Polarization-adjustable AlGaN optical pumping deep ultraviolet laser and preparation method thereof

Abstract

The invention relates to a polarization-adjustable AlGaN optical pumping deep ultraviolet laser and a preparation method thereof, and belongs to the technical field of semiconductor deep ultraviolet light emitting. The laser comprises a substrate, an AlGaN stress regulation and control layer, an internal n-type AlGaN layer, an i-type AlGaN protection layer, a multi-quantum well layer, an i-type AlGaN protection layer and a transparent n-type AlGaN layer, wherein the multi-quantum well layer comprises a periodic AlyGa < 1-y > N / Al < x > Ga < 1-x > N / AlyGa < 1-y > N structures; the device further comprises an n-type upper electrode and an n-type lower electrode. According to the AlGaN deep ultraviolet laser, the Al component change of the AlGaN stress regulation and control layer is used for carrying out light emitting polarization regulation and control on the multi-quantum well layer, the internal n-type AlGaN layer and the transparent n-type AlGaN layer are used for applying an electric field to the multi-quantum well layer, the laser polarization of the laser is regulated and controlled under the condition of optical pumping lasing, and therefore the AlGaN deep ultraviolet laser with the polarization adjustable in the TE state and the TM state is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor deep ultraviolet light emission, and particularly to a polarization-tunable AlGaN optically pumped deep ultraviolet laser and a preparation method thereof. Background Art

[0002] Because the AlGaN material has a bandgap of 3.4 - 6.2 eV with the change of the Al component, covering the emission wavelength of 210 nm - 400 nm, it is a semiconductor material very suitable for making ultraviolet optoelectronic devices and has great application prospects in ultraviolet light emission.

[0003] Due to the different physical properties between the crystal field split-off hole (CH) band, heavy hole (HH) band and light hole (LH) band in the valence band, the recombination between the conduction band electrons and the valence band holes will generate transverse electric field (TE) or transverse magnetic field (TM) polarization radiation transitions, and correspondingly mainly radiate photons with TE or TM polarization. Research shows that the change of energy bands and wave functions can regulate the emission polarization of AlGaN multiple quantum wells, and for a laser, under the action of stimulated emission, only light of one polarization mode can be lasing.

[0004] Therefore, through the method of stress regulation, an AlGaN multiple quantum well structure with almost the same TE radiation transition and TM radiation transition intensities under spontaneous emission can be designed. When optically pumped lasing, by changing the electric field, the TE and TM transition intensities can be regulated, so as to realize the transition of the lasing laser between the TE and TM modes. Summary of the Invention

[0005] In view of this, the object of the present invention is to propose a polarization-tunable structure to achieve TE and TM polarization tunability based on the problem of laser polarization mode regulation of AlGaN deep ultraviolet lasers, and provide a polarization-tunable AlGaN optically pumped deep ultraviolet laser and a preparation method thereof. The laser of the present invention is an AlGaN optically pumped laser applicable to the deep ultraviolet band. The AlGaN stress regulation layer can make the initial spontaneous emission TE radiation transition and TM radiation transition intensities of the laser almost the same. By using an internal n-type AlGaN layer and a transparent n-type AlGaN layer to apply an electric field to the multiple quantum well layer, the laser polarization of the laser is regulated under the condition of optically pumped lasing, and the polarization can be adjusted between the TE and TM states.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A polarization-tunable AlGaN optically pumped deep ultraviolet laser, comprising a substrate, and an AlGaN stress regulation layer, an internal n-type AlGaN layer, an i-type AlGaN protection layer grown on the substrate in sequence, and including a periods of Aly Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y A multi - quantum well layer with an N structure, a type - i AlGaN protective layer, and a transparent n - type AlGaN layer; it also includes an n - type upper electrode and an n - type lower electrode;

[0008] Among them, it contains a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y In the multi - quantum well layer with an N structure, 0 < x < 1, x < y, a ≥ 1;

[0009] The n - type lower electrode region is etched from the transparent n - type AlGaN layer to the internal n - type AlGaN layer; the n - type upper electrode region is etched to the transparent n - type AlGaN layer;

[0010] The n - type lower electrode is located above the internal n - type AlGaN layer; the n - type upper electrode is located above the transparent n - type AlGaN layer;

[0011] The AlGaN stress - regulating layer regulates the energy band of the multi - quantum well layer containing a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y to regulate the initial emission polarization degree of the multi - quantum well;

