Cr2O3 / GaN heterogeneous pn diode and preparation method thereof

Abstract

The invention discloses a Cr2O3 / GaN heterogeneous pn diode and a preparation method thereof. The diode comprises a substrate layer, a Buffer layer and an N + GaN layer which are sequentially arranged from bottom to top, the N + GaN layer is of a fin type structure; the cathodes are arranged in two end areas of the upper surface of the N + GaN layer; the N-GaN drift layer is arranged in a protruding area on the upper surface of the N + GaN layer; the P-Cr2O3 layer is arranged on the upper surface of the N-GaN drift layer; the N-GaN drift layer and the P-Cr2O3 layer form a heterogeneous pn junction structure; and the anode is arranged on the upper surface of the P-Cr2O3 layer. The N-GaN drift layer and the P-Cr2O3 layer form a heterogeneous pn junction structure, and compared with a traditional gallium nitride SBD structure, the structure has the advantages that the leakage current is smaller, and the breakdown voltage is higher. The p-type material is p-Cr2O3, the forbidden band width of the p-type material is 3.4 eV, the forbidden band width of the p-type material is basically consistent with that of gallium nitride, and the p-type material and the gallium nitride belong to wide-forbidden-band semiconductors and are excellent in high-voltage resistance.

Description

Technical Field

[0001] The invention belongs to the field of wide bandgap high voltage devices, and in particular relates to a Cr2O3 / GaN heterogeneous pn diode and a preparation method thereof. Background Art

[0002] With the increasing demand for efficient and complete power conversion circuits and systems, power devices with low power consumption and high speed characteristics have attracted a lot of attention recently. GaN is a third-generation wide bandgap semiconductor material. Due to its large bandgap width (3.4eV), high electron saturation velocity (2e7cm / s), high breakdown electric field (1e10-3e10V / cm), high thermal conductivity, corrosion resistance and radiation resistance, it has strong advantages under high voltage, high frequency, high temperature, high power and radiation resistance conditions. It is considered to be the best material for studying short-wave optoelectronic devices and high-voltage, high-frequency and high-power devices. Therefore, power devices based on gallium nitride have good heat dissipation performance and high saturation velocity. GaN power devices have broad application prospects in high-power and high-frequency energy conversion and high-frequency microwave communications.

[0003] For GaN power diodes, the p-type terminal is the most effective terminal structure. The pn junction diode has been widely studied in other materials (such as SiC) due to its low leakage and high withstand voltage. However, the doping problem of p-type GaN materials has always been a scientific problem that needs to be solved. The large bandgap makes p-type doping of GaN difficult, the impurity activation rate is low, and it is impossible to achieve efficient and controllable hole concentration, which in turn affects the development of high-power GaN devices. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a Cr2O3 / GaN heterogeneous pn diode and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0005] In a first aspect, the present invention provides a Cr2O3 / GaN heterogeneous pn diode, comprising:

[0006] The substrate layer, buffer layer and N+GaN layer are arranged in sequence from bottom to top; the N+GaN layer is a fin structure;

[0007] The cathode is arranged at the two end regions of the upper surface of the N+GaN layer;

[0008] The N-GaN drift layer is disposed in a protruding region on the upper surface of the N+GaN layer;

[0009] The P-Cr2O3 layer is disposed on the upper surface of the N-GaN drift layer; the N-GaN drift layer and the P-Cr2O3 layer form a heterogeneous pn junction structure;

[0010] The anode is arranged on the upper surface of the P-Cr2O3 layer.

[0011] In one embodiment of the present invention, the thickness of the N+GaN layer is 1 μm to 50 μm, and the doping concentration is 10 17 cm -3 ~10 20 cm -3 .

[0012] In one embodiment of the present invention, the thickness of the N-GaN drift layer is 0.5 μm to 30 μm, and the doping concentration is 10 15 cm -3 ~10 17 cm -3 .

[0013] In one embodiment of the present invention, the thickness of the P-Cr2O3 layer is 10nm-1μm, and the hole concentration is 10 16 cm -3 ~10 20 cm -3 .

