A two-dimensional vertical heterojunction photodetector and its preparation method

Abstract

The present invention relates to a two-dimensional vertical heterojunction photodetector and a preparation method thereof. The preparation method directly prepares a two-dimensional chalcogenide / germanium selenide vertical heterojunction through a two-step physical vapor deposition process. By controlling the temperature of the source and the growth substrate by partitioning, the nucleation density is adjusted, the film formation quality is improved, the introduction of impurities is avoided, and the interface quality problem is effectively solved. A large-sized, high-crystallinity and high-flatness heterojunction can be obtained. During the preparation process, the present invention can also use visualization equipment to observe the deposition growth process and timely adjust the process parameters to avoid premature deposition and oversaturated growth of the compound. The photodetector obtained by the growth exhibits characteristics such as good rectification effect and good photoelectric performance, has stable performance, and has high application value. It can be used in the field of optoelectronic devices or polarized infrared imaging equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of two-dimensional van der Waals vertical heterojunctions of materials, and in particular to a photoelectric detector of a visualized physical vapor deposition chalcogenide / germanium selenide (GeSe) two-dimensional vertical heterojunction and a preparation method thereof. Background Art

[0002] With the development of the times, photodetectors based on two-dimensional materials have excellent optoelectronic properties and broad application prospects, playing an immeasurable role in military, industrial production and people's lives. Compared with traditional photodetectors, the preparation method of heterojunction is extremely important, mainly including top-down and bottom-up methods. Compared with the top-down method, the bottom-up method has the advantages of horizontal and vertical heterojunction growth and high interface quality. By using a visual multi-functional high-temperature hot stage, we say goodbye to inefficient blind burning. Combining high-speed thermal imaging and optical imaging technology, we can achieve real-time observation of the material growth process, provide intuitive information on material morphology changes, improve the success rate of vertical heterojunctions, and have broad application prospects in large-scale preparation.

[0003] Among chalcogenides, WSe2 is a semiconductor material with an adjustable band gap (~1.68eV) and has a unique bipolarity in electricity and a strong optical absorption coefficient in the visible band. However, WSe2 prepared by mechanical exfoliation is small in size and its thickness is uncontrollable. At the same time, GeSe is a p-type narrow band gap semiconductor material with an ultra-high carrier mobility (4032.64cm 2 / Vs), ultra-high light absorption coefficient (8×10 5 cm -1 ), because of its low symmetry structure and obvious anisotropy, the use of mechanical exfoliation method to prepare WSe2 / GeSe heterojunction has its limitations in batch synthesis and thickness control.

[0004] Previous studies have used mechanical exfoliation and transfer techniques to create WSe2 / GeSe heterojunctions, but the size, morphology, and thickness are difficult to control, hindering large-scale sample and device fabrication. Furthermore, existing vapor deposition processes often produce films with poor quality. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention aims to provide a two-dimensional vertical heterojunction photodetector and a method for its preparation. This preparation method is based on a physical vapor deposition process and improves film quality by controlling the temperature of the source and growth substrate in different zones. This method uses a two-step physical vapor deposition method to prepare a two-dimensional vertical heterojunction, eliminating the need for tedious steps such as peeling and transfer, reducing heterojunction interface defects, avoiding the introduction of impurities, and improving the performance of the vertical heterojunction. The present invention adopts at least the following technical solutions:

[0006] In one aspect, the present invention provides a method for preparing a two-dimensional vertical heterojunction photodetector, comprising the following steps:

[0007] Step S1: Weigh a certain amount of chalcogenide powder and place it in temperature zone I of a high-temperature hot plate in a physical vapor deposition chamber; place a growth substrate in temperature zone II of the high-temperature hot plate; introduce an inert gas purge gas path and then adjust the gas flow rate to a first target temperature; then heat temperature zone I to a first target temperature and heat temperature zone II to a second target temperature lower than the first target temperature; after reaching the first target temperature and the second target temperature, adjust the gas flow rate to a second target temperature, maintain the temperature for a certain period of time, and then cool it naturally to obtain a chalcogenide nanofilm of a predetermined thickness on the growth substrate;