[0012] The internal n - type AlGaN layer serves as an ohmic contact layer to contact the n - type lower electrode, and at the same time serves as a voltage - regulating layer to keep the potential in the layer basically consistent;

[0013] The multi - quantum well layer containing a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y serves as the active region of the laser, playing the role of confining photo - generated electron - hole pairs and generating and regulating stimulated transitions;

[0014] The Al component of the type - i AlGaN protective layer is higher than that of the internal n - type AlGaN layer and the transparent n - type AlGaN layer, serving to prevent carriers from entering or leaving the multi - quantum well layer containing a periods of Al y Ga 1-y N / Alx Ga 1-x N / Al y Ga 1-y The function of the multi - quantum well layer of the GaN structure;

[0015] The transparent n - type AlGaN layer serves as a voltage - regulating layer and is transparent to the pump light source at the same time.

[0016] In the above technical solution, the material of the substrate is a hetero - substrate material or a homo - substrate material;

[0017] The hetero - substrate material is any one of sapphire, silicon carbide, and silicon;

[0018] The homo - substrate material is GaN or AlN.

[0019] In the above technical solution, the Al component of the AlGaN stress - regulating layer is 0 - 1; the Al component change range of the internal n - type AlGaN layer is 0 - 1, which is consistent with the AlGaN stress - regulating layer.

[0020] In the above technical solution, the one containing a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y In the multi - quantum well layer of the GaN structure, the quantum barrier thickness is 4 - 20 nm, and the quantum well thickness is 0.5 - 3 nm.

[0021] In the above technical solution, the Al component in the i - type AlGaN protective layer is greater than y, and the Al component in the transparent n - type AlGaN layer is greater than x.

[0022] In the above technical solution, both the n - type upper electrode and the n - type lower electrode are ohmic electrodes, and the material is any one, two or more alloys of Pt, Ti, Al, Ni, and Au.

[0023] A preparation method of a polarization - tunable AlGaN optical - pumped deep - ultraviolet laser, comprising the following steps:

[0024] S1: Growing the device epitaxial material:

[0025] Growing the AlGaN stress - regulating layer, the internal n - type AlGaN layer, the i - type AlGaN protective layer, and the one containing a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-yThe multi-quantum well layer of N structure, the i-type AlGaN protective layer, and the transparent n-type AlGaN layer;

[0026] S2: Prepare the mesa structure:

[0027] Use PECVD technology to grow a SiO2 mask layer on the outermost layer of the device epitaxial material, use photolithography technology to lithograph the device mesa pattern on the SiO2 mask layer, use RIE technology to etch away the SiO2 mask layer without photoresist coverage in the non-mesa area, use ICP technology to etch the area without the SiO2 mask layer coverage to the internal n-type AlGaN layer, and use HF to remove the SiO2 mask layer in the mesa area;

[0028] S3: Prepare the n-type lower electrode:

[0029] Use photolithography technology to prepare the photoresist mask pattern of the n-type lower electrode above the internal n-type AlGaN layer. After development, the photoresist in the electrode pattern area is removed, and the photoresist in the non-electrode area is retained. Then, deposit the n-type lower electrode material on the photoresist mask pattern, and use Lift Off technology to remove the photoresist and the electrode material covered on it. Finally, perform rapid annealing treatment;

[0030] S4: Prepare the n-type upper electrode:

[0031] Use photolithography technology to prepare the photoresist mask pattern of the n-type upper electrode above the transparent n-type AlGaN layer. After development, the photoresist in the electrode pattern area is removed, and the photoresist in the non-electrode area is retained. Then, deposit the n-type upper electrode material on the photoresist mask pattern, and use Lift Off technology to remove the photoresist and the electrode material covered on it. Finally, perform rapid annealing treatment.

[0032] In the above technical solution, the method for growing the device epitaxial material in step S1 is MOCVD;

[0033] In step S2, using photolithography technology, the selection of positive and negative photoresists is determined according to the design of the photomask pattern window, so that the photoresist in the mesa area is retained after development, and the photoresist in the non-mesa area is removed;

[0034] In steps S3 and S4, using photolithography technology, the selection of positive and negative photoresists is determined according to the design of the photomask pattern window, so that the photoresist in the electrode pattern area is removed after development, and the photoresist in the non-electrode area is retained.

