A wavelength-tunable AlGaN-based laser diode on a single wafer and a preparation method thereof

Abstract

The present invention discloses a wavelength-tunable AlGaN-based laser diode on a single wafer and a preparation method thereof. The present invention uses an etching method combining dry etching and wet etching at room temperature to prepare a plurality of ridge pattern arrays arranged two-dimensionally. Each ridge pattern array has a plurality of different ridges. Each ridge with a set width and shape corresponds to a lasing wavelength, and the plurality of different ridges respectively correspond to a plurality of different lasing wavelengths. The ridge pattern array is designed by the effective refractive index. The width and shape of the ridge affect the effective refractive index, which has a restrictive effect on the transverse optical mode field and carriers, thereby affecting the bandgap of the atomically ultrathin quantum well light-emitting layer, and further adjusting the lasing wavelength to realize a wavelength-tunable AlGaN-based laser diode on a single wafer substrate. The present invention can achieve fine regulation of a shorter lasing wavelength, the method is simple and easy to control, significantly reducing the production time and growth cost, and has wide applications in the field of laser diodes with tunable lasing wavelengths.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor laser diodes, and particularly to an AlGaN-based laser diode with tunable wavelength on a single wafer and a preparation method thereof. Background Art

[0002] AlGaN-based laser diodes play a crucial role in future human life and the field of science and technology. Since their first successful development by Hiroshi Amano, the 2022 Nobel laureate, AlGaN-based laser diodes have become a popular research field at home and abroad. Compared with traditional gas and solid-state lasers, AlGaN-based laser diodes have shown great application prospects in military defense, laser weapons, chip processing, encryption communication, pure water purification, and biomedical fields due to their advantages such as small size, low cost, long life, and high energy density.

[0003] Currently, in order to meet the requirements of different application scenarios, it is crucial to provide a convenient and wavelength-tunable AlGaN-based laser diode. However, there are still the following challenges in realizing an AlGaN-based laser diode with tunable wavelength on a single wafer:

[0004] 1. Difficult component regulation: The Al and Ga components grown on a single wafer are usually fixed. Changing the components requires multiple epitaxies on different wafers, which is not only time-consuming but also costly and inefficient.

[0005] 2. Process complexity: When manufacturing the resonant cavity surface, due to different Al and Ga components, the etching rates are also different, resulting in complex process manufacturing and difficult to achieve precise control. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention proposes an AlGaN-based laser diode with tunable wavelength on a single wafer and a preparation method thereof. Through the mode field and carrier confinement effects, the ridge pattern array designed on the single wafer can achieve precise bandgap regulation of the atomically thin quantum well light-emitting layer, thereby realizing a wavelength-tunable AlGaN-based laser diode to meet the requirements of future different application scenarios and laying a foundation for the technological progress of laser diodes at the same time.

[0007] An object of the present invention is to provide an AlGaN-based laser diode with tunable wavelength on a single wafer.

[0008] The wavelength-tunable AlGaN-based laser diode on a single wafer of the present invention includes: an AlGaN-based laser diode, which includes a single wafer substrate, an AlN buffer layer, a multi-period superlattice thin film layer, an n-type cladding layer, an n-type waveguide layer, an atomically ultrathin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer, and a p-type GaN layer, a ridge pattern array, a p-type electrode, and an n-type electrode; wherein, an AlN buffer layer is grown on the upper surface of the single wafer substrate; an AlGaN thin film layer with a thickness of micrometers is grown on the upper surface of the AlN buffer layer by means of temperature gradient combined with the flow rate gradient of Ga source and Al source; a multi-period superlattice thin film layer is grown on the upper surface of the AlGaN thin film layer; an n-type cladding layer, an n-type waveguide layer, an atomically ultrathin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer, and a p-type GaN layer are sequentially grown on the upper surface of the superlattice thin film layer; a plurality of two-dimensionally arranged ridge pattern arrays are fabricated by using an etching method combining room-temperature dry etching and wet etching; each ridge pattern array includes a plurality of one-dimensionally arranged ridges, and each ridge pattern array has a plurality of ridges arranged in one dimension along the width direction, and each ridge has a different width and / or shape. The side where the ridge width is located serves as the light-emitting surface of the laser diode, and the two sides where the ridge length is located serve as the resonant cavity. The etching depth exceeds the atomically ultrathin quantum well light-emitting layer but does not exceed the upper surface of the superlattice thin film layer. Each ridge with a set width and shape corresponds to a lasing wavelength. In each ridge pattern array, a plurality of different ridges correspond to a plurality of different lasing wavelengths; the effective refractive index is set according to the lasing wavelength, and the ridge is designed based on the effective refractive index; the effective refractive index is related to the width and shape of the ridge, and the width and shape of the ridge have a restrictive effect on the transverse optical mode field and carriers, thereby affecting the bandgap of the atomically ultrathin quantum well light-emitting layer, and further adjusting the lasing wavelength; a p-type electrode and an n-type electrode are respectively fabricated on the upper surface of the ridge and the upper surface of the end face; the AlGaN-based laser diode chip is obtained by cutting from the back surface of the single wafer substrate.

