A Schottky diode based on cubic boron nitride (c-BN) single crystal material

Abstract

This invention discloses a Schottky diode based on cubic boron nitride (c-BN) single crystal material. The fabrication method includes the following steps: A cleaned bulk c-BN single crystal is covered with tape, exposing only the area to be plated with electrodes. An Au metal electrode is deposited on one side of the bulk c-BN single crystal, and then the tape is removed. In a glove box, the oxide layer on the surface of a lithium sheet is scraped off, and the sheet is placed on the Ag-plated side of a PCB board. The unplated side of the bulk c-BN single crystal is then tightly attached to the lithium sheet. Fine metal wires are used to connect and fix the Ag electrode on the PCB board to the Au electrode on the bulk c-BN single crystal. After electrochemical doping, an Au metal electrode is deposited on the lithium-doped side of the c-BN crystal. In this invention, lithium atoms are introduced onto the c-BN surface, and their energy levels are located at shallow levels, thereby effectively improving the interfacial contact quality between the metal and c-BN. This improvement further reduces the contact barrier ΦB between the c-BN single crystal and the metal by reducing the interfacial state density.

Description

Technical Field

[0001] This invention relates to the field of electronic devices, and more specifically to a Schottky diode based on cubic boron nitride (c-BN) single crystal material. Background Technology

[0002] Schottky diodes are unipolar switching devices with rectification effects. Compared to PN junction diodes, they possess numerous superior characteristics, including lower turn-on voltage, lower on-resistance, and ultra-short reverse recovery time. They are widely used as core components in switching circuits, power factor correction circuits, and inverters, and also hold a place in power amplifiers, high-power frequency converters, phased array radar, solar cells, and ultraviolet and radiation detectors. However, silicon-based Schottky diodes currently have limited applications due to their low breakdown voltage and inability to operate above 200°C, making them unsuitable for high-temperature and high-pressure environments. Researchers have gradually shifted their focus to wide-bandgap semiconductors with superior physical properties, such as diamond, aluminum nitride (AlN), and cubic boron nitride (c-BN), which possess higher critical electric field strengths and other superior physical properties.

[0003] Since its artificial synthesis in 1957, cubic boron nitride (CBN) crystals have attracted widespread attention due to their ultra-wide bandgap, unique optical properties, high breakdown strength, and controllable carrier types. Furthermore, CBN is one of the very few ultra-wide bandgap semiconductors that can achieve thermodynamic stability and different conductivity types (p-type and n-type) within a certain range through doping with different types of elements, giving it broad application potential in high-frequency, high-voltage, and high-temperature electronic devices.

[0004] However, the currently fabricated c-BN single crystals are extremely small in size, and they also possess negative electroaffinity, making it difficult to form high-quality ohmic contacts. Numerous experiments have shown that regardless of whether a metal electrode with a high or low work function is used, a Schottky barrier of varying heights is generated at the contact interface between the electrode and the c-BN single crystal. Therefore, it is difficult to fabricate Schottky diodes based on c-BN. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention constructs a Schottky diode based on cubic boron nitride (c-BN) single crystal material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention provides a method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material, comprising the following steps:

[0008] (1) Cleaning the bulk c-BN single crystal;

[0009] (2) Cover the area around the cleaned bulk c-BN single crystal with tape, leaving only the area to be plated exposed. Deposit Au metal electrode on one side of the bulk c-BN single crystal using magnetron sputtering of a metal target, and then peel off the tape.

[0010] (3) Use insulating tweezers in the glove box to scrape off the oxide layer on the surface of the lithium sheet, then place it on the side of the PCB board plated with Ag, and then press the side of the block c-BN single crystal without Au plating onto the lithium sheet.

[0011] (4) The Ag electrode of the PCB board is connected to the Au electrode of the bulk c-BN single crystal by using a metal wire, and then the electrode is fixed with an insulating clamp. After completing the electrochemical doping, the Au metal electrode is further deposited on the lithium-doped side of the c-BN crystal by magnetron sputtering, thereby preparing a Schottky diode.

