A high-low barrier diamond Schottky diode, its preparation method and application

Abstract

The present invention relates to a high-low barrier diamond Schottky diode and its preparation method and application. By using different types of metals with asymmetric sizes, high and low barriers are formed at the two electrodes of the diamond, and a diamond high-low barrier Schottky diode is prepared to realize a self-powered X-ray detection device. The preparation method includes: preparing single-crystal diamond and etching the upper surface of the single-crystal diamond; depositing a silver film on the upper surface of the single-crystal diamond and a gold film on the lower surface by magnetron sputtering; on the upper surface of the single-crystal diamond deposited with silver, preparing n×n adjacent diodes by photolithography. The diamond high-low barrier Schottky diode prepared by the present invention generates electron-hole pairs under the irradiation of a certain dose of X-rays, and the electron-hole pairs are quickly separated to form a current under the action of the built-in electric field, realizing self-driving and having high repeatability and stability of the light-to-dark current ratio.

Description

Technical Field

[0001] The present invention relates to a high-low barrier diamond Schottky diode and its preparation method and application, belonging to the technical field of optoelectronic device preparation. Background Art

[0002] X-rays are electromagnetic waves with wavelengths between vacuum ultraviolet and γ rays. Among them, X-ray detectors are widely used in medical imaging, industrial flaw detection, crystal structure analysis and other fields. When X-rays pass through human tissues or workpieces with different densities and thicknesses, the degree of X-ray absorption is also different. Therefore, X-rays can be used to detect the internal structure of objects. Due to the limitations of the material itself and the device detection mechanism, it is extremely challenging to develop X-ray detectors with high sensitivity, high response speed and high stability.

[0003] To solve these problems, there are currently indirect and direct conversion X-ray detectors. The indirect X-ray detector absorbs X-rays through a scintillator material and converts them into fluorescence signals, and then the photodiode converts the fluorescence signals into electrical signals. The indirect X-ray detector has a low photoelectric conversion efficiency and a low response speed due to the long afterglow effect of the scintillator. The detection method of the direct X-ray detector shows a light conversion process without a scintillator, so it has a high quantum efficiency. Commonly used direct X-ray detection materials include semiconductor materials with medium and low bandgaps such as amorphous Se, PbI2, HgI2 and CdTe, but the materials with medium and low bandgaps have poor high-voltage resistance and radiation resistance.

[0004] With the research and development of X-ray detection materials, the third-generation wide-bandgap semiconductors represented by gallium nitride, gallium oxide, silicon carbide and diamond have become ideal X-ray detection materials, which have the ability of high breakdown electric field, high carrier mobility, high thermal conductivity, radiation resistance and high temperature resistance. Since the atomic number of diamond is closest to the effective atomic numbers of human muscle and soft tissue (muscle 7.42, fat 5.99), diamond's response to radiation can better represent the degree of damage to the human body, and it is the best material for preparing detectors in the field of radiation medicine. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a high-low barrier diamond Schottky diode and its preparation method and application. By using different types of metals with asymmetric sizes (one work function is greater than that of diamond and the other is less than that of diamond), high and low barriers are formed at the two electrodes of the diamond, and a diamond high-low barrier Schottky diode is prepared to realize a self-powered X-ray detection device.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A high-low barrier diamond Schottky diode, the diode comprising a diamond substrate; the diamond is single crystal diamond, the upper surface of the single crystal diamond is etched with a channel and a silver thin film is deposited, and a gold thin film is deposited on the lower surface of the single crystal diamond.

[0008] The silver thin film is an n×n array structure, and the size of each silver thin film pixel is 0.2×0.2 mm 2 ; wherein, n is a positive integer (such as 4×4, 5×5 or 6×6).

[0009] The preparation method of the high-low barrier diamond Schottky diode includes the following steps:

[0010] (1) Prepare single crystal diamond and etch the upper surface of the single crystal diamond;

[0011] (2) Deposit a silver thin film on the upper surface of the single crystal diamond and a gold thin film on the lower surface by magnetron sputtering;

[0012] (3) On the upper surface of the single crystal diamond deposited with silver, prepare n×n adjacent diodes by photolithography; wherein, n is a positive integer.

