A PN-junction-based optoelectronic synapse device and a preparation method thereof

Abstract

The application discloses a kind of photoelectric synapse devices based on PN junction and preparation method thereof, purpose is to solve the problem that two-dimensional semiconductor material photoelectric synapse device can only work in single mode, cannot realize bright and dark vision adaptive problem.The photoelectric synapse device of the application is composed of substrate, source electrode, two-dimensional n-type semiconductor film, gate, two-dimensional p-type semiconductor film and drain electrode.The preparation method is to prepare two-dimensional n-type semiconductor film by using positive light response n-type two-dimensional semiconductor material, to prepare two-dimensional p-type semiconductor film by using negative light response p-type two-dimensional semiconductor material, gate is connected into PN junction by two films, two-dimensional n-type semiconductor film simulates light excitation generation unit in biological coupling mechanism, and two-dimensional p-type semiconductor film simulates light inhibition generation unit.The application realizes non-monotonic light response in an integrated device, can effectively simulate biological coupling mechanism to realize bright and dark vision adaptive, simple structure, low power consumption, preparation method has low process complexity, and cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of artificial vision systems, and particularly relates to a phototransistor device based on a two-dimensional semiconductor material PN junction and a preparation method thereof. BACKGROUND

[0002] The phototransistor device can simulate the synaptic connection function between the photoreceptor cells and neurons in the human eye retina, and at the same time realize the reception, conversion and processing of the light signal, and is one of the key components for constructing an advanced artificial vision system. With the promotion of artificial intelligence and machine learning, the phototransistor device can enhance the learning ability of the artificial vision system, and perform more complex image recognition, scene understanding and decision making, and has wide application prospects in medical treatment, safety, automatic driving and many other fields. However, the phototransistor device based on the CMOS transistor technology still faces many challenges in response delay and power consumption, for example, the traditional silicon-based semiconductor needs a large working voltage for light signal sensing, and the high power consumption problem caused thereby becomes increasingly prominent with the increase of the integrated scale. In addition, due to the limitation of the traditional storage and calculation separation architecture, the artificial vision system based on the CMOS technology needs to digitize the analog signal before transmission, which not only leads to a large amount of redundancy in the data processing process, but also causes high response delay problem of the equipment operation. The above problems limit the application range and efficiency of the traditional artificial vision system to some extent.

[0003] In order to solve the above problems, in recent years, researchers are exploring the use of new materials to construct phototransistor devices in order to reduce power consumption and response delay while maintaining or improving performance and realizing a more efficient artificial vision system. Inspired by the function of the human retina, researchers have noticed that the phototransistor device based on new nanomaterials has both light signal sensing (photosensitive property) and information storage and processing (synaptic plasticity, spatiotemporal resolution property) functions, which are similar to the functions of the retina, which means that a single device can simulate visual function, and is expected to realize the ability to imitate the perception and processing of information of the biological vision system in the full analog domain, thereby breaking through the bottleneck of the existing artificial vision system. As an important branch of nanomaterials, two-dimensional semiconductor materials have the advantages of wide spectral response, high flexibility and carrier mobility, not easy to degrade and oxidize, strong light absorption capacity, etc., so they stand out among many new nanomaterials used to construct phototransistor devices.

[0004] Currently, most optoelectronic synaptic devices based on two-dimensional semiconductor materials are single-element structures of a single material or heterogeneous structures formed by stacking multiple materials. This type of optoelectronic synaptic device can only operate in a single mode (photoexcitation or photoinhibition) under light stimulation, showing a unidirectional increase or decrease in conductance. This unidirectional response mechanism seriously restricts the efficiency of visual adaptation (such as light-dark adaptation function). However, maintaining a relatively stable light-dark adaptation mechanism under different lighting conditions is crucial for smart devices to complete information acquisition in different environments. Currently, there is no public literature involving optoelectronic synaptic devices with different materials in series to achieve visual adaptation functions under light-dark conditions. Therefore, how to overcome these limitations and develop optoelectronic synaptic devices with simpler structures, low power consumption and the ability to adapt to vision under different lighting conditions has become the focus and difficulty of related research work. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the current optoelectronic synaptic devices based on two-dimensional semiconductor materials with single-element or heterogeneous structures can only operate in a single mode and cannot effectively present non-monotonic light response (that is, its response does not always increase or decrease with changes in lighting conditions), resulting in the inability to effectively simulate the biological coupling mechanism to achieve light and dark visual adaptation. A optoelectronic synaptic device based on PN junction and a preparation method thereof are proposed to solve the unidirectional response problem of traditional two-dimensional semiconductor optoelectronic synaptic devices, realize visual adaptation function under light and dark conditions, simplify the structure and reduce power consumption.

