A photoconductive switch and a method for manufacturing the same

Abstract

The present invention relates to a photoconductive switch and a preparation method thereof. The photoconductive switch comprises: a substrate layer, a graphene layer, an anode and a cathode, wherein the graphene layer is located on the upper surface of the substrate layer; the anode is a ring structure and is located on the upper surface of the graphene layer; and the cathode is located on the lower surface of the substrate layer. The present invention provides a graphene layer between the substrate layer and the anode, so that the photoconductive switch can generate more photogenerated carriers, thereby further improving the quantum efficiency of the device. In addition, since the surface of the graphene material is flat and dense, it can effectively improve the electromigration of metals under large pulses, improve the stability and life of the device, and thus improve the reliability of the device. In addition, due to the semi-metallic characteristics of graphene, the current originally distributed vertically inside the device has a radial component, thereby reducing the aggregation effect at the edge of the anode and improving the voltage resistance of the device.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a photoconductive switch and a preparation method thereof. Background Art

[0002] In the application of power electronic devices, switch applications occupy a very important position and often play a key role in the system. With the development of power electronic technology, the performance indicators and reliability requirements of switches have increased. Traditional spark gap switches can only reach 10 4 The operating frequency of the order of magnitude, and there are also problems of large size and short life. Insulated gate bipolar transistors can achieve high withstand voltage and high on-current, but they have defects in high-frequency applications.

[0003] Photoconductive switches have the advantages of high withstand voltage, small size, high operating frequency and long life. Photoconductive switches are usually composed of metal electrodes and semiconductor substrates, in which the substrate is used to absorb photons to generate electron-hole pairs, and the positive and negative metal electrodes are used to connect the semiconductor material and the outside. The resistivity is very large when there is no light irradiation, that is, the switch is in the off state. When there is light irradiation of appropriate wavelength and intensity, the semiconductor substrate generates a large number of electron-hole pairs, which form current under the action of the external electric field, that is, the switch is in the on state. Photoconductive switches can be divided into two types: planar and vertical. Planar photoconductive switches have a large illumination area, fast response speed, and good output stability, but their crystal surface is exposed to the entire electric field, and breakdown is prone to occur at the surface of the material, which is not suitable for high-voltage scenarios. Vertical photoconductive switches are suitable for high-voltage scenarios, but vertical photoconductive switches require the electrodes to be light-transmissive, and the device needs to have high withstand voltage, high quantum efficiency and reliability.

[0004] The existing technology covers a layer of zinc oxide aluminum AZO semiconductor material on the anode as an anti-reflection film to enhance the absorption of incident light by the vertical photoconductive switch. Although AZO improves the quantum efficiency of the device to a certain extent, the improvement effect is limited and it cannot effectively improve the pressure resistance and reliability of the device. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a photoconductive switch and a method for manufacturing the same. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a photoconductive switch, comprising: a substrate layer, a graphene layer, an anode and a cathode, wherein:

[0007] The graphene layer is located on the upper surface of the substrate layer;

[0008] The anode is a ring-shaped structure and is located on the upper surface of the graphene layer;

[0009] The cathode is located on the lower surface of the substrate layer.

[0010] In a specific embodiment, the material of the substrate layer includes SiC.

[0011] In a specific embodiment, the anode is a ring-shaped structure; and the graphene layer is a circular structure.

[0012] In a specific embodiment, the cathode includes: a first sub-cathode, a sub-contact layer, a first protective layer, a second sub-cathode, a second protective layer and a third sub-cathode, wherein:

[0013] The first sub-cathode is a ring-shaped structure and is located on the lower surface of the substrate layer;

[0014] The sub-contact layer is located inside the first sub-cathode and on the lower surface of the first sub-cathode;

[0015] The first protective layer is an annular structure and is located on the lower surface of the sub-contact layer;

[0016] The second sub-cathode is located inside the first protective layer and on the lower surface of the first protective layer;

[0017] The second protective layer is an annular structure and is located on the lower surface of the second sub-cathode;

[0018] The third sub-cathode is located inside the second protection layer and on the lower surface of the second protection layer.

[0019] In a specific embodiment, the material of the first sub-cathode includes Ni;

[0020] The material of the second sub-cathode includes Ag.

[0021] A second aspect of the present invention provides a method for preparing a photoconductive switch, characterized in that it comprises the following steps:

[0022] S1: Get the substrate layer;

[0023] S2: preparing a graphene material on the upper surface of the substrate layer;

[0024] S3: preparing a first sub-anode on the upper surface of the graphene material;

[0025] S4: etching the graphene material to obtain a graphene layer; etching the first sub-anode to obtain a first sub-anode with a ring structure;

[0026] S5: preparing a second sub-anode on the upper surface of the first sub-anode of the annular structure, wherein the first sub-anode of the annular structure and the second sub-anode form an anode of the annular structure;

[0027] S6: preparing a cathode on the lower surface of the substrate layer.