[0012] This invention uses elemental lithium as the doping source. Compared with other lithium compounds, elemental lithium has higher purity and better electrochemical properties, which can effectively improve the doping efficiency of c-BN. Lithium was chosen as the doping element because its atomic radius is smaller than that of other atoms. This makes it easier for lithium atoms to enter the c-BN lattice while reducing lattice distortion.

[0013] Before electrochemical doping, to prevent short circuits caused by metal connections on the sides of the c-BN crystal, the area around the crystal is covered with adhesive tape, leaving only the area to be plated with the electrode exposed. A gold (Au) electrode with a thickness of approximately 100 nm is deposited on the c-BN surface using a magnetron sputtering metal target, and then the adhesive tape is removed. At this point, the Au electrode fabrication is complete. This process ensures good contact between the electrode and the c-BN crystal during the electrochemical doping process.

[0014] In this invention, the gas atmosphere for electrochemical lithium doping is Ar, which can prevent elemental lithium from reacting with oxygen or water vapor in the air.

[0015] Preferably, the bulk c-BN single crystal contains Na, K, and Li elements, and the energy levels of these elements in the crystal are deep energy levels with a maximum width of 1.5 ± 0.2 mm.

[0016] Preferably, in step (1), the bulk c-BN single crystal is immersed in aqua regia solution, sonicated, removed, immersed in anhydrous ethanol solution, sonicated, removed, immersed in deionized water, sonicated again, removed, rinsed with deionized water, and finally dried with nitrogen gas and dried in a drying oven. Specifically, the cleaning steps are as follows: 3 ml of concentrated hydrochloric acid and 1 ml of concentrated nitric acid (volume ratio approximately 3:1) are poured into a sample bottle and thoroughly mixed to prepare aqua regia solution. Simultaneously, the bulk c-BN single crystal is placed in this solution, sonicated for 5 min, and then soaked for 15 min. The c-BN single crystal is then removed and placed in anhydrous ethanol solution, sonicated for 15 min, and further immersed in deionized water, sonicated for 15 min. Then, it is repeatedly rinsed with deionized water to thoroughly clean the aqua regia and anhydrous ethanol. Finally, it is dried with nitrogen gas and placed in a drying oven for 1 hour.

[0017] Preferably, in step (2), the thickness of the deposited Au metal electrode is 100±10nm.

[0018] Preferably, in step (3), the effective contact area between the bulk c-BN single crystal and the lithium sheet is 1.4-1.6 mm. 2 This invention controls the effective contact area between the bulk c-BN single crystal and the lithium sheet, ensuring uniform doping and improving doping efficiency.

[0019] Preferably, in step (4), the electrochemical doping time is 0-36 h; more preferably, the electrochemical doping time is 30 h. The doping concentration is adjusted by controlling the Li atom doping time.

[0020] Preferably, in step (4), the thickness of the deposited Au metal electrode is 100±10nm.

[0021] A second aspect of the present invention provides a Schottky diode, which is prepared by the method for preparing a Schottky diode based on cubic boron nitride (c-BN) single crystal material.

[0022] Preferably, the ideality factor of the Schottky diode is 5-15, and the turn-on voltage is 3-5V.

[0023] The third aspect of the present invention provides the application of the Schottky diode in the fabrication of power diodes, particularly in the application of high-temperature, high-voltage, and high-frequency diodes.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] In this invention, a Schottky contact is formed between the c-BN crystal and the Au electrode, and Li atoms are doped onto the surface of the c-BN single crystal using an electrochemical method. During this process, lithium atoms are introduced onto the c-BN surface, and their energy levels are localized to shallow levels, thereby effectively improving the interfacial contact quality between the metal and c-BN. This improvement further reduces the contact barrier ΦB between the c-BN single crystal and the metal by decreasing the interfacial state density. Attached Figure Description