[0008] Step S2: Weigh a certain amount of GeSe powder and place it in the high-temperature hot plate temperature zone I of the physical vapor deposition chamber; place the growth substrate on which the chalcogenide nanofilm of predetermined thickness is grown in the high-temperature hot plate temperature zone II; introduce argon gas to purge the gas path, then adjust the gas flow to 10-20 sccm, and set the physical vapor deposition chamber to a low-pressure environment; then heat the temperature zone I to 500-600 degrees Celsius and the temperature zone II to 400-500 degrees Celsius. If the temperature of the temperature zone II is too low, the growth thickness of GeSe will be too thick. When the target temperature is reached, adjust the gas flow to 25-45 sccm, maintain the target temperature for 3-4 minutes, and then cool it naturally to obtain a GeSe nanofilm of predetermined thickness on the growth substrate, wherein the chalcogenide nanofilm and the GeSe nanofilm form a two-dimensional vertical heterojunction;

[0009] Step S3: preparing a first electrode on the chalcogenide nanofilm and a second electrode on the GeSe film, followed by annealing in an inert atmosphere to obtain the photodetector.

[0010] The chalcogenide compound is WS2 or WSe2, and the first target temperature is 1050°C to 1150°C. When the first target temperature exceeds 1150°C, the grown chalcogenide nanofilm is too thick and exceeds the thickness range of the two-dimensional film layer.

[0011] The second target temperature is 600°C to 900°C.

[0012] The first flow rate is 10 to 20 sccm, the second flow rate is 25 to 45 sccm, and the holding time is 5 to 20 minutes.

[0013] The physical vapor deposition chamber has a visualization function, which combines high-speed thermal imaging and optical imaging to observe the deposition conditions of chalcogenides and GeSe in real time, and controls the size, thickness or nucleation density of the film layer by adjusting process parameters.

[0014] The annealing temperature is 100-150° C., and the annealing time is 30-60 minutes.

[0015] In one aspect, the present invention provides a two-dimensional vertical heterojunction photodetector, comprising a substrate, a two-dimensional chalcogenide nanofilm layer on the substrate, a GeSe nanofilm layer on the two-dimensional chalcogenide nanofilm layer, the two-dimensional chalcogenide nanofilm layer and the GeSe nanofilm layer forming a two-dimensional vertical heterojunction, a first electrode in contact with the two-dimensional chalcogenide nanofilm layer, and a second electrode in contact with the GeSe nanofilm layer, wherein a clean interface exists between the two-dimensional chalcogenide nanofilm layer and the GeSe nanofilm layer. The clean interface means that no other compounds are present at the interface.

[0016] The two-dimensional chalcogenide nanofilm layer is triangular or hexagonal, and the GeSe nanofilm layer is rectangular.

[0017] The thickness of the chalcogenide nanofilm is 3-20 nm, showing p-type or bipolar characteristics. The thickness of the GeSe nanofilm is 30-60 nm, and the chalcogenide nanofilm and the GeSe nanofilm form a pp junction.

[0018] The first electrode and the second electrode are Au electrodes, and the thickness of the Au electrodes is 20-50 nm.

[0019] The substrate is a SiO2 / Si substrate.

[0020] This invention directly fabricates a tungsten selenide / germanium selenide vertical heterojunction using a two-step physical vapor deposition process on a visualized multifunctional high-temperature hot stage. A photodetector is constructed using micro-nanofabrication methods. The microphysical and optoelectronic properties are characterized using optical microscopy, Raman spectroscopy, atomic force microscopy, and a Keithley 2636B source meter probe station at room temperature. The photodiode based on the WSe2 / GeSe two-dimensional vertical heterojunction is also used in optoelectronic devices or polarization-sensitive photodetectors.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The present invention controls the temperature of the source and the growth substrate in a zoned manner, first physically vapor deposits a high-quality two-dimensional chalcogenide nanofilm on the substrate, and then physically vapor deposits a GeSe nanofilm on the two-dimensional chalcogenide nanofilm, thereby obtaining a large-sized, highly crystallinity- and flattened two-dimensional vertical heterojunction having a highly clean interface. Moreover, the method does not require tedious steps such as peeling and transferring, thereby reducing heterojunction interface defects, avoiding the introduction of impurities, ensuring the high quality of the film layer and the heterojunction, and improving the performance of the vertical heterojunction.

[0023] Furthermore, the physical vapor deposition method of the present invention can use visualization function to combine high-speed thermal imaging and optical imaging to observe the deposition status of the film layer in real time during the preparation process, adjust the process parameters in time according to the deposition status of the film layer, optimize the growth conditions, and improve the growth efficiency; the present invention can adjust the nucleation density and improve the film quality by partitioning the temperature of the source and the growth substrate.

