A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring

Abstract

The present application relates to the technical field of flexible solar blind ultraviolet photodetector, and particularly relates to a flexible solar blind ultraviolet photodetector for ultraviolet protection monitoring. No flexible solar blind ultraviolet photodetector based on a flexible substrate has been found. In view of the above problem, the present application provides a flexible solar blind ultraviolet photodetector for ultraviolet protection monitoring, which overcomes the contradiction between flexibility and high performance of the existing flexible solar blind ultraviolet photodetector, and makes significant progress in device flexibility, dark current suppression, response speed, bending reliability and wearable applicability, and has important practical value and broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of flexible solar-blind ultraviolet photodetector technology, and specifically to a flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring. Background Technology

[0002] Solar-blind ultraviolet (UV) light typically refers to ultraviolet light with wavelengths ranging from 200 nm to 280 nm. This wavelength is strongly absorbed by the ozone layer as it passes through the Earth's atmosphere, resulting in virtually no background radiation in this band in near-Earth space. Therefore, solar-blind UV detection has an extremely low false alarm rate and demonstrates irreplaceable application value in fields such as military early warning, flame detection, non-line-of-sight communication, and space exploration.

[0003] Gallium oxide, as an ultrawide bandgap semiconductor material, has a bandgap of approximately 4.5–4.9 eV, with its intrinsic absorption edge located precisely in the solar-blind ultraviolet band. This material possesses outstanding advantages such as high absorption coefficient, good thermal and chemical stability, and the ability to achieve intrinsic solar-blind response without alloying to control the bandgap. Therefore, it is considered an ideal candidate material for fabricating high-performance flexible solar-blind ultraviolet photodetectors.

[0004] In recent years, the rapid development of wearable electronics, health monitoring, and intelligent protective equipment has placed new demands on flexible solar-blind ultraviolet photodetectors, requiring greater flexibility, lightweight design, low power consumption, and high stability. However, several technical bottlenecks remain in existing technologies, specifically in the following aspects.

[0005] First, most traditional gallium oxide detectors are based on rigid substrates such as sapphire, silicon, or strontium titanate. These substrates cannot be bent and are difficult to fit the curved surface of the human body or adapt to non-planar scenes, thus failing to meet the basic requirements of wearable applications.

[0006] Second, if gallium oxide thin films are directly deposited on flexible organic substrates, the organic substrates are not heat-resistant, and the films can only be grown at low temperatures. Gallium oxide thin films prepared at low temperatures often have poor crystal quality and high internal oxygen vacancy concentrations, resulting in large dark currents, slow response speeds, and significant persistent photoconductivity effects, which seriously affect detection performance.

[0007] Third, in order to obtain high-quality gallium oxide single crystal or polycrystalline thin films, a high growth temperature is usually required, but conventional flexible substrates cannot withstand such high-temperature processes, making high-quality thin films incompatible with flexible substrates.

[0008] Fourth, existing sacrificial layer separation technology is mainly used in the preparation of gallium nitride self-supporting substrates, and a mature process capable of achieving lossless flexible transfer has not yet been developed for ferroelectric materials or oxide heterojunctions.

[0009] Fifth, the devices reported so far that utilize ferroelectric materials to modulate the performance of gallium oxide detectors or construct oxide heterojunctions all employ rigid structures and fail to integrate ferroelectric modulation, stress buffering, and flexible wearable functionality into one unit.

[0010] In summary, current technologies cannot simultaneously meet the requirements of high-quality crystallization, low dark current, fast response, mechanical flexibility, and wearable applicability. Therefore, there is an urgent need to develop a novel device structure and fabrication strategy to provide a feasible technical solution for high-performance flexible solar-blind ultraviolet photodetectors for civilian ultraviolet protection applications. Summary of the Invention

[0011] A problem with existing technologies is that no flexible solar-blind ultraviolet photodetector based on a flexible substrate has been found. To address this problem, this invention provides a flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring, comprising a flexible conductive substrate and a functional layer covering one conductive side of the flexible conductive substrate, wherein the conductive side of the flexible conductive substrate has a conductive substrate area not covered by the functional layer; The functional layer has a layered structure, consisting of a barium titanate layer (BTO layer) and a Ga2O3 layer from bottom to top; Uniformly and independently disposed dot-shaped metal electrodes are arranged on the surface of the Ga2O3 layer, and the dot-shaped electrodes are connected to form a common electrode by metal wires. The dot-shaped metal electrode is composed of a Ti layer and an Au layer, with the Au layer covering the Ti layer and the Ti layer loaded on the surface of the Ga2O3 layer.

