Groove gate delta doped diamond junction field effect transistor and preparation method thereof

Abstract

The invention provides a groove 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 groove 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 groove gate. The preparation method comprises the step of preparing the structures in sequence. According to the groove gate delta doped diamond junction field effect transistor and the preparation method thereof provided by the invention, the i-p + +-i three-layer delta doped structure has a doped channel with high carrier concentration and high mobility, a PN junction can be formed to deplete channel carriers, a device switch can be effectively regulated and controlled, a longitudinal PN junction is formed in a gate-drain drift region to modulate electric field distribution, and the field effect transistor can be applied to the field effect transistor. The breakdown voltage of the device is effectively improved, parasitic resistance increase caused by formation of a space charge region can be avoided, and the breakdown voltage of the device can be improved by modulating an electric field while the structure is realized through the groove gate.

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] As a representative of ultra-wide bandgap semiconductors, diamond has excellent properties such as ultra-wide bandgap (5.45eV), high breakdown field strength (10MV / cm), high carrier saturation drift velocity and carrier mobility. The quality factors (Johnson, Keyes, Baliga figures of merit) of its microwave power devices are the highest, 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 "self-heating effect" and "avalanche breakdown" of power electronic devices at this stage, and realize 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 hybrid 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 is correspondingly reduced to 0eV, and the delocalization caused by the quantum confinement effect allows carriers to stay away from ionized impurities, reducing Coulomb scattering and making the mobility very high. However, due to the high carrier concentration of the delta-doped channel, the device is difficult to turn off, and it cannot be turned off even until the device breaks down. By introducing an N-type doped layer to form a PN junction, a built-in potential of about 3V can be obtained. The formed PN junction capacitance is used to deplete the channel carriers to realize an enhancement-mode device, but the space charge region formed near the source and drain will greatly increase the parasitic resistance of the device, thereby affecting the device performance. Summary of the invention

[0004] The object of the present invention is to provide a groove gate delta-doped diamond junction field effect transistor and a preparation method thereof, aiming to solve the technical problems that the delta-doped diamond junction field effect transistor is difficult to prepare and the performance of the prepared device is weak.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a recessed gate delta-doped diamond junction field effect transistor, comprising: Diamond substrate; A first diamond epitaxial layer is 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 the upper surface of the delta-doped P-type channel layer; 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, 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 groove is formed by etching the upper surface of the N-type doped single crystal diamond epitaxial film, wherein the gate groove extends to 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.

[0006] 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.

[0007] In a possible implementation manner, the source electrode and the drain electrode respectively form ohmic contacts with the delta-doped P-type channel layer.

[0008] 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.

[0009] In a 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 , the half-peak width of X-ray diffraction 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 , mobility is 20-200cm2 / V·s, sheet resistance is less than 2KΩ / □; The N-type doped single crystal diamond epitaxial film has a thickness of 10-200 nm and a nitrogen doping concentration of 1×10 19 cm -3 -1×10 21 cm -3 , the sheet resistance is greater than 10MΩ / □.

[0010] The invention provides a recessed gate delta-doped diamond junction field effect transistor with a beneficial effect in that: compared with the prior art, the recessed gate delta-doped diamond junction field effect transistor of the 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 The upper surface of the delta-doped P-type channel layer is doped; the drain electrode is formed on the upper surface of the delta-doped P-type channel layer and is spaced from the source electrode; the 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 the upper surface of the second diamond epitaxial layer is etched to form a gate groove; an N-type doped single-crystalline 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-crystalline 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.

[0011] The present invention also provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, comprising the following steps: 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, forming a second diamond epitaxial layer on the upper surface of the delta-doped P-type channel layer, 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 three, arranging a source electrode and a drain electrode on the upper surface of the delta-doped P-type channel layer, and arranging 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 groove, wherein the gate groove extends to 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 7, 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 in the gate groove.

[0012] 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.

[0013] In a possible implementation, the electrical isolation process is performed on the area not covered by the N-type doped single crystal diamond epitaxial film, and the resistivity of the area is made greater than 100 MΩ·cm.

[0014] In a possible implementation, a gate metal layer is formed at the gate groove position, which sequentially includes: Using a photolithography process to process 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.

[0015] 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.

[0016] The invention provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, which has the following beneficial effects: compared with the prior art, the invention provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, which comprises cleaning and drying a diamond substrate, growing an i-p++-i three-layer delta-doped structure on the diamond substrate, and performing acid boiling to remove a non-diamond phase; forming a source electrode and a drain electrode on the doped structure, performing selective etching on the doped structure to form a gate groove, and extending the gate groove to 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 on the upper surface of the N-type doped single crystal diamond epitaxial film and in the gate groove; making the source electrode and the drain electrode form ohmic contacts with the delta-doped P-type channel layer respectively; and subjecting the surface of the delta-doped P-type channel layer to electrical isolation treatment in areas other than 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

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0018] 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; 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.

