High-voltage lateral GaN-on-silicon schottky diode with reduced junction leakage current
High-voltage, gallium-nitride Schottky diodes are described that are capable of withstanding reverse-bias voltages of up to and in excess of 2000 V with reverse current leakage as low as 0.4 microamp/millimeter. A Schottky diode may comprise a lateral geometry having an anode located between two cathodes, where the anode-to-cathode spacing can be less than about 20 microns. A diode may include at least one field plate connected to the anode that extends above and beyond the anode towards the cathodes.
1. A Schottky diode comprising:
a gallium-nitride conduction layer;
a barrier layer formed adjacent to the gallium-nitride conduction layer;
a first cathode and a second cathode spaced apart and formed in electrical contact with the gallium-nitride conduction layer, the first cathode and the second cathode being electrically connected to each other as a cathode of the Schottky diode;
an anode formed adjacent to the barrier layer between the first cathode and the second cathode; and
a gallium-oxide layer formed between the anode and the barrier layer and that extends under a center of the anode.
2. The Schottky diode of claim 1 , further comprising one or more anode-connected field plates electrically connected to the anode and extending on opposite edges beyond the anode toward the first cathode and the second cathode.
3. The Schottky diode of claim 2 , wherein the one or more anode-connected field plates comprise:
a first anode-connected field plate electrically connected to the anode and extending on opposite edges beyond the anode toward the first cathode and the second cathode by a first distance; and
a second anode-connected field plate electrically connected to the first anode-connected field plate and extending on opposite edges beyond the first anode-connected field plate toward the first cathode and the second cathode by a second distance.
4. The Schottky diode of claim 3 , wherein the second distance is less than the first distance.
5. The Schottky diode of claim 2 capable of withstanding a reverse-bias voltage of up to 1200 volts.
6. The Schottky diode of claim 2 capable of withstanding a reverse-bias voltage of up to 2000 volts.
7. The Schottky diode of claim 6 , wherein a reverse-bias current is between 0.4 microamp/millimeter and 40 microamp/millimeter at a reverse bias of 2000 volts.
8. The Schottky diode of claim 6 , wherein a thickness of the gallium-oxide layer is between approximately 1 nm and approximately 5 nm.
9. The Schottky diode of claim 2 , wherein the anode, first cathode, second cathode, and a first anode-connected field plate are formed of a same material.
10. The Schottky diode of claim 2 , wherein the anode comprises a multilayer composition selected from the following group: Ni/Pd/Au/Ti, Ni/Pt/Au/Ti, Ni/Ti/Al/W, Ni/W/Al/W, W/Al/W, Ni/Wn/Al/W, WN/AI/W, and Pt/Au/Ti.
11. The Schottky diode of claim 2 , wherein an anode-connected field plate of the one or more anode-connected field plates comprises a multilayer composition selected from the following group: Ti/Pt/Au, Al/Cu, or TiN/Cu.
12. The Schottky diode of claim 2 , further comprising an insulating layer having a thickness between approximately 100 nm and approximately 300 nm that is formed between a first extension of a first anode-connected field plate of the one or more anode-connected field plates and the barrier layer.
13. The Schottky diode of claim 12 , wherein the first extension of the first anode-connected field plate extends beyond an outer edge of the anode by at least one micron.
14. The Schottky diode of claim 12 , wherein the one or more anode-connected field plates includes a second anode-connected field plate having a second extension that extends beyond an outer edge of the first anode-connected field plate between approximately 1 micron and approximately 3 microns.
15. The Schottky diode of claim 14 , wherein an outer edge of the second extension is spaced horizontally from the first or second cathode by at least 3 microns.
16. The Schottky diode of claim 1 , further comprising a buffer layer formed on a substrate, wherein a combined thickness of the buffer layer and gallium-nitride conduction layer is at least 4.5 microns.
17. The Schottky diode of claim 16 , wherein the substrate comprises silicon.
18. The Schottky diode of claim 16 , wherein the barrier layer comprises aluminum gallium nitride having a thickness between approximately 10 nm and approximately 50 nm.
19. The Schottky diode of claim 16 , further comprising a gallium-nitride cap layer formed over the barrier layer.
20. The Schottky diode of claim 19 , wherein a thickness of the gallium-nitride cap layer is between approximately 1 nm and approximately 10 nm.
21. The Schottky diode of claim 16 , further comprising electrical isolation regions formed adjacent to the first and the second cathodes, wherein the electrical isolation regions comprise damaged crystalline semiconductor that includes one or more of the following implanted ion species: nitrogen, phosphorous, boron, and argon.
22. The Schottky diode of claim 1 , wherein a distance between an edge of the first or the second cathode and an edge of the anode is between approximately 5 microns and approximately 25 microns.
23. The Schottky diode of claim 1 , wherein a length of the anode is between approximately 2 microns and approximately 20 microns.
24. The Schottky diode of claim 1 , included in a power converter.
25. A method for making a Schottky diode, the method comprising:
forming a gallium-nitride conduction layer on a substrate;
forming a barrier layer adjacent to the gallium-nitride conduction layer;
forming a first cathode and a second cathode spaced apart and in electrical contact with the gallium-nitride conduction layer, the first cathode and the second cathode being electrically connected to each other as a cathode of the Schottky diode;
forming an anode adjacent to the barrier layer between the first cathode and the second cathode; and
forming a gallium-oxide layer between the anode and the barrier layer such that the gallium-oxide layer extends under a center of the anode.
26. The method of claim 25 , wherein forming the gallium-oxide layer comprises:
opening a via to expose a region of a gallium-nitride layer for the anode prior to forming the anode; and
subjecting the exposed region to an oxygen plasma for a period of time.
27. The method of claim 26 , wherein the period of time is between 10 seconds and approximately 120 seconds.
28. The method of claim 26 , further comprising maintaining a pressure during the oxygen plasma between approximately 0.5 Torr and approximately 3 Torr.
29. The method of claim 26 , further comprising forming a gallium-nitride cap layer between the barrier layer and the anode, wherein the gallium-oxide layer is formed from the gallium-nitride cap layer.
30. The method of claim 26 , further comprising forming one or more anode-connected field plates in electrical contact with the anode that extend beyond outer edges of the anode.