A tungsten oxide-based photodetector and a preparation method and application thereof

Abstract

A tungsten oxide-based photodetector, its fabrication method, and its application are disclosed, belonging to the field of semiconductor technology. This tungsten oxide-based photodetector includes a Si substrate and an Eu-WO3 thin film grown on the surface of the Si substrate, and a thin metal electrode deposited on the surface of the Eu-WO3 thin film. This tungsten oxide-based photodetector is a single photodetector based on an Eu-doped WO3 thin film, fabricated by radio frequency magnetron sputtering, utilizing rare-earth Eu... 3+ Doping enables a single detector to achieve broadband detection covering ultraviolet, visible, and near-infrared light, with high detection sensitivity and fast response.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a tungsten oxide-based photodetector, its preparation method, and its application. Background Technology

[0002] With the rapid development of information sensing and intelligent systems, photoelectric detection technology is reshaping the connection boundary between the physical world and digital systems with its "ultra-sensitive perception" and "breakthrough in performance limits." Broadband response technology is becoming the core direction of photoelectric detector development, with its potential particularly prominent in fields such as intelligent systems, quantum communication, and space exploration. Through continuous optimization of material and structural design, future detectors will achieve higher performance and a wider range of applications. As photoelectric detection missions become increasingly complex, photoelectric detectors operating in different bands are gradually being integrated for broadband detection of the same scene. Due to limitations in the size of integrated systems and mission modules, conventional broadband detection missions often require multiple detectors in different bands to work together, greatly increasing system complexity. Therefore, ultra-wideband photoelectric detectors (UB-PDs) with ultra-wideband detection (ultraviolet-visible-infrared-terahertz) capabilities are gradually becoming a cutting-edge research hotspot internationally. Traditional detectors are limited by material band gaps and device structures, and can usually only respond to a single band (such as ultraviolet or infrared). For example, silicon-based detectors are sensitive to visible light but cannot detect infrared, while materials such as InGaAs cover short-wave infrared but cannot respond to ultraviolet. Achieving multi-band coordinated detection in the ultraviolet-visible-infrared spectrum requires addressing core issues such as materials bandgap engineering and optimizing photoelectric conversion efficiency. UB-PDs generally refer to photodiodes capable of covering at least three bands: ultraviolet, visible, short-wave infrared, mid-wave infrared, long-wave infrared, and terahertz. Although the concept of UB-PDs has only been around for about 10 years, numerous UB-PDs based on different materials and types have already been reported, and performance parameters such as responsivity, response time, noise equivalent power, and linear dynamic range are continuously being optimized. However, the development of existing UB-PDs still faces many challenges, such as the trade-off between response time and responsivity, insufficient overall device performance, and significant performance differences across different bands.

[0003] Tungsten oxide (WO3), as an n-type wide-bandgap semiconductor (bandgap of approximately 3 eV), possesses excellent photoelectrochemical properties such as good electron transport performance, high exciton binding energy (60 meV), electrochromism, and photochromism, and has been applied in the field of photoelectric detection in recent years. Primitive tungsten oxide has been extensively explored due to its application in ultraviolet photodetectors. However, its detection range is limited to the ultraviolet band, and its quantum efficiency and responsivity are low, which can be attributed to the high recombination rate of photogenerated carriers. Therefore, the effectiveness of tungsten oxide in broadband photodetectors remains a challenge.

[0004] Rare earth ions (such as Yb) 3+Er 3+ Eu 3+ Rare earth ions, with their 4f electronic transition characteristics, have been widely used in the field of light emission (LEDs, phosphors, lasers), possessing advantages such as narrow linewidth emission, large Stokes shift, and excellent photostability. However, their direct photosensitive application in photodetectors has long been overlooked, mainly because the traditional understanding is that rare earth ions have small absorption cross-sections and non-radiative transitions dominate, making it difficult to efficiently generate photogenerated carriers. Summary of the Invention

[0005] The purpose of this invention is to address the problems of narrow detection range, low detection sensitivity, and slow response of existing tungsten oxide photodetectors by providing a tungsten oxide-based photodetector, its fabrication method, and its application. This tungsten oxide-based photodetector is a single photodetector based on an Eu-doped WO3 thin film prepared by radio frequency magnetron sputtering, utilizing rare earth Eu... 3+ Doping enables a single detector to achieve broadband detection covering ultraviolet, visible, and near-infrared light, with high detection sensitivity and fast response.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a tungsten oxide-based photodetector, comprising a Si substrate and an Eu-WO3 thin film grown on the surface of the Si substrate, and a thin metal electrode deposited on the surface of the Eu-WO3 thin film.

