High electron mobility transistor based on N-type diamond and preparation method thereof

Abstract

The embodiment of the invention provides a high electron mobility transistor based on N-type diamond and a preparation method thereof, and belongs to the technical field of semiconductors. The high electron mobility transistor comprises a diamond substrate; the N-type diamond layer is arranged on the diamond substrate and is used for forming a two-dimensional electron gas channel; the barrier layer is arranged on the N-type diamond layer, and the material of the barrier layer comprises one of Al2O3, hexagonal boron nitride and Cs; the source electrode and the drain electrode are arranged on the N-type diamond layer in a spaced mode and located on the two sides of the area where the barrier layer is located respectively; the grid electrode is arranged on the barrier layer. According to the invention, the performance of the HEMT can be optimized, so that the HEMT can be better suitable for high-temperature, high-voltage, high-frequency and high-power scenes, and the reliability of the HEMT is effectively improved.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor technology, and in particular to a high electron mobility transistor based on N-type diamond and a preparation method thereof. Background Art

[0002] A high electron mobility transistor (HEMT) is a field-effect transistor that uses two-dimensional electron gas (2DEG) or two-dimensional hole gas (2DHG) at a heterojunction interface to achieve high performance. It is widely used in fields such as radio frequency communications, power electronics, and radar systems.

[0003] In the related art, a HEMT includes: a substrate; a GaN channel layer disposed on the substrate; an AlGaN barrier layer disposed on the GaN channel layer; a source and a drain disposed at intervals on the GaN channel layer and located on both sides of the region where the AlGaN barrier layer is located; and a gate disposed on the AlGaN barrier layer.

[0004] However, GaN and AlGaN materials have low thermal conductivity and poor thermal stability. They may experience performance degradation in extreme scenarios such as high temperature, high pressure, high frequency, high power and high radiation, resulting in poor performance of HEMTs. This will limit the application of HEMTs in these extreme scenarios and affect device reliability. Summary of the Invention

[0005] This disclosure provides a high electron mobility transistor based on N-type diamond and a method for fabricating the same, which can optimize the performance of the HEMT, making it more suitable for high-temperature, high-voltage, high-frequency, and high-power scenarios, thereby effectively improving the reliability of the HEMT. The technical solution includes at least the following solutions: On the one hand, a high electron mobility transistor is provided, comprising: a diamond substrate; an N-type diamond layer, disposed on the diamond substrate, for forming a two-dimensional electron gas channel; a barrier layer, disposed on the N-type diamond layer, the material of the barrier layer comprising one of Al2O3, hexagonal boron nitride and Cs; a source electrode and a drain electrode, spaced apart and respectively located on either side of a region where the barrier layer is located; and a gate electrode, disposed on the barrier layer.

[0006] Optionally, the material of the barrier layer includes one of Al2O3 and hexagonal boron nitride, and the thickness of the barrier layer is 3 nm to 10 nm.

[0007] Optionally, the material of the barrier layer includes Cs, and the thickness of the barrier layer is 0.1 nm to 6 nm.

[0008] Optionally, the material of the N-type diamond layer is boron and nitrogen co-doped diamond.

[0009] Optionally, the doping concentration of the N-type diamond layer is 1×10 16 cm -3 to 1×10 19 cm -3 .

[0010] Optionally, the N-type diamond layer has a thickness of 10 nm to 100 nm.

[0011] On the other hand, a method for preparing a high electron mobility transistor is provided, comprising: forming an N-type diamond layer on a diamond substrate, the N-type diamond layer being used to form a two-dimensional electron gas channel; forming a barrier layer on the N-type diamond layer, the material of the barrier layer comprising one of Al2O3, hexagonal boron nitride and Cs; forming a source and a drain on the N-type diamond layer, the source and the drain being spaced apart on the N-type diamond layer and respectively located on both sides of a region where the barrier layer is located; and forming a gate on the barrier layer.

[0012] Optionally, the material of the N-type diamond layer is boron-nitrogen co-doped diamond, and the forming of the N-type diamond layer on the diamond substrate includes: using microwave plasma chemical vapor deposition technology, introducing a boron source and a nitrogen source, and depositing the boron-nitrogen co-doped diamond on the diamond substrate to obtain the N-type diamond layer.

