Semiconductor epitaxial structure, method of making and use thereof

Abstract

The application provides a semiconductor epitaxial structure and a preparation method and application thereof, and belongs to the technical field of semiconductor optoelectronic devices. The semiconductor epitaxial structure based on a double-layer metal micro-nano and graphene composite structure comprises, from bottom to top, a substrate, an AlN layer, an N-AlGaN layer, an AlGaN multi-quantum well, a P-AlGaN electron blocking layer, a P-AlGaN layer, an Al metal micro-nano structure layer, a P-GaN layer, an Al metal periodic structure layer and a graphene layer. The Al metal micro-nano structure layer is prepared below the P-GaN layer, the Al metal periodic structure layer and the graphene layer composite micro-nano structure are prepared above the P-GaN layer, the resonance coupling effect between surface plasmons and excited states is utilized, the problem that the plasmon skin depth is insufficient and cannot match the energy of the excited state is solved, and the light extraction efficiency is greatly enhanced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device technology, and particularly relates to a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, its preparation method and application. Background Technology

[0002] Deep ultraviolet (DUV) light sources have enormous application prospects in numerous fields such as air / water purification, biochemical detection, UV curing, UV communication, and photolithography. Mercury lamps have long played a vital role as traditional UV light sources in social production and daily life. However, metallic mercury is toxic, causing serious environmental pollution and harming human health during its production and disposal. Therefore, a new type of environmentally friendly UV light source is needed. AlGaN, a typical representative of third-generation semiconductor materials, can have its bandgap continuously tunable between 3.4 and 6.1 eV by changing its composition, covering the UV band from 210 nm to 360 nm, making it an ideal material for fabricating DUV LEDs. AlGaN-based DUV LEDs are not only environmentally friendly but also possess advantages such as long lifespan, miniaturization, and narrow spectral density, and have seen initial applications in small- to medium-scale commercial air / water purification and sterilization. However, the external quantum efficiency of AlGaN-based DUV LEDs is very low, dropping sharply to below 1% with decreasing wavelength, and mostly below 10%, which greatly hinders their large-scale commercial application. External quantum efficiency comprises two important components: internal quantum efficiency (IQE) and light extraction efficiency (LEE). The main factors affecting the IQE of deep ultraviolet (DUV) LEDs are the high dislocation density in high-Al composition AlGaN films, low P-type doping efficiency, electron leakage, and the quantum confinement Stark effect. Regarding LEE, due to the significant refractive index difference, severe total internal reflection (TIR) ​​occurs at the epitaxial layer / substrate interface and the substrate / air interface. Furthermore, the predominantly TM mode polarization in high-Al composition light confines a large number of photons within the LED chip, which are then dissipated as heat after multiple internal reflections, ultimately resulting in a low LEE value. Therefore, LEE plays a crucial role in improving the performance of DUV LED devices.

[0003] Surface plasmons (SPs) have proven feasible for improving light extraction efficiency in blue and visible LEDs. Here, a surface plasmon is a near-field electromagnetic wave propagating along the metal surface, formed when free electrons on the metal surface undergo collective oscillations upon light incident on the metal-dielectric interface. In a resonant state, the energy of the electromagnetic field is effectively converted into the collective vibration of free electrons—the electromagnetic field is confined to a small area on the metal surface and amplified—resulting in surface plasmons. When the energy of the excited state from radiative recombination in the active region of the semiconductor matches or approaches the energy of the surface plasmons, the excited state energy can be transferred to the surface plasmons, further exciting the SPs. When momentum matching is achieved, resonant coupling occurs with the surface plasmons, generating photons at the metal / air interface (top emission) or metal / semiconductor (bottom emission), thus enhancing light extraction efficiency. By growing metal micro / nano structures in the top layer of the LED and utilizing the surface plasmon resonance effect, the LED's light efficiency (LEE) can be significantly improved. By growing metal micro / nano structures of different sizes, the resonant wavelength of plasmons can be adjusted to achieve momentum matching with the excited states inside semiconductor materials, thereby significantly enhancing the LEE.