[0006] The present invention utilizes a two-dimensional n-type semiconductor film (made of positive light-responsive n-type two-dimensional semiconductor material) and a two-dimensional p-type semiconductor film (made of negative light-responsive p-type two-dimensional semiconductor material) connected in series with a gate to form a PN junction. The two-dimensional n-type semiconductor film simulates the light excitation generating unit in the biological coupling mechanism, and the two-dimensional p-type semiconductor film simulates the light inhibition generating unit in the biological coupling mechanism. A PN structure forms a photoelectric synapse, thereby achieving non-monotonic light response under illumination conditions and realizing visual adaptive function under different light and dark conditions.

[0007] The application is based on a PN junction photoelectric synapse device which is composed of a substrate, a source electrode, a two-dimensional n-type semiconductor film, a gate electrode, a two-dimensional p-type semiconductor film and a drain electrode. The source electrode, the two-dimensional n-type semiconductor film, the gate electrode, the two-dimensional p-type semiconductor film and the drain electrode are sequentially arranged on the upper surface of the substrate from left to right. The right side of the source electrode is connected to the two-dimensional n-type semiconductor film; the left side of the two-dimensional n-type semiconductor film is connected to the source electrode and the right side thereof is connected to the gate electrode; the left side of the gate electrode is connected to the two-dimensional n-type semiconductor film and the right side thereof is connected to the two-dimensional p-type semiconductor film; the left side of the two-dimensional p-type semiconductor film is connected to the gate electrode and the right side thereof is connected to the drain electrode; and the left side of the drain electrode is connected to the two-dimensional p-type semiconductor film. The two-dimensional n-type semiconductor film and the two-dimensional p-type semiconductor film are connected in series through the gate electrode to form a PN junction, and the two-dimensional n-type semiconductor film, the two-dimensional p-type semiconductor film and the gate electrode form the PN junction photoelectric synapse device.

[0008] The substrate is a rectangular body, is selected as SiO2 material, can be commercially purchased, has a thickness of 500 nanometers, and has no requirements on the length and width, and can only meet the requirements of bearing the source electrode, the two-dimensional n-type semiconductor film, the gate electrode, the two-dimensional p-type semiconductor film and the drain electrode, that is, the area of the upper surface of the substrate is greater than the total area of the lower surfaces of the source electrode, the two-dimensional n-type semiconductor film, the gate electrode, the two-dimensional p-type semiconductor film and the drain electrode.

[0009] The two-dimensional p-type semiconductor film is prepared by using a negative photoresponse p-type two-dimensional semiconductor material (such as PtSe2, PtTe2, PdSe2, etc.), has a width w5 of 20-40 microns, a length l5 of 30-50 microns and a thickness h5 of 1.5-2 nanometers, and is used as a p-type channel of the PN junction photoelectric synapse device, and the negative photoconductivity effect under light irradiation is applied to a light inhibitory unit in the simulation of a biological coupling mechanism.

[0010] The two-dimensional n-type semiconductor film is prepared by using a positive photoresponse n-type two-dimensional semiconductor material (such as ReS 2、 MoS2, MoTe2, etc.), has a length l3 of 10-30 microns, a width w3 of 10-20 microns and a thickness h3 of 4.5-5.5 nanometers, and is used as an n-type conductive channel of the PN junction photoelectric synapse device, and the positive photoconductivity effect under light irradiation is applied to a light excitatory unit in the simulation of a biological coupling mechanism.

[0011] The source electrode, the gate electrode and the drain electrode are all rectangular bodies, and are made of a metal (such as a metal with a conductivity higher than 40×10 6The 2D n-type semiconductor film is covered on the right side of the source electrode, the 2D p-type semiconductor film on the left side of the drain electrode, and the 2D n-type semiconductor film on the right side of the gate electrode. The overlap width of these coverings is approximately 5 microns, ensuring good contact between the electrodes and the material.

[0012] The method for preparing a PN junction-based photoelectric synapse device of the present invention comprises the following steps:

[0013] In the first step, a triangular two-dimensional p-type semiconductor film 5 with a side length greater than 1 mm is synthesized on the substrate 1 by chemical vapor deposition (see Keyshar Kunttal et al., "Chemical vapor deposition of monolayerrhenium disulfide (ReS2)" in the journal Advanced Materials, 2015).