[0014] In one embodiment of the present invention, the material of the cathode is Ti / Al / Ti / Au or Ti / Al / Ni / Au or Ti / Al / Mo / Au; wherein the thickness of the first metal layer is 20 to 60 nm, the thickness of the second metal layer is 80 to 300 nm, the thickness of the third metal layer is 20 to 200 nm, and the thickness of the fourth metal layer is 30 to 3000 nm.

[0015] In one embodiment of the present invention, the material of the anode is Ni / Au or Ni / Pt or Pt / Au or Pd / Au; wherein the thickness of the first metal layer is 10-200 nm, and the thickness of the second metal layer is 30-2000 nm.

[0016] In a second aspect, the present invention provides a method for preparing a Cr2O3 / GaN heterogeneous pn diode, comprising:

[0017] Obtaining a Si / SiC substrate, and pre-treating the Si / SiC substrate to obtain a substrate layer;

[0018] A buffer layer is grown on the substrate layer using an MOCVD process;

[0019] The MOCVD process is used to deposit a thickness of 1μm to 50μm on the buffer layer, and the doping concentration is 10 17 cm -3 ~10 20 cm -3 N+GaN layer;

[0020] The MOCVD process is used to grow the N+GaN layer with a thickness of 0.5μm to 30μm and a doping concentration of 10 15 cm -3 ~10 17 cm -3 N-GaN drift layer;

[0021] The ICP equipment is used to etch the two end regions of the N-GaN drift layer, and the etching depth is greater than the thickness of the N-GaN drift layer, so that the N+GaN layer forms a fin structure;

[0022] Performing photolithography on the upper surface of the etched N+GaN layer to make a mask, and using magnetron sputtering or electron beam evaporation to prepare cathodes at both end regions of the upper surface of the etched N+GaN layer;

[0023] A pattern mask is made on the upper surface of the N-GaN drift layer, and a P-Cr2O3 layer is prepared by a magnetron sputtering process;

[0024] The anode was prepared on the upper surface of the P-Cr2O3 layer by magnetron sputtering process.

[0025] In one embodiment of the present invention, the process parameters of the ICP equipment include:

[0026] The etching gases are BCl3 and Cl2, with a flow rate of 1 to 10 sccm;

[0027] The pressure is 0.1~10mtorr;

[0028] ICP power is 50~300W;

[0029] The RF power is 150~500W.

[0030] In one embodiment of the present invention, the process parameters for preparing the P-Cr2O3 layer by a magnetron sputtering process include:

[0031] The magnetron sputtering target material is chromium or chromium oxide target with a purity of 99.99%;

[0032] The pressure in the reaction chamber is 0.3-1 Pa;

[0033] The temperature of the reaction chamber is 25-75°C;

[0034] The reaction carrier gas is argon and oxygen, and the ratio of argon to oxygen is 20:1 to 2:1;

[0035] The RF power during sputtering is 100 to 300 W.

[0036] In one embodiment of the present invention, P-Cr2O3 with different thicknesses and different doping concentrations is obtained by adjusting the process parameters of the magnetron sputtering process during the preparation of the P-Cr2O3 layer.

[0037] Beneficial effects of the present invention:

[0038] In the solution provided by the present invention, a heterogeneous pn junction structure is formed by an N-GaN drift layer and a P-Cr2O3 layer. Compared with the traditional gallium nitride SBD structure, the structure has a smaller leakage current and a higher breakdown voltage. The p-type material used in the present invention is p-Cr2O3, which has a bandgap width of 3.4eV, which is basically the same as gallium nitride, and both are wide bandgap semiconductors with excellent high-voltage resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the structure of a Cr2O3 / GaN heterogeneous pn diode provided in an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the steps of a method for preparing a Cr2O3 / GaN heterogeneous pn diode provided in an embodiment of the present invention;

[0041] Figure 3 A process flow chart of a method for preparing a Cr2O3 / GaN heterogeneous pn diode provided in an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of a magnetron sputtering preparation method provided in an embodiment of the present invention.

