Photoelectric synapse device based on PN junction and preparation method thereof

Abstract

The invention discloses a PN junction-based photoelectric synapse device and a preparation method thereof, and aims to solve the problem that a two-dimensional semiconductor material photoelectric synapse device can only work in a single mode and cannot realize light and shade vision self-adaption. The photoelectric synapse device is composed of a substrate, a source electrode, a two-dimensional n-type semiconductor film, a grid electrode, a two-dimensional p-type semiconductor film and a drain electrode. The preparation method comprises the following steps: preparing a two-dimensional n-type semiconductor film by adopting a positive light response n-type two-dimensional semiconductor material, preparing a two-dimensional p-type semiconductor film by adopting a negative light response p-type two-dimensional semiconductor material, connecting the two films in series to form a PN junction by a grid electrode, and simulating a light excitation generation unit in a biological coupling mechanism by the two-dimensional n-type semiconductor film. The two-dimensional p-type semiconductor film simulates a light suppression generation unit. Non-monotonic photoresponse is realized in the integrated device, a biological coupling mechanism can be effectively simulated to realize light and shade vision self-adaption, the structure is simple, the power consumption is low, and the preparation method is low in process complexity and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial vision systems, and in particular to a photoelectric synapse device based on a two-dimensional semiconductor material PN junction and a preparation method thereof. Background Art

[0002] Photoelectric synaptic devices can simulate the synaptic connection function between photoreceptor cells and neurons in the retina of the human eye, and realize the reception, conversion and processing of light signals at the same time. They are one of the key components for building advanced artificial vision systems. Driven by artificial intelligence and machine learning, photoelectric synaptic devices can enhance the learning ability of artificial vision systems, perform more complex image recognition, scene understanding and decision-making, and have broad application prospects in many fields such as medicine, security, and autonomous driving. However, photoelectric synaptic devices based on CMOS transistor technology still face many challenges in response delay and power consumption. For example, traditional silicon-based semiconductors require a large operating voltage for light signal perception, and the resulting high power consumption problem becomes increasingly prominent as the integration scale increases. In addition, in information processing, due to the limitations of the traditional storage and computing separation architecture, artificial vision systems based on CMOS technology need to digitize analog signals before transmission, which not only leads to a large amount of redundancy in the data processing process, but also brings about high response delay problems in equipment operation. The above problems limit the application scope and efficiency of traditional artificial vision systems to a certain extent.

[0003] In order to solve the above problems, in recent years, researchers are exploring the use of new materials to construct optoelectronic synaptic devices, in order to maintain or improve performance while reducing power consumption and response delay and realizing a more efficient artificial vision system. Inspired by the function of the human retina, researchers have noticed that optoelectronic synaptic devices based on new nanomaterials have both light signal perception (photosensitive characteristics) and information storage and processing (synaptic plasticity, spatiotemporal resolution characteristics) functions, which are very similar to some functions of the retina. This means that a single device can simulate visual functions, and it is expected to achieve the ability to imitate the biological visual system to perceive and process information in the entire simulation domain, thereby breaking through the bottleneck of the existing artificial vision system. As an important branch of nanomaterials, two-dimensional semiconductor materials stand out among many new nanomaterials used to construct optoelectronic synaptic devices because of their advantages such as wide spectral response, high flexibility and carrier mobility, not easy to degrade and oxidize, and strong light absorption ability.

[0004] At present, most optoelectronic synaptic devices based on two-dimensional semiconductor materials are single-material single-element structures or heterogeneous structures formed by stacking multiple materials. This type of optoelectronic synaptic device can only work in a single mode (photoexcitation or photoinhibition) under light stimulation, showing a unidirectional conductance that always increases or decreases. 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 visual adaptation capabilities 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 synapse devices of two-dimensional semiconductor materials based on single-element structure or heterogeneous structure can only work in a single mode, and cannot effectively present non-monotonic light response (that is, its response does not always increase or decrease with the change of lighting conditions), resulting in the inability to effectively simulate the biological coupling mechanism to achieve light and dark visual adaptation. A optoelectronic synapse device based on PN junction and a preparation method thereof are proposed to solve the unidirectional response problem of traditional two-dimensional semiconductor optoelectronic synapse devices, realize the 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 (prepared by using a positive light-responsive n-type two-dimensional semiconductor material) and a two-dimensional p-type semiconductor film (prepared by using a negative light-responsive p-type two-dimensional semiconductor material) to form a PN junction by connecting gates in series. The two-dimensional n-type semiconductor film simulates a light excitation generating unit in a biological coupling mechanism, and the two-dimensional p-type semiconductor film simulates a light inhibition generating unit in a biological coupling mechanism. A PN structure forms a photoelectric synapse, thereby realizing a non-monotonic light response under illumination conditions, and realizing a visual adaptive function under different light and dark conditions.

