A recessed gate delta doped diamond junction field effect transistor and a method of making the same

Abstract

The application provides a recess gate delta-doped diamond junction field effect transistor and a preparation method thereof, and belongs to the technical field of semiconductor devices and manufacturing methods. The recess gate delta-doped diamond junction field effect transistor comprises a diamond substrate, an i-p++-i three-layer delta-doped structure, a source electrode, a drain electrode, an N-type doped single crystal diamond epitaxial film and a recess gate. The preparation method comprises sequentially preparing the above structures. The recess gate delta-doped diamond junction field effect transistor and the preparation method thereof have the advantages that the i-p++-i three-layer delta-doped structure has a doped channel with high carrier concentration and high mobility, can form a PN junction to deplete channel carriers, can effectively regulate and control the switching of the device, and in the gate-drain drift region, the formation of a longitudinal PN junction can modulate the electric field distribution, effectively improve the breakdown voltage of the device, and can avoid the increase of parasitic resistance caused by the formation of a space charge region. Through the recess gate, the above structure can be realized, and the electric field can be modulated to improve the breakdown voltage of the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices and manufacturing methods, and more specifically, relates to a recessed gate delta-doped diamond junction field effect transistor and a preparation method thereof. Background Art

[0002] Diamond, a representative of ultra-wide bandgap semiconductors, possesses excellent properties such as an ultra-wide bandgap (5.45 eV), a high breakdown field strength (10 MV / cm), a high current saturation drift velocity, and carrier mobility. Its microwave power devices have the highest quality factors (Johnson, Keyes, and Baliga figures of merit), and its room-temperature carrier mobility is much higher than that of GaN and SiC. Therefore, electronic devices made of diamond are expected to overcome the two major technical bottlenecks of current power electronic devices, namely the "self-heating effect" and "avalanche breakdown", and achieve a revolutionary change in power devices.

[0003] Although diamond can be doped with different types of elements such as boron and phosphorus like silicon, due to the small lattice constant of diamond, SP 3 The orbital hybridization carbon-carbon bond energy is strong, resulting in a deeper impurity energy level in diamond, a higher activation energy, and a lower doping activation rate. If the doping concentration is increased, the impurity ion scattering and surface roughness scattering effects will increase sharply, and the mobility will decrease. The delta doping technology can solve the problems of high activation energy and impurity ion scattering. It consists of two layers of high-purity diamond with an ultra-thin layer (ideally a single layer) of highly doped diamond sandwiched between them. Due to the high doping concentration (more than 10 20 cm -3 ), its activation energy correspondingly drops to 0eV, and the delocalization caused by the quantum confinement effect allows carriers to move away from ionized impurities, reducing Coulomb scattering and achieving very high mobility. However, the high carrier concentration in the delta-doped channel makes it difficult to turn off the device, even until the device breaks down. Introducing an N-type doped layer to form a PN junction can achieve a built-in potential of approximately 3V. The resulting PN junction capacitance is used to deplete channel carriers, realizing an enhancement-mode device. However, the space charge region formed near the source and drain significantly increases the device's parasitic resistance, thereby affecting device performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a recessed gate delta-doped diamond junction field effect transistor and a preparation method thereof, aiming to solve the technical problems that delta-doped diamond junction field effect transistors are difficult to prepare and have poor performance after preparation.

[0005] To achieve the above-mentioned object, the technical solution adopted by the present invention is to provide a recessed gate delta-doped diamond junction field effect transistor, comprising:

[0006] Diamond substrate;

[0007] a first diamond epitaxial layer formed on the upper surface of the diamond substrate;

[0008] A delta-doped P-type channel layer formed on the upper surface of the first diamond epitaxial layer;

[0009] a source electrode formed on an upper surface of the delta-doped P-type channel layer;

[0010] a drain electrode formed on the upper surface of the delta-doped P-type channel layer and spaced apart from the source electrode;

[0011] a second diamond epitaxial layer formed on the upper surface of the delta-doped P-type channel layer and located between the source electrode and the drain electrode;

[0012] An N-type doped single crystal diamond epitaxial film is formed on the upper surface of the second diamond epitaxial layer, and a gate trench is etched on the upper surface of the N-type doped single crystal diamond epitaxial film, wherein the gate trench extends toward the delta-doped P-type channel layer;

[0013] A recessed gate is formed on the upper surface of the N-type doped single crystal diamond epitaxial film in the gate groove to form a recessed gate structure.

