High-mobility co-doped diamond and preparation method thereof

Abstract

The invention relates to a high-mobility co-doped diamond and a preparation method thereof. The preparation method comprises the following steps: providing an unintentionally doped diamond; preparing a hydrogen terminal structure on the surface of the unintentionally doped diamond to form a hydrogen terminal diamond; preparing an intrinsic film of a to-be-doped element on the surface of the hydrogen terminal structure of the hydrogen terminal diamond; and etching the intrinsic thin film at a preset temperature, so that to-be-doped elements of the intrinsic thin film are thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond and p-type doping is formed, and the co-doped diamond layer is obtained. According to the preparation method, damage of magnetron sputtering to crystal lattices on the surface of the diamond can be effectively repaired, the surface roughness is reduced, the interface quality of the co-doped diamond is improved, meanwhile, under the combined action of the p-type doped element and the p-type conductive hydrogen terminal structure, the carrier mobility of the hydrogen terminal diamond is greatly improved, and the service life of the hydrogen terminal diamond is prolonged. Therefore, the performance of the co-doped diamond layer is improved, and the co-doped diamond layer can be used for preparing a high-performance diamond microwave power device.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor materials, and in particular relates to a high-mobility co-doped diamond and a preparation method thereof. Background Art

[0002] Ultra-wide bandgap semiconductor diamond has many advantages such as large bandgap width, high breakdown field strength, high carrier mobility, high thermal conductivity, and radiation resistance. At present, there has been no major breakthrough in efficient diamond body doping, and hydrogen-terminated diamond field-effect transistors that use surface hydrogen termination to induce two-dimensional hole gas as a conductive channel have become the current mainstream device choice and have great potential in power electronic device applications.

[0003] Research has long found that a key weakness of hydrogen-terminated diamond two-dimensional hole gas (2DHG) conductivity is that the mobility is too low. Specifically, the carrier concentration of hydrogen-terminated diamond 2DHG conductivity is high enough, but the mobility is generally around 200 cm 2 / Vs or less, the corresponding sheet resistance is usually 10kΩ / sq or higher. For the same reason, due to the low channel carrier mobility, the transconductance, maximum current and power gain of diamond FETs are limited. Even if the current swing is fully utilized, it is still difficult to obtain sufficient output power density. It can be said that the low hole mobility of hydrogen-terminated diamond has become a key bottleneck limiting the performance improvement of its microwave power devices.

[0004] In recent years, new diamond materials such as silicon termination and boron doping have attracted wide attention, as the performance of single-crystal diamond materials with single doping is difficult to further improve. Although silicon-terminated diamond materials can help improve the stability of diamond surface conductivity, they have problems such as complex preparation process and high process precision requirements. As for diamond doped with a single element such as boron doping, not only is the doping difficult, but the contact resistance with the metal is also large, making it difficult to improve device performance.

[0005] Therefore, how to improve the carrier mobility of diamond materials and then prepare high-performance diamond microwave power devices has become a problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a high-mobility co-doped diamond and a preparation method. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0007] The embodiment of the present invention provides a method for preparing a high-mobility co-doped diamond, comprising the steps of:

[0008] Provide diamonds that are not intentionally doped;

[0009] Prepare a hydrogen-terminated structure on the surface of the unintentionally doped diamond to form a hydrogen-terminated diamond;

[0010] Prepare an intrinsic film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond;

[0011] The intrinsic film is etched at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

[0012] In one embodiment of the present invention, preparing an intrinsic thin film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond comprises:

[0013] The intrinsic film of the element to be doped is prepared on the surface of the hydrogen terminal structure by using magnetron sputtering technology.

[0014] In one embodiment of the present invention, the element to be doped includes boron.

[0015] In one embodiment of the present invention, the thickness of the intrinsic film is 100-500 nm.

[0016] In one embodiment of the present invention, etching the intrinsic film at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to obtain a co-doped diamond layer comprises:

[0017] In a microwave plasma chemical vapor deposition system, the intrinsic film is etched at a preset temperature of 800-1200°C using high-temperature hydrogen plasma, so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

[0018] In one embodiment of the present invention, along the direction from the hydrogen termination structure to the unintentionally doped diamond, the depth of the doping element entering the unintentionally doped diamond is 1-3 μm.

[0019] In one embodiment of the present invention, before preparing the intrinsic film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond, the method further comprises the following steps:

[0020] The surface density, sheet resistance and carrier mobility of the hydrogen-terminated diamond are tested. When it is determined that the surface density meets the preset surface density, the sheet resistance meets the preset sheet resistance and the carrier mobility meets the preset carrier mobility, a step of preparing an intrinsic thin film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond is performed.

