Field modulation schottky diode and method of making same

Abstract

The application discloses a field modulation type Schottky diode and a manufacturing method thereof, and mainly solves the problems of high opening voltage, small conduction current and low breakdown voltage of the existing Schottky diode. The Schottky diode comprises, from bottom to top, a cathode (7), a substrate (1), a drift layer (2), a gradient contact layer (3), and 2n-1 rectangular tunneling holes (8) with different intervals but same size are arranged in the gradient contact layer; a high-K tunneling layer (4) is arranged in the tunneling hole and is staggered with the gradient contact layer (3); a P-type groove (9) with same size is arranged in the high-K tunneling layer, and a P-type modulation layer (5) is arranged in the P-type groove; the gradient contact layer (3), the high-K tunneling layer (4) and the P-type modulation layer (5) are all covered by an anode (6), and the high-K tunneling layer (4) and the P-type modulation layer (5) form a field modulation junction (10). The application reduces the opening voltage and the off-state leakage current, improves the conduction current and the breakdown voltage, and can be used as a power switching device of a power electronic system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microelectronics, and particularly relates to a Schottky diode device that can be used in power electronic systems. TECHNICAL BACKGROUND

[0002] As the core support of modern energy conversion, power electronics technology has been widely used in aerospace propulsion systems, new energy vehicle electronic systems, medical device power modules, and intelligent household appliance frequency conversion control, etc. In such applications, Schottky diodes, with their low forward voltage drop and fast switching characteristics, bear the core functions of electrical energy regulation and topology conversion, and their performance parameters are directly related to the overall energy efficiency and operation reliability of the system. Current silicon-based power devices are limited by narrow band gap width and low critical breakdown field, and their power density has approached the theoretical limit of the material. In the face of the stringent requirements of the next generation of power electronic systems for high temperature, high voltage and high frequency, traditional silicon-based power devices show limitations in terms of on-state loss and thermal management efficiency. The third generation of wide bandgap semiconductor materials represented by gallium nitride provide a breakthrough path for building new power devices with low on-state resistance, high switching frequency and high power density due to their outstanding physical characteristics: high breakdown field, high electron saturation velocity, excellent thermal conductivity, etc., and are expected to promote the evolution of power electronic systems towards higher energy efficiency and more compactness.

[0003] Vertical gallium nitride Schottky diodes are widely used as rectifier devices in power electronic systems, and how to obtain high-performance vertical gallium nitride Schottky diodes has become a research hotspot at home and abroad. When the vertical gallium nitride Schottky diode is reverse blocked, the device has a large reverse leakage current and high off-state loss due to the Schottky barrier lowering effect, and the reverse electric field is easily concentrated at the anode edge, resulting in a high electric field peak that causes the device to break down prematurely, resulting in a small breakdown voltage of the device.

[0004] Reference 1. 7-kV Vertical GaN-on-GaN Schottky Barrier Diodes With Helium-Implanted Edge Termination, IEEE Transactions on Electron Devices, Vol. 69, No. 4, April 2022, like Figure 1As shown, it comprises: a substrate 1, a drift layer 2, an anode 3, a cathode 4 and a terminal 5; in the structure, the anode 3 and the drift layer 2 form a Schottky junction, when a positive bias is applied, the Schottky junction turns on the device, the terminal 5 does not participate in the forward conduction, when a reverse bias is applied, the terminal structure redistributes the electric field at the anode edge, weakens the electric field peak at the edge, and improves the device breakdown voltage. Although this structure can suppress part of the edge electric field, there is still an electric field peak at the terminal edge, resulting in uneven electric field distribution under the anode, limiting the device voltage withstand capability; and the terminal does not participate in the conduction when the device is turned on, occupying the effective conduction area, resulting in increased device on-resistance and reduced forward conduction current. In addition, due to the influence of the Schottky barrier lowering effect, the reverse leakage current is large, and the device off-state loss is high. Therefore, it is necessary to develop more effective electric field modulation technology to realize a vertical gallium nitride Schottky diode with high breakdown voltage, low reverse leakage, high forward conduction current and low on-resistance. SUMMARY

[0005] The purpose of the present application is to propose a field modulation type Schottky diode to solve the problems of low breakdown voltage and large reverse leakage of traditional junction barrier Schottky diodes, to reduce the reverse leakage of the device while achieving low on-voltage, and to improve the reverse breakdown voltage.