[0035] In the above technical solution, in steps S3 and S4, the method for depositing the n-type lower electrode material and the n-type upper electrode material is electron beam evaporation or thermal evaporation technology;

[0036] The thicknesses of the deposited n-type lower electrode material and n-type upper electrode material are both 200 - 400 nm.

[0037] In the above technical solution, in steps S3 and S4, the Lift Off technique is used to dissolve the photoresist, and acetone solution is selected as the dissolving solution;

[0038] The rapid annealing treatment is to use a rapid annealing furnace to anneal the n-type lower electrode and the n-type upper electrode in a nitrogen atmosphere. The annealing temperature and time are determined by the electrode material.

[0039] The beneficial effects of the present invention are:

[0040] In a polarization-tunable AlGaN optically pumped deep ultraviolet laser of the present invention, a resonant cavity is formed on the side wall of the device mesa. The pump light source is incident from the top of the device and is absorbed by the multi-quantum well layer after passing through the transparent n-type AlGaN layer, so that the multi-quantum well layer generates laser light; the i-type AlGaN protective layer prevents the electrons in the transparent n-type AlGaN layer from diffusing into the multi-quantum well layer. At the same time, a voltage is applied to the electrode to directly regulate the electric field intensity of the multi-quantum well layer, thereby changing the intensity of TE and TM transitions, and further enabling the stimulated emission to switch between TE transition and TM transition, and further enabling the polarization characteristic of the edge-emitted laser of the laser to be adjustable between TE polarization and TM polarization. This structure has broad application prospects in deep ultraviolet AlGaN-based lasers.

[0041] A polarization-tunable AlGaN optically pumped deep ultraviolet laser of the present invention includes an AlGaN stress regulation layer that can make the initial spontaneous emission TE radiation transition and TM radiation transition intensities of the laser almost the same. The change in the Al component of the AlGaN stress regulation layer is used to regulate the emission polarization of a multi-quantum well layer with a structure of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N (0 < x < 1, x < y, a ≥ 1). An internal n-type AlGaN layer and a transparent n-type AlGaN layer are used to apply an electric field to the multi-quantum well layer, and the laser polarization of the laser is regulated under the condition of optically pumped lasing, so as to realize an AlGaN deep ultraviolet laser with adjustable polarization in two states of TE and TM. Description of the Drawings

[0042] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0043] Figure 1 It is a schematic structural diagram of the polarization-tunable AlGaN optically pumped deep ultraviolet laser of the present invention.

[0044] Figure 2This is the flowchart for fabricating a polarization-tunable AlGaN optically pumped deep ultraviolet laser of the present invention.

[0045] The reference numerals in the figure are as follows:

[0046] 1 - Substrate; 2 - AlGaN stress control layer; 3 - Internal n-type AlGaN layer; 4 - Multiple quantum well layer including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N structure; 5 - i-type AlGaN protective layer; 6 - Transparent n-type AlGaN layer; 7 - n-type upper electrode; 8 - n-type lower electrode. Detailed implementation manners

[0047] The present invention will be specifically described below with reference to the accompanying drawings to more clearly illustrate the purpose, advantages, principles, and device structure of the present invention.

[0048] Combined with Figure 1 Specifically describe the polarization-tunable AlGaN optically pumped deep ultraviolet laser of the present invention, including: substrate 1, and an AlGaN stress control layer 2, an internal n-type AlGaN layer 3, an i-type AlGaN protective layer 5, and a multiple quantum well layer 4 including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N (0 < x < 1, x < y, a ≥ 1) structure, an i-type AlGaN protective layer 5, and a transparent n-type AlGaN layer 6; and also including an n-type upper electrode 7 and an n-type lower electrode 8;

[0049] On the substrate 1, the AlGaN stress control layer 2, the internal n-type AlGaN layer 3, the i-type AlGaN protective layer 5, and the multiple quantum well layer 4 including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N (0 < x < 1, x < y, a ≥ 1) structure, the i-type AlGaN protective layer 5, and the transparent n-type AlGaN layer 6 are successively grown into a thin film structure; etching treatment is performed in the area of the n-type lower electrode 8, and the internal n-type AlGaN layer 3 and the multiple quantum well layer 4 including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al yGa 1-y N(0 <x<1,x<y,a≥1)结构的多量子阱层4、i型AlGaN保护层5、透明n型AlGaN层6被刻蚀,使得内部n型AlGaN层3与n型下电极8接触。在n型上电极7区使得透明n型AlGaN层6和n型上电极7接触。所述n型下电极8区由透明n型AlGaN层6刻蚀至内部n型AlGaN层3;所述n型上电极7区被刻蚀至透明n型AlGaN层6;n型下电极8位于内部n型AlGaN层3上方;n型上电极7位于透明n型AlGaN层6上方。