[0013] Optionally, in the boron source and the nitrogen source, the ratio of boron element to nitrogen element is 1:1 to 1:4.

[0014] Optionally, the boron source is diborane, the nitrogen source is nitrogen gas, the flow rate of the diborane is 1 sccm to 20 sccm, and the flow rate of the nitrogen gas is 0.1 sccm to 10 sccm.

[0015] The beneficial effects of the technical solutions provided by the embodiments of the present disclosure include at least: In the disclosed embodiments, an N-type diamond layer is formed on a diamond substrate. Diamond has a high breakdown field strength and high carrier mobility, allowing the formation of a 2DEG channel through the N-type diamond layer. A barrier layer is then formed on the N-type diamond layer. The barrier layer material comprises one of Al2O3, hexagonal boron nitride (h-BN), and Cs. Al2O3 and h-BN have high electron affinities and can induce interfacial conduction band bending through surface polarization effects. Cs, a low-work-function material, can reduce the surface work function of the N-type diamond layer, changing the surface potential distribution, forming a strong interfacial barrier, and inducing band gap bending and 2DEG formation. The barrier layer, using these materials, synergizes with the N-type diamond layer to provide a sufficient electron source for the formation of a high-density 2DEG, promoting the formation of a 2DEG channel with high carrier density and high mobility. This facilitates the HEMT to achieve higher operating frequencies and greater output power, improves the device breakdown voltage, and thus optimizes HEMT performance. In addition, diamond has extremely high thermal conductivity and high-temperature resistance. The N-type diamond layer and diamond substrate can quickly dissipate heat from the HEMT's interior, improving the HEMT's heat dissipation capacity and thermal stability. This makes the HEMT better suited for scenarios such as high temperature, high pressure, high frequency, high power, and high radiation, thereby effectively improving the HEMT's reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 1 is a schematic structural diagram of a HEMT provided by an embodiment of the present disclosure; Figure 2 is a flow chart of a method for preparing a HEMT provided in an embodiment of the present disclosure; Figure 3 is a flow chart of another method for preparing a HEMT provided in an embodiment of the present disclosure; Figures 4 to 8 Schematic diagram of a preparation process of a HEMT provided in an embodiment of the present disclosure.

[0018] Reference numerals: 10: diamond substrate; 20: N-type diamond layer; 30: barrier layer; 40: source; 50: drain; 60: gate; 70: diamond buffer layer; 80: passivation layer. DETAILED DESCRIPTION

[0019] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by a person of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," "third," and similar terms used in the patent specification and claims of this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish between different components. Similarly, terms such as "a" or "an" do not indicate a quantitative limitation, but rather indicate the presence of at least one. Terms such as "include" or "comprising" mean that the elements or objects preceding "include" or "comprising" encompass the elements or objects listed after "include" or "comprising," and their equivalents, and do not exclude other elements or objects. Terms such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. "A and / or B" indicates three situations: A, B, and A and B.

[0020] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0021] Figure 1 Schematic diagram of the structure of a HEMT provided by an embodiment of the present disclosure. Figure 1 As shown, the HEMT includes: a diamond substrate 10; an N-type diamond layer 20, disposed on the diamond substrate 10, for forming a 2DEG channel; a barrier layer 30, disposed on the N-type diamond layer 20, wherein the material of the barrier layer 30 includes one of Al2O3, h-BN and Cs; a source 40 and a drain 50, spaced apart and disposed on the N-type diamond layer 20 and respectively located on both sides of the region where the barrier layer 30 is located; and a gate 60, disposed on the barrier layer 30.