[0043] Reference numerals

[0044] 1-substrate layer, 2-buffer layer, 3-N+GaN layer, 4-cathode, 5-N-GaN drift layer, 6-P-Cr2O3 layer, 7-anode. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0046] In a first aspect, an embodiment of the present invention provides a Cr2O3 / GaN heterogeneous pn diode, such as Figure 1 As shown, this may include:

[0047] A substrate layer 1, a buffer layer 2 and an N+GaN layer 3 are arranged in sequence from bottom to top; the N+GaN layer 3 is a fin structure;

[0048] The cathode 4 is arranged at both end regions of the upper surface of the N+GaN layer 3;

[0049] The N-GaN drift layer 5 is provided in a protruding region on the upper surface of the N+GaN layer 3;

[0050] The P-Cr2O3 layer 6 is disposed on the upper surface of the N-GaN drift layer 5; the N-GaN drift layer 5 and the P-Cr2O3 layer 6 form a heterogeneous pn junction structure;

[0051] The anode 7 is disposed on the upper surface of the P—Cr 2 O 3 layer 6 .

[0052] In the Cr2O3 / GaN heterogeneous pn diode provided by the embodiment of the present invention, the N-GaN drift layer and the P-Cr2O3 layer form a heterogeneous pn junction structure, which has a smaller leakage current and a higher breakdown voltage than the traditional gallium nitride SBD structure. The Cr2O3 / GaN heterogeneous pn diode is a quasi-vertical structure.

[0053] Optionally, the material of the substrate layer 1 can be Si or SiC. The embodiment of the present invention uses a heterojunction epitaxial wafer, and the Si or SiC substrate used has good compatibility with devices that are currently mass-produced or commercially available; and compared with the homogeneous structure of gallium nitride, these two epitaxial wafers are more economical and have obvious economic benefits.

[0054] Optionally, the thickness of the N+GaN layer 3 is 1 μm to 50 μm, and the doping concentration is 10 17 cm -3 ~10 20 cm -3 .

[0055] Optionally, the thickness of the N-GaN drift layer 5 is 0.5 μm to 30 μm, and the doping concentration is 10 15 cm -3 ~10 17 cm -3 .

[0056] Optionally, the thickness of the P-Cr2O3 layer 6 is 10 nm to 1 μm, and the hole concentration is 10 16 cm -3 ~10 20 cm -3 .

[0057] It is understandable that in the application field of high-voltage devices of wide-bandgap semiconductors, the pn junction is of great help in reducing the on-resistance and increasing the breakdown voltage. However, the p-type doping of wide-bandgap materials is difficult, which makes it difficult to prepare floating field ring diodes, junction barrier Schottky diodes, and enhancement mode field effect transistors. The chromium oxide materials prepared by the prior art do not have good p-type doping and poor crystal quality, which will cause the leakage of gallium nitride power devices to be large and the high reliability to be poor. In the quasi-vertical p-Cr2O3 / n-GaN heterojunction diode provided by the present invention, p-Cr2O3 and n-GaN are combined to form a heterogeneous pn junction structure, which reduces the on-resistance and leakage current of the device while increasing the breakdown voltage of the device, and is suitable for high-voltage and high-power fields.

[0058] Optionally, the material of cathode 4 is Ti / Al / Ti / Au or Ti / Al / Ni / Au or Ti / Al / Mo / Au; wherein the thickness of the first metal layer is 20 to 60 nm, the thickness of the second metal layer is 80 to 300 nm, the thickness of the third metal layer is 20 to 200 nm, and the thickness of the fourth metal layer is 30 to 3000 nm.

[0059] Optionally, the material of the anode 7 is Ni / Au or Ni / Pt or Pt / Au or Pd / Au; wherein the thickness of the first metal layer is 10-200 nm, and the thickness of the second metal layer is 30-2000 nm.

[0060] It can be understood that the embodiment of the present invention forms a heterogeneous pn junction structure through the N-GaN drift layer and the P-Cr2O3 layer. Compared with the traditional gallium nitride SBD structure, the structure has a smaller leakage current and a higher breakdown voltage. The p-type material used in the present invention is p-Cr2O3, which has a bandgap width of 3.4eV, which is basically the same as gallium nitride, and both belong to wide bandgap semiconductors with excellent high-voltage resistance.

[0061] A schematic diagram of the steps of a method for preparing a Cr2O3 / GaN heterogeneous pn diode provided in an embodiment of the present invention is shown in FIG. Figure 2 , the process flow chart of the preparation method, see Figure 3 , the following will combine Figure 2 and Figure 3 , the preparation method is introduced in detail.

