Large-current vertical GaN-based diode

Abstract

The invention discloses a high-current vertical GaN-based diode, which comprises an AlN / GaN superlattice formed by arranging multi-period AlN and GaN at intervals, and the AlN / GaN superlattice is used as a vertical high-current diode of a conducting channel region. The non-polar GaN growing in the vertical direction and the AlN are transversely arranged, the polar surface of the GaN and the AlN generate two-dimensional electron gas, and a longitudinal multi-channel structure is formed. According to the invention, the InN with a narrow forbidden bandwidth and the non-polar GaN material are used to achieve the purposes of easily forming ohmic contact and keeping the thermal stability of the device under high power; meanwhile, the multi-channel structure is manufactured by adopting the multi-period AlN / GaN superlattice so as to achieve the purpose of improving the current density and the voltage endurance capability of the device.

Description

Technical Field

[0001] The invention belongs to the technical field of GaN-based diodes, and in particular relates to a high-current vertical GaN-based diode. Background Art

[0002] At present, common vertical GaN-based diodes are mainly based on GaN self-supporting substrates. The cathode is directly plated on the back of the GaN single crystal substrate, and the anode is above the low-doped epitaxial layer. The current flows completely vertically between the anode and the cathode.

[0003] Since the work functions of GaN and metal are quite different, it is difficult to make ohmic contacts. At the same time, the thermal stability of this vertical GaN-based diode is also poor under high power.

[0004] The existing technology mainly has the following defects:

[0005] Disadvantage 1: For traditional vertical GaN-based diodes, due to the large bandgap of GaN materials, the carrier concentration is low at room temperature, which is not conducive to recombination and transmission with carriers in metals; at the same time, the work function matching degree between GaN materials and metal electrodes is low, making it difficult to form a low-barrier ohmic contact; therefore, the formed ohmic contact performance is poor;

[0006] Disadvantage 2: Most of the GaN used in traditional GaN diodes is polar GaN. Due to the polarity of its crystal structure, a large polarization electric field is generated inside. This polarization electric field may cause carrier separation and instability at high temperatures, thus affecting the performance and reliability of the device. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a high-current vertical GaN-based diode. The present invention uses InN and non-polar GaN materials with narrow bandgap width to easily form ohmic contact and maintain the thermal stability of the device under high power; at the same time, a multi-period AlN / GaN superlattice is used to make a multi-channel structure to achieve the purpose of improving the current density and voltage resistance of the device.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A high current vertical GaN-based diode comprises an AlN / GaN superlattice formed by periodically arranging AlN and GaN in a lateral space, wherein the AlN / GaN superlattice serves as a conductive channel region, and an ohmic contact layer and a Schottky contact layer are respectively arranged on two opposite sides thereof in the longitudinal direction, and a cathode and an anode are respectively arranged on the ohmic contact layer and the Schottky contact layer.

[0010] The GaN grows in the longitudinal direction, and its polar surface generates a two-dimensional electron gas with AlN to form a longitudinal multi-channel structure.

[0011] The period of the superlattice structure is 1000-1500. The optimal period is 1350. A Schottky contact layer is arranged on the top layer of the diode, and an ohmic contact layer is arranged on the bottom layer of the diode.

[0012] The ohmic contact layer is InN, InSb, InAs or InAsSb with a narrow bandgap.

[0013] The Schottky contact layer is also made of InN, InSb or InAs with a narrow bandgap.

[0014] A method for preparing a high current vertical GaN-based diode comprises the following steps:

[0015] Step 1: First, clean the substrate to remove organic and inorganic residues;

[0016] Step 2: Growing AlN / GaN (non-polar a-plane or m-plane) superlattice on the substrate using MOCVD process;

[0017] Step 3: peeling off the substrate using a lift-off process, and rotating the resulting superlattice structure 90° in a counterclockwise direction to form a lateral superlattice structure;

[0018] Step 4: Use MOCVD process to grow n-InN material on the upper and lower sides of the obtained superlattice for subsequent production of ohmic contacts and Schottky contacts;

[0019] Step 5: Clean the epitaxial wafer to remove impurities remaining on it;

[0020] Step 6: On the n-InN epitaxial layer on one side, Ti / Al / Ni / Au metal (20nm / 160nm / 55nm / 45nm) is deposited by electron beam evaporation process, and then rapidly thermally annealed at 900°C in N2 environment to form an ohmic contact as a cathode, completing the process flow of a single device;

[0021] Step 7: On the other side of the n-InN epitaxial layer, Ni / Au metal (60nm / 100nm) is deposited by electron beam evaporation to form a Schottky contact as an anode, completing the process flow of a single device.

[0022] The substrate in step 1 is a Si / sapphire / SiC substrate.