[0013] The specific method of step (1) is:

[0014] 1) Use microwave plasma chemical vapor deposition method to grow a diamond wafer to obtain single crystal diamond;

[0015] 2) Use a laser cutting machine to etch the upper surface of the single crystal diamond. When etching, the current is 15 - 25 A, the laser cutting time is 10 - 30 s, and the cutting depth is 40 - 160 μm;

[0016] 3) Place the etched single crystal diamond in aqua regia for 3 h, and then perform annealing treatment at 500 °C for 30 min in an Ar atmosphere.

[0017] The thickness of the single crystal diamond obtained in step 1) is 800 μm.

[0018] After etching, use hydrogen plasma to remove the graphite left on the surface of the single crystal diamond by etching; the volume ratio of HCl to HNO3 in aqua regia is 3:1; after annealing treatment, ultrasonically clean in acetone, alcohol, and deionized water for 10 min each.

[0019] The specific method of step (2) is:

[0020] Use magnetron sputtering method, adjust the temperature to 30 °C, and pump the vacuum degree to 5×10 -4Pa, the sputtering gas is argon, the argon flow rate is 100 sccm, adjust the growth pressure and turn on the DC power supply; start depositing gold on the lower surface of the single-crystal diamond, the deposition time is 2 - 3 min, and the deposition thickness is 80 - 120 nm; after completion, start depositing silver on the upper surface of the single-crystal diamond, using an n×n metal silver thin film array, and the size of each silver thin film pixel is 0.2×0.2 mm 2 , the deposition time is 2 - 3 min, and the deposition thickness is 80 - 120 nm; where n is a positive integer.

[0021] The specific method of step (3) is as follows:

[0022] 1) Cleaning: Clean and dry the single-crystal diamond, and then heat it on a heating table at 115 °C for 60 s;

[0023] 2) Coating and pre-baking: Uniformly coat a layer of photoresist on the upper surface of the single-crystal diamond deposited with silver through a spin coater, and then pre-bake it on a heating table at 115 °C for 60 s;

[0024] 3) Exposure and mid-baking: Place a mask plate above the single-crystal diamond, and use a micro lithography machine for ultraviolet exposure. The exposure time is 2 min, and mid-baking is carried out after exposure;

[0025] 4) Development and post-baking:

[0026] Put the exposed single-crystal diamond into the developer. After complete development, rinse the single-crystal diamond with deionized water and blow off the water droplets on the surface of the single-crystal diamond with a high-purity nitrogen gun; then heat it on a heating table at 115 °C for 1 min;

[0027] 5) De-gluing: Put the single-crystal diamond into the de-gluing solution to remove the excess photoresist on the surface, and finally rinse it successively with alcohol and deionized water, and dry it after cleaning;

[0028] 6) Place the single-crystal diamond in a CVD vacuum tube furnace for annealing treatment. The annealing temperature is 500 °C and the annealing time is 30 min;

[0029] 7) Press indium grains on the two electrodes of the single-crystal diamond deposited with gold and silver coatings respectively to obtain a diamond Schottky diode.

[0030] Application of the high-low barrier diamond Schottky diode obtained by the said method in X-ray detection.

[0031] Application of the high-low barrier diamond Schottky diode obtained by the said method in array imaging.

[0032] Advantages of the present invention:

[0033] The present invention selects single-crystal diamond as the detection material for preparing the X-ray detector. Since diamond has high temperature resistance, high pressure resistance, radiation resistance, excellent chemical stability and high thermal conductivity, its carrier mobility > 2000 cm 2 V -1 S -1 , the thermal conductivity > 2000 W / (m×k), the high breakdown electric field > 10 MV / cm, and the optoelectronic properties of the single-crystal diamond without grain boundary constraints are more advantageous. Therefore, the X-ray detector prepared from single-crystal diamond can detect X-rays in complex environments such as high temperature, high pressure and high radiation, and the device has good stability and heat dissipation effect during the detection process.

