A bimodal aluminum scandium nitride-based ultraviolet photodetector and a preparation method thereof

Abstract

This invention discloses a dual-mode aluminum scandium nitride-based ultraviolet photodetector and its fabrication method, belonging to the field of ultraviolet photodetection technology. It includes interdigitated electrode pairs and, from bottom to top, a substrate, an aluminum nitride buffer layer, an aluminum gallium nitride transition layer, and an aluminum scandium nitride ferroelectric functional layer. The interdigitated electrode pairs include a first set of electrodes and a second set of electrodes. The lower end of the first set of electrodes extends into the interior of the aluminum scandium nitride ferroelectric functional layer. The second set of electrodes is located on the aluminum scandium nitride ferroelectric functional layer. Electrode one of the first set of electrodes and electrode two of the second set of electrodes are interleaved and alternately arranged without contacting each other, forming an interdigitated structure. This invention achieves dual-mode operation in SAW and MSM modes, and exhibits high sensitivity and strong wireless sensing capabilities.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet photodetector technology, specifically relating to a dual-mode aluminum scandium nitride-based ultraviolet photodetector and its preparation method. Background Technology

[0002] Ultraviolet (UV) detection has important applications in fields such as flame early warning, UV communication, corona discharge monitoring, and missile guidance. Aluminum scandium nitride (AlScN), as a novel ferroelectric wide-bandgap semiconductor material, possesses advantages such as tunable bandgap, strong ferroelectric polarization, and high thermal stability, demonstrating significant potential in the field of UV detection.

[0003] Currently, some research progress has been made in ultraviolet photodetectors involving AlScN materials. Professor Yang Guofeng's team at Jiangnan University has further realized a bias-reconfigurable multifunctional ultraviolet photodetector based on AlScN / GaN heterojunction. Under low bias, it exhibits a high-speed, high-sensitivity ultraviolet detector (specific detectivity of 9.37×10¹² Jones, where Jones is the unit of specific detectivity). Under high bias, it exhibits a significant persistent photoconductivity effect.

[0004] However, existing AlScN-based ultraviolet detectors operate in a single mode, making it difficult to simultaneously achieve high-sensitivity, rapid detection and wireless passive sensing in the same structure. Furthermore, the lack of a design that integrates the SAW mode (Metal-Semiconductor-Metal) and the MSM mode (Surface Acoustic Wave) limits the complementary advantages of the two modes. Summary of the Invention

[0005] Purpose of the invention: To address the problem that AlScN-based ultraviolet detectors have a single operating mode and it is difficult to simultaneously achieve high-sensitivity, fast detection and wireless passive sensing in the same structure, this invention provides a dual-mode aluminum scandium nitride-based ultraviolet photodetector.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows: A dual-mode aluminum scandium nitride-based ultraviolet photodetector includes interdigitated electrode pairs and, from bottom to top, a substrate, an aluminum nitride buffer layer, an aluminum gallium nitride transition layer, and an aluminum scandium nitride ferroelectric functional layer. The interdigitated electrode pairs include a first set of electrodes and a second set of electrodes, wherein: The first set of electrodes is located on the aluminum scandium nitride ferroelectric functional layer, and the lower end of the first set of electrodes extends into the interior of the aluminum scandium nitride ferroelectric functional layer. The first set of electrodes is an aluminum gallium nitride electrode.

[0007] The second set of electrodes is located on the aluminum scandium nitride ferroelectric functional layer, and the second set of electrodes is in contact with the upper surface of the aluminum scandium nitride ferroelectric functional layer. At the same time, the second set of electrodes is an aluminum scandium nitride electrode.

[0008] Electrode one in the first group of electrodes and electrode two in the second group of electrodes are arranged alternately and without contact with each other, forming an interdigitated structure.

[0009] Preferably, in the metal-semiconductor-metal mode, the first set of electrodes in the interdigitated electrode pair is the anode, the second set of electrodes in the interdigitated electrode pair is the cathode, and the interdigitated electrode pair is used to collect photogenerated carriers.

