Bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-energized photoelectric synapse device and preparation method thereof

Abstract

The invention discloses a bismuth telluride / gallium nitride ultraviolet-near-infrared broadband self-powered photoelectric synapse device and a preparation method thereof, and belongs to the technical field of two-dimensional semiconductor materials and neuromorphic devices. The bismuth telluride / gallium nitride photoelectric synapse device specifically comprises a gallium nitride substrate, a bismuth telluride layer and gold electrodes, the gallium nitride substrate and the bismuth telluride layer are stacked through a transfer technology, a bismuth telluride / gallium nitride heterojunction is formed between the gallium nitride substrate and the bismuth telluride layer, and the two gold electrodes are located on the gallium nitride substrate and the bismuth telluride layer respectively. The photoelectric synaptic device is wide in response range, shows a remarkable photosynaptic behavior in a spectral range from ultraviolet to near infrared (350-1064nm), can work under light stimulation with the power of 8 * 10 <-8 > W / cm < 2 >, has self-energy-supply working capability, can simulate basic synaptic behaviors such as long-time-interval enhancement, short-time-interval enhancement and a double-pulse facilitation effect of biological synapses, and has a good application prospect. The method can be applied to low-power artificial intelligence and other fields.

Description

Technical Field

[0001] The present invention belongs to the technical fields of two-dimensional semiconductor materials and neuromorphic devices, and particularly relates to a bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered optoelectronic synaptic device and a preparation method thereof. Background Art

[0002] Traditional computing architectures based on the von Neumann structure have independent processing units and storage units, which lead to problems such as redundant data transmission, huge energy consumption, and low computing efficiency during the operation process, and cannot meet the computing requirements of the artificial intelligence era. Neuromorphic computing integrates computing and storage units together, can simulate the operation mode of the human brain, and is a new computing model with the characteristics of low power consumption and high speed. As a basic component of artificial neural networks, artificial synapses can simulate the plasticity of human brain synapses and have received increasing attention. A variety of types of electrically regulated neuromorphic devices have been proposed to simulate synaptic functions. However, due to bandwidth, connection density trade-off, and interconnection problems involved, the speed of neural computing has been limited, and optoelectronic synapses have been developed based on this. Optoelectronic synaptic devices can combine optical signals with synaptic plasticity. Compared with the widely studied neuromorphic devices regulated by electrical signals, optoelectronic synaptic devices have many remarkable characteristics, such as low crosstalk, high anti-interference ability, and low power consumption, and are more suitable for ultra-high-speed computing.

[0003] Currently, the research on optoelectronic synaptic devices still remains at the primary stage and still faces many challenges. There are about 10 15 synapses in the human brain, but the total power is only 20 W, and the energy consumption of a single synapse firing once is only 10 fJ. At such low energy consumption, the heat generated during operation is extremely small and will not affect the normal operation of the brain. However, currently existing optoelectronic synaptic devices generally have the problem of high energy consumption, and it is urgent to prepare optoelectronic synaptic devices with ultra-low energy consumption. In addition, the current optoelectronic synaptic devices have a narrow optical response wavelength range and generally can only work under ultraviolet light signals, while the response to visible light and infrared light is weak or non-responsive, which severely restricts the application scenarios of optoelectronic synaptic devices. Developing wide-spectrum response optoelectronic synapses that can work under visible light and near infrared light can not only be used for human visual function simulation, but also is expected to realize the application interconnection with optical communication technology. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of high energy consumption and narrow response wavelength range that currently existing optoelectronic synaptic devices generally have, and to provide a bismuth telluride / gallium nitride heterojunction two-terminal optoelectronic synaptic device with ultraviolet-near infrared broadband response, simple structure, and self-powered working ability, and a preparation method thereof.

[0005] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] A bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered optoelectronic synaptic device, the optoelectronic synaptic device includes a gallium nitride substrate, a bismuth telluride layer and two gold electrodes, a bismuth telluride / gallium nitride heterojunction is formed between the gallium nitride substrate and the bismuth telluride layer, and the two gold electrodes are respectively located on the gallium nitride substrate and the bismuth telluride layer.

[0007] In the present invention, the optoelectronic synaptic device can simulate the synaptic behavior of the human brain under ultraviolet-near infrared light signal stimulation. The synaptic behavior of the optoelectronic synaptic device can be adjusted by applying an external bias voltage. The optoelectronic synaptic device can operate at 0 bias voltage.

[0008] Further, the thickness of the bismuth telluride layer is 6-10 nm.

[0009] Further, the thickness of the gallium nitride substrate is 2-3 microns.

[0010] Further, the thickness of the gold electrode is 100-300 nm.

[0011] Further, the gold electrode is divided into a source electrode and a drain electrode, the source electrode is located on the bismuth telluride layer, and the drain electrode is located on the gallium nitride substrate.

[0012] Further, the source electrode and the drain electrode are symmetric about the horizontal dividing line of the bismuth telluride layer and the gallium nitride substrate, the electrode width is 50-200 microns, and the distance between the source electrode and the drain electrode is 10-300 microns ( Figure 2 the distance between the upper and lower two Au electrodes).