[0004] However, compared to the visible band, the surface plasmon-enhanced light extraction efficiency in the ultraviolet band is relatively low, predicted to be only about 10-15%. There are many reasons for this problem, including (1) the scarcity of metal resources suitable for improving ultraviolet light extraction efficiency, with only Al metal currently being suitable; and (2) the redshift of the resonant absorption peak of metal nanoparticles as the metal size increases, thus requiring the fabrication of small-sized metal particles. However, achieving this goal is difficult, and the fabrication process may severely affect device performance, so there is no mature method for preparing small-sized metal nanostructures. The smallest reported diameter of Al nanoparticles is 40 nm, achieved by South Korea's Pohang University in 2020. Summary of the Invention

[0005] Therefore, to solve the above-mentioned technical problems, this invention proposes a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, its preparation method and application. An Al metal micro / nano structure layer is prepared below the P-GaN layer, and an Al metal periodic structure layer and graphene layer composite micro / nano structure are prepared above the P-GaN layer. By utilizing the resonant coupling effect between surface plasmons and excited states, the bilayer metal micro / nano structure can solve the problem of insufficient plasmon skin depth causing the inability to match the energy with the excited state, and significantly enhance the light extraction efficiency.

[0006] To achieve the above objectives, the present invention provides a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, comprising, from bottom to top, a substrate, an AlN layer, an N-AlGaN layer, an AlGaN multiple quantum well, a P-AlGaN electron blocking layer, a P-AlGaN layer, an Al metal micro / nano structure layer, a P-GaN layer, an Al metal periodic structure layer, and a graphene layer.

[0007] Preferably, the Al metal micro / nano structure is an Al metal nanoparticle or an Al metal nanostructure array.

[0008] Preferably, the periodic structure is any one of the following: grating structure, triangular pyramid array, cylindrical array, triangular prism array, and ring array.

[0009] Preferably, the substrate is made of any one or two of sapphire, SiC, Si, and AlN.

[0010] The present invention also provides a method for preparing the above-mentioned semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, comprising the following steps:

[0011] The AlN layer, the N-AlGaN layer, the AlGaN multiple quantum well, the P-AlGaN electron blocking layer, and the P-AlGaN layer are epitaxially grown sequentially on the substrate.

[0012] The Al metal micro / nano structure layer is fabricated on the P-AlGaN layer;

[0013] The P-GaN layer is epitaxially grown on the Al metal micro / nano structure layer;

[0014] The Al metal periodic structure layer is prepared on the P-GaN layer;

[0015] The graphene layer is prepared on the Al metal periodic structure layer.

[0016] Preferably, the fabrication process of the Al metal micro / nano structure layer is any one of rapid thermal annealing, polystyrene film sphere method, photolithography, and anodizing;

[0017] The fabrication process of the Al metal periodic structure layer is any one of nanoimprinting, two-beam interference, and selective etching.

[0018] The graphene layer is prepared by direct transfer or in-situ growth; the direct transfer method includes wet transfer, bubbling transfer, dry transfer, roll-to-roll transfer and unsupported transfer.

[0019] The present invention also provides a deep ultraviolet LED device structure, which uses the semiconductor epitaxial structure based on the double-layer metal micro-nano and graphene composite structure as described above as the epitaxial structure of the deep ultraviolet LED device, and further includes an N electrode and a P electrode.

[0020] An LED mesa is fabricated by etching on the deep ultraviolet LED epitaxial structure to the depth of the N-AlGaN layer. The N-electrode is fabricated above the N-AlGaN layer in the etched region, and the P-electrode is fabricated above the composite micro / nano structure of the Al metal periodic structure layer and the graphene layer.

[0021] Preferably, the P electrode is an ohmic contact electrode, and the material is any one of Ni, Au, ITO and Pt.

[0022] Preferably, the N electrode is an ohmic contact electrode, which is a composite multilayer structure in which Ti, Al, Ni and Au are deposited sequentially.

[0023] The present invention also provides an application of the semiconductor epitaxial structure based on the bilayer metal micro / nano and graphene composite structure as described above in visible light LEDs, detectors, lasers, or solar cells.

