Application of Ga-doped ZnO nanowires in the fabrication of photoelectrochemical ultraviolet photodetectors

Abstract

This invention discloses the application of Ga-doped ZnO nanowires in the fabrication of photoelectrochemical ultraviolet photodetectors. The fabricated Ga-doped ZnO (ZnO:Ga) PEC-type ultraviolet photodetector exhibits excellent self-powered ultraviolet light response performance, surpassing most previously reported PEC-type ultraviolet photodetectors. Furthermore, the device demonstrates good repeatability and long-term stability. Based on this, this invention also designs an ultraviolet light communication system based on international Morse code transmission, confirming that the ZnO nanowire PEC-type ultraviolet photodetector possesses the capability to function as a self-powered optical receiver. This invention provides a new approach for constructing highly stable, low-cost, and high-performance PEC-type ultraviolet photodetectors, with broad application prospects in the fields of multifunctional optoelectronic devices for future sensing, communication, and imaging systems.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet photodetector technology, and relates to the application of Ga-doped ZnO nanowires in the preparation of photoelectrochemical ultraviolet photodetectors. Background Technology

[0002] Ultraviolet photoelectric detection technology has broad application prospects in civilian and military fields such as flame detection, secure communication, and national defense early warning. [1] To meet the detector's requirements for small size, portability, and low power consumption. [2] Researchers have explored self-powered photodetectors based on traditional solid-state structures (such as pn junctions, pin junctions, and Schottky junctions), achieving ultraviolet photodetection without an external power source. Despite significant progress, several limiting factors hinder further development, such as complex fabrication, high material quality requirements, and lattice mismatch.

[0003] In recent years, to overcome the above limitations, scientists have proposed novel photoelectrochemical (PEC) ultraviolet photodetectors based on semiconductor / electrolyte structures, opening up new research areas. [3,4] To date, various semiconductor materials have been studied for the design of PEC-type ultraviolet photodetectors, including metal oxides (such as ZnO). [5] In2O3 [6] ), nitrides [7] and two-dimensional materials (such as Bi2O2S) [8] InSe [9] Among these, low-dimensional ZnO materials are considered the preferred materials for fabricating high-performance PEC ultraviolet detectors due to their high chemical stability, environmental friendliness, and ease of synthesis. [1] However, the original ZnO material suffers from problems such as poor conductivity and severe electron-hole recombination. [1] To date, several strategies have been developed to overcome the aforementioned problems, such as surface decoration.

[10] And heterostructures (such as ZnO / PdSe2)

[11] ZnO / KNbO3

[12] and ZnO / ZnS

[13] Among these, constructing ZnO heterojunctions is the mainstream approach in this field. However, new problems inevitably arise, such as insufficient interfacial contact, high fabrication costs, and lattice mismatch. Therefore, there is an urgent need to develop new strategies to further improve the performance of ZnO photodetectors.

[0004] Research has found that elemental doping is a potential technique to enhance charge carrier transfer kinetics in the photoelectrochemical water splitting process of metal oxide-based semiconductors. Impurity elements play a crucial role in increasing carrier concentration, promoting charge separation and transfer, extending charge lifetime, and reducing charge transfer resistance. [14,15] Therefore, we hypothesize that introducing heteroatoms into ZnO may be an effective method to improve the performance of PEC-type photodetectors. To our knowledge, although much progress has been made in the preparation of ZnO nanomaterials with different dopants, there are no reports on improving the performance of ZnO-based PEC-type ultraviolet photodetectors through doping. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide the application of Ga-doped ZnO nanowires in the preparation of photoelectrochemical ultraviolet photodetectors.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] Application of Ga-doped ZnO nanowires in the fabrication of photoelectrochemical ultraviolet photodetectors.

[0008] As one of the preferred technical solutions, the Ga-doped ZnO nanowires are obtained by a carbothermal reduction reaction on a silicon substrate using a mixture of zinc oxide, gallium oxide and graphite powder as the source material.

[0009] As one of the further preferred technical solutions, the mass ratio of zinc oxide, gallium oxide and graphite powder is 4:1:5, 4:2:6, 4:3:7 or 4:4:8, and even more preferably 4:2:6.