[0014] In a possible implementation, the first diamond epitaxial layer, the delta-doped P-type channel layer, and the second diamond epitaxial layer are combined to form an i-p++-i three-layer delta-doped structure.

[0015] In a possible implementation, the source electrode and the drain electrode respectively form ohmic contacts with the delta-doped P-type channel layer.

[0016] In a possible implementation, an area on the surface of the delta-doped P-type channel layer other than the source electrode, the drain electrode, and a portion between the source electrode and the drain electrode is electrically isolated.

[0017] In one possible implementation, the first diamond epitaxial layer and the second diamond epitaxial layer are both undoped diamond epitaxial films, and the undoped diamond epitaxial films are intrinsic diamond materials; the undoped diamond epitaxial films have a thickness of 10-200 nm, a root mean square surface roughness of less than 0.5 nm, and a Raman half-peak width of less than 10 cm. -1 , X-ray diffraction half-peak width is less than 0.1°;

[0018] The delta-doped P-type channel layer has a thickness of 0.4-3 nm and a boron doping concentration of 1×10 20 cm -3 -8×10 20 cm -3 , the mobility is 20-200cm 2 / V·s, sheet resistance is less than 2KΩ / □;

[0019] The thickness of the N-type doped single crystal diamond epitaxial film is 10-200 nm, and the nitrogen doping concentration is 1×10 19 cm -3 -1×10 21 cm -3 , the sheet resistance is greater than 10MΩ / □.

[0020] The present invention provides a recessed gate delta-doped diamond junction field effect transistor with the following beneficial effects: compared with the prior art, the recessed gate delta-doped diamond junction field effect transistor of the present invention comprises a diamond substrate, a first diamond epitaxial layer, a delta-doped P-type channel layer, a second diamond epitaxial layer, a source electrode, a drain electrode, an N-type doped single crystal diamond epitaxial film and a recessed gate arranged in sequence from bottom to top, wherein the first diamond epitaxial layer is formed on the upper surface of the diamond substrate; the delta-doped P-type channel layer is formed on the upper surface of the first diamond epitaxial layer; the source electrode is formed on the delta-doped P-type channel layer; the second diamond epitaxial layer ... A doped P-type channel layer is formed on the upper surface; a drain electrode is formed on the upper surface of the delta-doped P-type channel layer and is spaced apart from the source electrode; a second diamond epitaxial layer is formed on the upper surface of the delta-doped P-type channel layer and is located between the source electrode and the drain electrode, and a gate groove is formed on the upper surface of the second diamond epitaxial layer; an N-type doped single-crystal diamond epitaxial film is formed on the upper surface of the second diamond epitaxial layer; a recessed gate is formed on the upper surface of the N-type doped single-crystal diamond epitaxial film in the gate groove to form a recessed gate structure, thereby improving the breakdown voltage of the device and preparing a high-performance recessed gate junction field-effect transistor based on the delta-doped channel.

[0021] The present invention also provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, comprising the following steps:

[0022] Step 1: cleaning the diamond substrate and drying it after cleaning;

[0023] Step 2: forming a first diamond epitaxial layer on the upper surface of the diamond substrate, forming a delta-doped P-type channel layer on the upper surface of the first diamond epitaxial layer, and forming a second diamond epitaxial layer on the upper surface of the delta-doped P-type channel layer, wherein the first diamond epitaxial layer, the delta-doped P-type channel layer, and the second diamond epitaxial layer are combined to form an i-p++-i three-layer delta-doped structure, and acid boiling is performed to remove non-diamond phases;

[0024] Step 3: arranging a source electrode and a drain electrode on the upper surface of the delta-doped P-type channel layer, and positioning the second diamond epitaxial layer between the source electrode and the drain electrode;

[0025] Step 4: forming an N-type doped single crystal diamond epitaxial film on the upper surface of the second diamond epitaxial layer;

[0026] Step 5: selectively etching the upper surface of the N-type doped single crystal diamond epitaxial film to form a gate trench, wherein the gate trench extends toward the delta-doped P-type channel layer;

[0027] Step six, making the source electrode and the drain electrode form ohmic contacts with the delta-doped P-type channel layer respectively;

[0028] Step seven, electrically isolating the surface of the delta-doped P-type channel layer except for the source electrode, the drain electrode, and the portion between the source electrode and the drain electrode;

[0029] Step eight: forming a recessed gate on the upper surface of the N-type doped single crystal diamond epitaxial film and located in the gate trench.

