Preparation method of AlGaN-based edge-emitting laser cavity surface
By combining dry and wet etching techniques at room temperature, the resonant cavity surface of the AlGaN base side emission laser was prepared, which solved the problems of rough cavity surface and high-temperature etching damage in the prior art, and achieved efficient and safe cavity surface preparation.
Patent Information
- Application Number
- CN202411557555.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-04
- Publication Date
- 2025-02-18
AI Technical Summary
The prior art is difficult to prepare vertical, smooth and damage-free resonant cavity surfaces for AlGaN base side emission lasers at room temperature, and traditional wet etching processes have problems of high temperature damage and safety hazards.
By designing a simple process at room temperature, using dry etching technology to prepare ridges and end faces, and using wet etching solution at room temperature to etch out vertically smooth resonant cavity surfaces to avoid high-temperature etching.
A vertical, smooth and damage-free resonant cavity surface is achieved at room temperature, which shortens etching time, reduces safety risks, and improves production efficiency.
Smart Images
Figure CN119481957A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of semiconductor optoelectronics, and in particular to a method for preparing a cavity surface of an AlGaN-based edge-emitting laser. Background Art
[0002] Semiconductor lasers are widely used in communication, storage, medical treatment, sensing, display, military security and other fields due to their advantages of small size, high efficiency, low cost and long life. In particular, ultraviolet edge-emitting semiconductor lasers based on AlGaN materials can achieve laser wavelength regulation from near ultraviolet to deep ultraviolet by adjusting the composition of Al and Ga, making them an ideal choice for future ultraviolet lasers.
[0003] At present, due to the scarcity and high cost of homogeneous substrates, AlGaN-based edge-emitting lasers usually need to be heteroepitaxially grown on c-plane sapphire substrates. However, due to the large lattice mismatch and high sapphire hardness, traditional cutting and cleavage methods make it difficult to form vertical, smooth and damage-free resonant cavity surfaces. In addition, although dry etching can be used to form cavity surfaces, ion bombardment can cause the cavity surface roughness to be as high as tens of nanometers, seriously affecting the optical performance of the laser. On the other hand, some recent literature mentions that combining dry and wet etching processes can improve the quality of the cavity surface, but its wet process usually needs to be carried out under high temperature conditions, which will not only cause serious damage to the laser epitaxial structure, but also lead to long etching time, low efficiency, and greater safety hazards. Even more challenging is that researchers have tried to perform wet etching directly at room temperature, but traditional process designs often result in cavity surfaces that are too rough.
[0004] Therefore, there is an urgent need for an advanced process design that can achieve vertical, smooth and damage-free resonant cavity surfaces at room temperature, so as to shorten etching time, reduce safety risks and improve production efficiency, which will be a key step towards the mass production of ultraviolet semiconductor lasers. Summary of the invention
[0005] In order to solve the above deficiencies in the prior art, the present invention proposes a method for preparing the cavity surface of an AlGaN-based edge-emitting laser, which does not require a high-risk high-temperature wet etching process and complex process steps, but only requires a simple process design to achieve a vertical, smooth and damage-free resonant cavity surface at room temperature.
[0006] The method for preparing the AlGaN-based edge-emitting laser cavity facet of the present invention comprises the following steps:
[0007] 1) Growth of laser epitaxial layer:
[0008] Growing a laser epitaxial layer on a substrate, wherein the laser epitaxial layer is, from bottom to top, an AlN template, an n-type cladding layer, an n-type waveguide layer, an AlGaN / AlGaN quantum well layer, a p-type waveguide layer, a p-type cladding layer and a p-type GaN layer, to obtain an AlGaN base edge emitting laser epitaxial wafer;
[0009] 2) Design ridges and end faces:
[0010] The surface of the laser epitaxial layer is designed to have a plurality of periodically evenly distributed units, each unit including a ridge and an end face, the ridge is located on the end face, the width of the end face is greater than the width of the ridge, the length of the ridge is greater than the length of the end face, and the two ends of the ridge grow out of the two ends of the end face respectively, and the distance of each end growing out is not less than 30 microns to 100 microns;
[0011] 3) Dry etching to prepare ridges:
[0012] a) Cleaning AlGaN base edge emitting laser epitaxial wafer;
[0013] b) depositing a first protective film on the surface of the laser epitaxial layer;
[0014] c) preparing a ridge pattern on the first protective film;
[0015] d) using dry etching technology to carve out periodic ridges, the etching depth of the ridges from top to bottom should at least reach the upper surface of the n-type waveguide, and at most reach the lower surface of the n-type waveguide, exposing the side wall of the AlGaN / AlGaN quantum well layer;
