A PbSe thin film Schottky junction detector, a preparation method thereof and an application thereof

Abstract

A PbSe thin film Schottky junction detector, a preparation method and an application thereof according to the present invention include a strontium titanate substrate, a PbSe thin film on the strontium titanate substrate, a graphene sheet transferred to one end of the PbSe thin film, and electrodes are respectively prepared on the PbSe thin film and the graphene sheet. The electrodes on the PbSe thin film and the graphene sheet are a source electrode and a drain electrode respectively; the source electrode and the drain electrode are a composite electrode of lower layer metal Cr and upper layer metal Au. The PbSe thin film and the graphene respectively form a Schottky junction and an ohmic contact with Cr, and a PbSe thin film Schottky junction detector is prepared. The present invention has high specific detectivity and high sensitivity gas detection in the room temperature mid-wave infrared range, and at the same time, the device is miniaturized and has low power consumption, which is convenient for integration and suitable for multi-scenario applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic detection, and particularly relates to a PbSe thin film Schottky junction detector, a preparation method thereof, and an application thereof. Background Art

[0002] Gas detection plays a very important role in the production of industrial enterprises. It is the key to preventing accidents and ensuring the smooth progress of enterprise production safety, and is the guarantee for the safety of production personnel and surrounding people. An infrared gas detector is a gas sensing device that detects gas components and determines their concentrations based on the infrared spectral selective absorption characteristics of different gas molecules and the relationship between gas concentration and absorption intensity.

[0003] PbSe is a direct bandgap material with advantages such as high electron mobility, high light absorption coefficient, and high stability. It shows a narrow bandgap of about 0.27 eV at room temperature and is thus widely used in mid-infrared detectors. However, the response time of PbSe phototransistors is relatively long, which limits their use in application scenarios that require fast response. With the increase in light intensity, the responsivity and detectivity of PbSe phototransistors will gradually decrease, and the sensitivity of the device may decrease under strong light irradiation. There are still certain limitations in the sensitivity and selectivity of PbSe. Summary of the Invention

[0004] The first object of the present invention is to provide a PbSe thin film Schottky junction detector for the problems in the prior art.

[0005] To achieve the above object of the present invention, the following technical solutions are adopted:

[0006] A PbSe thin film Schottky junction detector, characterized in that: it includes a strontium titanate substrate, a PbSe thin film on the strontium titanate substrate, a graphene sheet transferred to one end of the PbSe thin film, electrodes are respectively prepared on the PbSe thin film and the graphene sheet, and the electrodes on the PbSe thin film and the graphene sheet are a source electrode and a drain electrode respectively; the source electrode and the drain electrode are a composite electrode of a lower layer of metal Cr and an upper layer of metal Au, the PbSe thin film and the graphene sheet respectively form a Schottky junction and an ohmic contact with Cr, and a PbSe thin film Schottky junction detector is prepared.

[0007] While adopting the above technical solutions, the present invention can also adopt or combine the following technical solutions:

[0008] As a preferred technical solution of the present invention: the strontium titanate substrate is a sheet-like structure with a size of 1 cm × 1 cm.

[0009] As a preferred technical solution of the present invention: the PbSe thin film is a single crystal thin film with a thickness of 80 nm, and its size is about 30 μm × 100 μm.

[0010] As a preferred technical solution of the present invention: the graphene flakes are flakes with a thickness of 15 nm.

[0011] As a preferred technical solution of the present invention: in the source electrode and the drain electrode, the thickness of the metal Cr is 15 nm respectively, and the thicknesses of the metal Au are 15 nm and 45 nm.

[0012] The second object of the present invention is to provide a method for a PbSe thin film Schottky junction detector in view of the problems in the prior art.