[0007] The thickness of the Eu-WO3 film is 200 nm to 250 nm.

[0008] The thin metal electrode is preferably made of one or two of the following metals: gold (Au), platinum (Pt), silver (Ag), chromium (Cr), titanium (Ti), copper (Cu), and nickel (Ni).

[0009] The thin metal electrode has a thickness of 10–40 nm, an electrode spacing of 100–200 μm, and a width of 200–300 μm.

[0010] This invention also provides a method for preparing the above-mentioned tungsten oxide-based photodetector, which specifically includes the following steps: S1: Remove stains from the surface of the Si wafer, dry it, then remove the natural oxide layer, clean it, dry it, and obtain a cleaned Si wafer; S2: Eu2O3 sheets with a thickness of 1~2mm, a diameter of Φ8~10mm, and a purity of 99.9% or higher; S3: Using a cleaned Si wafer as a substrate and a WO3 target with an embedded Eu2O3 wafer as a sputtering target, an Eu-WO3 thin film is grown on the cleaned Si wafer by radio frequency magnetron sputtering. S4: Thin metal electrodes are deposited on the surface of Eu-WO3 thin film using thermal evaporation or electron beam deposition to obtain tungsten oxide-based photodetectors.

[0011] In step S1, the cleaning step of the Si substrate includes: In S1, the surface stains of the Si wafer are removed by ultrasonic cleaning of the silicon wafer for 10-15 minutes in sequence with anhydrous ethanol, acetone and deionized water.

[0012] In S1, the removal of the natural oxide layer on the surface of the Si wafer is achieved by immersing the silicon wafer in a hydrofluoric acid solution, or by immersing it in a hydrofluoric acid solution and then rinsing it with a hydrochloric acid solution; wherein, the mass concentration of the hydrofluoric acid solution is preferably 5% to 10%, and the mass concentration of the hydrochloric acid solution is 1% to 2%.

[0013] In step S1, the cleaning process involves sequentially cleaning the silicon wafer with ethanol and deionized water to remove hydrofluoric acid impurities from the surface of the silicon wafer.

[0014] In step S1, after removing the surface contaminants of the Si wafer, oxygen plasma treatment is performed to remove surface organic residues. The oxygen plasma treatment process has a power of 80~100W and a time of 5~6 minutes.

[0015] In S2, the raw material selected for the Eu2O3 sheet is Eu2O3 powder with a purity of 99.9% or higher, and the average particle size of the Eu2O3 powder is 120~180 micrometers, preferably 150 micrometers.

[0016] In S2, the pressing is performed by slowly increasing the pressure to 20 MPa and maintaining the pressure for 10 minutes, or by using a step-by-step pressurization: first pressurizing to 10 MPa, and then pressurizing to 25 MPa.

[0017] In S3, the WO3 target material embedded with Eu2O3 sheets is a WO3 target material with 1-4 Eu2O3 sheets embedded, wherein the Eu2O3 sheets are preferably symmetrically and uniformly distributed on circular etching tracks in the embedding position of the WO3 target material.

[0018] In S3, the pre-sputtering process is as follows: Ar is slowly introduced into the magnetron sputtering growth chamber under vacuum and the pressure is adjusted to 0.3-0.5 Pa. The sputtering power supply is turned on, and WO3 target material with Eu2O3 embedded in it is sputtered at low power to remove stains on the target surface. The pre-sputtering power is 20-100W and the pre-sputtering time is 10-30 minutes.

