Deep ultraviolet photodetector based on large-size hexagonal boron nitride single crystal and preparation method thereof

Abstract

A deep ultraviolet photodetector based on large-size hexagonal boron nitride single crystals and a preparation method thereof, comprising: a substrate; an adhesive, spin-coated on the upper surface of the substrate; a large-size hexagonal boron nitride single crystal, covering the surface of the substrate spin-coated with the adhesive; and a pair of electrodes, partially covering the upper surface of the large-size hexagonal boron nitride single crystal. The present invention prepares a deep ultraviolet photodetector with high response speed, high switching ratio, and high spectral selectivity in the deep ultraviolet region through large-area, high-quality, and moderately thick large-size hexagonal boron nitride single crystals. The detector has great application prospects in space optical communications, military early warning detection, ozone hole monitoring, and aerospace fields.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor photoelectric detection, and relates to a deep ultraviolet photoelectric detector based on a large-size hexagonal boron nitride single crystal and a preparation method thereof. Background Art

[0002] A photodetector is a device that can convert the energy of incident photons into electrical signals. This type of device is very important in our daily lives and has a wide range of applications. Ultraviolet photodetectors that can detect light in the ultraviolet band have been widely used in chemical exploration, space optical communications, combustion detection, military attack warning, and ozone hole monitoring. Since the atmosphere has a very strong absorption effect on deep ultraviolet light with a wavelength less than 280nm in the ultraviolet band, there is basically no deep ultraviolet light in the atmosphere. Based on this characteristic, its application in the field of optical communications will have the advantages of all-weather operation and high confidentiality. Therefore, deep ultraviolet photodetectors have important development significance and application prospects in the field of national security.

[0003] The detection range of semiconductor photodetectors is mainly determined by the band gap of the semiconductor material itself. Hexagonal boron nitride, as a two-dimensional layered material with an ultra-wide band gap (6.4 eV), is the preferred material for preparing deep ultraviolet photodetectors. At present, the application of hexagonal boron nitride to prepare deep ultraviolet photodetectors faces the following problems. Although the hexagonal boron nitride film prepared by chemical vapor deposition (CVD) has good crystal quality, it is only a few nanometers thick, which will affect the sensitivity of the detector. The film prepared by radio frequency magnetron sputtering (RFMS), pulsed laser deposition (PLD), physical vapor deposition (PVD) and other methods with lower growth temperatures has lower quality and more stacking faults, dislocations, grain boundaries, and point defects, which will introduce recombination centers, thereby reducing the responsivity and sensitivity of the detector. Therefore, the most important point to improve the performance of deep ultraviolet photodetectors is to prepare large-area, high-crystal quality, and moderately thick hexagonal boron nitride single crystal materials. Summary of the invention

[0004] Based on the above technical background, the present invention provides a deep ultraviolet photodetector based on large-size hexagonal boron nitride single crystal and a preparation method thereof, which uses large-area, high-quality, moderately thick large-size hexagonal boron nitride single crystals as the semiconductor layer of the deep ultraviolet photodetector, thereby ensuring that the detector has the advantages of low dark current, high switching ratio, high response speed, and high spectral selectivity in the deep ultraviolet region. At the same time, the device preparation process is simple and the cost is low.

[0005] As a first object of the present invention, a deep ultraviolet photodetector based on a large-size single crystal of hexagonal boron nitride is provided, such as Figure 1As shown, from bottom to top, they are: a substrate; an adhesive, which is spin-coated on the upper surface of the substrate using a coating machine; a large-sized hexagonal boron nitride single crystal, which covers the surface of the substrate spin-coated with the adhesive; and a pair of electrodes, which partially cover the upper surface of the large-sized hexagonal boron nitride single crystal.

[0006] In the structure of the large-size single crystal deep ultraviolet photodetector based on hexagonal boron nitride, the substrate can be diamond, quartz glass, sapphire or silicon.

[0007] In the structure of the large-size single crystal deep ultraviolet photodetector based on hexagonal boron nitride, the adhesive can be selected from insulating materials with bonding properties such as polydimethylsiloxane, polymethyl methacrylate, and ethyl cyanoacrylate.

[0008] In the structure of the deep ultraviolet photodetector based on large-size hexagonal boron nitride single crystal, the large-size hexagonal boron nitride single crystal is characterized by: a thickness of 5 to 50 μm and an area of ​​1 cm 2 The above large-size single crystal of hexagonal boron nitride.