[0013] A preparation method of the above-mentioned bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered optoelectronic synaptic device, the method includes the following steps:

[0014] Step 1, grow a bismuth telluride thin film on a SiO 2 / Si substrate by chemical vapor deposition;

[0015] Step 2, transfer the bismuth telluride thin film to the gallium nitride substrate by a wet transfer process to form a bismuth telluride / gallium nitride heterostructure;

[0016] Step 3, deposit the source electrode and the drain electrode by electron beam evaporation technology to prepare a bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered optoelectronic synaptic device.

[0017] Further, in step 2, the wet transfer process is specifically:

[0018] (1) Use a PMMA thin film as a support layer and an HF solution with a mass fraction of 3%-5% as an etching solution;

[0019] (2) Place the bismuth telluride / gallium nitride heterojunction in a tube furnace and anneal it at 150 °C for 1 h under an argon atmosphere. Then, use acetone to remove the PMMA film on the surface of the heterojunction.

[0020] Further, in step three, the electron beam current for evaporating the gold electrode is 90 - 100 mA.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device described in the present invention has a wide response range, exhibits significant optoelectronic synaptic behavior in the ultraviolet to near-infrared (350 - 1064 nm) spectral range, has application potential in the field of human vision function simulation, and is expected to achieve application interconnection with optical communication technology.

[0023] 2. The bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device described in the present invention has low energy consumption. This device can exhibit obvious optoelectronic synaptic behavior under light stimulation with a power of 10 -8 W / cm 2 and has the ability to work self-powered.

[0024] 3. The bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device described in the present invention has a simple principle, a simple structure, and a small size, and has the potential for integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device;

[0026] Figure 2 is an optical microscope picture of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1;

[0027] Figure 3 is the dark state I-V curve graph of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1;

[0028] Figure 4 is the continuous scan I-V curve graph of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1;

[0029] Figure 5 is the I-t curve graph of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1 under light stimulation at 367 nm, 520 nm, 638 nm, 850 nm, and 1064 nm;

[0030] Figure 6 is the I-t curve graph of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1 at a bias voltage of 20 - 100 mV;

[0031] Figure 7 I - t curve (0 bias) diagrams of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1 under illumination times of 1 s, 5 s, 15 s, 30 s, and 50 s;

[0032] Figure 8 PPF behavior (0 bias) diagram of the bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device prepared in Example 1. Detailed implementation manners

[0033] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and examples, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0034] Example 1:

[0035] The present invention provides a bismuth telluride / gallium nitride ultraviolet - near - infrared broadband self - powered optoelectronic synaptic device with a simple structure. The device structure diagram is as Figure 1 shown. Using the wet transfer technology, the bismuth telluride thin film (6 - 10 microns) grown by CVD is transferred onto a 2 - micron - thick commercial gallium nitride substrate to form a bismuth telluride / gallium nitride heterojunction. Then, gold electrodes with a thickness of 300 nm are respectively evaporated on the gallium nitride substrate and the bismuth telluride layer to prepare a two - terminal optoelectronic synaptic device. Among them: the gold electrodes are divided into a source electrode and a drain electrode. The source electrode is located on the bismuth telluride layer, and the drain electrode is located on the gallium nitride substrate. The source electrode and the drain electrode are symmetric with respect to the interface between the bismuth telluride layer and the gallium nitride substrate. The electrode width is 200 microns, and the electrode spacing is 10 microns. The specific preparation steps are as follows:

[0036] Step 1. Grow a bismuth telluride thin film on a SiO 2 / Si substrate by CVD method;

[0037] Step 2. Place the SiO 2 / Si substrate with the grown bismuth telluride thin film on a heating table at 90 °C, drop 3 - 5 drops of PMMA solution with a mass fraction of 6%, wait for 5 minutes to make the PMMA solidify into a film, and then take the substrate off the heating table and let it cool naturally;

[0038] Step 3. Put the SiO 2 / Si substrate with the PMMA thin film into a HF solution with a mass fraction of 3%. After soaking for 20 - 60 min, the PMMA thin film and the bismuth telluride thin film are separated from the SiO 2 / Si substrate;

[0039] Step 4. Pick up the separated PMMA thin film and bismuth telluride thin film, wash them 3 - 5 times with deionized water, then pick them up with a gallium nitride substrate and place them vertically to dry.

[0040] Step 5: Place the gallium nitride substrate-bismuth telluride thin film-PMMA thin film stack into a tube furnace and anneal it at 150 °C for 1 h under an argon atmosphere to improve the interfacial contact between the gallium nitride substrate and the bismuth telluride thin film;

[0041] Step 6: Immerse the annealed gallium nitride substrate-bismuth telluride thin film-PMMA thin film stack in acetone solution for 24 h to remove the PMMA thin film and obtain a bismuth telluride / gallium nitride heterojunction;

[0042] Step 7: Using the method of electron beam evaporation, keep the pressure in the chamber below 4.5×10 -4 Pa, and evaporate the source electrode and drain electrode on the bismuth telluride / gallium nitride heterojunction to obtain a bismuth telluride / gallium nitride heterojunction optoelectronic synaptic device.

