PbSe thin film Schottky junction detector, preparation method and application of PbSe thin film Schottky junction detector

Abstract

The invention discloses a PbSe thin film Schottky junction detector, a preparation method and application thereof. The PbSe thin film Schottky junction detector comprises a strontium titanate substrate, a PbSe thin film on the strontium titanate substrate, a graphene sheet transferred at one end of the PbSe thin film, and electrodes prepared on the PbSe thin film and the graphene sheet respectively. The electrodes on the PbSe thin film and the graphene sheet are respectively a source electrode and a drain electrode; the source electrode and the drain electrode are lower-layer metal Cr and upper-layer metal Au composite electrodes, the PbSe thin film and the graphene form Schottky junction and ohmic contact with Cr respectively, and the PbSe thin film Schottky junction detector is prepared. The device has the advantages of room-temperature medium-wave infrared high-ratio detection rate and high-sensitivity gas detection, and meanwhile, the device is miniaturized, low in power consumption, convenient to integrate and suitable for multi-scene application.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detection, and in particular relates to a PbSe thin film Schottky junction detector, a preparation method 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 prevent accidents and ensure the smooth operation of enterprise safety production. It is also the guarantee of the safety of production personnel and surrounding people. Infrared gas detector is a gas sensing device that detects gas components and determines their concentration based on the selective absorption characteristics of infrared spectra of different gas molecules and the relationship between gas concentration and absorption intensity.

[0003] PbSe is a direct bandgap material with the advantages of high electron mobility, high light absorption coefficient and high stability. It shows a narrow bandgap of about 0.27 eV at room temperature, so it is 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. As the light intensity increases, the response rate and detection rate of PbSe phototransistors will gradually decrease, and the sensitivity of the device may decrease under strong light. PbSe still has certain limitations in sensitivity and selectivity. Summary of the invention

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

[0005] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: A PbSe thin film Schottky junction detector is characterized in that it comprises a strontium titanate substrate, a PbSe thin film on the strontium titanate substrate, a graphene sheet is transferred to one end of the PbSe thin film, electrodes are prepared on the PbSe thin film and the graphene sheet respectively, 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 metal Cr and an upper metal Au, the PbSe thin film and the graphene sheet form a Schottky junction and an ohmic contact with Cr respectively, and a PbSe thin film Schottky junction detector is prepared.

[0006] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: the strontium titanate substrate is a sheet structure with a size of 1 cm×1 cm.

[0007] As a preferred technical solution of the present invention: the PbSe film is a single crystal film with a thickness of 80 nm and a size of about 30 μm×100 μm.

[0008] As a preferred technical solution of the present invention: the graphene sheet is a sheet with a thickness of 15 nm.

[0009] 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, and the thickness of the metal Au is 15 nm and 45 nm respectively.

[0010] 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.

[0011] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: A method for preparing a PbSe thin film Schottky junction detector comprises the following steps: S1, single-crystalline PbSe thin film grown by CVD; S2, etching of small-size PbSe thin films into rectangular strips of 30 μm × 100 μm; S3, graphene flake preparation and transfer, using tape, a mechanical exfoliation method to prepare graphene flakes of different thicknesses, transfer them to a glass slide covered with PDMS, and then transfer the graphene flakes on PMDS to the PbSe film through a transfer platform; S4, PbSe film and graphene sheet source and drain electrodes are prepared, AZ5214 photoresist is spin-coated on the substrate surface, the electrode pattern is exposed by laser direct writing mask, and then Cr and Au of different thicknesses are evaporated by thermal evaporation.

[0012] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: Step S1 comprises the following steps: S101, using high-purity PbSe powder (Sigma-Aldrich, 99.99%) as a compensation source for the Se content in the film; S102, the track boat filled with PbSe powder was placed in the middle of the quartz tube, Se powder was placed upstream of the quartz tube as a compensation source, and the strontium titanate substrate was placed downstream of the carrier gas Ar. The lead selenide in the quartz tube was heated to 750 °C for 75 minutes at 8.6 × 10 -2 The growth was maintained at a temperature of pa for 5 minutes. After the growth was completed, it was allowed to cool naturally to obtain a PbSe film. The PbSe powder is 99.99% pure lead selenide powder.

[0013] 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.

