Solar blind ultraviolet photoelectric detector based on diamond / Ga2O3 heterojunction and preparation method thereof

Abstract

The invention discloses a preparation method of a solar-blind ultraviolet photoelectric detector based on a diamond / Ga2O3 heterojunction. The preparation method comprises the following steps: 1) performing hydrogen plasma etching on single crystal diamond to form a surface hydrogen terminal; (2) depositing a Ga2O3 film on the monocrystal diamond substrate by adopting a magnetron sputtering method; (3) carrying out post-annealing treatment on the deposited Ga2O3 thin film in an inert atmosphere; and 4) preparing a metal interdigital electrode on the surface of the annealed Ga2O3 film as a top electrode, and preparing a metal electrode on the other surface of the monocrystal diamond as a bottom electrode to obtain the solar blind ultraviolet photoelectric detector. A magnetron sputtering method is adopted, a high-quality amorphous Ga2O3 thin film is grown on the surface of the monocrystal diamond, and a post-annealing process is combined, so that the Ga2O3 thin film and a monocrystal diamond substrate form an II-type heterojunction; meanwhile, the monocrystal diamond gives full play to the advantage of ultrahigh thermal conductivity, and the heat dissipation performance of the device is remarkably improved; and an ideal solution is provided for the next generation of high-performance and low-power-consumption solar blind ultraviolet detection.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device technology, specifically relating to a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction and its fabrication method. Background Technology

[0002] Solar-blind ultraviolet photodetectors have attracted much attention due to their significant application value in military and civilian fields such as fire early warning, radiation monitoring, biochemical detection, and military early warning. These detectors need to have high responsivity in the deep ultraviolet band (200-280 nm) while being unresponsive to visible light to achieve accurate target detection. Heterojunctions based on wide-bandgap semiconductor materials are an important approach to achieving high-performance solar-blind ultraviolet detection. Diamond and Ga2O3, due to their excellent photoelectric properties, are excellent choices for high-performance heterojunction materials and are ideal materials for fabricating solar-blind detection devices.

[0003] Diamond has a bandgap of approximately 5.47 eV and a cutoff wavelength of 225 nm, while also possessing high carrier mobility and excellent thermal conductivity. Ga₂O₃, with a bandgap of approximately 4.79 eV and a cutoff wavelength of approximately 280 nm, exhibits significant advantages in solar-blind ultraviolet detection. However, Ga₂O₃ has extremely low thermal conductivity, only about 10 W / mK, making it prone to heat accumulation, leading to increased dark current and device failure. These key scientific issues severely restrict the practical application of solar-blind ultraviolet photodetectors. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, which features efficient photogenerated carrier separation and transport capabilities, intrinsic solar-blind ultraviolet selective detection, excellent thermal management capabilities, and good process compatibility.

[0005] The present invention also provides a method for fabricating the solar-blind ultraviolet photodetector based on the diamond / Ga2O3 heterojunction.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, comprising the following steps: 1) Hydrogen plasma etching is used to form surface hydrogen terminals on single-crystal diamond; 2) A Ga2O3 thin film was deposited on a single-crystal diamond substrate using magnetron sputtering; 3) The deposited Ga2O3 film was post-annealed in an inert atmosphere; 4) Prepare a metal interdigitated electrode as the top electrode on the surface of the annealed Ga2O3 thin film, and prepare a metal electrode as the bottom electrode on the other side of the single crystal diamond to obtain a solar-blind ultraviolet photodetector.

[0007] In some specific embodiments, the single-crystal diamond in step 1) is further subjected to acid washing with aqua regia, followed by ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water in sequence.

[0008] In some specific embodiments, the single-crystal diamond is (001) oriented.

[0009] In some specific implementations, the hydrogen plasma etching of single-crystal diamond described in step 1) specifically involves using a microwave plasma chemical vapor deposition device with a power of 3-6 kW, a temperature of 600-1000℃, and a holding time of 10-20 min.

[0010] In some specific embodiments, the background vacuum of magnetron sputtering in step 2) is ≤1×10⁻⁶. -4 Pa, working gas pressure is 0.4-0.6 Pa, sputtering power is 140-160 W.