[0006] To achieve the above purpose, the technical scheme of the present application is as follows:

[0007] 1. A field modulation type Schottky diode, comprising: a substrate 1, a drift layer 2, an anode 6, a cathode 7, characterized in that:

[0008] A graded contact layer 3 is arranged above the drift layer 2, the graded contact layer 3 is arranged with 2n-1 rectangular tunneling holes 8 of different intervals and same size in the middle, a high-K tunneling layer 4 is arranged in the tunneling hole 8, and n is the number of tunneling holes from the edge to the center;

[0009] The high-K tunneling layer 4 is arranged with P-type grooves 9 of the same size in the middle, the P-type modulation layer 5 is arranged in the P-type groove 9, and the P-type modulation layer and the high-K tunneling layer 4 constitute a field modulation junction 10;

[0010] The anode 6 covers the upper surface of the graded contact layer 3, the high-K tunneling layer 4 and the P-type modulation layer 5, and forms a Schottky contact with the graded contact layer 3.

[0011] Further, the substrate 1 adopts gallium nitride material; the graded contact layer 3 adopts AlGaN material with gradually increasing Al component from bottom to top, and the Al component x satisfies 5%≤x≤60%. When the device is in forward conduction, it forms AlGaN / GaN heterojunction structure with the drift layer 2, polarizes three-dimensional electron gas, increases the device forward conduction current density, and can increase the current in the opening process by improving the tunneling probability of carriers, and reduce the device forward opening voltage; when the device is in reverse blocking, it is beneficial to increase the barrier height of the Schottky junction, and reduce the reverse leakage current.

[0012] Further, the high-K tunneling layer 4 adopts any one of Ta2O5, ZrO2, HfO2, TiO2 high-K dielectric material with dielectric constant greater than that of AlGaN material, for improving the tunneling probability of carriers, increasing the forward conduction current, and reducing the opening voltage.

[0013] The P-type modulation layer 5 adopts one of P-type NiO or P-type GaN material, and the hole concentration is 1×10 18 ~8×10 20 cm -3 , for weakening the electric field of the device edge, improving the uniformity of the surface electric field distribution, thereby reducing the reverse leakage current of the device and improving the breakdown voltage of the device.

[0014] Further, the tunneling hole 8 is composed of 2n-1 holes with the same size, and is symmetric to the center of the nth hole, the width a of each tunneling hole is 0.5-0.8μm, and the spacing between adjacent two tunneling holes is r n , and the spacing between the tunneling holes increases from the left and right sides to the middle, i.e. r1 n ;

[0015] The P-type groove 9 is composed of 2n-1 grooves with the same size, and the width m of each P-type groove is 0.2-0.6μm, and satisfies 0

[0016] Further, the high-K tunneling layer 4 and the graded contact layer 3 are staggered, and the difference in dielectric constant between the two adjacent materials promotes the generation of a new electric field peak at the interface, so as to reduce the barrier width of the interface between the high-K tunneling layer 4 and the graded contact layer 3, improve the forward tunneling probability of electrons, increase the forward conduction current, and reduce the opening voltage.

[0017] 2. A field modulation type Schottky diode manufacturing method, comprising the following steps:

[0018] S1) epitaxially growing n-type gallium nitride semiconductor material on the substrate 1 to form the drift layer 2;

[0019] S2) epitaxially growing AlGaN semiconductor material with gradually increasing Al component from bottom to top on the drift layer 2 to form a graded contact layer 3;

[0020] S3) making a first mask on the graded contact layer 3, and etching the graded contact layer 3 by using the mask to form a tunnel hole 8;

[0021] S4) making a second mask on the graded contact layer 3, and depositing high-K dielectric in the tunnel hole 8 by using the mask to form a high-K tunnel layer 4 staggered with the graded contact layer 3;

[0022] S5) making a third mask on the graded contact layer 3 and the high-K tunnel layer 4, and etching the high-K tunnel layer 4 by using the mask to form a P-type groove 9;

[0023] S6) making a fourth mask on the graded contact layer 3 and the high-K tunnel layer 4, and depositing P-type semiconductor material in the P-type groove 9 by using the mask to form a P-type modulation layer 5;

[0024] S7) making a fifth mask on the back of the substrate 1, and depositing metal on the back of the substrate 1 by using the mask and performing rapid thermal annealing to form a cathode 7;

[0025] S8) making a sixth mask on the graded contact layer 3, the high-K tunnel layer 4 and the P-type modulation layer 5, and depositing metal by using the mask to form an anode 8, thereby completing the preparation of the whole device.