[0013] For this reason, the above object of the present invention is achieved by the following technical solutions:

[0014] A preparation method of a PbSe thin film Schottky junction detector includes the following steps:

[0015] S1, growing single-crystal PbSe thin film by CVD;

[0016] S2, etching the PbSe small-size thin film into a rectangular strip with dimensions of 30 μm×100 μm;

[0017] S3, preparation and transfer of graphene flakes. Use tape to prepare graphene flakes with different thicknesses by mechanical exfoliation method, transfer them to a glass slide coated with PDMS, and then transfer the graphene flakes on the PMDS to the PbSe thin film at a fixed point through a transfer platform;

[0018] S4, preparation of source and drain electrodes for the PbSe thin film and graphene flakes. Spin-coat AZ5214 photoresist on the substrate surface, expose the electrode pattern by laser direct writing mask, and then thermally evaporate and deposit Cr and Au with different thicknesses.

[0019] While adopting the above technical solutions, the present invention can also adopt or combine the following technical solutions:

[0020] As a preferred technical solution of the present invention: step S1 includes the following steps:

[0021] S101, using high-purity PbSe powder (Sigma-Aldrich, 99.99%) as a compensation source for the selenium content in the thin film;

[0022] S102, place the boat with PbSe powder in the middle of the quartz tube, place the Se powder as a compensation source upstream of the quartz tube, place the strontium titanate substrate downstream of the carrier gas Ar, heat the lead selenide in the quartz tube to 750 °C for 75 minutes, and keep growing at a temperature of 8.6×10 -2 pa for 5 minutes. After the growth is completed, let it cool naturally to obtain the PbSe thin film.

[0023] Among them, the PbSe powder is lead selenide powder with a purity of 99.99%.

[0024] The third object of the present invention is to provide an application of a PbSe thin film Schottky junction detector in view of the problems in the prior art.

[0025] To achieve the above object, the present invention is realized by the following technical solutions:

[0026] The application of the PbSe thin film Schottky junction detector is applied to a room temperature mid-wave infrared high specific detectivity and high sensitivity gas detection system. In the system, a light source emits light with a specific wavelength. When passing through the gas chamber, the target gas will absorb a part of the light, and the unabsorbed light reaches the PbSe thin film Schottky junction detector. The PbSe thin film Schottky junction detector converts the optical signal into an electrical signal, and the signal processing module processes the electrical signal output by the PbSe thin film Schottky junction detector, and calculates the concentration or other relevant parameters of the target gas according to the attenuation degree of the optical signal.

[0027] Compared with the prior art, an optoelectronic detector, a preparation method and an application thereof based on a PbSe thin film Schottky junction of the present invention have the following beneficial effects: In the present invention, Cr metal and graphene flakes are respectively used as the PbSe thin film contact electrodes. A metal-semiconductor contact is formed between the Cr metal and the PbSe thin film to generate a Schottky barrier. An ohmic contact is formed between the graphene flake and the PbSe thin film to form a single Schottky junction detector. Under illumination conditions, the photo-generated carriers generated inside the PbSe are separated under the drive of the built-in electric field formed at the Cr-PbSe contact interface. By utilizing the high electron mobility and low resistance characteristics of graphene, effective electron collection is realized. At the same time, the low resistance at the ohmic contact formed by graphene and PbSe is used to realize the near-lossless transport of electrons, thereby improving the conductivity of the device. In the present invention, the Schottky barrier formed at the Cr-PbSe contact interface will block the drift of majority carrier electrons, but this structure is beneficial to the transport of minority carrier holes. By the transport of these minority carrier holes, the noise current is reduced at room temperature. Therefore, the present invention uses the PbSe thin film and the graphene flake to form a Schottky junction and an ohmic contact with the Cr metal respectively, and realizes a low noise current and high detection performance of the PbSe detector at room temperature without cryogenic refrigeration. The large-area PbSe thin film is grown by CVD technology. The thickness distribution of the PbSe thin film is uniform and has a low defect density, and has good single crystal properties. The optoelectronic detector based on the PbSe thin film Schottky junction of the present invention simplifies the manufacturing process of the detector, reduces the structural complexity and energy consumption of the device, and provides the possibility for the wide application of the PbSe thin film detector.