[0024] In one embodiment, the two-dimensional vertical heterojunction WSe2 / GeSe photodetector of the present invention has a high current switching ratio of 10 6 Under 635nm light, as the light power density continues to increase, the source-drain current continues to increase, showing a good photoconductive effect. The maximum photoresponsivity and specific detectivity are 300A / W and 7.5x10 13 Jones, light on / off ratio up to 10 5 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a simulation diagram of the preparation process of WSe2 / GeSe two-dimensional vertical heterojunction in Example 1 of the present invention.

[0026] Figure 2 These are optical micrographs of WSe2 deposited on the substrate at different temperatures of 600°C, 750°C and 900°C in an embodiment of the present invention.

[0027] Figure 3 This is a micrograph of the WSe2 / GeSe two-dimensional vertical heterojunction prepared in Example 1 of the present invention.

[0028] Figure 4 This is the Raman spectrum of the WSe2 / GeSe two-dimensional vertical heterojunction prepared in Example 1 of the present invention.

[0029] Figure 5 This is a microscope image of the WSe2 / GeSe two-dimensional vertical heterojunction photodetector prepared in Example 1 of the present invention.

[0030] Figure 6 KPFM image and potential distribution diagram of the WSe2 / GeSe two-dimensional vertical heterojunction photodetector prepared in Example 1 of the present invention.

[0031] Figure 7 This is a transfer characteristic curve of the WSe2 / GeSe two-dimensional vertical heterojunction photodetector prepared in Example 1 of the present invention.

[0032] Figure 8 This is the IV characteristic curve of the WSe2 / GeSe two-dimensional vertical heterojunction photodetector prepared in Example 1 under 635nm light.

[0033] Figure 9 This is an AFM image of the WSe2 / GeSe two-dimensional vertical heterojunction prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present invention. The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can be obtained from public commercial channels.

[0035] Spatially relative terms such as "below," "beneath," "below," "above," "upper," etc. are used in this specification to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures.

[0036] In addition, the use of terms such as "first," "second," and the like to describe various elements, layers, regions, sections, and the like is not intended to be limiting. The use of "having," "containing," "including," and "comprising" are open-ended terms that indicate the presence of stated elements or features, but do not exclude additional elements or features, unless the context clearly indicates otherwise.

[0037] The WSe2 powder and GeSe powder used in the present invention are both industrial products purchased from the market with a purity greater than 99.99%.

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0039] Example 1

[0040] Step S1: In the first physical vapor deposition process, take an appropriate amount of WSe2 solid powder and place it in the middle position of the visualized multifunctional high-temperature hot plate temperature zone I. Cut the SiO2 / Si substrate into 4mm×15mm rectangular pieces as the growth substrate, ultrasonically clean it with ethanol solution for 10 minutes, and place it in the visualized multifunctional high-temperature hot plate temperature zone II. Before heating, introduce argon gas with a flow rate of 100sccm to clean the gas path for 10-20 minutes. Then adjust the argon gas flow to 10-20sccm, heat the visualized multifunctional high-temperature hot plate temperature zone I to 1050-1100℃, heat the visualized multifunctional high-temperature hot plate temperature zone II to 900℃, adjust the gas flow to 25-45sccm, maintain the target temperature for 10-20 minutes and then cool it down naturally. During this period, the growth of the WSe2 film is observed in real time in the visualized multifunctional high-temperature hot plate temperature zone II by microscope imaging. After the insulation is completed, a WSe2 nanofilm is obtained on the SiO2 / Si growth substrate. The growth simulation process of the WSe2 film is as follows Figure 1 As shown, the optical microscope image of the obtained WSe2 nanofilm is as follows Figure 2 As shown in Figure (c).

[0041] Step S2: In the second physical vapor deposition process, a certain amount of solid GeSe powder was weighed and placed in the temperature zone I of the visualized multifunctional high-temperature hot plate. Then, the SiO2 / Si substrate with the WSe2 nanofilm grown thereon was placed in the temperature zone II of the visualized multifunctional high-temperature hot plate. Argon gas with a flow rate of 100 sccm was introduced to purge the gas path for 10-20 minutes. Subsequently, the argon gas flow was maintained at 10-20 sccm. The vacuum pump was turned on to maintain the growth process in a low-pressure environment, which means a pressure of less than 8×10 3 Pa. Then, the visual multifunctional high-temperature hot plate temperature zone I was heated to 570 degrees Celsius, and the temperature zone II was heated to 500 degrees Celsius. The air flow was adjusted to 25-45 sccm and kept warm for 4 minutes. During this period, the growth of GeSe on the WSe2 film was observed in real time in the visual multifunctional high-temperature hot plate temperature zone II by microscope imaging. The growth process simulation diagram is shown in the figure below. Figure 1 As shown in Step II of the previous figure, a WSe2 / GeSe two-dimensional vertical heterojunction is prepared after the growth is completed.