[0026] Compared with the junction barrier Schottky diode device, the device of the present application has the following advantages:

[0027] Firstly, the device of the present application is additionally provided with the graded contact layer formed by using AlGaN material and the high-K tunnel layer formed by using high-K dielectric material, which can form multilayer two-dimensional electron gas between AlGaN materials with different Al components, generate three-dimensional electron gas through superposition, and form high-concentration electron distribution in the graded contact layer; on the other hand, the staggered distribution of the graded contact layer and the high-K tunnel layer can utilize the difference in dielectric constant of the adjacent two materials to promote the generation of new electric field peaks at the interface, generate high electron tunneling probability under small positive bias, form high output current, and reduce the turn-on voltage and on-resistance.

[0028] Secondly, the device of the present application is additionally provided with a gradual contact layer and a P-type modulation layer structure formed by using AlGaN material. On one hand, the height and width of the Schottky barrier can be significantly increased by the gradual contact layer with high band gap, so as to inhibit the probability of the electron tunneling from the metal into the semiconductor in the reverse bias, and reduce the reverse leakage current of the device. On the other hand, the space charge zone formed by the P-type modulation layer and the drift layer can be combined to clamp the conductive path on the surface of the Schottky junction, and reduce the reverse leakage of the device. In addition, the PN junction formed by the P-type modulation layer and the drift layer can be biased in the reverse direction, and 2n-1 electric field peaks can be generated on the surface of the device, so as to weaken the electric field on the edge of the device to the maximum, improve the uniformity of the surface electric field distribution, thereby reducing the reverse leakage current of the device and improving the breakdown voltage of the device. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structure diagram of a conventional vertical gallium nitride Schottky diode with terminal protection;

[0030] Figure 2 is a structure diagram of the field modulation type Schottky diode of the present application;

[0031] Figure 3 is a flowchart for realizing the field modulation type Schottky diode of the present application;

[0032] Figure 4 is a forward conduction characteristic curve of the device of the present application and a conventional device;

[0033] Figure 5 is a reverse breakdown characteristic curve of the device of the present application and a conventional device. DETAILED DESCRIPTION

[0034] The embodiments and effects of the present application will be further described in detail below with reference to the accompanying drawings.

[0035] Reference Figure 2 The vertical gallium nitride tunneling power diode of the present example comprises a substrate 1, a drift layer 2, a gradual contact layer 3, a high-K tunneling layer 4, a P-type modulation layer 5, an anode 6, a cathode 7, a tunneling hole 8, a P-type groove 9 and a field modulation junction 10. Wherein:

[0036] The substrate 1 is a gallium nitride homogeneous substrate;

[0037] The drift layer 2 is located on the upper part of the substrate 1;

[0038] The gradual contact layer 3 is located on the upper part of the drift layer 2, which is made of AlGaN material with gradually increasing Al component from bottom to top, and the Al component x satisfies 5%≤x≤60%;

[0039] The tunneling hole 8 is located in the graded contact layer 3, which is composed of 2n-1 holes with the same size and is symmetric to the middle n hole, the width a of each tunneling hole is 0.5-0.8 μm, and the interval of adjacent two tunneling holes is r n The interval of the tunneling holes increases from left and right to the middle direction, that is, r1 < r2 < r3 < r4 < ··· < r n ;

[0040] The high-K tunneling layer 4 is located in the tunneling hole 8, which is staggered with the graded contact layer 3 and adopts high-K dielectric with a dielectric constant greater than AlGaN material, that is, any one of Ta2O5, ZrO2, HfO2 and TiO2;

[0041] The P-type groove 9 is located in the high-K tunneling layer 4 and is composed of 2n-1 grooves with the same size, the width m of each P-type groove is 0.2-0.6 μm, and 0 < m < a is satisfied;

[0042] The P-type modulation layer 5 is located in the P-type groove 9 and adopts one of P-type NiO or P-type GaN material, and the hole concentration is 1×10 18 -8×10 20 cm -3 ;

[0043] The anode 6 is located on the upper surface of the graded contact layer 3, the high-K tunneling layer 4 and the P-type modulation layer 5;

[0044] The cathode 7 is located on the back surface of the substrate 1;

[0045] The field modulation junction 10 is composed of the high-K tunneling layer 4 and the P-type modulation layer 5.

[0046] Referring to Figure 3 , the method for manufacturing the vertical gallium nitride tunneling power diode is given as follows.

[0047] Example one: the field modulation Schottky diode is manufactured by taking TiO2 as the high-K tunneling layer 4, taking P-type NiO as the P-type modulation layer 5, taking 11 holes with the same size as the tunneling hole 8, taking 0.8 μm as the width a of each tunneling hole, and taking 9 grooves with the same size as the P-type groove 9 and taking 0.6 μm as the width m of each P-type groove.

