A GaN-based multiple heterojunction photoelectrode and a preparation method and application thereof

Abstract

This invention discloses a GaN-based multiple heterojunction photoelectrode, its fabrication method, and its application, belonging to the field of semiconductor photoelectrochemical energy conversion technology. The photoelectrode comprises, from bottom to top: a substrate, an n-type GaN layer, an InGaN / GaN multiple quantum well layer, a p-type GaN layer, an n⁺-type InGaN layer, and a p-type Co₃O₄ layer. The p-type GaN layer and the n-type GaN layer form a bulk junction, and the p-type Co₃O₄ layer and the n⁺-type InGaN layer form a surface heterojunction. The electric field generated by the surface heterojunction is in the same direction as the electric field generated by the bulk junction. Through the synergistic geometric and bandgap engineering of the "bulk p-n junction / tunnel layer / surface heterojunction," the built-in electric fields generated by the two heterojunctions are aligned and their potentials are superimposed, fundamentally solving the problem of insufficient driving force in single-junction devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photoelectrochemical energy conversion technology, specifically relating to a GaN-based multiple heterojunction photoelectrode, its preparation method, and its application. Background Technology

[0002] Among numerous hydrogen production technologies, solar-driven photoelectrochemical (PEC) water splitting technology can directly convert solar energy into chemical energy, offering significant advantages such as a simple process flow, mild reaction conditions, and clean products. Gallium nitride (GaN), as a representative of third-generation wide-bandgap semiconductors, is considered an ideal material system for achieving long-lifetime, high-efficiency PEC reactions due to its excellent chemical stability, resistance to photocorrosion, and tunable bandgap width (which can cover the near-ultraviolet to visible light band by adjusting the In composition).

[0003] An ideal self-driven water splitting process (PEC) requires the output photovoltage generated by the photoelectrode to overcome the theoretical electrolysis voltage of water (1.23 V) and the kinetic overpotential required for the anode and cathode reactions. However, most existing planar GaN-based photoelectrodes employ a single pn junction structure. Limited by the physical limits of the Fermi level difference within a single heterojunction, the generated photovoltage is typically far below the threshold required for self-driven reactions (usually between 0.8 and 1.0 V). This forces most GaN-based photoelectrodes to rely on an external bias voltage to achieve a considerable photocurrent output, significantly limiting the system's energy conversion efficiency and ease of independent operation.

[0004] In practical photoelectrochemical processes, the efficiency of carrier separation and extraction is crucial to performance. Due to its large effective hole mass and deep-level acceptor characteristics, p-GaN materials face difficulties in increasing hole concentration and exhibit low mobility, resulting in significant interfacial resistance at the electrode surface. Furthermore, while traditional surface modification methods (such as simple supported catalysts) can improve surface reaction kinetics, they cannot alter the bandgap at the electrode surface. This means a substantial barrier remains in place for hole migration from the bulk to the surface, leading to severe recombination losses of photogenerated carriers at the interface.

[0005] The situation becomes more complex when applications expand to marine resource utilization (such as direct seawater decomposition for hydrogen production). The high salinity, multi-ion competition reactions, and potential electrode scaling in seawater place higher demands on the onset potential of the photoelectrode. To achieve the dual-function synergistic output of hydrogen production and chlorine production (disinfection) in a complex system containing chloride ions, the photoelectrode must be endowed with extremely strong self-driving capabilities. Currently, how to achieve a breakthrough in photovoltage by constructing multiple superimposed built-in electric fields through structural engineering while ensuring high crystal quality of GaN devices, and to establish reliable ohmic contacts (such as through optimized n-GaN contact electrode processes), has become a key scientific problem urgently needing to be solved in this field.

[0006] In summary, existing GaN-based photoelectrodes suffer from bottlenecks such as insufficient driving force. Although tunnel junction technology has been applied in optoelectronic devices (such as LEDs), in the field of PEC photoelectrodes, there is still a lack of mature, systematic, and highly self-driving device solutions for effectively coupling it with surface-catalyzed heterojunctions to construct cascaded built-in electric fields to achieve ultra-high photovoltage output. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a GaN-based multiple heterojunction photoelectrode, its fabrication method, and its application, thereby solving the problems in the prior art.

