Method for preparing dual-band Bi2O2Se / CdS heterojunction photoelectric detector

Abstract

The invention discloses a method for preparing a dual-band Bi2O2Se / CdS heterojunction photoelectric detector, which comprises the following steps of: preparing a Bi2O2Se nanosheet and a CdS nanobelt by using a chemical vapor deposition method, and then preparing the Bi2O2Se / CdS NBs heterojunction photoelectric detector by using a mechanical transfer method in combination with a photoetching method. The dual-band heterojunction photoelectric detector constructed by the Bi2O2Se nanosheets and the CdS nanoribbons shows excellent light detection performance in visible light of 450 nm and near infrared regions of 1150 nm, and has the advantages of high switch ratio, higher responsivity, higher specific detection rate, high external quantum efficiency and fast response speed. Meanwhile, the Bi2O2Se / CdS heterojunction photoelectric detector disclosed by the invention has high-resolution imaging capability, and has great potential in image sensing and encryption application.

Description

Technical Field

[0001] The invention belongs to the field of photoelectric detector preparation, and in particular relates to a method for preparing a dual-band Bi2O2Se / CdS heterojunction photoelectric detector. Background Art

[0002] Layered bismuth oxide calcium oxides (Bi2O2X, including Bi2O2S, Bi2O2Se, and Bi2O2Te) exhibit excellent stability, tunable band structures, and high carrier mobility, making them promising candidates for next-generation electronic devices. Although bulk Bi2O2Se can be easily synthesized via solid-state reactions at high temperatures of 500-850°C, the development of its ultrathin crystal structure has been elusive for decades.

[0003] In recent years, ultrathin nanosheets of Bi2O2Se have been successfully synthesized using chemical vapor deposition (CVD) technology. 2 V -1 s -1 ) and good air stability, low-dimensional Bi2O2Te is an ideal choice for visible-near-infrared photodetection. However, the ultra-thin thickness of Bi2O2Se nanosheets leads to low photocurrent in the device, which makes the on / off ratio and response rate of the photodetector very small, which greatly hinders its further development and application in the field of high-performance photodetection. Constructing heterojunctions to fully utilize the advantages of different materials and their synergistic effects is considered to be one of the effective means to improve the performance of photodetectors and realize dual-band / multi-band detection. In recent years, heterojunction photodetectors with high response rate, fast response speed, wide energy spectrum range and low noise based on Bi2O2Se nanosheets have been reported one after another. However, most reports only focus on the significant improvement of a single performance indicator of the photodetector in a specific narrow band, which limits its further development. Therefore, a lot of work needs to be done to realize photodetectors with excellent comprehensive performance in dual-band / multi-band.

[0004] Meanwhile, although layered Bi2O2Se nanosheets have attracted much attention for their potential applications in electronics and photonics due to their low band gap, high electron mobility, and good air stability, the photocurrent generated by a single Bi2O2Se nanosheet photodetector is relatively low, resulting in a reduced on / off ratio and response rate, thus limiting the overall performance of Bi2O2Se-based photodetectors. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a dual-band Bi2O2Se / CdS heterojunction photodetector, comprising:

[0006] Bi2O2Se nanosheets and CdS nanobelts were prepared by chemical vapor deposition;

[0007] According to the Bi2O2Se nanosheet and the CdS nanobelt, a Bi2O2Se / CdSNBs heterojunction photodetector is prepared by combining a mechanical transfer method with a photolithography method.

[0008] Preferably, the process of preparing Bi2O2Se nanosheets by chemical vapor deposition comprises:

[0009] A quartz tube of 120 cm in length and 50 mm in diameter was used in a dual-temperature zone tube furnace, with Aladdin 99.999% Bi2O3 powder and Aladdin 99.999% Bi2Se3 powder, and 99.999% high-purity argon as carrier gas for the growth process, and the growth substrate was 9-12 cm away from the hot center zone, and the quartz tube was evacuated until a basic pressure of 10 Pa was reached;

[0010] At room temperature, argon gas was purged at a flow rate of 100 sccm to remove O2 impurities;

[0011] The source temperature of the first temperature zone was raised to 710°C and maintained at a base pressure of 20-40 Pa for 30 minutes;

[0012] The fluorophlogopite substrate is placed at a temperature of 500° C. in the second temperature zone, the Bi2O2Se nanosheets are grown on the fluorophlogopite sheet, and then the system is allowed to slowly cool to room temperature.