[0010] As a further preferred technical solution, the silicon substrate should be cleaned. The specific method is as follows: First, the silicon substrate is immersed in hydrofluoric acid for 10 minutes to remove the oxide layer on the surface; then, it is ultrasonically cleaned for 10 minutes each with anhydrous ethanol, acetone and deionized water respectively; wherein, the volume concentration of the hydrofluoric acid is 1%.

[0011] As one of the further preferred technical solutions, a silicon substrate is placed in a tube furnace, the source material is evenly spread on the surface of the silicon substrate, a vacuum is drawn, a mixture of nitrogen and oxygen is continuously introduced from the inlet of the tube furnace and flows out from the outlet of the tube furnace, the reaction is carried out at 1100°C for 20 minutes, and then naturally cooled to room temperature, so that Ga-doped ZnO nanowires can be obtained on the surface of the silicon substrate.

[0012] As a further preferred technical solution, the volume flow ratio of nitrogen to oxygen in the mixed gas is 120:5.

[0013] The photoelectrochemical ultraviolet photodetector is fabricated by encapsulating Ga-doped ZnO nanowires as photoanodes.

[0014] The core component of an ultraviolet light communication system based on international Morse code transmission is the aforementioned ultraviolet photodetector.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention is the first to demonstrate the remarkable effect of introducing gallium (Ga) atoms into ZnO nanowire photoanodes on the design of high-performance PECPDs. The prepared Ga-doped ZnO (ZnO:Ga) PEC-type ultraviolet photodetector exhibits excellent self-powered ultraviolet light response performance (an ultra-high responsivity of 233.26 mA / W, 4.18 × 10⁻⁶ Ω·cm). 12 Jones's superior detectivity and fast response / recovery time of 159 / 150 ms surpass most reported PEC-type ultraviolet photodetectors. Furthermore, the device exhibits good repeatability and long-term stability. This is due to the unique material properties of ZnO:Ga nanowires (including enhanced donor concentration and steeper band bending at the solid-liquid interface), which significantly enhances the generation, transfer, and separation efficiency of photogenerated carriers, thereby improving the photoelectric performance of the photodetector. Based on this, the present invention also designed an ultraviolet optical communication system based on international Morse code transmission, confirming that the ZnO nanowire PEC-type ultraviolet photodetector has the capability to function as a self-powered optical receiver. This invention provides a new approach for constructing highly stable, low-cost, and high-performance PEC-type ultraviolet photodetectors, with broad application prospects in multifunctional optoelectronic devices for future sensing, communication, and imaging systems. Attached Figure Description

[0017] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following drawings are provided for illustration.

[0018] Figure 1 This is a schematic diagram of the experimental setup for ZnO and ZnO:Ga nanowires.

[0019] Figure 2 Optical images of ZnO and ZnO:Ga nanowire photoanodes.

[0020] Figure 3 For structural and morphological characterization: (a) XRD patterns; (bc) SEM images; (df) EDS surface scan, TEM and FTT images of Ga, Zn and O elements; (gi) XPS patterns of Zn, Ga and O elements.

[0021] Figure 4 The PL spectra of ZnO and ZnO:Ga nanowires are shown.

[0022] Figure 5 At 0.5mW / cm2 It curves for samples with different doping concentrations under 0V bias voltage.

[0023] Figure 6 The photoresponse behavior of the device is shown in the following figures: (a) schematic diagram of the test system; (b) It response curve; (c) photocurrent density; (d) EQE; (e) R; (f) D*; (g) normalized spectral response curve.

[0024] Figure 7 The photo-dark current ratio (PDCR) of ZnO and ZnO:Ga nanowire photoanodes.

[0025] Figure 8 This is the normalized spectral response curve of the ZnO PEC type photodetector under a 0V bias voltage.

[0026] Figure 9 To illustrate the charge transfer behavior and the PEC performance enhancement mechanism: (a) Mott-Schottky curves of ZnO and ZnO:Ga samples at 1000 Hz; (b) schematic diagram of band structure; (c) EIS spectrum.