[0030] In a possible implementation, the etching of the gate groove is dry etching, using plasma to etch diamond, and the root mean square surface roughness of the obtained etching interface is less than 0.5 nm.

[0031] In a possible implementation, the electrical isolation process is performed on the region not covered by the N-type doped single crystal diamond epitaxial film, and the region has a resistivity greater than 100 MΩ·cm.

[0032] In a possible implementation, forming a gate metal layer at the gate groove position sequentially includes:

[0033] Performing photolithography on the area corresponding to the gate groove to obtain a gate morphology;

[0034] Depositing gate metal at the gate groove position, and stripping the photoresist to form a groove gate;

[0035] The gate metal and the N-type doped single crystal diamond epitaxial film form a Schottky junction, and the groove gate has a T-type gate structure.

[0036] In a possible implementation, the gate metal material is one or a combination of two or more of Al, Ti, Ni, Pt and Au, and the thickness of the gate metal is between 50 nm and 50 μm.

[0037] The present invention provides a method for preparing a recessed gate delta-doped diamond junction field-effect transistor, which has the following advantages: compared with the prior art, the method comprises cleaning and drying a diamond substrate, growing an i-p++-i three-layer delta-doped structure on the diamond substrate, and acid boiling to remove non-diamond phases; forming a source electrode and a drain electrode on the doped structure, selectively etching the doped structure to form a gate groove, and extending the gate groove toward a delta-doped P-type channel layer; forming an N-type doped single crystal diamond epitaxial film on the upper surface of the doped structure; forming a recessed gate electrode on the upper surface of the N-type doped single crystal diamond epitaxial film and within the gate groove; forming an ohmic contact between the source electrode and the drain electrode and the delta-doped P-type channel layer; and electrically isolating the surface of the delta-doped P-type channel layer except for the source electrode, the drain electrode, and the portion between the source electrode and the drain electrode. The method for preparing a recessed gate delta-doped diamond junction field effect transistor of the present invention improves the breakdown voltage of the device, and prepares a high-performance recessed gate junction field effect transistor based on a delta-doped channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 A schematic structural diagram of a recessed gate delta-doped diamond junction field-effect transistor provided in an embodiment of the present invention;

[0040] Figure 2 A schematic flow chart of the steps of a method for preparing a recessed gate delta-doped diamond junction field effect transistor provided in an embodiment of the present invention.

[0041] Description of reference numerals:

[0042] 1. Diamond substrate; 2. First diamond epitaxial layer; 3. Delta-doped P-type channel layer; 4. Second diamond epitaxial layer; 5. Source electrode; 6. Drain electrode; 7. N-type doped single crystal diamond epitaxial film; 8. Recessed gate. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] Please also refer to Figures 1 to 2 The present invention provides a groove gate delta-doped diamond junction field effect transistor. The groove gate delta-doped diamond junction field effect transistor comprises a diamond substrate 1, a first diamond epitaxial layer 2, a delta-doped P-type channel layer 3, a second diamond epitaxial layer 4, a source electrode 5, a drain electrode 6, an N-type doped single crystal diamond epitaxial film 7 and a groove gate 8, which are arranged in sequence from bottom to top. The first diamond epitaxial layer 2 is formed on the upper surface of the diamond substrate 1; the delta-doped P-type channel layer 3 is formed on the upper surface of the first diamond epitaxial layer 2; the source electrode 5 is formed on the upper surface of the delta-doped P-type channel layer 3; the drain electrode 6 is formed on the upper surface of the N-type doped single crystal diamond epitaxial film 7; and the drain electrode 6 is formed on the upper surface of the N-type doped single crystal diamond epitaxial film 7. A second diamond epitaxial layer 4 is formed on the upper surface of the delta-doped P-type channel layer 3 and is spaced apart from the source electrode 5; an N-type doped single crystal diamond epitaxial film 7 is formed on the upper surface of the second diamond epitaxial layer 4, and a gate groove is etched on the upper surface of the N-type doped single crystal diamond epitaxial film 7, and the gate groove extends toward the delta-doped P-type channel layer 3; a groove gate 8 is formed on the upper surface of the N-type doped single crystal diamond epitaxial film 7 in the gate groove to form a groove gate structure.