[0007] The PN junction-based photoelectric synaptic device of the present invention 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 placed 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 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 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 is connected to the drain electrode; 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 constitute the PN junction photoelectric synaptic device of the present invention.

[0008] The substrate is a rectangular body, and is selected to be SiO2 material, which can be purchased commercially, with a thickness of 500 nanometers. There is no requirement for length and width, as long as it can support the source, two-dimensional n-type semiconductor film, gate, two-dimensional p-type semiconductor film, and drain. That is, the area of ​​the upper surface of the substrate is larger than the total area of ​​the lower surface supporting the source, two-dimensional n-type semiconductor film, gate, two-dimensional p-type semiconductor film, and drain.

[0009] The two-dimensional p-type semiconductor film is prepared by using a negative light-responsive p-type two-dimensional semiconductor material (such as PtSe2, PtTe2, PdSe2, etc.), with 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, and is used as a p-type channel of a photoelectric synaptic device based on a PN junction. Its negative photoconductivity effect under illumination conditions is used to simulate the light inhibition unit in the biological coupling mechanism;

[0010] The two-dimensional n-type semiconductor film adopts n-type two-dimensional semiconductor materials with positive photoresponse (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, as an n-type conductive channel of a photoelectric synaptic device based on a PN junction, and its positive photoconductivity effect under illumination conditions is used to simulate the photoexcited unit in the biological coupling mechanism;

[0011] The source, gate and drain are all rectangular and made of metal with good electrical conductivity and high conductivity (such as higher than 40×10 6S / m of gold and copper), the thickness is h1, h1 is 50 nanometers; the width w2 of the source electrode and the width w6 of the drain electrode are 20 microns, and the width w4 of the gate electrode is 40 microns. The right side of the source electrode is covered on the two-dimensional n-type semiconductor film, the left side of the drain electrode is covered on the two-dimensional p-type semiconductor film, the left side of the gate electrode is covered on the two-dimensional n-type semiconductor film, and the right side is covered on the two-dimensional p-type semiconductor film. The overlapping width of the above covering is about 5 microns, ensuring good contact between the electrode and the material.

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

[0013] The first step is to synthesize a triangular two-dimensional p-type semiconductor film 5 with a side length greater than 1 mm on the substrate 1 by a chemical vapor deposition method (refer to the paper "Chemical vapor deposition of monolayerrhenium disulfide (ReS2)" by Keyshar Kunttal et al. 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 on page 7 of the paper "All-electrical skyrmionic magnetic tunnel junction" by Shaohai Chen et al. in the journal Nature, 2024). The strip film serves as the p-type channel of the optoelectronic synapse device based on the PN junction.

[0015] In the third step, the commercially purchased two-dimensional n-type semiconductor bulk material is thinned to a height h3 of 4.5 to 5.5 nanometers by mechanical stripping (refer to the paper "Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2" by Yujun Deng et al. in the journal Nature (Methods, 2018, page 7) and a width w3 of 10-20 microns and a length l3 of 10-30 microns. Then, the mechanically stripped two-dimensional p-type semiconductor material is transferred to the substrate 1 by the fixed-point transfer method (refer to the paper "Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2" by Yujun Deng et al. in the journal Nature (Methods, 2018, page 7) to obtain a two-dimensional n-type semiconductor film 3 as an n-type channel of a photovoltaic synaptic device based on a PN junction.

[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, the gate 4, and the drain 6, that is, photolithograph the position of the source 2 at the left end of the two-dimensional n-type semiconductor film 3, photolithograph the position of the drain 6 at the right end of the two-dimensional p-type semiconductor film 5, and photolithograph 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, an electron beam evaporation method is used (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 (Nature), 2024) to deposit a high-conductivity metal electrode (preferably gold or copper) at the electrode position of the fourth step photolithography, 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, h 1 It is 50 nanometers, the widths of the source 2 and the drain 6 are w2 and w6 respectively, the width of the gate 4 is w4, w2 and w6 are 20 microns, and w4 is 40 microns.