[0021] In one embodiment of the present invention, the preset surface density is 5×10 11 -1×10 13 cm -2 The preset square resistance is 5-10 ohm / sq, and the preset carrier mobility is 50-100 cm 2 / (V·s).

[0022] Another embodiment of the present invention provides a high-mobility co-doped diamond, which is prepared by the preparation method described in the above embodiment.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The preparation method of the present invention prepares an intrinsic film of the element to be doped on the surface of the hydrogen terminal structure, and etches the intrinsic film, so that the element to be doped is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby effectively repairing the damage to the diamond surface lattice caused by magnetron sputtering, reducing the surface roughness, and improving the interface quality of the co-doped diamond. At the same time, under the joint action of the p-type doping element and the hydrogen terminal structure which is also p-type conductive, the carrier mobility of the hydrogen terminal diamond is greatly improved, thereby improving the performance of the co-doped diamond layer, and further can be used to prepare high-performance diamond microwave power devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic flow chart of a method for preparing a high-mobility co-doped diamond provided by an embodiment of the present invention;

[0026] Figure 2 A schematic flow chart of another method for preparing high-mobility co-doped diamond provided by an embodiment of the present invention;

[0027] Figure 3a-3e A schematic diagram of the process of preparing a high-mobility co-doped diamond provided by an embodiment of the present invention;

[0028] Figure 4 A diagram showing the contact Hall test results of co-doped diamond provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] 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.

[0030] Embodiment 1

[0031] See also Figure 1 , Figure 1A schematic flow chart of a method for preparing a high-mobility co-doped diamond provided in an embodiment of the present invention. The method for preparing a high-mobility co-doped diamond comprises the following steps:

[0032] S1. Provide diamonds that are not intentionally doped.

[0033] Specifically, a non-intentionally doped diamond grown by chemical vapor deposition (CVD) is selected as a substrate, the diamond is cut and polished for pretreatment, and then the treated diamond is ultrasonically cleaned in a strong acid mixed solution (H2SO4:HNO3), acetone, anhydrous ethanol and deionized water at 200°C in turn to obtain a clean diamond substrate. The thickness of the diamond is 500-1000μm.

[0034] S2. Preparing a hydrogen-terminated structure on the surface of an unintentionally doped diamond to form a hydrogen-terminated diamond.

[0035] Specifically, a layer of hydrogen terminal structure is prepared on the cleaned substrate by microwave plasma chemical vapor deposition (Microwave PCVD, MPCVD) technology, and the thickness of the hydrogen terminal is less than 5nm, so as to form hydrogen terminal diamond.

[0036] S3. Preparing an intrinsic thin film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond.

[0037] Specifically, magnetron sputtering technology is used to prepare an intrinsic film of the element to be doped on the surface of the hydrogen terminal structure. The element to be doped is a p-type doping element, including but not limited to boron. Boron is a common element for p-type diamond doping. In combination with diamond hydrogen terminals that are also p-type conductive, boron has low preparation difficulty, high success rate, and high preparation cost.

[0038] Specifically, the thickness of the intrinsic film is 100-500 nm. Exemplarily, a 100 nm high-purity intrinsic boron film is deposited on the surface of the hydrogen termination structure of the hydrogen termination diamond using magnetron sputtering technology to obtain a diamond sample with a boron intrinsic film and a hydrogen termination structure on the surface.

[0039] S4. Etching the intrinsic film at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

[0040] Specifically, in a microwave plasma chemical vapor deposition (MPCVD) system, under the ignition condition of a hydrogen flow rate of 300-600 sccm, a high temperature hydrogen plasma is used to etch the intrinsic film at a preset temperature of 800-1200°C, so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form a p-type doping, thereby obtaining a co-doped diamond layer. Exemplarily, a diamond sample with a boron film and a hydrogen terminal on the surface is placed in an MPCVD device again, hydrogen is introduced, and the ignition is carried out under the condition of a hydrogen flow rate of 600 sccm and the temperature is raised to 900°C for surface etching, thereby obtaining a boron-hydrogen co-doped diamond sheet with boron thermal diffusion doping.

[0041] In this embodiment, high temperature hydrogen plasma is used to etch the intrinsic film at high temperature. Under high temperature conditions, the element to be doped enters the hydrogen terminal structure and the diamond from one side of the hydrogen terminal structure through thermal diffusion. At the same time, the hydrogen plasma carries the element to be doped into the hydrogen terminal structure and the diamond, thereby forming p-type doping in the hydrogen terminal structure and the diamond. Further, after high temperature hydrogen plasma etching, the intrinsic film is completely etched away, and the surface of the hydrogen terminal is exposed.