[0048] Step one. The drift layer 2 is manufactured, such as Figure 3 (a).

[0049] The n-type GaN with a thickness of 10 μm and a doping concentration of 5 x 1018cm-3 is epitaxially grown on the GaN substrate 1 by using the metal organic chemical vapor deposition technique under the process conditions of a temperature of 900°C, a pressure of 45 Torr, a hydrogen flow rate of 5000 seem, an ammonia flow rate of 4600 seem, and a gallium source flow rate of 160 μmol / min, to form the drift layer 2. 15 cm -3 - The n-type GaN with a thickness of 10 μm and a doping concentration of 5 x 1018cm-3 is epitaxially grown on the GaN substrate 1 by using the metal organic chemical vapor deposition technique under the process conditions of a temperature of 900°C, a pressure of 45 Torr, a hydrogen flow rate of 5000 seem, an ammonia flow rate of 4600 seem, and a gallium source flow rate of 160 μmol / min, to form the drift layer 2.

[0050] Step two, the graded contact layer 3 is made as shown in Figure 3 (b).

[0051] The AlGaN material is epitaxially grown on the drift layer 2 by using the metal organic chemical vapor deposition technique under the process conditions of a temperature of 950°C, a pressure of 45 Torr, a hydrogen flow rate of 5000 seem, an ammonia flow rate of 3800 seem, a gallium source flow rate of 40 μmol / min, and an aluminum source flow rate of 5 μmol / min, to form the graded contact layer 3.

[0052] Step three, the tunnel hole 8 is made as shown in Figure 3 (c).

[0053] The first mask is made on the graded contact layer 3, and the reactive ion etching technique is used to etch the graded contact layer 3 to a width of 0.8 μm by using the mask under the process conditions of a Cl2 flow rate of 15 seem, a pressure of 10 mTorr, and a power of 110 W, to form the tunnel hole 8.

[0054] Step four, the high-K tunnel layer 4 is made as shown in Figure 3 (d).

[0055] The second mask is made on the graded contact layer 3, and the radio frequency magnetron reactive sputtering technique is used to deposit TiO2 in the tunnel hole 8 by using the mask under the process conditions of a sputtering pressure of about 50 Pa, O2 and Ar flow rates of 10 seem and 50 seem, respectively, and a temperature of 200°C, to form the high-K tunnel layer 4.

[0056] Step five, the P-type slot 9 is made as shown in Figure 3 (e).

[0057] The third mask is made on the graded contact layer 3 and the high-K tunnel layer 4, and the reactive ion etching technique is used to etch the high-K tunnel layer 4 to a width of 0.6 μm by using the mask under the process conditions of a Cl2 flow rate of 10 seem, a pressure of 5 mTorr, and a power of 50 W, to form the P-type slot 9.

[0058] Step six, the P-type modulation layer 5 is made as shown in Figure 3 (f).​

[0059] The fourth mask is made on the graded contact layer 3 and the high-K tunneling layer 4, and the P-type modulation layer 5 is sputtered on the P-type groove 9 using the radio frequency magnetron reactive sputtering technique under the process conditions of a vacuum degree of 3.0 x 10 -4 Pa, a radio frequency power of 100 W, an O2flow rate of 1 sccm, and an Ar flow rate of 1 sccm.

[0060] Step seven. The cathode 7 is made as follows: Figure 3 (g).

[0061] 7.1) The fifth mask is made on the back of the substrate 1, and the Ti / Al / Au / Ni metal combination is deposited on the back of the substrate 1 using the electron beam evaporation technique under the process conditions of a vacuum degree of 8 x 10 -4 Pa, a power of 400 W, and an evaporation rate of 0.02 μm, 0.14 μm, 0.055 μm, and 0.045 μm, respectively.

[0062] 7.2) The deposited metal is subjected to rapid thermal annealing under the process conditions of a temperature of 860 °C and a time of 30 s, and the cathode 7 is formed.

[0063] Step eight. The anode 8 is made as follows: Figure 3 (h).

[0064] The sixth mask is made on the graded contact layer 3, the high-K tunneling layer 4, and the P-type modulation layer 5, and the metal Wu is deposited on the upper part of the graded contact layer 3, the high-K tunneling layer 4, and the P-type modulation layer 5 using the electron beam evaporation technique under the process conditions of a vacuum degree of 1.6 x 10 -3 Pa, a power of 350 W, and an evaporation rate of 0.02 μm, 0.14 μm, 0.055 μm, and 0.045 μm, respectively, and the anode 8 is formed, thus completing the preparation of the entire device.

