A quasi-vertical structure AlGaN Schottky diode and a preparation method thereof

Abstract

The application discloses a quasi-vertical structure AlGaN Schottky diode and a preparation method thereof. The AlGaN Schottky diode comprises, from bottom to top, a substrate, a buffer layer, an AlGaN transition layer, a superlattice layer and an AlGaN drift layer, wherein an anode is arranged on the upper surface of the AlGaN drift layer, and a cathode is arranged on the upper surface of the superlattice layer of the etched part of the AlGaN drift layer. The superlattice layer is a periodic structure formed by the growth of AlN and GaN alternately, or a periodic structure formed by the growth of AlGaN and GaN alternately, so as to form a high-concentration 2DEG channel. Compared with a conventional quasi-vertical structure GaN Schottky diode, the quasi-vertical structure AlGaN Schottky diode has a higher breakdown voltage, a lower on-resistance and a higher current density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor devices, and particularly relates to a quasi-vertical structure AlGaN Schottky diode and a preparation method. BACKGROUND

[0002] GaN material and AlGaN material have the advantages of large band gap, high breakdown field strength, high electron mobility, radiation resistance and high temperature resistance relative to Si and GaAs. For a GaN diode of a lateral structure, due to the existence of strong spontaneous polarization and piezoelectric polarization effects, a high-density two-dimensional electron gas can be formed in an AlGaN / GaN heterojunction material without doping, so as to realize low material square resistance, thereby ensuring good forward conduction characteristics of the device. However, the development of the lateral diode is restricted by problems such as current collapse. The GaN diode of a vertical structure mainly relies on carriers in a GaN bulk material for conduction. In comparison, the GaN diode of a vertical structure has a large forward current density, and almost does not have the phenomenon of current collapse.

[0003] A traditional quasi-vertical structure GaN Schottky diode has a structure as shown in Figure 1 from bottom to top, including a substrate, a GaN buffer layer, a GaN transport layer and a GaN drift layer, wherein an anode is arranged on the GaN drift layer, and a cathode is arranged on the GaN transport layer. Compared with a GaN Schottky diode of a full vertical structure, the quasi-vertical structure GaN Schottky diode has the advantages of high power density, high reliability and low cost, but the breakdown voltage and current density still have the potential for further improvement. SUMMARY

[0004] In order to solve the above problems in the prior art, the application provides a quasi-vertical structure AlGaN Schottky diode and a preparation method. The technical problems to be solved by the application are solved by the following technical scheme.

[0005] A quasi-vertical structure AlGaN Schottky diode, from bottom to top, includes a substrate, a buffer layer, a transition layer, a superlattice layer and an AlGaN drift layer, and an anode is arranged on the upper surface of the AlGaN drift layer, and a cathode is arranged on the upper surface of the superlattice layer of the etched part of the AlGaN drift layer. The superlattice layer is a periodic structure formed by the growth of AlN and GaN alternately, or a periodic structure formed by the growth of AlGaN and GaN alternately, so as to form a high-concentration 2DEG channel.

[0006] In an embodiment of the application, the substrate is any one of sapphire, SiC, Si and GaN.

[0007] In one embodiment of the present application, the buffer layer is AlN, and the thickness is 500nm-2000nm.

[0008] In one embodiment of the present application, the transition layer is AlGaN, and the thickness is 300nm-1000nm.

[0009] In one embodiment of the present application, the total thickness of the superlattice layer is 10nm-100nm.

[0010] In one embodiment of the present application, the AlGaN drift layer is a lightly doped AlGaN drift layer, and the lightly doped AlGaN drift layer is N-type doped with a doping concentration of 1x1018cm-9x1019cm-3. 16 cm -3 -9x1019cm-3. 16 cm -3

[0011] In one embodiment of the present application, the cathode is formed by using a metal combination of Ti / Al / Ni / Au or Ti / Al / Pt / Au to form an ohmic contact.

[0012] In one embodiment of the present application, the anode is formed by using Ni / Au to form a Schottky contact.