[0019] In S3, the sputtering growth process of Eu-WO3 thin film is as follows: WO3 target material embedded with 1-4 Eu2O3 sheets is pre-sputtered, then O2 is slowly introduced and the growth chamber pressure is adjusted. The sputtering power supply is turned on and the power value is set. The baffle on the surface of the Si substrate is opened to grow the Eu-WO3 thin film. After the growth is completed, the baffle on the surface of the Si substrate is closed, the sputtering power supply is turned off, and the substrate heating power supply is turned off. The substrate is allowed to cool naturally to room temperature. During Eu-WO3 thin film growth, the Si substrate temperature is 0-400℃, the sputtering power is 50-200W, and the Ar / O2 ratio is (10-5):1 according to the gas flow rate ratio, preferably dynamically adjusted. The gradient distribution of O2 content can balance carrier concentration, mobility, and optical properties, optimizing the sensitivity and response speed of the photodetector. The RF magnetron sputtering growth chamber pressure is 0.1-2 Pa, and the deposition time is 30-60 minutes.

[0020] The Si substrate is preferably rotated at a speed of 5-10 rpm.

[0021] The present invention also provides the application of the above-mentioned tungsten oxide-based photodetector in selective photodetection under a wide spectrum of 300-900nm, ultraviolet of 300-340nm, or visible-near infrared wavelength of 380-900nm; with an external quantum efficiency of over 90%.

[0022] The tungsten oxide-based photodetector, its preparation method, and its application, as described in this invention, offer the following advantages compared to existing technologies: (1) The present invention constructs a metal-semiconductor-metal (MSM) photodetector by preparing europium-doped tungsten oxide thin film material on the surface of Si silicon substrate and then depositing thin metal electrodes on the europium-doped tungsten oxide thin film material; the formed europium-doped tungsten oxide-based photodetector can achieve the purpose of ultraviolet-visible-near infrared broadband detection, and it can perform optical detection in the broadband ultraviolet-near infrared wavelength of 300-900nm, which has strong industrial applicability.

[0023] (2) The tungsten oxide-based photodetector prepared in this invention has a wide spectral response range, covering the entire ultraviolet-visible-near-infrared band. By controlling the band structure of tungsten oxide through europium doping, it achieves a wide spectral detection capability of 300-900 nm (the traditional WO3 detector only covers 350-550 nm). The external quantum efficiency reaches over 90%, indicating that the overall photoelectric conversion efficiency of the tungsten oxide-based photodetector is significant.

[0024] (3) The performance of the tungsten oxide-based photodetector prepared by this invention has achieved a breakthrough, with a responsivity (A / W) of 0.75 and a specific detectivity (Jones) of 3×10⁻⁶. 12 The response time is as low as 20ms.

[0025] (4) The tungsten oxide-based photodetector of the present invention has advantages in manufacturing process and cost. The present invention adopts low-temperature radio frequency magnetron sputtering process with a substrate temperature of ≤400℃ (the traditional process requires annealing at 500℃ or above), is compatible with flexible substrates, and achieves structural simplification and mass production potential through Eu2O3 pressing and doping process.

[0026] (5) Through material doping innovation, device structure optimization and low temperature process breakthrough, this invention achieves a synergistic improvement of wide spectrum, high sensitivity and low cost, and has significant competitive advantages in fields such as intelligent sensing and new energy monitoring. Attached Figure Description

[0027] Figure 1 XPS pattern of Eu-WO3 thin film according to an embodiment of the present invention; Figure 2 A schematic diagram of a WO3-based photodetector according to an embodiment of the present invention; Figure 3 Example 1: Optical switching curves of a tungsten oxide-based photodetector under a 1V bias voltage under illumination of 365nm, 532nm, and 808nm light. Figure 4 Example 2: Optical switching curves of a tungsten oxide-based photodetector under a 1V bias voltage under illumination of 365nm, 532nm, and 808nm. Detailed Implementation

[0028] This invention employs radio frequency magnetron sputtering technology, utilizing a self-designed WO3 ceramic target to etch tracks and embed Eu2O3 wafers, depositing Eu-WO3 films on Si semiconductor substrates, and then using thermal evaporation or electron beam deposition to deposit thin metal electrodes on the surface of the Eu-WO3 thin film to construct a metal-semiconductor-metal (MSM) structure photodetector, thus forming a device.