[0009] Another object of the present invention is to provide a method for preparing a wavelength-tunable AlGaN-based laser diode on a single wafer.

[0010] The method for preparing a wavelength-tunable AlGaN-based laser diode on a single wafer of the present invention includes the following steps:

[0011] 1) Place the single wafer substrate in the growth chamber of the epitaxial device, and grow an AlN buffer layer on the upper surface of the single wafer substrate;

[0012] 2) On the upper surface of the AlN buffer layer, a high-quality AlGaN thin film layer with a low dislocation density and a thickness in the micron range is grown by combining a temperature gradient with a gradient in the flow rates of the Ga source and the Al source. During the growth process, multi-cycle growth is carried out. In each growth cycle, the temperature gradually increases from low to high, while the Ga source gradually decreases and the Al source gradually increases. After multiple cycle repetitions, a high-quality AlGaN thin film layer is obtained.

[0013] 3) A multi-cycle superlattice thin film layer is grown on the upper surface of the AlGaN thin film layer to release the stress in the underlying layer and reduce surface cracks.

[0014] 4) An n-type cladding layer, an n-type waveguide layer, an atomically ultrathin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer, and a p-type GaN layer are successively grown on the upper surface of the superlattice thin film layer to obtain an efficient AlGaN-based laser diode epitaxial wafer.

[0015] 5) Design the effective refractive index of the atomically ultrathin quantum well light-emitting layer:

[0016] Set the effective refractive index according to the lasing wavelength, and design the ridge based on the effective refractive index. The effective refractive index is related to the width and shape of the ridge. The width and shape of the ridge have a restrictive effect on the transverse optical mode field and carriers, thereby affecting the bandgap of the atomically ultrathin quantum well light-emitting layer and then adjusting the lasing wavelength.

[0017] 6) Fabricate a ridge pattern array:

[0018] Use a combination of room-temperature dry and wet etching methods to fabricate multiple two-dimensionally arranged ridge pattern arrays. Each ridge pattern array includes multiple ridges arranged one-dimensionally along the width direction on the end face. Each ridge has a different width and / or shape. The side where the ridge width is located serves as the light-emitting surface of the laser diode, and the two sides where the ridge length is located serve as the resonant cavity. The etching depth exceeds the atomically ultrathin quantum well light-emitting layer but does not exceed the upper surface of the superlattice thin film layer. Each ridge with a set width and shape corresponds to a lasing wavelength. In each ridge pattern array, multiple different ridges correspond to multiple different lasing wavelengths.

[0019] 7) Fabricate a p-type electrode and an n-type electrode on the upper surface of the ridge and the upper surface of the end face respectively. After cleaning the AlGaN-based laser diode epitaxial wafer with a two-dimensionally arranged ridge pattern array on the front side, cut it from the back side of the single-wafer substrate to obtain an AlGaN-based laser diode chip.

[0020] 8) Place the AlGaN-based laser diode chip at the sample position on the optical platform, connect it to the pump source, collect the laser signal, and test the various different lasing wavelengths of the laser diode chip with the ridge pattern array.