[0043] Observe the above-prepared synaptic device with an optical microscope, see Figure 2 for details. Test the optoelectronic properties of the device, and the results are shown in Figures 3 - 8 for details. The I-V curve of the device in the dark state ( Figure 3 ) shows obvious rectifying characteristics, which confirms the formation of the bismuth telluride / gallium nitride heterojunction. Further, within the bias voltage range of 0 - 5 V, the continuous scanning I-V curve of the device is obtained by continuously scanning 10 cycles, see Figure 4 for details, showing the non-volatile switching characteristics of the device. To study the response law of the device to different wavelength light stimuli, apply continuous 10 s light stimuli of 367 nm, 520 nm, 638 nm, 850 nm, and 1064 nm to the device respectively, and read the curve of the device current changing with time, as shown in Figure 5 . After the device is stimulated by light, the current continuously increases. When the light stimulus is removed, the current does not immediately return to the initial state, but slowly decreases, showing a strong persistent photoconductivity effect and having a memory effect on the stimulation of light signals, and can be used to simulate the function of biological synapses. And the device has obvious responses to light signals from ultraviolet to near-infrared. In addition, the power of the above 367 nm light signal is only 8×10 -8 W / cm 2 , indicating the great potential of the device in the field of low-power applications.

[0044] Under different bias voltage (20 mV, 40 mV, 60 mV, 80 mV, and 100 mV) states, apply continuous 10 s light stimulus of 405 nm to the device, and the photocurrent response is shown in Figure 6 . The excitatory postsynaptic current of the device increases with the increase of the applied bias voltage, and the transition of the device from STP to LTP behavior can be controlled by bias modulation.

[0045] At the 0-bias state, a light pulse with a wavelength of 405 nm is applied to the synaptic device, and the light stimulation time is changed. The photocurrent response is as Figure 7 shown. It can be found that the post-synaptic excitatory current of the device increases as the light stimulation time becomes longer. By adjusting the light stimulation time, the transition of the device from STP to LTP behavior can be controlled. At the 0-bias state, two consecutive light pulses (pulse time is 0.2 s, pulse interval is 5 s, and light pulse wavelength is 405 nm) are applied to the synaptic device. The photocurrent response is as Figure 8 shown. It can be observed that the device exhibits a larger post-synaptic excitatory current after the second light signal stimulation, indicating that the device can simulate the paired-pulse facilitation (PPF) effect of biological synapses. The above device can well simulate the behaviors of biological synapses such as STP, LTP, and PPF at the 0-bias state, verifying its self-powered working ability.

[0046] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synaptic device, characterized in that: The photoelectric synapse device comprises a gallium nitride substrate, a bismuth telluride layer and two gold electrodes, a bismuth telluride / gallium nitride heterojunction is formed between the gallium nitride substrate and the bismuth telluride layer, and the two gold electrodes are respectively located on the gallium nitride substrate and the bismuth telluride layer.

2. The bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 1, characterized in that: The thickness of the bismuth telluride layer is 6-10 nm.

3. The bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 1, characterized in that: The thickness of the gallium nitride substrate is 2 to 3 microns.

4. The bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 1, characterized in that: The thickness of the gold electrode is 100-300 nm.

5. The bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 1, characterized in that: The gold electrode is divided into a source electrode and a drain electrode, the source electrode is located on the bismuth telluride layer, and the drain electrode is located on the gallium nitride substrate.

6. The bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 5, characterized in that: The source electrode and the drain electrode are symmetrical about the horizontal boundary line of the bismuth telluride layer and the gallium nitride substrate, the electrode width is 50 to 200 microns, and the distance between the source electrode and the drain electrode is 10 to 300 microns.

7. A method for preparing the bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: Step 1: growing a bismuth telluride thin film on a SiO2 / Si substrate by chemical vapor deposition; Step 2: transferring the bismuth telluride film onto the gallium nitride substrate by a wet transfer process to form a bismuth telluride / gallium nitride heterostructure; Step 3: Use electron beam evaporation technology to evaporate the source and drain to prepare a bismuth telluride / gallium nitride ultraviolet-near infrared wide-band self-powered optoelectronic synapse device.

8. The method for preparing a bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 7, characterized in that: In step 2, the wet transfer process is specifically as follows: (1) Using PMMA film as the support layer and HF solution with a mass fraction of 3% to 5% as the etching solution; (2) The bismuth telluride / gallium nitride heterojunction was placed in a tube furnace and annealed at 150° C. for 1 h in an argon atmosphere, and then the PMMA film on the surface of the heterojunction was removed with acetone.

9. The method for preparing a bismuth telluride / gallium nitride ultraviolet-near infrared broadband self-powered photoelectric synapse device according to claim 7, characterized in that: In step 3, the electron beam current for evaporating the gold electrode is 90-100 mA.

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