[0009] In the structure of the large-size single crystal deep ultraviolet photodetector based on hexagonal boron nitride, the material of the electrode can be molybdenum, nickel, titanium, chromium, gold or silver, and the shape of the electrode can be an interdigitated electrode, a cylindrical electrode, a plane parallel electrode, etc., with a thickness of 80 to 120 nm and a channel width of 5 to 40 μm.

[0010] As another object of the present invention, a method for preparing a large-size single crystal deep ultraviolet photodetector based on hexagonal boron nitride is also provided, the method comprising the following steps:

[0011] Step 1, preparing large-size single crystals of hexagonal boron nitride;

[0012] Step 2, providing a substrate;

[0013] Step 3, connecting the large-size single crystal of hexagonal boron nitride to the substrate using an adhesive;

[0014] Step 4: Prepare electrodes.

[0015] The step 1 prepares large-sized hexagonal boron nitride single crystals, which are large-sized hexagonal boron nitride single crystals prepared by single crystal growth methods such as atmospheric pressure metal flux method, high temperature and high pressure method, high pressure temperature gradient method, and metal flux method.

[0016] As a preferred method, the specific method for preparing large-sized hexagonal boron nitride single crystals is as follows: first, nickel, chromium and boron powder are prepared into nickel-chromium-boron alloy by mechanical alloying, then melted at high temperature in a protective gas atmosphere, and then cooled and segregated in a mixed atmosphere of protective gas and reaction gas to synthesize hexagonal boron nitride single crystals, and finally, hexagonal boron nitride large-sized single crystals are obtained by chemical etching and peeling, and cut into 1 cm pieces as needed. 2Large-sized hexagonal boron nitride single crystals with the above area size and thickness of 5 to 50 μm.

[0017] Preferably, the prepared large-size hexagonal boron nitride single crystal has the following characteristics: the large-size hexagonal boron nitride single crystal is a photoelectric sensitive material, and is a large-size hexagonal boron nitride single crystal with a thickness of 5 to 50 μm; the overall crystal face is (002), the sides are in the [1-100] and [11-20] directions, and the single crystal property is excellent; the crystallinity is high, the half-peak width of the (002) peak of XRD is less than 0.03°, and the Raman spectrum E 2g The half-peak width of the vibration peak is less than 10 cm -1 ; Good electrical insulation, surface resistivity is 10 15 Ω or above; low impurity defect density, transparent, good light transmittance; can be cut into 1cm as needed 2 Above area size.

[0018] In the step 2, the substrate is cut into a required size and shape as required, and then simply cleaned. The substrate material can be diamond, quartz glass, sapphire or silicon.

[0019] In the step three, the specific method of connecting the large-sized hexagonal boron nitride single crystal to the substrate using an adhesive is as follows: drop the selected adhesive on the surface of the substrate, the adhesive can be selected from polydimethylsiloxane, polymethyl methacrylate, ethyl cyanoacrylate, etc., use a glue spreader to spin coat at a speed of 1500 to 4000 r / min, set the time to 60 to 120 s, and then cover the large-sized hexagonal boron nitride single crystal on the surface of the substrate spin-coated with the adhesive, and then put it into a blast drying oven at 60 to 90° C. and dry it for 30 to 60 minutes.

[0020] Preferably, ethyl cyanoacrylate is selected as the adhesive, and the rotation speed of the spin coating process is set to 3000 r / min and the time is 90 s. After the large-size hexagonal boron nitride single crystal is covered, it is dried in a forced air drying oven at 80° C. for 60 min.

[0021] In the step 4, the specific method for preparing the electrode is as follows: use a mask plate suitable for the designed electrode structure to cover the upper surface of the large-size single crystal of hexagonal boron nitride, and place the whole into a radio frequency magnetron sputtering instrument to prepare the electrode. The material of the electrode can be molybdenum, nickel, titanium, chromium, gold or silver. The electrode channel width is set to 5 to 40 μm, and the electrode thickness is 80 to 120 nm.

[0022] Preferably, the width of the electrode channel is set to 10 μm.

[0023] Beneficial Effects

[0024] The beneficial effects of the present invention are mainly reflected in:

[0025] 1. The deep ultraviolet photodetector prepared by the present invention using large-area, high-quality large-size hexagonal boron nitride single crystals as the semiconductor layer has extremely low dark current and very high breakdown voltage. It can work in a high temperature environment and does not require additional refrigeration equipment to offset the dark current.