[0062] In a second aspect, an embodiment of the present invention provides a method for preparing a Cr2O3 / GaN heterogeneous pn diode, such as Figure 2 As shown, this may include:

[0063] S1, obtaining a Si / SiC substrate, and pre-treating the Si / SiC substrate to obtain a substrate layer 1.

[0064] Specifically, the surface of the Si / SiC substrate is pre-treated to eliminate dangling bonds, thereby obtaining the substrate layer 1 .

[0065] Preprocessing methods may include:

[0066] The substrate was ultrasonically cleaned for 5-10 minutes using acetone, anhydrous ethanol and deionized water, and the substrate was blown dry using a nitrogen gun to obtain a cleaned substrate.

[0067] By selecting a substrate with a flat and smooth surface and performing corresponding cleaning, impurities on the substrate surface can be reduced to improve the quality of the deposited film.

[0068] S2, growing a buffer layer 2 on the substrate layer 1 by using an MOCVD process.

[0069] Specifically, the pretreated substrate is placed in a reaction chamber with a H2 atmosphere for heat treatment at a high temperature of 950°C, and then an MOCVD process is used to epitaxially grow an AlN nucleation layer with a thickness of 30 to 90 nm on the substrate; a buffer layer with a thickness of 0.5 to 5 μm is deposited on the AlN nucleation layer using an MOCVD process; the nucleation layer and the buffer layer together constitute a Buffer layer 2.

[0070] S3, using MOCVD process to deposit a thickness of 1μm to 50μm on the Buffer layer 2, with a doping concentration of 10 17 cm -3 ~10 20 cm -3 N+GaN layer 3.

[0071] It can be understood that the N+GaN layer 3 is an n+ type gallium nitride heavily doped layer.

[0072] S4, using MOCVD process to grow a 0.5μm to 30μm thick GaN layer 3 with a doping concentration of 10 15 cm -3 ~10 17 cm -3 N-GaN drift layer 5.

[0073] It can be understood that the device obtained after steps S1-S4 is as follows Figure 3 As shown in the upper left center, the device has not yet been etched.

[0074] S5, using ICP equipment to etch the two end regions of the N-GaN drift layer 5, the etching depth is greater than the thickness of the N-GaN drift layer 5, so that the N+GaN layer 3 forms a fin structure.

[0075] Specifically, a mask is made on the surface of the N-GaN drift layer 5, and the two end regions of the N-GaN drift layer 5 are etched. The ICP equipment is used for etching, and the etching depth is greater than the thickness of the N-GaN drift layer 5. The etched gallium nitride surface is located on the N+GaN layer 3, so that the N+GaN layer 3 forms a fin structure. Figure 3 It can be seen from the figure that after etching, both ends of the N-GaN drift layer 5 are etched away, and part of the N+GaN layer 3 is also etched, so that the N+GaN layer 3 forms a fin structure.

[0076] The process parameters of ICP equipment can include:

[0077] The etching gases are BCl3 and Cl2, with a flow rate of 1 to 10 sccm;

[0078] The pressure is 0.1~10mtorr;

[0079] ICP power is 50~300W;

[0080] The RF power is 150~500W.

[0081] S6, photolithography is performed on the upper surface of the etched N+GaN layer 3 to make a mask, and cathodes 4 are prepared at both end regions of the upper surface of the etched N+GaN layer 3 by magnetron sputtering or electron beam evaporation.

[0082] Specifically, photolithography is performed on the upper surface of the etched N+GaN layer 3 to make a mask, and cathode metal is deposited on both end regions of the upper surface of the etched N+GaN layer 3 by magnetron sputtering or electron beam evaporation, and then placed in a rapid annealing furnace for high-temperature annealing to form an ohmic contact. Figure 3 The specific position of the cathode 4 can be seen in FIG. It can be understood that the MESA region is formed after photolithography on the upper surface of the N+GaN layer 3. In the semiconductor chip structure, the MESA region is a conductive region formed on the insulating layer. The region forms a certain potential barrier with the surrounding insulating layer, so that the current can flow in the MESA region and is not easy to leak into the surrounding insulating layer. The formation of the MESA region is usually achieved by chemical etching or ion implantation.