[0029] The specific embodiments of the present invention will be described below with reference to the accompanying drawings. Unless otherwise specified, all raw materials used in the following embodiments are commercially available. The materials include: a single-sided polished p-type monocrystalline silicon wafer, a WO3 target material (75 mm in diameter) with a purity of 99.99%, and Eu2O3 powder with a purity of 99.9%. Other materials include anhydrous ethanol, acetone, hydrofluoric acid (5% concentration), high-purity argon (Ar), and oxygen (O2).

[0030] Example 1

[0031] Step 1: Preparation of Eu2O3 tablets (1) Weighing and filling: Weigh 0.6 g of Eu2O3 powder (99.9% purity) and fill it evenly into a Φ8 mm circular mold cavity, avoiding accumulation.

[0032] (2) Tableting: The pressure was slowly increased to 20 MPa on a hydraulic press and maintained for 10 minutes to obtain a dense Eu2O3 sheet. The Eu2O3 sheet was then embedded into the circular etched track surface of the WO3 target (two sheets were embedded, symmetrically distributed).

[0033] Step 2: Cleaning the silicon substrate The silicon wafer was sequentially immersed in anhydrous ethanol, acetone, and deionized water, and ultrasonically cleaned for 15 minutes in each solution to remove surface organic matter and particles. It was then soaked in a 5% hydrofluoric acid solution to remove the natural oxide layer. The silicon wafer surface was then dried with high-purity nitrogen gas.

[0034] Step 3: Growth of Eu-WO3 thin film by radio frequency magnetron sputtering (1) Vacuum pretreatment: The WO3 target material embedded with the Eu2O3 sheet and the cleaned silicon substrate are placed in the vacuum chamber. The chamber is evacuated to a base pressure ≤ 5 × 10⁻⁶. -4 Pa.

[0035] (2) Pre-sputtering of target material: Ar gas was introduced, the chamber pressure was adjusted to 0.5 Pa, the sputtering power was turned on, the power was set to 100 W, and pre-sputtering was performed for 20 minutes to remove contaminants from the target surface.

[0036] (3) Thin film deposition: Adjust the Ar / O2 gas flow ratio to 8:1 (total flow rate 32 sccm: 4 sccm), and the chamber pressure to 1.5 Pa.

[0037] The sputtering power was set to 150 W, the substrate temperature to 200℃, the substrate rotation was started (10 rpm), and the baffle was opened to begin deposition. The deposition time was 60 minutes to obtain an Eu-WO3 thin film.

[0038] Turn off the sputtering power supply and allow the substrate to cool naturally to room temperature before removing it. Measure the XPS pattern of the thin film as follows: Figure 1 As shown, W near 31, 33, 35, and 37 eV 4f The four peaks are associated with the metals W(0) and W. 6+ The binding energy match is good, with Eu appearing at 1125, 1155, 1135, and 1165 eV. 3d The four peaks are Eu 2+ and Eu 3+ The binding energy indicates that Eu-WO3 thin films were successfully prepared.

[0039] Step 4: Metal Electrode Preparation (1) Mask design: Interdigitated electrode masks (electrode spacing 200 μm, width 300 μm) were coated on the surface of the Eu-WO3 thin film.

[0040] (2) Vacuum evaporation of Ag metal electrodes: A photomask was fixed onto the thin film surface, and then the film with the photomask attached was placed on the base of a vacuum thermal evaporation apparatus. A high-purity silver wire (99.999%) about 1 cm long was placed inside a tungsten blue container, and electrode deposition was performed using a thermal evaporation method. Under vacuum conditions, the silver wire was heated and evaporated into silver vapor. When the silver vapor came into contact with the thin film surface, it cooled and deposited uniformly. The photomask was then removed, forming a metal-semiconductor-metal (MSM) structure, i.e., the Ag / Eu-WO3 / Ag device was successfully fabricated, as shown in the schematic diagram. Figure 2 .

[0041] The Ag / Eu-WO3 / Ag device prepared in this embodiment was tested in the wavelength range of 300-900 nm. The results showed that the responsivity was not less than 0.75 A / W. Figure 3 The optical switching curves of the tungsten oxide-based photodetector in this embodiment under a 1V bias voltage under illumination at 365nm, 532nm, and 808nm are presented respectively. The curves show that the tungsten oxide-based photodetector exhibits high photoresponsivity and short response time in the ultraviolet, visible, and near-infrared bands.