[0022] In the embodiment of the present disclosure, by providing an N-type diamond layer 20 on the diamond substrate 10, the diamond has a high breakdown field strength (>10MV / cm) and a high carrier mobility (holes are about 3800cm 2 / V·S, electrons at approximately 4500 cm 2 / V·S), a 2DEG channel can be formed through the N-type diamond layer 20. A barrier layer 30 is provided on the N-type diamond layer 20. The material of the barrier layer 30 includes one of Al2O3, h-BN, and Cs. Al2O3 and h-BN have high electron affinity and can induce interface conduction band bending through surface polarization effects. Cs is a low work function material that can reduce the surface work function of the N-type diamond layer 20, change the surface potential distribution, form a strong interface barrier, and induce band gap bending and 2DEG formation. The barrier layer 30 uses these materials to cooperate with the N-type diamond layer 20 to provide a sufficient electron source for the formation of a high-density 2DEG, promoting the formation of a 2DEG channel with high carrier density and high mobility. This helps the HEMT achieve higher operating frequency and greater output power, improve the device breakdown voltage, and thus optimize the performance of the HEMT. Diamond also has extremely high thermal conductivity (>2000W / m·K) and high-temperature resistance. The N-type diamond layer 20 and diamond substrate 10 can quickly dissipate heat from the HEMT's interior, improving the HEMT's heat dissipation capacity and thermal stability. This makes the HEMT more suitable for scenarios such as high temperature, high pressure, high frequency, high power, and high radiation, thereby effectively improving the HEMT's reliability.

[0023] Illustratively, the diamond substrate 10 may be single crystal diamond.

[0024] Optionally, the material of the N-type diamond layer 20 is boron-nitrogen co-doped diamond, which is conducive to forming a 2DEG channel with high carrier density and high mobility.

[0025] In other embodiments, the material of the N-type diamond layer 20 may also be phosphorus-doped diamond, which is not limited in the present disclosure.

[0026] Optionally, the doping concentration of the N-type diamond layer 20 is 1×10 16 cm -3 to 1×10 19 cm -3 The doping concentration of boron and nitrogen co-doped diamond is within this range, which is beneficial to improving the 2DEG density and electron mobility.

[0027] For example, the doping concentration of the N-type diamond layer 20 may be 1×10 16 cm -3 , 1×10 17 cm -3 , 1×10 18 cm -3 or 1×10 19 cm -3 wait.

[0028] Optionally, the thickness of the N-type diamond layer 20 is 10 nm to 100 nm. When the thickness of the N-type diamond layer 20 is within this range, a stable 2DEG channel can be formed and the heat dissipation capability and thermal stability of the HEMT can be effectively improved.

[0029] For example, the thickness of the N-type diamond layer 20 may be 10 nm, 50 nm, or 100 nm.

[0030] In the embodiment of the present disclosure, the carrier mobility of HEMT can be 10 cm 2 / V·S to 1500 cm 2 / V·S.

[0031] like Figure 1 As shown, the HEMT further includes a diamond buffer layer 70, which is disposed between the diamond substrate 10 and the N-type diamond layer 20. The diamond buffer layer 70 can reduce interface defects, ensuring better quality of the N-type diamond layer 20 and thus better quality of the HEMT.

[0032] For example, the material of the diamond buffer layer 70 may be undoped diamond.

[0033] Optionally, the thickness of the diamond buffer layer 70 is 100 nm to 500 nm. If the thickness of the diamond buffer layer 70 is too thin, it may result in a large number of interface defects in the N-type diamond layer 20, affecting the quality of the HEMT. If the thickness of the diamond buffer layer 70 is too thick, it may lead to a long preparation time, affecting the device cost. Within this range, the thickness of the diamond buffer layer 70 can effectively reduce interface defects while ensuring a low cost of the HEMT, thereby improving the quality of the N-type diamond layer 20 and ensuring high device reliability.

[0034] For example, the thickness of the diamond buffer layer 70 may be 100 nm, 300 nm, or 500 nm.

[0035] In one possible embodiment, the material of the barrier layer 30 includes one of Al2O3 and h-BN, and the thickness of the barrier layer 30 is 3 nm to 10 nm. When the material of the barrier layer 30 is Al2O3 or h-BN, which have high electron affinity, the thickness of the barrier layer 30 within this range can better induce interfacial conduction band bending through the polarization effect, forming a stable 2DEG and promoting the formation of a high-mobility 2DEG channel. For example, when the material of the barrier layer 30 is Al2O3 or h-BN, the thickness of the barrier layer 30 can be 3 nm, 7 nm, or 10 nm, etc.