[0013] Preferably, the process of preparing CdS nanoribbons by chemical vapor deposition comprises:

[0014] 0.02g of CdS powder was placed in a high-purity quartz boat, the silicon substrate was cleaned and dried, and then a layer of gold film was deposited on the surface by sputtering to form catalyst particles;

[0015] Place the quartz boat containing CdS powder in a tube furnace, place the gold-coated silicon substrate 15-20 cm away from the evaporation source, evacuate the air in the system before heating, and then continuously introduce high-purity argon into the growth system at a flow rate of 200 sccm;

[0016] After 10 minutes, the gas flow rate was adjusted to 100 sccm, the temperature of the tube furnace was raised to 950°C, the temperature of the cadmium powder area reached 800°C, and the temperature of the substrate area was maintained at 700°C;

[0017] After 2 h of growth, the Si / SiO2 substrate was allowed to cool naturally to room temperature with argon gas continuously supplied throughout the cooling stage.

[0018] Preferably, according to the Bi2O2Se nanosheets and the CdS nanobelts, the process of preparing the Bi2O2Se / CdSNBs heterojunction photodetector by using a mechanical transfer method combined with a photolithography method comprises:

[0019] The synthesized CdS nanobelts were dispersed in alcohol, then liquid-deposited onto a clean silicon wafer, and then dried in an oven;

[0020] The CdS nanoribbons were transferred onto a micrometer-sized Bi2O2Se silicon wafer using a transfer platform, and then the wafer was spin-coated with photoresist using photolithography technology;

[0021] Titanium / gold electrodes were deposited on a silicon dioxide substrate using an electron beam evaporation system, and the electrode coating samples were finally etched to obtain a Bi2O2Se / CdS heterojunction photodetector.

[0022] Preferably, the photoresist spin coating includes soft baking, exposure, development and post-baking processes.

[0023] Preferably, the minimum conduction band and maximum valence band of the Bi2O2Se nanosheet are -4.21eV and -5.01eV respectively;

[0024] The minimum conduction band and maximum valence band of the CdS nanoribbon are -4.05 eV and -6.50 eV respectively.

[0025] The Fermi level of the CdS nanoribbon is 0.26 eV lower than that of the Bi2O2Se nanosheet.

[0026] Preferably, the Bi2O2Se nanosheets are square, with a maximum size of 100 μm, and a band gap of 0.8 eV;

[0027] All diffraction peaks in the crystal structure of the Bi2O2Se nanosheets conform to the body-centered tetragonal structure;

[0028] The crystal structure of the Bi2O2Se nanosheet is a tetragonal crystal structure;

[0029] The lattice spacing of the tetragonal crystal structure is 0.28 nm.

[0030] Preferably, the performance evaluation indicators of the photodetector include photoresponsivity, specific detectivity and external quantum efficiency;

[0031] The definition expressions corresponding to the photoresponsivity, specific detectivity and external quantum efficiency are:

[0032]

[0033] Where R is the light response rate, D *is the specific detectivity, EQE is the external quantum efficiency, I p is the photocurrent, I d is the dark current, P is the light power density, A is the effective irradiation area, e is the basic charge, h is the Planck constant, c is the speed of light, B is the electrical bandwidth, i noise is the measured noise current, and λ is the incident wavelength.

[0034] Preferably, under 450nm illumination, the maximum on / off current ratio of the heterojunction photodetector is 2.26×10 4 , the photoresponsivity is 6.22×10 4 AW -1 , the specific detection rate is 1.96×10 15 Jones, the peak value of external quantum efficiency is 1.72×10 7 %, under 5V bias condition, the response speed is 50.6μs, the rising response time and falling response time are 50.6μs and 69.3μs respectively.

[0035] Preferably, under 1150 nm illumination, the maximum on / off current ratio of the heterojunction photodetector is 2.57×10 3 , the photoresponsivity is 5.65×10 3 AW -1 , the specific detection rate is 1.78×10 14 Jones, the peak external quantum efficiency is 6.1×10 5 %, the rise response time and fall response time are 1.4ms and 10.8ms respectively.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] The present invention uses chemical vapor deposition to prepare Bi2O2Se nanosheets and CdS nanobelts, and then uses mechanical transfer combined with photolithography to prepare Bi2O2Se / CdSNBs heterojunction photodetectors. The dual-band heterojunction photodetector constructed by Bi2O2Se nanosheets and CdS nanobelts exhibits excellent light detection performance in both visible light (450nm) and near-infrared (1150nm) regions, and has a high switching ratio, higher responsivity, higher specific detection rate, high external quantum efficiency and fast response speed. At the same time, the Bi2O2Se / CdS heterojunction photodetector of the present invention has high-resolution imaging capabilities and great potential in image sensing and encryption applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0039] Figure 1 Schematic diagram of the growth and structural characterization of Bi2O2Se and CdS in an embodiment of the present invention; wherein, (a) is a schematic diagram of the growth of Bi2O2Se nanosheets by CVD and the growth of CdS nanobelts by PVD; (b) is an elemental composition diagram of Bi2O2Se in a scanning electron microscope of Bi2O2Se nanosheets; (c) is an XRD diagram of Bi2O2Se nanosheets; (d) is an ultraviolet-visible absorption spectrum diagram of Bi2O2Se nanosheets; (e) is a Raman spectrum diagram of Bi2O2Se nanosheets; (f) is an atomic HRTEM image of the grown Bi2O2Se nanosheets; and (g) is a SAED diagram of the grown Bi2O2Se nanosheets;