[0050] In the laser of the present invention, the AlGaN stress regulating layer 2 comprises a period of Al y Ga 1-y N / A x Ga 1-x N / A y Ga 1-y N(0 <x<1,x<y,a≥1)结构的多量子阱层4的能带进行调控,起到调控多量子阱初始发光偏振度的作用;所述内部n型AlGaN层3作为欧姆接触层与n型下电极8接触,同时作为电压调控层保持层内电位基本一致;所述包含a个周期Al y Ga 1-y N / A x Ga 1-x N / A y Ga 1-y N(0 <x<1,x<y,a≥1)结构的多量子阱层4作为激光器的有源区,起到束缚光生电子-空穴对,产生并调控受激跃迁的作用;所述i型AlGaN保护层5的Al组分高于内部n型AlGaN层3、和透明n型AlGaN层6的Al组分,起到阻止载流子进入或流出包含a个周期Al y Ga 1-y N / A x Ga 1-x N / A y Ga 1-y N(0 <x<1,x<y,a≥1)结构的多量子阱层4的作用;所述透明n型AlGaN层6作为电压调控层同时对泵浦光源透明。

[0051] Among them, the material of the substrate is a hetero-substrate material or a homo-substrate material; the hetero-substrate material is any one of sapphire, silicon carbide, and silicon; the homo-substrate material is GaN or AlN. The Al component of the AlGaN stress control layer 2 is 0-1; the Al component change range of the internal n-type AlGaN layer 3 is 0-1, which is consistent with the AlGaN stress control layer 2. In the multi-quantum well layer 4 with the structure of a period of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N(0 < x < 1, x < y, a ≥ 1), x ≤ y, the quantum barrier thickness is 4-20 nm, and the quantum well thickness is 0.5-3 nm. The Al component in the i-type AlGaN protection layer 5 is greater than y, and the Al component in the transparent n-type AlGaN layer 6 is greater than x. Both the n-type upper electrode 7 and the n-type lower electrode 8 are ohmic electrodes, and the material is any one, two or more alloys of Pt, Ti, Al, Ni, and Au.

[0052] Combined with Figure 2 Specifically described, the preparation method of the above-mentioned polarization-tunable AlGaN optical-pumped deep ultraviolet laser provided by the present invention is as follows:

[0053] S1: Growing the device epitaxial material:

[0054] On the substrate 1, the AlGaN stress control layer 2, the internal n-type AlGaN layer 3, the i-type AlGaN protection layer 5, and the structure containing a period of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N(0 < x < 1, x < y, a ≥ 1), the multi-quantum well layer 4, the i-type AlGaN protection layer 5, and the transparent n-type AlGaN layer 6 are grown in sequence;

[0055] S2: Preparing the mesa structure:

[0056] Using the PECVD technology to grow the SiO2 mask layer on the outermost layer of the device epitaxial material obtained in step S1, using the photolithography technology to lithograph the device mesa pattern on the SiO2 mask layer, using the RIE technology to etch and remove the SiO2 mask layer without photoresist coverage in the non-mesa area, using the ICP technology to etch the area without the SiO2 mask layer coverage to the internal n-type AlGaN layer 3, and using HF to remove the SiO2 mask layer in the mesa area;

[0057] S3: Fabricate the n-type lower electrode 8:

[0058] Use photolithography technology to fabricate a photoresist mask pattern of the n-type lower electrode 8 above the internal n-type AlGaN layer 3. After development, the photoresist in the electrode pattern area is removed, and the photoresist in the non-electrode area is retained. Then, deposit the material of the n-type lower electrode 8 on the photoresist mask pattern, and use the Lift Off technology to remove the photoresist and the electrode material covered on it. Finally, perform a rapid annealing treatment;

[0059] S4: Fabricate the n-type upper electrode 7:

[0060] Use photolithography technology to fabricate a photoresist mask pattern of the n-type upper electrode 7 above the transparent n-type AlGaN layer 6. After development, the photoresist in the electrode pattern area is removed, and the photoresist in the non-electrode area is retained. Then, deposit the material of the n-type upper electrode 7 on the photoresist mask pattern, and use the Lift Off technology to remove the photoresist and the electrode material covered on it. Finally, perform a rapid annealing treatment.