[0012] Preferably, the flexible conductive substrate is an ITO-PET conductive flexible substrate.

[0013] Preferably, the thickness of the flexible conductive substrate is 0.12-0.13 mm.

[0014] Preferably, the thickness of the BTO layer is 100-120 nm.

[0015] Preferably, the thickness of the Ga2O3 layer is 100-120 nm.

[0016] Preferably, the dot-shaped metal electrode is prepared by masked electron beam evaporation.

[0017] Preferably, a flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring is prepared by the following steps: Step 1: Clean the STO substrate sequentially with acetone, ethanol, and deionized water, then immerse it in BOE etching solution for 30 seconds; then anneal it at 900°C for at least 1.5 hours. Step 2: Using a PLD system, a composite layer of strontium aluminate single crystal thin film (SAO sacrificial layer), BTO layer and Ga2O3 layer is sequentially deposited on an STO substrate; Step 3: Place the sample obtained in Step 2 in an oxygen atmosphere at 200 mbar and anneal at 800°C for at least 10 min, then cool to room temperature at a rate not exceeding 25°C / min. Step 4: Immerse the sample obtained in Step 3 in deionized water to dissolve and remove the SAO sacrificial layer, thereby obtaining a functional layer film floating on the surface of the deionized water. Step 5: Use a plasma cleaner to treat the conductive surface of the ITO-PET conductive flexible substrate to increase the hydrophilicity of the material surface; Step 6: Transfer the functional layer film from the aqueous solution in Step 4 to the surface of the hydrophilically treated ITO-PET conductive flexible substrate, and heat and dry the BTO layer in the functional layer film and the conductive surface of the ITO-PET conductive flexible substrate. The conductive side of the flexible conductive substrate will have a conductive substrate area not covered by the functional layer film. Step 7: Electron beam evaporation is used to form uniformly spaced dot-shaped metal electrodes on the surface of Ga2O3 in the sample obtained in step 6. The dot-shaped electrodes are connected by metal wires to form a common electrode, thus obtaining a flexible solar-blind ultraviolet photodetector.

[0018] Preferably, the BOE etching solution is prepared by mixing 49.9 wt.% HF aqueous solution and 40 wt.% NH4F aqueous solution at a volume ratio of 1:6.

[0019] Beneficial effects: (1) This invention is the first to apply the ferroelectric semiconductor heterojunction composed of barium ferroelectric titanate and gallium oxide to a flexible solar-blind ultraviolet photodetector, successfully breaking through the technical barriers of traditional rigid devices that cannot be bent or worn, and providing a brand-new device solution for achieving human body fit, curved surface adaptation and wearable ultraviolet protection monitoring. (2) This invention is the first to use water-soluble strontium aluminate as a sacrificial layer to achieve non-destructive aqueous phase stripping and flexible transfer of barium ferroelectric titanate and gallium oxide heterojunction. This technical approach completely avoids the industry problem of incompatibility between high-temperature processes and flexible substrates, enabling high-quality oxide films that can only be epitaxially grown at high temperatures on rigid substrates to be completely transferred to flexible substrates, thus solving the core contradiction that high-quality crystallization and flexibility are mutually exclusive; (3) In this invention, the barium titanate layer plays a triple synergistic role in the device by simultaneously regulating ferroelectric polarization, matching crystal lattice, and buffering stress. On the one hand, the ferroelectric polarization effect effectively modulates the band structure of the gallium oxide layer, significantly reduces dark current and suppresses persistent photoconductivity, thereby improving response speed and detection sensitivity. On the other hand, the good lattice matching between barium titanate and gallium oxide ensures the quality of the heterojunction interface, and the layer, as a stress buffer, enhances the mechanical reliability and electrical stability of the device under bending conditions. (4) The present invention adopts a dot-shaped metal electrode structure and uses a titanium / gold composite electrode to achieve optimized metal-semiconductor contact. This design effectively reduces contact loss, further suppresses dark current, and facilitates the uniform collection of photogenerated carriers, significantly improving the working stability of flexible devices under repeated bending conditions; (5) This invention is the first to apply flexible high-performance flexible solar-blind ultraviolet photodetector to the field of wearable ultraviolet protection monitoring. From the selection of ferroelectric semiconductor heterojunction materials, water-soluble sacrificial layer transfer process, point electrode structure design to flexible device packaging and application, it forms an original technical solution with a full chain of materials, structure, process and application, providing practical technical support for personal ultraviolet protection, intelligent health monitoring and portable solar-blind detection equipment. (6) This invention overcomes the contradiction between flexibility and high performance in existing flexible solar-blind ultraviolet photodetectors. It has made significant progress in terms of device flexibility, dark current suppression, response speed, bending reliability and wearability, and has important practical value and broad application prospects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the fabrication process of the flexible solar-blind ultraviolet photodetector obtained in Embodiment 1 of the present invention.