[0010] In the surface acoustic wave (SAW) mode, the interdigital electrode pair acts as an interdigital transducer for exciting and receiving SAW waves.

[0011] Preferably, a reflective grating is provided on the upper surface of the aluminum scandium nitride ferroelectric functional layer. The reflective grating is located on both sides of the interdigital electrode pair. The period of the reflective grating corresponds to the period of the interdigital electrode pair. The width of the reflective grating is equal to the width of the interdigital fingers of the interdigital electrode pair. The spacing of the reflective grating is equal to the spacing between the interdigital fingers of the interdigital electrode pair.

[0012] Preferably, the interdigitated electrode pair has an interdigitated finger width of 5–10 μm, an interdigitated finger spacing of 5–10 μm, and a number of interdigitated finger pairs of 20–30.

[0013] Preferably, the thickness of the aluminum nitride buffer layer is 100–2000 nm.

[0014] Preferably, the aluminum gallium nitride transition layer is Al. 0.3 Ga 0.7 The N transition layer has a thickness of 50–1000 nm, where N is nitrogen, Ga is gallium, and Al is aluminum.

[0015] Preferably, the aluminum nitride scandium ferroelectric functional layer is Al. 0.35 Sc 0.65 The N-ferroelectric functional layer has a thickness of 50–100 nm, where N is nitrogen, Sc is scandium, and Al is aluminum.

[0016] Preferably, the substrate is a silicon wafer or a sapphire substrate.

[0017] Another object of the present invention is to provide a method for fabricating a dual-mode aluminum scandium nitride-based ultraviolet photodetector, comprising the following steps: Step 1: Clean the substrate.

[0018] Step 2: Deposit an aluminum nitride buffer layer on the substrate.

[0019] Step 3: Apply an aluminum gallium nitride transition layer onto the aluminum nitride buffer layer.

[0020] Step 4: Deposit an aluminum scandium ferroelectric functional layer on the aluminum gallium nitride transition layer.

[0021] Step 5: Perform the first photolithography on the aluminum scandium nitride ferroelectric functional layer to form the reflective gate and the first set of electrodes. The photolithography window extends into the interior of the aluminum scandium nitride ferroelectric functional layer. Deposit aluminum gallium nitride electrode material and form the first set of electrodes embedded in the aluminum scandium nitride ferroelectric functional layer through a lift-off process.

[0022] Step 6: Perform a second photolithography on the aluminum scandium nitride ferroelectric functional layer to form the second set of electrodes. The photolithography window is located only on the upper surface of the aluminum scandium nitride ferroelectric functional layer and is alternately arranged with the first set of electrodes to form interdigitated electrode pairs. Deposit aluminum scandium nitride electrode material and form the second set of electrodes on the upper surface of the aluminum scandium nitride ferroelectric functional layer without embedding them through a lift-off process.

[0023] Preferably, after the aluminum nitride scandium ferroelectric functional layer is deposited in step 4, an annealing process is performed.

[0024] Compared with the prior art, the present invention has the following advantages: 1. Dual-mode integration: MSM mode zero-bias low-power detection and SAW resonant mode high-sensitivity wireless sensing complement each other and can be dynamically switched according to application requirements.

[0025] 2. In MSM mode, it features extremely low dark current and ultra-high sensitivity.

[0026] 3. In SAW mode, firstly, it has a fast response characteristic, with a small range of response and recovery times for UV on / off and good reversibility. Secondly, it has high-sensitivity SAW detection and linearity.

[0027] 4. Reflection grating enhancement: Forms a SAW resonant cavity, improving the signal-to-noise ratio and frequency stability.

[0028] 5. Good repeatability and stability: After multiple UV switching cycles, the SAW frequency offset amplitude remains stable, and the device has excellent fatigue resistance and long-term working stability. Attached Figure Description

[0029] Figure 1 A cross-sectional view of a dual-mode aluminum nitride scandium-based ultraviolet photodetector. Figure 2 A top view of a dual-mode aluminum nitride scandium-based ultraviolet photodetector; Figure 3 This is a graph showing the IV characteristics under MSM mode; Figure 4 This is a time-frequency offset response curve in SAW mode; Figure 5 This is a graph showing the relationship between frequency offset and optical power density in SAW mode.