[0065] In the second embodiment, the high-K tunneling layer 4 is made of HfO2material, the P-type modulation layer 5 is made of P-type NiO material, the tunneling hole 8 is composed of nine holes of the same size, the width a of each hole is 0.5 μm, the P-type groove 9 is composed of nine grooves of the same size, the width m of each groove is 0.3 μm, and the field modulation type Schottky diode is prepared.

[0066] Step 1. The drift layer 2 is made as follows: Figure 3 (a).

[0067] The metal organic chemical vapor deposition technique is used to epitaxially deposit a gallium nitride substrate 1 with a thickness of 5 μm and a doping concentration of 1 x 10 14 cm -3N-type GaN is formed as the drift layer 2. The process conditions are: temperature 800 °C, pressure 30 Torr, SiH4 as the doping source, hydrogen flow rate 4000 seem, ammonia flow rate 4000 seem, and gallium source flow rate 100 μmol / min.

[0068] Step 2. The graded contact layer 3 is formed as follows: Figure 3 (b).

[0069] The AlGaN material is epitaxially grown on the drift layer 2 using the metal organic chemical vapor deposition technique to form the graded contact layer 3. The process conditions are: temperature 800 °C, pressure 30 Torr, hydrogen flow rate 4000 seem, ammonia flow rate 3500 seem, gallium source flow rate 30 μmol / min, and aluminum source flow rate 5 μmol / min.

[0070] Step 3. The tunnel hole 8 is formed as follows: Figure 3 (c).

[0071] The first mask is formed on the graded contact layer 3, and the graded contact layer 3 is etched using the reactive ion etching technique to form the tunnel hole 8. The etching process conditions are: Cl2 flow rate 15 seem, pressure 10 mTorr, and power 100 W.

[0072] Step 4. The high-K tunnel layer 4 is formed as follows: Figure 3 (d).

[0073] The second mask is formed on the graded contact layer 3, and the HfO2 material is deposited in the tunnel hole 8 using the radio frequency magnetron reactive sputtering technique to form the high-K tunnel layer 4. The process conditions are: reaction chamber sputtering pressure 0.1 Pa, O2 and Ar flow rates 1 seem and 8 seem, respectively, and temperature 200 °C.

[0074] Step 5. The P-type slot 9 is formed as follows: Figure 3 (e).

[0075] The third mask is formed on the graded contact layer 3 and the high-K tunnel layer 4, and the high-K tunnel layer 4 is etched using the reactive ion etching technique to form the P-type slot 9. The process conditions are: Cl2 flow rate 10 seem, pressure 5 mTorr, and power 50 W.

[0076] Step 6. The P-type modulation layer 5 is formed as follows: Figure 3 (f).

[0077] A fourth mask is made on the graded contact layer 3 and the high-K tunneling layer 4. A P-type NiO material is sputtered in the P-type groove 9 using a low-temperature sputtering technique to form the P-type modulation layer 5. The process conditions are: a vacuum degree of 4.0 x 10 -4 Pa, a radio frequency power of 100 W, an O2 flow of 1 sccm, and an Ar flow of 1 sccm.

[0078] Step 7. The cathode 7 is made as follows: Figure 3 (g).

[0079] A fifth mask is made on the back of the substrate 1. A metal is deposited on the back of the substrate 1 using an electron beam evaporation technique. The deposited metal is a Ti / Au / Ni metal combination, i.e., Ti, Au, and Ni from bottom to top, with thicknesses of 0.02 μm, 0.3 μm, and 0.05 μm, respectively. The electron beam evaporation process conditions are: a vacuum degree of 1.8 x 10 -3 Pa, a power of 350 W, and an evaporation rate of

[0080] The deposited metal is then subjected to rapid thermal annealing to form the cathode 7. The thermal annealing process conditions are: a temperature of 850°C and a time of 35 s.

[0081] Step 8. The anode 8 is made as follows: Figure 3 (h).

[0082] A sixth mask is made on the graded contact layer 3, the high-K tunneling layer 4, and the P-type modulation layer 5. A metal is deposited on the graded tunneling layer 4 and the upper portion of the modulation layer 7 using an electron beam evaporation technique. The deposited metal is Ni, with a thickness of 0.207 μm. The process conditions are: a vacuum degree of 5 x 10 -4 Pa, a power of 200 W, and an evaporation rate of The anode 8 is formed, and the entire device is completed.