[0021] Among them, in step 1), ensure that the surface of the single-wafer substrate is clean and flat in the growth chamber. The AlN buffer layer is used to improve the quality of the subsequently grown AlGaN thin film. The substrate is a sapphire substrate, a silicon carbide substrate, a silicon substrate, or a multi-layer composite substrate of an AlN template prepared by strain optimization. The epitaxial equipment uses a metal organic chemical vapor deposition (MOCVD) equipment, a molecular beam epitaxy chemical vapor deposition (MBE) equipment, a halide vapor phase epitaxy (HVPE) equipment, or an atomic layer deposition (ALD) equipment. The growth thickness of the AlN buffer layer is 200 to 400 nanometers.

[0022] In step 2), the range of the gradient temperature is 1000~1200 °C, and the interval of the gradient temperature is 50 °C; the number of cycles is 50~100 times. The average Al composition of the AlGaN thin film layer is 90% to 98%, and the growth thickness of the AlGaN thin film layer is 3 to 8 micrometers. The Ga source is 5~15 sccm; the Al source is 90~120 sccm.

[0023] In step 3), the superlattice thin film layer is used to release the stress of the underlying layer and reduce surface cracks. The multi-period superlattice thin film layer is AlGaN / AlGaN or AlN / AlGaN. The Al compositions of the two layers of AlGaN in AlGaN / AlGaN are different. The Al composition range of the first layer of AlGaN is 90% to 95%, and the Al composition range of the second layer of AlGaN is 70% to 85%. The average Al composition is 80% to 90%. The total growth thickness of the superlattice thin film layer is 100 to 500 nanometers. The period of the superlattice thin film layer is 50~100 times.

[0024] In step 4), the n-type cladding layer is AlGaN or graded AlGaN, with an average Al composition of 70% to 80% and a growth thickness of 1 to 6 micrometers; the n-type waveguide layer is AlGaN or graded AlGaN, with an average Al composition of 60% to 70% and a growth thickness of 10 to 100 nanometers; the atomically ultra-thin quantum well light-emitting layer includes multiple periods of quantum wells and barriers, using AlGaN / AlGaN, AlN / AlGaN, or AlN / GaN, with an average Al composition of 45% to 65%. The growth thickness of the quantum well is 0.1 to 3 nanometers, which is an atomic thickness, and the growth thickness of the barrier is 3 to 9 nanometers; the p-type waveguide layer is AlGaN or graded AlGaN, with an average Al composition of 60% to 70% and a growth thickness of 10 to 100 nanometers; the p-type cladding layer is graded AlGaN, with an average Al composition of 25% to 50% and a growth thickness of 50 to 300 nanometers; the growth thickness of the p-type GaN layer is 10 to 30 nanometers.

[0025] In step 5), the effective refractive index is set through theoretical calculations of light propagation in the medium. As the effective refractive index increases, the width of the ridge gradually decreases to a micron size comparable to that of the n-type cladding layer. This increases the confinement effect on the transverse optical mode field and carriers, thereby increasing the bandgap of the atomically ultrathin quantum well light-emitting layer and causing the lasing wavelength to gradually blue-shift. The effective refractive index is related to the width and shape of the ridge and is independent of the distance between adjacent ridges, as well as the length and depth of the ridge.

[0026] In step 6), first, the AlGaN-based laser diode epitaxial wafer is cleaned. The cleaning is carried out by organic cleaning, oxide layer removal, or final cleaning, and then dried. The cleaning time is 5 to 15 minutes to remove surface organic impurities and particles. Then, a protective film is formed. The material of the protective film is silicon dioxide, silicon nitride, photoresist, aluminum oxide, or polysilicon, and the thickness of the protective film is 50 to 600 nanometers.

[0027] In step 6), the shape of the ridge is a strip-shaped protrusion. The cross-sectional shape of the ridge perpendicular to the surface of the single-wafer substrate is rectangular or trapezoidal. The width of the ridge is 1 to 30 microns, the length of the ridge is 1000 to 3000 microns, and the depth of the ridge is 200 to 300 nanometers. The width of the trapezoid refers to the upper base of the trapezoid, and the lower base does not exceed the distance between the centers of two adjacent ridges. For ridges of the same width, the effective refractive index of the trapezoid is larger than that of the rectangle.