[0021] Figure 2 This is a test diagram of the core photoelectric performance of the flexible solar-blind ultraviolet photodetector obtained in Embodiment 1 of the present invention.

[0022] Figure 3 This is a process diagram of transferring the functional layer film to the surface of a hydrophilically treated ITO-PET conductive flexible substrate in Embodiment 1 of the present invention.

[0023] Figure 4 : This is a test diagram of the spectral response characteristics of the flexible solar-blind ultraviolet photodetector obtained in Embodiment 1 of the present invention. Detailed Implementation

[0024] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0025] The BOE etching solution in the following embodiments of the present invention was prepared by mixing 49.9 wt.% HF aqueous solution and 40 wt.% NH4F aqueous solution at a volume ratio of 1:6.

[0026] Example 1 A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring is fabricated as follows: Step 1: The STO substrate (strontium titanate single crystal, 5mm×5mm) was cleaned sequentially with acetone, ethanol and deionized water, then immersed in BOE etching solution for 30 s; then annealed in a muffle furnace at 900℃ for 1.5h. Step 2: A composite layer consisting of a SAO sacrificial layer, a BTO layer, and a Ga2O3 layer is sequentially deposited on an STO substrate using a PLD system. SAO sacrificial layer: 30 nm thick, laser energy 1.8 J / cm² 2 Oxygen partial pressure 5×10 -6 mbar, 800℃, 3Hz; BTO layer: thickness, 1.3 J / cm 2 Oxygen partial pressure 1×10 -1 mbar, 750 ℃, 4 Hz; Ga2O3 layer: thickness, 1.3 J / cm 2 Oxygen partial pressure 2×10 -2 mbar, 600 ℃, 5 Hz; Step 3: Place the sample obtained in Step 2 in an oxygen atmosphere at 200 mbar pressure and anneal it in situ at 800℃ for 10 min, then cool it to room temperature at a cooling rate of 25℃ / min. Step 4: Immerse the sample obtained in Step 3 in deionized water to dissolve and remove the SAO sacrificial layer, thereby obtaining a functional layer film floating on the surface of the deionized water. Step 5: Use a plasma cleaner to treat the conductive surface of the ITO-PET conductive flexible substrate (size is 1.5cm*1.5cm, thickness is 0.125mm, resistance is 5Ω) to increase the hydrophilicity of the material surface. The reaction gas is air, and the plasma ultraviolet activation treatment is 5min with a power of 100W. Step 6: Transfer the functional layer film from the aqueous solution in Step 4 (gently touch the BTO layer in the functional layer film with the conductive surface of the substrate and lift it up) to the surface of the hydrophilically treated ITO-PET conductive flexible substrate. Heat (80°C) the BTO layer in the functional layer film and the conductive surface of the ITO-PET conductive flexible substrate to dry. The conductive side of the flexible conductive substrate will have a conductive substrate area that is not covered by the functional layer film. Step 7: Electron beam evaporation is used to form uniformly distributed dot-shaped metal electrodes (a total of 625) on the surface of Ga2O3 in the sample obtained in step 6. The dot-shaped electrodes are connected by metal wires to form a common electrode, thus obtaining a flexible solar-blind ultraviolet photodetector.

[0027] The flexible solar-blind ultraviolet photodetector with a vertical structure obtained in Example 1 was subjected to relevant performance tests, including dark current test, photocurrent test, response time test, etc.

[0028] Instruction manual attached Figure 1 This is a schematic diagram of the process for preparing a flexible solar-blind ultraviolet photodetector in Example 1.

[0029] The solar-blind ultraviolet light source uses a 254 nm ultraviolet lamp. (See attached instruction manual.) Figure 3 The image shows the core photoelectric performance of the BTO / Ga2O3 flexible solar-blind ultraviolet photodetector: Figure 3 a comparison of IV characteristics under 254 nm ultraviolet light and dark conditions confirmed that the device dark current is as low as 10. -10 With an A-level increase in illumination current by 2 to 3 orders of magnitude, it possesses excellent light response and extremely low noise. Figure 3 b shows the IV curves under different optical power densities. The photocurrent increases monotonically with the optical power, and the dark current remains stable, which verifies the reliability of the device response under wide voltage and multiple light intensities. Figure 3 c The time response characteristics were tested under a 10 V bias voltage, and the rise time τᵣ = 1.44 s and the fall time τᵣ = 1.44 s were measured. d =1.26 s, demonstrating a fast switching response and good fit consistency; Figure 3 d compares the multi-cycle optical switching under bias voltages of 5 V, 10 V, and 15 V. The photocurrent increases with increasing bias voltage and shows no significant decay after multiple cycles, proving that the device has excellent cycle stability and flexible operational reliability, fully supporting the high-performance application potential of this flexible solar-blind detector.