[0024] The advantages of the above technical solution adopted in this invention are:

[0025] This invention relates to a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure. An Al metal micro / nano structure layer is fabricated below a P-GaN layer, and an Al metal periodic structure layer and a graphene layer composite micro / nano structure are fabricated above the P-GaN layer. Utilizing the resonant coupling effect between surface plasmons and excited states, the Al metal micro / nano structure layer avoids the problem of insufficient skin depth in Al metal, enabling the establishment of a fast energy transfer channel with the AlGaN multi-quantum well, achieving rapid coupling with the excited state. The Al metal periodic structure layer also participates in the resonant coupling effect, achieving another part of the resonant enhancement, which can further improve the light extraction efficiency. Furthermore, due to its large duty cycle, it does not have a reverse effect on photon emission. The graphene layer can increase the electric field strength at the metal interface, achieving resonant coupling enhancement of local surface plasmons and preventing metal oxidation. Simultaneously, as a current spreading layer, it realizes a novel light extraction structure for LED devices, reducing current blocking effects and improving internal quantum efficiency and device stability. The aforementioned bilayer metal micro / nano structure can solve the problem of insufficient plasmon skin depth causing inability to match the excited state energy, and can significantly enhance the light extraction efficiency.

[0026] The method for fabricating semiconductor epitaxial structures based on bilayer metal micro / nano and graphene composite structures of the present invention has simple process steps.

[0027] The deep ultraviolet LED device structure of the present invention includes a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, which has similar performance.

[0028] The semiconductor epitaxial structure based on the bilayer metal micro / nano and graphene composite structure of the present invention can also be applied to visible light LEDs, detectors, lasers, or solar cells, with very broad application prospects. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure according to the present invention.

[0031] Figure 2 This is a schematic diagram of the deep ultraviolet LED device structure of the present invention;

[0032] Figure descriptions: 1-Substrate, 2-AlN layer, 3-N-AlGaN layer, 4-AlGaN multiple quantum well, 5-P-AlGaN electron blocking layer, 6-P-AlGaN layer, 7-Al metal micro / nano structure layer, 8-P-GaN layer, 9-Al metal periodic structure layer, 10-Graphene layer; 11-P electrode, 12-N electrode. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] like Figure 1 The diagram shows a schematic of the semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure according to the present invention. From bottom to top, it includes a substrate 1, an AlN layer 2, an N-AlGaN layer 3, an AlGaN multiple quantum well 4, a P-AlGaN electron blocking layer 5, a P-AlGaN layer 6, an Al metal micro / nano structure layer 7, a P-GaN layer 8, an Al metal periodic structure layer 9, and a graphene layer 10.

[0035] The principle behind improving the light extraction efficiency of AlGaN-based deep ultraviolet LEDs using the bilayer metal micro / nano composite resonant coupling effect is as follows: When a periodic metal structure exists above the active region of the LED, plasmons are generated on the metal surface under the excitation of incident light. When the energy of the excited state of radiative recombination in the active region of the semiconductor matches or approaches the energy of the surface plasmons, the energy of the excited state can be transferred to the surface plasmons and further excite SPs. When momentum matching is achieved, resonant coupling will occur with the surface plasmons, generating photons at the metal / air interface (top emission) or metal / semiconductor (bottom emission), thus enhancing the light extraction efficiency.

[0036] For surface plasmons (SIPs), there exists a propagation depth, which is the farthest distance they can travel into the semiconductor interior. This distance can be calculated. If the LED top layer is too thick, SIPs will struggle to reach the vicinity of the active region and will annihilate during propagation. Therefore, the thickness of the top layer needs to be precisely designed and adjusted. In this case, growing a layer of metal micro / nanostructure below the top layer, at the interface between the top layer and the electron blocking layer, can effectively promote the transfer of excited-state energy to the plasmons, achieving resonant coupling and light emission. Simultaneously, the periodic surface metal structure can further improve the light emission efficiency (LEE), and due to its large duty cycle, it will not have a negative impact on photon emission. Therefore, using a double-layer metal micro / nanostructure can significantly enhance the LEE.

[0037] Simultaneously, transferring a layer of graphene onto the surface of a periodic metal structure to form a composite micro / nano structure can significantly improve the resonant coupling strength of the metal surface. Interfacial attraction, such as van der Waals forces, can tightly bond graphene to the substrate. Therefore, the large adhesion energy between the metal nanostructure and graphene is beneficial for complete electrical contact and strong interaction between graphene and metal, ultimately resulting in enhanced LSPRs supported by the composite metal micro / nano structure, achieving further enhancement of LEE. In addition, graphene can serve as a protective layer to prevent oxidation of the periodic metal structure; its high electrical conductivity can also act as a current spreading layer, reducing current blocking effects and improving internal quantum efficiency and device stability.