[0040] Figure 2 Graphs showing the photoelectron performance of the Bi2O2Se / CdS heterojunction photodetector of an embodiment of the present invention under 450nm illumination; wherein (a) is a microscopic schematic diagram of the Bi2O2Se / CdS heterojunction photodetector device; (b) is an optical microscope view of the Bi2O2Se / CdS heterojunction photodetector; (c) is a response spectrum graph of the Bi2O2Se / CdS heterojunction photodetector; (d) is an IV curve graph under different light power densities; (e) and (f) are corresponding R and EQE, D* and switching ratio graphs under different light power densities; (g) is the noise spectral density of the Bi2O2Se / CdS photodetector under 5V bias, and the corresponding D* graph at 1Hz and 10KHz; (h) is a corresponding fitting curve graph under different light power densities; (i) is a schematic diagram of the rise time and fall time;

[0041] Figure 3 The photoelectric performance diagram of the Bi2O2Se / CdS heterojunction photodetector of the embodiment of the present invention under 1150nm light illumination; wherein, (a) is an IV curve diagram under different light power densities; (b) and (c) are R, EQE, D* and switch ratio diagrams under different light power densities; (d) is a functional relationship diagram of photocurrent and light intensity; (e) is a rise time and fall time diagram; (f) is a photocurrent diagram generated by a device just prepared and exposed to air for 10 months without packaging under light illumination of 450 and 1150nm wavelengths;

[0042] Figure 4 A comparison diagram of the Bi2O2Se / CdS heterojunction photodetector according to an embodiment of the present invention and other Bi2O2Se-based devices in terms of R, on / off ratio, D* and response time;

[0043] Figure 5488nm laser irradiation, the parameters of the Bi2O2Se / CdS heterojunction photodetector of the embodiment of the present invention; wherein, (a) and (b) are micrographs and corresponding scanning photocurrent diagrams of the Bi2O2Se / CdS device under 488nm laser irradiation; (c) and (d) are schematic diagrams of the energy band structure before and after the heterojunction contact, the Fermi level (E F ), the maximum position of the valence band (E V ) and the conduction band minimum position (E C ) Figure; (e) and (f) are schematic diagrams of the photoexcitation process of the Bi2O2Se / CdS device under different incident light wavelengths;

[0044] Figure 6 The image sensing application diagram of the Bi2O2Se / CdS heterojunction photodetector according to an embodiment of the present invention; wherein, (a) is a schematic diagram of the Bi2O2Se / CdS heterojunction image sensing system; (b) is an imaging result diagram of the letter "U" under 450nm light; (c) is a schematic diagram of a communication system using the Bi2O2Se / CdS heterojunction photodetector as a signal receiver; (d) is a diagram of corresponding signals generated under different conditions; and (e) is a diagram of input and output signals used to transmit the ASCII code "T" in an encrypted communication system. DETAILED DESCRIPTION

[0045] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0047] like Figure 1-2 As shown, this embodiment provides a method for preparing a dual-band Bi2O2Se / CdS heterojunction photodetector, comprising:

[0048] Bi2O2Se nanosheets and CdS nanobelts were prepared by chemical vapor deposition;

[0049] According to the Bi2O2Se nanosheet and the CdS nanobelt, a Bi2O2Se / CdSNBs heterojunction photodetector is prepared by combining a mechanical transfer method with a photolithography method.

[0050] Further, the two-dimensional Bi2O2Se nanosheets of this embodiment are synthesized by chemical vapor deposition (CVD) in a dual-temperature zone tube furnace. The device uses a quartz tube with a length of 120 cm and a diameter of 50 mm. The precursors used are Bi2O3 powder (Aladdin, 99.999%) and Bi2Se3 powder (Aladdin, 99.999%). High-purity argon (99.999%) is used as the carrier gas for the growth process. The growth substrate is 9-12 cm away from the hot center zone.