[0013] A preparation method of an AlGaN Schottky diode with a quasi-vertical structure, comprising:

[0014] providing a substrate, and depositing AlN on the substrate to form a buffer layer;

[0015] depositing AlGaN on the buffer layer to form a transition layer;

[0016] forming a superlattice layer on the transition layer, wherein the superlattice layer is a periodic structure formed by alternately growing AlN and GaN, or a periodic structure formed by alternately growing AlGaN and GaN;

[0017] depositing AlGaN on the superlattice layer to form a drift layer;

[0018] etching the drift layer outside the AlGaN drift layer to expose the superlattice layer;

[0019] depositing a metal Ti / Al / Ni / Au on the exposed superlattice layer to form a cathode;

[0020] depositing a metal Ni / Au on the AlGaN drift layer to form an anode.

[0021] ​The AlGaN Schottky diode of the quasi-vertical structure and the preparation method thereof of the present application use AlGaN material instead of the GaN material of the conventional quasi-vertical diode as the drift layer, and introduce a superlattice structure, the superlattice layer and the AlGaN transition layer together constitute a new AlGaN system to replace the transmission layer of the conventional quasi-vertical SBD, and the quasi-vertical structure AlGaN Schottky diode prepared has higher breakdown voltage, lower on-resistance and higher current density compared with the conventional quasi-vertical structure GaN Schottky diode. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic diagram of a conventional quasi-vertical structure GaN Schottky diode;

[0023] Figure 2 is a structural schematic diagram of a quasi-vertical structure AlGaN Schottky diode provided by an embodiment of the present application;

[0024] Figure 3 is a flowchart of a preparation method of a quasi-vertical structure AlGaN Schottky diode provided by an embodiment of the present application. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with specific embodiments, but the embodiments of the present application are not limited thereto.

[0026] Please refer to Figure 2 , Figure 2 is a structural schematic diagram of a quasi-vertical structure AlGaN Schottky diode provided by an embodiment of the present application, the quasi-vertical structure AlGaN Schottky diode of the present application comprises, from bottom to top, a substrate 1, a buffer layer 2, a transition layer 3, a superlattice layer 4 and an AlGaN drift layer 5, and an anode 7 is arranged on the upper surface of the AlGaN drift layer 5, and a cathode 6 is arranged on the upper surface of the superlattice layer 4 of the etched part of the AlGaN drift layer 5; wherein the superlattice layer is a periodic structure formed by alternately growing AlN and GaN, or a periodic structure formed by alternately growing AlGaN and GaN.

[0027] The quasi-vertical structure AlGaN Schottky diode of the embodiment of the present application, the substrate 1 can be any one of sapphire, SiC, Si and GaN; the material of the buffer layer 2 is preferably AlN, and the thickness is 500nm-2000nm; the material of the transition layer 3 is preferably AlGaN, and the thickness is 300nm-1000nm; the total thickness of the superlattice layer 4 is preferably 10nm-100nm.

[0028] Further, the AlGaN drift layer 5 of the present application is a lightly doped AlGaN drift layer, and the lightly doped AlGaN drift layer has a doping concentration of 1x1016 cm -3 ~9×10 16 cm -3 N-type doping.

[0029] Furthermore, the cathode 6 of the present invention adopts a metal combination of Ti / Al / Ni / Au or Ti / Al / Pt / Au to form an ohmic contact; the cathode 6 adopts a metal combination of Ti / Al / Ni / Au or Ti / Al / Pt / Au to form an ohmic contact.

[0030] like Figure 1 The conventional quasi-vertical GaN Schottky diode shown in the diagram flows from the anode through a lightly doped drift layer, then through a heavily doped transport layer to the cathode. Because the anode and cathode are not on the same horizontal plane, the current in the drift region concentrates at the lower edge of the anode, resulting in a decrease in the overall average current density and an increase in on-resistance. While increasing the doping concentration in the drift region can generally improve the current distribution, continuously increasing the doping concentration of GaN and AlGaN materials can negatively impact other device performance characteristics. Therefore, the quasi-vertical AlGaN Schottky diode provided by this invention utilizes an extremely thin GaN / AlN or GaN / AlGaN superlattice structure layer. This superlattice structure contains multiple GaN / AlN or GaN / AlGaN heterojunctions. Due to the inherent properties of the superlattice structure, while increasing the Al content, it maintains a relatively good material surface, improving the carrier characteristics of the heterojunctions. The entire superlattice layer forms a conductor with a high concentration of 2DEG. Replacing the original highly doped transport layer with a system formed by a superlattice structure and an AlGaN transition layer below the drift region improves current distribution, reduces current pooling, and lowers on-resistance. Furthermore, the high concentration of 2DEG in the superlattice structure, directly connected to the cathode, facilitates better ohmic contact formation and reduces ohmic contact resistance. The quasi-vertical AlGaN Schottky diode provided by this invention, compared to traditional quasi-vertical GaN Schottky diodes, utilizes AlGaN material instead of GaN material, resulting in higher breakdown voltage and better high-temperature characteristics.