[0034] The present invention adopts the method of depositing asymmetric metal films on the upper and lower surfaces of diamond respectively, where metals with different sizes and types (one work function is greater than that of diamond and the other is less than that of diamond) are used to form high and low potential barriers at the two electrodes of diamond. The diamond high-low potential barrier Schottky diode prepared by the present invention generates electron-hole pairs under the irradiation of X-rays with a certain dose, and the electron-hole pairs are rapidly separated to form current under the action of the built-in electric field, realizing self-driving and having high repeatability and stability of the light-dark current ratio.

[0035] The present invention uses a laser cutting machine to etch diamond samples. As the laser cutting time increases, the corresponding etching depth also increases. The present invention adopts a laser cutting time of 30 s, and the cutting depth is about 157 μm. At this cutting depth, the diamond is not cut off and a channel with a certain depth is formed on the diamond, which is beneficial to reducing the crosstalk between pixel points. Description of the Drawings

[0036] Figure 1 Raman spectrum of the single-crystal diamond grown in Example 1;

[0037] Figure 2 XRD pattern of the single-crystal diamond grown in Example 1;

[0038] Figure 3 Attenuation coefficients of different substances for X-rays;

[0039] Figure 4 Optical picture of the diamond X-ray detection array in Example 1;

[0040] Figure 5 Cross-sectional view of the surface of the single-crystal diamond after cutting in Example 1;

[0041] Figure 6 I-V characteristic curve of the diamond Schottky diode in Example 4;

[0042] Figure 7, I-T characteristic curves of diamond Schottky diodes in Example 4 under different voltages and the same current (X-ray dose);

[0043] Figure 8 , I-T characteristic curves of diamond Schottky diodes in Example 4 under different voltages;

[0044] Figure 9 , I-T characteristic curve of diamond Schottky diode in Example 4 under 0V voltage. Detailed implementation manners

[0045] The following further details the specific implementation manners of the present invention in conjunction with the examples.

[0046] Example 1 Preparation of single-crystal diamond 1

[0047] (1) Using microwave plasma chemical vapor deposition method to grow diamond wafers; growing diamond wafers on Ib-type diamond with (100) crystal plane orientation, the size of the Ib-type diamond is 8×8×1 mm 3 , during growth, the volume ratio of CH4 to H2 is 1:20, the total flow rate is 200 sccm, the substrate temperature is maintained near 950 °C, and an infrared high-temperature detector is used for monitoring. After deposition for 100 h, the Ib-type diamond substrate is removed by laser cutting, and the grown diamond layer is polished into an independent wafer with a thickness of 800 μm (size 6×6×0.8 mm 3 ).

[0048] Then soak the polished diamond wafer in a solution of concentrated H2SO4 + 50% H2O2 (or concentrated H2SO4 + HNO3) for 3 h, and perform surface oxidation treatment to eliminate the non-diamond phase on the diamond surface, obtaining single-crystal diamond.

[0049] Place the single-crystal diamond in acetone, alcohol, and deionized water in sequence, and ultrasonicate for 10 mins each to remove the organic substances and impurities on the surface of the single-crystal diamond, and perform Raman spectroscopy and X-ray diffraction tests. It can be known from the Raman spectroscopy test that the full width at half maximum of the single-crystal diamond is 3.54 cm -1 , and the crystallization quality of the single-crystal diamond is good ( Figure 1 ). It can be known from the XRD test that the obtained diamond is single-crystal diamond with (400) crystal orientation ( Figure 2 ).

[0050] (2) Etching the single-crystal diamond by a laser cutter:

[0051] Using a BL6050 ultrafast laser glass cutter to etch the upper surface of the single-crystal diamond, leaving a channel with a certain depth on the upper surface of the single-crystal diamond (such as Figure 5as shown); the current used by the instrument is 20.3 A, the laser cutting time is 30 s, and the cutting depth is 157.41 μm; after etching, hydrogen plasma is used to remove the graphite left on the surface of the single-crystal diamond by etching.

[0052] (3) Place the etched single-crystal diamond in aqua regia (HCl:HNO3 volume ratio = 3:1) for 3 h to remove the metal contaminants on the surface of the diamond, and then anneal it in an Ar atmosphere at 500 °C for 30 min to reduce the hydrogen content and increase the resistivity; finally, ultrasonically clean it in acetone, alcohol, and deionized water for 10 min each to remove the organic contaminants.

