A multilayer WSe2 thin film photodetector based on mild treatment of hydrogen-argon mixed plasma and its preparation method

Abstract

The present invention discloses a multilayer WSe2 thin film photodetector based on mild treatment of hydrogen-argon mixed plasma and a preparation method thereof. The detector is a two-terminal device that uses a multilayer WSe2 thin film to realize light detection, and the multilayer WSe2 thin film is treated by hydrogen-argon mixed plasma to reduce the number of layers of the WSe2 thin film and repair the intrinsic defects of the multilayer WSe2 crystal. The photodetector of the present invention takes into account the advantages of high detection rate, fast response speed and low dark current, has ultra-high detection sensitivity, and can be used to detect weak light signals.

Description

Technical Field

[0001] The invention belongs to the field of nano functional materials and optoelectronic devices, and in particular relates to a multilayer WSe2 thin film photoelectric detector based on mild treatment of hydrogen-argon mixed plasma and a preparation method thereof. Background Art

[0002] Photodetectors can convert light signals into electrical signals. From a practical point of view, they are of great significance in many innovative technologies in modern society, including video and medical imaging, optical communications, environmental monitoring, military, etc. At present, high-performance photodetectors made of crystalline silicon have visible light and near-infrared (NIR) detection ranges and dominate the optical detection market. However, these detectors usually have serious disadvantages, including large raw material inputs and expensive manufacturing processes. These bulk materials are mostly brittle, making the detectors unsuitable for some novel device concepts, such as special applications that require transparency, flexibility and bendability. The emergence of two-dimensional transition metal halide compounds (TMDs) materials has attracted great attention. Their high transparency, strong light interaction, good flexibility, and easy processing have supplemented the shortcomings of current silicon technology and provided great hope for the realization of high-performance photodetectors. People have a deep understanding of the theoretical mechanisms of photodetectors, including photoconductivity effect, grating pressure effect, photovoltaic effect, photothermoelectric effect and radiation thermal effect. Based on the theoretical mechanism, photodetectors can be divided into two categories: photon (or quantum) detectors (including photoconductors / phototransistors and photodiodes, etc.) and thermal detectors. The photoconductivity effect involves a simple process in which the absorption of photons by the semiconductor generates excess free carriers, which in turn leads to an increase in conductivity. A typical photoconductive device is a semiconductor as a channel, and two ohmic contact metal points are fixed at the two ends of the corresponding channel as source and drain electrodes. The excellent overall performance of the photodetector is usually adjusted by adjusting between gain and response speed (Wang, QH, Kalantar-Zadeh, K., Kis, A., Coleman, JN & Strano, MS Electronics and optoelectronics of two-dimensional transitionmetal dichalcogenides. Nat Nanotechnol 7, 699-712, doi: 10.1038 / nnano.2012.193 (2012).).

[0003] Plasma functionalization provides a fast and simple method to change the crystal structure of on-chip layered materials (such as graphene, black phosphorus, hexagonal boron nitride, etc.), which can achieve large-scale, multi-sampling and rapid adjustment of the optoelectronic properties of devices based on layered semiconductors. However, the specific process conditions of plasma functionalization, such as the specific composition of the plasma used, the treatment time, the location of the plasma glow of the sample to be treated, etc., will have a great impact on the performance of the device (Cheng, C.-C. et al. Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma. Nano Energy 30, 846-852, doi: 10.1016 / j.nanoen.2016.09.010 (2016).; Tosun, M. et al. Air-Stable n-Dopingof WSe2 by Anion Vacancy Formation with Mild Plasma Treatment. ACS Nano 10, 6853-6860, doi: 10.1021 / acsnano.6b02521 (2016).; Zhu, J. et al. Argon Plasma Induced Phase Transition in Monolayer MoS2. J Am Chem Soc 139, 10216-10219, doi:10.1021 / jacs.7b05765(2017).). Summary of the invention

[0004] The present invention discloses a multilayer WSe2 thin film photodetector based on mild treatment of hydrogen-argon mixed plasma and a preparation method thereof. The pure multilayer WSe2 thin film is thinned and surface modified by hydrogen-argon (the volume ratio of the two is 1:9) mixed plasma, so that the obtained photodetector has an ultra-high specific detection rate and a fast response time, and has a smaller dark current, and can better detect weak signals.

[0005] To achieve the purpose, the present invention adopts the following technical solution:

[0006] A multilayer WSe2 thin film photodetector based on mild treatment of hydrogen-argon mixed plasma, characterized in that: the photodetector is a two-terminal device that uses multilayer WSe2 thin films to achieve light detection, and the multilayer WSe2 thin films are treated with hydrogen-argon mixed plasma to reduce the number of layers of the WSe2 thin film and repair the intrinsic defects of the multilayer WSe2 crystal.