[0008] The objective of this invention can be achieved through the following technical solutions: A GaN-based multiple heterojunction photoelectrode comprises, from bottom to top: a substrate, an n-type GaN layer, an InGaN / GaN multiple quantum well layer, a p-type GaN layer, an n⁺-type InGaN layer, and a p-type Co3O4 layer; The p-type GaN layer and the n-type GaN layer form a bulk junction, and the p-type Co3O4 layer and the n⁺-type InGaN layer are in contact to form a surface heterojunction; the electric field generated by the surface heterojunction is in the same direction as the electric field generated by the bulk junction.

[0009] Furthermore, the upper surface of the n-type GaN layer includes an uncovered exposed area, on the surface of which an ohmic electrode structure is bonded.

[0010] Furthermore, the ohmic electrode structure is a multilayer metal consisting of Ti / Al / Ni / Au stacked sequentially from bottom to top, with thicknesses of 30 / 120 / 50 / 100 nm, respectively, wherein the Ti layer contacts the exposed surface of the n-type GaN layer.

[0011] Furthermore, the n + The doping concentration of the InGaN layer is .

[0012] Furthermore, the thickness of the p-type Co3O4 layer is 10-30 nm; n + The thickness of the p-type GaN layer is 2-5 nm; the thickness of the p-type GaN layer is 100-400 nm; and the thickness of the n-type GaN layer is 0.5-2 µm.

[0013] Furthermore, the InGaN / GaN multi-quantum-well layer has 8-20 cycles, with the InGaN well layer thickness being 3 nm and the GaN barrier layer thickness being 15 nm within each cycle.

[0014] The above-mentioned method for fabricating a GaN-based multiple heterojunction photoelectrode includes the following steps: The n-type GaN layer, the InGaN / GaN multiple quantum well layer, the p-type GaN layer, and the n-type GaN layer are sequentially grown on the substrate. + To obtain an epitaxial wafer, a type InGaN layer is formed. Partial removal of n on the epitaxial wafer using an etching process + n-type GaN layers, p-type GaN layers, and InGaN / GaN multiple quantum well layers are constructed until a portion of the n-type GaN layer surface is exposed, and an ohmic electrode is fabricated on the exposed n-type GaN layer surface. The n in the unetched region + A p-type Co3O4 layer is deposited on the surface of the InGaN layer to form the surface heterojunction.

[0015] Furthermore, the process of preparing the ohmic electrode includes: depositing a metal layer constituting the ohmic electrode on the surface of the exposed n-type GaN layer, placing the epitaxial wafer in a nitrogen atmosphere, and annealing it at a temperature of 400-900°C for 30-120 s.

[0016] Furthermore, the process of depositing the p-type Co3O4 layer includes: during the deposition process, using For cobalt source, A precursor solution was prepared for the electron acceptor / co-oxidant, and the epitaxial wafer was placed in the precursor solution for photodeposition under ultraviolet light irradiation.

[0017] The above-mentioned GaN-based multiple heterojunction photoelectrode is used in water splitting for hydrogen production.

[0018] The beneficial effects of this invention are: 1. This invention achieves consistent direction of the built-in electric fields generated by the two heterojunctions and superposition of potentials through the coordinated geometric and bandgap engineering of "body pn junction / tunnel layer / surface heterojunction". Experimental data shows that the absolute value of the device's photovoltage increases from 0.8271 V in ordinary GaN structures to 1.6021 V, an increase of nearly 100%, fundamentally solving the problem of insufficient driving force for single-junction devices.

[0019] 2. This invention utilizes heavily doped n + The introduction of the InGaN layer constructs an efficient tunneling path, solving the problem of high resistance to hole migration on the p-GaN surface, significantly reducing carrier recombination losses at the interface, and improving photoelectrochemical conversion efficiency.

[0020] 3. This invention employs multilayer metal electrodes and an annealing process to establish a stable electrical signal transmission channel at the n-GaN end; combined with the corrosion resistance of GaN material itself and the protective effect of Co3O4, the device can exhibit good chemical stability and cycle life in complex electrolyte environments.