[0026] Figure 1 A schematic diagram of the fabrication process for a Schottky diode made of cubic boron nitride (c-BN) single crystal material;

[0027] Figure 2 To evaluate the IV characteristics of Au / Li:c-BN / Au Schottky diodes under different Li atom doping times;

[0028] Figure 3 The ideal factor of the Au / Li:c-BN / Au Schottky diode when the Li atom doping time is 30h;

[0029] Figure 4 The breakdown voltage of the Au / Li:c-BN / Au Schottky diode when the Li atom doping time is 30h. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0032] Example 1

[0033] The c-BN crystal was subjected to Li atom doping using a chemical doping method, as shown in the schematic diagram below. Figure 1 As shown. Its preparation method is as follows:

[0034] (1) Chemically clean the bulk c-BN single crystal to remove impurities present on the surface of the c-BN single crystal.

[0035] Pour 3 ml of concentrated hydrochloric acid and 1 ml of concentrated nitric acid (volume ratio approximately 3:1) into a sample vial and mix thoroughly to prepare an aqua regia solution. Place the blocky c-BN single crystal into this solution and sonicate for 5 min, then soak for 15 min. Remove the c-BN single crystal and sonicate it in anhydrous ethanol solution for 15 min, then further immerse it in deionized water and sonicate for 15 min. Rinse repeatedly with deionized water to thoroughly remove the aqua regia and anhydrous ethanol. Finally, dry it with nitrogen gas and place it in a drying oven for 1 hour.

[0036] (2) Doping c-BN crystal with Li atoms.

[0037] Due to the extremely small size of c-BN crystals, surface electrodes cannot be directly fabricated using photolithography. Therefore, the method used in this embodiment is as follows: A cleaned bulk c-BN single crystal is taken. To avoid short circuits caused by metal connections on the sides of the c-BN crystal, the area around the crystal is covered with tape, exposing only the area to be plated. A gold (Au) metal electrode with a thickness of approximately 100 nm is deposited on the c-BN surface using magnetron sputtering of a metal target. The tape is then removed and the sample is cleaned. This step ensures good contact between the electrode and the c-BN crystal and prepares the surface for subsequent electrochemical doping. The c-BN single crystal with the Au electrode and the PCB board with the Ag electrode are then placed together in a glove box filled with Ar. Ar provides a stable and inert atmosphere to prevent unnecessary chemical reactions. Simultaneously, elemental lithium is selected as the lithium source for doping. Compared to other lithium compounds, elemental lithium has higher purity and better electrochemical properties, effectively improving the doping efficiency of c-BN and reducing other chemical reactions. However, since lithium is a reactive metal, its surface is oxidized. Therefore, the oxide layer on the surface of the lithium sheet was scraped off using insulating tweezers in a glove box, and it was placed on one side of a PCB board with Ag plating. Then, the side of the bulk c-BN single crystal without Au plating was tightly attached to the lithium sheet, and the Ag electrode of the PCB board was connected to the Au electrode of the bulk c-BN single crystal using fine metal wires. At the same time, it was tightly clamped with an insulating clip. It was placed in an Ar-filled glove box for 0h, 18h, 30h, and 36h to complete the electrochemical doping of Li, and its surface was cleaned. The area around the bulk c-BN single crystal was covered with tape, leaving only the area to be plated with the electrode exposed. A gold (Au) metal electrode with a thickness of about 100nm was deposited on the other surface of the c-BN using a magnetron sputtering metal target, resulting in a Schottky diode based on cubic boron nitride (c-BN) single crystal material.