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

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

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

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

[0022] 4. The present invention forms a PN junction by connecting a two-dimensional n-type semiconductor film and a two-dimensional p-type semiconductor film in series. This series structure does not require the construction of a heterojunction, reduces process complexity, and achieves the practical requirement of simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a front view of the overall structure of the photoelectric synapse device based on PN junction of the present invention;

[0024] Figure 2 It is a top view of the overall structure of the photoelectric synapse device based on PN junction of the present invention;

[0025] Figure 3 This is a top view of the embodiment 1 of the photoelectric synapse device based on the PN junction of the present invention (optical microscope photo, equivalent to Figure 2 Rotate clockwise approximately 135 degrees). Figure 3 This is a photo taken under a microscope, and the scale bar is located in the lower left corner of the picture. ;

[0026] Figure 4 The input-output and Gaussian transfer characteristic curves of the photoelectric synaptic device based on the PN junction in Example 1 of the present invention under dark conditions are shown in FIG. Figure 4 (a) is the input-output curve of the photoelectric synapse device based on PN junction in Example 1 of the present invention under dark conditions, Figure 4 (b) is the Gaussian transfer characteristic curve of Example 1 of the PN junction-based photoelectric synapse device of the present invention under dark conditions.

[0027] Figure 5 The two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 of the embodiment 1 of the present invention are at a wavelength of 532nm (power 1.41nWμm -2 The upper part corresponds to the curve of the photocurrent changing with time in the two-dimensional n-type semiconductor thin film 3ReS2 material, and the lower part corresponds to the curve of the photocurrent changing with time in the two-dimensional p-type semiconductor thin film 5PtSe2 material. Figure 5 (a) shows the current change when a single laser pulse is irradiated on Example 1. The positive increase in current can be compared to the positive increase in current after synaptic excitatory activity, and the negative increase in current can be compared to the negative increase in current after synaptic inhibition. Figure 5 (b) shows the current change of Example 1 under continuous pulse stimulation with an interval of 2s. The current change curves repeated twice can be compared to the double pulse facilitation and inhibition of the synapse under double stimulation. Figure 5 (c) shows that under the stimulation of multiple identical pulses (with an interval of 0.5s), the repeated current change curve can be analogous to the long-term enhancement and inhibition of the synaptic response after external stimulation.

[0028] Figure 6 is a Gaussian transfer characteristic curve of the drain-source current changing with the gate-source voltage under 532nm wavelength light stimulation in Example 1 of the present invention; Figure 6 (a) is the curve of Gaussian transfer characteristics changing with optical power density. Figure 6 (b) is the curve of Gaussian transfer characteristics changing with light duration. Figure 6 (c) is a curve showing the Gaussian transfer characteristic changing with the light removal time.

[0029] Figure 7The blue light (power 4.72nWμm) at 450nm of Example 1 of the present invention -2 The curve of the change of the drain-source current over time under different gate voltages under irradiation (100V, 5s duration). Under the gate voltage of 20V and -20V, the current shows negative and positive current changes respectively, indicating that the photoelectric synaptic device based on PN junction shows positive and negative photoconductivity effect regulated by gate voltage under the gate voltage.

[0030] Figure 8 is a graph of the attenuation amplitude of the normalized photoresponse current changing with time under 450nm blue light irradiation of 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 reference numerals: 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 modes of the present invention are further described below in conjunction with the accompanying drawings and examples so that those skilled in the art can better understand the present invention and implement it, but the examples are not intended to limit the present invention.

[0033] like Figure 1 and Figure 2 As shown, the PN junction-based photoelectric synaptic device of the present invention is composed of a substrate 1, a source 2, a two-dimensional n-type semiconductor film 3, a gate 4, a two-dimensional p-type semiconductor film 5, and a drain 6. The source 2, the two-dimensional n-type semiconductor film 3, the gate 4, the two-dimensional p-type semiconductor film 5, and the drain 6 are placed on the upper surface of the substrate 1 from left to right. The right side of the source 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 2, and the right side is connected to the gate 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, and the two-dimensional n-type semiconductor film 3, the two-dimensional p-type semiconductor film 5, and the gate 4 constitute the PN junction photoelectric synaptic device of the present invention.

[0034] The substrate 1 is a rectangular body, and is selected to be SiO2 material, which can be purchased commercially, with a thickness of 500 nanometers. There is no requirement for length and width, as long as it can support the source 2, the two-dimensional n-type semiconductor film 3, the gate 4, the two-dimensional p-type semiconductor film 5, and the drain 6. That is, the area of ​​the upper surface of the substrate 1 is larger than the total area of ​​the lower surface supporting the source 2, the two-dimensional n-type semiconductor film 3, the gate 4, the two-dimensional p-type semiconductor film 5, and the drain 6.

