Two-dimensional vertical heterojunction photoelectric detector and preparation method thereof

Abstract

According to the preparation method, a two-dimensional chalcogenide / germanium selenide vertical heterojunction is directly prepared through a two-step physical vapor deposition process, the temperature of a source and a growth substrate is controlled in a partitioned mode, the nucleation density is adjusted, the film forming quality is improved, impurities are prevented from being introduced, and the photoelectric detector is prepared. According to the preparation method, the problem of interface quality is effectively solved, large-size, high-crystallinity and flatness heterojunction can be obtained, visual equipment can be adopted in the preparation process, and advanced deposition and supersaturated growth of a compound are avoided by observing the deposition and growth process and adjusting process parameters in time; the photoelectric detector obtained through growth shows the characteristics of good rectification effect, good photoelectric performance and the like, is stable in performance and high in application value, and can be used in the field of photoelectric devices or polarization infrared imaging equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of two-dimensional material van der Waals vertical heterojunction, 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 photoelectric properties and broad application prospects, and have played an immeasurable role in military, industrial production and people's life. 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 characteristics of horizontal and vertical heterojunction growth and high interface quality. By visualizing the multifunctional high-temperature hot stage, we say goodbye to inefficient blind burning. Combined with high-speed thermal imaging and optical imaging technology, we can realize real-time observation of the material growth process, provide intuitive information on material morphology changes, and improve the success rate of vertical heterojunctions. It has 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 stripping 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 to prepare WSe2 / GeSe heterojunction has its limitations in batch synthesis and thickness control.

[0004] Previous studies have used mechanical exfoliation and transfer technology to obtain WSe2 / GeSe heterojunctions, but the size, morphology and thickness are difficult to control, which is not conducive to large-scale preparation of samples and devices. However, the film layer prepared by the existing vapor deposition process has the defect of low quality. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a two-dimensional vertical heterojunction photodetector and a preparation method thereof. The preparation method is based on a physical vapor deposition process, and improves the film quality by controlling the temperature of the source and the growth substrate by partitioning. The method adopts a two-step physical vapor deposition method to prepare a two-dimensional vertical heterojunction, without the need for tedious steps such as peeling and transfer, reduces heterojunction interface defects, avoids the introduction of impurities, and improves 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 the high-temperature hot plate temperature zone I of the physical vapor deposition chamber; place the growth substrate in the high-temperature hot plate temperature zone II; introduce an inert gas to clean the gas path, and then adjust the gas to a first flow rate; then heat the temperature zone I to a first target temperature, and heat the temperature zone II to a second target temperature lower than the first target temperature; when the first target temperature and the second target temperature are reached, adjust the gas flow to a second flow rate, keep 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 clean the gas path, then adjust the gas 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 heat 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 down naturally to obtain a GeSe nanofilm of predetermined thickness on the growth substrate, and 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 insulation 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] On one hand, the present invention provides a two-dimensional vertical heterojunction photodetector, comprising a substrate, a two-dimensional chalcogenide nanofilm layer located on the substrate, a GeSe nanofilm layer located 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, a second electrode in contact with the GeSe nanofilm layer, and a clean interface between the two-dimensional chalcogenide nanofilm layer and the GeSe nanofilm layer. The clean interface means that no other compounds exist on the interface.

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

[0017] The thickness of the chalcogenide nanofilm is 3-20nm, showing p-type or bipolar characteristics, the thickness of the GeSe nanofilm is 30-60nm, 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] The present invention directly prepares a tungsten selenide / germanium selenide vertical heterojunction by two-step physical vapor deposition using a visualized multifunctional high-temperature hot stage, and constructs a photodetector using a micro-nano processing method, and describes the microscopic physical and photoelectric properties using an optical microscope, Raman spectroscopy, atomic force microscope, and a Keithley 2636B source meter probe station at room temperature. The photodiode based on the WSe2 / GeSe two-dimensional vertical heterojunction is applied in the field of photoelectric 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 by partitioning, 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 two-dimensional vertical heterojunction with large size, high crystallinity and flatness. The heterojunction has a highly clean interface, and the method does not require tedious steps such as stripping and transfer, 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 the 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 illumination, as the light power density continues to increase, its source-drain current continues to increase, showing a good photoconductivity effect. The maximum photoresponsivity and specific detection rate 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 the WSe2 / GeSe two-dimensional vertical heterojunction in Example 1 of the present invention.