[0038] Performance testing

[0039] After the electrodes are plated on both the upper and lower surfaces of the diode, one electrode needs to be brought out for testing. To do this, indium (In) is first melted with a soldering iron and applied to the PCB board. Then, the c-BN diode is placed on top. Next, the heated soldering iron is gently touched to the In metal around the diode. The In metal will melt rapidly at the high temperature. At this point, the soldering iron is removed, and the In will immediately solidify and solder to the Au electrode on the lower surface of the c-BN diode. The IV characteristic curve of this diode under dark conditions is shown below. Figure 2 As shown, the IV curve exhibits a clear rectification characteristic, with a rectification coefficient reaching approximately 63. This indicates that Li doping on the surface of c-BN was effectively performed using electrochemical methods, thereby reducing the potential barrier height. Its forward threshold voltage or turn-on voltage is approximately 4V. The relatively high forward threshold voltage or turn-on voltage of this diode may be due to a large Schottky barrier formed by the energy level difference between the c-BN crystal and the metal Au, or the poor quality of the ohmic contact formed between the Li-doped side of the bulk c-BN single crystal and the metal Au, resulting in a small potential barrier.

[0040] Figure 3 The ideal factor for Au / Li:c-BN / Au Schottky diodes is determined by... Figure 3 The ideality factor of the Schottky diode is 12.72, and the effective barrier height is 0.89 eV. This result confirms that Li doping on the c-BN single crystal surface via electrochemical methods is successful, thereby significantly reducing the height of the Schottky barrier.

[0041] Figure 4 The breakdown voltage of the Au / Li:c-BN / Au Schottky diode is given by... Figure 4 It is known that when a reverse bias voltage greater than 73V is applied, a large number of holes are injected into the interior of the bulk c-BN single crystal, causing a sharp increase in current and resulting in breakdown of the Au / Li:c-BN / Au diode. Therefore, the breakdown voltage of this Au / Li:c-BN / Au Schottky diode is approximately 73V.

[0042] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material, characterized in that, Includes the following steps: (1) Cleaning the bulk c-BN single crystal; (2) Cover the area around the cleaned bulk c-BN single crystal with tape, leaving only the area to be plated exposed. Deposit Au metal electrode on one side of the bulk c-BN single crystal using magnetron sputtering of a metal target, and then peel off the tape. (3) Use insulating tweezers in the glove box to scrape off the oxide layer on the surface of the lithium sheet, then place it on the side of the PCB board plated with Ag, and then press the side of the block c-BN single crystal without Au plating onto the lithium sheet. (4) The Ag electrode of the PCB board is connected to the Au electrode of the bulk c-BN single crystal by using a metal wire, and then the electrode is fixed with an insulating clamp. After completing the electrochemical doping, the Au metal electrode is further deposited on the lithium-doped side of the c-BN crystal by magnetron sputtering, thereby preparing a Schottky diode.

2. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, The bulk c-BN single crystal contains Na, K, and Li elements. These elements are located in deep energy levels in the crystal, with a maximum width of 1.5 ± 0.2 mm.

3. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, In step (1), the cleaning steps are as follows: immerse the blocky c-BN single crystal in aqua regia solution, sonicate, take it out, immerse it in anhydrous ethanol solution and sonicate, take it out, immerse it in deionized water and sonicate, take it out again, rinse it with deionized water, and finally blow it dry with nitrogen gas and dry it in a drying oven.

4. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, In step (2), the thickness of the deposited Au metal electrode is 100±10nm.

5. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, In step (3), the effective contact area between the bulk c-BN single crystal and the lithium sheet is 1.4-1.6 mm. 2 .

6. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, In step (4), the electrochemical doping time is 0-36h.

7. The method for fabricating a Schottky diode based on cubic boron nitride (c-BN) single crystal material according to claim 1, characterized in that, In step (4), the thickness of the deposited Au metal electrode is 100±10nm.

8. A Schottky diode, characterized in that, The Schottky diode based on cubic boron nitride (c-BN) single crystal material as described in any one of claims 1-7 is prepared.

9. The Schottky diode according to claim 8, characterized in that, The ideal factor of the Schottky diode is 5-15, and the turn-on voltage is 3-5V.

10. The application of the Schottky diode according to claim 8 or 9 in the fabrication of power diodes.

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