[0011] In some specific embodiments, the temperature of the post-annealing treatment in step 3) is 250-450°C, the holding time is 0.5-1.5 hours, and the annealing atmosphere is argon.

[0012] In some specific embodiments, the Ga2O3 thin film is an amorphous thin film with a thickness of 300-600 nm.

[0013] In some specific implementations, step 4) uses thermal evaporation coating technology and interdigitated electrode mask to prepare the metal interdigitated electrode as the top electrode, and prepares the metal electrode as the bottom electrode on the other side of the single crystal diamond.

[0014] As part of the same inventive concept, this invention provides a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction. The solar-blind ultraviolet photodetector includes a metal bottom electrode, a single-crystal diamond, an amorphous Ga2O3 thin film, and a metal interdigitated electrode arranged sequentially. The single-crystal diamond and Ga2O3 form a type II heterojunction.

[0015] As part of the same inventive concept, this invention also provides applications of the aforementioned solar-blind ultraviolet photodetector based on diamond / Ga2O3 heterojunction in civilian and military fields.

[0016] Compared with the prior art, the present invention has at least the following advantages: 1) This invention forms a type II heterojunction between hydrogen-terminated single-crystal diamond and Ga2O3, and combines it with an interdigitated electrode design to induce a strong built-in electric field, promoting rapid separation and transport of photogenerated carriers. This achieves high responsivity, high detectivity, and fast response speed, resulting in excellent overall photoelectric detection performance. In this invention, both diamond (~5.47 eV) and Ga2O3 (~4.9 eV) are ultra-wide bandgap materials. Their heterojunction itself has a natural selectivity for solar-blind ultraviolet light (200-280 nm) while being insensitive to visible light, thus avoiding the efficiency loss caused by the reliance on filters in traditional detection devices from the material's inherent nature. 2) This invention uses single-crystal diamond as the substrate and bottom electrode channel, giving full play to its ultra-high thermal conductivity (>2000W / m·K), greatly overcoming the bottleneck of poor heat dissipation of Ga2O3 material. The interdigitated electrode structure effectively increases the photosensitive area and improves the power tolerance and high temperature stability of the device. 3) The preparation process of this invention is compatible with mainstream semiconductor processes, has high repeatability, and has the potential for large-scale production. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 This is a schematic diagram of the structure of the solar-blind ultraviolet detector provided by the present invention; Figure 2 This is a process flow diagram of the fabrication method of the solar-blind ultraviolet photodetector based on diamond / Ga2O3 heterojunction provided by the present invention. Figure 3 These are scanning electron microscope images of the Ga2O3 thin films after post-annealing treatment in Embodiments 1 and 2 of the present invention: where (a) is annealed at 300°C and (b) is annealed at 400°C; Figure 4 These are atomic force microscopy images of the roughness of Ga2O3 films after post-annealing treatment in Embodiments 1 and 2 of the present invention: (a) annealed at 300℃, (b) annealed at 400℃; Figure 5 The X-ray photoelectron spectra of the Ga2O3 thin films after post-annealing treatment in Embodiments 1 and 2 of the present invention are as follows: (a) annealed at 300℃, (b) annealed at 400℃. Figure 6 The voltage-current diagrams of the solar-blind ultraviolet photodetectors prepared in Examples 1 and 2 of this invention are as follows: 220nm ultraviolet light (a) annealed at 300℃, (b) annealed at 400℃; 254nm ultraviolet light (c) annealed at 300℃, (d) annealed at 400℃. Figure 7This is a time-current graph of the solar-blind ultraviolet photodetector prepared in Embodiment 1 of the present invention at a working voltage of 0V; Figure 8 This is the voltage-current diagram of the solar-blind ultraviolet photodetector prepared in Comparative Example 1 of this invention; Figure 9 This is the voltage-current diagram of the solar-blind ultraviolet photodetector prepared in Comparative Example 2 of this invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0020] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0021] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0022] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0023] This invention provides a method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, the process flow of which is as follows: Figure 2 As shown, the specific steps include the following: 1) Substrate pretreatment: A (100) oriented single crystal diamond substrate was selected. It was first acid-washed with aqua regia, and then ultrasonically cleaned with acetone, isopropanol and deionized water in sequence, and then dried under high-purity nitrogen. 2) Hydrogen plasma etching: Single-crystal diamond is etched in a hydrogen atmosphere using a microwave plasma chemical vapor deposition device to obtain hydrogen-terminated single-crystal diamond. 3) Ga2O3 thin film deposition: Ga2O3 thin film was deposited on a single crystal diamond substrate at room temperature in a high vacuum environment using an RF magnetron sputtering system. 4) Post-annealing of Ga2O3 thin films: The deposited samples are annealed in an argon atmosphere to improve the crystallinity of the thin films; 5) Electrode preparation: Using thermal evaporation coating technology, gold electrodes are deposited on the surface of Ga2O3 as top electrodes through interdigitated electrode mask; gold is deposited on the other side of single crystal diamond as bottom electrodes.