[0035] The two-dimensional p-type semiconductor film 5 is made of negative light-responsive p-type two-dimensional semiconductor materials (such as PtSe2, PtTe2, PdSe2, etc.), with 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, and serves as a p-type channel of a photoelectric synaptic device based on a PN junction. Its negative photoconductivity effect under illumination conditions is used to simulate a light inhibition unit in a biological coupling mechanism;

[0036] The two-dimensional n-type semiconductor film 3 is made of n-type two-dimensional semiconductor material with positive light response (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, as an n-type conductive channel of a photoelectric synaptic device based on a PN junction, and its positive photoconductivity effect under illumination conditions is used to simulate the photoexcited unit in the biological coupling mechanism;

[0037] The source 2, gate 4 and drain 6 are all rectangular and have a conductivity higher than 40×10 6 The metal of S / m (such as gold, copper) has a thickness of h1, h1 is 50 nanometers; the width w2 of the source electrode 2 and the width w6 of the drain electrode 6 are 20 micrometers, and the width w4 of the gate electrode 4 is 40 micrometers. 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 also covered on the two-dimensional p-type semiconductor film 5, and the left and right sides of the gate electrode 4 are respectively covered on the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5, and the overlapping width of the above covering is about 5 micrometers, which ensures that the electrode and the material form a good contact.

[0038] Example 1 is described in detail below in conjunction with the specific material selection of the two-dimensional semiconductor.

[0039] First, the preparation method of Example 1 is: synthesize a two-dimensional p-type semiconductor film 5 (using PtSe2, with a thickness h5 of 1.5 nanometers ( Figure 1The thickness of the two-dimensional semiconductor film 5 is 20 μm, which should be less than h3), with a length of 50 μm and a width of 35 μm. Then, the bulk material (using ReS2) is thinned to about 5.2 nanometers of h3 by mechanical stripping, forming a two-dimensional n-type semiconductor film 3 (with a length of 20 μm and a width of 12 μm), and then placed next to the two-dimensional p-type semiconductor film 5 by a fixed-point transfer method (the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5 are not connected laterally). Then, metal electrodes (gold Au is selected) are deposited between the two-dimensional n-type semiconductor film 3 and the two-dimensional p-type semiconductor film 5, on the left end of the two-dimensional n-type semiconductor film 3, and on the right end of the two-dimensional p-type semiconductor film 5 by ultraviolet lithography, electron beam evaporation, stripping and other technologies, as the source 2 (width w2 is 20 μm), the gate 4 (width w4 is 40 μm), and the drain 6 (width w6 is 20 μm). 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 a source 2 , and the right end of the two-dimensional p-type semiconductor film 5 is a 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, and the drain electrode 6 is completely covered on the two-dimensional p-type semiconductor film 5. Good ohmic contacts are formed between the electrodes and the materials, and there is no obvious Schottky barrier, which is convenient for subsequent electrical testing.

[0041] Figure 4 (a) is a curve showing the change of the current between the drain 6 and the source 2 (i.e., the drain-source current) 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 approximately linear current change indicates that the PN junction-based photoelectric synapse device of the present invention has excellent conductive properties. Figure 4 (b) represents 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 value. 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 5The two-dimensional n-type semiconductor film 3 (ReS2) and the two-dimensional p-type semiconductor film 5 (PtSe2) of Example 1 are at a wavelength of 532nm (power 1.41nWμm -2 , duration 3s) curve of current changing with time under light stimulation. Figure 5 (a) shows the effect of a single light pulse (wavelength 532 nm, power 1.41 nW μm) on the performance of ReS2 and PtSe2. -2 , duration 3s) under the curve of current change with time, it can be seen that the ReS2 current response shows a positive response, which can be compared to the excitatory potential exhibited by the synapse after external stimulation, and the PtSe2 current response shows a negative response, which can be compared to the inhibitory potential exhibited by the synapse after external stimulation. Figure 5 (b) shows the time-varying curves of ReS2 and PtSe2 currents under the irradiation of two consecutive light pulses with an interval of 2s, which can be respectively analogized to the synapse under two external stimuli at intervals. The first pulse causes the synaptic potential to change, and the second pulse enhances or inhibits this change, which corresponds to the double-pulse facilitation response and double-pulse inhibition response, respectively. Figure 5 (c) shows the time-varying curves of the ReS2 and PtSe2 currents under continuous illumination of multiple light pulses with an interval of 0.5 s, which can be respectively analogous to the sustained increase and sustained decrease in potential changes of synapses after repeated stimulation, that is, corresponding to long-term potentiation and long-term inhibition of plasticity, respectively.