[0028] In a specific embodiment, step S1 includes: obtaining a substrate material, and performing N ion implantation on the lower surface of the substrate material to obtain a substrate layer.

[0029] In a specific embodiment, step S2 includes:

[0030] S201: etching the upper surface of the substrate layer to obtain a substrate layer having nucleation points;

[0031] S202: preparing graphene material on the upper surface of the substrate layer having nucleation points.

[0032] In a specific embodiment, step S4 includes: etching the graphene material to obtain a graphene layer with a circular structure; etching the first sub-anode to obtain a first sub-anode with a circular ring structure.

[0033] In a specific embodiment, step S6 includes:

[0034] S601: preparing a first sub-cathode on the lower surface of the substrate layer; the first sub-cathode is a ring structure;

[0035] S602: preparing a sub-contact layer inside the first sub-cathode and on the lower surface of the first sub-cathode;

[0036] S603: preparing a first protective layer on the lower surface of the sub-contact layer; the first protective layer is a ring-shaped structure;

[0037] S604: preparing a second sub-cathode inside the first protective layer and on a lower surface of the first protective layer;

[0038] S605: preparing a second protective layer on the lower surface of the second sub-cathode; the second protective layer is a ring-shaped structure;

[0039] S606: preparing a third sub-cathode inside the second protective layer and on the lower surface of the second protective layer.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention arranges a graphene layer between the substrate layer and the anode, and utilizes the high light absorption efficiency of the graphene layer to enable the photoconductive switch to generate more photogenerated carriers, thereby further improving the quantum efficiency of the device. In addition, since the surface of the graphene material is flat and dense, it can effectively improve the electromigration of metals under large pulses, improve the stability and life of the device, and thus improve the reliability of the device. In addition, due to the semi-metallic properties of graphene, the current originally distributed vertically inside the device has a radial component, thereby reducing the aggregation effect at the edge of the anode and improving the voltage resistance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic cross-sectional structure diagram of a photoconductive switch provided by an embodiment of the present invention;

[0043] Figure 2 is a front view of a photoconductive switch provided by an embodiment of the present invention;

[0044] Figure 3 is a top view of a photoconductive switch provided by an embodiment of the present invention;

[0045] Figure 4 is a bottom view of a photoconductive switch provided by an embodiment of the present invention;

[0046] Figure 5a to Figure 5g It is a schematic diagram of the steps of a method for preparing a photoconductive switch provided by an embodiment of the present invention.

[0047] Reference numerals:

[0048] 1: substrate layer; 2: graphene layer; 3: anode; 301: first sub-anode; 302: second sub-anode; 4: first sub-cathode; 5: sub-contact layer; 6: first protective layer; 7: second sub-cathode; 8: second protective layer; 9: third sub-cathode. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0050] Embodiment 1

[0051] See also Figure 1 , Figure 2 and Figure 3 , Figure 1 is a schematic cross-sectional structure diagram of a photoconductive switch provided by an embodiment of the present invention, Figure 2 is a front view of a photoconductive switch provided by an embodiment of the present invention, Figure 3 It is a top view of a photoconductive switch provided by an embodiment of the present invention.

[0052] The present embodiment provides a photoconductive switch, comprising: a substrate layer 1, a graphene layer 2, an anode 3 and a cathode. The graphene layer 2 is located on the upper surface of the substrate layer 1. The anode 3 is a ring structure and is located on the upper surface of the graphene layer 2. The cathode is located on the lower surface of the substrate layer 1.