[0028] The PbSe thin film Schottky junction detector of the present invention has a device response cutoff at 4 μm under room temperature optoelectronic testing, with a low-noise current of 4.2×10 -27 A 2 Hz -1 and a specific detectivity of 7.58×10 9 cm Hz 1 / 2 W −1 optoelectronic performance. Under the built gas detection system, methane and propane gases can be detected respectively, achieving the lowest ppB-level detection, realizing sensitive gas detection, possessing high specific detectivity and high sensitivity for gas detection at room temperature in the mid-wave infrared range. At the same time, the device is miniaturized and low-power, facilitating integration and adapting to multi-scenario applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic cross-sectional view of a PbSe thin film Schottky junction detector of the present invention;

[0030] In the drawings, the PbSe thin film Schottky junction detector 100; the strontium titanate substrate 1; the PbSe thin film 3; the graphene sheet 4; the source electrode 2; the drain electrode 5;

[0031] Figure 2 is the gas detection system;

[0032] In the drawings, the light source 6; the gas chamber 7; the inlet 8; the outlet 9; the target gas 10; the signal processing module 11;

[0033] Figure 3a is a scanning electron microscope (STEM) cross-sectional view of Graphene / PbSe, Figure 3b is the energy band mechanism diagram of the PbSe thin film Schottky junction detector, Figure 3c is the I-V characteristic curve diagram of the PbSe thin film Schottky junction detector, Figure 3d is the I-V characteristic curve diagram with both ends of the electrodes being graphene, Figure 3e is the noise current diagram of the PbSe thin film Schottky junction detector;

[0034] Figure 4a is the specific detectivity and responsivity spectrum diagram of the PbSe thin film Schottky junction detector at room temperature of 1200 K, Figure 4b is the linear fitting diagram for methane gas detection and its detection sensitivity limit, Figure 4c is the linear fitting diagram for propane gas detection and its detection sensitivity limit. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. Embodiment 1

[0036] AsFigure 1 As shown in the figure, a PbSe thin film Schottky junction detector for gas detection and its preparation method according to the present invention. A Schottky junction and an ohmic contact are respectively formed by a PbSe thin film with Cr and graphene, and a PbSe thin film Schottky junction detector is prepared. This device has high specific detectivity and high-sensitivity gas detection performance in the mid-wave infrared range at room temperature.

[0037] The structure of the detector is as follows: A graphene sheet 4 is transferred to one end of the PbSe thin film 3 on the strontium titanate substrate 1, and electrodes are respectively prepared on the PbSe and graphene. The electrodes on the PbSe thin film and graphene are the source electrode 2 and the drain electrode 5 respectively.

[0038] The strontium titanate substrate 1 is a piece with a size of 1 cm × 1 cm;

[0039] The PbSe thin film 3 is a single crystal thin film with a thickness of about 80 nm and a size of about 30 μm × 100 μm;

[0040] The graphene sheet 4 is a sheet with a thickness of about 15 nm;

[0041] The source electrode 2 or the drain electrode 5 is metal Cr and metal Au, with thicknesses of about 15 nm and 45 nm respectively.

[0042] As Figure 2 shown, the gas detection system is composed of: a light source 6, a gas chamber 7, an inlet 8 and an outlet 9, a target gas 10, a PbSe thin film Schottky junction detector 100, and a signal processing module 11.

[0043] The light source 6 is a blackbody radiation light source, with the model number HFY-200B.

[0044] The gas chamber 7 is a cylinder with a pore diameter of 5 cm and a length of 20 cm.

[0045] The inlet 8 and the outlet 9 are cylinders with a pore diameter of 1 cm and a length of 4 cm.

[0046] The light source 6: Used to generate an optical signal, usually infrared light, to excite the specific absorption characteristics of the target gas.

[0047] The gas chamber 7: A space for accommodating the target gas to ensure that the optical signal can fully contact the gas.

[0048] The inlet 8 and the outlet 9: Used to introduce and discharge the target gas into and out of the gas chamber to achieve the flow and renewal of the gas.

[0049] The target gas 10: A specific gas to be detected, and its absorption characteristics will be measured.