[0083] S7, making a pattern mask on the upper surface of the N-GaN drift layer 5, and preparing the P-Cr2O3 layer 6 by using a magnetron sputtering process.

[0084] Chromium oxide can be prepared by a variety of methods, such as: liquid phase method, arc ion method, pulsed laser deposition method, plasma spraying method, electrochemical deposition method, magnetron sputtering method, reactive sputtering method, electron beam evaporation method, spray pyrolysis method, ion implantation method and chemical vapor deposition method.

[0085] Among them, when preparing chromium oxide film by pulse atomization thermal evaporation chemical vapor deposition, acetyl lactone is first dissolved in ethanol to obtain a precursor solution, and the resulting solution enters an excitation chamber maintained at a high temperature for thermal excitation; then nitrogen and oxygen bring the thermally evaporated gas into the transmission cavity; finally, the chromium oxide film is deposited on the heated substrate in the deposition chamber. The deposition rate of the chromium oxide film can be changed by changing the oxygen flow rate. However, the chromium oxide film prepared by pulse atomization thermal evaporation chemical vapor deposition has a loose surface structure and a large number of oxygen vacancies on its surface.

[0086] The chromium oxide film is prepared by arc ion plating physical vapor deposition, using a chromium target with a purity of 99.9% as a cathode target, high-purity argon (concentration of 99.99%) as a sputtering gas, and high-purity oxygen (concentration of 99.99%) as a reaction gas to deposit the chromium oxide film. However, the chromium oxide film prepared by arc ion plating physical vapor deposition has poor surface uniformity and poor stability, so other process steps need to be introduced to optimize the quality of the obtained chromium oxide film.

[0087] In the process of preparing the P-Cr2O3 layer 6 by using the magnetron sputtering process, the P-Cr2O3 layer 6 can be prepared by adjusting the process parameters using the magnetron sputtering system.

[0088] The specific process of preparing the P-Cr2O3 layer 6 may include:

[0089] placing a chromium or chromium oxide target and a substrate in a magnetron sputtering system, and evacuating the magnetron sputtering system;

[0090] Argon gas is introduced into the magnetron sputtering system, and oxygen gas is introduced after reaching the preset target, and then ignition is performed;

[0091] Set the process parameters, increase the power to the power required for sputtering, close the baffle above the substrate, and perform pre-sputtering;

[0092] After the pre-sputtering is completed, the baffle above the substrate is opened to obtain the P-Cr2O3 layer 6.

[0093] The process parameters for preparing the P-Cr2O3 layer 6 by magnetron sputtering process may include:

[0094] The magnetron sputtering target material is chromium or chromium oxide target with a purity of 99.99%;

[0095] The pressure in the reaction chamber is 0.3-1 Pa;

[0096] The temperature of the reaction chamber is 25-75°C;

[0097] The reaction carrier gas is argon and oxygen, and the ratio of argon to oxygen is 20:1 to 2:1;

[0098] The RF power during sputtering is 100 to 300 W.

[0099] The application of chromium oxide (Cr2O3) in semiconductor devices is mainly focused on its high chemical stability and thermal stability. It can be used as a surface passivation layer to protect devices from oxidation or corrosion, and can also be used as an antiferromagnetic material in spin electronics, suitable for dielectric layers or gate oxide layers in high-temperature electronic devices. In addition, chromium oxide films can be used to make thin-film resistors, transparent conductive films (TCO), optical filters and photodetectors, especially when working in harsh environments or high temperature conditions. Although the scope of application is relatively limited, Cr2O3 has potential value in these semiconductor fields. The preparation method of chromium oxide films based on the above applications is often simple in process and has a fast deposition rate. However, the research on chromium oxide based on power devices in gallium nitride is still blank. This is because the growth rate of high-quality chromium oxide materials is relatively slow, and chromium oxide films with high crystal quality and low defect density are the basic requirements of this patent. Through the radio frequency magnetron sputtering method, from the selection of target materials to the exploration of growth parameters, the feasibility of p-type chromium oxide heterojunction diodes in gallium nitride devices was finally verified, and excellent performance was shown in terms of reverse withstand voltage / leakage current of the device.