[0030] In this design, 1 is the substrate, 2 is the aluminum nitride buffer layer, 3 is the aluminum gallium nitride transition layer, 4 is the aluminum scandium ferroelectric functional layer, 5 is the reflective grating, 6 is the first set of electrodes, and 7 is the second set of electrodes. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0032] Example 1 To address the issue of AlScN-based ultraviolet detectors having a single operating mode, making it difficult to simultaneously achieve high-sensitivity, rapid detection and wireless passive sensing within the same structure, this embodiment provides a dual-mode aluminum scandium nitride-based ultraviolet photodetector, such as... Figure 1-2 As shown, the structure includes interdigitated electrode pairs and, from bottom to top, a substrate 1, an aluminum nitride buffer layer 2, an aluminum gallium nitride transition layer 3, and an aluminum scandium nitride ferroelectric functional layer 4. The aluminum nitride buffer layer 2 is an AlN buffer layer, the aluminum gallium nitride transition layer 3 is an AlGaN transition layer, and the aluminum scandium nitride ferroelectric functional layer 4 is an AlScN ferroelectric functional layer, where N is nitrogen, Ga is gallium, Al is aluminum, and Sc is scandium. In some examples, the substrate 1 is a silicon wafer or a sapphire substrate. In some examples, the thickness of the aluminum nitride buffer layer 2 is 100–2000 nm. In some examples, the aluminum gallium nitride transition layer 3 is Al... 0.3 Ga 0.7 The N-transition layer has an absorption cutoff wavelength in the solar blind band; where N is nitrogen, Ga is gallium, and Al is aluminum. In some examples, the thickness of the aluminum gallium nitride transition layer 3 is 50–1000 nm. In some examples, the aluminum scandium nitride ferroelectric functional layer 4 is Al. 0.35 Sc 0.65 The N-ferroelectric functional layer, wherein N is nitrogen, Sc is scandium, and Al is aluminum, has a thickness of 50–100 nm in some examples.

[0033] In some examples, the interdigitated electrode pair has an interdigital width of 5–10 μm, an interdigital spacing of 5–10 μm, and 20–30 interdigital pairs. The interdigitated electrode pair includes a first group of electrodes 6 and a second group of electrodes 7, wherein: The first set of electrodes 6 is located on the aluminum scandium nitride ferroelectric functional layer 4, and the lower end of the first set of electrodes 6 extends into the interior of the aluminum scandium nitride ferroelectric functional layer 4. At the same time, the first set of electrodes 6 is an aluminum gallium nitride electrode.

[0034] The second set of electrodes 7 is located on the aluminum scandium nitride ferroelectric functional layer 4, and the second set of electrodes 7 is in contact with the upper surface of the aluminum scandium nitride ferroelectric functional layer 4. At the same time, the second set of electrodes 7 is an aluminum scandium nitride electrode.

[0035] The first electrode in the first group of electrodes 6 and the second electrode in the second group of electrodes 7 are arranged alternately and without contact with each other, forming an interdigitated structure.

[0036] In the metal-semiconductor-metal mode, the first set of electrodes 6 in the interdigitated electrode pair is the anode, and the second set of electrodes 7 in the interdigitated electrode pair is the cathode. The interdigitated electrode pair is used to collect photogenerated carriers.

[0037] In the surface acoustic wave (SAW) mode, the interdigital electrode pair acts as an interdigital transducer for exciting and receiving SAW waves.

[0038] In some examples, a reflective grating 5 is provided on the upper surface of the aluminum scandium nitride ferroelectric functional layer 4. The reflective grating 5 is located on both sides of the interdigital electrode pair. The period of the reflective grating 5 corresponds to the period of the interdigital electrode pair. The width of the reflective grating 5 is equal to the width of the interdigital fingers of the interdigital electrode pair. The spacing of the reflective grating 5 is equal to the spacing between the interdigital fingers of the interdigital electrode pair.