[0007] The preparation method of the photodetector described in the present invention is: firstly, a multilayer WSe2 film is grown by atmospheric pressure chemical vapor deposition; then, the multilayer WSe2 film is treated by hydrogen-argon mixed plasma to form a plasma-thinned WSe2 film; finally, an electrode is evaporated on the plasma-thinned WSe2 film to obtain a photodetector. Specifically, the steps include:

[0008] Step 1: Preparation of multilayer WSe2 films

[0009] Selenium powder is placed in the first ceramic boat in the heating zone of the tube furnace, and a mixed powder composed of NaCl and WO3 in a mass ratio of 1:90 is placed in the second ceramic boat in the heating zone of the tube furnace, and the first ceramic boat is placed upstream of the second ceramic boat; a silicon wafer is placed on the second ceramic boat with the crystal surface facing downward; the tube furnace is heated to 900°C under the protection of high-purity argon gas, and then kept warm for 15 minutes in a mixed atmosphere of hydrogen and argon gas; after the growth is completed, it is naturally cooled to room temperature to obtain a multilayer WSe2 film;

[0010] Step 2: Treat multilayer WSe2 films with hydrogen-argon mixed plasma

[0011] In a plasma treatment device, a multilayer WSe2 film is placed 0.5 cm downstream of the tail of the hydrogen-argon mixed plasma glow, and treated with a hydrogen-argon mixed plasma with a volume ratio of hydrogen to argon of 1:9 for 5 to 15 seconds to obtain a plasma-thinned WSe2 film.

[0012] Step 3: Prepare the photodetector

[0013] A pair of source and drain electrodes are made on the plasma-thinned WSe2 film using ultraviolet lithography and electron beam evaporation to form a two-terminal device, that is, a photodetector is obtained.

[0014] Furthermore, in step 1, the mass ratio of selenium powder to mixed powder is 10:1.

[0015] Furthermore, in step 1, the flow rate of argon gas is 100 sccm, and the flow rate of hydrogen gas is 4 sccm.

[0016] Furthermore, in step 3, the source-drain electrodes are Ti / Au electrodes.

[0017] The beneficial effects of the present invention are embodied in:

[0018] The present invention utilizes hydrogen-argon (1:9) mixed plasma to treat WSe2 thin film. The hydrogen-containing plasma tends to form a substoichiometric amount of hydrogen on the surface of WSe2 to repair the intrinsic defects of the material and the atomic layer peeling caused by the body-sheath collision. Hydrogen can be used as a dopant to modify the surface of the multilayer WSe2 film and ultimately control the newly formed hydrogen-doped WSe2 / lower layer WSe2 heterostructure. Compared with the detector that has not been treated with hydrogen-argon mixed plasma, the detection rate, response time and other performance of the detector of the present invention are improved by several orders of magnitude. The device treated with 325nm laser irradiation under 2V bias voltage has a specific detection rate of 7.52×10 11 Jones, the switching response time reaches 61μs and the dark current reaches 4.17×10 -11 A. And the electrical performance of the treated device is more stable under normal temperature and pressure. The photodetector of the present invention has the advantages of high detection rate, fast response speed and low dark current, has ultra-high detection sensitivity, and can be used to detect weak light signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a multilayer WSe2 thin film material grown by atmospheric pressure chemical vapor deposition in Example 1.

[0020] Figure 2 (a) shows the change in thickness of the WSe2 film treated with hydrogen-argon mixed plasma at different times as the treatment time increases in Example 1. Figure 2 (b) shows the change of WSe2 thinning degree when the processing time is 5s, 10s, and 15s. Figure 2 (c) is the AFM image, and the dotted line is the baseline of the test.

[0021] Figure 3 (a) and (b) are XPS curves of the orbital binding energy of Se of the treated and untreated WSe2 thin film crystals prepared in Example 1, respectively.

[0022] Figure 4 The IT characteristic curves of the original sample before treatment and the samples after different treatment times of the photodetector prepared in Example 1 under laser irradiation with a wavelength of 365nm and an optical power of 6.98mW, wherein Figure (a) is the IT curves of the original sample and the sample after treatment, and (b) and (c) are respectively enlarged versions of the graphical curves in Figure (a), as indicated by the arrows in the figure.

[0023] Figure 5 1 and 2 are the rise time and fall time curves of the switch response of the detector with different processing times in Example 1.

[0024] Figure 6The stability test of the optical and electrical properties of the photodetector prepared by WSe2 thin film treated with hydrogen-argon (1:9) mixed plasma for 15s in air was conducted.

[0025] Figure 7 The data shown in (a), (b), (c), and (d) are the changes in dark current, response time, specific detection rate, and equivalent noise power before and after hydrogen-argon (1:9) mixed plasma treatment. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. The specific implementation described here is only used to explain the present invention and is not used to limit the present invention.