[0014] In the second step, the synthesized two-dimensional p-type semiconductor film 5 is etched into a single strip (the strip film width w5 is 20-40 microns and the length l5 is 30-50 microns) by ion beam etching technology (refer to the device fabrication in the paper "All-electrical skyrmionic magnetic tunnel junction" by Shaohai Chen et al. in the journal Nature, 2024, page 7). The strip film serves as the p-type channel of the PN junction-based optoelectronic synapse device.

[0015] In the third step, the commercially available 2D n-type semiconductor bulk material is thinned to a height h3 of 4.5-5.5 nanometers, a width w3 of 10-20 micrometers, and a length l3 of 10-30 micrometers using a mechanical exfoliation method (see Yujun Deng et al., "Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2" in Nature, page 7, 2018). The mechanically exfoliated 2D p-type semiconductor material is then transferred to substrate 1 using a fixed-point transfer method (see Yujun Deng et al., "Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2" in Nature, page 7, 2018), yielding a 2D n-type semiconductor thin film 3, which serves as the n-type channel of the PN junction-based optoelectronic synapse device.

[0016] Step 4: Use ultraviolet photolithography (refer to the device fabrication on page 7 of the paper "All-electrical skyrmionic magnetic tunnel junction" by Shaohai Chen et al. in the journal Nature, 2024) to determine the positions of the source 2, gate 4, and drain 6, that is, photolithography the position of the source 2 at the left end of the two-dimensional n-type semiconductor film 3, photolithography the position of the drain 6 at the right end of the two-dimensional p-type semiconductor film 5, and photolithography the position of the gate 4 between the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5.

[0017] In the fifth step, a high-conductivity metal electrode (preferably gold or copper) is deposited on the electrode position lithographed in the fourth step by using an electron beam evaporation method (Device fabrication in the paper "All-electrical skyrmionic magnetic tunnel junction" by Shaohai Chen et al. in the journal Nature, page 7, 2024) to connect the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 in series through the gate 4 to form a PN junction, with the left end of the two-dimensional n-type semiconductor film 3 being the source 2 and the right end of the two-dimensional p-type semiconductor film 5 being the drain 6. The thicknesses of the source 2, the gate 4, and the drain 6 are all h1, h 1 50 nanometers, and the widths of the source 2 and the drain 6 are w2 and w6, respectively, and the width of the gate 4 is w4, with w2 and w6 being 20 micrometers and w4 being 40 micrometers.

[0018] Compared with the prior art, the present application can achieve the following technical effects:

[0019] 1. The preparation method of the present application prepares a PN junction-based optoelectronic synapse device by connecting a two-dimensional n-type semiconductor film and a two-dimensional p-type semiconductor film in series to form a PN junction, and the positive light response characteristics of the two-dimensional n-type semiconductor film and the negative light response characteristics of the two-dimensional p-type semiconductor film are coupled by the series connection, so that non-monotonic light response is achieved in an integrated device, and the prepared PN junction-based optoelectronic synapse device can effectively simulate the biological coupling mechanism to achieve bright-dark vision adaptation, and has a simple structure and low power consumption.

[0020] 2. The first step of the preparation method of the present application uses a chemical vapor deposition method to prepare a two-dimensional p-type semiconductor film, which has high production efficiency, uniform film formation, and low cost, and is easy to organize mass production.

[0021] 3. The present application uses semiconductor-compatible ultraviolet lithography, ion beam etching, and electron beam evaporation processes to complete device structure preparation, which has high technical maturity and strong compatibility.

[0022] 4. The present application connects a two-dimensional n-type semiconductor film and a two-dimensional p-type semiconductor film in series to form a PN junction, which does not require the construction of a heterojunction, reduces the process complexity, and realizes the practical requirement of a simple process. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the overall structure front view of the PN junction-based optoelectronic synapse device of the present application;

[0024] Figure 2 is the overall structure top view of the PN junction-based optoelectronic synapse device of the present application;

[0025] Figure 3 is the top view (optical microscope photo, equivalent to Figure 2 a rotation of about 135 degrees clockwise) of the PN junction based optoelectronic synapse device embodiment 1 of the present invention. Figure 3 is a microscope photo, the scale bar is located at the lower left corner of the picture.