[0061] In the above preparation method of the present invention, the method for growing the device epitaxial material in step S1 is MOCVD. In step S2, photolithography technology is used, and the selection of positive and negative photoresists is determined according to the design of the photomask pattern window, so that the photoresist in the mesa area is retained after development, and the photoresist in the non-mesa area is removed; in steps S3 and S4, photolithography technology is used, and the selection of positive and negative photoresists is determined according to the design of the photomask pattern window, so that the photoresist in the electrode pattern area is removed after development, and the photoresist in the non-electrode area is retained. In steps S3 and S4, the methods for depositing the materials of the n-type lower electrode 8 and the n-type upper electrode 7 are electron beam evaporation or thermal evaporation technology; the thickness of the deposited materials of the n-type lower electrode 8 and the n-type upper electrode 7 is both 200 - 400 nm. In steps S3 and S4, the Lift Off technology is used to dissolve the photoresist, and the dissolving solution is selected as acetone solution; the rapid annealing treatment is to anneal the n-type lower electrode 8 and the n-type upper electrode 7 in a nitrogen atmosphere using a rapid annealing furnace, and the annealing temperature and time are determined by the electrode material.

[0062] The manufacturing method of the present invention is not limited to the above steps. The above steps are only a preparation means, and all those with a final structure similar to that of the present invention should be protected by this application. The process parameters of each step in the above preparation method can be set with reference to the conventional parameters of lasers in the art. The present invention has no special requirements for them, and the present invention also has no special requirements for the material or thickness of each layer.

[0063] In summary, the laser of the present invention is an AlGaN optically pumped laser applicable to the deep ultraviolet band. The AlGaN stress regulation layer can make the intensities of the initial spontaneous emission light TE radiation transition and TM radiation transition of the laser almost the same. The internal n-type AlGaN layer and the transparent n-type AlGaN layer are used to apply an electric field to the multiple quantum well layer, and the laser polarization of the laser is regulated under the condition of optically pumped lasing, realizing that the polarization is adjustable between the TE and TM states.

[0064] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A polarization-tunable AlGaN optically pumped deep ultraviolet laser, characterized in that, Including a substrate (1), an AlGaN stress control layer (2) grown successively on the substrate (1), an internal n-type AlGaN layer (3), an i-type AlGaN protective layer (5), a multi-quantum well layer (4) including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N structure, an i-type AlGaN protective layer (5) and a transparent n-type AlGaN layer (6); and also including an n-type upper electrode (7) and an n-type lower electrode (8); Among them, it contains a period of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y In the multiple quantum well layer with the GaN structure, 0 < x < 1, x < y, a ≥ 1; The n-type lower electrode (8) region is etched from the transparent n-type AlGaN layer (6) to the internal n-type AlGaN layer (3); the n-type upper electrode (7) region is etched to the transparent n-type AlGaN layer (6); The n-type lower electrode (8) is located above the internal n-type AlGaN layer (3); the n-type upper electrode (7) is located above the transparent n-type AlGaN layer (6); The AlGaN stress regulation layer (2) regulates the energy band of the multi-quantum well layer (4) with a structure of containing a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1- y N, so as to regulate the initial emission polarization degree of the multi-quantum well The internal n-type AlGaN layer (3) serves as an ohmic contact layer to contact the n-type lower electrode (8), and at the same time serves as a voltage regulation layer to keep the potential in the layer basically consistent; The Al containing a periods y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y The multi - quantum well layer (4) of the GaN structure serves as the active region of the laser, playing a role in confining photo - generated electron - hole pairs, generating and regulating stimulated transitions; The Al composition of the type-I AlGaN protection layer (5) is higher than that of the internal n-type AlGaN layer (3) and the transparent n-type AlGaN layer (6), which serves to prevent carriers from entering or exiting the multi-quantum well layer (4) including a period of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N structure; The transparent n-type AlGaN layer (6) serves as a voltage regulation layer and is transparent to the pump light source at the same time.

2. The polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 1, wherein The material of the substrate (1) is a hetero-substrate material or a homo-substrate material; The hetero-substrate material is any one of sapphire, silicon carbide, and silicon; The homo-substrate material is GaN or AlN.