[0024] The thermal evaporation coating technology and the metal mask process in the following embodiments are the same, and the specific method steps can be the conventional method steps in the art. Example 1 This embodiment provides a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction and its fabrication method, including the following steps: 1) Substrate preparation: A (100) oriented single crystal diamond substrate (7 mm × 7 mm) was used. First, it was acid-washed with aqua regia until no bubbles were generated on the surface of the single crystal diamond. Then, it was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 min each, and then dried with high-purity nitrogen. 2) Hydrogen plasma etching: The pretreated single-crystal diamond was placed in a microwave plasma chemical vapor deposition system, and the base vacuum was evacuated to 0.5 Pa. Hydrogen gas flow rate was 400 sccm, and then the microwave power was increased at a rate of 100 W / min, while the cavity gas pressure was increased at a rate of 0.35 KPa / min until the target power of 5 kW and the target gas pressure of 17.5 KPa were reached. Etching was performed under these power and pressure conditions for 15 min, during which the substrate temperature was stabilized at 800℃. After etching, the microwave power was decreased at a rate of 100 W / min, while the cavity gas pressure was decreased at a rate of 0.35 KPa / min until the plasma was extinguished. The sample was then cooled to below 300℃ in a hydrogen atmosphere to obtain hydrogen-terminated single-crystal diamond. 3) Thin film deposition: The hydrogen-terminated single-crystal diamond substrate is placed in an RF magnetron sputtering system, wherein the base vacuum of the magnetron system is evacuated to 1×10⁻⁶. -5 Pa, high-purity argon gas was introduced, and the working pressure was maintained at 0.4 Pa; the radio frequency power was set to 150 W, and sputtering was performed at room temperature for 45 min to obtain a Ga2O3 film with a thickness of 600 nm; 4) Post-annealing: Place the sample with the deposited Ga2O3 film into a tube furnace, and start annealing with an argon flow rate of 100 sccm. At the same time, raise the temperature to 300℃ at a rate of 2℃ / min and hold for 1 h. 5) Electrode preparation: Thermal evaporation coating technology was used, and a 50 nm thick interdigitated Au electrode was deposited on the surface of the Ga2O3 thin film as the top electrode through a metal mask. Then, a 50 nm Au electrode was deposited on the other side of the single crystal diamond as the bottom electrode to obtain a solar-blind ultraviolet photodetector.