[0042] Specifically, the depth of the doped element entering the diamond is positively correlated with the thickness of the intrinsic film. The thicker the intrinsic film, the deeper the doped element enters the diamond. Specifically, along the direction from the hydrogen terminal structure to the unintentionally doped diamond, the depth of the doped element entering the unintentionally doped diamond is 1-3 μm.

[0043] The preparation method of this embodiment prepares an intrinsic thin film of the element to be doped on the surface of the hydrogen terminal structure, and etches the intrinsic thin film, so that the element to be doped is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby effectively repairing the damage to the diamond surface lattice caused by magnetron sputtering, reducing the surface roughness, and improving the interface quality of the co-doped diamond. At the same time, under the joint action of the p-type doping element and the hydrogen terminal structure that is also p-type conductive, the carrier mobility of the hydrogen terminal diamond is greatly improved, thereby improving the performance of the co-doped diamond layer, and can be used to prepare high-performance diamond microwave power devices.

[0044] This embodiment uses magnetron sputtering of an intrinsic thin film of the element to be doped, combined with the advantage of the hydrogen terminal surface of diamond, to achieve co-doping of the diamond element to be doped with hydrogen through thermal diffusion, which can be achieved based on ordinary MPCVD equipment, effectively reducing the difficulty of the process.

[0045] Embodiment 2

[0046] Based on Example 1, see Figure 2 , Figure 2A schematic flow chart of another method for preparing a high-mobility co-doped diamond provided in an embodiment of the present invention, the method comprising the steps of:

[0047] S1. Provide diamonds that are not intentionally doped;

[0048] S2, preparing a hydrogen-terminated structure on the surface of unintentionally doped diamond to form a hydrogen-terminated diamond;

[0049] S3, testing the surface density, sheet resistance and carrier mobility of the hydrogen-terminated diamond. When it is determined that the surface density meets the preset surface density, the sheet resistance meets the preset sheet resistance and the carrier mobility meets the preset carrier mobility, proceed to step S3.

[0050] Specifically, the surface density, sheet resistance and carrier mobility are tested by a contact Hall test method, and hydrogen-terminated diamonds with a surface density within a preset surface density range, a sheet resistance within a preset sheet resistance range, and a carrier mobility within a preset carrier mobility range are selected for the next step of intrinsic thin film growth.

[0051] Specifically, the preset surface density is 5e 11 -1e 13 cm -2 , the preset square resistance is 5-10ohm / sq, and the preset carrier mobility is 50-100cm 2 / (V·s).

[0052] This embodiment can obtain hydrogen-terminated diamond with good carrier mobility by screening the area density, sheet resistance and carrier mobility, and then prepare co-doped diamond with higher mobility in subsequent steps.

[0053] S4, preparing an intrinsic thin film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond;

[0054] S5. Etching the intrinsic film at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

[0055] For the specific implementation and beneficial effects of steps S1, S2, S4, and S5, please refer to Example 1, which will not be described in detail in this example.

[0056] Embodiment 3

[0057] Based on Example 2, see Figure 3a-3e , Figure 3a-3e A schematic diagram of the process of preparing high-mobility co-doped diamond provided in an embodiment of the present invention.

[0058] S1. Provide diamonds that are not intentionally doped, see Figure 3a.

[0059] Specifically, unintentionally doped diamonds are selected as substrates, the diamonds are cut and polished for pretreatment, and then the treated diamonds are ultrasonically cleaned in a strong acid mixed solution (H2SO4:HNO3), acetone, anhydrous ethanol and deionized water at 200°C in turn to obtain a clean diamond substrate.

[0060] S2. Preparation of hydrogen-terminated structures CH on the surface of unintentionally doped diamond to form hydrogen-terminated diamond, see Figure 3b .

[0061] Specifically, a layer of hydrogen terminal structure is prepared on the cleaned substrate by microwave plasma chemical vapor deposition (Microwave PCVD, MPCVD) technology.

[0062] S3. Test the surface density, square resistance and carrier mobility of hydrogen-terminated diamonds, and select hydrogen-terminated diamonds that meet the requirements.

[0063] Specifically, the prepared hydrogen-terminated diamonds were screened by contact Hall test, and the surface density was controlled at 5×10 11 -1×10 13 cm -2 The square resistance is within 5-10ohm / sq, and the carrier mobility is within 50-100cm 2 / (V·s).

[0064] S4. Preparation of intrinsic thin films of the elements to be doped on the surface of the hydrogen-terminated structure of hydrogen-terminated diamond, see Figure 3c .

[0065] Specifically, a 100 nm high-purity intrinsic boron film B is deposited on the surface of the screened hydrogen-terminated diamond by a magnetron sputtering process to obtain a diamond sample having a boron film and hydrogen terminations on the surface.