[0053] Specifically, graphene materials have ultra-high electrical conductivity, ultra-high carrier mobility, excellent optical properties, flexibility, impermeability, excellent mechanical strength, and high thermal conductivity. The transmittance of visible light is theoretically as high as 97%. In this embodiment, the graphene layer 2 is used as a light absorption medium, with a wide spectrum width, high response speed, and high efficiency in light absorption. Under the same lighting conditions, graphene materials can generate more photogenerated carriers, with higher quantum efficiency and higher peak current of photogenerated current. In addition, since the thickness of a single-layer graphene is a single-atom thickness, that is, the graphene layer 2 is very thin, electrons can tunnel through the graphene layer 2 into the substrate layer 1, and are enriched in the interface thin layer of the substrate layer 1 close to the graphene layer 2. The electrons diffused into the substrate layer 1 and the graphene layer 2 will not be scattered by ionized impurities, and the mobility in the horizontal direction will be very high. When photons with energy greater than the graphene bandgap width are irradiated on the device, a large number of photogenerated electron-hole pairs will be generated inside the device and diffused to the graphene layer 2, and then quickly collected by the electrode in the high-mobility conductive channel, thereby obtaining a higher electron mobility channel, further improving the quantum efficiency and response speed of the device. In addition, since the surface of the graphene material is flat and dense, it is of great help to obtain more uniform and excellent contact, and the penetration ability of large atoms and molecules in graphene is particularly weak. Therefore, by setting the graphene layer 2 between the substrate layer 1 and the anode 3, the electromigration of the metal under large pulses can be effectively improved, the stability and life of the device can be improved, and the reliability of the device can be improved. Furthermore, since the anode 3 is a ring structure, there is a high concentration of carriers at the contact interface between the central region of the graphene layer 2 and the SiC substrate layer 1, which can effectively reduce the gradient of the electric field inside the anode 3. Moreover, due to the semi-metallic properties of graphene, it can be regarded as a whole after contacting the metal, that is, the graphene layer 2 and the anode 3 can be regarded as an electrode as a whole, so that the original vertically distributed current inside the device has a radial component, thereby reducing the aggregation effect at the edge of the anode 3 and improving the voltage resistance of the device.

[0054] Specifically, the material of the substrate layer 1 includes SiC, and N ions are implanted into the lower surface. The material of the anode 3 includes one or more of Au, Ni, Al, Pt, and Ti.

[0055] In this embodiment, the anode 3 can form an ohmic contact without high temperature annealing. Specifically, since the present embodiment uses SiC material as the substrate layer 1, the surface state concentration of the contact interface between the SiC material and the graphene material is very high, the height of the contact barrier is pinned by the high-density surface state, and a part of the barrier height falls inside the semiconductor material, and does not completely depend on the work function of the anode metal material, which reduces the barrier height formed by the contact between SiC and graphene. In addition, at the interface between the substrate layer 1 and the graphene layer 2, the carrier concentration is very high, and electrons and holes are transported in a composite manner, so that the forward and reverse composite currents are very large, which destroys the Schottky barrier formed by the contact between graphene and SiC, reduces the contact resistance, and promotes the formation of ohmic contact. On the other hand, graphene contacts SiC, and the narrow bandgap semiconductor (graphene) and the wide bandgap semiconductor (SiC) form a slow heterojunction, which further reduces the contact barrier, thereby promoting the formation of ohmic contact, and ohmic contact can be formed without high temperature annealing.

[0056] Specifically, please combine Figure 1 , Figure 2 and Figure 4 , Figure 4 : is a bottom view of a photoconductive switch provided by an embodiment of the present invention. The cathode of the photoconductive switch provided by this embodiment includes: a first sub-cathode 4, a sub-contact layer 5, a first protective layer 6, a second sub-cathode 7, a second protective layer 8 and a third sub-cathode 9. Among them, the first sub-cathode 4 is an annular structure and is located on the lower surface of the substrate layer 1. The sub-contact layer 5 is located inside the first sub-cathode 4 and on the lower surface of the first sub-cathode 4. The first protective layer 6 is an annular structure and is located on the lower surface of the sub-contact layer 5. The second sub-cathode 7 is located inside the first protective layer 6 and on the lower surface of the first protective layer 6. The second protective layer 8 is an annular structure and is located on the lower surface of the second sub-cathode 7. The third sub-cathode 9 is located inside the second protective layer 8 and on the lower surface of the second protective layer 8. It should be understood that the second sub-cathode 7 is located inside the first protective layer 6 and on the lower surface of the first protective layer 6, that is, a part of the second sub-cathode 7 is located inside the ring of the first protective layer 6, and the other part is located on the ring surface of the first protective layer 6.

[0057] Specifically, under an external bias voltage, the graphene layer 2 and the cathode can transfer a certain electric field concentration to the substrate layer 1, changing the surface breakdown to substrate breakdown, further improving the voltage resistance of the device. When there is external light, the substrate layer 1 and the graphene layer 2 absorb photons with energy greater than their own bandgap width, and the electrons at the top of the valence band absorb energy and transition to the conduction band, while leaving the same number of holes in the valence band, generating photogenerated carriers, these electron-hole pairs will diffuse into the graphene layer 2, and then be quickly collected in the high-mobility conductive channel. Under an external bias voltage, the photogenerated electron-hole pairs separate, the electrons move to the anode 3, and the holes move to the cathode, generating a photocurrent, and the second sub-cathode 7 can enhance reflection, further improving the device's utilization of light.