[0028] The ridge pattern array is prepared by using a dry and wet combined etching method at room temperature, including the following steps:

[0029] i. Shape of the ridge and end face:

[0030] Each ridge pattern array has multiple ridges and end faces. The multiple ridges are located on the end face. The length of the ridge is greater than the length of the end face, and both ends of the ridge extend beyond the two ends of the end face, and the extension distance at each end is not less than 30 microns to 100 microns.

[0031] ii. Preparation of the ridge by dry etching:

[0032] a) Clean the AlGaN-based laser diode epitaxial wafer;

[0033] b) Deposit a first protective film on the surface of the AlGaN-based laser diode epitaxial wafer;

[0034] c) Prepare a ridge pattern on the first protective film;

[0035] d) Use dry etching technology to etch out ridges arranged in one dimension. The etching depth of the ridge should be etched at least to the upper surface of the n-type waveguide layer from top to bottom and at most to the upper surface of the n-type cladding layer, exposing the sidewalls of the atomically ultrathin quantum well light-emitting layer.

[0036] iii. Preparation of end faces by dry etching:

[0037] a) Clean the surface of the AlGaN-based laser diode epitaxial wafer to remove the residual first protective film;

[0038] b) Deposit a second protective film on the surface of the AlGaN-based laser diode epitaxial wafer with one-dimensional arranged ridges;

[0039] c) Prepare an end face pattern on the second protective film;

[0040] d) Use dry etching technology to etch out the end faces. The etching depth of the end faces is etched from top to bottom to the n-type cladding layer, not exceeding the upper surface of the superlattice thin film layer. After the dry etching is completed, the length of the part of the end face covered by the ridge is the same as the length of the ridge, and the two side walls at both ends where the ridge extends out of the end face are in the same plane as the two side walls of the part of the end face covered by the ridge;

[0041] iv. Wet etching to obtain a vertical, smooth and damage-free resonant cavity surface:

[0042] Prepare a wet etching solution at room temperature, and immerse the AlGaN-based laser diode epitaxial wafer with ridges and end faces formed by dry etching in the prepared wet etching solution at room temperature. The wet etching solution etches the two side walls at both ends where the ridge extends out of the end face and the two side walls of the part of the end face covered by the ridge, which are in the same plane, from a rough surface to a smooth surface and perpendicular to the surface of the end face. At room temperature, the etching rate of the m-plane, i.e., the (1-100) crystal plane, by wet etching is slower than that of the (11-20) crystal plane. Room temperature wet etching exposes the m-plane of the two side walls at both ends of the end face, and exposes the m-plane of the two side walls at both ends where the ridge extends out of the end face and the two side walls of the part of the end face covered by the ridge, which are in the same plane. And the wet etching rate at room temperature is relatively slow, 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 two side walls at both ends of the end face with a large width, so it is easier to control the m-plane of the end face to become smooth. When the m-plane of the end face is smooth, the two side walls at both ends of the ridge, which are in the same plane as the m-plane of the end face, will also become smooth along with the smoothness of the m-plane of the end face. Taking the two side walls at both ends where the ridge extends out of the end face as the resonant cavity surface, a vertical, smooth and damage-free resonant cavity surface can be obtained without using a high-precision lithography machine.

[0043] Cleaning is carried out by organic cleaning, oxide layer removal or final cleaning, followed by drying; the cleaning time is 5 to 15 minutes to remove surface organic impurities and particles. The deposition method is chemical vapor deposition, atomic layer deposition, physical vapor deposition or spin coating, and the deposition temperature is 50 to 350 °C; 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 nm. 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 μm; the exposure time is 15 to 40 seconds; the development time is 35 to 100 seconds. The instrument for dry etching is a plasma etching machine or a reactive ion etching machine; the gas for dry etching is chlorine, boron trichloride, hydrogen chloride or argon; the etching time is 70 to 90 seconds. 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 °C; 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 nm. 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 μm; the exposure time is 15 to 40 seconds; the development time is 35 to 100 seconds. 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 °C; the soaking time is 30 to 240 minutes.