[0030] Instruction manual attached Figure 2 This is a diagram illustrating the process of transferring the functional layer film onto the surface of a hydrophilically treated ITO-PET conductive flexible substrate.

[0031] Comparative Example 1 is the same as Example 1, except that the BTO layer in Comparative Example 1 is too thin, with a thickness of 50 nm. Experimental results show that the functional layer film after being peeled off in aqueous solution is brittle and has poor flatness. It will break during the transfer to the conductive surface of the hydrophilically treated ITO-PET conductive flexible substrate (stress mismatch between the BTO layer and the gallium oxide layer causes curling and breakage), and a flexible solar-blind detector cannot be obtained.

[0032] Instruction manual attached Figure 4The spectral response characteristics of a flexible BTO / Ga2O3 solar-blind ultraviolet detector were demonstrated. The responsivity curves in the 200-1000 nm range show that it exhibits significant photoelectric response only in the solar-blind ultraviolet band (200-280 nm), with a peak responsivity of approximately 28 mA / W, corresponding to a wavelength of approximately 255 nm, consistent with the intrinsic absorption edge of gallium oxide. Above 280 nm in the visible and near-infrared bands, the device responsivity drops to almost zero, demonstrating excellent solar-blind spectral selectivity and visible light interference resistance, enabling accurate ultraviolet exposure monitoring in complex natural light environments.

[0033] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring, characterized in that, It includes a flexible conductive substrate and a functional layer covering the conductive side of the flexible conductive substrate, wherein the conductive side of the flexible conductive substrate has a conductive substrate area not covered by the functional layer. The functional layer has a layered structure, consisting of a BTO layer and a Ga2O3 layer from bottom to top. Uniformly and independently disposed dot-shaped metal electrodes are arranged on the surface of the Ga2O3 layer, and the dot-shaped electrodes are connected to form a common electrode by metal wires. The dot-shaped metal electrode is composed of a Ti layer and an Au layer, with the Au layer covering the Ti layer and the Ti layer loaded on the surface of the Ga2O3 layer.

2. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The flexible conductive substrate is an ITO-PET conductive flexible substrate.

3. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The thickness of the flexible conductive substrate is 0.12-0.13 mm.

4. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The thickness of the BTO layer is 100nm-120nm.

5. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The thickness of the Ga2O3 layer is 100nm-120nm.

6. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The dot-shaped metal electrode was prepared by masked electron beam evaporation.

7. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 1, characterized in that, The preparation method includes the following steps: Step 1: Clean the STO substrate sequentially with acetone, ethanol, and deionized water, then immerse it in BOE etching solution for 30 seconds; then anneal it at 900°C for at least 1.5 hours. Step 2: A composite layer consisting of a SAO sacrificial layer, a BTO layer, and a Ga2O3 layer is sequentially deposited on an STO substrate using a PLD system. Step 3: Place the sample obtained in Step 2 in an oxygen atmosphere at 200 mbar and anneal at 800°C for at least 10 min, then cool to room temperature at a rate not exceeding 25°C / min. Step 4: Immerse the sample obtained in Step 3 in deionized water to dissolve and remove the SAO sacrificial layer, and obtain a functional layer film floating on the surface of deionized water. Step 5: Use a plasma cleaner to treat the conductive surface of the ITO-PET conductive flexible substrate to increase the hydrophilicity of the material surface; Step 6: Transfer the functional layer film from the aqueous solution in Step 4 to the surface of the hydrophilically treated ITO-PET conductive flexible substrate, and heat and dry the BTO layer in the functional layer film and the conductive surface of the ITO-PET conductive flexible substrate. The conductive side of the flexible conductive substrate will have a conductive substrate area not covered by the functional layer film. Step 7: Electron beam evaporation is used to form uniformly spaced dot-shaped metal electrodes on the surface of Ga2O3 in the sample obtained in step 6. The dot-shaped electrodes are connected by metal wires to form a common electrode, thus obtaining a flexible solar-blind ultraviolet photodetector.

8. A flexible solar-blind ultraviolet photodetector for ultraviolet protection monitoring according to claim 7, characterized in that, The BOE etching solution was prepared by mixing 49.9 wt.% HF aqueous solution and 40 wt.% NH4F aqueous solution at a volume ratio of 1:6.

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