[0026] Figure 4 is the input-output and Gaussian shaped transfer characteristics curve of the PN junction based optoelectronic synapse device embodiment 1 of the present invention under dark condition, Figure 4 (a) is the input-output curve of the PN junction based optoelectronic synapse device embodiment 1 of the present invention under dark condition, Figure 4 (b) is the Gaussian shaped transfer characteristics curve of the PN junction based optoelectronic synapse device embodiment 1 of the present invention under dark condition.

[0027] Figure 5 is the current versus time curve of the 2D n-type semiconductor thin film 3 and 2D p-type semiconductor thin film 5 of embodiment 1 of the present invention under 532 nm wavelength (power 1.41 nW pm -2 , duration 3 s) light stimulation, where the upper half corresponds to the photocurrent versus time curve in the 2D n-type semiconductor thin film 3 ReS2 material, and the lower half corresponds to the photocurrent versus time curve in the 2D p-type semiconductor thin film 5 PtSe2 material. Figure 5 (a) represents the current change of embodiment 1 under single laser pulse irradiation, the positive current increase can be analogous to the positive current increase after excitatory synapse, and the negative current increase can be analogous to the negative current increase after inhibitory synapse. Figure 5 (b) represents the current change of embodiment 1 under continuous pulse stimulation with 2 s interval, the two repeated current change curves can be analogous to the double pulse facilitation and inhibition of synapse under double stimulation. Figure 5 (c) represents the current change of embodiment 1 under multiple identical pulse stimulation (with 0.5 s interval), the repeated current change curves can be analogous to the long-term potentiation and depression of synapse response after external stimulation.

[0028] Figure 6 is the Gaussian shaped transfer characteristics curve of the drain-source current versus gate-source voltage of embodiment 1 of the present invention under 532 nm wavelength light stimulation; Figure 6 (a) is the curve of Gaussian shaped transfer characteristics versus light power density, Figure 6 (b) is the curve of Gaussian shaped transfer characteristics versus light duration, Figure 6 (c) is the curve of Gaussian shaped transfer characteristics versus light removal time.

[0029] Figure 7The blue light of Example 1 of the present invention at 450nm (power 4.72nWμm -2 The time-dependent current curves between the drain and source under different gate voltages are shown under illumination (for 5 seconds). At gate voltages of 20V and -20V, the current exhibits negative and positive current variations, respectively, demonstrating that the PN junction-based photosynaptic device exhibits gate-voltage-regulated positive and negative photoconductivity effects.

[0030] Figure 8 is a graph showing the attenuation amplitude of the normalized photoresponse current over time when irradiated with 450nm blue light according to Example 1 of the present invention; Figure 8 (a) is the curve of normalized photoresponse current changing with light power density, Figure 8 (b) is the curve of normalized photoresponse current changing with light power density and light duration.

[0031] Explanation of the accompanying symbols: 1. substrate; 2. source; 3. two-dimensional n-type semiconductor thin film; 4. gate; 5. two-dimensional p-type semiconductor thin film; 6. drain. DETAILED DESCRIPTION

[0032] The specific implementation methods of the present invention are further described below in conjunction with the drawings and examples so that those skilled in the art can better understand the present invention and implement it. However, the examples are not intended to limit the present invention.

[0033] like Figure 1 and Figure 2 As shown, the PN junction-based photoelectric synapse device of the present invention comprises a substrate 1, a source electrode 2, a two-dimensional n-type semiconductor film 3, a gate electrode 4, a two-dimensional p-type semiconductor film 5, and a drain electrode 6. The source electrode 2, the two-dimensional n-type semiconductor film 3, the gate electrode 4, the two-dimensional p-type semiconductor film 5, and the drain electrode 6 are arranged on the top surface of substrate 1, from left to right. The right side of the source electrode 2 is connected to the two-dimensional n-type semiconductor film 3; the left side of the two-dimensional n-type semiconductor film 3 is connected to the source electrode 2 and the right side is connected to the gate electrode 4; the left side of the gate electrode 4 is connected to the two-dimensional n-type semiconductor film 3 and the right side is connected to the two-dimensional p-type semiconductor film 5; the left side of the two-dimensional p-type semiconductor film 5 is connected to the gate electrode 4 and the right side is connected to the drain electrode 6; the left side of the drain electrode 6 is connected to the two-dimensional p-type semiconductor film 5. The two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 are connected in series through the gate electrode 4 to form a PN junction. The two-dimensional n-type semiconductor film 3, the two-dimensional p-type semiconductor film 5, and the gate electrode 4 constitute the PN junction photoelectric synapse device of the present invention.