[0042] Example 2:

[0043] Step 1: Preparation of Eu2O3 tablets (1) Weighing and filling: Weigh 0.6 g of Eu2O3 powder (99.9% purity) and fill it evenly into a Φ8 mm circular mold cavity, avoiding accumulation.

[0044] (2) Tableting: The pressure was slowly increased to 20 MPa on a hydraulic press and maintained for 10 minutes to obtain dense Eu2O3 sheets. The Eu2O3 sheets were then embedded into the circular etched track surface of the WO3 target (4 sheets were embedded, symmetrically distributed).

[0045] Step 2: Cleaning the silicon substrate The silicon wafer was sequentially immersed in anhydrous ethanol, acetone, and deionized water, and ultrasonically cleaned for 15 minutes in each step to remove surface organic matter and particles. The surface of the silicon wafer was then dried with high-purity nitrogen gas.

[0046] Step 3: Growth of Eu-WO3 thin film by radio frequency magnetron sputtering (1) Vacuum pretreatment: The WO3 target material embedded with the Eu2O3 sheet and the cleaned silicon substrate are placed in the vacuum chamber. The chamber is evacuated to a base pressure ≤ 5 × 10⁻⁶. -4 Pa.

[0047] (2) Pre-sputtering of target material: Ar gas was introduced, the chamber pressure was adjusted to 0.5 Pa, the sputtering power was turned on, the power was set to 100 W, and pre-sputtering was performed for 20 minutes to remove contaminants from the target surface.

[0048] (3) Thin film deposition: Adjust the Ar / O2 gas flow ratio to 8:1 (total flow rate 32 sccm: 4 sccm), and the chamber pressure to 1.5 Pa.

[0049] The sputtering power was set to 150 W, the substrate temperature to 200℃, the substrate rotation was started (10 rpm), and the baffle was opened to begin deposition. The deposition time was 60 minutes to obtain an Eu-WO3 thin film.

[0050] Turn off the sputtering power supply and remove the substrate after it has cooled to room temperature naturally.

[0051] Step 4: Metal Electrode Preparation (1) Mask design: Interdigitated electrode masks (electrode spacing 200 μm, width 300 μm) were coated on the surface of the Eu-WO3 thin film.

[0052] (2) Vacuum evaporation of Ag metal electrodes: A photomask was fixed onto the thin film surface, and then the film with the photomask attached was placed on the base of a vacuum thermal evaporation apparatus. A high-purity silver wire (99.999%) about 1 cm long was placed inside a tungsten blue container, and electrode deposition was performed using a thermal evaporation method. Under vacuum conditions, the silver wire was heated and evaporated into silver vapor. When the silver vapor came into contact with the thin film surface, it cooled and deposited uniformly. The photomask was then removed, forming a metal-semiconductor-metal (MSM) structure, i.e., the Ag / Eu-WO3 / Ag device was successfully fabricated.

[0053] The Ag / Eu-WO3 / Ag device prepared in this embodiment was tested in the wavelength range of 300-900 nm for its photocurrent response. Figure 4 The optical switching curves of the tungsten oxide-based photodetector in this embodiment under a 1V bias voltage under illumination at 365nm, 532nm, and 808nm are presented. The curves show that the photoresponsivity is relatively high and the response time is short in the ultraviolet, visible, and near-infrared bands.

[0054] Example 3:

[0055] Similar to Example 1, except that in step one, during the preparation of Eu2O3 tablets, a staged pressurization method is used. The pressure is first increased to 10 MPa and maintained for 5 minutes, and then increased to 25 MPa and maintained for 5 minutes.

[0056] Example 4:

[0057] Same as Example 1, except that: Step 3: RF magnetron sputtering growth of Eu-WO3 thin film, (2) in target pre-sputtering: Ar gas was introduced, the chamber pressure was adjusted to 0.3 Pa, the sputtering power was turned on, the power was set to 80 W, and pre-sputtering was performed for 25 minutes to remove contaminants from the target surface.

[0058] Example 5:

[0059] Same as Example 1, except that: Step 3: In the (3) film deposition of the radio frequency magnetron sputtering growth of Eu-WO3 thin film: Adjust the Ar / O2 gas flow rate ratio to 10:1 (total flow rate 40 sccm: 4 sccm), and the chamber pressure to 0.5 Pa.