[0025] Example 2 This embodiment provides a method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, comprising the following steps: 1) Substrate preparation: A (100) oriented single crystal diamond substrate (7 mm × 7 mm) was used. First, it was acid-washed with aqua regia until no bubbles were generated on the surface of the single crystal diamond. Then, it was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 min each, and then dried with high-purity nitrogen. 2) Hydrogen plasma etching: The pretreated single-crystal diamond was placed in a microwave plasma chemical vapor deposition system, and the base vacuum was evacuated to 0.5 Pa. Hydrogen gas flow rate was 400 sccm, and then the microwave power was increased at a rate of 100 W / min, while the cavity gas pressure was increased at a rate of 0.35 KPa / min until the target power of 5 kW and the target gas pressure of 17.5 KPa were reached. Etching was performed under these power and pressure conditions for 15 min, during which the substrate temperature was stabilized at 800℃. After etching, the microwave power was decreased at a rate of 100 W / min, while the cavity gas pressure was decreased at a rate of 0.35 KPa / min until the plasma was extinguished. The sample was then cooled to below 300℃ in a hydrogen atmosphere to obtain hydrogen-terminated single-crystal diamond. 3) Thin film deposition: The hydrogen-terminated single-crystal diamond substrate is placed in an RF magnetron sputtering system, wherein the base vacuum of the magnetron system is evacuated to 1×10⁻⁶. -5 High-purity argon gas was introduced at 0.5 Pa, and the working pressure was maintained at 0.5 Pa. The radio frequency power was set to 100 W, and sputtering was performed at room temperature for 45 min to obtain a Ga2O3 film with a thickness of 300 nm. 4) Post-annealing: The sample after the Ga2O3 film has been deposited is placed in a tube furnace, and the argon flow rate is 100 sccm to start annealing. At the same time, the temperature is increased to 400℃ at a rate of 2℃ / min and held for 1 h. 5) Electrode fabrication: A 50 nm thick interdigitated Au electrode is deposited on the surface of a Ga2O3 thin film using thermal evaporation coating technology and a metal mask as the top electrode. Then, a 50 nm thick Au electrode is deposited on the other side of the single crystal diamond as the bottom electrode to obtain a solar-blind ultraviolet photodetector.

[0026] A schematic diagram of the structure of the solar-blind ultraviolet photodetector device prepared in this application is shown below. Figure 1 As shown in the figure, from bottom to top, the layers are a metal bottom electrode layer, a single-crystal diamond layer, a Ga2O3 thin film layer, and a metal interdigitated electrode.

[0027] Comparative Example 1 This comparative example provides a method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, which is basically the same as that in Example 2, except that the post-annealing treatment of the deposited Ga2O3 film is not performed. The specific steps include the following: 1) Substrate preparation: A (100) oriented single crystal diamond substrate (7 mm × 7 mm) was used. First, it was acid-washed with aqua regia until no bubbles were generated on the surface of the single crystal diamond. Then, it was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 min each, and then dried with high-purity nitrogen. 2) Hydrogen plasma etching: The pretreated single-crystal diamond was placed in a microwave plasma chemical vapor deposition system, and the base vacuum was evacuated to 0.5 Pa. Hydrogen gas flow rate was 400 sccm, and then the microwave power was increased at a rate of 100 W / min, while the cavity gas pressure was increased at a rate of 0.35 KPa / min until the target power of 5 kW and the target gas pressure of 17.5 KPa were reached. Etching was performed under these power and pressure conditions for 15 min, during which the substrate temperature was stabilized at 800℃. After etching, the microwave power was decreased at a rate of 100 W / min, while the cavity gas pressure was decreased at a rate of 0.35 KPa / min until the plasma was extinguished. The sample was then cooled to below 300℃ in a hydrogen atmosphere to obtain hydrogen-terminated single-crystal diamond. 3) Thin film deposition: The hydrogen-terminated single-crystal diamond substrate is placed in an RF magnetron sputtering system, wherein the base vacuum of the magnetron system is evacuated to 1×10⁻⁶. -5 High-purity argon gas was introduced at 0.5 Pa, and the working pressure was maintained at 0.5 Pa. The radio frequency power was set to 100 W, and sputtering was performed at room temperature for 45 min to obtain a Ga2O3 film with a thickness of 300 nm. 4) Electrode preparation: A 50 nm thick interdigitated Au electrode is deposited on the surface of the deposited Ga2O3 film using thermal evaporation coating technology and a metal mask as the top electrode. Then, a 50 nm thick Au electrode is deposited on the other side of the single crystal diamond as the bottom electrode to obtain a solar-blind ultraviolet photodetector.