[0034] The substrate 1 is a rectangular body, selected as SiO2 material, commercially available, with a thickness of 500 nanometers, and no requirement for length and width, as long as it can carry the source electrode 2, the two-dimensional n-type semiconductor film 3, the gate electrode 4, the two-dimensional p-type semiconductor film 5, and the drain electrode 6, that is, the area of the upper surface of the substrate 1 is greater than the total area of the lower surfaces of the source electrode 2, the two-dimensional n-type semiconductor film 3, the gate electrode 4, the two-dimensional p-type semiconductor film 5, and the drain electrode 6.

[0035] The two-dimensional p-type semiconductor film 5 is prepared by using a negative photoresponse p-type two-dimensional semiconductor material (such as PtSe2, PtTe2, PdSe2, etc.), with a width w5 of 20-40 microns, a length l5 of 30-50 microns, and a thickness h5 of 1.5-2 nanometers, serving as a p-type channel of the photonic synapse device based on a PN junction, and the negative photoconductivity effect under light conditions is used in the light inhibition unit simulating the biological coupling mechanism.

[0036] The two-dimensional n-type semiconductor film 3 is prepared by using a positive photoresponse n-type two-dimensional semiconductor material (such as ReS 2、 MoS2, MoTe2, etc.), with a length l3 of 10-30 microns, a width w3 of 10-20 microns, and a thickness h3 of 4.5-5.5 nanometers, serving as an n-type conductive channel of the photonic synapse device based on a PN junction, and the positive photoconductivity effect under light conditions is used in the light excitation unit simulating the biological coupling mechanism.

[0037] The source electrode 2, the gate electrode 4, and the drain electrode 6 are all rectangular bodies, made of a metal (such as gold or copper) with an electrical conductivity higher than 40×10 6 S / m, with a thickness of h1, and h1 is 50 nanometers; the width w2 of the source electrode 2 and the width w6 of the drain electrode 6 are both 20 microns, and the width w4 of the gate electrode 4 is 40 microns. The right side of the source electrode 2 covers the two-dimensional n-type semiconductor film 3, the left side of the drain electrode 6 also covers the two-dimensional p-type semiconductor film 5, and the left and right sides of the gate electrode 4 cover the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5, respectively, and the overlapping width of the above-mentioned coverings is about 5 microns, which ensures that the electrodes and the materials form good contact.

[0038] The following will describe the embodiment 1 in detail in combination with the specific material selection of the two-dimensional semiconductor.

[0039] First, the preparation method of the embodiment 1 is as follows: a two-dimensional p-type semiconductor film 5 (using PtSe2, with a thickness h5 of 1.5 nanometers Figure 1The bulk material (using ReS2) is then thinned to approximately 5.2 nanometers (h3) using mechanical exfoliation, forming a two-dimensional n-type semiconductor film 3 (length l3 20 microns, width w3 12 microns). This is then placed next to the two-dimensional p-type semiconductor film 5 using a fixed-point transfer method (the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 are not laterally connected). Metal electrodes (gold Au) are then deposited between the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5, on the left side of the two-dimensional n-type semiconductor film 3, and on the right side of the two-dimensional p-type semiconductor film 5, using techniques such as ultraviolet lithography, electron beam evaporation, and exfoliation. These electrodes serve as the source electrode 2 (width w2 20 microns), the gate electrode 4 (width w4 40 microns), and the drain electrode 6 (width w6 20 microns). The two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 are connected via a gate 4 . The left end of the two-dimensional n-type semiconductor film 3 is the source 2 , and the right end of the two-dimensional p-type semiconductor film 5 is the drain 6 .

[0040] Figure 3 This is an optical microscope photograph of Example 1. Figure 3 The blue area in the upper middle part is the two-dimensional n-type semiconductor film 3 (using ReS2), and the blue area in the lower part is the two-dimensional p-type semiconductor film 5 (using PtSe2). The image scale is located in the lower left corner and is 50μm long. The upper white area is the source 2, the middle white area is the gate 4, and the lower white area is the drain 6. Figure 3 It can be seen that the lower half of the source electrode 2 covers the upper side of the two-dimensional n-type semiconductor film 3, the upper part of the gate electrode 4 covers the lower side of the two-dimensional n-type semiconductor film 3, and the lower part covers the upper side of the two-dimensional p-type semiconductor film 5. The drain electrode 6 is completely covered on the two-dimensional p-type semiconductor film 5. Good ohmic contact is formed between the electrodes and the materials, without obvious Schottky barriers, facilitating subsequent electrical testing.

