 1.85 to 1.91 eV (corresponding to the range of 649 to 670 nm in light wavelength). In the GaInP crystal, a crystal lattice is formed by group III elements Ga and In and group V element P, and Ga and In are arranged irregularly in a disordered state. On the other hand, when grown on a crystal having a specific crystal growth condition and a substrate plane, Ga and In are regularly arranged, and an ordered state in which Ga planes and In planes are alternately arranged may occur. This ordered state is called a natural superlattice because a GaP-type InP superlattice is spontaneously formed. In the state where this natural superlattice is formed, the bandgap is reduced and the bandgap of the GaInP layer is changed. When the inclination is changed from the surface on which the natural superlattice is formed, the regularity of the natural superlattice is gradually disturbed according to the inclination, and the forbidden bandwidth gradually increases. It can be changed gradually. The formation of a natural superlattice is a phenomenon inherent in 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 .

If the crystal growth conditions such as the V/III ratio of the raw material gas and the growth temperature are changed, the formation of the natural superlattice is spontaneously suppressed, and the variation of the forbidden band width is almost eliminated regardless of the crystal plane orientation of the substrate surface. Sometimes. For this reason, it is necessary to adopt crystal growth conditions for obtaining a desired wavelength difference according to the wavelength range of the semiconductor laser LA. However, even if the crystal growth conditions with such a large wavelength change are set, there is no adverse effect such as deterioration of the quality of the grown (Al)GaInP crystal or deterioration of the characteristics and performance of the fabricated semiconductor laser LA. . Therefore, it is possible to select the crystal growth conditions under which the desired wavelength difference can be obtained within the range of the crystal growth conditions under which the semiconductor laser LA with the desired performance can be realized.

As described above, according to the above-described embodiments, on the n-type semiconductor substrate 11, the stripe-shaped waveguide structure extends at the position where each light-emitting layer is arranged, and the inclined planes MA1 to By forming MAm and controlling the tilt angles θ1 to θm with respect to the substrate surface for each light-emitting layer, the light-emitting wavelength can be adjusted for each light-emitting layer. A semiconductor that operates at a different wavelength for each light-emitting layer with a simple manufacturing process. A laser LA can be constructed. 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 according to the tilt angles θ1 to θm. As a result, the forbidden band width of the active layer 23 can be changed according to the tilt angles θ1 to θm, and the oscillation wavelength can be changed for every m light emitting layers. Also, an example in which the tilt angles θ1 to θm change stepwise is shown, but it is not necessary to change the tilt angles θ1 to θm at equal intervals. ˜θm need not all be different.

Further, in the semiconductor laser LA, the wavelength control of each light emitting layer can be realized by adjusting the tilt angles θ1 to θm of the inclined surfaces MA1 to MAm provided on the n-type semiconductor substrate 11 for each light emitting layer. Therefore, the semiconductor laser LA can be manufactured without repeating the multi-layer crystal growth for forming the semiconductor laminated structure 12, and the cost increase can be suppressed. In addition, since it is possible to prevent exposure to multiple thermal histories without repeating multilayer crystal growth multiple times, diffusion of dopants in the crystal, desorption / substitution / oxidation of constituent elements near the crystal surface, etc. It is possible to prevent deterioration of the crystal quality of the crystal, contamination of impurities from the outside, and the like. Furthermore, since the light-emitting layers emitting laser beams of different wavelengths can be formed in one step, it is no longer necessary to form insulating layers with different aperture ratios on the n-type semiconductor substrate 11 as selective growth masks. It is possible to prevent the deposition of polycrystals on the light-emitting layer, the crystal structure different from the desired layer structure due to the compositional deviation of the light-emitting layer, and the occurrence of crystal defects. As a result, the wavelength multi-beam can be achieved while suppressing deterioration of the quality of the semiconductor laser LA.

FIG. 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 FIG. 3 shows an example of the relationship between the tilt angle of the GaAs substrate from the (001) plane and the emission wavelength of the GaInP crystal grown thereon due to photoluminescence.

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, the wavelength difference between the light-emitting layers is about 20 nm. It can be seen that the beam laser can be easily produced. Although the diagram shows the emission wavelength in the GaInP layer formed on the GaAs substrate, even when the GaInP layer or the AlGaInP layer is used as the well layer of the multiple quantum well structure, the prohibition of the multiple quantum well layer A change in bandwidth appears as a difference in emission wavelength.