[0050] PbSe thin-film Schottky junction detector 100: used to detect the change in the intensity of the optical signal after passing through the gas chamber.

[0051] Signal processing module 11: responsible for receiving the signal output by the detector, amplifying, filtering, and analyzing it, and finally providing the detection result.

[0052] The light source 6 emits light of a specific wavelength. When passing through the gas chamber 7, the target gas 10 will absorb a part of the light.

[0053] The unabsorbed light reaches the PbSe thin-film Schottky junction detector 100, and the PbSe thin-film Schottky junction detector 100 converts the optical signal into an electrical signal. The signal processing module 11 processes the electrical signal output by the PbSe thin-film Schottky junction detector 100 and calculates the concentration of the target gas or other relevant parameters according to the attenuation degree of the optical signal.

[0054] The present invention proposes a preparation method based on a PbSe thin-film Schottky junction detector, and the steps are as follows:

[0055] S1, CVD growth of single-crystal PbSe thin film:

[0056] Place the boat containing PbSe powder (Sigma-Aldrich, 99.99%) in the middle of the quartz tube. The Se (Sigma-Aldrich, 99.99%) powder is placed as a compensation source upstream of the quartz tube. The strontium titanate substrate is placed downstream of the carrier gas Ar. The lead selenide in the quartz tube is heated to 750 °C for 75 minutes. Keep growing at a temperature of 8.6×10-2 pa for 5 minutes, and then let it cool naturally.

[0057] S2, etching of small-size PbSe thin film:

[0058] Use an ultraviolet maskless lithography machine to perform lithography on the PbSe thin film. The thin film is etched by a plasma etching machine to obtain a rectangular strip with a shape of 30 μm × 100 μm.

[0059] S3, preparation and transfer of graphene flakes:

[0060] Use tape to prepare graphene flakes with different thicknesses by mechanical exfoliation method, transfer them to a glass slide coated with PDMS, and then transfer the graphene flakes on PMDS to the PbSe thin film at a fixed point through a transfer platform.

[0061] S4, preparation of source and drain electrodes for PbSe thin film and graphene flakes:

[0062] Spin coat AZ5214 photoresist on the surface of the wafer, expose the electrode pattern by laser direct writing mask exposure, and then evaporate Cr and Au with different thicknesses (the thicknesses of Cr and Au are about 15 nm and 45 nm respectively) by thermal evaporation.

[0063] In this application, CVD is chemical vapor deposition, which is a technique for depositing thin films on solid surfaces using chemical reactions.

[0064] An PbSe thin film Schottky junction detector according to the present invention has the following operating steps in gas detection applications:

[0065] 1. Turn on the system power. Turn on the light source 6 and turn on the power supply g of the signal processing module.

[0066] 2. Introduce the target gas. Introduce the target gas 10 from the inlet 8 so that it gradually fills the gas chamber 7. After filling, the excess target gas 10 is discharged from the outlet 9.

[0067] 3. Place and adjust the detector. Place the PbSe thin film Schottky junction detector 100, adjust the position of the detector so that it is on the same horizontal reference line as the radiation optical path, and ensure that the detector can generate a photoelectric signal and transmit it to the signal processing module g.

[0068] 4. Change the concentration of the target gas. By introducing a certain concentration of nitrogen into the gas chamber 7, the target gas 10 with the corresponding concentration is discharged, thereby achieving a change in the concentration of the target gas 10.

[0069] 5. Detect the gas concentration detection limit of the detector. Since the target gas 10 will absorb the light radiated by the light source 6, the light intensity irradiating the PbSe thin film Schottky junction detector 100 will become weaker, and further cause the photoelectric signal generated by the PbSe thin film Schottky junction detector 100 to become weaker. Therefore, at different concentrations of the target gas 10, collect the photoelectric signals with different intensities generated by the PbSe thin film Schottky junction detector 100. The photoelectric signals are transmitted to the signal processing module 11, and the signal processing module 11 performs linear fitting on the photoelectric signals and calculates the gas concentration detection limit.