[0016] 4) Dry etching to prepare the end face:
[0017] a) cleaning the surface of the laser epitaxial layer to remove the residual first protective film;
[0018] b) depositing a second protective film on the surface of the laser epitaxial layer having a periodic ridge pattern;
[0019] c) preparing an end surface pattern on the second protective film;
[0020] d) using dry etching technology to etch out periodic end faces, and the end face etching depth is from top to bottom to the n-type cladding layer; after the dry etching is completed, the length of the end face located under the ridge is the same as the length of the ridge, and the two side walls at both ends of the end face where the ridge grows out are in the same plane as the two side walls of the end face covered by the ridge;
[0021] 5) Wet etching to produce a vertical, smooth and damage-free resonant cavity surface:
[0022] a) preparing a wet etching solution at room temperature, and immersing the laser epitaxial layer formed with a ridge and an end face by dry etching in the prepared wet etching solution at room temperature; the wet etching solution etches the two side walls at both ends of the end face grown from the ridge and the two side walls of the part of the end face covered by the ridge in the same plane from the rough surface to a smooth surface, and the surface is perpendicular to the end face; at room temperature, the wet etching rate of the m-plane, i.e., the (1-100) crystal plane, is slower than the etching rate of the (11-20) crystal plane, and the room temperature wet etching exposes the m-plane of the side walls at both ends of the end face, as well as the two side walls at both ends of the end face grown from the ridge in the same plane and the two side walls of the part of the end face covered by the ridge m-surface; and the wet etching rate is relatively slow at room temperature, so it is easier to accurately control the wet etching rate. By using room temperature wet etching, it is easier to control the etching rate of the side walls at both ends of the end face with a large width, so it is easier to control the m-surface of the end face to become smooth. When the m-surface of the end face is smooth, the two side walls at both ends of the ridge that are in the same plane as the m-surface of the end face will also become smooth as the m-surface of the end face becomes smooth; the two side walls at both ends of the end face grown at both ends of the ridge are used as the resonant cavity surface, so that a vertical, smooth and damage-free resonant cavity surface is obtained without using a high-precision precision lithography machine, and the side walls of the exposed AlGaN / AlGaN quantum well layer are used as the light-emitting surface to realize deep ultraviolet laser emission;
[0023] b) Cleaning the surface of the laser epitaxial layer with a vertical, smooth and damage-free resonant cavity surface to remove surface residues, and characterizing the cavity surface by scanning electron microscopy.
[0024] Wherein, in step 1), the substrate is a sapphire substrate, the growth of the laser epitaxial layer adopts metal organic chemical vapor deposition or molecular beam epitaxy, and the thickness of the AlN template is 1 to 4 microns.
[0025] In step 2), the shape of the ridge is rectangular or trapezoidal, the width of the ridge is 1 to 15 microns, and the length of the ridge is 1030 to 1100 microns; the shape of the end face is rectangular or trapezoidal, the width is 50 to 100 microns, and the length of the end face is 950 to 1000 microns.
[0026] In step 3) a), cleaning is performed by organic cleaning, oxide layer removal or final cleaning, followed by drying; the cleaning time is 5 to 15 minutes to remove organic impurities and particles on the surface.
[0027] In step 3) b), the deposition method is chemical vapor deposition, atomic layer deposition, physical vapor deposition or spin coating, and the deposition temperature is 50 to 350 degrees Celsius; the material of the first protective film is silicon dioxide, silicon nitride, photoresist, aluminum oxide or polysilicon; the thickness of the first protective film is 50 to 400 nanometers.
[0028] In step 3) c), the instrument for preparing the ridge pattern is an electron beam lithography machine, an ion beam lithography machine or an ultraviolet lithography machine; the thickness of the photoresist is 0.5 to 2 microns; the exposure time is 15 to 40 seconds; and the development time is 35 to 100 seconds.
[0029] In step 3) d), the dry etching instrument is a plasma etcher or a reactive ion etcher; the dry etching gas is chlorine, boron trichloride, hydrogen chloride or argon; and the etching time is 70 to 90 seconds.
[0030] In step 4) a), cleaning is performed by organic cleaning, oxide layer removal or final cleaning, followed by drying; the cleaning time is 5 to 30 seconds.
[0031] In step 4) b), the method for depositing the second protective film is chemical vapor deposition, atomic layer deposition, physical vapor deposition or spin coating, and the deposition temperature is 150 to 350 degrees Celsius; the material of the second protective film is silicon dioxide, silicon nitride, photoresist, aluminum oxide or polysilicon; the thickness of the second protective film is 400 to 800 nanometers.