[0036] In another possible embodiment, the material of the barrier layer 30 includes Cs, and the thickness of the barrier layer 30 is 0.1nm to 6nm. When the material of the barrier layer 30 is the low work function material Cs, if the thickness of the barrier layer 30 is too small, it may affect the formation of the interface barrier and 2DEG; if the thickness of the barrier layer 30 is too large, it may affect the electron mobility of the 2DEG channel; the thickness of the barrier layer 30 within this range can effectively reduce the surface work function of the N-type diamond layer 20, change the surface potential distribution, and promote the formation of 2DEG. Exemplarily, the material of the barrier layer 30 is Cs, and the thickness of the barrier layer 30 can be 0.1nm, 0.5nm, 1nm, 3nm or 6nm, etc. For example, the barrier layer 30 can be a Cs layer with a thickness of sub-monolayer to 1 to 2 monolayers.

[0037] Exemplarily, the source 40 and the drain 50 also cover the sidewalls of the N-type diamond layer 20 and the surface of the diamond buffer layer 70 away from the diamond substrate 10 .

[0038] Alternatively, the source electrode 40 and the drain electrode 50 may be made of a metal material. For example, the source electrode 40 and the drain electrode 50 may be a Ti layer, an Al layer, a Ni layer, and an Au layer stacked in sequence. The Ti layer can serve as an adhesion layer to form a low work function contact with the N-type diamond layer 20, the Al layer and the Ni layer can help reduce contact resistance, and the Au layer can help improve the electrode's oxidation resistance and welding performance.

[0039] Optionally, the gate 60 can be made of a metal. For example, the gate 60 can be a Ti layer, or a Ti layer and an Al layer stacked in sequence. Using these materials for the gate 60 facilitates optimizing the work function and achieving precise control of the threshold voltage of the HEMT device.

[0040] It should be noted that the materials of the source 40 , drain 50 and gate 60 are merely examples. In other embodiments, the materials of the source 40 , drain 50 and gate 60 can be adjusted according to actual needs, and the present disclosure does not impose any restrictions on this.

[0041] like Figure 1 As shown, the HEMT further includes a passivation layer 80, which is disposed on a side of the barrier layer 30, source electrode 40, drain electrode 50, and gate electrode 60 that is away from the N-type diamond layer 20. Exemplarily, the passivation layer 80 also covers at least a portion of the sidewalls of the diamond substrate 10, diamond buffer layer 70, barrier layer 30, source electrode 40, drain electrode 50, and gate electrode 60. The provision of the passivation layer 80 effectively prevents external moisture, oxygen, and the like from corroding the metal electrodes and interfaces, and helps reduce the surface trap state density and leakage current of the HEMT, stabilizing the device's electrical characteristics, thereby improving the reliability and lifespan of the HEMT in high-temperature, high-voltage environments.

[0042] Optionally, the material of the passivation layer 80 includes one of SiN and Al 2 O 3 . These materials have good insulation properties and corrosion resistance, which can ensure high reliability of the HEMT.

[0043] In other embodiments, the material of the passivation layer 80 may also be adjusted according to actual needs, and the present disclosure does not limit this.

[0044] Optionally, the passivation layer 80 disposed on the gate 60 may have a thickness of 20 nm to 100 nm. For example, the passivation layer 80 may have a thickness of 20 nm, 60 nm, or 100 nm.

[0045] Figure 2 FIG. 1 is a flow chart of a method for preparing a HEMT according to an embodiment of the present disclosure. Figure 2 As shown, the preparation method comprises: In step S101 , an N-type diamond layer is formed on a diamond substrate.

[0046] The N-type diamond layer is used to form a 2DEG channel.

[0047] In step S102 , a barrier layer is formed on the N-type diamond layer.

[0048] The material of the barrier layer includes one of Al2O3, h-BN and Cs.

[0049] In step S103 , a source electrode and a drain electrode are formed on the N-type diamond layer.

[0050] The source electrode and the drain electrode are spaced apart and arranged on the N-type diamond layer and are respectively located on two sides of the region where the barrier layer is located.

[0051] In step S104 , a gate is formed on the barrier layer.

[0052] It should be noted that the preparation method embodiment is the same as the above Figure 1 The structural embodiments are based on the same inventive concept. The beneficial effects of the embodiments of the present disclosure can be found in the above structural embodiments and will not be repeated here.