[0039] The interdigitated electrode pair is composed of different materials forming a single unit. In MSM mode, the anode is AlGaN, embedded (partially buried) on the surface of the AlScN layer, while the cathode is AlScN, fabricated directly on the surface of the AlScN layer without embedding. They are arranged alternately and interleaved without contacting each other, forming an interdigitated structure for collecting photogenerated carriers. In SAW mode, the entire assembly acts as an interdigitated transducer for exciting and receiving surface acoustic waves. A reflective grating is fabricated on both sides of the interdigitated transducer, consisting of periodically arranged metal strips tens to hundreds of nanometers wide, to form the SAW resonant cavity and enhance signal strength and sensitivity.

[0040] The detector has two operating modes: MSM mode: Under zero bias, the built-in electric field of the AlScN / AlGaN heterojunction separates photogenerated carriers, enabling high-sensitivity and fast detection; SAW mode: Surface acoustic waves are excited by interdigital transducers, and the reflection grating forms a resonance enhancement. Ultraviolet radiation changes the properties of AlScN material, causing the resonant frequency to shift, thus achieving high-sensitivity wireless passive detection.

[0041] The invention allows for dynamic switching or collaborative operation between two modes.

[0042] This invention enables dual-mode operation of SAW and MSM modes, with high sensitivity and strong wireless sensing capability. It solves the problem that AlScN-based ultraviolet detectors have a single operating mode, making it difficult to achieve both high-sensitivity, fast detection and wireless passive sensing in the same structure.

[0043] Another embodiment of the present invention provides a method for fabricating a dual-mode aluminum scandium nitride-based ultraviolet photodetector, comprising the following steps: Step 1: Clean the substrate 1.

[0044] A sapphire substrate was selected as substrate 1 and ultrasonically cleaned with acetone, isopropanol and deionized water for 10 minutes each, and then dried with nitrogen.

[0045] Step 2: Deposit aluminum nitride buffer layer 2 on substrate 1.

[0046] An aluminum nitride buffer layer (AlN buffer layer) 2 with a thickness of 100-2000 nm was deposited on the substrate using magnetron sputtering. The deposition temperature was 350°C, the sputtering pressure was 0.5 Pa, the Ar / N2 flow ratio was 1:1, the RF power was 150 W, and Ar was argon gas and N2 was nitrogen gas.

[0047] Step 3: Apply an aluminum gallium nitride transition layer 3 on the aluminum nitride buffer layer 2.

[0048] An aluminum gallium nitride transition layer 3 with a thickness of 50-1000 nm was deposited on the aluminum nitride buffer layer 2. The deposition temperature was 350°C, and the deposition method was RF magnetron sputtering with an Al target. 0.3 Ga 0.7 N, sputtering pressure 0.5 Pa.

[0049] Step 4: Deposit an aluminum scandium ferroelectric functional layer 4 on the aluminum gallium nitride transition layer 3.

[0050] An aluminum scandium nitride ferroelectric functional layer 4 with a thickness of 50-100 nm was deposited on the aluminum gallium nitride transition layer 3. The deposition temperature was 380 °C, and Al was used. 0.35 Sc 0.65 The N alloy target was sputtered at a pressure of 0.6 Pa. In some examples, rapid thermal annealing was performed after deposition at 550 °C for 45 seconds to enhance ferroelectricity.

[0051] Step 5: Perform the first photolithography on the aluminum scandium nitride ferroelectric functional layer 4 to form the reflective gate 5 and the first set of electrodes 6. The photolithography window extends into the interior of the aluminum scandium nitride ferroelectric functional layer 4. Deposit aluminum gallium nitride electrode material and form the first set of electrodes 6 embedded in the aluminum scandium nitride ferroelectric functional layer 4 through a lift-off process.