[0031] Please see Figure 3 , Figure 3 This is a schematic flowchart illustrating a fabrication method for a quasi-vertical AlGaN Schottky diode according to an embodiment of the present invention. Based on the above structural embodiment, the present invention provides a fabrication method for a quasi-vertical AlGaN Schottky diode, comprising:

[0032] S1. Provide a substrate 1, and deposit AlN on the substrate to form a buffer layer 2.

[0033] Specifically, the step can include:

[0034] The substrate 1 is provided, and the substrate is soaked in HF acid solution for 1 min, and then sequentially soaked in acetone solution, anhydrous ethanol solution and deionized water for ultrasonic cleaning for 10 min respectively to eliminate surface dangling bonds. The cleaned and dried substrate is subjected to heat treatment at a temperature of 1050°C in an H2 atmosphere reaction chamber for 10 min to remove surface contaminants. A 500 nm-2000 nm AlN buffer layer 2 is deposited and grown by using a MOCVD process.

[0035] S2, depositing AlGaN on the buffer layer 2 to form a transition layer 3.

[0036] Specifically, the step can include:

[0037] On the buffer layer 2, a 300 nm-1000 nm AlGaN transition layer 3 is deposited by using a MOCVD process.

[0038] S3, depositing a superlattice layer 4 on the transition layer 3, wherein the superlattice layer 4 is a periodic structure formed by alternating growth of AlN and GaN, or a periodic structure formed by alternating growth of AlGaN and GaN; specifically, the step can include:

[0039] On the transition layer 3, a superlattice layer 4 with a thickness of 10 nm-100 nm is deposited on the GaN buffer layer 2 by using a MOCVD process. One way of deposition is multilayer alternating deposition of AlN and GaN; another way is multilayer alternating deposition of AlGaN and GaN.

[0040] S4, depositing AlGaN on the superlattice layer 4 to form a drift layer 5.

[0041] Specifically, the step can include:

[0042] On the superlattice layer 4, an AlGaN drift layer 5 is deposited by using a MOCVD process. The AlGaN drift layer 5 is a lightly doped AlGaN drift layer, and the lightly doped AlGaN drift layer is N-type doping with a doping concentration of 1×10 16 cm -3 ~ 9×10 16 cm -3 .

[0043] S5, etching the drift layer outside the AlGaN drift layer 5 to expose the superlattice layer 4.

[0044] Specifically, the step can include:

[0045] Etching the remaining drift layer outside the last remaining AlGaN drift layer 5 to expose the superlattice layer 4, so as to facilitate the fabrication of an electrode on the superlattice layer in the next step.

[0046] S6, depositing metal Ti / Al / Ni / Au on the exposed superlattice layer 4 to form a cathode 6.

[0047] Specifically, the step can include:

[0048] Making a mask on the AlGaN layer 5 to form an ohmic window, and placing the sample into an E-Beam electron beam evaporation device to deposit the cathode 6 by using an electron beam evaporation process, wherein the Ti / Al / Ni / Au metal is used as the cathode 6 to form an ohmic contact.

[0049] S7, depositing metal Ni / Au on the AlGaN drift layer 5 to form an anode 7.

[0050] Specifically, the step can include:

[0051] Making a mask on the superlattice layer 4 to form a Schottky window, and placing the sample for forming a gate window into an electron beam evaporation reaction chamber to deposit the metal Ni / Au as the anode 7 by using an electron beam evaporation process to form a Schottky contact.