[0053] Figure 3 4 is a flow chart of another method for preparing a HEMT provided in an embodiment of the present disclosure. Figures 4 to 8 FIG. 1 is a schematic diagram of a HEMT preparation process provided by an embodiment of the present disclosure. Figures 3 to 8 As shown, the preparation method comprises: In step S201 , a diamond buffer layer is formed on a diamond substrate.

[0054] like Figure 4As shown, high-quality single crystal diamond can be used and mechanically polished and chemically cleaned. For example, after mechanical polishing, it can be boiled in aqua regia acid and then ultrasonically rinsed with acetone, anhydrous ethanol and deionized water in sequence to obtain a smooth and defect-free surface to obtain a diamond substrate 10.

[0055] For example, the diamond buffer layer 70 may be formed on the diamond substrate 10 by depositing undoped diamond using a microwave plasma chemical vapor deposition (MPCVD) technique to obtain the diamond buffer layer 70 .

[0056] In step S202 , an N-type diamond layer is formed on the diamond buffer layer.

[0057] like Figure 5 As shown, the MPCVD technology can be used to introduce a boron source and a nitrogen source to deposit boron-nitrogen co-doped diamond on the diamond buffer layer to obtain an N-type diamond layer 20 .

[0058] Optionally, the ratio of boron to nitrogen in the boron source and nitrogen source is 1:1 to 1:4. Here, the ratio of boron to nitrogen refers to the molar ratio of boron to nitrogen. If the ratio of boron to nitrogen is too high or too low, it may affect the carrier generation efficiency, the conductivity type of the boron-nitrogen co-doped diamond, and the quality, stability, and performance of the HEMT. Within this range, the ratio of boron to nitrogen can achieve N-type conductivity in the boron-nitrogen co-doped diamond through mutual compensation between the deep donor energy levels of boron and the deep acceptor energy levels of nitrogen, resulting in a high-quality N-type diamond layer 20, which is beneficial for improving carrier mobility and carrier concentration.

[0059] For example, in the boron source and the nitrogen source, the ratio of boron element to nitrogen element can be 1:1, 1:2, 1:3 or 1:4, etc.

[0060] Optionally, the boron source is diborane, and the nitrogen source is nitrogen gas. The flow rate of diborane is 1 sccm to 20 sccm, and the flow rate of nitrogen gas is 0.1 sccm to 10 sccm. Using diborane and nitrogen gas as the boron source and nitrogen source, respectively, with flow rates within this range can effectively improve carrier mobility and carrier concentration, and ensure good quality of the N-type diamond layer 20.

[0061] For example, diborane with a flow rate of 1 sccm to 20 sccm and nitrogen with a flow rate of 0.1 sccm to 10 sccm can be introduced into the MPCVD reaction chamber, and the overall ratio of boron and nitrogen elements is maintained in the range of 1:1 to 1:4 to deposit boron and nitrogen co-doped diamond to obtain the N-type diamond layer 20.

[0062] In terms of formation energy, charge compensation mechanism, energy level structure control ability and structural stability, conventional deposition of phosphorus-doped diamond or boron-oxygen co-doped diamond as N-type diamond layer is compared with this method of depositing boron-nitrogen co-doped diamond as N-type diamond layer: In phosphorus-doped diamond, when incorporated as a single impurity, phosphorus, due to its much larger atomic radius than diamond, causes significant lattice distortion, easily leading to local structural relaxation and even the formation of amorphous regions. This results in a high formation energy, which is thermodynamically unfavorable, making it difficult to achieve high-concentration, stable doping and resulting in poor stability. Furthermore, phosphorus is a typical N-type donor. Its deep energy level (approximately 0.6 eV) and significant self-compensation effects (such as the formation of PV pairs) hinder the generation of effective carriers, resulting in low activation efficiency, limited carrier concentration, and the potential introduction of impurity states that affect device performance.