[0052] Photolithography is used to spin-coat photoresist onto the surface of the aluminum scandium nitride ferroelectric functional layer 4. Exposure and development are then performed to form a reflective gate 5 (with a period corresponding to the interdigital cells, equal stripe width and spacing, and 20-100 stripes) and a first set of electrodes 6. The first set of electrodes 6 serves as the anode in MSM mode and as a set of electrodes for the interdigital transducer in SAW mode. The first set of electrodes 6 is designed to be embedded, with the photolithographic window extending into the interior of the aluminum scandium nitride ferroelectric functional layer 4. Then, AlGaN electrode material (Al composition 0.6%) is deposited using electron beam evaporation to a thickness of 80 nm. After lift-off, the reflective gate 5 and the first set of electrodes 6 embedded in the aluminum scandium nitride ferroelectric functional layer 4 are formed.

[0053] Step 6: Perform a second photolithography on the aluminum scandium nitride ferroelectric functional layer 4 to form the second set of electrodes 7. The photolithography window is located only on the upper surface of the aluminum scandium nitride ferroelectric functional layer 4, and is alternately arranged with the first set of electrodes 6 to form interdigitated electrode pairs. Deposit aluminum scandium nitride electrode material, and form the second set of electrodes 7 on the upper surface of the aluminum scandium nitride ferroelectric functional layer 4 without embedding them through a lift-off process.

[0054] A second photolithography step is performed to form the second set of electrodes 7. The second set of electrodes 7 serves as the cathode in MSM mode and as another set of electrodes for the interdigital transducer in SAW mode, together with the first set of electrodes 6 to form a complete interdigital transducer. The second set of electrodes 7 is designed as a surface type, with the photolithography window located only on the upper surface of the aluminum scandium nitride ferroelectric functional layer 4, and is arranged alternately with the first set of electrodes 6. AlScN electrode material (Al2ScN) is deposited using magnetron sputtering. 0.35 Sc 0.65 A second set of electrodes 7, 80 nm thick, is formed directly on the surface of the aluminum nitride scandium ferroelectric functional layer 4 without being embedded, using a lift-off process. The first set of electrodes 6 and the second set of electrodes 7 are arranged alternately and do not contact each other, together forming a complete interdigitated electrode pair (interdigital width 5-10 μm, interdigital spacing 5-10 μm, number of interdigital pairs 20-30). This interdigitated electrode pair is used to collect photogenerated carriers in MSM mode and as an interdigitated transducer to excite and receive surface acoustic waves in SAW mode.

[0055] The fabricated detector was tested at room temperature, with the center wavelength of the solar-blind ultraviolet light source at 280 nm.

[0056] (1) IV characteristics under MSM mode (e.g.) Figure 3 (As shown) The current-voltage characteristics of the device were measured under dark conditions and strong solar-blind ultraviolet illumination. The results show that the dark current at zero bias is as low as 3.11 × 10⁻⁶. -12 A indicates that the device has extremely low dark current; under strong light irradiation, the photocurrent in the negative bias region reaches 7.51 × 10⁻⁶. - 4 A, the positive bias region reaches 1.16 × 10-3 A, Light-to-dark current ratio exceeds 10 8 The magnitude indicates that the device has extremely high detection sensitivity. The IV curve shows good rectification characteristics, indicating that the built-in electric field of the AlScN / AlGaN heterojunction effectively separates photogenerated carriers.

[0057] In summary, the device exhibits extremely low dark current and ultra-high sensitivity in MSM mode.

[0058] (2) Time-frequency response under SAW mode (e.g.) Figure 4 (As shown) A radio frequency signal (center frequency 300 MHz) was applied to the interdigital transducer, and the ultraviolet light source (optical power density 0.5 mW / cm²) was alternately turned on and off. The change of SAW frequency shift over time was recorded. The results showed that when the ultraviolet light was on, the SAW frequency shifted rapidly with a response time of less than 5 seconds (typical value 1-3 seconds); the recovery time after turning off was also less than 5 seconds; after multiple cycles, the frequency shift amplitude remained stable, proving that the device has good reversibility and repeatability.