As for how to swing the tilt angle at the position where the light-emitting layer is arranged, if the tilt angle of the substrate surface is set to swing in the range of 0 degrees to 15 degrees, the wavelength difference between the light-emitting layers can be maximized, and the wavelength difference is 20 nm or more. wavelength difference can be obtained. A wavelength difference of this magnitude is sufficient to improve image quality. Therefore, the tilt angle of the substrate surface at the position where each light-emitting layer is arranged can be changed from 0 degrees to 15 degrees at the maximum, and the required wavelength difference can be obtained according to the requirements of the system in which the semiconductor laser is actually used. Therefore, the tilt angle of each light-emitting layer may be changed as much as necessary. For example, in order to obtain a wavelength difference of 10 nm, the tilt angle of the position where the light-emitting layer is arranged should be changed within the range of 7 degrees to 12 degrees.

The original substrate tilt angle of the semiconductor substrate may be selected in the same manner as in the case of manufacturing a single-wavelength semiconductor laser. It is preferable to take the approximate mean value of the amplitude of . In the above-described embodiments, the ridge structure formed on a plane that is more inclined than the original surface of the semiconductor substrate is tilted, and the light-emitting layers (especially the outer two light-emitting layers in FIG. 1) are also tilted. This tilt angle is preferably 15 degrees or less so as not to significantly affect the fabrication process and performance of the semiconductor laser.

In the configuration of FIG. 1, in order to provide a plurality of tilt angles on the n-type GaAs semiconductor substrate, the n-type GaAs semiconductor substrate ((001) 10° off substrate) is processed to have a semicylindrical shape extending in the cavity direction of the laser. slope formation was performed. At this time, as a method of processing the substrate surface, for example, a method of performing microlens processing on the surface of a semiconductor material or a glass material can be applied.

However, as shown in FIG. 1, when a large semi-cylindrical slope is formed, the step between the top of the curved surface KMA and the position inclined by 15 degrees becomes large. For this reason, it is necessary to adjust the photoresist coating conditions and etching conditions when performing various processing and pattern formation in the wafer process. Therefore, by setting the substrate tilt angle of the semiconductor substrate itself to approximately the average value of the tilt angles of the positions where the light-emitting layers are arranged, the tilt angle of the positions where the light-emitting layers are arranged can be reduced, and the likelihood of the process surface can be improved. .

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

Next, the semiconductor wafer W with the resist pattern 31 formed thereon is heated at about 200° C. for several minutes to 20 minutes. At this time, the pattern shape is deformed by the thermoplasticity of the resist pattern 31, and a semicylindrical resist pattern 32 is formed on the semiconductor wafer W. As shown in FIG. (Fig. 4B)

Next, the thickness of the resist pattern 32 is reduced by dry etching from the upper surface of the semiconductor wafer W. Next, as shown in FIG. At this time, the thinning of the resist pattern 32 progresses while the surface of the semiconductor wafer W exposed from the resist pattern 32 is also etched. Therefore, in the portion where the thickness of the resist pattern 32 is thin, the etching amount in the thickness direction of the semiconductor wafer W increases, and the curved surfaces KMA periodically arranged in the direction perpendicular to the resonator direction are formed on the surface of the semiconductor wafer W. formed in (Fig. 4C)

In this embodiment, an example in which the curved surfaces KMA are arranged periodically on the semiconductor wafer W is shown, but the arrangement is not limited to the periodic arrangement of the curved surfaces KMA. Depending on how the wavelength of each light-emitting layer is changed or the arrangement of chips on the semiconductor wafer W, a non-periodic pattern arrangement or a structure in which the period is partially changed may be employed. Further, in this process step, a method of directly processing the semiconductor wafer W using the resist pattern 32 as an etching mask has been shown. In some cases, it is difficult to adjust the selection ratio. In this case, an intermediate layer such as a hard mask made of SiO ₂ or the like is sandwiched between the resist pattern 32 and the semiconductor wafer W, the resist pattern 32 is temporarily transferred to the hard mask, and then the hard mask is used as an etching mask. A semiconductor wafer W may be processed.

When the shape of the resist pattern is transferred to the semiconductor substrate in order to form an inclined surface on the semiconductor substrate using the microlens processing method, the etching selectivity between the material of the resist pattern and the semiconductor substrate is A height of a feature to be formed on a semiconductor substrate is determined. The etching selectivity can be freely adjusted to some extent by adjusting the etching gas and dry etching conditions or by using an intermediate layer such as a SiO ₂ film.

However, there is a possibility that the tilt angle of the surface of the semiconductor substrate at the position where each light-emitting layer is arranged varies due to process variations during processing of the semiconductor substrate. For example, even if the tilt angle of the semiconductor surface deviates by ±1 degree at the position of each light-emitting layer or a specific light-emitting layer, the wavelength difference for each light-emitting layer is sufficiently secured from the relationship between the substrate tilt angle and the wavelength change in FIG. be able to.