[0063] In boron-oxygen co-doped diamond, boron acts as an acceptor and oxygen as a donor, forming charge-compensating pairs to a certain extent, thereby lowering the formation energy. However, oxygen is highly chemically active and can easily introduce unstable structural defects into the crystal, leading to non-ideal bonding or oxygen vacancies. This is particularly prone to B-O bond breakage and oxygen vacancy formation under high-temperature processing or chemical vapor deposition conditions, resulting in poor thermal stability and a tendency to degrade structural integrity. While boron and oxygen can form B-O pairs to modulate carrier concentration, the potential for oxygen to induce deep energy traps leads to suboptimal overall ionization energy and unstable charge compensation. Furthermore, boron-oxygen co-doping can introduce neutral defect states in the band gap, creating electronic recombination centers that are detrimental to improved conductivity.

[0064] In boron-nitrogen co-doped diamond, boron and nitrogen form stable covalent bonds. Charge compensation by the BN pair reduces the total energy of the system, resulting in a low doping formation energy. Furthermore, the BN pair has a better spatial fit within the crystal lattice, resulting in less lattice distortion and thermodynamically easier realization. Its bond length and bond energy are closer to those of the C–C bonds in the diamond crystal structure, resulting in less perturbation of the diamond crystal structure after doping, better stability, and ease of industrial control. Furthermore, boron provides holes and nitrogen provides electrons, forming a charge-neutral pair doping, which facilitates local potential regulation and suppresses self-compensation behavior. Specifically, in diamond, boron-nitrogen co-doping can significantly reduce the band gap while introducing shallow donor levels, optimizing the conduction band edge, thereby improving electron mobility and carrier concentration, improving the overall electronic structure and ionization efficiency, and enhancing N-type conductivity.

[0065] The formation energy, electron mobility, and electron concentration of deposited boron-oxygen co-doped diamond and boron-nitrogen co-doped diamond as N-type diamond layers are described below. Specific test results are shown in Tables 1 and 2.

[0066] Table 1

[0067] Table 2

[0068] As shown in Table 1, the formation energies of the four different boron-nitrogen co-doped diamonds are all lower than the formation energies of the corresponding four different boron-oxygen co-doped diamonds, i.e., the formation energies of the boron-nitrogen co-doped diamonds are lower. As shown in Table 2, the electron mobilities of the boron-nitrogen co-doped diamonds obtained with two different boron-nitrogen doping ratios are all higher than the electron mobilities of the boron-oxygen co-doped diamonds obtained with two different boron-oxygen doping ratios; and the electron concentrations of the boron-nitrogen co-doped diamonds obtained with two different boron-nitrogen doping ratios are all higher than the electron concentrations of the boron-oxygen co-doped diamonds obtained with two different boron-oxygen doping ratios, i.e., the electron mobility and electron concentration of the boron-nitrogen co-doped diamonds are higher.

[0069] It should be noted that when the diamond buffer layer 70 is not provided, the above steps S201 to S202 may be used to form the N-type diamond layer 20 on the diamond substrate 10. For example, MPCVD technology may be used to introduce a boron source and a nitrogen source to deposit boron-nitrogen co-doped diamond on the diamond substrate 10 to obtain the N-type diamond layer 20. The process conditions for depositing the boron-nitrogen co-doped diamond can be found in the above steps S201 to S202, and a detailed description thereof is omitted here.

[0070] In step S203 , a barrier layer is formed on the N-type diamond layer.

[0071] like Figure 6 As shown, the material of the barrier layer 30 is Al 2 O 3 or h-BN. Step S203 may include: depositing Al 2 O 3 or h-BN on the N-type diamond layer 20 using an atomic layer deposition (ALD) technique to obtain the barrier layer 30 .

[0072] In another possible implementation, the material of the barrier layer 30 is Cs, and step S203 may include the following steps: In the first step, the sample obtained in step S202 is transferred to an ultra-high vacuum (UHV) system, and the system base pressure is controlled at 1×10 -8 Torr or less to avoid contamination of the sample surface.

[0073] In the second step, low-energy ion bombardment (such as argon ion bombardment) or thermal annealing at 300°C to 400°C is performed to remove surface oxides and impurity adsorbates to ensure the uniformity and stability of the subsequently formed Cs layer.

[0074] In the third step, Cs is evaporated by a thermal evaporation source to form a Cs layer on the N-type diamond layer 20 .