[0059] (3) Optical power density dependence under SAW mode operation (e.g.) Figure 5 (As shown) The steady-state frequency shift was recorded by varying the ultraviolet light power density (0.2, 0.4, 0.6, 0.8, 1.0 mW / cm²). The results showed that the frequency shift was linearly correlated with the light power density (R²>0.99), with a sensitivity of approximately 2.55 MHz / (mW / cm²), and a frequency shift reaching 2.551 MHz at 1.0 mW / cm². This linear relationship indicates that the device can be used for the quantitative detection of solar-blind ultraviolet light intensity.

[0060] In summary, the device exhibits the following advantages in SAW mode: First, it demonstrates rapid response characteristics, with response and recovery times for UV on / off ranging from less than 5 seconds (typically 1-3 seconds), and good reversibility. Second, it exhibits high sensitivity and linearity in SAW detection. Within an optical power density range of 0.22 ~ 0.88 mW / cm², the SAW frequency shift ranges from 1.22 ~ 2.50 MHz. Linear fitting yields a sensitivity of approximately 2.55 MHz / (mW / cm²), with a sensitivity range of 2.3 ~ 2.84 MHz / (mW / cm²). At an optical power density of 1.0 mW / cm², the frequency shift reaches 2.551 MHz, showing a good linear relationship between frequency shift and optical power density (R0). 2 >0.99), this linear relationship indicates that the device can be used for quantitative detection of solar-blind ultraviolet light intensity.

[0061] 3. Dual-modal operation mode MSM mode: When the bias voltage is set to 0 V, the device operates in this mode. The photocurrent response speed is extremely fast (<0.1 seconds), which is suitable for real-time high-sensitivity monitoring, such as flame warning and corona discharge detection.

[0062] SAW resonant mode: When the DC bias is disconnected and an RF signal is applied to the interdigital transducer, the device operates in this mode. Ultraviolet detection is achieved by wirelessly reading the frequency offset. The reflective grating enhances signal strength and signal-to-noise ratio, making it suitable for harsh environments or remote monitoring.

[0063] The two modes can be dynamically switched or enabled simultaneously according to actual needs.

[0064] The detector of this invention has a dark current as low as 3.11 × 10⁻⁶ in MSM mode. -12 A can meet the high signal-to-noise ratio detection requirements for flame early warning, corona discharge monitoring, etc.

[0065] In SAW mode, the response time is less than 5 seconds, the sensitivity reaches 2.84 MHz / (mW / cm²), and the frequency shift is linearly correlated with the optical power density (R). 2 >0.99), suitable for real-time wireless sensing scenarios such as ultraviolet communication and missile guidance; light-dark current ratio exceeds 10. 8 It has the capability to accurately capture weak solar-blind ultraviolet signals.

[0066] The detector of this invention features dual modes of MSM and SAW: in MSM mode, the zero-bias dark current is as low as 3.11 × 10⁻⁶. - ¹²A, photocurrent reaches 1.16 × 10⁻⁶ under strong light. - ³ A, light-dark current ratio exceeding 10 8 The response time in SAW mode is less than 5 seconds, the frequency shift is linearly related to the optical power density (R²>0.99), the sensitivity is approximately 2.55 MHz / (mW / cm²), and the frequency shift reaches 2.551 MHz at 1.0 mW / cm². This invention offers complementary advantages in both modes and is suitable for applications such as flame early warning, ultraviolet communication, corona discharge monitoring, and missile guidance.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dual-mode aluminum nitride scandium-based ultraviolet photodetector, characterized in that, The interdigitated electrode pairs include a substrate (1), an aluminum nitride buffer layer (2), an aluminum gallium nitride transition layer (3), and an aluminum scandium nitride ferroelectric functional layer (4) arranged sequentially from bottom to top; the interdigitated electrode pairs include a first group of electrodes (6) and a second group of electrodes (7), wherein: The first set of electrodes (6) is located on the aluminum scandium nitride ferroelectric functional layer (4), and the lower end of the first set of electrodes (6) extends into the interior of the aluminum scandium nitride ferroelectric functional layer (4). At the same time, the first set of electrodes (6) is an aluminum gallium nitride electrode. The second set of electrodes (7) is located on the aluminum scandium nitride ferroelectric functional layer (4), and the second set of electrodes (7) is in contact with the upper surface of the aluminum scandium nitride ferroelectric functional layer (4). At the same time, the second set of electrodes (7) is an aluminum scandium nitride electrode. The first electrode in the first group of electrodes (6) and the second electrode in the second group of electrodes (7) are interlaced and alternately arranged without contacting each other, forming an interdigitated structure.

2. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 1, characterized in that: In the metal-semiconductor-metal mode, the first set of electrodes (6) in the interdigitated electrode pair is the anode, and the second set of electrodes (7) in the interdigitated electrode pair is the cathode. The interdigitated electrode pair is used to collect photogenerated carriers. In the surface acoustic wave (SAW) mode, the interdigital electrode pair acts as an interdigital transducer for exciting and receiving SAW waves.

3. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 2, characterized in that: The upper surface of the aluminum nitride scandium ferroelectric functional layer (4) is provided with a reflective grating (5). The reflective grating (5) is located on both sides of the interdigital electrode pair. The period of the reflective grating (5) corresponds to the period of the interdigital electrode pair. The width of the reflective grating (5) is equal to the width of the interdigital fingers of the interdigital electrode pair. The spacing of the reflective grating (5) is equal to the spacing between the interdigital fingers of the interdigital electrode pair.

4. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 3, characterized in that: The interdigitated electrode pairs have an interdigitated finger width of 5–10 μm, an interdigitated finger spacing of 5–10 μm, and a number of interdigitated finger pairs of 20–30.

5. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 4, characterized in that: The thickness of the aluminum nitride buffer layer (2) is 100–2000 nm.

6. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 5, characterized in that: The aluminum gallium nitride transition layer (3) is Al 0.3 Ga 0.7 The N transition layer has a thickness of 50–1000 nm, where N is nitrogen, Ga is gallium, and Al is aluminum.

7. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 6, characterized in that: The aluminum nitride scandium ferroelectric functional layer (4) is Al 0.35 Sc 0.65 The N-ferroelectric functional layer has a thickness of 50–100 nm, where N is nitrogen, Sc is scandium, and Al is aluminum.

8. The dual-mode aluminum nitride scandium-based ultraviolet photodetector according to claim 7, characterized in that: The substrate (1) is a silicon wafer or a sapphire substrate.

9. A method for fabricating a dual-mode aluminum scandium nitride-based ultraviolet photodetector as described in claim 1, characterized in that, Includes the following steps: Step 1: Clean the substrate (1); Step 2: Deposit an aluminum nitride buffer layer (2) on the substrate (1); Step 3: Apply an aluminum gallium nitride transition layer (3) to the aluminum nitride buffer layer (2); Step 4: Deposit an aluminum scandium ferroelectric functional layer (4) on the aluminum gallium nitride transition layer (3); Step 5: Perform the first photolithography on the aluminum scandium nitride ferroelectric functional layer (4) to form a reflective gate (5) and the first set of electrodes (6). The photolithography window extends into the interior of the aluminum scandium nitride ferroelectric functional layer (4). Deposit aluminum gallium nitride electrode material and form the first set of electrodes (6) embedded in the aluminum scandium nitride ferroelectric functional layer (4) through a lift-off process. Step 6: Perform a second photolithography on the aluminum scandium nitride ferroelectric functional layer (4) to form a second set of electrodes (7). The photolithography window is located only on the upper surface of the aluminum scandium nitride ferroelectric functional layer (4) and is alternately arranged with the first set of electrodes (6) to form interdigitated electrode pairs. Deposit aluminum scandium nitride electrode material and form a second set of electrodes (7) on the upper surface of the aluminum scandium nitride ferroelectric functional layer (4) without embedding them by a lift-off process.

10. The preparation method according to claim 9, characterized in that: After the aluminum nitride scandium ferroelectric functional layer (4) is deposited in step 4, annealing is performed.

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