[0019] Description of reference numerals: 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

[0020] 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 in conjunction with 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.

[0021] Please also read Figure 1 to Figure 2 Now, a groove gate delta-doped diamond junction field effect transistor provided by the present invention is described. 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 first diamond epitaxial layer 2; The second diamond epitaxial layer 4 is formed on the upper surface of the delta-doped P-type channel layer 3 and is spaced from the source electrode 5; the second diamond epitaxial layer 4 is formed on the upper surface of the delta-doped P-type channel layer 3 and is located between the source electrode 5 and the drain electrode 6; 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 formed by etching on the upper surface of the N-type doped single crystal diamond epitaxial film 7, and the gate groove extends to 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.

[0022] The invention provides a recessed gate delta-doped diamond junction field effect transistor, which improves the breakdown voltage of the device compared with the prior art, and prepares a high-performance recessed gate junction field effect transistor based on a delta-doped channel.

[0023] In some embodiments, see Figure 1 to Figure 2 , 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. 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, and forms a PN junction under the groove gate 8 to deplete the channel carriers, so that the gate voltage can effectively regulate the device switch, and in the gate-drain drift region, the longitudinal PN junction formed can modulate the electric field distribution and effectively improve the breakdown voltage of the device. An i-type diamond epitaxial layer is introduced in 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 realize the above structure while realizing the groove gate 8 to modulate the electric field and improve the breakdown voltage of the device.

[0024] The N-type doped single crystal diamond epitaxial film 7 is formed by photolithography, dielectric mask deposition, etching and selective growth. The gate groove is formed by photolithography, metal mask deposition, stripping and etching. The recessed gate 8 is formed by photolithography, metal mask deposition and stripping to obtain a recessed gate delta doped diamond junction field effect transistor.

[0025] In some embodiments, see Figure 1 to Figure 2 The source electrode 5 and the drain electrode 6 respectively form ohmic contacts with the delta-doped P-type channel layer 3 .

[0026] In some embodiments, see Figure 1 to Figure 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.

[0027] In some embodiments, see Figure 1 to Figure 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 undoped diamond epitaxial film has a thickness of 10-200nm, a root mean square surface roughness of less than 0.5nm, and a Raman half peak width of less than 10cm -1 , the half-peak width of X-ray diffraction is less than 0.1°; 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 , mobility is 20-200cm 2 / V·s, sheet resistance is less than 2KΩ / □; The N-type doped single crystal diamond epitaxial film 7 has a thickness of 10-200 nm and a nitrogen doping concentration of 1×10 19 cm -3 -1×10 21 cm -3 , the sheet resistance is greater than 10MΩ / □.

[0028] 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, etc. The thickness of the source electrode 5 and the drain electrode 6 is 0.05-50 μm.

[0029] The present invention also provides a method for preparing a recessed gate delta-doped diamond junction field effect transistor, comprising the following steps: 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.

[0030] Step 2: forming a first diamond epitaxial layer 2 on the upper surface of the diamond substrate 1, forming a delta-doped P-type channel layer 3 on the upper surface of the first diamond epitaxial layer 2, forming a second diamond epitaxial layer 4 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, and acid boiling is performed to remove the non-diamond phase; using MPCVD equipment to grow the i-p++-i three-layer delta-doped structure, the growth conditions are power 1.5KW, chamber pressure 50Torr, total gas flow 500sccm. After the growth is completed, nitric acid, sulfuric acid and hydrochloric acid are used to acid boil the grown substrate, and then cooled and cleaned.

[0031] The sample surface is spin-coated with photoresist, and after the pattern is photolithographically formed, 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 position of the drain electrode 6 is etched close to the P++ layer.

[0032] Step three, a source electrode 5 and a drain electrode 6 are spaced apart on the upper surface of the delta-doped P-type channel layer 3, and the second diamond epitaxial layer 4 is located between the source electrode 5 and the drain electrode 6; Step 4, forming an N-type doped single crystal diamond epitaxial film 7 on the upper surface of the second diamond epitaxial layer 4; Step 5, selectively etching the upper surface of the N-type doped single crystal diamond epitaxial film 7 to form a gate groove, wherein the gate groove extends to the delta-doped P-type channel layer 3; Step six, making the source electrode 5 and the drain electrode 6 form ohmic contacts with the delta-doped P-type channel layer 3 respectively; wherein the source region and the drain region are formed by photolithography, and the deposited metal is Ti / Au, which is 50 / 300nm respectively. After peeling, it is placed in an annealing furnace and annealed at 500°C for 30 minutes to form ohmic contacts.