[0058] In an achievable manner, the graphene layer 2 is a circular structure, the anode 3 is a circular ring structure, and the outer diameter of the anode 3 is equal to the diameter of the graphene layer 2. The first sub-cathode 4, the first protective layer 6, and the second protective layer 8 are all circular ring structures with the same inner diameter and outer diameter as the anode 3, and are all coaxially arranged. The sub-contact layer 5 is composed of a first diameter portion and a second diameter portion, the diameter of the first diameter portion of the sub-contact layer 5 is equal to the inner diameter of the first sub-cathode 4, and is arranged at the center of the first sub-cathode 4, and the diameter of the second diameter portion of the sub-contact layer 5 is equal to the outer diameter of the first sub-cathode 4, and is arranged on the lower surface of the first sub-cathode 4. The shapes of the second sub-cathode 7 and the third sub-cathode 9 are the same as those of the sub-contact layer 5. It should be understood that the first sub-cathode 4, the sub-contact layer 5, the first protective layer 6, the second sub-cathode 7, the second protective layer 8, and the third sub-cathode 9 form a circular cathode.

[0059] In another achievable manner, the graphene layer 2 is a square structure, the anode 3 is a square ring structure, and the outer side length of the anode 3 is equal to the side length of the graphene layer 2. The first sub-cathode 4, the first protective layer 6, and the second protective layer 8 are all square ring structures of equal size to the anode 3, and are all coaxially arranged. The sub-contact layer 5 is composed of a first side length portion and a second side length portion, the side length of the first side length portion of the sub-contact layer 5 is equal to the inner side length of the first sub-cathode 4, and is arranged in the ring of the first sub-cathode 4, and the side length of the second side length portion of the sub-contact layer 5 is equal to the outer side length of the first sub-cathode 4, and is arranged on the lower surface of the first sub-cathode 4. The shapes of the second sub-cathode 7 and the third sub-cathode 9 are the same as those of the sub-contact layer 5. It should be understood that the first sub-cathode 4, the sub-contact layer 5, the first protective layer 6, the second sub-cathode 7, the second protective layer 8, and the third sub-cathode 9 form a square cathode.

[0060] Specifically, the material of the first sub-cathode 4 includes Ni, and the material of the second sub-cathode 7 includes Ag. The sub-contact layer 5 is used to improve the contact characteristics between the second sub-cathode 7 and the substrate layer 1. The material of the sub-contact layer 5 is a material with strong light transmittance and can improve the contact resistance between Ag and SiC, such as AZO, ITO conductive film, and organic conductive film. The first protective layer 6 and the second protective layer 8 are used to protect the second sub-cathode 7 and prevent the second sub-cathode 7 from oxidation. The materials of the first protective layer 6 and the second protective layer 8 both include corrosion-resistant and oxidation-resistant metal materials such as Ti and Pt. The material of the third sub-cathode 9 includes one of Au, Ti, Ni, Al / Ni, and Au / Ni.

[0061] This embodiment arranges a graphene layer 2 between the substrate layer 1 and the anode 3, and utilizes the characteristics of the graphene layer with high light absorption efficiency, so that the photoconductive switch can generate more photogenerated carriers, further improving the quantum efficiency of the device. In addition, since the surface of the graphene material is flat and dense, it can effectively improve the electromigration of metals under large pulses, improve the stability and life of the device, and thus improve the reliability of the device. In addition, due to the semi-metallic properties of graphene, the current originally vertically distributed inside the device has a radial component, thereby reducing the aggregation effect at the edge of the anode and improving the voltage resistance of the device. The device provided by this embodiment has higher quantum efficiency, good reliability and voltage resistance.

[0062] Embodiment 2

[0063] See also Figure 5a to Figure 5g , Figure 5a to Figure 5g It is a schematic diagram of the steps of a method for preparing a photoconductive switch provided by an embodiment of the present invention.

[0064] This embodiment provides a method for preparing a photoconductive switch, comprising the following steps:

[0065] S1: Obtain substrate layer 1.

[0066] Specifically, step S1 includes: obtaining a substrate material, and performing N ion implantation on the lower surface of the substrate material to obtain a substrate layer 1 .

[0067] In this embodiment, step S1 includes:

[0068] S101: Control the oxidation temperature to 1180°C, the oxygen flow rate to 540ml / min, the oxidation time to 165min, and deposit SiO2 with a thickness of 100nm on the lower surface of the SiC substrate material as an ion implantation mask. After the deposition is completed, keep the oxidation temperature unchanged, introduce N2 annealing for 30min, and gradually cool the sample to 300°C in the N2 atmosphere.