[0028] Comparative Example 2 This comparative example provides a method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, which is basically the same as that in Example 2, except that the process parameters for post-annealing of the deposited Ga2O3 thin film are different. Specifically, it includes the following steps: 1) Substrate preparation: A (100) oriented single crystal diamond substrate (7 mm × 7 mm) was used. First, it was acid-washed with aqua regia until no bubbles were generated on the surface of the single crystal diamond. Then, it was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 min each, and then dried with high-purity nitrogen. 2) Hydrogen plasma etching: The pretreated single-crystal diamond was placed in a microwave plasma chemical vapor deposition system, and the base vacuum was evacuated to 0.5 Pa. Hydrogen gas flow rate was 400 sccm, and then the microwave power was increased at a rate of 100 W / min, while the cavity gas pressure was increased at a rate of 0.35 KPa / min until the target power of 5 kW and the target gas pressure of 17.5 KPa were reached. Etching was performed under these power and pressure conditions for 15 min, during which the substrate temperature was stabilized at 800℃. After etching, the microwave power was decreased at a rate of 100 W / min, while the cavity gas pressure was decreased at a rate of 0.35 KPa / min until the plasma was extinguished. The sample was then cooled to below 300℃ in a hydrogen atmosphere to obtain hydrogen-terminated single-crystal diamond. 3) Thin film deposition: The hydrogen-terminated single-crystal diamond substrate is placed in an RF magnetron sputtering system, wherein the base vacuum of the magnetron system is evacuated to 1×10⁻⁶. -5 High-purity argon gas was introduced at 0.5 Pa, and the working pressure was maintained at 0.5 Pa. The radio frequency power was set to 100 W, and sputtering was performed at room temperature for 45 min to obtain a Ga2O3 film with a thickness of 300 nm. 4) Post-annealing: Place the sample with the deposited Ga2O3 film into a tube furnace, and start annealing with an argon flow rate of 100 sccm. At the same time, raise the temperature to 500℃ at a rate of 2℃ / min and hold for 1 h. 5) Electrode fabrication: A 50 nm thick interdigitated Au electrode is deposited on the surface of a Ga2O3 thin film using thermal evaporation coating technology and a metal mask as the top electrode. Then, a 50 nm thick Au electrode is deposited on the other side of the single crystal diamond as the bottom electrode to obtain a solar-blind ultraviolet photodetector.

[0029] Product characterization and performance testing This application uses Examples 1 and 2 as examples to characterize and test the solar-blind ultraviolet photodetector devices prepared in Examples 1 and 2, and to test the photoelectric performance of Examples 1, 2, Comparative Example 1, and Comparative Example 2. Specifically: 1) Scanning electron microscopy test This application uses scanning electron microscopy to characterize the Ga2O3 films after post-annealing treatment in Examples 1 and 2, and the results are as follows: Figure 3As shown, Example 1 was annealed at 300℃, resulting in a continuous and dense surface without cracks, composed of fine and uniform nanoparticles, and exhibiting excellent surface smoothness. Example 2 was annealed at 400℃, resulting in obvious microcracks on the surface, forming significant stress release channels, reducing the mechanical strength of the thin film, and becoming carrier recombination centers and leakage channels. The higher annealing temperature exacerbated the mismatch in thermal expansion coefficients between the thin film and the diamond substrate, generating greater thermal stress and microcracks. These defects became carrier recombination centers, increasing leakage current and thus degrading the photoelectric response performance of the device.

[0030] 2) Atomic force microscopy test This application uses atomic force microscopy to characterize the Ga2O3 films after post-annealing treatment in Examples 1 and 2, and the results are as follows: Figure 4 As shown, Example 1 was annealed at 300℃, and the surface was relatively smooth and uniform, exhibiting a typical nanocrystalline thin film morphology. From the three-dimensional image, the undulations were gentle, and it was composed of fine particles. The maximum height difference was 5.5 nm, indicating that the Ga2O3 film had extremely low surface roughness, and the film layer was dense and uniform, with a high degree of interface matching with the diamond substrate. Example 2 was annealed at 400℃, and the surface showed island-like structures and large undulations. The three-dimensional morphology showed significant peak and valley structures, with a maximum height difference of 12.7 nm, and the film roughness increased significantly.

[0031] 3) X-ray photoelectron spectroscopy test This application characterizes the annealed Ga2O3 films in Examples 1 and 2 using X-ray photoelectron spectroscopy, and the results are as follows: Figure 5 As shown, the XPS full spectrum comparison of Ga2O3 films annealed at 300℃ and 400℃ on single-crystal diamond substrates is presented.