[0027] Figure 10 The effects of solution concentration and external bias voltage on device performance are shown in the following figures: (ab) It curves of photocurrent of ZnO:Ga PEC-PD as a function of electrolyte concentration and bias voltage; (c) corresponding photocurrent density; (de) response time; (f) performance comparison; and (g) stability.

[0028] Figure 11 For international Morse code transmission experiments.

[0029] Figure 12 The experimental setup for an ultraviolet communication system includes (a) a schematic diagram of the ultraviolet communication system and (b) the waveform of the received international Morse code transmission data.

[0030] Figure 13 It is the international Morse code. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0032] 1.1 Synthesis of ZnO and ZnO:Ga nanowires

[0033] ZnO nanowires were synthesized on a silicon substrate using a carbothermal reduction method. 16 A high-purity ZnO and graphite powder (C) precursor mixture with a mass ratio of 1:1 was used as the source material. A schematic diagram of the growth equipment is shown below. Figure 1First, the silicon substrate was immersed in a 1% HF dilute solution for 10 min to remove the oxide layer on the surface; then, it was ultrasonically cleaned sequentially with anhydrous ethanol, acetone, and deionized water for 10 min each. After evacuation, a mixture of nitrogen and oxygen (99.99%, N2:O2 = 120:5 sccm) was introduced for CVD. During the synthesis process, the source temperature was maintained at 1000℃, and the tube furnace was allowed to cool naturally to room temperature after 20 min of reaction. Considering the different carbothermic reaction threshold temperatures of ZnO (900℃) and Ga2O3 (1100℃) […]. 17 It was necessary to adjust the growth temperature to 1100℃ to ensure effective incorporation of Ga into ZnO. Four precursor mixtures of ZnO:Ga2O3:C with different mass ratios (4:1:5, 4:2:6, 4:3:7, 4:4:8) were used as source materials.

[0034] 1.2 Characterization of ZnO and ZnO:Ga nanowires

[0035] The morphology and microstructure of ZnO and ZnO:Ga nanowire samples were characterized by field emission scanning electron microscopy and transmission electron microscopy. The crystal structure of the samples was studied by X-ray diffraction (Cu Kα1 rays, λ = 0.1540598 nm) and Raman spectroscopy. The chemical state of each element was investigated by X-ray photoelectron spectroscopy and a monochromatic Al Kα source. All binding energies were calibrated through the C1s peak at 284.8 eV.

[0036] 1.3 Device fabrication and performance testing

[0037] ZnO and ZnO:Ga nanowires were further fabricated into photoanodes to evaluate their photoelectrochemical properties. An image of the encapsulated photoanode is shown (see...). Figure 2 First, one side of the silicon substrate was bonded to the copper wire using conductive silver paste, and then encapsulated with epoxy resin. A plastic ring with an inner diameter of 6 mm was used to determine the photosensitive area of ​​the photoelectrode. Photoelectric performance testing, Mott-Schottky plotting, and electrochemical impedance spectroscopy (EIS) were performed on an electrochemical workstation (CHI660C, Shanghai Chenhua). Under dark conditions, the EIS measured an AC voltage amplitude of 5 mV with a scan frequency from 100 kHz to 0.1 Hz; at 1000 Hz and 10 mVs... -1 The scan rate was measured using the Mott-Schottky plot.