[0075] For example, the evaporation temperature can be controlled to be 180° C. to 220° C., the evaporation rate can be controlled to be 0.1 Å / s to 0.5 Å / s, and the evaporation time can be controlled to be 30s to 120s to form a Cs layer with a thickness ranging from sub-monolayer to 1 to 2 monolayers on the N-type diamond layer 20 .

[0076] For example, during the evaporation process, the sample temperature may be 25° C. to 100° C. This can improve the adsorption stability of Cs atoms on the surface of the N-type diamond layer 20 and inhibit agglomeration, thereby ensuring good quality of the Cs layer.

[0077] In the fourth step, the sample with the Cs layer formed thereon is subjected to low-temperature annealing.

[0078] For example, the sample with the Cs layer formed thereon may be annealed at 100° C. to 150° C. for 12 minutes. This is beneficial for improving the quality of the Cs layer and enhancing the surface polarization effect induced by Cs.

[0079] It should be noted that after the low-temperature annealing, the sample does not need to be cleaned and can be directly transferred to the subsequent processing chamber. The Cs layer is stably adsorbed on the surface of the N-type diamond layer 20, which can effectively induce the formation of interface barriers and the accumulation of 2DEG channels.

[0080] Through the above first to fourth steps, a Cs layer can be formed on the N-type diamond layer 20 to obtain the barrier layer 30 .

[0081] In step S204 , a source and a drain are formed on the N-type diamond layer.

[0082] like Figure 7 As shown, the source and drain regions can be precisely defined using UV lithography, then etched using reactive ion etching (RIE). Metal material is then deposited using electron beam evaporation or magnetron sputtering, followed by rapid thermal annealing (RTA) at 600°C to 800°C to form the source 40 and drain 50. This allows for precise etching, reduces contact resistance, and improves the conductivity of the source 40 and drain 50, thereby ensuring the high current output capability of the HEMT.

[0083] Illustratively, a layer of positive photoresist or negative photoresist with a thickness of 1 μm to 2 μm can be spin-coated on the surface of the sample obtained in step S203 using high-precision ultraviolet lithography technology, and exposed using an ultraviolet lithography machine with a wavelength of 193 nm or 248 nm under the protection of a mask to transfer the design pattern to the photoresist surface; after exposure, the sample is developed using a developer such as a tetramethylammonium hydroxide (TMAH) solution to form a clear graphic structure; then, RIE equipment is used for etching to form clear source and drain openings; and then a metal stack of Ti, Al, Ni, and Au layers stacked in sequence is deposited, and annealed for 30 min to 60 min at 600° C. to 800° C. in a protective atmosphere (nitrogen or argon) using an RTA process to obtain the source 40 and the drain 50.

[0084] Optionally, during the etching process, the etching gas can be a mixture of O2 and Ar with a ratio of O2 to Ar of 1:4, or a mixture of CHF3 and Ar with a ratio of CHF3 to Ar of 3:7, with the etching performed at an RF power of 200W to 300W and a pressure of 5mTorr to 10mTorr. This ensures highly selective etching, reduces damage to the sample surface, facilitates precise control of the etching rate, and ensures good verticality of the opening sidewalls, thereby ensuring good adhesion and contact quality of the deposited electrode.

[0085] In step S205 , a gate is formed on the barrier layer.

[0086] like Figure 8 As shown, a metal stack of Ti layer and Al layer stacked in sequence can be deposited on the barrier layer 30 by photolithography and metal deposition technology to obtain the gate 60.

[0087] For example, the sample can be transferred to an electron beam exposure system, and a layer of electron beam sensitive resist, such as polymethylmethacrylate (PMMA) with a thickness of 200nm to 300nm, is spin-coated on the surface of the barrier layer 30, and baked at 80°C to 100°C for 60s to remove the solvent; then, an electron beam with an acceleration voltage of 50kV to 100kV and a beam current of 10pA to 50pA is used to write nanoscale patterns according to a preset digital pattern file for electron beam exposure; after the exposure is completed, a developer, such as methyl isobutyl ketone (MIBK) and isopropyl alcohol (Isopropyl alcohol) is used. The gate electrode 60 is then developed using a mixed solution of IPA (Isopropyl Alcohol) in a ratio of 1:3 for 30 to 60 seconds. Etching is then performed using an RIE process, using either a mixture of O2 and Ar in a ratio of 1:4, or a mixture of CHF3 and Ar in a ratio of 3:7, to obtain a high-resolution gate opening. A metal stack of Ti and Al layers is then deposited to form the gate 60. By introducing an electron beam lithography process, the gate channel length can be precisely controlled (e.g., 50nm or less), and the gate opening resolution can be as high as 10nm to 20nm, achieving higher gate pattern resolution. This improves the high-frequency performance and switching speed of HEMT devices while also meeting the need to suppress short-channel effects.