[0032] As shown in the figure, the XPS spectra of both samples clearly exhibit characteristic peaks such as Ga 2p (approximately 1118 eV), Ga 3d (approximately 20 eV), and O 1s (approximately 531 eV), confirming that the main component of the film is Ga2O3. Simultaneously, a distinct C1s peak (approximately 285 eV) is observed in the spectrum, originating from the single-crystal diamond substrate. Furthermore, the C1s signal intensity of the 400℃ annealed sample is significantly higher than that of the 300℃ sample, indicating that the increased surface roughness or decreased local coverage of the film after high-temperature annealing leads to the detection of more substrate signals. In addition, by comparing the peak intensity ratios of Ga 2p and O 1s in the two samples, it was found that the core stoichiometry (Ga:O ≈ 2:3) did not change significantly, indicating that the annealing temperature mainly affects the physical structure of the film rather than its overall composition.

[0033] 4) Photoelectric performance testing This application uses a Keithley 2450 source table to test the solar-blind ultraviolet photodetectors prepared in Examples 1 and 2, as well as Comparative Examples 1 (unannealed) and 2 (annealed at 500°C). The results are as follows: Figure 6 As shown in (a)-(d), LEDs with different wavelengths (220 nm and 254 nm) were used as light sources in the test, and the optical power density of each light source at the sample position was precisely calibrated using an optical power meter to comprehensively study the influence of different annealing processes on the photoelectric response characteristics of the device.

[0034] (a) Comparison of Example 1 (annealed at 300 °C) and Example 2 (annealed at 400 °C) The test results are in high agreement with the morphological characterization by scanning electron microscopy and atomic force microscopy. Specifically, under 220 nm illumination, the photocurrent of the annealed sample in Example 1 (300 °C) increased by approximately three orders of magnitude compared to the dark current, exhibiting a significant photoelectric response. Figure 6 a); In contrast, the increase in photocurrent of the sample in Example 2 was relatively small ( Figure 6 b); Under 254 nm wavelength illumination, both samples showed a significant increase in photocurrent, but the photocurrent to dark current ratio of the sample in Example 1 was still higher than that of the sample in Example 2 ( Figure 6 c and 6d).

[0035] The aforementioned differences in photoelectric performance mainly stem from the influence of different annealing processes on the interface quality of the heterojunction. The sample from Example 1 exhibits a continuous and dense film with a smooth interface, which is beneficial for the efficient separation and transport of photogenerated carriers. In contrast, the sample from Example 2, due to its higher annealing temperature, introduces interface defects such as microcracks and increased surface roughness. These defects may become recombination centers for carriers, thereby increasing leakage current and degrading photoelectric response performance. Test results show that the 300℃ annealing process helps to obtain better interface characteristics, thus exhibiting higher photoelectric responsivity and detection sensitivity in the solar-blind ultraviolet band.

[0036] To further verify the driving effect of the built-in electric field of the heterojunction on the separation of photogenerated carriers, the time-current (IT) characteristics of the sample of Example 1 were tested under 0V bias. The test was carried out under 220 nm illumination using a periodic optical switching (illumination-dark state alternation) mode.

[0037] The results are as follows Figure 7As shown in the figure, even under 0V bias (i.e., no external electric field), the sample still generates a significant photocurrent response when illumination is turned on, and the current quickly returns to the dark current level after illumination is turned off. This phenomenon indicates that an effective built-in electric field exists at the diamond / Ga2O3 interface, which can drive the spatial separation of photogenerated electron-hole pairs, thereby generating photocurrent under no external bias. This characteristic is typical of semiconductor heterojunctions, further confirming the successful formation of a heterojunction structure with a built-in electric field in the sample of Example 1.

[0038] It should be noted that this test result is consistent with the aforementioned IV rectification characteristic test ( Figure 6 These findings corroborate each other, jointly confirming the formation of the heterojunction. The photocurrent response under 0V bias directly proves the existence of the built-in electric field, while the IV rectification characteristics verify the formation of the junction region from the perspective of electrical transport.