[0069] S102: N ion implantation is performed on the lower surface of the sample obtained in step S101, the implantation temperature is 500°C, and the implantation is performed in sequence from the first implantation parameter to the fourth implantation parameter. The first implantation parameter includes: implantation energy 150keV, implantation dose 3.1×10 15 cm -2 The second implantation parameters include: implantation energy 100 keV, implantation dose 1.75×10 15 cm -2 The third implantation parameters include: implantation energy 62keV, implantation dose 1.45×10 15 cm -2 The fourth implantation parameters include: implantation energy 35keV, implantation dose 1.1×10 15 cm -2 .

[0070] S103: At room temperature, immerse the sample obtained in step S102 in a 1% HF solution, take it out after 14 minutes, and repeatedly rinse it with deionized water to remove the SiO2 ion implantation masking film.

[0071] S104: Prepare a C film on the surface of the sample obtained in step S103.

[0072] S105: Place the sample obtained in step S104 in an annealing device, evacuate the annealing device to 4 mbar, and then fill the annealing device with nitrogen at a nitrogen flow rate of 2000 sccm. After the nitrogen is filled, heat the annealing device to 400°C and maintain for 10 seconds. Then, heat the temperature to 1700°C at a heating rate of 10°C / s and maintain for 30 minutes. Anneal the sample obtained in step S104. After annealing, cool down and open the annealing chamber after cooling with cooling water for 420 seconds.

[0073] S106: remove the C film on the surface of the sample and clean the sample into a light sheet.

[0074] S2: preparing graphene material on the upper surface of the substrate layer 1.

[0075] Specifically, see Figure 5a , step S2 comprises:

[0076] S201: Etching is performed on the upper surface of the substrate layer 1 to obtain the substrate layer 1 having nucleation points.

[0077] Specifically, etching is performed on the upper surface of the substrate layer 1 at an etching temperature of 1600° C., an etching time of 90 min, an etching pressure of 96 mbar, and a hydrogen flow rate of 90 L / min to obtain the substrate layer 1 having nucleation points. The substrate layer 1 having nucleation points is etched according to a preset etching procedure to remove derivatives such as Si2C, SiC2, and Si2O3 on the surface.

[0078] In this embodiment, the preset etching procedure includes:

[0079] The etching temperature was slowly reduced from 1600°C to 1000°C, and hydrogen was introduced at a flow rate of 2 L / min for 15 min;

[0080] Under low vacuum, the etching temperature was reduced to 850°C, and SiH4 was introduced at a flow rate of 0.5 ml / min for 10 min;

[0081] Under low vacuum, the etching temperature was raised to 1000°C and maintained for 5 min;

[0082] Under low vacuum, the etching temperature was raised to 1100°C and maintained for 5 min;

[0083] Under low vacuum, the etching temperature was raised to 1250°C and maintained for 10 min.

[0084] S202: preparing graphene material on the upper surface of the substrate layer 1 having nucleation points.

[0085] Specifically, in an environment of 900 mbar high-purity argon, the growth temperature is controlled to be 1650° C. to achieve uniform heating, prevent the generation of temperature gradients, and make the heating rate as fast as possible to control the duration of growth to obtain a single-layer SiC-based epitaxial graphene. It should be understood that in this embodiment, epitaxial growth of graphene on the upper surface of the substrate layer 1 to obtain a graphene material is only an exemplary description, and a pre-prepared graphene film can also be directly transferred to the upper surface of the substrate layer 1 to obtain a graphene material.

[0086] S3: preparing a first sub-anode 301 on the upper surface of the graphene material.

[0087] Specifically, step S3 includes:

[0088] Deposition: See Figure 5b , Au with a thickness of 20nm is pre-deposited on the upper surface of the graphene material as the first sub-anode 301 to prevent the graphene from being oxidized and contaminated. Since wet etching is required on the pre-deposited Au later, the metal thickness should not be too thick. Therefore, the pre-deposited thickness in this embodiment is 20nm. The process parameters of the pre-deposition include: -7 Torr high vacuum environment, using a molybdenum crucible, a vaporization distance of 60 cm, an electron gun voltage of 10 kV, an electron gun current of 1 A, a substrate temperature of 20 ° C, and an evaporation rate of 1 nm / s.

[0089] Cleaning: Clean the sample obtained in step S301 through a preset cleaning procedure. It should be noted that since graphene materials cannot be cleaned by ultrasound and RCA, the present embodiment cleans the sample through a preset cleaning procedure. In the present embodiment, the preset cleaning procedure includes: soaking the sample in acetone solution, isopropanol solution, acetone solution and isopropanol solution for 5 minutes respectively, and after soaking, repeatedly rinsing the sample with deionized water, and blowing the sample dry with a nitrogen gun.