[0066] S5. Etching the intrinsic film at a preset temperature allows the doped element of the intrinsic film to thermally diffuse into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer. Figure 3d .

[0067] Specifically, the diamond sample with a boron film and hydrogen termination on the surface is placed in the MPCVD device again, hydrogen is introduced, and the surface is etched after starting at a hydrogen flow rate of 600 sccm and heating to 1000°C to obtain a boron-hydrogen co-doped diamond sheet with boron thermal diffusion doping.

[0068] S6. Preparation of ohmic contact electrode on the surface of co-doped diamond layer, see Figure 3e .

[0069] Specifically, a Ti / Au layer with a thickness of 20 / 100 nm is deposited on the surface of the co-doped diamond layer after doping, and the deposited boron silicon co-doped diamond is annealed in a rapid thermal annealing device for 5 minutes to complete the preparation of the ohmic electrode, wherein the annealing temperature is 800° C. Alternatively, a gold layer with a thickness of 10 nm is deposited on the surface of the co-doped diamond layer after doping as an electrode to complete the preparation of the ohmic electrode. Further, the ohmic contact electrodes are located at the two ends of the surface of the co-doped diamond layer.

[0070] The co-doped diamond layer of this embodiment can reduce the resistance of the ohmic contact electrode due to its high interface quality.

[0071] The co-doped diamond after the ohmic contact electrode was prepared was subjected to contact Hall test using the four-probe method. The test structure can be found in Figure 4 , Figure 4 The contact Hall test result diagram of the co-doped diamond provided by the embodiment of the present invention, wherein Rs represents the sheet resistance, RHs represents the Hall coefficient, and Ns represents the carrier surface density. Figure 4 It can be seen that the carrier mobility of co-doped diamond is 733 cm 2 / (V·s), showing a relatively high value, proving that under the combined effect of p-type doping elements and the hydrogen-terminated structure which is also p-type conductive, the carrier mobility of hydrogen-terminated diamond is greatly improved.

[0072] Embodiment 4

[0073] Based on the above embodiments, this embodiment provides a high-mobility co-doped diamond, including: unintentionally doped diamond and a hydrogen terminal structure, the hydrogen terminal structure is located on the surface of the unintentionally doped diamond, and p-type doping elements are formed in the hydrogen terminal structure and in the portion of the unintentionally doped diamond close to the hydrogen terminal structure, and the p-type doping element and the hydrogen terminal structure form a co-doping.

[0074] 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 method for preparing high-mobility co-doped diamond, characterized in that: Includes steps: Provide diamonds that are not intentionally doped; Prepare a hydrogen-terminated structure on the surface of the unintentionally doped diamond to form a hydrogen-terminated diamond; Prepare an intrinsic film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond; The intrinsic film is etched at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

2. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: The method comprises preparing an intrinsic film of an element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond, comprising: The intrinsic film of the element to be doped is prepared on the surface of the hydrogen terminal structure by using magnetron sputtering technology.

3. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: The element to be doped includes boron.

4. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: The thickness of the intrinsic film is 100-500nm.

5. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: The intrinsic film is etched at a preset temperature so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to obtain a co-doped diamond layer, comprising: In a microwave plasma chemical vapor deposition system, the intrinsic film is etched at a preset temperature of 800-1200°C using high-temperature hydrogen plasma, so that the element to be doped in the intrinsic film is thermally diffused into the hydrogen terminal structure and the unintentionally doped diamond to form p-type doping, thereby obtaining a co-doped diamond layer.

6. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: Along the direction from the hydrogen terminal structure to the unintentionally doped diamond, the depth of the doping element entering the unintentionally doped diamond is 1-3 μm.

7. The method for preparing high-mobility co-doped diamond according to claim 1, characterized in that: Before preparing the intrinsic film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond, the step further includes: The surface density, sheet resistance and carrier mobility of the hydrogen-terminated diamond are tested. When it is determined that the surface density meets the preset surface density, the sheet resistance meets the preset sheet resistance and the carrier mobility meets the preset carrier mobility, a step of preparing an intrinsic thin film of the element to be doped on the surface of the hydrogen-terminated structure of the hydrogen-terminated diamond is performed.

8. The method for preparing high-mobility co-doped diamond according to claim 7, characterized in that: The preset surface density is 5×10 11 -1×10 13 cm -2 The preset square resistance is 5-10 ohm / sq, and the preset carrier mobility is 50-100 cm 2 / (V·s).

9. A high mobility co-doped diamond, characterized in that: The method is prepared according to any one of claims 1 to 8.

Images