[0045] The present invention provides a recessed gate delta-doped diamond junction field effect transistor, which achieves an improvement in device breakdown voltage compared with the prior art, and prepares a high-performance recessed gate junction field effect transistor based on a delta-doped channel.

[0046] In some embodiments, see Figures 1 to 2The first diamond epitaxial layer 2, the delta-doped P-type channel layer 3, and the second diamond epitaxial layer 4 are combined to form an i-p++-i three-layer delta-doped structure. A doped channel with high carrier concentration and high mobility is formed, and a source electrode 5 and a drain electrode 6 are provided on the doped channel. The present invention introduces an N-type doped single-crystal diamond epitaxial film 7 to form a PN junction under the groove gate 8 to deplete the channel carriers, so that the gate voltage can effectively control the device switch. In addition, the vertical PN junction formed in the gate-drain drift region can modulate the electric field distribution and effectively improve the breakdown voltage of the device. An i-type diamond epitaxial layer is introduced into the N-type doped single-crystal diamond epitaxial film 7 near the source electrode 5 and the drain electrode 6 to avoid the formation of a space charge region, which leads to an increase in parasitic resistance. The use of a groove gate 8 can achieve the above structure while realizing the groove gate 8 to modulate the electric field and improve the breakdown voltage of the device.

[0047] The N-type doped single-crystal diamond epitaxial film 7 is formed using photolithography, dielectric mask deposition, etching, and selective growth techniques. The gate trench is formed using photolithography, metal mask deposition, lift-off, and etching techniques. The recessed gate 8 is formed using photolithography, metal mask deposition, and lift-off techniques, resulting in a recessed gate delta-doped diamond junction field-effect transistor.

[0048] In some embodiments, see Figures 1 to 2 The source electrode 5 and the drain electrode 6 respectively form ohmic contacts with the delta-doped P-type channel layer 3 .

[0049] In some embodiments, see Figures 1 to 2 On the surface of the delta-doped P-type channel layer 3, the area other than the source electrode 5, the drain electrode 6 and the portion between the source electrode 5 and the drain electrode 6 is electrically isolated.

[0050] In some embodiments, see Figures 1 to 2 The first diamond epitaxial layer 2 and the second diamond epitaxial layer 4 are both undoped diamond epitaxial films, and the undoped diamond epitaxial films are intrinsic diamond materials; the thickness of the undoped diamond epitaxial film is 10-200nm, the root mean square surface roughness is less than 0.5nm, and the Raman half-peak width is less than 10cm -1 , X-ray diffraction half-peak width is less than 0.1°;

[0051] The delta-doped P-type channel layer 3 has a thickness of 0.4-3 nm and a boron doping concentration of 1×10 20 cm -3 -8×10 20 cm -3 , the mobility is 20-200cm 2 / V·s, sheet resistance is less than 2KΩ / □;

[0052] The thickness of the N-type doped single crystal diamond epitaxial film 7 is 10-200 nm, and the nitrogen doping concentration is 1×10 19 cm -3 -1×10 21 cm -3 , the sheet resistance is greater than 10MΩ / □.

[0053] Specifically, the source electrode 5 and the drain electrode 6 are made of one or more metals such as Ti, Au, Al, W, Ir, Pd and Pt, and have a thickness of 0.05-50 μm.

[0054] The present invention also provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, comprising the following steps:

[0055] Step 1: Clean the diamond substrate 1 and dry it after cleaning; use an acid-base cleaning process to remove the non-diamond phase on the surface, then use anhydrous ethanol, acetone and deionized water to clean it, and use nitrogen to blow dry the diamond substrate 1.