[0100] In addition, homogeneous p-type materials in gallium nitride still face some shortcomings and challenges in a wide range of applications, which limit their performance in electronic devices. The shortcomings of p-type GaN materials are as follows: First, the doping efficiency of p-type GaN is low, especially when magnesium (Mg) is used as an acceptor dopant. Although magnesium is currently the most commonly used p-type dopant, there is a high acceptor activation energy in GaN (about 150–250meV), which results in fewer acceptors being ionized and unable to effectively provide hole carriers. This leads to a low hole concentration in p-type GaN, poor conductivity, and difficulty in improving device performance; secondly, the hole concentration in GaN materials is difficult to effectively increase, which is mainly related to the low ionization rate of magnesium doping. Even if the doping concentration is increased, the number of active acceptors is small; thirdly, due to the low hole mobility of p-type GaN materials (usually much lower than the electron mobility), coupled with the low hole concentration, the resistivity of p-type GaN materials is relatively high. High resistivity is detrimental to device performance, especially in power devices, where it can cause excessive power loss, reduce device efficiency and lifespan; in addition, in order to activate magnesium doping in p-type GaN, high-temperature annealing (usually in the range of 800-900°C) is required to expel hydrogen atoms associated with magnesium. Hydrogen atoms, combined with magnesium doping, cause them to be passivated before annealing. High-temperature annealing not only increases process complexity, but may also introduce other thermal stresses and material defects, affecting the structural integrity of the GaN layer; finally, p-type GaN materials have relatively poor thermal conductivity, which is particularly important in high-power or high-frequency devices. Especially when working in high current or high-temperature environments, thermal management issues are more prominent. In summary, the main problems of p-type GaN materials include low doping efficiency, low hole concentration, high resistivity, high contact resistance, and self-compensation effects, which limit their application in high-performance electronic and optoelectronic devices. Although some progress has been made, these issues are still the key to further improvement of p-type GaN materials.

[0101] Choosing to use chromium oxide material instead of p-type gallium nitride has the following advantages: first, the hole doping concentration can be easily changed by adjusting the oxygen doping concentration during growth, and p-type ohmic contact is very easy to form at a lower concentration; second, chromium oxide material is a typical ceramic high-temperature resistant material, and the film layer has excellent reliability under high current and high power conditions and is not prone to premature failure; finally, the manufacturing process is simple and the cost is low, and economic feasibility is a factor that must be considered for large-scale and industrialization.

[0102] It can be understood that by adjusting the process parameters of the magnetron sputtering process during the preparation of the P-Cr2O3 layer 6, P-Cr2O3 with different thicknesses and different doping concentrations can be obtained. Specifically, the three variables of argon oxygen flow, power and pressure in the process parameters can be adjusted to control the generation of high-quality P-Cr2O3. During the preparation process, chromium oxide films with different thicknesses and different doping concentrations can be accurately obtained by adjusting the process parameters, and the preparation of in-situ single-layer or multi-layer chromium oxide films with different thicknesses and different doping concentrations can be completed. By adjusting the preset magnetron sputtering parameters, high-quality chromium oxide films are prepared by magnetron sputtering. It has high density and high reliability, and the concentration ranges from 1×10 16 cm -3 -5×10 18 cm -3 Adjustable hole doping. The key point of the embodiment of the present invention is to adjust the three variables of argon oxygen flow, power and pressure to control the growth of high-quality p-type chromium oxide film. The obtained p-type chromium oxide film can be used as a heterogeneous terminal of wide bandgap semiconductor materials to make up for the deficiency of homogeneous p-type of these two wide bandgap semiconductors.

[0103] A high-quality, surface-dense, and highly reliable p-type chromium oxide film is prepared by adjusting the preset magnetron sputtering parameters using a magnetron sputtering system, as well as hole doping with an adjustable concentration within a preset range, thereby solving the problems of different thermal expansion coefficients and elastic mismatch between the film and the substrate, and eliminating the need for additional process steps.