[0026] 2. The present invention adopts large-size single crystals of hexagonal boron nitride with high crystal quality to prepare deep ultraviolet photodetectors, which effectively utilizes the optical properties of band edge absorption of hexagonal boron nitride. Since the optical band gap of hexagonal boron nitride is about 6eV, using large-size single crystals of hexagonal boron nitride as the semiconductor layer of the photodetector will obtain high spectral selectivity, and light with a wavelength higher than 250nm can hardly generate electrical signals.

[0027] 3. Impurities and defects will act as charge traps to capture photogenerated carriers during the operation of the photodetector, thereby reducing the response speed of the detector. The present invention uses large-size hexagonal boron nitride single crystals with low defect density as the semiconductor layer of the photodetector, which will achieve a high response speed.

[0028] 4. The large-size single crystal of hexagonal boron nitride prepared by this method has a thickness of more than microns, which can effectively absorb the incident light and produce electrical signals through photoconductivity effect. The deep ultraviolet photodetector prepared with large-size single crystal of hexagonal boron nitride at the micron level will have extremely high external quantum efficiency.

[0029] 5. The process of preparing deep ultraviolet photodetectors in this invention does not involve complicated experimental procedures, does not involve expensive material growth equipment and transfer operating tables, and has a simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a deep ultraviolet photodetector prepared by the present invention;

[0031] Figure 2 This is an optical microscope photo of a deep ultraviolet photodetector prepared in an embodiment of the present invention;

[0032] Figure 3 The time-resolved photocurrent curve of the deep ultraviolet photodetector prepared in the embodiment of the present invention under 185nm light;

[0033] Figure 4 This is a time-resolved photocurrent curve of the deep ultraviolet photodetector prepared in an embodiment of the present invention under 222nm light. DETAILED DESCRIPTION

[0034] In order to more clearly introduce the above advantages and features of the present invention, specific embodiments of the present invention are described below in conjunction with the accompanying drawings.

[0035] Reference Figure 1This embodiment specifically discloses a deep ultraviolet photodetector based on a large-size single crystal of hexagonal boron nitride.

[0036] The deep ultraviolet photodetector includes a substrate 1, an adhesive 2, a large-size hexagonal boron nitride single crystal 3, an electrode 4, and a photoelectric detection device 5.

[0037] An adhesive 2 is spin-coated on the substrate 1, and a large hexagonal boron nitride single crystal 3 is connected to the substrate 1 through the adhesive 2. An electrode 4 is located on the upper surface of the large hexagonal boron nitride single crystal 3, and the electrode 4 is connected to a photoelectric detection device 5 through a wire.

[0038] The preparation method of a large-size single crystal deep ultraviolet photodetector based on hexagonal boron nitride specifically includes the following steps:

[0039] Preparation of large-size single crystals of hexagonal boron nitride: 1) Put metal nickel and chromium in a mass ratio of 1:0.1 to 1.5, and the two metals and elemental boron powder in a mass ratio of 1:0.1 to 0.4 into a ball mill, and the ball powder weight ratio is 1.5 to 2.5:1. The ball mill is evacuated to vacuum, filled with argon to normal pressure, and ball milled at a speed of 600 to 1000 rpm for 20 to 50 hours to finally obtain nickel-chromium-boron alloy powder. 2) The prepared nickel-chromium-boron alloy powder is quickly transferred to a high-temperature crucible, and the crucible is placed in the heating temperature zone of a tubular furnace. The furnace tube is evacuated to vacuum, and hydrogen / argon mixed gas is passed to normal pressure, and repeated 3 to 5 times; then the furnace temperature is heated to 1400 to 1700°C in a hydrogen / argon mixed atmosphere with a flow rate of 50 to 200 sccm, and after the temperature stabilizes, it is maintained for 1 to 4 hours. 3) After the heat preservation is completed, nitrogen and hydrogen / argon mixed gas are introduced at a gas flow ratio of 1:0.5-1.2, with a total flow rate of 200-300sccm, and then the temperature is reduced to 1300-1600°C at a rate not higher than 6°C / h, and then naturally cooled to room temperature to obtain a large-sized hexagonal boron nitride single crystal on the upper surface of the alloy block. 4). The cooled alloy block is placed in a mixed solution of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1 and heated, and the temperature is controlled at 40-60°C until the large-sized hexagonal boron nitride single crystal on the upper surface falls off naturally, and a complete and continuous large-sized hexagonal boron nitride single crystal is obtained.

[0040] Providing substrate: Cut the silicon substrate into 1×1 cm slices as needed and simply clean the surface.