[0041] Figure 4 (a) is a curve showing the change in current (i.e., drain-source current) between the drain 6 and the source 2 when the voltage between the drain 6 and the source 2 changes from -2 V to 2 V (the gate-source voltage is set to -5 V). The nearly linear current change indicates that the PN junction-based photoelectric synapse device of the present invention has excellent conductive properties. Figure 4 (b) shows the transfer characteristic curve of the present invention under dark conditions. When the voltage of the gate 4 changes from -30 V to +30 V, the current between the drain 6 and the source 2 (i.e., the drain-source current) first rises and then falls to form a peak. The overall shape is similar to a Gaussian curve, indicating that the non-monotonic light response of the present invention is successfully achieved in this embodiment.

[0042] Figure 5is the current vs. time curve of the two-dimensional n-type semiconductor thin film 3 (ReS2) and the two-dimensional p-type semiconductor thin film 5 (PtSe2) of Example 1 under light stimulation at a wavelength of 532 nm (power 1.41 nW pm -2 , duration 3 s). Figure 5 (a) shows the current vs. time curve of ReS2 and PtSe2 under single light pulse stimulation (wavelength 532 nm, power 1.41 nW pm -2 , duration 3 s), it can be seen that the current response of ReS2 presents a positive response, which can be analogous to the excitatory potential exhibited by a nerve synapse after external stimulation, and the current response of PtSe2 presents a negative response, which can be analogous to the inhibitory potential exhibited by a nerve synapse after external stimulation. Figure 5 (b) shows the current vs. time curve of ReS2 and PtSe2 under two consecutive light pulse irradiation with an interval time of 2 s, which can be respectively analogous to the change in nerve synapse potential caused by the first pulse and the enhancement or inhibition of this change by the second pulse under two spaced external stimuli, i.e. respectively corresponding to the double-pulse facilitation response and the double-pulse inhibition response. Figure 5 (c) shows the current vs. time curve of ReS2 and PtSe2 under continuous multiple light pulse irradiation with an interval time of 0.5 s, which can be respectively analogous to the persistent increase and persistent decrease in potential change of a nerve synapse after repeated stimulation, i.e. respectively corresponding to long-term potentiation and long-term depression plasticity.

[0043] Figure 6 shows the Gaussian transfer characteristic curve of Example 1 under 532 nm light stimulation. When the gate-source voltage is greater than the threshold voltage of PtSe2, PtSe2 is in the off state, and since the resistance of ReS2 is very small compared to that of PtSe2, the resistance of the ReS2-PtSe2 series PN junction is very large at this time, regardless of whether ReS2 is in the on state or not, the current in the channel of the series device is prevented from being transmitted. Then, as the gate-source voltage decreases, the resistance of the PtSe2-PtSe2 series PN junction decreases sharply, so the current increases exponentially and reaches a peak value afterwards. When the gate-source voltage is lower than the threshold voltage of ReS2, the resistance of the series device is dominated by ReS2, i.e. the current decreases exponentially with the gate voltage, thus the PN junction resistance of the series ReS2-PtSe2 presents a Gaussian transfer characteristic curve. Figure 6 (a) shows that as the light power increases, the gate-source voltage corresponding to the maximum drain-source current decreases, the main reason being that the threshold voltage of PtSe2 and ReS2 is shifted to the left, so that when the maximum current is reached, its gate-source voltage is also shifted to the left. Figure 6(b) shows that the Gaussian transfer curve decreases with increasing illumination duration, and the gate-source voltage corresponding to the maximum current also decreases. This is because longer illumination duration injects more photons into ReS2, which in turn causes more oxygen molecules to desorb from the PtSe2 surface, resulting in a larger leftward shift in the gate-source voltage corresponding to the maximum current. Figure 6 (c) shows that the Gaussian transfer curve can be maintained for a period of time after the light is removed, with the peak position gradually shifting to the right over time and eventually returning to the initial state. This relaxation behavior indicates that Example 1 has memory properties similar to those of traditional optoelectronic synaptic devices.