[0027] Example 1

[0028] In this embodiment, the photodetector is prepared according to the following steps:

[0029] Step 1: Preparation of multilayer WSe2 films

[0030] The synthesis of WSe2 thin films with multilayer non-uniform thickness was achieved by ambient pressure chemical vapor deposition, and the specific steps were as follows: 1.0 g of selenium powder (Macklin, 99.9%) was placed in the first ceramic boat in the heating zone of the tube furnace, 0.1 g of a mixed powder consisting of NaCl and WO3 (Macklin, 99.99%) in a mass ratio of 1:90 was placed in the second ceramic boat in the heating zone of the tube furnace, and the first ceramic boat was placed 20 cm upstream of the second ceramic boat; 300 nm of SiO 2 / The Si substrate is placed on the second ceramic boat with its polished side; the heating center is placed on the second ceramic boat. Under the protection of 100 sccm of high-purity argon (>99.99%), the tube furnace is heated to 900°C at a heating rate of 20°C / min, and then 4 sccm of hydrogen is introduced and kept warm for 15 minutes of growth; after the growth is completed, it is naturally cooled to room temperature to obtain a multilayer WSe2 film. The uniformly grown multilayer WSe2 film is cut into several samples for subsequent processing.

[0031] Step 2: Treat multilayer WSe2 thin films with hydrogen-argon (1:9) mixed plasma

[0032] In the plasma processing device, a multilayer WSe2 film is placed in a quartz tube. When the reaction system is pumped to a pressure of 35mTorr, a hydrogen-argon mixed plasma is generated with a radio frequency power of 50W. The position of the tail of the plasma glow is marked, and the side on which WSe2 is grown is placed face up 0.5cm downstream of the tail of the plasma glow and treated for different times (0s, 5s, 10s, 15s) (the detector samples obtained later are marked in the figure as Pristine, H2-Ar plasma 5s, H2-Ar plasma10s, and H2-Ar plasma 15s, respectively).

[0033] Step 3: Preparation of optoelectronic devices

[0034] UV lithography and electron beam evaporation were used to make a pair of Ti (5nm) / Au (50nm) electrodes (5nm Ti was first evaporated, and then 50nm Au was evaporated) on the WSe2 film after plasma thinning for different times as source and drain electrodes (channel is 5 microns), forming a two-terminal device, that is, a photodetector was obtained. The photoconductive response of the device was measured at room temperature using a semiconductor parameter analyzer (KEITHLEY 2636B SYSTEM), and a 365nm laser was used during the measurement process.

[0035] Figure 1 The multilayer WSe2 thin film material prepared in this embodiment has a substrate of a silicon wafer with a crystal orientation (100) oxide layer thickness of 300nm, and the size of the continuous WSe2 thin film is about 1.0cm×0.5cm (as shown in the dotted box in the figure). After plasma treatment, only a small number of WSe2 layers are peeled off at the atomic scale, and no physical damage is caused to the material itself (such as surface etching holes, etc.).

[0036] Figure 2 (a) shows the change in thickness of the WSe2 film treated with hydrogen-argon mixed plasma for different time periods as the treatment time increases. Figure 2 (b) shows the change of WSe2 thinning degree when the processing time is 5s, 10s, and 15s. Figure 2 (c) is an AFM image, and the dotted line is the baseline of the test. The thickness of WSe2 thinned to the maximum when the plasma exposure reached 15s, which was about 10nm. The total spacing between the single layer of WSe2 and the adjacent layers was about 1.5nm. Therefore, after 15s of hydrogen-argon (1:9) mixed plasma treatment, the number of peeled layers was about several layers.

[0037] Figure 3(a) and (b) are XPS curves of Se orbital binding energy of treated and untreated WSe2 thin film crystals prepared in Example 1, respectively. The orbital binding energy of the double lines of Se3d5 / 2 and Se3d3 / 2 changed from 54.98eV and 55.86eV of the original sample to 54.14eV and 54.87eV after hydrogen-argon (1:9) mixed plasma treatment, respectively. The difference in orbital binding energy is due to the role played by the hydrogen element in the hydrogen-argon plasma stripping process. The hydrogen element hydrogen bonds with the atomic vacancies on the surface of WSe2. When new valence bonds are formed, the increase in the electron density around the new chemical bonds makes the repulsion between electrons stronger, so that the orbital binding energy of the WSe2 thin film crystal treated with hydrogen-argon plasma is slightly higher than that of the original WSe2.