[0038] 2. Results and Discussion

[0039] 2.1 Characterization of sample structure and morphology

[0040] Figure 3Figure a shows the XRD patterns of ZnO and ZnO:Ga nanowire samples. The diffraction peaks at 32.12°, 34.48°, 36.6°, 47.76°, 56.84°, and 63.02° correspond well to the (100), (002), (101), (102), (110), and (103) crystal planes of ZnO [PDF No. 36-1451]. No additional phases appeared after Ga doping, indicating that the ZnO crystal structure remained unchanged. The size of the ZnO nanowires remained almost unchanged before and after Ga doping, with an average diameter of approximately 60 nm and a length of approximately 10 μm. Figure 3 (b, c). Furthermore, EDS spectra confirmed the uniform distribution of Zn, Ga, and O elements in the ZnO:Ga nanomaterials. Figure 3 (d) indicates that Ga has been doped into the ZnO lattice. Further HRTEM analysis of the ZnO:Ga sample revealed clear lattice fringes with a spacing of 0.514 nm that could be indexed onto the (001) plane of ZnO. Figure 3 As shown in e. Figure 3 Figure f shows the results of the Fast Fourier Transform (FFT). The diffraction points obtained by the FFT also fit well with the (100), (101), and (002) planes of ZnO, consistent with the XRD test results. The XPS pattern was used to further confirm the successful doping of Ga into the ZnO lattice, such as... Figure 3 As shown in the figure, the appearance of the Ga 2p peak clearly indicates the presence of Ga in the ZnO lattice. Figure 3 The binding energies of 1117.9 and 1144.7 eV (in g) are attributed to Ga 2p. 3 / 2 and Ga 2p 1 / 2 This indicates that Ga ions are Ga 3+ The valence state is located at the Zn site in the ZnO lattice. For example... Figure 3 As shown in Figure 1, compared with the original ZnO, the Zn 2p and O 1s peaks in the ZnO:Ga sample shift slightly to higher binding energies, indicating a change in the local coordination environment of Zn and O ions. This can be attributed to the difference in electronegativity between Zn (χ = 1.65) and Ga (χ = 1.81).

[18] Furthermore, the O 1s map ( Figure 3 In the middle (i), it can be decomposed into 530.2 (O). I ) and 531.7eV (O II The two peaks correspond to lattice oxygen (Zn-O or Ga-O) and O in the oxygen-deficient region, respectively. 2- Ions (i.e., oxygen vacancies) 18,19] After Ga is incorporated, O II A slight increase in peak intensity indicates an increase in oxygen vacancy defects. Furthermore, the enhanced visible region in the photoluminescence spectrum further confirms this phenomenon. Figure 4 )

[19] .

[0041] 2.2 Device Performance Analysis

[0042] To evaluate the PEC photoresponse behavior of the ZnO photoanode before and after Ga doping, a PEC-type photodetector was fabricated using a simple packaging process. We used a three-electrode cell with a quartz window, including a ZnO photoanode (photosensitive area of ​​0.2827 cm²). 2 Counter electrode (1.5×1.5cm) 2 Platinum sheet), reference electrode (saturated calomel electrode, SCE), and Na2SO4 electrolyte, such as Figure 6 As shown in Figure a, the redox potential difference between the ZnO nanowires and the Na₂SO₄ electrolyte helps establish a built-in electric field and an upward band bend at the interface between the photoanode and the electrolyte. Under ultraviolet light irradiation, electron-hole pairs will be generated in the ZnO nanowires and separated under the influence of the built-in electric field. Photogenerated holes cross the nanowire / electrolyte interface to participate in the oxidation reaction (2H₂O + 2e⁻). – =2OH – +H2), while photogenerated electrons are transferred to the counter electrode via an external circuit to participate in the reaction: 4OH- – +4h + =O2 + 2H2O. Finally, the photocurrent was collected by the electrochemical workstation, while OH... - The current loop is completed through electrolyte transport. Therefore, PEC-type detectors have self-powering capabilities.

[0043] At 0.5mW / cm 2 Preliminary photoelectrochemical measurements were performed on Ga-doped and pristine ZnO nanowire samples in a 0.5 mol / L Na₂SO₄ solution under an external bias of 0 V. Based on the measured photocurrent density (see...),... Figure 5 The weight ratio of the precursor mixture (ZnO:Ga2O3:C) used for Ga doping was optimized, and the optimal ratio of 4:2:6 was selected for further PEC studies. Figure 6 Figure b shows the current-time (It) curves of the original and optimized gallium-doped ZnO PEC-type PDs. Under 365 nm illumination, all samples exhibit typical switching response characteristics. In contrast, the optimized gallium-doped ZnO sample shows stronger PEC photoresponse performance. Furthermore, the photocurrent density (Io) is higher. p It is displayed as a function of optical power intensity. Figure 6 In the middle c. A higher optical power intensity can generate more photogenerated carriers, making I... p Higher. When the optical power intensity increases from 30 μW / cm² 2 Increased to 500 μW / cm2 At that time, the I of ZnO:Ga PEC-PD p From 7μA / cm 2 It increased linearly to 70.64 μA / cm 2 The original ZnO PEC-PD's I p From 2.24 μA / cm 2 Increased to 6.47 μA / cm 2 The calculated photo-dark current ratio (PDCR) is in Figure 7 In the middle. The PDCR value of the ZnO:Ga sample is higher than that of the original sample when it is at 0V. For example, at 500 μW / cm 2 Under illumination, the PDCR value of ZnO:Ga PEC-PD is 1786, while the PDCR of the original ZnO is only 199.