[0051] The growth conditions and process are as follows: First, the quartz tube is evacuated until a base pressure of 10Pa is reached. At room temperature, argon gas is purged at a flow rate of about 100sccm to remove O2 impurities. In order to obtain a few atomically thin layers of Bi2O2Se, the source temperature in the first temperature zone is increased to about 710°C and maintained at a base pressure of 20-40Pa for 30 minutes. The fluorophlogopite substrate is placed in the second temperature zone at a temperature of about 500°C, and a few layers of Bi2O2Se nanosheets are grown on the fluorophlogopite sheet, and then the system is allowed to slowly cool down to room temperature.

[0052] Furthermore, the process of preparing CdS nanoribbons by chemical vapor deposition in this embodiment includes:

[0053] A total of 0.02 g of CdS powder was placed in a high-purity quartz boat, and the silicon substrate was cleaned and dried, and then a layer of gold film was deposited on its surface by sputtering to form catalyst particles for the growth of CdS nanoribbons at high temperature. The quartz boat with CdS powder was placed in a tube furnace, and the gold-coated silicon substrate was placed about 15-20 cm away from the evaporation source. Before heating, the air in the system was evacuated to avoid contamination of the experimental results. High-purity argon gas was continuously introduced into the growth system, and the flow rate was maintained at 200 sccm. After 10 minutes, the gas flow rate was adjusted to 100 sccm, and the temperature of the tube furnace was raised to 950°C. The temperature of the cadmium powder area reached about 800°C, while the temperature of the substrate area was maintained at about 700°C. After 2 hours of growth, the Si / SiO2 substrate was allowed to cool naturally to room temperature, and argon was continuously supplied throughout the cooling stage to ensure the consistency of the growth conditions of the CdS nanoribbons.

[0054] Furthermore, in order to prepare the Bi2O2Se / CdS heterojunction photodetector, the synthesized CdS nanoribbons were first dispersed in alcohol, and then the solution was deposited onto a clean silicon wafer and dried in an oven. The CdS nanoribbons were transferred to micrometer-sized Bi2O2Se silicon wafers that were previously grown on mica substrates using a transfer platform. Subsequently, the wafers were spin-coated with photoresist using photolithography technology, including soft baking, exposure, development, and post-baking processes. After these steps were completed, titanium (5nm) / gold (25nm) electrodes were deposited on the silicon dioxide substrate using an electron beam evaporation system. Finally, the electrode coating sample was etched to obtain a Bi2O2Se / CdS heterojunction photodetector.

[0055] Furthermore, CdS is a direct bandgap (2.4 eV) semiconductor with environmental stability and good optical properties in the visible light region, and has good application prospects in the fields of photodetectors, field effect transistors and light-emitting diodes. Experimental results show that heterojunction photodetectors exhibit excellent comprehensive performance in both visible and near-infrared regions. Under 450nm illumination, the maximum on / off current ratio of the heterojunction photodetector is 2.26×10 4 , the response rate is as high as 6.22×10 4 AW -1 , the specific detection rate is as high as 1.96×10 15 Jones, the response speed is 50.6μs under 5V bias condition. Under 1150nm light, the on-off ratio of the heterojunction photodetector is 2.57×10 3 , the response rate is as high as 5.65×10 3 AW -1 , the specific detection rate is as high as 1.78×10 14 Jones, with a response speed of 1.4ms under 5V bias. The charge transfer mechanism between the Bi2O2Se / CdS heterojunction was revealed through band alignment and photocurrent diagrams. This heterojunction photodetector not only achieves dual-band detection, but also significantly improves the comprehensive detection performance of each corresponding band compared with other reported Bi2O2Se-based photodetectors, indicating that it can be used in many fields such as environmental monitoring, medical imaging, military reconnaissance and secure optical communications.

[0056] Furthermore, if Figure 1 (a) shows two-dimensional Bi2O2Se nanosheets and CdS nanobelts prepared by chemical vapor deposition (CVD). The Bi2O2Se nanosheets prepared in this example are squares of different sizes, with the largest size being about 100 μm. Figure 1(b) shows the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the prepared Bi2O2Se nanosheets. It can be seen that the surface of the Bi2O2Se nanosheets is very smooth and the Bi, O and Se elements are evenly distributed. The crystal structure of the Bi2O2Se nanosheets was studied by X-ray diffraction (XRD). Figure 1 (c) All diffraction peaks are consistent with the body-centered tetragonal structure (JCPDS: 73-1316), and no impurity peaks are observed in the standard pattern. This proves that the prepared crystal is single-phase and has high purity. Figure 1 (d) shows the UV-visible absorption spectrum of Bi2O2Se, and the band gap of Bi2O2Se nanosheets was measured to be 0.8 eV, which is consistent with the previously reported value. Figure 1 (e) shows the Raman spectrum of Bi2O2Se at 159 cm -1 There is an obvious characteristic peak at the A1g vibration mode. This example further uses transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) to characterize the microstructure of the prepared Bi2O2Se nanosheets. Figure 1 (f)- Figure 1 All the results show that the prepared two-dimensional Bi2O2Se nanosheets have high crystalline quality and the lattice spacing of the tetragonal crystal structure (110) is 0.28nm. Figure 1 The XRD, SEM, TEM, HRTEM and SAED images of the prepared CdS nanobelts are shown, indicating that the prepared CdS nanobelts have high crystalline quality.