[0056] In step 2, a first diamond epitaxial layer 2 is formed on the upper surface of the diamond substrate 1, a delta-doped P-type channel layer 3 is formed on the upper surface of the first diamond epitaxial layer 2, and a second diamond epitaxial layer 4 is formed on the upper surface of the delta-doped P-type channel layer 3. The first diamond epitaxial layer 2, the delta-doped P-type channel layer 3, and the second diamond epitaxial layer 4 are combined to form an i-p++-i three-layer delta-doped structure. The structure is then acid-cooked to remove non-diamond phases. The i-p++-i three-layer delta-doped structure is grown using MPCVD equipment under growth conditions of 1.5 kW power, 50 Torr chamber pressure, and 500 sccm total gas flow rate. After growth is complete, the grown substrate is acid-cooked using nitric acid, sulfuric acid, and hydrochloric acid, and then cooled and cleaned.

[0057] The sample surface is spin-coated with photoresist, and after patterning is photoetched, a Ni metal mask is formed by evaporation and peeling. The sample is then placed in an ICP device and etched using oxygen plasma until the drain electrode 6 is etched close to the P++ layer.

[0058] Step 3: Disposing a source electrode 5 and a drain electrode 6 on the upper surface of the delta-doped P-type channel layer 3, and positioning the second diamond epitaxial layer 4 between the source electrode 5 and the drain electrode 6;

[0059] Step 4: forming an N-type doped single crystal diamond epitaxial film 7 on the upper surface of the second diamond epitaxial layer 4;

[0060] Step 5: selectively etching the upper surface of the N-type doped single crystal diamond epitaxial film 7 to form a gate trench, wherein the gate trench extends toward the delta-doped P-type channel layer 3;

[0061] Step 6: The source electrode 5 and the drain electrode 6 are respectively formed into ohmic contacts with the delta-doped P-type channel layer 3; wherein the source region and the drain region are formed by photolithography, and the metal is deposited as Ti / Au, with a thickness of 50 / 300 nm respectively. After peeling, the metal is placed in an annealing furnace and annealed at 500°C for 30 minutes to form an ohmic contact.

[0062] In step seven, the delta-doped P-type channel layer 3 is electrically isolated from the surface of the source electrode 5, the drain electrode 6, and the region between the source and drain electrodes 5 and 6. The active area pattern is photolithographically formed and treated in a plasma cleaner for 10 minutes to achieve electrical isolation between devices. The photoresist is then removed by cleaning with acetone, anhydrous ethanol, and deionized water. The gate trench pattern is photolithographically formed, and a Ni metal mask is obtained by evaporation and stripping. The gate trench is then etched using ICP etching, followed by resist removal. A 300nm SiO2 mask layer is deposited using PECVD, followed by photolithography to form a selective growth pattern. The SiO2 in the growth area is etched cleanly using wet etching. After this, the substrate is placed in an MPCVD apparatus and selectively grown with an N-doped single-crystal diamond epitaxial film. Growth conditions are: 1kW power, 40 Torr chamber pressure, and 200 sccm total gas flow rate. After the epitaxial film is grown, the SiO2 mask is removed using wet etching, and the substrate surface is cleaned. The gate morphology is formed by electron beam lithography, 300nm gate metal Al is deposited, and then a "T"-shaped gate electrode is formed by lift-off.

[0063] In step eight, a recessed gate 8 is formed on the upper surface of the N-type doped single crystal diamond epitaxial film 7 and located in the gate trench. The recessed gate 8 is T-shaped and can be a T-shaped gate electrode.

[0064] The present invention provides a method for preparing a recessed gate delta-doped diamond junction field-effect transistor, which has the following advantages: compared with the prior art, the present invention comprises cleaning and drying a diamond substrate 1, growing an i-p++-i three-layer delta-doped structure on the diamond substrate 1, and acid boiling to remove non-diamond phases; forming a source electrode 5 and a drain electrode 6 on the doped structure; selectively etching the doped structure to form a gate groove, so that the gate groove extends toward a delta-doped P-type channel layer 3; forming an N-type doped single-crystal diamond epitaxial film 7 on the upper surface of the doped structure; forming a recessed gate 8 on the upper surface of the N-type doped single-crystal diamond epitaxial film 7 and located within the gate groove; making the source electrode 5 and the drain electrode 6 form ohmic contacts with the delta-doped P-type channel layer 3 respectively; and electrically isolating the surface of the delta-doped P-type channel layer 3 except for the source electrode 5, the drain electrode 6, and the portion between the source electrode 5 and the drain electrode 6. The method for preparing a recessed gate delta-doped diamond junction field effect transistor of the present invention improves the breakdown voltage of the device, and prepares a high-performance recessed gate junction field effect transistor based on a delta-doped channel.