[0038] Figure 4 The photodetector prepared in Example 1 is irradiated with a laser of 365 nm and a light power of 6.98 mW, and the IT characteristic curves of the original sample before treatment and samples with different treatment times, wherein Figure (a) is the IT curve of the original sample and the sample after treatment, and (b) and (c) are respectively the enlarged curves of the graph in Figure (a), as indicated by the arrows in the figure. The photoelectric performance of the original WSe2 sample is extremely unstable, with a long switching response time (>5s) and a high dark current (>2*10 -6 A). The IT characteristics of the treated WSe2 thin film device significantly improved the deficiency of the original WSe2 sample. The mechanism of this effect can be explained as the plasma stripping the sample layers while participating in the WSe2 surface reconstruction process, making the atomic vacancies on the WSe2 surface less defective and more flat, optimizing the free carrier transport behavior and exciton effect on the WSe2 surface, improving the photoelectric performance of the WSe2 thin film device, and also facilitating the contact between the metal electrode and the sample.

[0039] Figure 5 The rise time and fall time curves of the detector with different treatment times in Example 1, (a), (b), and (c) correspond to the fast switching response of hydrogen-argon mixed plasma treatment for 5s, 10s, and 15s, respectively. When the treatment is 15s, the fast response performance of the device is the best, and the turn-on time and turn-off time remain relatively balanced, while the rise time and fall time of the samples treated for 5s and 10s are unbalanced.

[0040] Figure 6The stability test of the optical and electrical properties of the photodetector prepared by the WSe2 film treated with hydrogen-argon (1:9) mixed plasma for 15s in air. This example characterizes the IT characteristics of the device treated with hydrogen-argon mixed plasma for 15s and placed in air for a period of time. After two months, it still maintains relatively stable electrical properties. The mechanism of its stability is that hydrogen doping reduces the atomic vacancies in the WSe2 sample, and the disappearance of the dangling bonds originally existing in the vacancies enhances the stability of the device.

[0041] Figure 7 The data shown in (a), (b), (c), and (d) are the changes in dark current, response time, specific detection rate, and equivalent noise power before and after hydrogen-argon (1:9) mixed plasma treatment. The device performance after hydrogen-argon plasma treatment for 15s is the best, far superior to the original WSe2 thin film photoelectric device, and the dark current obtained is smaller (about 4.17E -11 A), the switch response speed is faster (the response time is about 6.1×10 -5 s), with a higher detection rate (7.52×10 11 Jones). This device with extremely low dark current and high specific detection rate is more friendly to detecting weak signals in the environment.

[0042] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multilayer WSe2 thin film photodetector based on mild treatment of hydrogen-argon mixed plasma, characterized in that: The photodetector is a two-terminal device that uses a multilayer WSe2 film to achieve light detection, and the multilayer WSe2 film is treated with a hydrogen-argon mixed plasma with a volume ratio of hydrogen to argon of 1:9 to reduce the number of layers of the WSe2 film and repair the intrinsic defects of the multilayer WSe2 crystal.

2. A method for preparing the photoelectric detector according to claim 1, characterized in that: First, a multilayer WSe2 film is grown by atmospheric pressure chemical vapor deposition. Then, the multilayer WSe2 film is treated by a hydrogen-argon mixed plasma with a volume ratio of hydrogen to argon of 1:9 to form a plasma-thinned WSe2 film. Finally, an electrode is evaporated on the plasma-thinned WSe2 film to obtain a photodetector.

3. The method for preparing a photoelectric detector according to claim 2, characterized in that: The specific steps include: Step 1: Preparation of multilayer WSe2 films Selenium powder is placed in the first ceramic boat in the heating zone of the tube furnace, and a mixed powder composed of NaCl and WO3 in a mass ratio of 1:90 is placed in the second ceramic boat in the heating zone of the tube furnace, and the first ceramic boat is placed upstream of the second ceramic boat; a silicon wafer is placed on the second ceramic boat with the crystal surface facing downward; the tube furnace is heated to 900°C under the protection of high-purity argon gas, and then kept warm for 15 minutes in a mixed atmosphere of hydrogen and argon gas; after the growth is completed, it is naturally cooled to room temperature to obtain a multilayer WSe2 film; Step 2: Treat multilayer WSe2 films with hydrogen-argon mixed plasma In a plasma treatment device, a multilayer WSe2 film is placed 0.5 cm downstream of the tail of the hydrogen-argon mixed plasma glow, and treated with a hydrogen-argon mixed plasma with a volume ratio of hydrogen to argon of 1:9 for 5 to 15 seconds to obtain a plasma-thinned WSe2 film. Step 3: Prepare the photodetector A pair of source and drain electrodes are made on the plasma-thinned WSe2 film using ultraviolet lithography and electron beam evaporation to form a two-terminal device, that is, a photodetector is obtained.

4. The preparation method according to claim 3, characterized in that: In step 1, the mass ratio of selenium powder to mixed powder is 10:

1.

5. The preparation method according to claim 3, characterized in that: In step 1, the flow rate of argon gas is 100 sccm, and the flow rate of hydrogen gas is 4 sccm.

6. The preparation method according to claim 3, characterized in that: In step 3, the source-drain electrodes are Ti / Au electrodes.

Images