As for the angle deviation of the inclined surface of the semi-cylindrical curved surface KMA with respect to the direction of the cavity, it is only necessary to ensure the pattern alignment accuracy during fabrication of the single-wavelength laser. For example, for one laser chip, the pattern shape of the inclined surface may be arranged at an angle of 1 to 2 degrees with respect to the cavity direction. In the single-wavelength semiconductor laser fabrication process, the angular displacement of the pattern is suppressed to within about ±0.03° in order to prevent cleavage position displacement in the bar-shaped cleavage during facet coating. Also in the multi-wavelength semiconductor laser manufacturing process, pattern formation may be performed with the same alignment accuracy as in 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 manufactured by performing a semiconductor lamination process similar to the semiconductor lamination process for a single-wavelength semiconductor laser. At this time, as shown in FIG. 4D, the semiconductor laminated 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, by dry-etching the semiconductor laminated structure 12 using a hard mask such as an SiO ₂ film as an etching mask, ridge stripe structures SA1 to SAm are formed for each of the element regions RA1 to RA4, as shown in FIG. 4E. Detailed manufacturing process steps are shown in FIGS. 5A to 5J, and in FIG. 4E, after removing the hard mask from the semiconductor wafer W, a protective film such as a SiO ₂ film is formed to cover the ridge stripe structures SA1-SAm. 13 are formed on the semiconductor wafer W. FIG.
Next, an opening is formed in the protective film 13 for passing current through the ridge stripe structures SA1 to SAm.
Next, the p-side electrodes 14 are formed in contact with the top surfaces of the ridge stripe structures SA1 to SAm through the openings formed in the protective film 13 for each of the ridge stripe structures SA1 to SAm in the element regions RA1 to RA4.

Although the ridge stripe structures SA1 to SAm protected by the insulating film are shown in the above-described embodiments, a laser structure in which GaAs, AlInP, or the like is buried and grown may be used instead of the insulating film.
Moreover, in this embodiment, the structure in which each light-emitting layer is formed in a portion having a step of one to several microns is shown. At this time, the p-type electrode 14 may be plated with Au to adjust the height of the upper portion of each light-emitting layer and planarize the chip surface.

In this embodiment, the case of the red laser using GaAs as the semiconductor substrate and the AlGaInP-based semiconductor material as the constituent material of the semiconductor laser is shown, but the constituent materials of the semiconductor substrate and the semiconductor laser are not limited to this material system. . For example, it may be applied to a semiconductor laser in the red to near-infrared region using GaAs for the semiconductor substrate and InGaAsP for the semiconductor material of the active layer, or GaN for the semiconductor substrate and nitrides such as AlGaN and InGaN for the constituent materials of the semiconductor laser. It may also be applied to a GaN-based blue-violet to green semiconductor laser using a solid semiconductor.

For example, when fabricating a blue semiconductor laser with an oscillation wavelength of 450 to 460 nm, In _x Ga _1-x N (0.18 ≤ x ≤ 0.2) is used. In order to obtain a wavelength difference of 10 nm between the light-emitting layers, it is sufficient that the In composition difference is about 0.015 to 0.02. A light-emitting layer may be provided on each inclined surface.

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

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

Next, as shown in FIG. 5C, the entire surface of the SiO ₂ film 33 is coated with a resist film by a method such as spin coating. Then, a stripe-shaped resist pattern 34 is formed on the SiO ₂ film 33 by patterning the resist film by photolithography.

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

Next, as shown in FIG. 5E, using the SiO ₂ film 33 patterned in stripes as an etching mask, the p-type cladding layer of the semiconductor multilayer structure 12 is partially removed by dry etching to form the ridge stripe structures SA1 to SAm. Form.

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

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

Next, as shown in FIG. 5H, in order to independently drive each light emitting layer, a p-side electrode 14 connected to the top surface of the semiconductor laminated structure 12 through the opening 15 is placed on each of the ridge stripe structures SA1 to SAm. to form. At this time, the p-type electrode 14 may be plated with Au to make the height of the p-type electrode 14 uniform. In this case, the plating thickness can be adjusted for each of the ridge stripe structures SA1 to SAm by adjusting the energization time for electroplating the p-side electrode 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 surface of the semiconductor wafer W. As shown in FIG.