3. The polarization tunable AlGaN optically pumped deep ultraviolet laser according to claim 1, wherein The Al component of the AlGaN stress regulation layer (2) is 0 - 1; the Al component of the internal n-type AlGaN layer (3) varies in the range of 0 - 1, which is consistent with the AlGaN stress regulation layer (2).

4. The polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 1, wherein The Al with a periods included y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y In the multiple quantum well layer (4) of the GaN structure, the quantum barrier thickness is 4 - 20 nm, and the quantum well thickness is 0.5 - 3 nm.

5. The polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 1, characterized in that, The Al component in the i-type AlGaN protective layer (5) is greater than y, and the Al component in the transparent n-type AlGaN layer (6) is greater than x.

6. The polarization-adjustable AlGaN optically pumped deep ultraviolet laser according to claim 1, characterized in that Both the n-type upper electrode (7) and the n-type lower electrode (8) are ohmic electrodes, and the material is an alloy of any one, two or more of Pt, Ti, Al, Ni, and Au.

7. A method for preparing a polarization-tunable AlGaN optically pumped deep ultraviolet laser according to any one of claims 1-6, characterized in that, It includes the following steps: S1: Growing the device epitaxial material: The AlGaN stress control layer (2), the internal n-type AlGaN layer (3), the i-type AlGaN protection layer (5), the multi-quantum well layer (4) including a periods of Al y Ga 1-y N / Al x Ga 1-x N / Al y Ga 1-y N structure, the i-type AlGaN protection layer (5) and the transparent n-type AlGaN layer (6) are sequentially grown on the substrate (1); S2: Preparing the mesa structure: Using PECVD technology to grow a SiO2 mask layer on the outermost layer of the device epitaxial material, using photolithography technology to lithograph the device mesa pattern on the SiO2 mask layer, using RIE technology to etch and remove the SiO2 mask layer without photoresist coverage in the non-mesa area, using ICP technology to etch the area without SiO2 mask layer coverage to the internal n-type AlGaN layer (3), and using HF to remove the SiO2 mask layer in the mesa area; S3: Preparing the n-type lower electrode (8): Using photolithography technology to prepare the photoresist mask pattern of the n-type lower electrode (8) above the internal n-type AlGaN layer (3), removing the photoresist in the electrode pattern area after development, retaining the photoresist in the non-electrode area, then evaporating the n-type lower electrode (8) material on the photoresist mask pattern, and then using Lift Off technology to remove the photoresist and the electrode material covered thereon, and finally performing rapid annealing treatment; S4: Preparing the n-type upper electrode (7): Using photolithography technology to prepare the photoresist mask pattern of the n-type upper electrode (7) above the transparent n-type AlGaN layer (6), removing the photoresist in the electrode pattern area after development, retaining the photoresist in the non-electrode area, then evaporating the n-type upper electrode (7) material on the photoresist mask pattern, and then using Lift Off technology to remove the photoresist and the electrode material covered thereon, and finally performing rapid annealing treatment.

8. The preparation method of the polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 7, characterized in that, The method for growing the device epitaxial material in step S1 is MOCVD; In step S2, a lithography technique is adopted. The selection of positive and negative photoresists is determined according to the design of the lithography mask pattern window, so that the photoresist in the mesa area remains after development, and the photoresist in the non-mesa area is removed. In steps S3 and S4, a lithography technique is adopted. The selection of positive and negative photoresists is determined according to the design of the lithography mask pattern window, so that the photoresist in the electrode pattern area is removed after development, and the photoresist in the non-electrode area remains.

9. The preparation method of the polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 7, characterized in that, In the said steps S3 and S4, the method of evaporating the n-type lower electrode (8) material and the n-type upper electrode (7) material is electron beam evaporation or thermal evaporation technique. The thickness of both the evaporated n-type lower electrode (8) material and the n-type upper electrode (7) material is 200 - 400 nm.

10. The preparation method of the polarization-tunable AlGaN optically pumped deep ultraviolet laser according to claim 7, characterized in that, In the said steps S3 and S4, the Lift Off technique is adopted to dissolve the photoresist, and the dissolution liquid is acetone solution. The rapid annealing treatment is to anneal the n-type lower electrode (8) and the n-type upper electrode (7) in a nitrogen atmosphere using a rapid annealing furnace, and the annealing temperature and time are determined by the electrode materials.

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