[0021] 4. This invention is not a simple physical loading of a co-catalyst, but rather achieves a precise, stepped band arrangement at the atomic scale through a deep integration of epitaxial stacked design and surface interface engineering. Unlike existing technologies that rely solely on a single junction for power, this invention utilizes a heavily doped tunnel layer to "connect" the bulk junction and the surface heterojunction, achieving a cascaded multiplication of photovoltage. This structural breakthrough enables GaN-based photoelectrodes to, for the first time, possess the abundant power to drive complex electrochemical reactions (such as the complete splitting of water or reactions in complex seawater systems) without external bias, demonstrating significant technological advancement and engineering value. Attached Figure Description

[0022] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a bar chart comparing the photovoltage measured by four different structured photoelectrodes; Figure 2 This is a schematic diagram of the band structure and carrier transport of the Co3O4 / TJ-GaN photoelectrode with a double junction structure described in this invention; Figure 3 This is a schematic diagram of a typical GaN PCD (photo-chemical diode) structure used as a comparison group; Figure 4The TJ-GaN PCD (containing n) used as the control group + Schematic diagram of the InGaN layer structure; Figure 5 This is a schematic diagram of the Co3O4 / GaN PCD (surface loading only) structure used as a control group; Figure 6 This is a schematic diagram of the Co3O4 / TJ-GaN PCD double-junction stacked structure (GaN-based multi-heterojunction photoelectrode) provided by the present invention. Detailed Implementation

[0024] 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.

[0025] like Figure 6 As shown, a GaN-based multiple heterojunction photoelectrode comprises, from bottom to top, the following components: Substrate layer; An n-type GaN layer has an upper surface that includes a region covered by the overlying stacked structure and an exposed region that is not covered, with an ohmic electrode plated on the surface of the exposed region. InGaN / GaN multiple quantum well layers; p-type GaN layer; n + Type InGaN layer; p-type Co3O4 layer is loaded on the surface of the n⁺-type InGaN layer; Wherein, the p-type GaN layer and the n-type GaN layer form a bulk junction, and the p-type Co3O4 layer and the n-type GaN layer form a bulk junction. + A surface heterojunction is formed by contacting the InGaN layer; the direction of the electric field generated by the surface heterojunction is the same as the direction of the electric field generated by the bulk junction.

[0026] The n + The In composition of the InGaN layer is 0.12-0.2 (when the In composition is 0.12, i.e., In...). 0.12 Ga 0.88 N), with a thickness of 2-5 nm and a doping concentration of 1×10⁻⁶. 19 cm -3 -1×10 20 cm -3 .

[0027] The thickness of the p-type Co3O4 layer is 10-30 nm.

[0028] The substrate layer is a (0001)c-plane sapphire substrate.

[0029] The thickness of the n-type GaN layer is 0.5-2 μm, and the doping concentration is 1×10⁻⁶. 17 -1×10 20 cm -3 .

[0030] The ohmic electrode is a Ti / Al / Ni / Au electrode with a thickness of 30 / 120 / 50 / 100 nm, wherein the Ti layer contacts the surface of the n-type GaN layer.

[0031] The InGaN / GaN multi-quantum well layer has 8-20 cycles, with an InGaN well layer thickness of 3 nm and a GaN barrier layer thickness of 15 nm in each cycle.

[0032] The p-GaN layer has a thickness of 100-400 nm and a doping concentration of 5 × 10⁻⁶. 18 cm -3 -1×10 20 cm -3 .

[0033] The present invention also discloses the application of the above-mentioned GaN-based multiple heterojunction photoelectrode in water splitting for hydrogen production.

[0034] This invention also discloses a method for fabricating the above-mentioned GaN-based multiple heterojunction photoelectrode, the steps of which include: (1) An n-type GaN layer, an InGaN / GaN multi-quantum-well layer, a p-type GaN layer, and an n-type GaN layer are sequentially grown on the substrate. + To obtain an epitaxial wafer, a type InGaN layer is formed. (2) Expose part of the n-type GaN layer surface on the epitaxial wafer by etching process, and fabricate ohmic electrodes thereon; (3) In n + A p-type Co3O4 layer is deposited on the surface of the InGaN layer to form a surface heterojunction.