[0039] (b) Test results of Comparative Example 1 (unannealed) To verify the necessity of post-annealing, this application also tested the photoelectric properties of Comparative Example 1 (electrode was directly prepared after Ga2O3 film deposition without annealing).

[0040] Test results are as follows Figure 8 As shown in the figure, under illumination at wavelengths of 220 nm and 254 nm, the solar-blind ultraviolet photodetector prepared in Comparative Example 1 exhibits only a weak light response signal, almost indistinguishable from the dark current. This result indicates that the unannealed device, due to poor crystallinity and excessively high interface state density, failed to form an effective type II heterojunction built-in electric field with the hydrogen-terminated single-crystal diamond, resulting in ineffective separation and transport of photogenerated carriers. This result conversely proves that post-annealing is an indispensable key step in activating and optimizing the photoelectric performance of diamond / Ga2O3 heterojunctions.

[0041] (c) Test results of Comparative Example 2 (annealed at 500 °C) To investigate the upper limit of the temperature, this application also tested the photoelectric properties of Comparative Example 2 (annealed at 500°C).

[0042] Test results are as follows Figure 9As shown in the figure, the dark current of the solar-blind ultraviolet photodetector in Comparative Example 2 is significantly increased compared to Examples 1 and 2. Furthermore, under 220 nm and 254 nm illumination, the photocurrent is almost completely submerged in the dark current background, making effective photoelectric response unobservable. Combined with the potentially more severe thin-film cracking and interface damage observed in the Comparative Example 2 sample, this data indicates that the excessively high annealing temperature (500°C) not only failed to promote heterojunction formation but also completely destroyed the junction's characteristics by introducing numerous defects, leading to device malfunction. This result clearly demonstrates that there is an optimal window for annealing temperature; high-temperature processing exceeding this window will have a fatal negative impact on device performance.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction, characterized in that, Includes the following steps: 1) Hydrogen plasma etching is used to form surface hydrogen terminals on single-crystal diamond; 2) A Ga2O3 thin film was deposited on a single-crystal diamond substrate using magnetron sputtering; 3) The deposited Ga2O3 film was post-annealed in an inert atmosphere; 4) Prepare a metal interdigitated electrode as the top electrode on the surface of the annealed Ga2O3 thin film, and prepare a metal electrode as the bottom electrode on the other side of the single crystal diamond to obtain a solar-blind ultraviolet photodetector.

2. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 1, characterized in that, It also includes acid washing of the single crystal diamond in step 1) with aqua regia, followed by ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water in sequence.

3. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 2, characterized in that, The single-crystal diamond is (001) oriented.

4. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 3, characterized in that, The hydrogen plasma etching of single-crystal diamond described in step 1) specifically involves using a microwave plasma chemical vapor deposition (PCCVD) device with a power of 3-6 kW, a temperature of 600-1000℃, and a holding time of 10-20 min.

5. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 4, characterized in that, In step 2), the background vacuum of magnetron sputtering in the magnetron sputtering method is ≤1×10⁻⁶. -4 Pa, working gas pressure is 0.4-0.6 Pa, sputtering power is 140-160 W.

6. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 5, characterized in that, The temperature of the post-annealing treatment in step 3) is 250-450℃, the holding time is 0.5-1.5 hours, and the annealing atmosphere is argon.

7. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 1, characterized in that, The Ga2O3 thin film is an amorphous thin film with a thickness of 300-600 nm.

8. The method for fabricating a solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction according to claim 7, characterized in that, In step 4), the metal interdigitated electrode is prepared as the top electrode using thermal evaporation coating technology and an interdigitated electrode mask, and the metal electrode is prepared as the bottom electrode on the other side of the single crystal diamond.

9. A solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction prepared by the preparation method according to claims 1-8, characterized in that, The solar-blind ultraviolet photodetector includes a metal bottom electrode, a single-crystal diamond, an amorphous Ga2O3 thin film, and a metal interdigitated electrode arranged sequentially; wherein the single-crystal diamond and Ga2O3 form a type II heterojunction.

10. An application of the solar-blind ultraviolet photodetector based on a diamond / Ga2O3 heterojunction as described in claim 9 in civilian and military fields.

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