[0042] The WSe2 / GeSe two-dimensional vertical heterojunction prepared on the SiO2 / Si substrate surface obtained in this step was characterized by optical microscopy, Raman spectroscopy, and atomic force microscopy. Figure 3 Optical microscopy data demonstrates uniform sample growth. The synthesized WSe2 is triangular or hexagonal, with its longest side measuring 100-200 μm. The GeSe layer above the WSe2 is rectangular, with its longest side measuring 30-40 μm.

[0043] Figure 4 Raman characterization results of WSe2, GeSe and WSe2 / GeSe two-dimensional vertical heterojunctions. The samples were detected at 150.7 cm -1 、186.7cm -1 and 248.9cm -1 There are significant peaks corresponding to the characteristic peaks of WSe2 and GeSe, indicating that good WSe2 and GeSe thin film samples have been prepared. -1 There is obvious quenching at the peak position, which proves that the high-quality WSe2 / GeSe heterojunction structure is successfully prepared. It can be seen from the Raman characterization results that there is no impurity peak in the heterojunction area, and the surface heterojunction has a clean interface, that is, there are no other compounds in the heterojunction area.

[0044] Step S3: The WSe2 / GeSe two-dimensional vertical heterojunction obtained in step S2 is subjected to maskless UV lithography and development process to prepare an electrode pattern, and an Au electrode is evaporated using an electron beam evaporation coating apparatus. The thickness of the Au electrode is 40-50 nm. The evaporated electrode is immersed in acetone to remove the unnecessary Au layer and excess photoresist, and annealed under inert gas conditions. The inert gas is nitrogen or argon. The annealing temperature is 100-150 degrees Celsius and the annealing time is 30-60 minutes to obtain a photodetector based on the WSe2 / GeSe heterojunction. Its optical microscope image is as shown below. Figure 5 shown.

[0045] Figure 6 The Kelvin probe force microscopy (KPFM) image and potential distribution diagram of the photodetector prepared above show that the surface potential difference of the WSe2 / GeSe two-dimensional vertical heterojunction is about 81.3mV. The photoelectric performance of the WSe2 / GeSe two-dimensional vertical heterojunction photodetector was measured using a Keithley 2636B source meter probe station at room temperature. Figure 7 As shown in the transfer characteristic curve, when the source-drain bias is 1V, the switching ratio is about 10 6 ; Figure 8 As shown in the figure, under 635nm incident light, as the optical power density continues to increase, the source-drain current of the device continues to increase, showing a good photoconductivity effect. The maximum photoresponsivity and specific detectivity are 300A / W and 7.5x10 13 Jones, light on / off ratio up to 10 5 . Figure 9 This is an atomic force microscope image of the WSe2 / GeSe two-dimensional vertical heterojunction. It can be seen that the grown GeSe and WSe2 have a flat surface, and the thickness of the GeSe film layer is 45.5nm.

[0046] Example 2

[0047] This embodiment 2 provides a method for preparing a WSe2 / GeSe two-dimensional vertical heterojunction photodetector. The steps of this method are basically the same as those of the method in embodiment 1, except that: during the first physical vapor deposition process, the temperature of the visual multifunctional high-temperature hot plate temperature zone II is heated to 750 degrees Celsius. The optical microscope image of the WSe2 film grown in step 1 is as follows: Figure 2 As shown in Figure (b).

[0048] Example 3

[0049] This embodiment 3 provides a method for preparing a WSe2 / GeSe two-dimensional vertical heterojunction photodetector. The steps of this method are basically the same as those of the method in embodiment 1, except that: during the first physical vapor deposition process, the temperature of the visual multifunctional high-temperature hot stage temperature zone II is heated to 600 degrees Celsius. The optical microscope image of the WSe2 film grown in step 1 is as follows: Figure 2 As shown in Figure (a).

[0050] The WSe2 nanofilms prepared in Examples 1 to 3 above demonstrate that the nucleation density can be adjusted and the film quality improved by controlling the source and substrate temperatures in different zones. The nucleation density decreases with increasing temperature in Zone II of the high-temperature hot platen. When Zone II is heated to 750°C, the distance between nucleated WSe2 films increases significantly, and the size of the films becomes more uniform. When the temperature rises to 900°C, the WSe2 films grown become larger.