[0083] In Example 3, the high-K tunneling layer 4 is made of Ta2O5 material, the P-type modulation layer 5 is made of P-type GaN material, the tunneling holes 8 are composed of 13 holes of the same size, each tunneling hole has a width a of 0.4 μm, the P-type groove 9 is composed of 9 grooves of the same size, each P-type groove has a width m of 0.2 μm, and the entire device is a field modulation type Schottky diode.

[0084] Step A. The drift layer 2 is made as follows: Figure 3 (a).

[0085] A vacuum degree of 1.0 x 10 -10 mbar, a radio frequency power of 400 W, and a process condition of a reaction agent using N2 and a high-purity Ga source. A molecular beam epitaxy technique is used to epitaxially grow a thickness of 12 μm and a doping concentration of 1 x 1016 cm -3 of n - type GaN, forming a drift layer 2.

[0086] Step B. Fabricating a graded contact layer 3, as Figure 3 (b).

[0087] A process condition of 900°C, 80 Torr, 4800 sccm of H2 flow, 4900 sccm of NH3 flow, 150 μmol / min of Ga source flow, and 50 μmol / min of Al source flow is set, and an AlGaN material is epitaxially grown on the drift layer 2 using a metal organic chemical vapor deposition technique, forming the graded contact layer 3.

[0088] Step C. Fabricating a tunnel hole 8, as Figure 3 (c).

[0089] A process condition of 60 sccm of Cl2 flow, 100 mTorr of pressure, and 500 W of power is set, a first mask is fabricated on the graded contact layer 3, and a recess is etched on the graded contact layer 3 using the mask and a reactive ion etching technique, forming the tunnel hole 8 with a width of 0.4 μm.

[0090] Step D. Fabricating a high-K tunnel layer 4, as Figure 3 (d).

[0091] A process condition of 300 Pa of sputtering pressure in a reaction chamber, 50 sccm of O2 flow and 100 sccm of Ar flow, and 900°C of temperature is set, a second mask is fabricated on the graded contact layer 3, and Ta2O5 is deposited in the tunnel hole 8 using the mask and a radio frequency magnetron reactive sputtering technique, forming the high-K tunnel layer 4.

[0092] Step E. Fabricating a P-type slot 9, as Figure 3 (e).

[0093] A process condition of 10 sccm of Cl2 flow, 5 mTorr of pressure, and 50 W of power is set, a third mask is fabricated on the graded contact layer 3 and the high-K tunnel layer 4, and a width of 0.2 μm is etched on the high-K tunnel layer 4 using the mask and a reactive ion etching technique, forming the P-type slot 9.

[0094] Step F. Fabricating a P-type modulation layer 5, as Figure 3 (f).

[0095] The fourth mask is made on the graded contact layer 3 and the high-K tunneling layer 4, and the process conditions are set as follows: the temperature is 900 DEG C, the pressure is 80 Torr, the hydrogen flow is 4800 sccm, the ammonia flow is 4900 sccm, the gallium source flow is 150 mu mol / min, and the aluminum source flow is 50 mu mol / min; the metal-organic chemical vapor deposition technology is used to epitaxially grow GaN material on the P-type groove 9 by using the mask, so as to form the P-type modulation layer 5.

[0096] Step G: the cathode 7 is made, as shown in Figure 4 (g).

[0097] The fifth mask is made on the back of the substrate 1, and the process conditions are set as follows: the vacuum degree is less than 1.8*10 -3 Pa, the power is 500 W, and the evaporation rate is The metal is deposited on the back of the substrate 1 by using the mask and the electron beam evaporation technology, wherein the deposited metal is a Ti / Al / Mo / Au metal combination, that is, Ti, Al, Mo and Au from bottom to top, and the thicknesses of the Ti, Al, Mo and Au are 0.02 mu m, 0.1 mu m, 0.03 mu m and 0.03 mu m respectively.

[0098] The sample with the Ti / Al / Mo / Au combination metal is subjected to rapid thermal annealing under the condition that the temperature is 860 DEG C and the time is 30 s, so as to form the cathode 7.

[0099] Step H: the anode 8 is made, as shown in Figure 4 (h).

[0100] The sixth mask is made on the graded contact layer 3, the high-K tunneling layer 4 and the P-type modulation layer 5, and the process conditions are set as follows: the vacuum degree is 1.8*10 -3 Pa, the power is 1000 W, and the evaporation rate is The metal Mo is deposited on the graded contact layer 3, the high-K tunneling layer 4 and the P-type modulation layer 5 by using the mask and the electron beam evaporation technology, so as to form the anode 8 and complete the whole device.