[0044] In step 7), a laser dicing machine is used to cut from the back of the single-wafer substrate, and the front of each AlGaN-based laser diode chip has one or more ridge pattern arrays.

[0045] In step 8), the pump source is an electrical pump, an optical pump or an electron beam pump.

[0046] Advantages of the present invention:

[0047] (1) Different from the theoretical method of regulating the laser wavelength by adjusting the components of Al and Ga, the present invention designs the ridge pattern array from the effective refractive index on the single-wafer substrate experimentally; the width and shape of the ridge affect the effective refractive index, which has a restrictive effect on the transverse optical mode field and carriers, thereby affecting the band gap of the atomically ultrathin quantum well light-emitting layer, and thus realizing a wavelength-tunable AlGaN-based laser diode on the single-wafer substrate;

[0048] (2) The present invention can achieve fine regulation of a shorter lasing wavelength, such as 250 to 280 nm, which takes a crucial step for the development of military defense and laser weapons;

[0049] (3) The method is simple and easy to control, significantly reducing the production time and growth cost, laying a foundation for the technological progress of laser diodes; it is applied to wavelength tunable lasers, portable ultraviolet Raman, encrypted communication, pure water purification, and biomedicine, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the ridge and end face on a single-wafer substrate obtained from an embodiment of the method for preparing a wavelength tunable AlGaN-based laser diode on a single wafer according to the present invention;

[0051] Figure 2 It is a transmission electron microscope image of an atomically ultrathin quantum well light-emitting layer obtained from an embodiment of the method for preparing a wavelength tunable AlGaN-based laser diode on a single wafer according to the present invention;

[0052] Figure 3 It is a test result diagram of adjustable lasing wavelength obtained from an embodiment of the method for preparing a wavelength tunable AlGaN-based laser diode on a single wafer according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] The present invention will be further described below with reference to the drawings and specific embodiments.

[0054] The method for preparing a wavelength tunable AlGaN-based laser diode on a single wafer in this embodiment includes the following steps:

[0055] 1) Place the single-wafer substrate on sapphire in the growth chamber of MOCVD, and grow an AlN buffer layer on the upper surface of the single-wafer substrate;

[0056] 2) On the upper surface of the AlN buffer layer, grow an AlGaN thin film layer with a dislocation density of 5×10 7 cm -2 and a thickness of 4 microns by combining temperature gradient with the flow rate gradient of Ga source and Al source; during the growth process, multi-cycle growth is carried out. In each growth cycle, the temperature gradually changes from low to high, while the Ga source gradually decreases and the Al source gradually increases. The cycle is repeated 80 times. In each growth cycle, the temperature rises from 1000 °C to 1200 °C, the flow rate of the Ga source gradually decreases from 15 sccm to 5 sccm, and the flow rate of the Al source gradually increases from 90 sccm to 120 sccm, so as to obtain a high-quality AlGaN thin film layer;

[0057] 3) Grow an AlGaN / AlGaN superlattice thin film layer with an Al composition of 85% and a thickness of 400 nm for 80 cycles on the upper surface of the AlGaN thin film layer. The Al composition of the first layer of AlGaN ranges from 90% to 95%, and the Al composition of the second layer of AlGaN ranges from 70% to 85% to release the stress of the underlying layer and reduce surface cracks;

[0058] 4) Grow successively on the upper surface of the superlattice thin film layer an n-type cladding layer of n-AlGaN with an average Al composition of 75%, a thickness of 2 μm, and an electron concentration of 5×10 19 cm -3 , an n-type waveguide layer of n-AlGaN with an average Al composition of 65%, a thickness of 50 nm, and an electron concentration of 8×10 17 cm -3 , an atomically ultrathin quantum well light-emitting layer of AlGaN / AlGaN with an average Al composition of 50% including three layers of quantum wells and barriers, the growth thickness of each quantum well being 0.3 nm and the growth thickness of the barrier being 6 nm, a p-type waveguide layer of p-AlGaN, a p-type cladding layer of p-AlGaN with an average Al composition of 70%, a thickness of 50 nm, and a hole concentration of 5×10 18 cm -3 , and a p-type GaN layer of p-GaN with a thickness of 10 nm and a hole concentration of 5×10 19 cm -3 to obtain a high-efficiency AlGaN-based laser diode epitaxial wafer;