[0044] Figure 7 The unique non-monotonic photoresponse behavior exhibited by Example 1 under 532nm laser stimulation was experimentally measured, and it has both photoexcitation and photoinhibition characteristics. Under different gate voltages, the photocurrent first rises and then falls, and an inflection point appears in the photocurrent curve, which means that the positive photoconductivity effect and the negative photoconductivity effect are successfully integrated into the PN junction of the series ReS2-PtSe2. In the rising stage, the positive photoconductivity effect of ReS2 dominates, wherein the light absorption of ReS2 causes the PN junction conductivity of the real series ReS2-PtSe2 to increase rapidly. Over time, the inflection point appears because the negative photoconductivity effect of PtSe2 gradually dominates under continuous illumination. As the gate voltage changes, the light response direction of the series ReS2-PtSe2 PN junction changes from positive increase to negative decrease (its light response increases positively under a gate voltage of -20V, and its light response increases negatively under a gate voltage of 20V). This shows that the series connection enables the coupling of the characteristics of complementary photoelectric synapses, and the light response of the series ReS2-PtSe2 PN junction can be regulated by voltage. This method provides a novel implementation path for simulating biological visual adaptation.

[0045] Figure 8 (a) shows the light power-dependent visual adaptive behavior of Example 1. As the light power increases (which can simulate the lighting conditions from dim to bright), at low power 0.005nWμm -2 (Under dim light conditions) the photocurrent rises and then reaches saturation and then remains, similar to the sensitivity of the retina increasing during dark adaptation. -2 Under these conditions, the photocurrent first reaches saturation and then exhibits a dynamic decay behavior over time, with the drain-source current reaching a peak in bright conditions and then gradually decreasing. This dynamic behavior of current under different light powers can be compared to the retinal light adaptation process (i.e., the retinal sensitivity gradually decreases under strong light conditions). Figure 8(b) shows the visual adaptation behavior of Example 1 under light stimulation of varying durations. As the duration of illumination increases, the degree of dynamic decay of the normalized drain-source current increases. This is similar to how humans become more able to accurately discern objects the longer they spend in a bright environment.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. It is intended that all variations within the meaning and range of equivalents of the claims be embraced herein, and any reference signs in the claims should not be construed as limiting the claims to which they relate.

[0047] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A photoelectric synaptic device based on a PN junction, characterized in that The photoelectric synaptic device based on PN junction is composed of a substrate (1), a source electrode (2), a two-dimensional n-type semiconductor film (3), a gate electrode (4), a two-dimensional p-type semiconductor film (5), and a drain electrode (6); the source electrode (2), the two-dimensional n-type semiconductor film (3), the gate electrode (4), the two-dimensional p-type semiconductor film (5), and the drain electrode (6) are placed on the upper surface of the substrate (1) from left to right; the right side of the source electrode (2) is connected to the two-dimensional n-type semiconductor film (3); the left side of the two-dimensional n-type semiconductor film (3) is connected to the source electrode (2), and the right side is connected to the gate electrode (4); The left side of the gate (4) is connected to the two-dimensional n-type semiconductor film (3), and the right side is connected to the two-dimensional p-type semiconductor film (5); the left side of the two-dimensional p-type semiconductor film (5) is connected to the gate (4), and the right side is connected to the drain (6); the left side of the drain (6) is connected to the two-dimensional p-type semiconductor film (5); the two-dimensional n-type semiconductor film (3) and the two-dimensional p-type semiconductor film (5) are connected in series through the gate (4) to form a PN junction; a PN structure forms a photoelectric synapse to achieve non-monotonic light response under illumination conditions, thereby achieving visual adaptive function under different light and dark conditions; The substrate (1) is a rectangular body and is made of SiO2 material. The area of ​​the upper surface of the substrate (1) is larger than the total area of ​​the lower surface carrying the source electrode (2), the two-dimensional n-type semiconductor film (3), the gate electrode (4), the two-dimensional p-type semiconductor film (5), and the drain electrode (6); The two-dimensional p-type semiconductor film (5) is prepared by using a negative light-responsive p-type two-dimensional semiconductor material, has a width of w5, a length of l5, and a thickness of h5, and serves as a p-type channel of a photoelectric synaptic device based on a PN junction. The negative photoconductivity effect under illumination conditions is used to simulate a light inhibition unit in a biological coupling mechanism. The two-dimensional n-type semiconductor film (3) is prepared by using an n-type two-dimensional semiconductor material with positive photoresponse, has a length of l3, a width of w3, and a thickness of h3, and serves as an n-type conductive channel of a photoelectric synaptic device based on a PN junction. The positive photoconductivity effect under light conditions is used to simulate a light-excited unit in a biological coupling mechanism. The source electrode (2), the gate electrode (4) and the drain electrode (6) are all rectangular bodies, made of metal, and have a thickness of h1; the right side of the source electrode (2) is covered on the two-dimensional n-type semiconductor film (3), the left side of the drain electrode (6) is covered on the two-dimensional p-type semiconductor film (5), and the left side of the gate electrode (4) is covered on the two-dimensional n-type semiconductor film (3), and the right side is covered on the two-dimensional p-type semiconductor film (5).