[0038] The Al metal micro / nanostructure can be either Al metal nanoparticles or Al metal nanostructure arrays. Al metal micro / nanostructures can be experimentally simulated using COMSOL software to determine parameters such as the size, shape, and density of Al metal nanoparticles or Al metal nanostructure arrays, as well as the different enhancement effects of oxidation on luminescence efficiency.

[0039] The periodic structure can be any one of the following: grating structure, triangular pyramid array, cylindrical array, triangular prism array, ring array, etc.

[0040] The substrate 1 is made of any one or two of sapphire, SiC, Si, and AlN. Preferably, an AlN layer is deposited on sapphire as substrate 1 to provide compressive stress to the N-AlGaN material, which is beneficial for dislocation suppression and can improve the quality of the epitaxial layer.

[0041] The present invention also provides a method for preparing the above-mentioned semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, comprising the following steps:

[0042] The AlN layer 2, the N-AlGaN layer 3, the AlGaN multiple quantum well 4, the P-AlGaN electron blocking layer 5, and the P-AlGaN layer 6 are epitaxially grown sequentially on the substrate 1.

[0043] The Al metal micro / nano structure layer 7 is prepared on the P-AlGaN layer 6;

[0044] The P-GaN layer 8 is epitaxially grown on the Al metal micro / nano structure layer 7;

[0045] The Al metal periodic structure layer 9 is prepared on the P-GaN layer 8;

[0046] The graphene layer 10 is prepared on the Al metal periodic structure layer 9.

[0047] The Al metal micro / nano structure layer 7 is prepared by any one of the following methods: rapid thermal annealing, polystyrene film sphere method, photolithography, and anodizing.

[0048] The fabrication process of the Al metal periodic structure layer 9 is any one of nanoimprinting technology, two-beam interference, and selective etching.

[0049] The graphene layer 10 is prepared by a direct transfer method or an in-situ growth method. The direct transfer method includes wet transfer, bubbling transfer, dry transfer, roll-to-roll transfer, and unsupported transfer. The number of graphene layers is one, two, or three. Preferably, an in-situ growth method is used, which not only avoids the cumbersome transfer process but also reduces damage during the transfer process, achieving a tight bond between the Al metal periodic structure layer 9 and the graphene, and improving the strength of the resonant coupling.

[0050] like Figure 2 As shown, the present invention also provides a deep ultraviolet LED device structure, which uses the semiconductor epitaxial structure based on the double-layer metal micro-nano and graphene composite structure as described above as the epitaxial structure of the deep ultraviolet LED device, and also includes an N electrode 12 and a P electrode 11.

[0051] An LED mesa is etched onto the deep ultraviolet LED epitaxial structure to the depth of the N-AlGaN layer 3. The N electrode 12 is then fabricated above the N-AlGaN layer 3 in the etched area, and the P electrode 11 is fabricated above the composite micro / nano structure of the Al metal periodic structure layer 9 and the graphene layer 10.

[0052] The P electrode 11 is an ohmic contact electrode made of any one of Ni, Au, ITO, and Pt. The N electrode 12 is an ohmic contact electrode, which is a composite multilayer structure formed by sequentially depositing Ti, Al, Ni, and Au. The P electrode 11 and N electrode 12 are prepared by depositing electrode materials using methods such as vacuum evaporation or magnetron sputtering, followed by rapid annealing.

[0053] The present invention also provides an application of the semiconductor epitaxial structure based on the bilayer metal micro / nano and graphene composite structure as described above in visible light LEDs, detectors, lasers, or solar cells.

[0054] Example 1

[0055] A deep ultraviolet LED device structure, the fabrication process of which is as follows:

[0056] Using MOCVD, a 400 nm AlN low-temperature nucleation layer was grown on sapphire as a substrate at a growth temperature of 580 °C.

[0057] A 600 nm AlN material was epitaxially grown at a high temperature of 1080 °C to obtain an AlN layer.