[0059] 5) Design the effective refractive index of the atomically ultrathin quantum well light-emitting layer:

[0060] Through theoretical calculation of light propagation in a medium, set the effective refractive index according to the lasing wavelength. The effective refractive index is related to the width and shape of the ridge. The ridge has a confinement effect on the transverse optical mode field and carriers, thus affecting the bandgap of the atomically ultrathin quantum well light-emitting layer and further controlling the lasing wavelength;

[0061] 6) Prepare a ridge pattern array:

[0062] Use an etching method combining dry and wet etching at room temperature to prepare a plurality of two-dimensionally arranged ridge pattern arrays; in each ridge pattern array, the shapes of the ridges are the same, all being rectangular strips, the widths of the ridges are 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, and 15 μm respectively, the length of the ridges is 1000 μm, and the depth of the ridges is 250 nm, as Figure 1As shown in the figure; the side where the short side of the ridge is located serves as the light-emitting surface of the laser diode, and the two sides where the long side of the ridge is located serve as the resonant cavity; the etching depth should exceed the atomically ultrathin quantum well light-emitting layer, but not exceed the upper surface of the superlattice thin film layer; each ridge corresponds to a lasing wavelength, and in each ridge pattern array, multiple different ridges respectively correspond to multiple different lasing wavelengths; the lasing wavelengths corresponding to the ridges with widths of 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, and 15 μm are 252 nm, 253 nm, 254 nm, 256 nm, 257 nm, and 259 nm respectively;

[0063] 7) Fabricate a p-type electrode and an n-type electrode on the upper surface of the ridge and the upper surface of the end face respectively. After cleaning the AlGaN-based laser diode epitaxial wafer with a two-dimensional array of ridge patterns on the front surface, use a laser dicing machine to cut from the back of the single-wafer substrate to separate each ridge pattern array. Each AlGaN-based laser diode chip has one or more ridge pattern arrays on the front surface to obtain the AlGaN-based laser diode chip;

[0064] 8) Place the AlGaN-based laser diode chip at the sample position on the optical platform, connect the pump source, and use multiple lenses to collect the laser signals emitted by the AlGaN-based laser diode chip to test the lasing wavelengths of the laser diode chips with different ridge pattern arrays.

[0065] The atomically ultrathin quantum well light-emitting layer has three quantum wells, as Figure 2 shown.

[0066] As Figure 3 shown, use a laser to test the AlGaN-based laser diode chip on the optical platform for inspection, showing that by changing the width of the ridge, the lasing wavelength of the semiconductor laser diode chip can be precisely controlled, verifying that the present invention has successfully developed an AlGaN-based laser diode with tunable wavelength on a single wafer.

[0067] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention. However, 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 content disclosed in the embodiments, and the scope of protection claimed by the present invention is defined by the scope of the claims.