[0035] The technical solution of the present invention will be described below through the following embodiments and comparative examples, wherein the sources of the relevant raw materials in the embodiments and comparative examples are as follows: The substrate was specifically a (0001)c-plane sapphire substrate (650μm±25μm thickness, c-plane polished), purchased from Huacan Optoelectronics. Cobalt nitrate (hexahydrate, analytical grade AR) and sodium iodate (analytical grade AR) were both purchased from Shanghai Maclean Biochemical Technology Co., Ltd. The Ti, Al, Ni, and Au evaporation materials used in electron beam evaporation were all 99.99% pure and were purchased from Zhongnuo New Materials. Unless otherwise specified, all other reagents and materials are commercially available high-purity / analytical-grade products.

[0036] Example 1 This embodiment describes the fabrication process of the Co3O4 / TJ-GaN PCD double-junction stacked structure (GaN-based multiple heterojunction photoelectrode), specifically including: (1) Epitaxial Growth and Device Fabrication of Multilayer Heterojunctions: Multilayer heterostructures were epitaxially grown on a sapphire substrate using metal-organic chemical vapor deposition (MOCVD). Specifically, trimethylgallium, trimethylindium, and ammonia were used as Ga, In, and N sources, respectively, and silane and magnesium diacene were used as n-type and p-type doping sources, respectively. A 2 μm thick layer with a doping concentration of 2×10⁻⁶ was epitaxially grown sequentially. 19 cm -3 The n-GaN layer, the 10-period InGaN / GaN multiple quantum well (MQWs) active layer, and the 200 nm doping concentration of 2×10 19 cm -3 The p-GaN layer and 5 nm In composition are 0.12 (i.e., In). 0.12 Ga 0.88 Heavy doping of N) + -InGaN layer; (2) Fabrication of n-GaN ohmic electrodes: Specifically, a pre-defined pattern was formed on the surface of the epitaxial wafer using photolithography. ROL7133 was used as the photoresist, and the homogenization conditions were: first step 600 rpm, 9 s; second step 4000 rpm, 40 s; pre-baking time 2 min; exposure time 7 s; post-baking time 2 min; development time 30 s; and hardening time 5 min. Subsequently, dry etching was performed using inductively coupled plasma etching. The etching gases were Cl2 / BCl3, with flow rates of 48 / 6 sccm, working pressure of 10 mTorr, upper electrode power of 100 W, lower electrode power of 300 W, and etching time of 3 min. Partial epitaxial layer was selectively etched until the underlying n-GaN surface was exposed. Electron beam evaporation was used to deposit a Ti / Al / Ni / Au (30 / 120 / 50 / 100 nm) multilayer metal contact layer (specifically Ti / Al / Ni / Au) on the exposed n-GaN surface. After deposition, the device was placed in a nitrogen atmosphere and subjected to rapid thermal annealing (RTA) at 850°C for 30 s. In this embodiment, parametric annealing of 850°C in a nitrogen atmosphere for 30 s was used to form a low-resistance ohmic contact between Ti / Al / Ni / Au and n-GaN, ensuring the smooth extraction of photogenerated electrons. (3) Surface heterojunction loading and functionalization: In the top layer n +- On the InGaN surface, a p-Co3O4 layer was selectively loaded by photodeposition or electrochemical deposition: Co(NO3)2 was used as the cobalt source and NaIO3 as the electron acceptor / auxiliary oxidant. A precursor solution was prepared with a 1:1 molar concentration ratio. In this experiment, 0.2 mol / L Co(NO3)2 and 0.2 mol / L NaIO3 were precisely used to prepare the precursor solution. The device was placed in the solution and irradiated under 365 nm ultraviolet light for 5 min to achieve photodeposition of Co3O4, and the deposition thickness was controlled to be about 20 nm.