[0041] Use adhesive to connect the large-sized hexagonal boron nitride single crystal to the substrate: place the silicon substrate on a glue spreader, use a dropper to take a small amount of dichloromethane solution of ethyl cyanoacrylate, and drop it on the upper surface of the silicon substrate, set the speed of the glue spreader to 1500-4000r / min, and the time to 60-90s, then cover the previously prepared large-sized hexagonal boron nitride single crystal on the silicon substrate spin-coated with the adhesive, and finally put the silicon substrate covered with the large-sized hexagonal boron nitride single crystal into a blast drying oven and dry it at a temperature of 60-90°C for 30-60min.

[0042] Preparation of electrodes: Cover the surface of a large-size single crystal of hexagonal boron nitride with a mask, use a radio frequency magnetron sputtering instrument to sputter gold atoms onto the sample surface, and prepare a layer of gold electrode with a thickness of 80-100 nm on the sample surface.

[0043] Figure 2 This is a prepared deep ultraviolet photodetector.

[0044] Figure 3 This is the time-resolved photocurrent curve of the large-size single crystal deep ultraviolet photodetector of hexagonal boron nitride under light of 185nm wavelength. It can be seen that the switching ratio is 170, the response time is less than 1s, and the performance is excellent.

[0045] Figure 4 This is the time-resolved photocurrent curve of the large-size single crystal deep purple appearance point detector of hexagonal boron nitride under light of 222nm wavelength. It can be seen that the switching ratio is 5 and the response time is less than 1s. It can be seen that when the wavelength of ultraviolet light exceeds the band gap range, the response of the detector decreases rapidly, indicating that the detector has excellent spectral selectivity.

Claims

1. A method for preparing a deep ultraviolet photodetector based on a large-size single crystal of hexagonal boron nitride, characterized in that: The large-size hexagonal boron nitride single crystal is a photoelectric sensitive material, and is a large-size hexagonal boron nitride single crystal with a thickness of 5 to 50 μm; the overall crystal plane is (002), the sides are in the [1-100] and [11-20] directions, and the single crystal property is excellent; the crystallinity is high, the half-peak width of the (002) peak of XRD is less than 0.03°, and the Raman spectrum E 2g The half-peak width of the vibration peak is less than 10 cm -1 ; Good electrical insulation, surface resistivity is 10 15 Ω or above; low impurity defect density, transparent, good light transmittance; can be cut into 1cm as needed 2 The above area size; The preparation method comprises the following steps: Step 1, preparing large-size single crystals of hexagonal boron nitride; Step 2, providing a substrate; Step 3, connecting the large-size single crystal of hexagonal boron nitride to the substrate using an adhesive; Step 4: Prepare electrodes.

2. The method for preparing a deep ultraviolet photodetector based on a large-size single crystal of hexagonal boron nitride according to claim 1, characterized in that: The step 1 prepares large-sized hexagonal boron nitride single crystals, which are large-sized hexagonal boron nitride single crystals prepared by single crystal growth methods such as atmospheric pressure metal flux method, high temperature and high pressure method, high pressure temperature gradient method, and metal flux method.

3. The method for preparing a deep ultraviolet photodetector based on a large-size hexagonal boron nitride single crystal according to claim 1, characterized in that: The specific method of connecting the large-sized hexagonal boron nitride single crystal to the substrate using an adhesive in the step three is as follows: drop the adhesive on the surface of the substrate, use a coating machine to spin coat it at a speed of 1500-4000r / min, set the time to 60-120s, then cover the large-sized hexagonal boron nitride single crystal on the surface of the substrate on which the adhesive is spin-coated, and then place it in a forced air drying oven at 60-90°C and dry it for 30-60min.

4. The method for preparing a deep ultraviolet photodetector based on a large-size hexagonal boron nitride single crystal according to claim 1, characterized in that: The adhesive may be polydimethylsiloxane, polymethyl methacrylate, ethyl cyanoacrylate, etc.

5. A method for preparing a deep ultraviolet photodetector based on a large-size single crystal of hexagonal boron nitride according to claims 1-4, characterized in that: The deep ultraviolet photodetector prepared using the above method has high spectral selectivity, that is, it only has a photoelectric response signal to deep ultraviolet light with a wavelength less than 280nm, and has no response signal to incident light with a wavelength greater than deep ultraviolet light. It also has a high switching ratio for deep ultraviolet light with a wavelength of around 200nm, and for light with a wavelength of 185nm, the switching ratio is 170; the photoelectric response speed is fast, with a response time of less than 1s; the dark current is extremely low, and under a bias of 100V, the dark current is still lower than the detection limit of the digital source meter of 1pA.

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