Claims

1. A method for preparing a wavelength tunable AlGaN-based laser diode on a single wafer, characterized in that: The preparation method comprises the following steps: 1) Placing a single wafer substrate in a growth chamber of an epitaxial device and growing an AlN buffer layer on the upper surface of the single wafer substrate; 2) On the upper surface of the AlN buffer layer, a micrometer-level AlGaN thin film layer is grown by temperature gradient combined with Ga source and Al source flow gradient; during the growth process, multiple cycles of cyclic growth are performed, and in each growth cycle, the temperature gradually changes from low to high, while the Ga source gradually decreases and the Al source gradually increases, and multiple cycles are repeated to obtain an AlGaN thin film layer; 3) Growing a multi-period superlattice film layer on the upper surface of the AlGaN film layer to release the stress of the bottom layer and reduce surface cracks; 4) On the upper surface of the superlattice thin film layer, an n-type cladding layer, an n-type waveguide layer, an atomic-level ultra-thin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer and a p-type GaN layer are sequentially grown to obtain an AlGaN-based laser diode epitaxial wafer; 5) Design the effective refractive index of the atomic-level ultra-thin quantum well light-emitting layer: The effective refractive index is set according to the lasing wavelength, and the ridge is designed based on the effective refractive index; the effective refractive index is related to the width and shape of the ridge, which has a limiting effect on the lateral optical mode field and carriers, thereby affecting the band gap of the atomic-level ultra-thin quantum well light-emitting layer, and then adjusting the lasing wavelength; 6) Preparation of ridge pattern arrays: A plurality of two-dimensionally arranged ridge pattern arrays are prepared by an etching method combining a room temperature dry method and a wet method; each ridge pattern array includes a plurality of ridges formed on an end face and arranged one-dimensionally along a width direction, and each ridge has a different width and / or shape; the side where the ridge width is located serves as a light-emitting surface of a laser diode, and the two side surfaces where the ridge length is located serve as a resonant cavity; the etching depth exceeds the atomic-level ultra-thin quantum well light-emitting layer and does not exceed the upper surface of the superlattice film layer; each ridge with a set width and shape corresponds to a lasing wavelength, and in each ridge pattern array, a plurality of different ridges correspond to a plurality of different lasing wavelengths respectively; 7) Making a p-type electrode and an n-type electrode on the upper surface of the ridge and the upper surface of the end face respectively, cleaning the AlGaN-based laser diode epitaxial wafer with a two-dimensionally arranged ridge pattern array on the front side, and cutting it from the back side of the single wafer substrate to obtain an AlGaN-based laser diode chip; 8) Place the AlGaN-based laser diode chip at the sample position of the optical platform, connect the pump source, collect the laser signal, and test the different lasing wavelengths of the laser diode chip with the ridge pattern array.

2. The preparation method according to claim 1, characterized in that In step 1), the epitaxial growth equipment is a metal organic chemical vapor deposition equipment, a molecular beam epitaxial chemical vapor deposition equipment, a halide vapor phase epitaxial growth equipment or an atomic layer deposition equipment; the growth thickness of the AlN buffer layer is 200 to 400 nanometers.

3. The preparation method according to claim 1, characterized in that: In step 2), the range of the gradual temperature is 1000-1200 °C, the interval of the gradual temperature is 50 °C, and the number of cycles is 50-100 times.

4. The preparation method according to claim 1, characterized in that: In step 2), the average Al composition of the AlGaN thin film layer is 90% to 98%, and the growth thickness of the AlGaN thin film layer is 3 to 8 microns.

5. The preparation method according to claim 1, characterized in that: In step 3), the superlattice thin film layer is AlGaN / AlGaN or AlN / AlGaN, the Al composition of the two AlGaN layers in AlGaN / AlGaN is different, and the average Al composition is 80% to 90%; the total growth thickness of the superlattice thin film layer is 100 to 500 nanometers.

6. The preparation method according to claim 1, characterized in that: In step 4), the atomic-level ultra-thin quantum well light-emitting layer includes multi-period quantum wells and potential barriers, the growth thickness of the quantum wells is 0.1 to 3 nanometers, and the growth thickness of the potential barriers is 3 to 9 nanometers.

7. The preparation method according to claim 1, characterized in that: In step 6), the shape of the ridge is columnar, the transverse cross-sectional shape of the ridge is rectangular or trapezoidal, the width of the ridge is 1 to 30 micrometers, and the length of the ridge is 1000 to 3000 micrometers.