[0023] The step 2 is specifically as follows:

[0024] In a vacuum environment, the pressure is maintained at 50-100Torr, the temperature is maintained at 1000℃, the Ga(CH3)3 gas flow rate is maintained at 250-750sccm, and 1000-1500 periods of AlN / GaN (non-polar a-plane or m-plane) superlattice are grown in the vertical direction; this multi-period non-polar plane superlattice structure grown in the vertical direction has a non-polar plane in the horizontal direction, with a small built-in electric field, and is easy to form ohmic contact; the plane in the vertical direction is a polar plane, which can form a two-dimensional electron gas, thereby improving the channel's ability to transport carriers, thereby increasing the current density of the device.

[0025] The step 4 is specifically as follows:

[0026] The MOCVD process is used to maintain the temperature at 500-600 degrees Celsius and the pressure at 50-100 Torr. Trimethyl indium is used as the In source and the flow rate is controlled at 10-30 sccm. At the same time, NH3 is used as the nitrogen source and the flow rate is controlled at 60-90 sccm. n-InN material is grown on the upper and lower sides of the obtained superlattice for subsequent electrode contact.

[0027] Beneficial effects of the present invention:

[0028] 1) The present invention uses narrow bandgap material InN to replace GaN. Since the work function difference between InN and metal is small, it is easier to form excellent ohmic contact with metal.

[0029] 2) At the same time, multiple non-polar GaN and AlN grown along the vertical direction are arranged laterally, so that the polar surface of GaN and AlN generate a two-dimensional electron gas, forming a vertical multi-channel structure, which greatly improves the current density of the device.

[0030] 3) Due to the non-polar characteristics of non-polar GaN, the polarization effect is avoided, reducing the electric field changes caused by polarization at high temperatures. Therefore, the device performs more stably in high temperature environments.

[0031] 4) Since the longitudinal thickness of the superlattice in the device structure is large, it can withstand a higher breakdown voltage. As a novel design idea, the device structure has broad application prospects in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of a high-current vertical diode grown under the present invention.

[0033] Figure 2 The invention is made Figure 1 Schematic diagram of the process flow of the meso-epitaxial structure. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0035] Example:

[0036] like Figure 1 , Figure 2 As shown, a preparation process of a high current vertical GaN-based diode includes the following steps:

[0037] Step 1: Clean and pretreat the substrate

[0038] The substrate is ultrasonically cleaned with acetone, and then the acetone is washed away with anhydrous ethanol and blown dry to remove organic and inorganic residues on the surface of the substrate.

[0039] Step 2: Epitaxial GaN

[0040] The cleaned substrate was placed in the MOCVD reaction chamber and the reaction chamber was evacuated to reduce the vacuum degree to 3×10 - 2 Torr, while maintaining the pressure at 75 Torr, pass Ga(CH3)3 at a flow rate of 500sccm, then raise the temperature to 1000℃, pass NH3 at a flow rate of 50L, and use MOCVD process to grow non-polar (a-plane) GaN epitaxial layer on the substrate.

[0041] Step 3: Epitaxial AlN

[0042] The pressure in the reaction chamber was maintained at 75 Torr, the introduction of nitrogen and trimethylgallium was stopped, and hydrogen with a flow rate of 190 L and trimethylaluminum with a flow rate of 327 sccm were introduced. The ammonia flow rate was reduced to 5 L, the temperature was maintained at 1000°C, and AlN was epitaxially grown on the GaN epitaxial layer.

[0043] Step 4: Multi-channel structure growth

[0044] Using the conditions of steps 3 and 4, the a-plane GaN / AlN superlattice with a total thickness of 2-3um is repeatedly grown for 1000-1500 cycles to form a non-polar superlattice structure required for high current density devices. This multi-period non-polar superlattice structure grown in the vertical direction has a non-polar surface in the horizontal direction, with a small built-in electric field, and is easy to form ohmic contact; the surface in the vertical direction is a polar surface, which can form a two-dimensional electron gas, improve the ability of the channel to transport carriers, and thus improve the current density of the device.

[0045] Step 5: Substrate peeling

[0046] Laser lift-off technology is used to strike the interface of the GaN substrate to expand the interface material through local heating, thereby reducing the adhesion between the GaN film and the substrate, thereby peeling the grown heterojunction structure off the substrate.

[0047] Step 6: Epitaxial InN contact layer

[0048] The AlN / GaN heterojunction is rotated 90°, and InN is grown on its sidewalls as the subsequent ohmic contact layer. The temperature is lowered to 550°C, the pressure is maintained at 75 Torr, trimethyl indium (TMIn) is used as the In source, and the flow rate is controlled at 15 sccm; NH3 is used as the nitrogen source, and the flow rate is controlled at 75 sccm; H2 is used as the carrier gas during the growth process, and the flow rate is 1000 sccm. Based on the above conditions, InN with a thickness of about 200 nm is grown on the sidewalls of both sides of the heterojunction.