[0044] To more comprehensively evaluate the photoresponse of ZnO's PEC PD, the external quantum efficiency (EQE), responsivity (R), and detectivity (D*) were calculated, such as... Figure 6 As shown in df. EQE can be derived from the following formula.

[20] :

[0045]

[0046] Where c, h, q, λ, and P are the speed of light, Planck's constant, electron charge, incident light wavelength, and light intensity, respectively. Figure 6 As shown in Figure d, the EQE increases as the optical power intensity decreases. Calculations show that the maximum EQE of the ZnO:Ga sample is 79.31%, three times that of the original device (25.37%), indicating a significant improvement in photoresponse after gallium doping.

[0047] Responsivity (R) is typically used to characterize the ability of a photodetector to convert incident light into an electrical signal, and can be given by the following formula.

[20] :

[0048]

[0049] Where, ΔI=I p (photocurrent)-I d (dark current), where S is the effective lighting area. Figure 6 Figure e shows the R values ​​of two PEC PDs at zero bias and different light intensities. As the light intensity decreases, the R value of the ZnO:Ga sample increases from 141.27 to 233.26 mA / W, exhibiting excellent photoresponse performance over a wide light intensity range. In contrast, the original ZnO PEC-PD shows a similar R value at 30 μW / cm². 2 Under light intensity, the maximum value of R is only 74.61 mA / W.

[0050] Detectability (D*) is another important parameter for evaluating the ability of a photodetector to detect weak signals, and it is obtained by the following formula.

[20] :

[0051]

[0052] Figure 6 Figure f shows the D* values ​​under different illumination intensities. It is noteworthy that the pristine and Ga-doped ZnO devices show differences at 30 μW / cm². 2 It exhibits a significant D* value, which is 7.79 × 10⁻⁶. 11 and 4.18×10 12 Jones. (Like) Figure 6 As shown in Figure g, the normalized spectral response curve confirms the excellent ultraviolet light detection capability of the ZnO:Ga PEC photodetector. The response spectrum estimated by linear extrapolation cuts off at 386 nm. Simultaneously, the ZnO:Ga PEC photodetector exhibits a high ultraviolet / visible light suppression ratio of 63.5, which is twice that of the ZnO PEC photodetector. Figure 8 ).

[0053] 2.3 Performance Enhancement Mechanism Analysis

[0054] Table 1. Calculated carrier concentration and flat-band potential of ZnO and ZnO:Ga nanowires

[0055]

[0056] To gain a deeper understanding of the intrinsic mechanism behind the enhanced PEC performance of ZnO:Ga nanowires, Mott-Schottky (MS) curves and EIS spectra were used to further investigate charge transport and transfer processes. Figure 9 As shown in Figure a, all samples exhibit a positive slope in the MS plot, a typical characteristic of n-type semiconductors. Importantly, the slope shown by the ZnO:Ga nanowires is significantly smaller than that of the ZnO sample, indicating that Ga doping effectively increases the donor density in ZnO. Although the MS curves are derived from a flat electrode model.

[21] While there may be errors in determining the donor density, a qualitative comparison of the slopes of the graphs clearly shows that Ga doping significantly enhances the carrier concentration in ZnO. Furthermore, the donor density (N...) d It can be calculated using the following formula.