[0032] In step 4) c), the instrument for preparing the end face pattern is an electron beam lithography machine, an ion beam lithography machine or an ultraviolet lithography machine; the thickness of the photoresist is 0.5 to 2 microns; the exposure time is 15 to 40 seconds; and the development time is 35 to 100 seconds.
[0033] In step 4) d), the dry etching instrument is a plasma etcher or a reactive ion etcher; the dry etching gas is chlorine, boron trichloride, hydrogen chloride or argon; and the etching time is 200 to 400 seconds.
[0034] In step 5) a), the wet etching solution is potassium hydroxide (KOH) or tetramethylammonium hydroxide solution; the concentration of the wet etching solution is 5% to 25%; the temperature of the wet etching solution is 25 to 35 degrees Celsius; and the immersion time is 30 to 240 minutes.
[0035] In step b) of step 5), cleaning is performed by organic cleaning, oxide layer removal or final cleaning, followed by drying, and the cleaning time is 5 to 15 minutes.
[0036] Advantages of the present invention:
[0037] The present invention not only solves the problem of rough and non-vertical laser resonant cavity surface in traditional processes, but also solves the problem of serious damage to the laser epitaxial structure caused by high temperature during wet etching. The present invention obtains a vertical, smooth and damage-free resonant cavity surface at room temperature on a sapphire substrate with a large lattice mismatch through a simple process design without the need for a high-risk high-temperature etching process and complex process steps. The present invention greatly improves production efficiency while reducing safety risks. BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Figure 1 A flow chart of an embodiment of a method for preparing an AlGaN-based edge-emitting laser cavity facet of the present invention;
[0039] Figure 2 A cross-sectional view of a ridge and an end face obtained by dry etching according to an embodiment of a method for preparing a cavity facet of an AlGaN-based edge-emitting laser of the present invention;
[0040] Figure 3 A top view of a ridge and an end face obtained by dry etching according to an embodiment of a method for preparing a cavity facet of an AlGaN-based edge-emitting laser of the present invention;
[0041] Figure 4 A cross-sectional scanning electron microscope image of an embodiment of a method for preparing an AlGaN basal edge emitting laser cavity facet according to the present invention;
[0042] Figure 5 This is a scanning electron microscope magnified image of a ridge of an embodiment of a method for preparing an AlGaN-based edge-emitting laser cavity facet of the present invention. DETAILED DESCRIPTION
[0043] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.
[0044] The method for preparing the AlGaN-based edge-emitting laser cavity facet of this embodiment is as follows: Figure 1 As shown, the following steps are included:
[0045] 1) Growth of laser epitaxial layer:
[0046] A laser epitaxial layer is grown on a sapphire substrate, wherein the laser epitaxial layers are AlN template, n-type cladding layer, n-type waveguide layer, AlGaN / AlGaN quantum well layer, p-type waveguide layer, p-type barrier layer, p-type cladding layer and p-type GaN layer from bottom to top; the thickness of the AlN template is 3.5 microns, the thickness of the n-type cladding layer is 2 microns, the thickness of the n-type waveguide layer is 50 nanometers, the thickness of the AlGaN / AlGaN quantum well layer is 3 quantum wells with a thickness of 36 nanometers, the thickness of the p-type waveguide layer is 50 nanometers, and the thickness of the p-type GaN layer is 10 nanometers, thereby obtaining an AlGaN base edge emitting laser epitaxial wafer;
[0047] 2) Design ridges and end faces:
[0048] The surface of the laser epitaxial layer is designed with multiple periodically evenly distributed units, each unit includes a ridge and an end face, the ridge is located on the end face, the width of the ridge is 15 microns, the width of the end face is 80 microns, the length of the ridge is 1050 microns, the length of the end face is 980 microns, and the two ends of the ridge grow out of the two ends of the end face respectively, and the distance of each end growing out is 35 microns;
[0049] 3) Dry etching to prepare ridges:
[0050] a) AlGaN base edge emitting laser epitaxial wafers are cleaned with organic matter and then dried to remove organic impurities and particles on the surface;