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 planes MB1 to MBm with different inclination angles θ1 to θm. The m light-emitting layers are laminated on the m inclined planes MB1 to MBm, respectively, and emit laser beams of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined planes MB1 to MBm can be provided using the plane where the elements of the n-type semiconductor substrate 41 form a natural superlattice as a reference plane. Here, the tilt angles θ1 to θm are individually set for the tilted surfaces MB1 to MBm for each of the light emitting layers formed thereon. At this time, the heights of the inclined planes 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 kept small.

A semiconductor laminated structure 42 including a light emitting layer is formed on an n-type semiconductor substrate 41 . The semiconductor laminated structure 42 includes 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 so as to be in contact with the top surfaces of the ridge stripe structures SB1 to SBm.

Note that the inclined surfaces MB1 to MBm on the n-type semiconductor substrate 41 can be formed by using wet etching. When wet-etching the GaAs substrate, a resist mask having a certain solubility in the etchant is used as an etching mask to form the inclined planes MB1 to MBm. When such an etching mask is used, the resist mask is dissolved during etching of the GaAs substrate, and the pattern boundary gradually recedes, so that the inclination angles θ1-θm of the inclined surfaces MB1-MBm can be controlled. The inclination angles θ1 to θm of the inclined surfaces MB1 to MBm can be adjusted, for example, by adjusting the mixing ratio of the etchant used, specifically, the mixing ratio of sulfuric acid and hydrogen peroxide.

In addition, by utilizing the effect of increasing the etching rate of the semiconductor crystal due to the photochemical reaction and proceeding with chemical etching while projecting the etching pattern, the inclined planes MB1 to MBm having the desired inclination angles θ1 to θm are formed on the n-type semiconductor substrate 41. You may make it form to. After forming the inclined planes MB1 to MBm on the n-type semiconductor substrate 41, a multi-wavelength multi-beam laser can be manufactured by the same process as in the first embodiment.

In this embodiment, since the positions of the light-emitting layers in the height direction are substantially aligned, height adjustment by additional Au plating as in the first embodiment can be omitted.

FIG. 7 is a sectional view showing the configuration of the 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 planes MC1 to MCm with different inclination angles θ1 to θm. The m light-emitting layers are laminated on the m inclined planes MC1 to MCm, respectively, and emit laser beams of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined planes MC1 to MCm can be provided using the plane where the elements of the n-type semiconductor substrate 51 form a natural superlattice as a reference plane. Here, the n-type semiconductor substrate 51 is formed with a curved surface KMC on which the inclined surfaces MC1 to MCm are set. The cross section of this curved surface KMC can have a shape that undulates periodically. The inclination angles θ1 to θm are individually set for each period of the undulation of the curved surface KMC. At this time, the difference in height between the inclined surfaces MC1 to MCm on the n-type semiconductor substrate 51 can be reduced as compared with the configuration in which the inclined surfaces MA1 to MAm are provided on one semicylindrical curved surface KMA in FIG. As a result, unevenness and steps on the chip surface can be kept small.

A semiconductor laminated structure 52 including a light emitting layer is formed on an n-type semiconductor substrate 51 . The semiconductor laminated structure 52 includes 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 so as to be in contact with the top surfaces of the ridge stripe structures SC1 to SCm.

When forming the curved surface KMC on the n-type semiconductor substrate 51, a microlens processing method can be used as shown in FIGS. 4A to 4C. At this time, if too small a pattern is formed, the processing accuracy is lowered. Therefore, in order to increase the processing accuracy and reduce the steps on the chip, after forming one semicylindrical curved surface KMA in the same manner as in the first embodiment, the curved surface KMA is partially dry-etched through a hard mask. The height position may be adjusted for each light-emitting layer by performing this method.

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.
In FIG. 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 . An 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. FIG. However, the n-type semiconductor substrate 61 can be made of the same material as the light emitting layer.

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

A semiconductor laminated structure 62 including a light emitting layer is formed on an n-type semiconductor substrate 61 . The semiconductor laminated structure 62 includes 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-SDm to contact the top surfaces of the ridge stripe structures SD1-SDm. An n-side electrode 65 is formed on the n-type semiconductor substrate 61 so as to be 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 . At this time, an n-type GaN layer of about 10 to 20 μm can be grown on the sapphire substrate 60, and inclined planes MD1 to MDm can be provided on the surface of the n-type GaN layer. On this n-type semiconductor substrate 61, 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, etc. are sequentially crystal-grown to form semiconductor lamination. A structure 62 may be formed.