[22] :

[0057]

[0058] Where q is the electron charge, ε is the dielectric constant of ZnO (ε = 8.5), ε0 is the dielectric constant of vacuum, V is the applied bias voltage on the electrode, C is the interface capacitance, and N... d This refers to the donor density. Calculations show that the Ng of ZnO and ZnO:Ga nanowires... d The values ​​are 3.04 × 10 17 cm -3 and 1.03×10 19 cm -3 As listed in Table 1. Therefore, the Fermi level of ZnO:Ga nanowires is higher than that of pristine ZnO. The flat band potentials (V) of ZnO and ZnO:Ga nanowires are shown in Table 1. fb It can be determined by the following formula.

[19] :

[0059]

[0060] Where K is the Boltzmann constant and T is the absolute temperature. Figure 9 As shown in Figure a, the flat-band potentials of the original ZnO and ZnO:Ga nanowires are -0.43V and -0.73V, respectively. Therefore, a more negative flat-band potential and N... d The increase in band bending and the reduction in depletion layer width jointly contribute to the formation of steeper band bends at the semiconductor / electrolyte interface. Steeper band bends can enhance charge separation and transfer capabilities at the interface, and can also block electrons and suppress charge recombination at the interface. Based on the above discussion, schematic diagrams of the band structures of ZnO and ZnO:Ga nanowires are drawn, as shown below. Figure 9 As shown in b.

[0061] To further confirm the enhanced charge separation and transport capabilities, the applicant measured the EIS in the frequency range of 0.01–100 kHz, such as Figure 9 As shown in c. The diameter of the semicircle in the EIS spectrum represents the charge transfer resistance (R). ct A smaller diameter means a smaller charge transfer resistance.

[20] It can be seen that the charge transport resistance (R) of the ZnO:Ga photoanode is... ct =62.86KΩ) is much smaller than that of the ZnO photoanode (138.52KΩ), indicating that doping can promote charge transport and separation at the photoanode and electrolyte interface. Furthermore, as Figure 4 As shown, the reduction of the near-band edge (NBE) peak at 385 nm further demonstrates the enhanced photogenerated electron-hole separation efficiency. Overall, these findings provide compelling evidence that the ZnO:Ga sample possesses unique properties, including increased donor density and steeper band bending. This significantly enhances the generation, transfer, and separation of photogenerated carriers, ultimately leading to excellent self-powered ultraviolet photoelectric response behavior.

[0062] 2.4 Effects of solution concentration and external bias voltage on device performance

[0063] Photoelectrochemical photodetectors are highly sensitive to external conditions, providing an effective way to modulate photoresponse behavior. Therefore, the applicant systematically investigated the effects of electrolyte concentration and bias voltage on the photoresponse performance of PEC-PD-based detectors, such as... Figure 10 As shown in Figure ac, ZnO:Ga PEC-PD exhibits good stability and repeatability under different electrolyte concentrations and external bias voltages. Photocurrent density (Ic) P The photocurrent initially increases and then decreases with increasing electrolyte concentration, reaching a maximum at 0.5 M. This can be attributed to the electrolyte concentration affecting mass transfer processes in the redox reaction. Excessively high ion concentrations also hinder oxidation reactions at the photoanode-electrolyte interface, ultimately leading to a decrease in photocurrent. Besides electrolyte concentration, the detector's performance is also highly sensitive to bias voltage. Specifically, the photocurrent density increases from 70.64 μA / cm² at zero bias. 2 The voltage was gradually increased to 134.4 μA / cm at 0.5 V. 2 This is because the bias voltage accelerates the separation and transport of photogenerated carriers in the photoelectrode. 6 ].

[0064] Table 2 Comparison of performance parameters of the present invention and reported PEC-type ultraviolet photodetectors

[0065]

[0066] Response speed is an important parameter for evaluating the photoelectric performance of PEC-PDs. For example... Figure 10 As shown in the figure, the response time of ZnO:GaPEC-PD (rise time ≈ 159 ms, fall time ≈ 150 ms) is shorter than that of ZnO PEC-PD, which is attributed to the enhanced built-in electric field and the smaller charge transport and transfer resistance. Figure 10 Table 2 and section f compare the detectivity and responsivity of self-powered PEC UV PDs from domestic and international sources. In comparison, our device exhibits superior overall performance. In practical applications, maintaining long-term stability of the photodetector across multiple cycles is crucial. Figure 10 The value of g is described at 500 μW / cm 2Under illumination, the continuous on / off response behavior of ZnO:Ga before and after one month of storage (without external bias voltage) was observed. It can be seen that the photocurrent of the ZnO:Ga sample showed almost no decay after a long period of operation (3600 seconds), demonstrating excellent periodicity and stability. After one month of storage, the photocurrent exhibited a decay rate of <10%, showing good long-term stability, indicating that the prepared ZnO photoanode has satisfactory long-term stability and reproducibility.