[0026] Figure 2 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] Fig. 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 creative work are all within the scope of protection of the present invention. The experimental methods described in the following embodiments 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", etc. to describe various elements, layers, regions, sections, etc. is not intended to be limiting. The use of "having", "containing", "including", "comprising", etc. is open-ended, indicating the presence of the stated elements or features, but does not exclude additional elements or features. Unless the context clearly states 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, pass argon gas at 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, the 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 is weighed and placed in the visualized multifunctional high-temperature hot plate temperature zone I, and then the SiO2 / Si substrate with the WSe2 nanofilm grown thereon is placed in the visualized multifunctional high-temperature hot plate temperature zone II, and argon gas with a flow rate of 100 sccm is introduced to purge the gas path for 10-20 minutes, and then the argon gas flow is maintained at 10-20 sccm, and the vacuum pump is turned on to maintain the growth process in a low-pressure environment, which means that the pressure is less than 8×10 3 Pa. Then, the visualized 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 gas 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 visualized multifunctional high-temperature hot plate temperature zone II by microscopic imaging. The growth process simulation diagram is shown in the figure below: Figure 1 As shown in Step ⅱ of FIG. After the growth is completed, a WSe2 / GeSe two-dimensional vertical heterojunction is prepared.

[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 The optical microscope characterization data shows that the sample grows uniformly. The synthesized WSe2 is triangular or hexagonal, with the longest side length of 100-200um; the GeSe above WSe2 is rectangular, with the longest side length of 30-40um.

[0043] Figure 4 Raman characterization results of WSe2, GeSe and WSe2 / GeSe two-dimensional vertical heterojunction. The samples were characterized 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, respectively, indicating that good WSe2 and GeSe thin film samples have been prepared. WSe2 / GeSe at 248.9cm -1 There is obvious quenching at the peak position, which proves that the high-quality WSe2 / GeSe heterojunction structure is successfully prepared. From the Raman characterization results, it can be seen that there is no impurity peak in the heterojunction region, and the surface heterojunction has a clean interface, that is, there are no other compounds in the heterojunction region.

[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 by an electron beam evaporation coating apparatus, the thickness of the Au electrode is 40-50 nm, and 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 is performed for 30-60 minutes to obtain a photodetector based on the WSe2 / GeSe heterojunction, and its optical microscope image is as shown in FIG. Figure 5 shown.

[0045] Figure 6 The Kelvin probe force microscope (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 room temperature probe station. 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 light 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 detection rate are 300A / W and 7.5x10 13 Jones, light on / off ratio up to 10 5 . Fig. 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 the preparation method are basically the same as those of the preparation method in embodiment 1, except that: in the first physical vapor deposition process, the temperature of the visualized multifunctional high-temperature hot stage 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 the preparation method are basically the same as those of the preparation method in embodiment 1, except that: in 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] It can be seen from the WSe2 nanofilms prepared in Examples 1 to 3 above that the nucleation density can be adjusted and the quality of the film can be improved by controlling the source and substrate temperature in different zones. The nucleation density decreases with the increase of the temperature of the high-temperature hot plate temperature zone II. When the high-temperature hot plate temperature zone II is heated to 750 degrees Celsius, the distance between the WSe2 films formed by nucleation increases significantly, and the size is more uniform. When the temperature rises to 900 degrees Celsius, the size of the WSe2 film grown is larger.

[0051] The chalcogenide / GeSe vertical heterojunction is directly prepared by two-step physical vapor deposition using a visualized multifunctional high-temperature hot stage, which reduces interface defects, avoids the introduction of impurities, ensures high product quality and device performance, improves the performance of the vertical heterojunction, and is simple and efficient to prepare, which is beneficial to large-scale preparation and shows great advantages in optoelectronics and other fields. The present invention can observe the growth process of the heterostructure in real time during the preparation process, and can adjust parameters in time according to the growth needs of the film layer to optimize the growth conditions and improve the growth efficiency; the chalcogenide / GeSe two-dimensional vertical heterojunction photodetector prepared by the visualized multifunctional high-temperature hot stage shows good rectification effect, good photoelectric performance and other characteristics, the device performance is stable, the application value is high, and it can be used in the field of 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 equivalent replacement methods and are included in the protection scope 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 the high-temperature hot plate temperature zone I of the physical vapor deposition chamber; place the growth substrate in the high-temperature hot plate temperature zone II; introduce an inert gas to clean the gas path, and then adjust the gas to a first flow rate; then heat the temperature zone I to a first target temperature, and heat the temperature zone II to a second target temperature lower than the first target temperature; when the first target temperature and the second target temperature are reached, adjust the gas flow to a second flow rate, keep 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 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 clean the gas path, then adjust the gas 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 heat the temperature zone II to 400-500 degrees Celsius. 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 down naturally to obtain a GeSe nanofilm of predetermined thickness on the growth substrate, and 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 to 1100°C, and the second target temperature is 600°C to 900°C.

3. The preparation method according to claim 2, characterized in that: The first flow rate is 10 to 20 sccm, the second flow rate is 25 to 45 sccm, and the insulation time is 5 to 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. A two-dimensional vertical heterojunction photodetector, characterized in that: It includes a substrate, a two-dimensional chalcogenide nanofilm layer located on the substrate, a GeSe nanofilm layer located 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.

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

8. The preparation method 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 preparation method according to claim 8, characterized in that: The first electrode and the second electrode are Au electrodes, and the thickness of the Au electrodes is 20-50 nm.

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

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