[0057] Figure 2 (a) is a schematic diagram of a Bi2O2Se / CdS heterojunction photodetector device. Figure 2 (b) is an optical microscope image of the heterojunction. Figure 2 As shown in (c), the spectral response of the Bi2O2Se / CdS heterojunction photodetector spans the visible to near-infrared range, with obvious peaks at 450nm and 1150nm. In order to evaluate the photoelectric performance of the Bi2O2Se / CdS heterojunction photodetector, this embodiment measures the IV characteristics at different optical power densities in the dark and at 450nm light, with a bias voltage range of -5V to +5V. Figure 2 The logarithmic curve shown in (d) shows that the photocurrent increases with the increase of optical power density. At +5V bias, the maximum on / off ratio reaches 2.26×10 4 , exceeding the reported Bi2O2Se nanosheets (3.12×10 2) and Bi2O2Se / p-Si (reaching 82 at +1V bias), indicating its excellent optical switching performance. In addition, photoresponsivity (R), specific detectivity (D*) and external quantum efficiency (EQE) are key parameters for evaluating the performance of photodetectors, which are defined as follows:

[0058]

[0059] Where R is the light response rate, D * is the specific detectivity, EQE is the external quantum efficiency, I p is the photocurrent, I d is the dark current, P is the light power density, A is the effective irradiation area, e is the basic charge, h is the Planck constant, c is the speed of light, B is the electrical bandwidth, i noise is the measured noise current, and λ is the incident wavelength.

[0060] If we assume that the frequency-independent radio noise is the main contribution to the noise current, D * It can also be written as

[0061]

[0062] Figure 2 (e) and 2(f) show the R, EQE, D*, and on / off ratio of the Bi2O2Se / CdS heterostructure photodetector measured under 450nm light irradiation. It is observed that R, EQE, and D* gradually decrease with increasing light intensity. The results show that the heterostructure photodetector has excellent performance, with peak R, EQE, and D* of 6.22×10 4 AW -1 , 1.72×10 7 % and 1.96×10 15 Jones, all exceeded Bi2O2Se / BP, WSe2 / Bi2O2Se and Bi2O2Se / CsBi3I 10 The corresponding value of EQE greater than 100% in the optoelectronic device may be due to the photoconductivity gain effect caused by interface transition. The on / off ratio increases with the increase of light intensity and reaches a maximum value of 2.26×10 at +5V bias. 4 It should be noted that equation (4) may overestimate the value of D*, so this embodiment also analyzes the noise current spectrum of the device, such as Figure 2 (g) Under 5V bias, the device noise current is mainly dominated by 1 / f noise, which increases from 1.84×10 -22 A 2 Hz -1 Down to 2.72×10 at 10kHz -26 A 2 Hz-1 At a frequency of 1 Hz, the D* of the device is significantly higher, at 1.58×10 14 Jones, increases to 1.42×10 at 10 kHz 15 Jones, close to the value obtained with RF noise, which is consistent with the high detection limit of the photodetector. Figure 2 As shown in (h), the functional relationship between photocurrent and light intensity is fitted as I ph ∝P α The fitting coefficient α = 0.56 indicates a deviation from the ideal value α = 1, which indicates a complex interaction between the effects of defects or impurities in the CdS or Bi2O2Se nanosheets and the induction of trapped states and adsorbed molecules at the Bi2O2Se / CdS interface. These factors trap the photogenerated charges and prevent the absorbed photons from being fully converted into photocurrent, thus explaining the observed sublinear response. To evaluate the charge separation and diffusion capabilities, Figure 2 (i) shows the normalized current versus time curve for a single response cycle. The rise and fall times are defined as the time required for the current to rise or fall between 10% and 90% of the maximum photocurrent. The calculated rise and fall times are 50.6μs and 69.3μs, respectively, indicating that the response speeds of Bi2O2Se / Bi2Se3 and Bi2O2Se / MoSe2 are faster than previously reported values. The improved response speed can be attributed to the high carrier mobility of Bi2O2Se and the established heterojunction that promotes the efficient separation of photogenerated electron-hole pairs.