[0049] Step 7: Preparation of ohmic contact cathode electrode

[0050] Ti / Al / Ni / Au (20nm / 160nm / 55nm / 45nm) was deposited on the InN contact layer on one side, followed by rapid thermal annealing at 850°C for 50s in a N2 environment to form the cathode of the diode.

[0051] Step 8: Preparation of Schottky contact anode electrode

[0052] Ni / Au (60nm / 100nm) metal is deposited on one side of the InN contact layer to form a Schottky contact, which serves as the anode of the diode.

[0053] The number of AlN / GaN periodic heterojunctions in the present invention may not be fixed. The present invention proposes growing a superlattice structure of 1000-1500 periods. On this basis, the device performance index of a higher current density can also be achieved by increasing the number of heterojunction periods.

[0054] The material used for the ohmic contact layer in the present invention can be various. In addition to InN, other narrow bandgap semiconductor materials such as InSb, InAs, InAsSb, etc. can also be used as the ohmic contact layer.

[0055] The present invention relates to a multi-channel vertical high-current diode prepared based on non-polar (a-plane or m-plane) GaN. Non-polar GaN grown in the vertical direction is used for lateral arrangement, and its polar surface forms a superlattice with the same number of AlN. Under the strong polarization effect, a two-dimensional electron gas (2DEG) is generated to realize multi-channel carrier transport and thus generate a large current. This longitudinally grown superlattice has a thicker longitudinal thickness and can withstand a larger voltage during operation. At the same time, due to the lack of polarization effect, non-polar surface GaN will not form a large built-in electric field when in contact with metal, which is beneficial to the injection and transmission of carriers and more effectively realizes ohmic contact. Therefore, the present invention can effectively solve the problem that the performance of vertical diodes is limited under high current density.

Claims

1. A high current vertical GaN-based diode, characterized in that: It includes an AlN / GaN superlattice formed by periodically arranging AlN and GaN in a lateral space, wherein the AlN / GaN superlattice serves as a conductive channel region, and an ohmic contact layer and a Schottky contact layer are respectively arranged on two opposite sides in the longitudinal direction, and a cathode and an anode are respectively arranged on the ohmic contact layer and the Schottky contact layer.

2. A high current vertical GaN-based diode according to claim 1, characterized in that: The GaN grows in the longitudinal direction, and its polar surface generates a two-dimensional electron gas with AlN to form a longitudinal multi-channel structure.

3. A high current vertical GaN-based diode according to claim 1, characterized in that: The period of the superlattice structure is 1000-1500.

4. A high current vertical GaN-based diode according to claim 3, characterized in that: The optimal superlattice period is 1350.

5. A high current vertical GaN-based diode according to claim 1, characterized in that: The ohmic contact layer is InN, InSb, InAs or InAsSb.

6. A high current vertical GaN-based diode according to claim 1, characterized in that: The Schottky contact layer is InN, InSb or InAs.

7. A method for preparing a high current vertical GaN-based diode according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: First, clean the substrate to remove organic and inorganic residues; Step 2: Growing AlN / GaN superlattice on substrate using MOCVD process; Step 3: peeling off the substrate using a lift-off process, and rotating the resulting superlattice structure 90° in a counterclockwise direction to form a lateral superlattice structure; Step 4: Use MOCVD process to grow n-InN material on the upper and lower sides of the obtained superlattice for subsequent production of ohmic contacts and Schottky contacts; Step 5: Clean the epitaxial wafer to remove impurities remaining on it; Step 6: On the n-InN epitaxial layer on one side, Ti / Al / Ni / Au metal is deposited by electron beam evaporation process, and then rapidly thermally annealed at 900°C in N2 environment to form an ohmic contact as a cathode, completing the process flow of a single device; Step 7: On the other side of the n-InN epitaxial layer, Ni / Au metal is deposited by electron beam evaporation to form a Schottky contact as an anode, completing the process flow of a single device.

8. The method for preparing a high current vertical GaN-based diode according to claim 7, characterized in that: The substrate in step 1 is a Si / sapphire / SiC substrate.

9. The method for preparing a high current vertical GaN-based diode according to claim 7, characterized in that: The step 2 is specifically as follows: In a vacuum environment, the pressure is maintained at 50-100 Torr, the temperature is maintained at 1000°C, the Ga(CH3)3 gas flow rate is maintained at 250-750sccm, and 1000-1500 periods of AlN / GaN (non-polar a-plane or m-plane) superlattice are grown in the vertical direction.

10. The method for preparing a high current vertical GaN-based diode according to claim 7, characterized in that: The step 4 is specifically as follows: The MOCVD process is used to maintain the temperature at 500-600 degrees Celsius and the pressure at 50-100 Torr. Trimethyl indium is used as the In source and the flow rate is controlled at 10-30 sccm. At the same time, NH3 is used as the nitrogen source and the flow rate is controlled at 60-90 sccm. n-InN material is grown on the upper and lower sides of the obtained superlattice for subsequent electrode contact.

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