[0037] p-Co3O4 and the n below + -InGaN layers are in close contact to form a surface heterojunction. The n + -The InGaN layer is heavily doped (preferably with a doping concentration of 1×10⁻⁶). 19 Up to 5×10 20 cm -3 This embodiment uses 1×10 20 cm -3 This significantly shortens the space charge region width, thereby establishing an efficient hole tunneling path between p-GaN and the surface heterojunction. The resulting Co3O4 / TJ-GaN PCD double-junction stacked device structure is shown below. Figure 6 As shown, its band structure and carrier transport direction are as follows: Figure 2 As shown, under light excitation, photogenerated electron-hole pairs are generated in MQWs. Driven by the built-in electric field of the p-n junction, electrons migrate to the n-side and reach the reaction interface to participate in the reduction reaction, while holes migrate to the p-side and further tunnel through the n+-InGaN layer to reach the Co3O4 surface to participate in the oxidation reaction.

[0038] Comparative Example 1 An n-GaN layer, an InGaN / GaN multiple quantum well (MQWs) active layer, and a p-GaN layer were sequentially epitaxially grown on a sapphire substrate using metal-organic chemical vapor deposition (MOCVD). Selective etching was performed on portions of the epitaxial layers until the underlying n-GaN surface was exposed. A Ti / Al / Ni / Au multilayer metal contact layer was deposited on the exposed n-GaN surface using electron beam evaporation. After deposition, the device was placed in a nitrogen atmosphere and subjected to rapid thermal annealing (RTA) at 850°C for 30 s to form ohmic contacts, resulting in a conventional GaN PCD with the following structure: Figure 3 As shown.

[0039] Comparative Example 2 On a sapphire substrate, an n-GaN layer, an InGaN / GaN multiple quantum well (MQWs) active layer, a p-GaN layer, and a heavily doped n-GaN layer were sequentially epitaxially grown using metal-organic chemical vapor deposition (MOCVD).+ The InGaN layer is selectively etched until the underlying n-GaN surface is exposed. A multilayer Ti / Al / Ni / Au metal contact layer is deposited on the exposed n-GaN surface using electron beam evaporation. After deposition, the device is placed in a nitrogen atmosphere and subjected to rapid thermal annealing (RTA) at 850°C for 30 s to form ohmic contacts, resulting in a TJ-GaN PCD with the following structure: Figure 4 As shown.

[0040] Comparative Example 3 An n-GaN layer, an InGaN / GaN multiple quantum well (MQWs) active layer, and a p-GaN layer were sequentially epitaxially grown on a sapphire substrate using metal-organic chemical vapor deposition (MOCVD). A Ti / Al / Ni / Au multilayer metal contact layer was deposited on the exposed n-GaN surface using electron beam evaporation. After deposition, the device was placed in a nitrogen atmosphere and subjected to rapid thermal annealing (RTA) at 850°C for 30 s to form ohmic contacts. A p-Co3O4 layer was selectively loaded onto the surface of the top p-GaN layer using photodeposition or electrochemical deposition to obtain a Co3O4 / GaN PCD, the structure of which is shown below. Figure 5 As shown.

[0041] Experimental Test The photovoltage of the devices prepared in Example 1 and Comparative Examples 1-3 was detected. The detection process specifically included: Test results as follows Figure 1 As shown, specifically: Comparative Example 1 (GaN PCD, Figure 3 The absolute value of the photovoltage of the first example is 0.8271V; Comparative Example 2 (TJ-GaN PCD, Figure 4 After introducing the tunneling layer, the photovoltage increased to 0.9320V; Comparative Example 3 (Co3O4 / GaN PCD, Figure 5 Without a tunnel layer, surface modification alone resulted in a photovoltage of 0.7987V, showing no significant improvement. Example 1 (Co3O4 / TJ-GaN PCD, Figure 6 Through the in vivo pn junction and the surface p-Co3O4 / n + The synergistic effect of the InGaN heterojunction significantly boosted the absolute value of the photovoltage to 1.6021 V. This demonstrates that introducing a tunnel layer alone only provides limited photovoltage gain, and simple surface Co3O4 modification is insufficient to effectively enhance the device's photo-driving force. Only when the bulk p-n junction and the surface heterojunction synergistically construct a dual-junction structure can the built-in electric field be effectively superimposed, significantly enhancing the device's photogenerated carrier separation capability and interfacial reaction driving force, thereby providing a more sufficient photo-driving force for subsequent unbiased photocatalytic reactions.