[0104] Wide bandgap semiconductor materials have a large bandgap width, and the activation energy is large when p-type doping is performed, making p-type doping difficult. Therefore, a common solution is to use other p-type materials instead. Since chromium oxide has a large dielectric constant and a wide bandgap width, the embodiment of the present invention uses a magnetron sputtering method to prepare P-Cr2O3 by adjusting the argon oxygen ratio to complete the preparation of high-quality p-type doped chromium oxide films. Therefore, it can be used as a heterogeneous terminal of gallium nitride materials and used in wide bandgap power devices to improve the withstand voltage. For example: For gallium nitride, its bandgap width is basically equal to that of chromium oxide, and its energy band offset is small. It is a suitable alternative material that can make up for the shortcomings caused by the difficulty of p-type gallium nitride doping. In addition, the preparation of p-type chromium oxide is simple and economical, and the hole concentration is adjustable. In the embodiment of the present invention, a p-type chromium oxide film is deposited on an n-type gallium nitride epitaxially, and the resulting device can be used as a gallium nitride heterogeneous pn junction diode with a kilovolt breakdown voltage.

[0105] For an understandable schematic diagram of magnetron sputtering preparation, see Figure 4The magnetron sputtering technology is to apply a magnetic field orthogonal to the direction of the electric field. The direction of the magnetic field is parallel to the surface of the cathode target (solid column chromium oxide or chromium target with a purity of 99.99%), forming a circular magnetic field, thereby realizing the control of electron movement. The magnetron sputtering system consists of an electric control system, a radio frequency power supply, a vacuum reaction chamber, a substrate temperature control system, a vacuum system, a circulating water cooling system and a data display system. The secondary electrons generated by sputtering are accelerated near the cathode. Under the action of the orthogonal electric and magnetic fields, these electrons will cross the magnetic flux lines and make spiral circular motion. The movement path of these electrons is limited to the plasma area near the surface of the target material, and can drift to the auxiliary anode near the cathode without directly hitting the anode. These electrons will collide with the sputtering gas (oxygen and argon) to produce a large amount of plasma (used to bombard the target material). During multiple collisions, the energy of the electrons gradually decreases. When the energy is exhausted, it will be deposited on the substrate substrate under the action of the electric field, avoiding the electrons from directly bombarding the anode substrate surface and causing damage. The substrate is usually a wide bandgap semiconductor material such as gallium nitride. The collision of secondary electrons improves the ionization efficiency of the gas, so sputtering can be carried out at low pressure (0.3-1Pa), which can reduce the scattering effect of oxygen and argon on the sputtered atoms in the target material, thereby increasing the atomic deposition rate and the adhesion of the film on the substrate; under the action of orthogonal electric and magnetic fields, high-density plasma is confined to the area near the target surface and will not contact the substrate, which can enable the incident ions to effectively bombard the target material while avoiding damage to the substrate.

[0106] S8, preparing the anode 7 on the upper surface of the P-Cr2O3 layer 6 by using a magnetron sputtering process.

[0107] Specifically, anode metal is deposited on the upper surface of the P-Cr2O3 layer 6 by a magnetron sputtering process, the device after the anode metal is deposited is peeled off, and is washed in an organic solution for 5 minutes to 10 minutes to remove excess photoresist residues, thereby completing the preparation of the device.

[0108] In the solution provided by the embodiment of the present invention, a heterogeneous pn junction structure is formed by an N-GaN drift layer and a P-Cr2O3 layer. Compared with the traditional gallium nitride SBD structure, the structure has a smaller leakage current and a higher breakdown voltage. The p-type material used in the present invention is p-Cr2O3, which has a bandgap width of 3.4eV, which is basically the same as gallium nitride, and both are wide bandgap semiconductors with excellent high-voltage resistance.

[0109] It should be noted that in the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A Cr2O3 / GaN heterogeneous pn diode, characterized in that: include: A substrate layer (1), a buffer layer (2) and an N+GaN layer (3) are arranged in sequence from bottom to top; the N+GaN layer (3) is a fin-type structure; The cathode (4) is arranged at two end regions of the upper surface of the N+GaN layer (3); The N-GaN drift layer (5) is arranged in a protruding area on the upper surface of the N+GaN layer (3); The P-Cr2O3 layer (6) is arranged on the upper surface of the N-GaN drift layer (5); the N-GaN drift layer (5) and the P-Cr2O3 layer (6) form a heterogeneous pn junction structure; The anode (7) is arranged on the upper surface of the P-Cr2O3 layer (6).