[0051] b) depositing a 200 nanometer thick SiO2 film on the surface of the laser epitaxial layer as a first protective film to protect the laser epitaxial layer;
[0052] c) using an ultraviolet lithography machine to prepare a ridge pattern on the first protective film;
[0053] d) performing dry etching using an inductively coupled plasma etcher to etch periodic ridges, wherein the etching depth of the ridges is from top to bottom to the lower surface of the n-type waveguide layer, exposing the sidewalls of the AlGaN / AlGaN quantum well layer;
[0054] 4) Dry etching to prepare the end face:
[0055] a) The surface of the laser epitaxial layer is cleaned with organic matter and then dried to remove the residual first protective film;
[0056] b) depositing a 500 nm thick SiO2 film on the surface of the laser epitaxial layer having a periodic ridge pattern as a second protective film;
[0057] c) using an ultraviolet lithography machine to prepare an end surface pattern on the second protective film;
[0058] d) performing dry etching using an inductively coupled plasma etcher to etch out periodic end faces, and the end face etching depth is from top to bottom to the n-type cladding layer region; after etching, the length of the end face under the ridge is the same as the length of the ridge, and the two side walls at both ends of the end face where the ridge grows out are in the same plane as the two side walls of the end face under the ridge, such as Figure 2 and 3 As shown;
[0059] 5) Room temperature wet etching to produce a vertical, smooth and damage-free resonant cavity surface:
[0060] a) preparing a 10% KOH solution at room temperature, and soaking the laser epitaxial layer formed with ridges and end faces by dry etching in a prepared wet etching solution at room temperature for 30 to 240 minutes; the wet etching solution etches the two side walls at both ends of the end face of the ridge growth and the two side walls of the part of the end face covered by the ridge in the same plane from the rough surface to a smooth surface, and the surface is perpendicular to the end face; at room temperature, the wet etching rate of the m-plane, i.e., the (1-100) crystal plane, is slower than the etching rate of the (11-20) crystal plane, and the room temperature wet etching exposes the m-plane of the side walls at both ends of the end face, and exposes the two side walls at both ends of the end face of the ridge growth and the part of the end face covered by the ridge in the same plane. m-surface; and the room temperature wet etching rate is relatively slow, so it is easier to accurately control the etching rate. By using room temperature wet etching, it is easier to control the etching rate of the end face with a large width, so it is easier to control the m-surface of the end face to become smooth. When the m-surface of the end face is smooth, the two side walls at both ends of the ridge that are in the same plane as the m-surface of the end face will also become smooth as the end face is smooth; the two side walls at both ends of the end face grown from the two ends of the ridge are used as the resonant cavity surface, so that a vertical, smooth and damage-free resonant cavity surface is obtained without using a high-precision precision lithography machine. The vertical smoothness makes the cavity surface have high reflectivity and a mirror-like effect, and the side wall of the exposed AlGaN / AlGaN quantum well layer is used as the light-emitting surface to realize deep ultraviolet laser emission;
[0061] b) Cleaning the surface of the laser epitaxial layer with a vertical, smooth and undamaged resonant cavity surface to remove residual thin film on the surface, and characterizing the cavity surface by scanning electron microscopy.
[0062] like Figure 4 As shown in the figure, the resonant cavity surface was inspected using a scanning electron microscope, showing that the ridge waveguide surface was very smooth and vertical, confirming that the adopted method successfully obtained a high-reflectivity, vertical and mirror-like damage-free AlGaN base edge emitting laser resonant cavity surface, as shown in the figure. Figure 5 shown.
[0063] Through the above embodiments, it can be effectively proved that the present invention achieves the expected effect, provides a method for preparing a semiconductor laser cavity surface with high reflectivity, vertical and mirror-like at room temperature, and has broad application potential.
[0064] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.