2. A PN junction-based optoelectronic synaptic device according to claim 1, characterized in that The thickness of the substrate (1) is 500 nanometers.

3. The photoelectric synaptic device based on a PN junction according to claim 1, characterized in that The negative light responsive p-type two-dimensional semiconductor material used in the two-dimensional p-type semiconductor film (5) includes any one of PtSe2, PtTe2, and PdSe2. The two-dimensional p-type semiconductor film (5) has a width w5 of 20 to 40 microns, a length l5 of 30 to 50 microns, and a thickness h5 of 1.5 to 2 nanometers.

4. The photoelectric synaptic device based on a PN junction according to claim 1, characterized in that The two-dimensional n-type semiconductor film (3) adopts an n-type two-dimensional semiconductor material with positive light response, including ReS 2、 Either MoS2 or MoTe2, with a length l3 of 10-30 microns, a width w3 of 10-20 microns, and a thickness h3 of 4.5-5.5 nanometers.

5. The photoelectric synaptic device based on PN junction according to claim 1, characterized in that The source electrode (2), gate electrode (4) and drain electrode (6) are made of a material with a conductivity higher than 40×10 6 The metal is made of S / m, the thickness h1 is 50 nanometers, the width w2 of the source (2) and the width w6 of the drain (6) are 20 micrometers, and the width w4 of the gate (4) is 40 micrometers.

6. A PN junction-based optoelectronic synaptic device as claimed in claim 5, characterized in that The metal used to prepare the source electrode (2), the gate electrode (4) and the drain electrode (6) is gold or copper.

7. The PN junction-based optoelectronic synaptic device according to claim 1, characterized in that The overlapping width of the source electrode (2), the gate electrode (4) and the drain electrode (6) covering the two-dimensional n-type semiconductor film (3) or the two-dimensional p-type semiconductor film (5) is 5 micrometers.

8. A method for preparing a PN junction-based optoelectronic synapse device according to claims 1 to 7, characterized in that The following steps are included: The first step is to synthesize a triangular two-dimensional p-type semiconductor film (5) with a side length greater than 1 mm on a substrate (1) by chemical vapor deposition; In the second step, the synthesized two-dimensional p-type semiconductor film (5) is etched into a single strip by ion beam etching technology, wherein the strip film has a width of w5 and a length of l5, and the strip film serves as a p-type channel of a photoelectric synaptic device based on a PN junction; The third step is to thin the two-dimensional n-type semiconductor bulk material to a height of h3, a width of w3, and a length of l3 by mechanical stripping; and to transfer the mechanically stripped two-dimensional p-type semiconductor material to a substrate (1) by a fixed-point transfer method to obtain a two-dimensional n-type semiconductor thin film (3) as an n-type channel of a PN junction-based optoelectronic synaptic device; Step 4: Using ultraviolet photolithography to determine the positions of the source electrode (2), the gate electrode (4), and the drain electrode (6), that is, photolithography to determine the position of the source electrode (2) at the left end of the two-dimensional n-type semiconductor film (3), photolithography to determine the position of the drain electrode (6) at the right end of the two-dimensional p-type semiconductor film (5), and photolithography to determine the position of the gate electrode (4) between the two-dimensional n-type semiconductor film (3) and the two-dimensional p-type semiconductor film (5); In the fifth step, a metal electrode is deposited at the electrode position of the fourth step photolithography by electron beam evaporation, so that the two-dimensional n-type semiconductor film (3) and the two-dimensional p-type semiconductor film (5) are connected in series through the gate (4) to form a PN junction, the left end of the two-dimensional n-type semiconductor film (3) is the source (2), and the right end of the two-dimensional p-type semiconductor film (5) is the drain (6); the thickness of the source (2), the gate (4), and the drain (6) are all h1, the width of the source (2) is w2, the width of the drain (6) is w6, and the width of the gate (4) is w4.

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