[0090] Spin coating: Place the cleaned sample into a spin coater, add positive photoresist to the center of the sample, and spin the sample at 4000 rpm for 1 minute to prepare a photoresist with a thickness of 2 μm on the sample surface.

[0091] Pre-baking: Place the sample after coating on a hot plate at 100°C and bake for 2 minutes. After baking, cool it to room temperature.

[0092] Exposure: Expose the pre-baked sample using mask M2, align the marks before exposure, and the exposure dose is 21mJ / cm 2 .

[0093] Post-baking: Place the exposed sample on a hot plate at 110°C and bake for 2 minutes.

[0094] Development: Immerse the post-baked sample in a corresponding developer for a preset time, which in this embodiment is 60 seconds.

[0095] Residual glue removal: Oxygen plasma was used to remove residual glue on the surface of the developed sample, wherein the oxygen flow rate was 10 sccm, the gas pressure was 3 Pa, the upper electrode power was 30 W, and the etching time was 20 s.

[0096] Hard film: Place the sample after removing the residual glue on a hot plate at 150°C and bake for 5 minutes. After baking, take out the sample, wash it with deionized water, and dry it with a nitrogen gun.

[0097] Wet etching: see Figure 5c The hardened sample is immersed in an etching solution for 2 seconds to remove the first sub-anode 301 outside the electrode area. After the immersion is completed, it is immediately taken out and washed with deionized water to obtain a circular first sub-anode 301. In this embodiment, the etching solution is a solution prepared by 100 ml H2O, 10 g KI and 2.5 g I2, and the electrode area is a circular area in the center of the sample surface.

[0098] S4: etching the graphene material to obtain the graphene layer 2; etching the first sub-anode 301 to obtain the first sub-anode 301 with a ring structure.

[0099] Specifically, step S4 includes:

[0100] S401: etching the graphene material to obtain a graphene layer 2.

[0101] Specifically, step S401 includes:

[0102] Oxygen plasma etching: see Figure 5d , using oxygen plasma to remove the graphene material outside the electrode region, to obtain a circular graphene layer 2. In this embodiment, the etching parameters include: pressure of 2Pa, power of 40W, oxygen flow rate of 40sccm, and etching time of 30s.

[0103] Degumming: The sample after oxygen plasma etching was immersed in an acetone solution for 12 hours. After the immersion was completed, acetone and ethanol were used to clean it in turn to obtain the sample after the first etching.

[0104] S402: etching the center of the first sub-anode 301 to obtain the first sub-anode 301 with a ring structure.

[0105] Specifically, see Figure 5e , step S402 includes:

[0106] The sample obtained in step S401 is sequentially cleaned, coated, pre-baked, exposed, post-baked, developed, residual glue removed, wet etched and stripped to remove the central area of ​​the circular first sub-anode 301 and obtain the first sub-anode 301 of the ring structure. It should be noted that the difference between the exposure in step S402 and the exposure in step S3 is that before exposure, it is necessary to find the alignment mark made previously through the microscope or display of the photolithography machine, and align it with the mark of the mask before exposure. The parameters of the remaining steps (i.e., cleaning, coating, pre-baked, post-baked, developed, residual glue removed, wet etched and stripped) are the same as those of step S3 and step S401, and will not be repeated here.

[0107] S5: preparing the second sub-anode 302 on the upper surface of the first sub-anode 301 of the ring structure, and the first sub-anode 301 and the second sub-anode 302 of the ring structure form the anode 3 of the ring structure.

[0108] Specifically, see Figure 5f , step S5 comprises:

[0109] The sample obtained in step S4 is sequentially cleaned, glued, pre-baked, exposed, post-baked, developed, residual glue removed, deposited and stripped. It should be noted that the deposition in this step includes preparing Au with a deposition thickness of 200nm on the upper surface of the first sub-anode 301 as the second sub-anode 302. The stripping in this step includes soaking the sample deposited with the second sub-anode 302 in an acetone solution for 12 hours. After the metal outside the annular area floats on a large area, use a disposable dropper to absorb acetone, gently wash away and absorb the raised metal, then rinse with acetone and ethanol solution, and rinse repeatedly with deionized water, and finally blow dry with a nitrogen gun. The parameters of the remaining steps of this step (i.e., cleaning, glued, pre-baked, exposed, post-baked, developed and residual glue removed) are the same as those of step S3, and will not be repeated here. In the present embodiment, the annular area is a circular ring outside the electrode area, that is, the outer diameter of the annular area is equal to the diameter of the electrode area.