Claims
1. A method for preparing an AlGaN-based edge-emitting laser cavity facet, characterized in that: The preparation method comprises the following steps: 1) Growth of laser epitaxial layer: Growing a laser epitaxial layer on a substrate, wherein the laser epitaxial layer is, from bottom to top, an AlN template, an n-type cladding layer, an n-type waveguide layer, an AlGaN / AlGaN quantum well layer, a p-type waveguide layer, a p-type cladding layer and a p-type GaN layer, to obtain an AlGaN base edge emitting laser epitaxial wafer; 2) Design ridges and end faces: The surface of the laser epitaxial layer is designed to have a plurality of periodically evenly distributed units, each unit including a ridge and an end face, the ridge is located on the end face, the width of the end face is greater than the width of the ridge, the length of the ridge is greater than the length of the end face, and the two ends of the ridge grow out of the two ends of the end face respectively, and the distance of each end growing out is not less than 30 microns to 100 microns; 3) Dry etching to prepare ridges: a) Cleaning AlGaN base edge emitting laser epitaxial wafer; b) depositing a first protective film on the surface of the laser epitaxial layer; c) preparing a ridge pattern on the first protective film; d) using dry etching technology to carve out periodic ridges, the etching depth of the ridges from top to bottom should at least reach the upper surface of the n-type waveguide, and at most reach the lower surface of the n-type waveguide, exposing the side wall of the AlGaN / AlGaN quantum well layer; 4) Dry etching to prepare the end face: a) cleaning the surface of the laser epitaxial layer to remove the residual first protective film; b) depositing a second protective film on the surface of the laser epitaxial layer having a periodic ridge pattern; c) preparing an end surface pattern on the second protective film; d) using dry etching technology to etch out periodic end faces, and the end face etching depth is from top to bottom to the n-type cladding layer; after the dry etching is completed, the length of the end face located under the ridge is the same as the length of the ridge, and the two side walls at both ends of the end face where the ridge grows out are in the same plane as the two side walls of the end face covered by the ridge; 5) Wet etching to produce a vertical, smooth and damage-free resonant cavity surface: a) preparing a wet etching solution at room temperature, and immersing the laser epitaxial layer formed with a ridge and an end face by dry etching in the prepared wet etching solution at room temperature; the wet etching solution etches the two side walls at both ends of the end face grown from the ridge and the two side walls of the part of the end face covered by the ridge in the same plane from the rough surface to a smooth surface, and the surface is perpendicular to the end face; at room temperature, the wet etching rate of the m-plane, i.e., the (1-100) crystal plane, is slower than the etching rate of the (11-20) crystal plane, and the room temperature wet etching exposes the m-plane of the side walls at both ends of the end face, as well as the two side walls at both ends of the end face grown from the ridge in the same plane and the two side walls of the part of the end face covered by the ridge m-surface; and the wet etching rate is relatively slow at room temperature, so it is easier to accurately control the wet etching rate. By using room temperature wet etching, it is easier to control the etching rate of the side walls at both ends of the end face with a large width, so it is easier to control the m-surface of the end face to become smooth. When the m-surface of the end face is smooth, the two side walls at both ends of the ridge that are in the same plane as the m-surface of the end face will also become smooth as the m-surface of the end face becomes smooth; the two side walls at both ends of the end face grown at both ends of the ridge are used as the resonant cavity surface, so that a vertical, smooth and damage-free resonant cavity surface is obtained without using a high-precision precision lithography machine, and the side walls of the exposed AlGaN / AlGaN quantum well layer are used as the light-emitting surface to realize deep ultraviolet laser emission; b) Cleaning the surface of the laser epitaxial layer with a vertical, smooth and damage-free resonant cavity surface to remove surface residues, and characterizing the cavity surface by scanning electron microscopy.
2. The preparation method according to claim 1, characterized in that In step 2), the width of the ridge is 1 to 15 micrometers, and the length of the ridge is 1030 to 1100 micrometers; the width of the end surface is 50 to 100 micrometers, and the length of the end surface is 950 to 1000 micrometers.
3. The preparation method according to claim 1, characterized in that: In step 3) b), the deposition method is chemical vapor deposition, atomic layer deposition, physical vapor deposition or spin coating; the deposition temperature is 50 to 350 degrees Celsius; The material of the first protective film is silicon dioxide, silicon nitride, photoresist, aluminum oxide or polysilicon; the thickness of the first protective film is 50 to 400 nanometers.
4. The preparation method according to claim 1, characterized in that: In step c) of step 3), the instrument for preparing the ridge pattern is an electron beam lithography machine, an ion beam lithography machine or an ultraviolet lithography machine.
5. The preparation method according to claim 1, characterized in that: In step 3) d), the dry etching apparatus is a plasma etcher or a reactive ion etcher.
6. The preparation method according to claim 1, characterized in that: In step b) of step 4), the method of depositing the second protective film is chemical vapor deposition, atomic layer deposition, physical vapor deposition or spin coating, and the deposition temperature is 150 to 350 degrees Celsius; The material of the second protective film is silicon dioxide, silicon nitride, photoresist, aluminum oxide or polysilicon; the thickness of the second protective film is 400 to 800 nanometers.
7. The preparation method according to claim 1, characterized in that: In step c) of step 4), the instrument for preparing the end surface pattern is an electron beam lithography machine, an ion beam lithography machine or an ultraviolet lithography machine.
8. The preparation method according to claim 1, characterized in that: In step 4) d), the dry etching apparatus is a plasma etcher or a reactive ion etcher.
9. The preparation method according to claim 1, characterized in that: In step 5) a), the wet etching solution is potassium hydroxide or tetramethylammonium hydroxide solution; the concentration of the wet etching solution is 5% to 25%.
10. The preparation method according to claim 1, characterized in that: In step 5) a), the temperature of the wet etching solution is 25 to 35 degrees Celsius; and the immersion time is 30 to 240 minutes.