[0101] The effect of the present application can be further illustrated by the following simulation results.

[0102] Simulation 1: the forward conduction characteristics of the traditional vertical gallium nitride Schottky diode with terminal protection and the device of the first embodiment of the present application are simulated by using the simulation software Silvaco, and the result is shown in Figure 5 It can be seen from Figure 5 that the opening voltage of the device of the present application is 0.27 V, and the opening voltage of the traditional vertical gallium nitride Schottky diode with terminal protection is 0.7 V. It is shown that the device of the present application can significantly increase the conduction current and obviously reduce the conduction resistance.

[0103] Simulation 2: using simulation software Silvaco, breakdown characteristics simulation of traditional vertical gallium nitride Schottky diode with terminal protection and the device of embodiment one of the present application is carried out, and the result is shown in ​ ​ It can be seen that the breakdown voltage of the device of the present application is about 1390V, the breakdown voltage of the traditional junction barrier Schottky diode is about 850V, the breakdown voltage of the device of the present application is increased by 540V compared with the breakdown voltage of the traditional device, which indicates that the device of the present application has better voltage resistance capacity compared with the traditional device.

[0104] The above description is only three specific embodiments of the present application, and does not constitute a limitation to the present application, and it is obvious for the person skilled in the art that after understanding the content and principle of the present application, various modifications and changes in form and details can be made according to the method of the present application without departing from the principle and scope of the present application, for example, in addition to using metal organic chemical vapor deposition technology and molecular beam epitaxy technology, hydride vapor phase epitaxy technology and atomic layer deposition technology can also be used to prepare AlGaN and GaN materials; in addition to using radio frequency magnetron reactive sputtering technology, atomic layer deposition technology and plasma enhanced chemical vapor deposition technology can also be used to prepare high-K tunneling layer; in addition to using Ta2O5, TiO2, HfO2 dielectric, ZrO2 dielectric can also be used for high-K tunneling layer; in addition to using the process condition of pressure 1.0x10 - 10 mbar and radio frequency power 400W, other process parameters in the range of pressure 1.0x10 -10 ~7.0x10 -10 mbar and radio frequency power 100~800W can also be used, but these modifications and changes based on the present application are still within the protection scope of the claims of the present application.​

Claims

1. A field-modulated Schottky diode, comprising: The substrate (1), drift layer (2), anode (6), and cathode (7) are characterized by: A gradient contact layer (3) is provided above the drift layer (2). The gradient contact layer (3) has 2n-1 rectangular tunneling holes (8) of different intervals and the same size in the middle. A high K tunneling layer (4) is provided inside the tunneling hole (8). n is the number of tunneling holes from the edge to the center. The gradient contact layer (3) is made of AlGaN material with the Al composition gradually increasing from bottom to top; The high-K tunneling layer (4) has a P-type groove (9) of the same size in the middle, and a P-type modulation layer (5) is provided in the P-type groove (9). The P-type modulation layer and the high-K tunneling layer (4) constitute a field modulation junction (10). The anode (6) covers the upper surface of the gradient contact layer (3), the high-K tunneling layer (4) and the P-type modulation layer (5), and forms a Schottky contact with the gradient contact layer (3).

2. The field-modulated Schottky diode according to claim 1, characterized in that: The substrate (1) is made of gallium nitride material; The Al component x in the gradient contact layer (3) satisfies 5%≤x≤60%. When the device is forward-biased, it forms an AlGaN / GaN heterojunction structure with the drift layer (2), polarizes a two-dimensional electron gas, increases the forward conduction current density of the device, and can increase the current during the turn-on process by increasing the tunneling probability of the charge carriers, thereby reducing the forward turn-on voltage of the device. When the device is reverse-biased, it is beneficial to increase the barrier layer height of the Schottky junction and reduce the reverse leakage current.

3. The field-modulated Schottky diode according to claim 1, characterized in that: The high-K tunneling layer (4) is made of any one of the high-K dielectric materials with a dielectric constant greater than that of AlGaN material, such as Ta2O5, ZrO2, HfO2, and TiO2, in order to increase the tunneling probability of charge carriers, increase the forward conduction current, and reduce the turn-on voltage. The P-type modulation layer (5) is made of either P-type NiO or P-type GaN material, with a hole concentration of 1×10⁻⁶. 18 ~8×10 20 cm -3 It is used to weaken the electric field at the edge of the device, improve the uniformity of the surface electric field distribution, thereby reducing the reverse leakage current of the device and increasing the breakdown voltage of the device.