2. A Cr2O3 / GaN heterogeneous pn diode according to claim 1, characterized in that: The thickness of the N+GaN layer (3) is 1 μm to 50 μm, and the doping concentration is 10 17 cm -3 ~10 20 cm -3 .

3. A Cr2O3 / GaN heterogeneous pn diode according to claim 1, characterized in that: The thickness of the N-GaN drift layer (5) is 0.5 μm to 30 μm, and the doping concentration is 10 15 cm -3 ~10 17 cm -3 .

4. A Cr2O3 / GaN heterogeneous pn diode according to claim 1, characterized in that: The thickness of the P-Cr2O3 layer (6) is 10nm-1μm, and the hole concentration is 10 16 cm -3 ~10 20 cm -3 .

5. The Cr2O3 / GaN heterogeneous pn diode according to claim 1, characterized in that: The material of the cathode (4) is Ti / Al / Ti / Au or Ti / Al / Ni / Au or Ti / Al / Mo / Au; wherein the thickness of the first metal layer is 20-60nm, the thickness of the second metal layer is 80-300nm, the thickness of the third metal layer is 20-200nm, and the thickness of the fourth metal layer is 30-3000nm.

6. A Cr2O3 / GaN heterogeneous pn diode according to claim 1, characterized in that: The material of the anode (7) is Ni / Au or Ni / Pt or Pt / Au or Pd / Au; wherein the thickness of the first metal layer is 10-200 nm, and the thickness of the second metal layer is 30-2000 nm.

7. A method for preparing a Cr2O3 / GaN heterogeneous pn diode, characterized in that: include: Obtaining a Si / SiC substrate, and pre-treating the Si / SiC substrate to obtain a substrate layer (1); Growing a buffer layer (2) on the substrate layer (1) using an MOCVD process; The MOCVD process is used to deposit a 1 μm to 50 μm thick, doping concentration of 10 17 cm -3 ~10 20 cm -3 N+GaN layer (3); The MOCVD process is used to grow a 0.5 μm to 30 μm thick GaN layer (3) with a doping concentration of 10 15 cm -3 ~10 17 cm -3 An N-GaN drift layer (5); Using ICP equipment to etch the two end regions of the N-GaN drift layer (5), wherein the etching depth is greater than the thickness of the N-GaN drift layer (5), so that the N+GaN layer (3) forms a fin structure; Performing photolithography on the upper surface of the etched N+GaN layer (3) to produce a mask, and using magnetron sputtering or electron beam evaporation technology to prepare cathodes (4) at both end regions of the upper surface of the etched N+GaN layer (3); A pattern mask is fabricated on the upper surface of the N-GaN drift layer (5), and a P-Cr2O3 layer (6) is prepared by a magnetron sputtering process; An anode (7) is prepared on the upper surface of the P-Cr2O3 layer (6) by using a magnetron sputtering process.

8. The method for preparing a Cr2O3 / GaN heterogeneous pn diode according to claim 7, characterized in that: The process parameters of the ICP equipment include: The etching gases are BCl3 and Cl2, with a flow rate of 1 to 10 sccm; The pressure is 0.1~10mtorr; ICP power is 50~300W; The RF power is 150~500W.

9. The method for preparing a Cr2O3 / GaN heterogeneous pn diode according to claim 7, characterized in that: The process parameters for preparing the P-Cr2O3 layer (6) by magnetron sputtering process include: The magnetron sputtering target material is chromium or chromium oxide target with a purity of 99.99%; The pressure in the reaction chamber is 0.3-1 Pa; The temperature of the reaction chamber is 25-75°C; The reaction carrier gas is argon and oxygen, and the ratio of argon to oxygen is 20:1 to 2:1; The RF power during sputtering is 100 to 300 W.

10. The method for preparing a Cr2O3 / GaN heterogeneous pn diode according to claim 9, characterized in that: By adjusting the process parameters of the magnetron sputtering process during the preparation of the P-Cr2O3 layer (6), P-Cr2O3 with different thicknesses and different doping concentrations can be obtained.

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