[0070] After preparing the PbSe thin film Schottky junction detector, by testing the room temperature photoresponse spectrum line and calculating the specific detectivity of the device, it shows a high specific detectivity. Through the gas detection system, methane and propane gases can be detected respectively, and the detection can reach the lowest ppB level, realizing sensitive detection of gases.

[0071] As Figure 3a shown, the PbSe thin film grown by CVD has good single crystallinity when observed under a scanning transmission electron microscope (STEM). As Figure 3bAs shown, from the perspective of the device energy band, a Schottky junction is formed due to the band bending at the PbSe and Cr contact region, while a good Ohmic contact is formed at the contact region with graphene. As Figure 3c shown, when testing the I-V characteristic curve of the PbSe thin film Schottky junction detector without light illumination, it has certain rectifying characteristics, indicating the formation of the Schottky junction. If both electrodes on both sides are graphene, when testing the I-V characteristic curve under the same conditions, as Figure 3d shown, the curve shows very linearity, proving that the contact between graphene and PbSe is an Ohmic contact. When testing the spectral noise current of the device, as Figure 3e shown, from the test results, the noise current is 4.2×10 -27 A 2 Hz -1 , and the device has a very low noise current. As Figure 4a shown, by testing the room-temperature optical response spectrum line and calculating the specific detectivity of the device, the peak specific detectivity is 7.58×10 9 cm Hz 1 / 2 W −1 , indicating a relatively high specific detectivity. As Figure 4b and Figure 4c shown, through the gas detection system, methane and propane gases can be detected respectively, and the detection can reach the lowest ppB level, realizing sensitive detection of gases.

[0072] Compared with the prior art, the PbSe thin film Schottky junction detector of the present invention: prepares a Schottky junction detector through a single-crystalline PbSe thin film grown by CVD, has a high specific detectivity in the room-temperature mid-wave infrared, and at the same time has the advantages of miniaturization, low power consumption, and high-sensitivity detection of the device, is convenient for integration and adapts to multi-scenario applications.

[0073] The above specific embodiments are used to explain and illustrate the present invention, and are only the preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and scope of the protection of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A PbSe thin film Schottky junction detector, characterized in that: The invention comprises a strontium titanate substrate, a PbSe film on the strontium titanate substrate, a graphene sheet transferred to one end of the PbSe film, electrodes are prepared on the PbSe film and the graphene sheet respectively, the electrodes on the PbSe film and the graphene sheet are a source electrode and a drain electrode respectively; the source electrode and the drain electrode are composite electrodes formed by stacking a lower metal Cr and an upper metal Au. Cr metal and graphene sheets are used as contact electrodes of PbSe film respectively. Metal-semiconductor contact is formed between Cr metal and PbSe film to generate Schottky barrier, and ohmic contact is formed between graphene sheet and PbSe film.

2. The PbSe thin film Schottky junction detector according to claim 1, characterized in that: The strontium titanate substrate is a sheet-like structure with a size of 1 cm×1 cm.

3. The PbSe thin film Schottky junction detector according to claim 1, characterized in that: The PbSe film is a single crystal film with a thickness of 80 nm and a size of 30 μm×100 μm.

4. The PbSe thin film Schottky junction detector according to claim 1, characterized in that: The graphene sheet is a sheet with a thickness of 15 nm.

5. The PbSe thin film Schottky junction detector according to claim 1, characterized in that: In the source electrode and the drain electrode, the thickness of metal Cr is 15 nm, and the thickness of metal Au is 45 nm.

6. Application of the PbSe thin film Schottky junction detector according to any one of claims 1 to 5, characterized in that: It is applied to a room temperature medium-wave infrared high-ratio detection rate and high-sensitivity gas detection system. In the system, a light source emits light of a specific wavelength. When passing through the air cavity, the target gas absorbs part of the light, and the unabsorbed light reaches the PbSe thin film Schottky junction detector. The PbSe thin film Schottky junction detector converts the optical signal into an electrical signal. The signal processing module processes the electrical signal output by the PbSe thin film Schottky junction detector and calculates the concentration of the target gas according to the attenuation degree of the optical signal.

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