[0051] The two-step physical vapor deposition method using a visualized multifunctional high-temperature hot stage directly prepares chalcogenide / GeSe vertical heterojunctions. This method reduces interface defects and avoids the introduction of impurities, ensuring high product quality and device performance. This improves the performance of the vertical heterojunction, making the preparation simple and efficient, beneficial for large-scale production, and exhibiting significant advantages in fields such as optoelectronics. During the preparation process, the present invention enables real-time observation of the heterostructure growth process, allowing for timely adjustment of parameters based on film growth requirements to optimize growth conditions and improve growth efficiency. The chalcogenide / GeSe two-dimensional vertical heterojunction photodetector prepared using this visualized multifunctional high-temperature hot stage exhibits excellent rectification and optoelectronic performance, with stable device performance and high application value, and can be used in optoelectronic devices or polarized infrared imaging equipment.

[0052] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional vertical heterojunction photodetector, characterized in that: The following steps are involved: Step S1: Weigh a certain amount of chalcogenide powder and place it in temperature zone I of a high-temperature hot plate in a physical vapor deposition chamber; place a growth substrate in temperature zone II of the high-temperature hot plate; introduce an inert gas purge gas path and then adjust the gas flow rate to a first target temperature; then heat temperature zone I to a first target temperature and heat temperature zone II to a second target temperature lower than the first target temperature; after reaching the first target temperature and the second target temperature, adjust the gas flow rate to a second target temperature, maintain the temperature for a certain period of time, and then cool it naturally to obtain a chalcogenide nanofilm of a predetermined thickness on the growth substrate; Step S2: Weigh a certain amount of GeSe powder and place it in temperature zone I of a high-temperature hot plate in a physical vapor deposition chamber. Place the growth substrate on which a chalcogenide nanofilm of predetermined thickness is grown in temperature zone II of the high-temperature hot plate. Argon is introduced into the purge gas path and then the gas flow is adjusted to 10-20 sccm. The physical vapor deposition chamber is set to a low-pressure environment. Next, temperature zone I is heated to 500-600 degrees Celsius and temperature zone II is heated to 400-500 degrees Celsius. After reaching the target temperature, the gas flow is adjusted to 25-45 sccm. The target temperature is maintained for 3-4 minutes and then cooled naturally to obtain a GeSe nanofilm of predetermined thickness on the growth substrate. The chalcogenide nanofilm and the GeSe nanofilm form a two-dimensional vertical heterojunction. Step S3: preparing a first electrode on the chalcogenide nanofilm and a second electrode on the GeSe film, followed by annealing in an inert atmosphere to obtain the photodetector.

2. The preparation method according to claim 1, characterized in that The chalcogenide compound is WS2 or WSe2, the first target temperature is 1050°C~1100°C, and the second target temperature is 600°C~900°C.

3. The preparation method according to claim 2, characterized in that The first flow rate is 10-20 sccm, the second flow rate is 25-45 sccm, and the holding time is 5-20 minutes.

4. The preparation method according to any one of claims 1 to 3, characterized in that The physical vapor deposition chamber has a visualization function, which combines high-speed thermal imaging and optical imaging to observe the deposition conditions of chalcogenides and GeSe in real time, and controls the size, thickness or nucleation density of the film layer by adjusting process parameters.

5. The preparation method according to any one of claims 1 to 3, characterized in that The annealing temperature is 100-150° C., and the annealing time is 30-60 minutes.

6. The two-dimensional vertical heterojunction photodetector prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The invention comprises a substrate, a two-dimensional chalcogenide nanofilm layer located on the substrate, a GeSe nanofilm layer located on the two-dimensional chalcogenide nanofilm layer, wherein the two-dimensional chalcogenide nanofilm layer and the GeSe nanofilm layer form a two-dimensional vertical heterojunction, a first electrode in contact with the two-dimensional chalcogenide nanofilm layer, and a second electrode in contact with the GeSe nanofilm layer, wherein a clean interface is formed between the two-dimensional chalcogenide nanofilm layer and the GeSe nanofilm layer.

7. The photodetector according to claim 6, wherein: The two-dimensional chalcogenide nanofilm layer is triangular or hexagonal, and the GeSe nanofilm layer is rectangular.

8. The photodetector according to claim 6 or 7, characterized in that: The thickness of the chalcogenide nanofilm is 3-20 nm, and the thickness of the GeSe nanofilm is 30-60 nm.

9. The photodetector according to claim 8, wherein The first electrode and the second electrode are Au electrodes, and the thickness of the Au electrodes is 20-50 nm.

10. The photodetector according to claim 6, 7 or 9, characterized in that: The substrate is a SiO2 / Si substrate.

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