8. The preparation method according to claim 1, characterized in that: In step 6), a ridge pattern array is prepared by a room temperature dry and wet etching method, including the following steps: i. Shape of ridges and end faces: Each ridge pattern array has a plurality of ridges and end faces, the plurality of ridges are located on the end faces, the length of the ridges is greater than the length of the end faces, and two ends of the ridges extend beyond two ends of the end faces respectively; ii. Dry etching to prepare ridges: a) Cleaning AlGaN-based laser diode epitaxial wafers; b) depositing a first protective film on the surface of the AlGaN-based laser diode epitaxial wafer; c) forming a ridge pattern on the first protective film; d) using dry etching technology to carve out one-dimensionally arranged ridges, the etching depth of the ridges from top to bottom should at least reach the upper surface of the n-type waveguide layer, and at most reach the upper surface of the n-type cladding layer, exposing the side wall of the atomic-level ultra-thin quantum well light-emitting layer; iii. Dry etching to prepare the end face: a) cleaning the surface of the AlGaN-based laser diode epitaxial wafer to remove the residual first protective film; b) depositing a second protective film on the surface of the AlGaN-based laser diode epitaxial wafer having one-dimensionally arranged ridges; c) preparing an end surface pattern on the second protective film; d) using dry etching technology to etch out the end face, the end face etching depth is from top to bottom to the n-type cladding layer, and does not exceed the upper surface of the superlattice thin film 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; iv. Wet etching to create a vertical, smooth, and damage-free resonant cavity surface: A wet etching solution is prepared at room temperature, and an AlGaN-based laser diode epitaxial wafer formed with a ridge and an end face by dry etching is immersed 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 of the ridge and the two side walls of the end face covered by the ridge in the same plane from a 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 that of the (11-20) The etching rate of the crystal face, wet etching at room temperature exposes the m-face of the side walls at both ends of the end face, as well as the m-face of the two side walls at both ends of the end face where the ridge grows out of the ridge and the two side walls of the part of the end face covered by the ridge. The wet etching rate at room temperature is relatively slow, so it is easier to accurately control the wet etching rate. By adopting wet etching at room temperature, it is easier to control the etching rate of the side walls at both ends of the end face with a large width, so that it is easier to control the m-face of the end face to become smooth. When the m-face of the end face is smooth, the two side walls at both ends of the ridge in the same plane as the m-face of the end face will also become smooth as the m-face of the end face becomes smooth. The two side walls at both ends of the end face grown out of the ridge at both ends are used as the resonant cavity surface, so as to obtain a vertical, smooth and damage-free resonant cavity surface.

9. A wavelength tunable AlGaN-based laser diode on a single wafer, characterized in that: The AlGaN-based laser diode comprises: a single wafer substrate, an AlN buffer layer, a multi-period superlattice film layer, an n-type cladding layer, an n-type waveguide layer, an atomic-level ultra-thin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer and a p-type GaN layer, a ridge pattern array, a p-type electrode and an n-type electrode; wherein, an AlN buffer layer is grown on the upper surface of the single wafer substrate; an AlGaN film layer with a thickness of micrometer level is grown on the upper surface of the AlN buffer layer by temperature gradient combined with Ga source and Al source flow gradient; a multi-period superlattice film layer is grown on the upper surface of the AlGaN film layer; an n-type cladding layer, an n-type waveguide layer, an atomic-level ultra-thin quantum well light-emitting layer, a p-type waveguide layer, a p-type cladding layer and a p-type GaN layer are grown in sequence on the upper surface of the superlattice film layer; a plurality of two-dimensionally arranged ridge pattern arrays are prepared by a room temperature dry method combined with a wet method etching method; each ridge pattern array comprises a plurality of one-dimensionally arranged ridges, each A ridge pattern array has multiple ridges arranged in one dimension along the width direction, each ridge has a different width and / or shape, the side where the ridge width is located serves as the light-emitting surface of the laser diode, the two sides where the ridge length is located serve as the resonant cavity, the etching depth exceeds the atomic-level ultra-thin quantum well light-emitting layer, but does not exceed the upper surface of the superlattice film layer, each ridge with a set width and shape corresponds to a lasing wavelength, and in each ridge pattern array, multiple different ridges correspond to multiple different lasing wavelengths; the effective refractive index is set according to the lasing wavelength, and the ridge is designed according to the effective refractive index; the effective refractive index is related to the width and shape of the ridge, and the width and shape of the ridge have a limiting effect on the lateral optical mode field and carriers, thereby affecting the band gap of the atomic-level ultra-thin quantum well light-emitting layer, and then adjusting the lasing wavelength; p-type electrodes and n-type electrodes are respectively made on the upper surface of the ridge and the upper surface of the end face; cutting is performed from the back side of the single wafer substrate to obtain an AlGaN-based laser diode chip.

10. The AlGaN-based laser diode according to claim 9, characterized in that: The ridge is columnar in shape, the transverse cross-section of the ridge is rectangular or trapezoidal in shape, the width of the ridge is 1 to 30 micrometers, and the length of the ridge is 1000 to 3000 micrometers.

Images