[0065] In some embodiments, see Figures 1 to 2 The etching of the gate groove is dry etching, using plasma to etch diamond, and the root mean square surface roughness of the obtained etching interface is less than 0.5nm.

[0066] In some embodiments, see Figures 1 to 2 The electrical isolation treatment is to treat the area not covered by the N-type doped single crystal diamond epitaxial film 7 and make its resistivity greater than 100 MΩ·cm.

[0067] In some embodiments, see Figures 1 to 2 , a gate metal layer is formed at the gate groove position, which sequentially includes:

[0068] Performing photolithography on the area corresponding to the gate groove to obtain a gate morphology;

[0069] At the gate groove position, gate metal is deposited, and the photoresist is stripped off to form a groove gate 8;

[0070] The gate metal and the N-type doped single crystal diamond epitaxial film 7 form a Schottky junction, and the groove gate 8 has a T-type gate structure.

[0071] In some embodiments, see Figures 1 to 2 The material of the gate metal or the groove gate 8 is one or a combination of two or more of Al, Ti, Ni, Pt and Au, and the thickness of the gate metal is between 50nm-50μm.

[0072] Due to the high carrier concentration in the delta-doped channel (delta-doped P-type channel layer 3), dielectric gate processes make it difficult to achieve channel (delta-doped P-type channel layer 3) shutdown. By introducing an N-type epitaxial thin film (N-type doped single-crystal diamond epitaxial thin film 7), a PN junction is formed under the gate to effectively deplete channel carriers. Furthermore, the vertical PN junction formed within the gate-drain drift region modulates the electric field distribution, effectively increasing the device's breakdown voltage. Simultaneously, an i-type undoped epitaxial layer (first diamond epitaxial layer 2 and second diamond epitaxial layer 4) is introduced near the source and drain electrodes 6 to prevent the formation of a space charge region that increases the series parasitic resistance between the gate, source, and drain. At the gate location, a recessed gate structure is formed through selective etching. This not only simplifies the implementation of the aforementioned structure but also facilitates the fabrication of a T-type gate, thereby improving the device's breakdown voltage. This results in the fabrication of a high-performance recessed-gate junction field-effect transistor based on a delta-doped channel.

[0073] The present invention provides a recessed gate delta-doped diamond junction field-effect transistor and a method for preparing the same. The i-p++-i three-layer delta-doped structure has an doped channel with high carrier concentration and high mobility, can form a PN junction to deplete channel carriers, and can effectively control device switching. In addition, the formation of a longitudinal PN junction in the gate-drain drift region can modulate the electric field distribution, effectively improving the device breakdown voltage and avoiding the formation of a space charge region that causes an increase in parasitic resistance. The recessed gate 8 can be used to achieve the above structure while modulating the electric field to increase the device breakdown voltage.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A recessed gate delta-doped diamond junction field effect transistor, characterized in that: include: Diamond substrate; a first diamond epitaxial layer formed on the upper surface of the diamond substrate; A delta-doped P-type channel layer formed on the upper surface of the first diamond epitaxial layer; a source electrode formed on an upper surface of the delta-doped P-type channel layer; a drain electrode formed on the upper surface of the delta-doped P-type channel layer and spaced apart from the source electrode; a second diamond epitaxial layer formed on the upper surface of the delta-doped P-type channel layer and located between the source electrode and the drain electrode; An N-type doped single crystal diamond epitaxial film is formed on the upper surface of the second diamond epitaxial layer, and a gate trench is etched on the upper surface of the N-type doped single crystal diamond epitaxial film, wherein the gate trench extends toward the delta-doped P-type channel layer; A recessed gate is formed on the upper surface of the N-type doped single crystal diamond epitaxial film in the gate groove to form a recessed gate structure.