[0058] A Si-doped N-AlGaN layer is grown on an AlN layer. The Si-doped N-AlGaN layer should ultimately have metallic polarity (Al, Ga). The Si-doped N-AlGaN layer is uniformly doped with a concentration of 1 × 10⁻⁶. 18 cm -3 The Al content is 0.53, the thickness is 2 μm, and the growth temperature is 850℃.

[0059] Unintentionally doped AlGaN multiple quantum wells were grown on Si-doped N-AlGaN layers at a growth temperature of 1000℃. The quantum well layer had an Al composition of 0.43 and a thickness of 1.5 nm, while the quantum barrier layer had an Al composition of 0.5, a thickness of 10 nm, and a period number of 5.

[0060] A 15 nm thick Mg-doped AlGaN electron blocking layer was grown on an AlGaN multi-quantum-well layer at a growth temperature of 1150 °C; the Mg was uniformly doped with a concentration of 2 × 10⁻⁶. 18 cm -3 The Al component is 0.53;

[0061] A 2 nm thick Mg-doped P-AlGaN layer was grown on a Mg-doped AlGaN electron blocking layer at a growth temperature of 1150 °C; Mg was uniformly doped with a concentration of 2 × 10⁻⁶. 18 cm -3 The Al component is 0.53;

[0062] A 10 nm thick Al layer was grown on a Mg-doped P-AlGaN layer by vacuum electron beam evaporation. After annealing at 550 °C for 30 minutes in a nitrogen atmosphere, nanoparticles with a diameter of about 170 nm were obtained, forming an Al metal micro / nano structure.

[0063] A 50 nm thick Mg-doped P-GaN layer was grown on an Al metal micro / nanostructure using MOCVD at a growth temperature of 550 °C. The Mg was uniformly doped at a concentration of 2 × 10⁻⁶. 18 cm -3 ;

[0064] A photoresist grating pattern with a period of 100 nm was prepared on a Mg-doped P-GaN layer using two-beam interference. Then, an electron beam deposition of metal Al was performed to form a metal thin film with a thickness of 20 nm. The epitaxial wafer was then cleaned in acetone to remove the remaining photoresist, forming an Al metal grating structure with a period of 100 nm.

[0065] Graphene layers were prepared on an Al metal grating structure using a direct transfer method, with three graphene layers.

[0066] A mesa mask pattern is prepared using photolithography, and then an inductively coupled plasma (ICP) etching technique is used with Cl2 and BCl3 as etching gases to etch to the Si-doped N-AlGaN layer.

[0067] Electrode pattern regions were formed on the graphene layer using photolithography. Ni and Au were deposited using vacuum electron beam deposition with thicknesses of 20 nm and 80 nm, respectively. After rapid annealing, the ohmic contact electrode P electrode was obtained.

[0068] Electrode pattern regions are formed on Si-doped N-AlGaN layers using photolithography. Ti, Al, Ni and Au are deposited sequentially by vacuum evaporation with thicknesses of 50 nm, 100 nm, 50 nm and 100 nm, respectively. After rapid annealing, ohmic contact N-electrode is obtained.

[0069] The deep ultraviolet LED device structure of this embodiment, at an emission wavelength of 265nm, shows a PL intensity four times higher than that of an AlGaN-based DUV LED, indicating that the double-layer metal micro / nano structure method of this invention can improve light extraction efficiency. The aforementioned AlGaN-based DUV LED is grown on c-plane sapphire using MOCVD. From bottom to top, it consists of a 200nm low-temperature AlN layer and a 500nm high-temperature Al layer; a 140nm AlN / AlGaN insertion layer; a 700nm Si-doped AlGaN layer with a composition of 0.6 and a 350nm layer with a composition of 0.5; and finally, a six-cycle MQW layer, where the well layer thickness is 2.5nm, the barrier layer thickness is 18nm (the first barrier layer is 37.5nm), and the composition is 0.65.