[0043] Figure 6 The Gaussian transfer characteristic curve of Example 1 under 532 nm light stimulation is shown. When the gate-source voltage is greater than the threshold voltage of PtSe2, PtSe2 is in the off state. Since the resistance of ReS2 is very small compared to 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, the current in the channel of the series device is prevented from transmitting. 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, that is, the current decreases exponentially with the gate voltage, and the PN junction resistance of the series ReS2-PtSe2 presents a Gaussian characteristic curve. Figure 6 (a) shows that as the optical power increases, the gate-source voltage corresponding to the maximum drain-source current decreases. The main reason is that the threshold voltage of PtSe2 and ReS2 shifts to the left, so their gate-source voltage also shifts to the left when the maximum current is reached. Figure 6(b) shows that the Gaussian transfer characteristic curve will decrease with the increase of light duration, and the gate-source voltage corresponding to the maximum current will also decrease. This is because the longer the light exposure time, the more photons are injected into ReS2, and the more oxygen molecules are desorbed from the surface of PtSe2, resulting in a larger left shift of the gate-source voltage corresponding to the maximum current. Figure 6 (c) shows that the Gaussian transfer characteristic curve can still be maintained for a period of time after the light is removed, and the peak position gradually moves to the right over time and finally returns to the initial state. This relaxation behavior shows that Example 1 has memory characteristics similar to 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 the characteristics of both photoexcitation and photoinhibition. Under different gate voltages, the photocurrent first rises and then falls, and the photocurrent curve shows an inflection point, 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 is dominant, in which the light absorption of ReS2 causes the PN junction conductivity of the real series ReS2-PtSe2 to increase rapidly. As time goes on, the inflection point appears because the negative photoconductivity effect of PtSe2 gradually dominates under continuous illumination. With the change of gate voltage, 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 (it can simulate the light 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 increase in the sensitivity of the retina during dark adaptation. -2 Under these conditions, the photocurrent will first reach saturation and then show dynamic decay behavior over time, that is, the drain-source current reaches a peak in a bright environment and then gradually decreases. The dynamic behavior of the above current under different light powers can be compared to the light adaptation process of the retina (that is, the sensitivity of the retina gradually decreases under strong light conditions). Figure 8(b) shows the visual adaptive behavior of Example 1 of the present invention under light stimulation of different durations. As the duration of illumination increases, the degree of dynamic attenuation of the normalized drain-source current under illumination increases with the duration. This is like the longer humans stay in a bright environment, the easier it is to accurately distinguish objects.

[0046] It is obvious 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 present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0047] In addition, it should be understood that although the present specification is described in terms of implementation modes, not every implementation mode 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 may also be appropriately combined to form other implementation modes 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 PN junction-based photoelectric synaptic device 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, and realize visual adaptive functions 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, with a width of w5, a length of l5, and a thickness of h5, and is used as a p-type channel of a photoelectric synaptic device based on a PN junction. Its 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. Its positive photoconductivity effect under illumination conditions is used to simulate a photoexcited 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), 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 synapse device as claimed in claim 1, characterized in that The thickness of the substrate (1) is 500 nanometers.

3. A PN junction-based optoelectronic synapse device as claimed in 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 width w5 of the two-dimensional p-type semiconductor film (5) is 20 to 40 microns, the length l5 is 30-50 microns, and the thickness h5 is 1.5 to 2 nanometers.

4. A PN junction-based optoelectronic synapse device as claimed in 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、 Any one of MoS2 and MoTe2, the length l3 is 10-30 microns, the width w3 is 10-20 microns, and the thickness h3 is 4.5-5.5 nanometers.

5. A PN junction based optoelectronic synapse device as claimed in claim 1, characterized in that The source electrode (2), the gate electrode (4) and the 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 synapse 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. A PN junction-based optoelectronic synapse device as claimed in 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 as claimed in 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; The second step is to etch the synthesized two-dimensional p-type semiconductor film (5) 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 synapse 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 exfoliation; and to transfer the mechanically exfoliated 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 photovoltaic synaptic device based on a PN junction; 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 is performed to determine the position of the source electrode (2) at the left end of the two-dimensional n-type semiconductor film (3), photolithography is performed to determine the position of the drain electrode (6) at the right end of the two-dimensional p-type semiconductor film (5), and photolithography is performed 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 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 electrode (4) to form a PN junction, the left end of the two-dimensional n-type semiconductor film (3) is the source electrode (2), and the right end of the two-dimensional p-type semiconductor film (5) is the drain electrode (6); the thickness of the source electrode (2), the gate electrode (4), and the drain electrode (6) are all h1, the width of the source electrode (2) is w2, the width of the drain electrode (6) is w6, and the width of the gate electrode (4) is w4.

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