[0014] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: The application of the PbSe thin film Schottky junction detector 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 an air cavity, a portion of the light is absorbed by the target gas, 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. A signal processing module processes the electrical signal output by the PbSe thin film Schottky junction detector, and calculates the concentration of the target gas or other related parameters according to the attenuation degree of the optical signal.

[0015] Compared with the prior art, the photodetector, preparation method and application of the present invention based on the Schottky junction of a PbSe thin film have the following beneficial effects: In the present invention, Cr metal and graphene flakes are used as PbSe thin film contact electrodes respectively, and metal semiconductor contact is formed between Cr metal and PbSe thin film to generate Schottky barriers, and ohmic contact is formed between graphene flakes and PbSe thin film to form a detector with a single Schottky junction. Under illumination conditions, the photogenerated carriers generated inside PbSe are separated under the driving of the built-in electric field formed at the Cr-PbSe contact interface, and the high electron mobility and low resistance characteristics of graphene are used to achieve effective collection of electrons. At the same time, the low resistance at the ohmic contact formed by graphene and PbSe is used to achieve 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 transmission of minority carrier holes. Through the transmission of these minority carrier holes, the noise current is reduced at room temperature. Therefore, the present invention utilizes PbSe thin film and graphene thin sheet to contact Cr metal respectively to form Schottky junction and Ohmic contact, and realizes low noise current and high detection performance of PbSe detector at room temperature without low temperature refrigeration. Large area PbSe thin film is grown by CVD technology, and the thickness distribution of PbSe thin film is uniform and has low defect density and good single crystallinity. The photoelectric detector based on 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 possibility for the wide application of PbSe thin film detector.

[0016] The PbSe thin film Schottky junction detector of the present invention has a device response cutoff of 4 μm under room temperature photoelectric testing and a 4.2×10 -27 A 2 Hz -1 Low noise current and 7.58×10 9 cm Hz 1 / 2 W −1Photoelectric performance with high specific detection rate. Under the constructed gas detection system, the detection of methane and propane gases can reach the lowest ppB level detection, realize sensitive gas detection, and have room temperature medium-wave infrared high specific detection rate and high-sensitivity gas detection. At the same time, the device is miniaturized and low-power, which is easy to integrate and adapt to multi-scenario applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic cross-sectional view of a PbSe thin film Schottky junction detector of the present invention; In the figure, PbSe thin film Schottky junction detector 100; strontium titanate substrate 1; PbSe thin film 3; graphene sheet 4; source electrode 2; drain electrode 5; Figure 2 For gas detection systems; In the figure, light source 6; air cavity 7; air inlet 8; air outlet 9; target gas 10; signal processing module 11; Figure 3a This is a scanning electron microscope (STEM) cross-sectional image of Graphene / PbSe. Figure 3b This is the energy band mechanism diagram of the PbSe thin film Schottky junction detector. Figure 3c The IV characteristic curve of the PbSe thin film Schottky junction detector is shown in Figure 2. Figure 3d The IV characteristic curve of graphene at both ends of the electrode is shown in Figure 2. Figure 3e This is the noise current diagram of the PbSe film Schottky junction detector; Figure 4a The specific detectivity and response rate spectra of the PbSe thin film Schottky junction detector at room temperature 1200K. Figure 4b This is the linear fitting diagram for methane gas detection and its detection sensitivity limit. Figure 4c This is the linear fitting diagram for propane gas detection and its detection sensitivity limit. DETAILED DESCRIPTION

[0018] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1

[0019] like Figure 1 As shown, the PbSe thin film Schottky junction detector for gas detection and the preparation method thereof of the present invention. The PbSe thin film Schottky junction detector is prepared by forming a Schottky junction and an ohmic contact with Cr and graphene respectively. The device has room temperature mid-wave infrared high specific detection rate and high sensitivity gas detection performance.

[0020] The structure of the detector is as follows: a graphene sheet 4 is transferred to one end of a PbSe film 3 on a strontium titanate substrate 1, and electrodes are prepared on the PbSe and graphene, respectively. The electrodes on the PbSe film and graphene are a source electrode 2 and a drain electrode 5, respectively.

[0021] The strontium titanate substrate 1 is a sheet with a size of 1 cm×1 cm; The PbSe film 3 is a single crystal film with a thickness of about 80 nm and a size of about 30 μm×100 μm; The graphene sheet 4 is a sheet with a thickness of about 15 nm; The source electrode 2 or the drain electrode 5 is metal Cr and metal Au, and the thickness is about 15nm and 45nm respectively.