When an insulating substrate is used as a supporting substrate for the n-type semiconductor substrate 61, as in the case of using the sapphire substrate 60, even if an n-side electrode is provided on the back surface of the n-type semiconductor substrate 61, the device cannot be electrically connected. Therefore, the n-side electrode 65 is formed after removing a part of the semiconductor laminated structure 62 on the surface side of the n-type semiconductor substrate 61 , and both the p-side electrode 64 and the n-side electrode 65 are connected to the n-type semiconductor substrate 61 . can be provided on the surface side of the Alternatively, a GaN layer or a GaAs layer may be formed on a Si substrate and used as a semiconductor substrate.

FIG. 9 is a perspective view showing the configuration of a semiconductor light emitting device according to the fifth embodiment. In addition, although the edge emitting semiconductor laser is taken as an example in the above-described embodiments, the vertical cavity semiconductor laser is taken as an example in this embodiment.

In FIG. 9, the semiconductor laser LE includes 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 planes 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 beams of m wavelengths according to the inclination angles θ1 to θm. At this time, the inclined planes ME1 to MEm can be provided using the plane where the elements of the n-type semiconductor substrate 71 form a natural superlattice as a reference plane. Here, one semicylindrical curved surface KME is formed on the n-type semiconductor substrate 71 in order to provide the inclined surfaces ME1 to MEm on the n-type semiconductor substrate 71 . The inclined surface formed on the n-type semiconductor substrate 71 may have the structure shown in FIG. 6 or the structure shown in FIG. Also, as shown in FIG. 8, an n-type semiconductor substrate 71 may be provided on the sapphire substrate.

A semiconductor laminated structure 72 including a light emitting layer is formed on an n-type semiconductor substrate 71 . The semiconductor laminated structure 72 includes m cylindrical ridge structures SE1 to SEm. A light emitting portion 73 for emitting a laser beam is provided on the top surface of each of the cylindrical ridge structures SE1 to SEm. Further, an electrode for injecting current into the light emitting layer is provided on the top surface of the cylindrical ridge structures SE1 to SEm so as to surround the light emitting portion 73 and is connected to the pad electrode 74. FIG.

As the semiconductor laminated structure 72, for example, 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, p A stack of type GaInP/AlInP DBR layers and GaAs contact layers can be used. At this time, a current constriction layer is formed by oxidizing the AlAs layer, and the conducting region and the transverse mode can be controlled.

Here, the wavelength change for each light-emitting layer depends on the tilt angles θ1 to θm of the position where the light-emitting layer is arranged, and the emission wavelength changes based on the bandgap of the MQW active layer crystal-grown in that portion. Therefore, the vertical cavity semiconductor laser LE can also be multi-wavelength multi-beam.

In this embodiment, a one-dimensional arrangement of the light-emitting layers is exemplified in the horizontal direction. You may make it so.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

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

Claims (11)

a semiconductor substrate having inclined surfaces with different inclination angles;
A semiconductor light-emitting device comprising a plurality of light-emitting layers stacked on the inclined surface and emitting laser light having a wavelength corresponding to the inclination angle. 2. The semiconductor light emitting device according to claim 1, wherein the inclined plane is provided with a crystal plane in which elements of the semiconductor substrate tend to form a natural superlattice as a reference plane. 2. The semiconductor light emitting device according to claim 1, wherein said inclined plane includes a growth plane that is not a specific crystal plane of said semiconductor substrate. The reference plane is set horizontally with respect to the back surface of the semiconductor substrate,
3. The semiconductor light emitting device according to claim 2, wherein an average value of inclination angles of said inclined planes is equal to an inclination angle of said reference plane with respect to said semiconductor substrate. 2. The semiconductor light-emitting device according to claim 1, wherein a plurality of light-emitting layers are stacked at positions with different inclinations of tangents to the curved surface formed on the semiconductor substrate. A ridge stripe structure formed on the semiconductor substrate,
2. The semiconductor according to claim 1, wherein said inclined surface extends at a constant angle with respect to said semiconductor substrate along said ridge stripe structure and is inclined in a direction orthogonal to said ridge stripe structure. light-emitting element. 7. The semiconductor light-emitting device according to claim 6, further comprising electrodes provided on the ridge stripe structure so as to have the same 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 and a GaInAsP crystal layer (including cases where the Al or As composition is zero). element. The semiconductor substrate is a GaN -based substrate,
2. The semiconductor light emitting device according to claim 1, wherein an active layer included in said light emitting layer includes at least one of an InGaN crystal layer and an AlGaInN crystal layer. The semiconductor substrate is formed on a support substrate composed of a semiconductor or dielectric of a different material,
2. The semiconductor light-emitting device according to claim 1, wherein said semiconductor substrate is made of the same material as said light-emitting layer. 2. The semiconductor light emitting device according to claim 1, wherein said laser beams have different wavelengths within the same color range.

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