[0060] The sputtering power was set to 200 W, the substrate temperature to 100℃, the substrate rotation was started (10 rpm), and the baffle was opened to begin deposition. The deposition time was 30 minutes to obtain an Eu-WO3 thin film.

[0061] Example 6:

[0062] Same as Example 1, except that: Step 3: In the (3) film deposition of the radio frequency magnetron sputtering growth of Eu-WO3 thin film: Adjust the Ar / O2 gas flow ratio to 5:1 (total flow rate 20 sccm: 4 sccm), and the chamber pressure to 0.1 Pa.

[0063] Set the sputtering power to 50 W, substrate temperature to room temperature, turn on substrate rotation (10 rpm), and open the baffle to begin deposition. Deposition time is 60 minutes to obtain Eu-WO3 thin film.

[0064] Example 7:

[0065] Same as Example 1, except that: Step four: metal electrode preparation, using electron beam evaporation for electrode deposition: The mask was fixed on the surface of the thin film. Silver particles with a purity of 99.9% or higher were used as the target material and placed in a water-cooled copper crucible under vacuum (3×10⁻⁶). -4 The electron gun cathode filament is preheated (Pa), and a high voltage (2kV) is gradually applied to generate and focus an electron beam, which is precisely hit on the silver target. The silver atoms fly towards the substrate in a straight line and form a metal-semiconductor-metal (MSM) structure with a predetermined pattern under the control of the mask. That is, the Ag / Eu-WO3 / Ag device is successfully fabricated.

[0066] Comparative Example 1: Step 1: Cleaning the silicon substrate The silicon wafer was sequentially immersed in anhydrous ethanol, acetone, and deionized water, and ultrasonically cleaned for 15 minutes in each step to remove surface organic matter and particles. The surface of the silicon wafer was then dried with high-purity nitrogen gas.

[0067] Step 2: RF magnetron sputtering growth of WO3 thin film (1) Vacuum pretreatment: Place the WO3 target and the cleaned silicon substrate into the vacuum chamber. Evacuate to a base pressure ≤ 5 × 10⁻⁶. -4 Pa.

[0068] (2) Pre-sputtering of target material: Ar gas was introduced, the chamber pressure was adjusted to 0.5 Pa, the sputtering power was turned on, the power was set to 100 W, and pre-sputtering was performed for 20 minutes to remove contaminants from the target surface.

[0069] (3) Thin film deposition: Adjust the Ar / O2 gas flow ratio to 8:1 (total flow rate 32 sccm: 4 sccm), and the chamber pressure to 1.5 Pa.

[0070] The sputtering power was set to 150 W, the substrate temperature to 200℃, the substrate rotation was started (10 rpm), and the baffle was opened to begin deposition. The deposition time was 60 minutes to obtain a WO3 thin film.

[0071] Turn off the sputtering power supply and remove the substrate after it has cooled to room temperature naturally.

[0072] Step 4: Metal Electrode Preparation (1) Mask design: An interdigitated electrode mask (electrode spacing 200 μm, width 300 μm) was applied to the surface of the WO3 thin film.

[0073] (2) Vacuum evaporation of Ag metal electrodes: A photomask was fixed onto the thin film surface, and then the film with the photomask attached was placed on the base of a vacuum thermal evaporation apparatus. A high-purity silver wire (99.999%) about 1 cm long was placed inside a tungsten blue container, and electrode deposition was performed using a thermal evaporation method. Under vacuum conditions, the silver wire was heated and evaporated into silver vapor. When the silver vapor came into contact with the thin film surface, it cooled and deposited uniformly. The photomask was then removed, forming a metal-semiconductor-metal (MSM) structure, i.e., the Ag / WO3 / Ag device was successfully fabricated.

[0074] The Ag / WO3 / Ag device prepared in this comparative example was tested in the 300-900 nm wavelength range for photocurrent response, and showed almost no photoresponse in the visible and near-infrared bands.

[0075] Comparative Example 2: By replacing Eu with rare earth Nd, and otherwise remaining the same as in Example 1, the resulting Ag / Nd-WO3 / Ag device exhibits low near-infrared light response and slow response speed.