[0053] Figure 3 is the attenuation coefficient of different substances to X-rays. It can be seen from the figure that diamond absorbs X-rays.

[0054] Example 2 Preparation of Single-Crystal Diamond 2

[0055] (1) Use microwave plasma chemical vapor deposition to grow diamond wafers; grow diamond wafers on Ib-type diamond with (100) crystal plane orientation. The size of the Ib-type diamond is 8×8×1 mm 3 , when growing, CH4 / H2 is 1:20, the total flow rate is 200 sccm, the substrate temperature is kept near 950 °C, and an infrared high-temperature detector is used for monitoring. After depositing for 100 h, remove the substrate by laser cutting, and polish the grown diamond layer into an independent wafer with a thickness of 800 μm (size 4×4×0.8 mm 3 ).

[0056] Then soak the polished diamond wafer in a solution of concentrated H2SO4 + 50% H2O2 (or concentrated H2SO4 + HNO3) for 3 h for surface oxidation treatment to eliminate the non-diamond phase on the surface of the diamond, and obtain single-crystal diamond.

[0057] (2) Use a laser cutting machine to etch the single-crystal diamond:

[0058] Use a BL6050 ultrafast laser glass cutting machine to etch the upper surface of the single-crystal diamond, leaving a certain depth of channel on the upper surface of the single-crystal diamond (such as Figure 5 as shown); the current used by the instrument is 16 A, the laser cutting time is 10 s, and the cutting depth is 53.35 μm; after etching, hydrogen plasma is used to remove the graphite left on the surface of the single-crystal diamond by etching.

[0059] (3) Place the etched single-crystal diamond in aqua regia (HCl:HNO3 volume ratio = 3:1) for 3 h to remove metal contaminants on the diamond surface. Then, anneal it in an Ar atmosphere at 500 °C for 30 min to reduce the hydrogen content and increase the resistivity. Finally, ultrasonically clean it in acetone, alcohol, and deionized water for 10 min each to remove organic contaminants.

[0060] Example 3 Preparation of Single-Crystal Diamond 3

[0061] (1) Use microwave plasma chemical vapor deposition to grow a diamond wafer; grow a diamond wafer on an Ib-type diamond with a (100) crystal plane orientation. The size of the Ib-type diamond is 8×8×1 mm 3 , with CH4 / H2 = 1:20 during growth, a total flow rate of 200 sccm, and the substrate temperature maintained near 950 °C, monitored using an infrared pyrometer. After deposition for 100 h, remove the substrate by laser cutting and polish the grown diamond layer into an independent wafer with a thickness of 800 μm (size 4×4×0.8 mm 3 ).

[0062] Then soak the polished diamond wafer in a solution of concentrated H2SO4 + 50% H2O2 (or concentrated H2SO4 + HNO3) for 3 h for surface oxidation treatment to eliminate the non-diamond phase on the diamond surface, obtaining single-crystal diamond.

[0063] (2) Use a laser cutter to etch the single-crystal diamond:

[0064] Use a BL6050 ultrafast laser glass cutter to etch the upper surface of the single-crystal diamond, leaving a channel with a certain depth on the upper surface of the single-crystal diamond (as Figure 5 shown); the instrument uses a current of 22 A, the laser cutting time is 20 s, and the cutting depth is 118.31 μm; after etching, use hydrogen plasma to remove the graphite left on the surface of the single-crystal diamond by etching.

[0065] (3) Place the etched single-crystal diamond in aqua regia (HCl:HNO3 volume ratio = 3:1) for 3 h to remove metal contaminants on the diamond surface. Then, anneal it in an Ar atmosphere at 500 °C for 30 min to reduce the hydrogen content and increase the resistivity. Finally, ultrasonically clean it in acetone, alcohol, and deionized water for 10 min each to remove organic contaminants.