[0110] S6: preparing a cathode on the lower surface of the substrate layer 1 .

[0111] Specifically, see Figure 5g , step S6 comprises:

[0112] S601: preparing a first sub-cathode 4 on the lower surface of the substrate layer 1; the first sub-cathode 4 is a ring-shaped structure.

[0113] Specifically, the sample obtained in step S5 is sequentially cleaned, coated, pre-baked, exposed, post-baked, developed, removed residual glue, deposited, peeled and annealed. In this step, deposition includes depositing Ni with a thickness of 200nm on the lower surface of the sample by magnetron sputtering as the first sub-cathode 4. Annealing includes: evacuating the annealing equipment to 4mbar, and then filling the annealing equipment with nitrogen, with a nitrogen flow rate of 2000sccm. After the nitrogen is filled, the annealing equipment is heated to 400℃, maintained for 10s, and then heated to 1000℃, maintained for 3min. After the annealing is completed, the temperature is lowered, and the annealing chamber is opened after the cooling water is cooled for 420s. The parameters of the remaining steps of this step (i.e., cleaning, coating, pre-baked, exposed, post-baked, developed, removed residual glue and peeled) are the same as those of step S5, and will not be repeated here. After peeling, the first sub-cathode 4 outside the annular area can be removed to obtain the first sub-cathode 4 of the annular structure.

[0114] S602 : preparing a sub-contact layer 5 inside the first sub-cathode 4 and on the lower surface of the first sub-cathode 4 .

[0115] Specifically, step S602 includes the following steps:

[0116] Magnetron sputtering: Place the sample obtained in step S601 into a magnetron sputtering instrument and evacuate the magnetron sputtering chamber to 5×10 -4After pa, Ar was introduced and the gas valve was adjusted to maintain the gas pressure in the chamber at 1.2 Pa. Under the conditions of RF power of 150 W and time of 18 min, an AZO film with a thickness of 362 nm was deposited on the sample obtained in step S601 to obtain a sub-contact layer 5.

[0117] Wet etching: The same photoresist, photolithography and development processes as in step S3 are used in sequence to remove the sub-contact layer 5 outside the electrode area to obtain the sub-contact layer 5 located inside the ring of the first sub-cathode 4 and on the lower surface of the first sub-cathode 4. The sample is then immersed in a 5% dilute HCl solution for 120 seconds, rinsed with pure water, and finally blown dry with high-purity N2.

[0118] S603: preparing a first protective layer 6 on the lower surface of the sub-contact layer 5; the first protective layer 6 is a ring structure.

[0119] Specifically, a magnetron sputtering method is used to sputter Pt with a thickness of 30 nm on the lower surface of the sample obtained in step S402 as the first protective layer 6, and wet etching is performed to remove the first protective layer 6 outside the annular area to obtain the first protective layer 6 of the annular structure.

[0120] S604 : preparing a second sub-cathode 7 inside the first protective layer 6 and on the lower surface of the first protective layer 6 .

[0121] Specifically, a magnetron sputtering method is used to sputter Ag with a thickness of 100 nm on the lower surface of the sample obtained in step S603 as the second sub-cathode 7, and wet etching is performed to remove the first protective layer 6 outside the electrode area to obtain the second sub-cathode 7 located within the ring of the first protective layer 6 and on the lower surface of the first protective layer 6.

[0122] S605: preparing a second protective layer 8 on the lower surface of the second sub-cathode 7; the second protective layer 8 is a ring-shaped structure.

[0123] Specifically, a magnetron sputtering method is used to sputter Pt with a thickness of 30 nm on the lower surface of the sample obtained in step S604 as the second protective layer 8, and wet etching is performed to remove the second protective layer 8 outside the annular area to obtain a second protective layer 8 with an annular structure.

[0124] S606 : preparing a third sub-cathode 9 inside the second protective layer 8 and on the lower surface of the second protective layer 8 .

[0125] Specifically, a magnetron sputtering method is used to sputter Au with a thickness of 100 nm on the lower surface of the sample obtained in step S605 as the third sub-cathode 9, and wet etching is performed to remove the third sub-cathode 9 outside the electrode area to obtain the third sub-cathode 9 located within the ring of the second protective layer 8 and on the lower surface of the second protective layer 8.