[0076] Comparative Example 3 By embedding Eu2O3 sheets into the circular etched track surface of the WO3 target (embedding 8 sheets symmetrically distributed), and otherwise the same as in Example 1, the prepared Ag / Eu-WO3 / Ag device has a larger dark current and a lower photoresponse.

[0077] Comparative Example 4: With the gas flow rate ratio of Ar / O2 being 1:1, and other steps being the same as in Example 1, the prepared Ag / Eu-WO3 / Ag device is obtained. It has a small dark current but a low optical on / off ratio and a low photoresponse.

[0078] Comparative Example 5: With the gas flow ratio of Ar / O2 being 20:1 and other steps being the same as in Example 1, the prepared Ag / Eu-WO3 / Ag device has a large dark current but a low optical on / off ratio and a low photoresponse.

[0079] Comparative Example 6: Similar to Example 1, the difference lies in the absence of the Eu2O3 tablet preparation process in step one. Instead, Eu2O3 powder is directly and uniformly spread on the WO3 target, resulting in almost no photoresponse. This may be due to the Eu2O3 powder being used in Example 1. 3+ Ineffective doping was not performed.

[0080] Comparing the photoelectric response data of Examples 1-2 and Comparative Example 1 clearly reveals that Eu doping has a significant modulating effect on the photoelectric performance of this tungsten oxide-based photodetector. Under different doping states, the detector exhibits drastically different response characteristics to different wavelengths of light. In Comparative Example 1 without Eu doping, the detector shows almost no photoelectric response. This is because the bandgap of pure tungsten oxide is approximately 2.6-2.8 eV, which only responds to visible light and part of the ultraviolet light, and its photogenerated carrier concentration is low with limited mobility. Without doping, pure tungsten oxide has fewer internal defects, making it difficult to form effective carrier separation and transport channels. When illuminated, the generated photogenerated electron-hole pairs recombine easily and cannot move directionally under an applied electric field to form a stable photocurrent, thus exhibiting almost no photoelectric response.

[0081] In Example 1, when the Eu doping content is low, the detector exhibits the highest responsivity to near-infrared light, followed by visible light, and lastly ultraviolet light. Figure 3This is mainly because the incorporation of a small amount of Eu ions introduces impurity energy levels into the tungsten oxide lattice. These impurity energy levels are located within the band gap of tungsten oxide and can absorb photon energy from near-infrared light, causing electrons to transition from the impurity energy levels to the conduction band, thereby broadening the detector's response band. Simultaneously, a small amount of Eu doping can also act as a shallow donor or acceptor, increasing the carrier concentration and promoting the separation and transport of photogenerated carriers. However, since the amount of Eu doping is small, it has little impact on the original band gap of tungsten oxide; its response to visible and ultraviolet light mainly depends on the intrinsic photoelectric effect of tungsten oxide itself. But the significant improvement in near-infrared light response makes its responsivity in this band exceed that of visible and ultraviolet light.

[0082] In Example 2, when the Eu doping content was high, the detector's response order was reversed, with the highest responsivity for visible light, followed by ultraviolet light, and the lowest responsivity for near-infrared light. This is because high Eu doping causes significant lattice distortion in tungsten oxide, leading to the aggregation of numerous Eu ions and the formation of deep-level impurities. These deep-level impurities become recombination centers for photogenerated carriers, greatly reducing carrier lifetime and mobility. For near-infrared light, the photon energy is relatively low, and electrons transitioning from impurity energy levels to the conduction band are more easily captured by these deep-level recombination centers, failing to effectively form a photocurrent. In contrast, visible and ultraviolet light have higher photon energies, directly exciting electrons in the valence band of tungsten oxide to transition to the conduction band, generating photogenerated carriers with higher energy that are less easily captured by recombination centers, thus maintaining a high responsivity. Furthermore, high-concentration Eu doping may also alter the band gap of tungsten oxide, enhancing its absorption capacity for visible light and further improving its visible light responsivity. In summary, Eu doping exerts a complex and significant influence on the photoelectric performance of tungsten oxide-based photodetectors by altering the electronic structure of tungsten oxide, introducing impurity energy levels, and affecting the crystal structure. By rationally controlling the Eu doping content, the detector's response to light in different wavelength bands can be optimized, providing more possibilities for its use in various optoelectronic applications.