[0066] Example 4 Preparation of Diamond Schottky Diode

[0067] (1) Use magnetron sputtering to deposit silver and gold thin films on the upper and lower surfaces of single-crystal diamond (obtained in Example 1):

[0068] Using a magnetron sputtering instrument, adjust the temperature to 30 °C, evacuate the vacuum to 5×10 -4 Pa, the sputtering gas is argon, the argon flow rate is 100 sccm, adjust the growth pressure and turn on the DC power supply; start depositing gold on the lower surface of the single-crystal diamond (the size of the gold thin film is 6×6 mm 2 ), the deposition time is 2.5 min, and the deposition thickness is 100 nm; after completion, start depositing silver on the upper surface of the single-crystal diamond (an array of 6×6 silver thin films, the size of a single silver thin film pixel is 0.2×0.2 mm 2 ), the deposition time is 2.5 min, and the deposition thickness is 100 nm; the target materials used for magnetron sputtering are a metal gold target and a silver target, and the purity of both the gold target and the silver target is 99.9%.

[0069] (2) On the upper surface of the single-crystal diamond deposited with silver, use photolithography to fabricate 6×6 adjacent diodes.

[0070] 1) Cleaning: Clean and dry the single-crystal diamond after depositing the gold and silver thin films to remove contaminants on the substrate surface, and then heat it on a heating table at 115 °C for 60 s to remove water vapor on the substrate surface and enhance the adhesion between the photoresist and the substrate.

[0071] 2) Coating and pre-baking: On the surface of the single-crystal diamond deposited with silver, evenly coat a layer of photoresist through a spin coater, and then pre-bake it on a heating table at 115 °C for 60 s.

[0072] 3) Exposure and mid-baking: Place a mask above the single-crystal diamond and perform ultraviolet exposure using a micro lithography machine. The exposure time is 2 min. After exposure, perform mid-baking to improve the accuracy of photolithography and make the developed pattern clearer.

[0073] 4) Development and post-baking:

[0074] Positive photoresist is used before exposure. Put the exposed sample into the developer and shake it. It can be seen that the photoresist in the ultraviolet-exposed part is dissolved by the developer and slowly falls off. The dissolved part is the exposed photoresist, and the expected pattern can be obtained on the substrate.

[0075] After complete development, immediately rinse the surface of the sample with deionized water to remove the residual developer to prevent overdevelopment. Use a high-purity nitrogen gun to slowly blow off the water droplets on the sample surface to prevent blowing off some unstable electrodes. Then heat it on a heating table at 115 °C for 1 min to volatilize the residual solvent in the developed photoresist film and enhance the adhesion of the photoresist.

[0076] 5) Resist stripping: Put the sample into the resist stripper to remove the excess photoresist on the surface, and finally rinse it with alcohol and deionized water. After cleaning, dry the sample, as Figure 4 shown.

[0077] 6) Place the sample in a CVD vacuum tube furnace for annealing treatment. The annealing temperature is 500 °C and the annealing time is 30 min;

[0078] 7) Press indium grains on the two electrodes of the sample with gold-silver coatings respectively, and a diamond Schottky diode is obtained.

[0079] Example 5

[0080] The diamond Schottky diode prepared in Example 4 is used to detect X-rays. At the same time, a semiconductor analyzer (4200-SCS) is used to test the optoelectronic properties of the diode during detection. The results are as follows:

[0081] Figure 6 is the current-voltage characteristic curve (I-V characteristic curve) of the diamond Schottky diode. It can be seen from the figure that the diamond Schottky diode for X-ray detection has a large light-dark current ratio, which can reach five orders of magnitude.

[0082] Figure 7 is the current-time characteristic curve (I-T characteristic curve) of the diamond Schottky diode under the conditions of different voltages and the same current (X-ray dose). It can be seen from the figure that the diamond Schottky diode has good energy resolution.

[0083] Figure 8 is the I-T characteristic curve of the diamond Schottky diode at different voltages. It can be seen from the figure that the diamond Schottky diode has good repeatability and stability.

[0084] Figure 9 is the I-T characteristic curve under 0 V bias. It can be seen from the figure that the light-dark current ratio of the diamond Schottky diode under 0 V bias is one order of magnitude. This is because the diamond Schottky diode generates electron-hole pairs under the irradiation of a certain dose of X-rays, and the electron-hole pairs are quickly separated under the action of the built-in electric field to form a current, realizing self-driving, and having a high light-dark current ratio, high repeatability and stability.

[0085] The above experimental results show that the high-low barrier diamond Schottky diode obtained by the present invention can be applied in X-ray detection.