[0126] In this embodiment, the anode 3 can form an ohmic contact without high temperature annealing. Specifically, since the present embodiment uses SiC material as the substrate layer 1, the surface state concentration of the contact interface between the substrate layer 1 and the graphene layer 2 is very high, the height of the contact barrier is pinned by the high-density surface state, and a part of the barrier height falls inside the semiconductor material, and does not completely depend on the work function of the anode metal, which reduces the barrier height formed by the contact between SiC and graphene. In addition, at the interface between the substrate layer 1 and the graphene layer 2, the carrier concentration is very high, and electrons and holes are transported in a composite manner, so that the forward and reverse composite currents are very large, which destroys the Schottky barrier formed by the contact between graphene and SiC, reduces the contact resistance, and promotes the formation of ohmic contact. On the other hand, when graphene contacts SiC, the narrow bandgap semiconductor (graphene) and the wide bandgap semiconductor (SiC) form a slow heterojunction, which further reduces the contact barrier, thereby promoting the formation of ohmic contact, and ohmic contact can be formed without high temperature annealing.

[0127] This embodiment provides a method for preparing a photoconductive switch. The photoconductive switch obtained by the method of this embodiment can generate more photogenerated carriers, further improving the quantum efficiency of the device. In addition, since the surface of the graphene material is flat and dense, it can effectively improve the electromigration of metals under large pulses, improve the stability and life of the device, and thus improve the reliability of the device. In addition, due to the semi-metallic properties of graphene, the current originally distributed vertically inside the device has a radial component, thereby reducing the aggregation effect at the edge of the anode and improving the voltage resistance of the device. The device prepared by this embodiment has higher quantum efficiency, good reliability and voltage resistance.

[0128] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A photoconductive switch, characterized in that: include: A substrate layer, a graphene layer, an anode and a cathode, wherein: The graphene layer is located on the upper surface of the substrate layer, and the material of the substrate layer includes SiC; The anode is a ring-shaped structure and is located on the upper surface of the graphene layer; The cathode is located on the lower surface of the substrate layer; The cathode comprises: a first sub-cathode, a sub-contact layer, a first protective layer, a second sub-cathode, a second protective layer and a third sub-cathode, wherein: The first sub-cathode is a ring-shaped structure and is located on the lower surface of the substrate layer; The sub-contact layer is located inside the first sub-cathode and on the lower surface of the first sub-cathode; The first protective layer is an annular structure and is located on the lower surface of the sub-contact layer; The second sub-cathode is located inside the first protective layer and on the lower surface of the first protective layer; The second protective layer is an annular structure and is located on the lower surface of the second sub-cathode; The third sub-cathode is located inside the second protection layer and on the lower surface of the second protection layer.

2. A photoconductive switch according to claim 1, characterized in that: The anode is a ring-shaped structure; the graphene layer is a circular structure.

3. The photoconductive switch according to claim 1, characterized in that: The material of the first sub-cathode includes Ni; The material of the second sub-cathode includes Ag.

4. A method for preparing a photoconductive switch, characterized in that: The following steps are involved: S1: Get the substrate layer; S2: preparing a graphene material on the upper surface of the substrate layer; S3: preparing a first sub-anode on the upper surface of the graphene material; S4: etching the graphene material to obtain a graphene layer; etching the first sub-anode to obtain a first sub-anode with a ring structure; S5: preparing a second sub-anode on the upper surface of the first sub-anode of the annular structure, wherein the first sub-anode of the annular structure and the second sub-anode form an anode of the annular structure; S6: preparing a cathode on the lower surface of the substrate layer; Step S1 includes: obtaining a substrate material, and performing N ion implantation on the lower surface of the substrate material to obtain a substrate layer; Step S6 includes: S601: preparing a first sub-cathode on the lower surface of the substrate layer; the first sub-cathode is a ring structure; S602: preparing a sub-contact layer inside the first sub-cathode and on the lower surface of the first sub-cathode; S603: preparing a first protective layer on the lower surface of the sub-contact layer; the first protective layer is a ring-shaped structure; S604: preparing a second sub-cathode inside the first protective layer and on a lower surface of the first protective layer; S605: preparing a second protective layer on the lower surface of the second sub-cathode; the second protective layer is a ring-shaped structure; S606: preparing a third sub-cathode inside the second protective layer and on the lower surface of the second protective layer.

5. The method for preparing a photoconductive switch according to claim 4, characterized in that: Step S2 includes: S201: etching the upper surface of the substrate layer to obtain a substrate layer having nucleation points; S202: preparing graphene material on the upper surface of the substrate layer having nucleation points.

6. The method for preparing a photoconductive switch according to claim 4, characterized in that: Step S4 includes: etching the graphene material to obtain a graphene layer with a circular structure; etching the first sub-anode to obtain a first sub-anode with a circular ring structure.

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