Claims

1. A tungsten oxide-based photodetector, characterized in that, The tungsten oxide-based photodetector includes a Si substrate and an Eu-WO3 thin film grown on the surface of the Si substrate, and a thin metal electrode deposited on the surface of the Eu-WO3 thin film.

2. The tungsten oxide-based photodetector according to claim 1, characterized in that, The thickness of the Eu-WO3 film is 200 nm to 250 nm.

3. The tungsten oxide-based photodetector according to claim 1, characterized in that, The thin metal electrode is preferably made of one or two of the following metals: gold, platinum, silver, chromium, titanium, copper, and nickel; the thickness of the thin metal electrode is 10–40 nm.

4. The method for preparing the tungsten oxide-based photodetector according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Remove stains from the surface of the Si wafer, dry it, then remove the natural oxide layer, clean it, dry it, and obtain a cleaned Si wafer; S2: Eu2O3 sheets with a thickness of 1~2mm, a diameter of Φ8~10mm, and a purity of 99.9%; S3: Using a cleaned Si wafer as a substrate and a WO3 target with an embedded Eu2O3 wafer as a sputtering target, an Eu-WO3 thin film is grown on the cleaned Si wafer by radio frequency magnetron sputtering. S4: Thin metal electrodes are deposited on the surface of Eu-WO3 thin film using thermal evaporation or electron beam deposition to obtain tungsten oxide-based photodetectors.

5. The method for preparing the tungsten oxide-based photodetector according to claim 4, characterized in that, In S2, the raw material selected for the Eu2O3 sheet is Eu2O3 powder with a purity of 99.9% or higher, and the average particle size of the Eu2O3 powder is 120~180 micrometers.

6. The method for preparing the tungsten oxide-based photodetector according to claim 4, characterized in that, In S2, the compression is performed by slowly increasing the pressure to 20 MPa and maintaining the pressure for 10 minutes, or by using a stepwise pressurization: first pressurizing to 10 MPa, and then pressurizing to 25 MPa.

7. The method for preparing the tungsten oxide-based photodetector according to claim 4, characterized in that, In S3, the WO3 target material embedded with Eu2O3 sheets is a WO3 target material with 1-4 Eu2O3 sheets embedded, wherein the Eu2O3 sheets are preferably symmetrically and uniformly distributed on circular etching tracks in the embedding position of the WO3 target material.

8. The method for preparing the tungsten oxide-based photodetector according to claim 4, characterized in that, In S3, the pre-sputtering process is as follows: Ar is slowly introduced into the magnetron sputtering growth chamber under vacuum and the pressure is adjusted to 0.3-0.5 Pa. The sputtering power supply is turned on, and WO3 target material with Eu2O3 embedded in it is sputtered at low power to remove stains on the target surface. The pre-sputtering power is 20-100W and the pre-sputtering time is 10-30 minutes.

9. The method for preparing a tungsten oxide-based photodetector according to claim 4, characterized in that, In S3, the sputtering growth process of Eu-WO3 thin film is as follows: after pre-sputtering WO3 target material embedded with 1-4 Eu2O3 sheets, O2 is slowly introduced and the growth chamber pressure is adjusted. The sputtering power supply is turned on and the power value is set. The baffle on the surface of the Si substrate is opened to grow the Eu-WO3 thin film. After the growth is completed, the baffle on the surface of the Si substrate is closed, the sputtering power supply is turned off, the substrate heating power supply is turned off, and the substrate naturally cools to room temperature. During the growth of Eu-WO3 thin film, the Si substrate temperature is 0-400℃, the sputtering power is 50-200W, the Ar / O2 ratio is (10-5):1 according to the gas flow ratio, the pressure of the RF magnetron sputtering growth chamber is 0.1-2Pa, and the deposition time is 30-60 minutes.

10. The tungsten oxide-based photodetector according to any one of claims 1-3 or the tungsten oxide-based photodetector prepared by the preparation method according to any one of claims 4-9 can be used in selective photodetection under a wide spectrum of 300-900nm, ultraviolet of 300-340nm, or visible-near infrared wavelength of 380-900nm; the external quantum efficiency is above 90%.

Images