[0067] 2.5 International Morse Code Transmission Experiment

[0068] Considering the device's excellent PEC photoresponse performance and self-powered capability, the potential application of ZnO:Ga PEC-PD in secure ultraviolet light communication was further explored. The designed system includes a PEC-PD as a self-powered optical signal receiver, and an optical signal generator with a programmable digital power supply and a 365nm UV-LED lamp. Figure 11 ). Figure 12 The diagram in Figure 'a' shows a schematic of a communication system. In the international Morse code system, each letter can be represented as a sequence of dots and hyphens, such as... Figure 13 As shown. First, the periodic ultraviolet light signal consisting of the four letters "CQNU" and the four numbers "1954" is encrypted using a programmable digital power supply with a sequence of dots and hyphens. Then, the ultraviolet signal is wirelessly transmitted in free space and identified by ZnO:Ga PEC-PDs; the received electrical signal waveform is shown below. Figure 12 As shown in Figure b, the waveform of the electrical signal exhibits three communication state sequences consisting of distinct dots, short horizontal lines, and intervals. Decoding these sequences using Morse code reveals the four letters "CQNU" and the four digits "1954". These results strongly demonstrate the feasibility and reliability of ZnO PEC-PD in ultraviolet light communication systems. Since the information is encoded in Morse code and the carrier is ultraviolet light invisible to the human eye, this is a highly secure communication method.

[0069] 3. Summary

[0070] This invention proposes a doping strategy to achieve a highly efficient and stable ZnO-based PEC-type ultraviolet photodetector. Benefiting from the higher donor density and steeper band bending of Ga-doped ZnO nanowires, the generation, transfer, and separation capabilities of photogenerated carriers are enhanced, resulting in a PEC-type photodetector exhibiting ultra-high responsivity (233.26 mA / W) and excellent detectivity (4.18 × 10⁻⁶ W / W). 12This invention demonstrates the device's fast response / recovery time (159 / 150 ms), as well as good repeatability and long-term stability. Furthermore, it confirms the device's potential applications in ultraviolet communication, exhibiting high accuracy in wireless transmission of international Morse code signals, with advantages such as low power consumption and high security. This doping strategy will open a new avenue for designing high-performance, multifunctional PEC-type optoelectronic devices in the future.

[0071] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

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Claims

1. A method for preparing a photoelectrochemical ultraviolet photodetector, characterized in that, It is made by encapsulating Ga-doped ZnO nanowires as photoanodes. The Ga-doped ZnO nanowires are obtained by carbothermal reduction reaction on a silicon substrate using a mixture of zinc oxide, gallium oxide and graphite powder as source materials. The mass ratio of zinc oxide, gallium oxide, and graphite powder is 4:2:6; The silicon substrate should be cleaned using the following method: First, immerse the silicon substrate in hydrofluoric acid for 10 minutes to remove the oxide layer on the surface; then, ultrasonically clean it sequentially with anhydrous ethanol, acetone, and deionized water for 10 minutes each; wherein the volume concentration of the hydrofluoric acid is 1%. The silicon substrate is placed in a tube furnace, the source material is evenly spread on the surface of the silicon substrate, a vacuum is drawn, and a mixture of nitrogen and oxygen is continuously introduced from the inlet of the tube furnace and flows out from the outlet of the tube furnace. The reaction is carried out at 1100℃ for 20 minutes and then naturally cooled to room temperature to obtain Ga-doped ZnO nanowires on the surface of the silicon substrate. The volumetric flow rate ratio of nitrogen to oxygen in the mixed gas is 120:5.

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