[0063] This embodiment further studies the performance of the Bi2O2Se / CdS heterostructure photodetector in the near-infrared (NIR) range with a wavelength of 1150 nm. Figure 3 (a) shows the IV curves of the device measured at different optical power densities in the dark and under 1150nm illumination. It can be seen that the photocurrent increases with the increase of light intensity, and the light on / off ratio reaches 2.57×10 at a bias voltage of +5V. 3 Compared with the IV curve of the device under 450nm illumination, the photocurrent under 1150nm illumination is significantly reduced by about one order of magnitude, even at higher light intensity (53.3μW / cm 2 ). In addition, the logarithmic IV curves show asymmetry under both forward and reverse bias, which may be caused by the interface barriers and trapped states at the heterojunction interface. Figure 3 (b)- Figure 3 As shown in (c), similar to the behavior observed under 450 nm illumination, R, EQE, and D* all decrease rapidly with increasing illumination intensity. This is because at higher illumination intensities, the recombination probability of charge carriers is higher and the scattering effect is greater.2 When R, EQE and D* are 5.65×10 3 AW -1 , 6.10×10 5 % and 1.78×10 14 Jones. Figure 3 As shown in (d), the optical power index value α is 0.47, which is smaller than the power index value under 450nm illumination. This is usually caused by the difference between the photon energy and the efficiency of the material absorbing these photons. Figure 3 (e) The calculated rise and fall times are 1.4 ms and 10.8 ms, respectively, which are faster than those of Bi2O2Se / CsBi3I 10 and Bi2O2Se / MoSe2, showing a good response speed. Comparing the performance of the photodetector under visible light (450nm), it was found that its detection ability was weakened in the near-infrared range (1150nm).

[0064] The performance degradation of infrared photodetectors compared to visible light photodetectors can be attributed to several factors: (1) The energy of infrared photons is lower than that of visible light photons, resulting in a lower efficiency in generating electron-hole pairs. (2) The absorption of infrared light usually involves indirect conversion or multi-phonon processes, which are generally less efficient than the direct conversion associated with visible light. (3) Infrared photodetectors are more susceptible to thermal noise during operation, which interferes with the signal and degrades the detection performance. Long-term stability is a key factor in the practical application of photodetectors. Figure 3 (f) is the photocurrent curve of the newly fabricated photodetector exposed to air for 10 months under 450nm and 1150nm light without packaging. Obviously, despite being stored in air for 10 months, the photocurrent of the device changes very little, indicating that the device has excellent long-term stability. To compare the performance of Bi2O2Se-based photodetectors, Figure 4 A summary of previously reported data is listed. Key parameters such as on / off ratio, responsivity, response speed, and specific detectivity of Bi2O2Se / CdS heterostructure photodetectors under 450nm and 1150nm illumination exceed the reported values ​​of most Bi2O2Se-based photodetectors. Therefore, Bi2O2Se / CdS low-dimensional heterostructures with cross-band structures provide a promising platform for improving the performance of dual-band photodetectors in the visible and near-infrared spectra.

[0065] In order to better understand the photoresponse mechanism of Bi2O2Se / CdS heterojunction, the photoresponse of Figure 5 The photodetector in the green area in (a) was scanned for photocurrent plotting. Figure 5(b) The photoresponse in the overlapping region is the strongest, indicating that the photocurrent comes from the heterojunction rather than the Schottky junction effect, and the effective separation of photogenerated electron-hole pairs in the overlapping region. In order to clarify the intrinsic mechanism of the heterojunction photodetector, the energy band arrangement of the Bi2O2Se / CdS heterojunction was further studied. Figure 5 The ultraviolet photoelectron spectroscopy (UPS) results in the figure show that the minimum conduction band (CBM) and maximum valence band (VBM) of Bi2O2Se nanosheets are -4.21eV and -5.01eV, respectively, while the CBM and VBM of CdS nanoribbons are -4.05eV and -6.50eV, respectively. The Fermi level of CdS nanoribbons is 0.26eV lower than that of Bi2O2Se nanosheets, as shown in Figure 2. Figure 5 (c) When Bi2O2Se and CdS are in contact, electrons will enter Bi2O2Se from CdS until their Fermi levels reach equilibrium, thus forming a depletion region and a built-in field pointing to the Bi2O2Se side, as shown in Figure 5 (d) As shown. Under 450nm light, photogenerated carriers exist in both CdS and Bi2O2Se regions. Photogenerated electrons are transferred from CdS to Bi2O2Se with the help of band offset and built-in electric field, and then collected by the electrode. However, photogenerated holes are blocked by the interface barrier and built-in electric field, and still remain in CdS when transferred to the electrode, as shown in Figure 5 (e) As shown. Therefore, in CdS, the accelerated separation of electron-hole pairs greatly reduces their recombination probability, thereby improving the optoelectronic performance of the device. Under 1150nm light, Bi2O2Se absorbs light to generate electron-hole pairs, while in CdS, mechanisms such as defect states, multiphoton absorption and thermal excitation also lead to the generation of a small amount of photogenerated carriers. Figure 5 As shown in (e), these carriers are subsequently transferred to Bi2O2Se, resulting in a heterojunction device with stronger optoelectronic performance than that of a single Bi2O2Se device.