[0033] Step 7: The area on the surface of the delta-doped P-type channel layer 3 other than the source electrode 5, the drain electrode 6 and the part between the source electrode 5 and the drain electrode 6 is electrically isolated. The active area pattern is photolithographically processed, and a plasma cleaning machine is used for processing for 10 minutes to achieve electrical isolation between devices, and then the photoresist is removed after cleaning with acetone, anhydrous ethanol and deionized water. The gate groove pattern is photolithographically processed, and the Ni metal mask is obtained by evaporation and peeling, and the gate groove is etched out by ICP; degumming. A 300nm SiO2 mask layer is deposited by PECVD, and photolithography is performed to form a selectively grown pattern. The SiO2 in the growth area is etched clean by wet etching, and then degumming is performed, and the MPCVD equipment is placed to selectively grow a layer of N-doped single-crystal diamond epitaxial film. The growth conditions are: power 1KW, chamber pressure 40Torr, and total gas flow 200sccm; after the epitaxial film is grown, the SiO2 mask is removed by 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 stripping.

[0034] Step eight, forming a recessed gate 8 on the upper surface of the N-type doped single crystal diamond epitaxial film 7 and in the gate groove, wherein the recessed gate 8 is T-shaped and can be a T-shaped gate electrode.

[0035] The method for preparing a recessed gate delta-doped diamond junction field effect transistor provided by the present invention has the following beneficial effects: compared with the prior art, the method for preparing a recessed gate delta-doped diamond junction field effect transistor provided by 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 a non-diamond phase; 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 to 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 in 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 area on the surface of the delta-doped P-type channel layer 3 other than 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.

[0036] In some embodiments, see Figure 1 to Figure 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.

[0037] In some embodiments, see Figure 1 to Figure 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.

[0038] In some embodiments, see Figure 1 to Figure 2 , a gate metal layer is formed at the gate groove position, which sequentially includes: Using a photolithography process to process the area corresponding to the gate groove to obtain a gate morphology; At the gate groove position, gate metal is deposited, and the photoresist is stripped to form a groove gate 8; The gate metal and the N-type doped single crystal diamond epitaxial film 7 form a Schottky junction, and the recessed gate 8 has a T-type gate structure.

[0039] In some embodiments, see Figure 1 to Figure 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.

[0040] Since the carrier concentration of the delta-doped channel (delta-doped P-type channel layer 3) is high, it is difficult to achieve channel (delta-doped P-type channel layer 3) shutdown by the dielectric gate process. By introducing an N-type epitaxial layer film (N-type doped single crystal diamond epitaxial film 7), a PN junction is formed under the gate to effectively deplete the channel carriers, and 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. At the same time, an i-type undoped epitaxial layer (the first diamond epitaxial layer 2 and the second diamond epitaxial layer 4) is introduced near the source and drain electrodes 6 to avoid the space charge region formed from increasing the series parasitic resistance between the gate, source, gate and drain. At the gate position, a groove gate structure is formed by selective etching, which can not only easily realize the above structure, but also facilitate the preparation of a T-type gate, thereby improving the breakdown voltage of the device, thereby realizing the preparation of a high-performance groove gate junction field effect transistor based on a delta-doped channel.

[0041] The present invention provides a groove gate delta-doped diamond junction field effect transistor and a preparation method thereof. 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 control the device switch, and in the gate-drain drift region, a longitudinal PN junction is formed to modulate the electric field distribution, effectively improve the device breakdown voltage, and can avoid the formation of a space charge region that causes an increase in parasitic resistance. The groove gate 8 can modulate the electric field to improve the device breakdown voltage while realizing the above structure.

[0042] 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 protection scope 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 is 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 the upper surface of the delta-doped P-type channel layer; 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, 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 groove is formed by etching the upper surface of the N-type doped single crystal diamond epitaxial film, wherein the gate groove extends to 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. A recessed gate delta-doped diamond junction field effect transistor as claimed in claim 1, characterized in that: 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, characterized in that: The source electrode and the drain electrode form ohmic contacts with the delta-doped P-type channel layer respectively.

4. The recessed gate delta-doped diamond junction field effect transistor according to claim 1, characterized in that: 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, characterized in that: 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 , the half-peak width of X-ray diffraction 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 , mobility is 20-200cm 2 / V·s, sheet resistance is less than 2KΩ / □; The N-type doped single crystal diamond epitaxial film has a thickness of 10-200 nm and a nitrogen doping concentration of 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, characterized in that: 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, forming a second diamond epitaxial layer on the upper surface of the delta-doped P-type channel layer, 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 three, arranging a source electrode and a drain electrode on the upper surface of the delta-doped P-type channel layer, and arranging 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 groove, wherein the gate groove extends to 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 7, 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 groove.

7. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 6, characterized in that: 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.

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

9. The method for preparing a recessed gate delta-doped diamond junction field effect transistor according to claim 6, characterized in that: The gate groove position forms a gate metal layer, which sequentially includes: Using a photolithography process to process 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, characterized in that: 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 50nm-50μm.

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