[0022] like Figure 2 As shown, the gas detection system comprises: a light source 6, an air cavity 7, an air inlet 8 and an air outlet 9, a target gas 10, a PbSe thin film Schottky junction detector 100, and a signal processing module 11.

[0023] The light source 6 is a black body radiation light source, model HFY-200B.

[0024] The air cavity 7 is a cylinder with a hole diameter of 5 cm and a length of 20 cm.

[0025] The air inlet 8 and the air outlet 9 are cylinders with a hole diameter of 1 cm and a length of 4 cm.

[0026] Light source 6: used to generate a light signal, usually infrared light, to excite the specific absorption characteristics of the target gas.

[0027] Gas cavity 7: a space for containing target gas, ensuring that the optical signal can fully contact with the gas.

[0028] The gas inlet 8 and the gas outlet 9 are used to introduce the target gas into and exhaust the gas cavity to achieve the flow and renewal of the gas.

[0029] Target gas 10: The specific gas to be detected, whose absorption characteristics are to be measured.

[0030] PbSe thin film Schottky junction detector 100: used to detect the intensity change of the optical signal after passing through the air cavity.

[0031] Signal processing module 11: responsible for receiving the signal output by the detector, amplifying, filtering and analyzing it, and finally providing the detection result.

[0032] The light source 6 emits light of a specific wavelength, and when passing through the gas cavity 7, the target gas 10 absorbs a portion of the light.

[0033] The unabsorbed light reaches the PbSe thin film Schottky junction detector 100, which 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 related parameters according to the attenuation degree of the optical signal.

[0034] The present invention proposes a method for preparing a Schottky junction detector based on a PbSe thin film, and the steps are as follows: S1, CVD growth of single crystal PbSe thin film: A track boat filled with PbSe powder (Sigma-Aldrich, 99.99%) was placed in the middle of the quartz tube. Se (Sigma-Aldrich, 99.99%) powder was placed upstream of the quartz tube as a compensation source. The strontium titanate substrate was placed downstream of the carrier gas Ar. The lead selenide in the quartz tube was heated to 750°C for 75 minutes. The growth was maintained at 8.6×10-2 Pa for 5 minutes and then allowed to cool naturally.

[0035] S2, etching of small-size PbSe thin films: The PbSe film was photolithographically processed using a UV maskless photolithography machine, and the film was etched by a plasma etcher to obtain a rectangular strip of 30 μm×100 μm.

[0036] S3, graphene sheet preparation and transfer: Graphene flakes of different thicknesses were prepared by mechanical exfoliation using tape and transferred to a glass slide covered with PDMS. The graphene flakes on PMDS were then point-transferred to the PbSe film via a transfer platform.

[0037] S4, preparation of PbSe film and graphene sheet source and drain electrodes: AZ5214 photoresist was spin-coated on the wafer surface, the electrode pattern was exposed through a laser direct writing mask, and then Cr and Au of different thicknesses were deposited by thermal evaporation (the thickness of Cr and Au was approximately 15nm and 45nm).

[0038] In the present application, CVD is chemical vapor deposition, which is a technology that uses chemical reactions to deposit thin films on solid surfaces.

[0039] The PbSe thin film Schottky junction detector of the present invention has the following operating steps in gas detection applications: 1. Turn on the system power. Turn on the light source 6 and the signal processing module power g.

[0040] 2. Introduce the target gas. Introduce the target gas 10 from the gas inlet 8 to gradually fill the gas cavity 7. After the gas cavity 7 is filled, the excess target gas 10 is discharged from the gas outlet 9.

[0041] 3. Install and debug the detector. Install the PbSe thin film Schottky junction detector 100 and adjust the detector position so that it is on the same horizontal reference line as the radiation light path to ensure that the detector can generate photoelectric signals and transmit them to the signal processing module g.

[0042] 4. Changing the concentration of the target gas. By introducing nitrogen of a certain concentration into the air cavity 7, the target gas 10 of the corresponding concentration is discharged, thereby changing the concentration of the target gas 10.