[0066] Considering the high performance of Bi2O2Se / CdS photodetector in visible and near-infrared regions, this embodiment further explores its imaging capability using an image sensing system, such as Figure 6 As shown in (a), a 450nm laser is placed in front of the pattern mask so that the beam illuminates the photodetector through the hollow pattern. The controller adjusts the movement of the mask in the X and Y directions. When the laser scans the pattern mask featuring the letter U, the semiconductor analyzer records the optical response and converts it into an image. Figure 6 As shown in (b), the “U” pattern is successfully reconstructed with high resolution, which indicates that heterojunction photodetectors have great promise for imaging applications.

[0067] Bi2O2Se / CdS heterojunction photodetectors exhibit high performance at both 450nm (visible light) and 1150nm (near infrared) wavelengths, making them ideal candidates for encrypted optical communications. In this system, visible light (450nm) is used as a transmitter, while near infrared light (1150nm) is used to encrypt and transmit information, and the Bi2O2Se / CdS heterojunction photodetector is used as a receiver, such as Figure 6 (c). Figure 6 As shown in (d), the photocurrent signal is transmitted by modulation of visible light and near-infrared light, and its function is similar to the "OR" gate in digital circuits, thereby improving the security of the output information. The confidential data is encoded as binary signals "1" and "0" and transmitted by modulating near-infrared light and visible light; here "1" and "0" correspond to the "on" and "off" states of light, respectively. The input signal "T" is converted into the American Standard Code for Information Interchange (ASCII) (010101010). To further ensure the security of the transmitted information, the input signal "T" is divided into two sequences: S" (010101000) and "Q" (010001010). Then, the signals "S" and "Q" are loaded onto near-infrared and visible light, respectively, and emitted as monochromatic light signals. As a receiving terminal, the device can use its dual-band response characteristics to identify light signals from the two bands, generate photocurrent, and successfully receive the confidential information "T" through subsequent decoding, as shown in Figure 2. Figure 6 (e). It is worth noting that no matter the photodetector designed for monochromatic near-infrared light or visible light, if the accurate transmission information is not available, the wrong code "S" or "Q" will be generated. Obviously, the Bi2O2Se / CdS heterojunction dual-band photodetector has great application potential in imaging systems, which can provide higher confidentiality than single-band photodetectors in future secure communications.

[0068] In summary, this embodiment has developed a dual-band heterostructure photodetector based on two-dimensional Bi2O2Se nanosheets and CdS nanoribbons, which exhibits excellent photoelectric performance in both visible and near-infrared regions. Under 450nm illumination, the photodetector achieves a 6.22×10 4 A / W ultra-high response rate, 2.26×10 4 The high on / off ratio and 15 Jones and 1.72×10 7 % significant ratio detection rate (D * ) and external quantum efficiency (EQE) values. Its response time is also fast, at 50.6μs (rise) and 69.3μs (fall), respectively. Under 1150nm illumination, the device maintains a 5.65×10 3Ultra-high A / W response rate, on / off ratio is 2.57×10 3 , D * and EQE values ​​are 1.78×10 14 Jones and 6.1×10 5 %, and the response times are 1.4ms (rise) and 10.8ms (fall), respectively, which are highly competitive among the reported two-dimensional Bi2O2Se-based photodetectors. In addition, the imaging capabilities of the Bi2O2Se / CdS photodetector were evaluated, and the results showed that it has excellent high-resolution and high-contrast imaging performance. These findings highlight the potential of manufacturing new dual-band high-performance photodetectors based on two-dimensional Bi2O2Se / CdS heterostructures.

[0069] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a dual-band Bi2O2Se / CdS heterojunction photodetector, characterized in that: include: Bi2O2Se nanosheets and CdS nanobelts were prepared by chemical vapor deposition; According to the Bi2O2Se nanosheet and the CdS nanobelt, a Bi2O2Se / CdSNBs heterojunction photodetector is prepared by combining a mechanical transfer method with a photolithography method.