[0088] Optionally, after completing steps S201 to S205 above, the preparation method may further include: In step S206 , a passivation layer is formed on the barrier layer, the source electrode, the drain electrode, and the gate electrode.

[0089] like Figure 1 As shown, the passivation layer 80 can be formed by plasma enhanced chemical vapor deposition (PECVD) technology or ALD technology. The passivation layer 80 is arranged on the side of the barrier layer 30, the source 40, the drain 50 and the gate 60 away from the N-type diamond layer 20, and the passivation layer 80 covers at least part of the sidewalls of the diamond substrate 10, the diamond buffer layer 70, the barrier layer 30, the source 40, the drain 50 and the gate 60.

[0090] It should be noted that the structure, material and thickness of each film layer in the preparation method embodiment can be found in Figure 1 Detailed description of the related structural embodiments is omitted here.

[0091] The above description is merely an optional embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

Claims

1. A high electron mobility transistor, characterized in that include: Diamond substrate; An N-type diamond layer is provided on the diamond substrate and is used to form a two-dimensional electron gas channel; A barrier layer is provided on the N-type diamond layer, wherein the material of the barrier layer comprises one of Al2O3, hexagonal boron nitride and Cs; A source electrode and a drain electrode are arranged on the N-type diamond layer at intervals and are respectively located on both sides of the region where the barrier layer is located; The gate is arranged on the barrier layer.

2. The high electron mobility transistor according to claim 1, wherein The barrier layer is made of a material selected from the group consisting of Al 2 O 3 and hexagonal boron nitride. The barrier layer has a thickness of 3 nm to 10 nm.

3. The high electron mobility transistor according to claim 1, wherein The barrier layer is made of Cs, and has a thickness of 0.1 nm to 6 nm.

4. The high electron mobility transistor according to any one of claims 1 to 3, characterized in that: The material of the N-type diamond layer is boron and nitrogen co-doped diamond.

5. The high electron mobility transistor according to claim 4, wherein: The doping concentration of the N-type diamond layer is 1×10 16 cm -3 to 1×10 19 cm -3 .

6. The high electron mobility transistor according to claim 4, wherein: The thickness of the N-type diamond layer is 10 nm to 100 nm.

7. A method for preparing a high electron mobility transistor, characterized in that: include: forming an N-type diamond layer on a diamond substrate, wherein the N-type diamond layer is used to form a two-dimensional electron gas channel; forming a barrier layer on the N-type diamond layer, wherein a material of the barrier layer comprises one of Al2O3, hexagonal boron nitride and Cs; forming a source electrode and a drain electrode on the N-type diamond layer, wherein the source electrode and the drain electrode are spaced apart from each other on the N-type diamond layer and are respectively located on both sides of the region where the barrier layer is located; A gate is formed on the barrier layer.

8. The preparation method according to claim 7, characterized in that The material of the N-type diamond layer is boron-nitrogen co-doped diamond, and the step of forming the N-type diamond layer on the diamond substrate includes: Microwave plasma chemical vapor deposition technology is adopted to introduce a boron source and a nitrogen source to deposit the boron-nitrogen co-doped diamond on the diamond substrate to obtain the N-type diamond layer.

9. The preparation method according to claim 8, characterized in that In the boron source and the nitrogen source, the ratio of boron element to nitrogen element is 1:1 to 1:

4.

10. The preparation method according to claim 9, characterized in that The boron source is diborane, the nitrogen source is nitrogen gas, the flow rate of the diborane is 1 sccm to 20 sccm, and the flow rate of the nitrogen gas is 0.1 sccm to 10 sccm.

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