[0042] The band structure and carrier transport process of the device (Co3O4 / TJ-GaN PCD) prepared in Example 1 are as follows: Figure 2 As shown, it can be seen that the photogenerated carriers generated by MQWs separate under the action of the bulk junction, and the holes tunnel through n through the junction. + The InGaN layer then migrates to the surface to participate in the oxidation reaction under the strong driving force of the surface heterojunction. This double-junction cascade stacking mechanism is the core reason for achieving an ultra-high photovoltage of 1.6 V.

[0043] Furthermore, the device in Example 1 ensures efficient charge removal by depositing a Ti / Al / Ni / Au layer on the n-GaN exposed surface and annealing it at 850°C.

[0044] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A GaN-based multiple heterojunction photoelectrode, characterized in that, From bottom to top, it includes: a substrate, an n-type GaN layer, an InGaN / GaN multiple quantum well layer, a p-type GaN layer, an n⁺-type InGaN layer, and a p-type Co3O4 layer; The p-type GaN layer and the n-type GaN layer form a bulk junction, and the p-type Co3O4 layer and the n⁺-type InGaN layer are in contact to form a surface heterojunction; the electric field generated by the surface heterojunction is in the same direction as the electric field generated by the bulk junction.

2. The GaN-based multiple heterojunction photoelectrode according to claim 1, characterized in that, The upper surface of the n-type GaN layer includes an uncovered exposed area, on which an ohmic electrode structure is bonded.

3. The GaN-based multiple heterojunction photoelectrode according to claim 2, characterized in that, The ohmic electrode structure is a Ti / Al / Ni / Au multilayer metal stacked sequentially from bottom to top, with thicknesses of 30 / 120 / 50 / 100nm respectively, wherein the Ti layer contacts the exposed surface of the n-type GaN layer.

4. The GaN-based multiple heterojunction photoelectrode according to claim 1, characterized in that, The n + The doping concentration of the InGaN layer is .

5. A GaN-based multiple heterojunction photoelectrode according to claim 1, characterized in that, The thickness of the p-type Co3O4 layer is 10-30 nm; n + The thickness of the p-type GaN layer is 2-5 nm; the thickness of the p-type GaN layer is 100-400 nm; and the thickness of the n-type GaN layer is 0.5-2 µm.

6. The GaN-based multiple heterojunction photoelectrode according to claim 1, characterized in that, The InGaN / GaN multi-quantum well layer has 8-20 cycles, with the InGaN well layer thickness being 3nm and the GaN barrier layer thickness being 15nm in each cycle.

7. The method for fabricating a GaN-based multiple heterojunction photoelectrode according to claims 1-6, characterized in that, Includes the following steps: The n-type GaN layer, the InGaN / GaN multiple quantum well layer, the p-type GaN layer, and the n-type GaN layer are sequentially grown on the substrate. + To obtain an epitaxial wafer, a type InGaN layer is formed. Partial removal of n on the epitaxial wafer using an etching process + n-type GaN layers, p-type GaN layers, and InGaN / GaN multiple quantum well layers are constructed until a portion of the n-type GaN layer surface is exposed, and an ohmic electrode is fabricated on the exposed n-type GaN layer surface. The n in the unetched region + A p-type Co3O4 layer is deposited on the surface of the InGaN layer to form the surface heterojunction.

8. The method for fabricating a GaN-based multiple heterojunction photoelectrode according to claim 7, characterized in that, The process of preparing the ohmic electrode includes: depositing a metal layer constituting the ohmic electrode on the surface of an exposed n-type GaN layer, placing the epitaxial wafer in a nitrogen atmosphere, and annealing it at a temperature of 400-900°C for 30-120 seconds.

9. The method for fabricating a GaN-based multiple heterojunction photoelectrode according to claim 7, characterized in that, The process of depositing p-type Co3O4 layers includes: during the deposition process, using For cobalt source, A precursor solution was prepared for the electron acceptor / co-oxidant, and the epitaxial wafer was placed in the precursor solution for photodeposition under ultraviolet light irradiation.

10. The application of the GaN-based multiple heterojunction photoelectrode according to any one of claims 1-6 in water splitting for hydrogen production.

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