[0043] 5. Detect the gas concentration detection limit of the detector. Since the target gas 10 absorbs the light radiated by the light source 6, the light intensity irradiated to the PbSe thin film Schottky junction detector 100 will become weaker, which in turn causes the photoelectric signal generated by the PbSe thin film Schottky junction detector 100 to become weaker. Therefore, under different concentrations of the target gas 10, the photoelectric signals of different intensities generated by the PbSe thin film Schottky junction detector 100 are collected and transmitted to the signal processing module 11. The signal processing module 11 performs linear fitting on the photoelectric signal and calculates the gas concentration detection limit.

[0044] After the PbSe thin film Schottky junction detector was prepared, the room temperature photoresponse spectrum was tested and the specific detection rate of the device was calculated, indicating that it has a high specific detection rate. Through the gas detection system, methane and propane gases were detected separately, and the lowest ppB level detection can be achieved, realizing sensitive detection of gases.

[0045] like Figure 3a As shown in Figure 1, the PbSe film grown by CVD has good single crystal properties when observed under a scanning transmission electron microscope (STEM). Figure 3b As shown in the figure, from the perspective of the device energy band, the PbSe and Cr contact regions have energy band bending to form a Schottky junction, while the PbSe and Cr contact regions form a good ohmic contact. Figure 3c As shown in the figure, the PbSe thin film Schottky junction detector is tested under no light irradiation, and the IV characteristic curve has certain rectification characteristics, indicating the generation of Schottky junction. If both electrodes are graphene, the IV characteristic curve is tested under the same conditions, such as Figure 3d As shown in Figure 2, the curve is very linear, proving that graphene and PbSe are in ohmic contact. The spectrum noise current of the test device is shown in Figure 2. Figure 3e As shown in the test results, the noise current is 4.2×10 -27 A 2 Hz -1 , the device has very low noise current. Figure 4aAs shown, by testing the room temperature photoresponse spectrum, the device's specific detection rate was calculated, and the peak specific detection rate was 7.58×10 9 cm Hz 1 / 2 W −1 , indicating a higher specific detection rate. Figure 4b and Figure 4c As shown, through the gas detection system, methane and propane gases can be detected separately, the lowest ppB level detection can be achieved, and sensitive detection of gases can be realized.

[0046] Compared with the prior art, the PbSe thin film Schottky junction detector of the present invention is prepared by a single crystal PbSe thin film grown by CVD, which has the advantages of high-ratio detection rate in the mid-wave infrared at room temperature, as well as the advantages of device miniaturization, low power consumption and high-sensitivity detection, which is easy to integrate and adapt to multi-scenario applications.

[0047] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall 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 the source electrode and the drain electrode respectively; the source electrode and the drain electrode are composite electrodes of lower metal Cr and upper metal Au, the PbSe film and the graphene sheet form Schottky junction and ohmic contact with Cr respectively.

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 about 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 15 nm and 45 nm respectively.

6. A method for preparing a PbSe thin film Schottky junction detector, comprising the following steps: S1, single-crystalline PbSe thin film grown by CVD; S2, etching of small-size PbSe thin films into rectangular strips of 30 μm × 100 μm; S3, graphene flake preparation and transfer, using tape, a mechanical exfoliation method to prepare graphene flakes of different thicknesses, transfer them to a glass slide covered with PDMS, and then transfer the graphene flakes on PMDS to the PbSe film through a transfer platform; S4, PbSe film and graphene sheet source and drain electrodes are prepared, AZ5214 photoresist is spin-coated on the substrate surface, the electrode pattern is exposed by laser direct writing mask, and then Cr and Au of different thicknesses are evaporated by thermal evaporation.

7. The method for preparing a PbSe thin film Schottky junction detector according to claim 6, characterized in that: Step S1 includes the following steps: S101, using high-purity PbSe powder (Sigma-Aldrich, 99.99%) as a compensation source for the Se content in the film; S102, place the track boat filled with PbSe powder in the middle of the quartz tube, place Se powder as a compensation source at the upstream of the quartz tube, place the strontium titanate substrate at the downstream of the carrier gas Ar, heat the lead selenide in the quartz tube to 750℃ for 75 minutes, keep growing at 8.6×10-2 Pa for 5 minutes, and after the growth is completed, let it cool naturally to obtain the PbSe film. The PbSe powder is 99.99% pure lead selenide powder.

8. The use 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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