4. The field-modulated Schottky diode according to claim 1, characterized in that: The tunneling hole (8) consists of 2n-1 holes of the same size, and is symmetrical about the middle nth hole. The width a of each tunneling hole is 0.5~0.8μm, and the distance between two adjacent tunneling holes is r. n The spacing between tunnel holes increases sequentially from the left and right sides towards the middle, thus satisfying r1. <r2<r3<r4<···<r n ; The P-shaped groove (9) consists of 2n-1 grooves of the same size, each P-shaped groove having a width m of 0.2~0.6μm, and satisfying 0 <m<a。 5. The field-modulated Schottky diode according to claim 1, characterized in that: The high-K tunneling layer (4) and the gradient contact layer (3) are staggered. By utilizing the difference in dielectric constants of the two adjacent materials, a new electric field peak is generated at the interface, which reduces the barrier width of the interface between the high-K tunneling layer (4) and the gradient contact layer (3), increases the probability of forward electron tunneling, increases the forward conduction current, and reduces the turn-on voltage.

6. A method for fabricating a field-modulated Schottky diode, comprising the following steps: S1) An n-type gallium nitride semiconductor material is epitaxially grown on a substrate (1) to form a drift layer (2). S2) An AlGaN semiconductor material with an Al composition that gradually increases from bottom to top is epitaxially grown on the drift layer (2) to form a gradient contact layer (3). S3) A mask is first fabricated on the gradient contact layer (3), and the mask is used to etch on the gradient contact layer (3) to form a tunnel hole (8). S4) A mask is fabricated a second time on the gradient contact layer (3), and a high-K medium is deposited in the tunnel hole (8) using the mask to form a high-K tunnel layer (4) that is staggered with the gradient contact layer (3). S5) A mask is fabricated for the third time on the gradient contact layer (3) and the high K tunneling layer (4). The mask is used to etch on the high K tunneling layer (4) to form a P-type groove (9). S6) A mask is fabricated for the fourth time on the gradient contact layer (3) and the high-K tunneling layer (4), and P-type semiconductor material is deposited in the P-type trench (9) using the mask to form a P-type modulation layer (5). S7) A mask is fabricated for the fifth time on the back of the substrate (1). Metal is deposited on the back of the substrate (1) using the mask and then rapidly annealed to form a cathode (7). S8) A sixth mask is fabricated on the gradient contact layer (3), the high-K tunneling layer (4) and the P-type modulation layer (5). Metal is deposited using the mask to form the anode (6), thus completing the fabrication of the entire device.

7. The method according to claim 6, characterized in that: In step S3), the tunnel hole is made and the step... The P-type trenches in S5 are fabricated using reactive ion etching technology, and the process conditions are as follows: Cl2 flow rate is 10~60 sccm Pressure is 5~100 mTorr. The power is 50~500W.

8. The method according to claim 6, characterized in that: Step S1) Epitaxial growth n - Both the AlGaN semiconductor material and the epitaxial growth of AlGaN semiconductor material in step S2) are performed using metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). The process conditions for the aforementioned organometallic chemical vapor deposition technique are as follows: Temperature: 800~1000℃, Pressure: 30~100 Torr, Hydrogen flow rate: 4000~6000 sccm Ammonia flow rate is 3500~5500 sccm, gallium source flow rate is 100~300 μmol / min. The aluminum source flow rate is 5~50 μmol / min; The molecular beam epitaxy technique has the following process conditions: The pressure is 1.0 × 10⁻⁶. -10 ~7.0×10 -10 mbar, RF power is 100~800W, The reactants are N2 and a high-purity Ga source.

9. The method according to claim 6, characterized in that: The fabrication of the high-k tunneling layer in step S4) and the fabrication of the NiO semiconductor material in step S6) both employ radio frequency magnetron reactive sputtering technology, with the following process conditions: The sputtering pressure in the reaction chamber is 0.1~300 Pa. O2 flow rates ranged from 1 to 50 sccm. Ar flow rate is 1~100 sccm The temperature ranges from 100 to 600 ℃.

10. The method according to claim 6, characterized in that: In step S7), the cathode is fabricated, and in step S8) The anodes are fabricated using electron beam evaporation to deposit metal, with the following process conditions: Vacuum degree is 5×10 -4 ~1.8×10 -3 Pa, The power is 200~1000W, and the evaporation rate is less than 3Å / s; The rapid hot annealing process conditions are: temperature 800~900℃, time 30~75s.

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