2. The method according to claim 1, characterized in that The process of preparing Bi2O2Se nanosheets by chemical vapor deposition includes: A quartz tube of 120 cm in length and 50 mm in diameter was used in a dual-temperature zone tube furnace, with Aladdin 99.999% Bi2O3 powder and Aladdin 99.999% Bi2Se3 powder, and 99.999% high-purity argon as carrier gas for the growth process, and the growth substrate was 9-12 cm away from the hot center zone, and the quartz tube was evacuated until a basic pressure of 10 Pa was reached; At room temperature, argon gas was purged at a flow rate of 100 sccm to remove O2 impurities; The source temperature of the first temperature zone was increased to 710°C and maintained at a base pressure of 20-40 Pa for 30 minutes; The fluorophlogopite substrate is placed at a temperature of 500° C. in the second temperature zone, the Bi2O2Se nanosheets are grown on the fluorophlogopite sheet, and then the system is allowed to slowly cool to room temperature.

3. The method according to claim 1, characterized in that The process of preparing CdS nanoribbons by chemical vapor deposition includes: 0.02g of CdS powder was placed in a high-purity quartz boat, the silicon substrate was cleaned and dried, and then a layer of gold film was deposited on the surface by sputtering to form catalyst particles; Place the quartz boat containing CdS powder in a tube furnace, place the gold-coated silicon substrate 15-20 cm away from the evaporation source, evacuate the air in the system before heating, and then continuously introduce high-purity argon into the growth system at a flow rate of 200 sccm; After 10 minutes, the gas flow rate was adjusted to 100 sccm, the temperature of the tube furnace was raised to 950°C, the temperature of the cadmium powder area reached 800°C, and the temperature of the substrate area was maintained at 700°C; After 2 h of growth, the Si / SiO2 substrate was allowed to cool naturally to room temperature with argon gas continuously supplied throughout the cooling stage.

4. The method according to claim 1, characterized in that: According to the Bi2O2Se nanosheet and the CdS nanobelt, the process of preparing the Bi2O2Se / CdSNBs heterojunction photodetector by mechanical transfer method combined with photolithography includes: The synthesized CdS nanobelts were dispersed in alcohol, then liquid-deposited onto a clean silicon wafer, and then dried in an oven; The CdS nanoribbons were transferred onto a micrometer-sized Bi2O2Se silicon wafer using a transfer platform, and then the wafer was spin-coated with photoresist using photolithography technology; Titanium / gold electrodes were deposited on a silicon dioxide substrate using an electron beam evaporation system, and the electrode coating samples were finally etched to obtain a Bi2O2Se / CdS heterojunction photodetector.

5. The method according to claim 4, characterized in that The photoresist spin coating includes soft baking, exposure, development and post-baking processes.

6. The method according to claim 1, characterized in that The minimum conduction band and maximum valence band of the Bi2O2Se nanosheet are located at -4.21 eV and -5.01 eV, respectively; The minimum conduction band and maximum valence band of the CdS nanoribbon are located at -4.05 eV and -6.50 eV, respectively. The Fermi level of the CdS nanoribbon is 0.26 eV lower than that of the Bi2O2Se nanosheet.

7. The method according to claim 1, characterized in that The Bi2O2Se nanosheets are square, with a maximum size of 100 μm, and a band gap of 0.8 eV; All diffraction peaks in the crystal structure of the Bi2O2Se nanosheets conform to the body-centered tetragonal structure; The crystal structure of the Bi2O2Se nanosheet is a tetragonal crystal structure; The lattice spacing of the tetragonal crystal structure is 0.28 nm.

8. The method according to claim 1, characterized in that The performance evaluation indicators of the photodetector include photoresponsivity, specific detectivity and external quantum efficiency; The definition expressions corresponding to the photoresponsivity, specific detectivity and external quantum efficiency are: Where R is the light response rate, D * is the specific detectivity, EQE is the external quantum efficiency, I p is the photocurrent, I d is the dark current, P is the light power density, A is the effective irradiation area, e is the basic charge, h is the Planck constant, c is the speed of light, B is the electrical bandwidth, i noise is the measured noise current, and λ is the incident wavelength.

9. The method according to claim 1, characterized in that: Under 450nm illumination, the maximum on / off current ratio of the heterojunction photodetector is 2.26×10 4 , the photoresponsivity is 6.22×10 4 AW -1 , the specific detection rate is 1.96×10 15 Jones, the peak value of external quantum efficiency is 1.72×10 7 %, under 5V bias condition, the response speed is 50.6μs, the rising response time and falling response time are 50.6μs and 69.3μs respectively.

10. The method according to claim 1, characterized in that Under 1150nm illumination, the maximum on / off current ratio of the heterojunction photodetector is 2.57×10 3 , the photoresponsivity is 5.65×10 3 AW -1 , the specific detection rate is 1.78×10 14 Jones, the peak external quantum efficiency is 6.1×10 5 %, the rise response time and fall response time are 1.4ms and 10.8ms respectively.

Images