[0052] The preparation method of the AlGaN Schottky diode with a quasi-vertical structure provided by the embodiment of the present application uses AlGaN material instead of the conventional GaN material of a quasi-vertical diode as a drift layer, and introduces a superlattice structure, wherein the superlattice layer and an AlGaN transition layer together form a new AlGaN system to replace the transmission layer of the conventional quasi-vertical SBD, and the quasi-vertical structure AlGaN Schottky diode prepared in this way has a higher breakdown voltage; and due to the introduction of the superlattice structure, a plurality of 2DEG channels with very high concentration are formed, and the superlattice layer with the 2DEG channels with very high concentration is directly connected with the cathode, so that an ohmic contact can be better formed to reduce the ohmic contact resistance. In addition, the system formed by the superlattice structure and the AlGaN transition layer under the drift region replaces the original high-doped transmission layer, which can better improve the current distribution and reduce the current crowding effect, and can reduce the on-resistance.

[0053] In summary, the AlGaN quasi-vertical Schottky diode based on a superlattice structure and the preparation method thereof provided by the present application have a higher breakdown voltage, a lower on-resistance and a higher current density compared with the conventional quasi-vertical structure GaN Schottky diode.

[0054] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or replacements can be made without departing from the concept of the present application, and all of these should be regarded as falling within the protection scope of the present application.

Claims

1. A quasi-vertical structure AlGaN Schottky diode, characterized in that, From bottom to top, the structure comprises a substrate, a buffer layer, an AlGaN transition layer, a superlattice layer and an AlGaN drift layer, and an anode is arranged on the upper surface of the AlGaN drift layer, and a cathode is arranged on the upper surface of the superlattice layer exposed after part of the AlGaN drift layer is etched off; wherein the superlattice layer is a periodic structure formed by alternately growing AlN and GaN, or a periodic structure formed by alternately growing AlGaN and GaN, so as to form a high-concentration 2DEG channel; wherein the superlattice layer forms a 2DEG conductor together with the AlGaN transition layer to form a transmission layer, for improving current distribution and reducing current crowding effect; the total thickness of the superlattice layer is 10-100 nm.

2. The quasi-vertical AlGaN Schottky diode of claim 1, wherein, The substrate is any one of sapphire, SiC, Si and GaN.

3. The AlGaN Schottky diode of claim 1, wherein the AlGaN Schottky diode is a vertical structure AlGaN Schottky diode. The buffer layer is AlN, and the thickness is 500-2000 nm.

4. The quasi-vertical AlGaN Schottky diode of claim 1, wherein, The thickness of the AlGaN transition layer is 300-1000 nm.

5. The quasi-vertical AlGaN Schottky diode of claim 1, wherein, The AlGaN drift layer is a lightly doped AlGaN drift layer, and the lightly doped AlGaN drift layer is N-type doping with a doping concentration of 1x10 16 cm -3 ~9x10 16 cm -3 .

6. The quasi-vertical AlGaN Schottky diode of claim 1, wherein, The cathode adopts a metal combination of Ti / Al / Ni / Au or Ti / Al / Pt / Au to form an ohmic contact.

7. The quasi-vertical AlGaN Schottky diode of claim 1, wherein, The anode adopts Ni / Au to form a Schottky contact.

8. A method for fabricating a quasi-vertical AlGaN Schottky diode, characterized in that, The structure comprises: a substrate is provided, and AlN is deposited on the substrate to form a buffer layer; an AlGaN transition layer is deposited on the buffer layer; a superlattice layer is deposited on the AlGaN transition layer, wherein the superlattice layer is a periodic structure formed by alternately growing AlN and GaN, or a periodic structure formed by alternately growing AlGaN and GaN; wherein the superlattice layer forms a 2DEG conductor together with the AlGaN transition layer to form a transmission layer, for improving current distribution and reducing current crowding effect; the total thickness of the superlattice layer is 10-100 nm; an AlGaN drift layer is deposited on the superlattice layer; the drift layer outside the AlGaN drift layer is etched to expose the superlattice layer; metal Ti / Al / Ni / Au is deposited on the exposed superlattice layer to form a cathode; metal Ni / Au is deposited on the AlGaN drift layer to form an anode.

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