[0070] The advantages of the above technical solution adopted in this invention are:

[0071] This invention relates to a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure. An Al metal micro / nano structure layer is fabricated below a P-GaN layer, and an Al metal periodic structure layer and a graphene layer composite micro / nano structure are fabricated above the P-GaN layer. Utilizing the resonant coupling effect between surface plasmons and excited states, the Al metal micro / nano structure layer avoids the problem of insufficient skin depth in Al metal, enabling the establishment of a fast energy transfer channel with the AlGaN multi-quantum well, achieving rapid coupling with the excited state. The Al metal periodic structure layer also participates in the resonant coupling effect, achieving another part of the resonant enhancement, which can further improve the light extraction efficiency. Furthermore, due to its large duty cycle, it does not have a reverse effect on photon emission. The graphene layer can increase the electric field strength at the metal interface, achieving resonant coupling enhancement of local surface plasmons and preventing metal oxidation. Simultaneously, as a current spreading layer, it realizes a novel light extraction structure for LED devices, reducing current blocking effects and improving internal quantum efficiency and device stability. The aforementioned bilayer metal micro / nano structure can solve the problem of insufficient plasmon skin depth causing inability to match the excited state energy, and can significantly enhance the light extraction efficiency.

[0072] The method for fabricating semiconductor epitaxial structures based on bilayer metal micro / nano and graphene composite structures of the present invention has simple process steps.

[0073] The deep ultraviolet LED device structure of the present invention includes a semiconductor epitaxial structure based on a bilayer metal micro / nano and graphene composite structure, which has similar performance.

[0074] The semiconductor epitaxial structure based on the bilayer metal micro / nano and graphene composite structure of the present invention can also be applied to visible light LEDs, detectors, lasers, or solar cells, with very broad application prospects.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A semiconductor epitaxial structure, characterized in that, From bottom to top, the structure comprises a substrate, an AlN layer, an N-AlGaN layer, an AlGaN multiple quantum well, a P-AlGaN electron blocking layer, a P-AlGaN layer, an Al metal micro / nanostructure layer, a P-GaN layer, an Al metal periodic structure layer, and a graphene layer; wherein the Al metal micro / nanostructure is an Al metal nanoparticle or an Al metal nanostructure array; and the periodic structure is any one of a grating structure, a triangular pyramid array, a cylindrical array, a triangular prism array, or a ring array.

2. The semiconductor epitaxial structure according to claim 1, characterized in that, The substrate is made of any one or two of sapphire, SiC, Si, and AlN.

3. A method for preparing a semiconductor epitaxial structure according to any one of claims 1-2, characterized in that, Includes the following steps: The AlN layer, the N-AlGaN layer, the AlGaN multiple quantum well, the P-AlGaN electron blocking layer, and the P-AlGaN layer are epitaxially grown sequentially on the substrate. The Al metal micro / nano structure layer is fabricated on the P-AlGaN layer; The P-GaN layer is epitaxially grown on the Al metal micro / nano structure layer; The Al metal periodic structure layer is prepared on the P-GaN layer; The graphene layer is prepared on the Al metal periodic structure layer.

4. The method for preparing a semiconductor epitaxial structure according to claim 3, characterized in that, The fabrication process of the Al metal micro / nano structure layer is any one of rapid thermal annealing, polystyrene film sphere method, photolithography and anodizing. The fabrication process of the Al metal periodic structure layer is any one of nanoimprinting, two-beam interference, and selective etching. The graphene layer is prepared by direct transfer or in-situ growth; the direct transfer method includes wet transfer, bubbling transfer, dry transfer, roll-to-roll transfer and unsupported transfer.

5. A deep ultraviolet LED device structure, characterized in that, The semiconductor epitaxial structure described in any one of claims 1-2 is used as the epitaxial structure of the deep ultraviolet LED device, and further includes an N electrode and a P electrode; An LED mesa is fabricated by etching on the deep ultraviolet LED epitaxial structure to the depth of the N-AlGaN layer. The N electrode is fabricated above the N-AlGaN layer in the etched area, and the P electrode is fabricated above the composite micro / nano structure of the Al metal periodic structure layer and the graphene layer.

6. The deep ultraviolet LED device structure according to claim 5, characterized in that, The P electrode is an ohmic contact electrode, and its material is any one of Ni, Au, ITO and Pt.

7. The deep ultraviolet LED device structure according to claim 5, characterized in that, The N electrode is an ohmic contact electrode, which is a composite multilayer structure with Ti, Al, Ni and Au deposited sequentially.

8. The application of a semiconductor epitaxial structure as described in any one of claims 1-2 in visible light LEDs, detectors, lasers, or solar cells.

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