Claims

1. A preparation method of a high-low barrier diamond Schottky diode, characterized in that, It includes the following steps: (1) Prepare single-crystal diamond, and etch the upper surface of the single-crystal diamond to form channels with a certain depth on the diamond, which is beneficial to reducing crosstalk between pixel points; (2)Deposit a silver film on the upper surface of single-crystal diamond and a gold film on the lower surface by magnetron sputtering method. Adjust the temperature to 30 °C, evacuate the vacuum to 5×10 -4 Pa, the sputtering gas is argon, the argon flow rate is 100 sccm, and turn on the DC power supply by adjusting the growth pressure; start depositing gold on the lower surface of single-crystal diamond, the deposition time is 2 - 3 min, and the deposition thickness is 80 - 120 nm; after completion, start depositing silver on the upper surface of single-crystal diamond, using an n×n metal silver film array, and the size of each silver film pixel is 0.2×0.2 mm 2 , the deposition time is 2 - 3 min, and the deposition thickness is 80 - 120 nm; where n is a positive integer; (3) On the upper surface of the single-crystal diamond deposited with silver, prepare n×n adjacent diodes by photolithography; where n is a positive integer.

2. The preparation method according to claim 1, wherein The specific method of step (1) is: 1) Use microwave plasma chemical vapor deposition method to grow diamond wafers to obtain single-crystal diamond; 2) Use a laser cutting machine to etch the upper surface of the single-crystal diamond. When etching, the current is 15 - 25A, the laser cutting time is 10 - 30s, and the cutting depth is 40 - 160μm; 3) Place the etched single-crystal diamond in aqua regia for 3h, and then perform annealing treatment at 500°C for 30min in an Ar atmosphere.

3. The preparation method according to claim 2, characterized in that, The thickness of the single-crystal diamond obtained in step 1) is 800μm.

4. The preparation method according to claim 2, characterized in that, After etching, use hydrogen plasma to remove the graphite left on the surface of the single-crystal diamond by etching; the volume ratio of HCl to HNO3 in aqua regia is 3:1; after annealing treatment, ultrasonically clean in acetone, alcohol, and deionized water for 10min each in turn.

5. The preparation method according to claim 1, characterized in that, The specific method of step (3) is: 1) Cleaning: Clean and dry the single-crystal diamond, and then heat it on a heating table at 115°C for 60s; 2) Glue coating and pre-baking: On the upper surface of the single-crystal diamond where silver is deposited, a layer of photoresist is evenly coated by a spin coater, and then pre-baked on a heating stage at 115 o °C for 60 s; 3) Exposure and medium baking: Place a mask plate above the single-crystal diamond, and perform ultraviolet exposure using a micro photolithography machine. The exposure time is 2min, and medium baking is performed after exposure; 4) Development and post-baking: Put the exposed single-crystal diamond into the developer. After complete development, rinse the single-crystal diamond with deionized water, and use a high-purity nitrogen gun to blow off the water droplets on the surface of the single-crystal diamond; then heat it on a heating table at 115°C for 1min; 5) Desizing: Put the single-crystal diamond into the desizing solution to remove the excess photoresist on the surface. Finally, rinse it with alcohol and deionized water in turn, and dry it after cleaning; 6) Place the single-crystal diamond in a CVD vacuum tube furnace for annealing treatment. The annealing temperature is 500°C and the annealing time is 30min; 7) Press indium grains on the two electrodes of the single-crystal diamond deposited with gold-silver plating layer to obtain a diamond Schottky diode.

6. A high-low barrier diamond Schottky diode prepared by the method according to any one of claims 1-5, characterized in that, The diode includes a diamond substrate; the diamond is single-crystal diamond. The upper surface of the single-crystal diamond is etched with channels and deposited with a silver thin film. The channels are beneficial to reducing crosstalk between pixel points, and the lower surface of the single-crystal diamond is deposited with a gold thin film.

7. Application of the high-low barrier diamond Schottky diode obtained by the method according to any one of claims 1 - 5 in X-ray detection.

8. Application of the high-low barrier diamond Schottky diode obtained by the method according to any one of claims 1 - 5 in array imaging.

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