2. The recessed gate delta-doped diamond junction field effect transistor according to claim 1, wherein: The first diamond epitaxial layer, the delta-doped P-type channel layer and the second diamond epitaxial layer are combined to form an i-p++-i three-layer delta-doped structure.

3. The recessed gate delta-doped diamond junction field effect transistor according to claim 1, wherein: The source electrode and the drain electrode respectively form ohmic contacts with the delta-doped P-type channel layer.

4. The recessed gate delta-doped diamond junction field effect transistor according to claim 1, wherein: The area on the surface of the delta-doped P-type channel layer other than the source electrode, the drain electrode, and the portion between the source electrode and the drain electrode is electrically isolated.

5. The recessed gate delta-doped diamond junction field effect transistor according to claim 1, wherein: The first diamond epitaxial layer and the second diamond epitaxial layer are both undoped diamond epitaxial films, and the undoped diamond epitaxial films are intrinsic diamond materials; the undoped diamond epitaxial films have a thickness of 10-200 nm, a root mean square surface roughness of less than 0.5 nm, and a Raman half-peak width of less than 10 cm -1 , X-ray diffraction half-peak width is less than 0.1°; The delta-doped P-type channel layer has a thickness of 0.4-3 nm and a boron doping concentration of 1×10 20 cm -3 -8×10 20 cm -3 , the mobility is 20-200cm 2 / V·s, sheet resistance is less than 2KΩ / □; The thickness of the N-type doped single crystal diamond epitaxial film is 10-200 nm, and the nitrogen doping concentration is 1×10 19 cm -3 -1×10 21 cm -3 , the sheet resistance is greater than 10MΩ / □.

6. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 1, wherein: The following steps are involved: Step 1: cleaning the diamond substrate and drying it after cleaning; Step 2: forming a first diamond epitaxial layer on the upper surface of the diamond substrate, forming a delta-doped P-type channel layer on the upper surface of the first diamond epitaxial layer, and forming a second diamond epitaxial layer on the upper surface of the delta-doped P-type channel layer, wherein the first diamond epitaxial layer, the delta-doped P-type channel layer, and the second diamond epitaxial layer are combined to form an i-p++-i three-layer delta-doped structure, and acid boiling is performed to remove non-diamond phases; Step 3: arranging a source electrode and a drain electrode on the upper surface of the delta-doped P-type channel layer, and positioning the second diamond epitaxial layer between the source electrode and the drain electrode; Step 4: forming an N-type doped single crystal diamond epitaxial film on the upper surface of the second diamond epitaxial layer; Step 5: selectively etching the upper surface of the N-type doped single crystal diamond epitaxial film to form a gate trench, wherein the gate trench extends toward the delta-doped P-type channel layer; Step six, making the source electrode and the drain electrode form ohmic contacts with the delta-doped P-type channel layer respectively; Step seven, electrically isolating the surface of the delta-doped P-type channel layer except for the source electrode, the drain electrode, and the portion between the source electrode and the drain electrode; Step eight: forming a recessed gate on the upper surface of the N-type doped single crystal diamond epitaxial film and located in the gate trench.

7. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 6, wherein: The etching of the gate groove is dry etching, using plasma to etch diamond, and the root mean square surface roughness of the obtained etching interface is less than 0.5 nm.

8. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 6, wherein: The electrical isolation treatment is performed on the area not covered by the N-type doped single crystal diamond epitaxial film, and the area has a resistivity greater than 100 MΩ·cm.

9. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 6, wherein: The gate metal layer is formed at the gate groove position, which sequentially includes: Performing photolithography on the area corresponding to the gate groove to obtain a gate morphology; Depositing gate metal at the gate groove position, and stripping the photoresist to form a groove gate; The gate metal and the N-type doped single crystal diamond epitaxial film form a Schottky junction, and the groove gate has a T-type gate structure.

10. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 9, wherein: The gate metal material is one or a combination of two or more of Al, Ti, Ni, Pt and Au, and the thickness of the gate metal is between 50 nm and 50 μm.

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