Structure of a high electron mobility transistor
An improved structure of the high electron mobility transistor (HEMT) and a fabrication method thereof are disclosed. The improved HEMT structure comprises a substrate, a channel layer, a spacing layer, a carrier supply layer, a Schottky layer, a first etch stop layer, a first n type doped layer formed by Al x Ga 1-x As, and a second n type doped layer. The fabrication method comprises steps of: etching a gate, a drain, and a source recess by using a multiple selective etching process. Below the gate, the drain, and the source recess is the Schottky layer. A gate electrode is deposited in the gate recess to form Schottky contact. A drain electrode and a source electrode are deposited to form ohmic contacts in the drain recess and the source recess respectively, and on the second n type doped layer surrounding the drain recess and the source recess respectively.
1. A high electron mobility transistor (HEMT) comprising sequentially:
a substrate;
a channel layer positioned above said substrate;
a spacing layer positioned above said channel layer;
a carrier supply layer positioned above said spacing layer;
a Schottky layer positioned above said carrier supply;
a first etch stop layer positioned above said Schottky layer;
a first n type doped layer positioned above said first etch stop layer, which is formed of Al x Ga 1-x As;
a second n type doped layer positioned above said first n type doped layer;
a gate recess formed by using a multiple selective etching process which is terminated at said Schottky layer;
a drain recess positioned at one end of said gate recess, which is formed by using a multiple selective etching process which is terminated at said Schottky layer;
a source recess positioned at the other end of said gate recess, which is formed by using a multiple selective etching process which is terminated at said Schottky layer;
a gate electrode positioned in said gate recess and formed Schottky contact to said Schottky layer;
a drain electrode positioned in said drain recess and said second n type doped layer surrounding said drain recess, which forms ohmic contact to said second n type doped layer and said Schottky layer; and
a source electrode positioned in said source recess and said second n type doped layer surrounding said source recess, which forms ohmic contact to said second n type doped layer and said Schottky layer.
2. The structure of HEMT according to claim 1 , wherein the material used for said first n type doped layer is Al x Ga 1-x As with an Al content, x, larger than 0.0 and smaller than 0.5, and the thickness of said first n type doped layer is larger than 0 and smaller than 100 nm.
3. The structure of HEMT according to claim 1 , wherein said drain recess is formed by three recesses, including sequentially:
a first drain recess, forming in said second n type doped layer;
a second drain recess, forming in said first etch stop layer;
a third drain recess, forming in said first n type doped layer,
wherein said first drain recess is larger than, equal to, or smaller than said third drain recess.
4. The structure of HEMT according to claim 1 , wherein said source recess is formed by three recesses, including sequentially:
a first source recess, forming in said second n type doped layer;
a second source recess, forming in said first etch stop layer;
a third source recess, forming in said first n type doped layer,
wherein said first drain recess is larger than, equal to, or smaller than said third drain recess.
5. The structure of HEMT according to claim 1 , wherein said drain electrode forms ohmic contact to said first n type doped layer and forms ohmic contact to said second n type doped layer in the meantime.
6. The structure of HEMT according to claim 1 , wherein said source electrode forms ohmic contact to said first n type doped layer and forms ohmic contact to said second n type doped layer in the meantime.
7. The structure of HEMT according to claim 1 , wherein a second etch stop layer is inserted between said first n type doped layer and said second n type doped layer.
8. The structure of HEMT according to claim 7 , wherein said second etch stop layer is formed of AlAs or InGaP.
9. The structure of HEMT according to claim 1 , wherein said second n type doped layer is formed of GaAs, and the thickness of said second n type doped layer is larger than 0 and smaller than 100 nm.
10. The structure of HEMT according to claim 1 , wherein said etching process is dry etching or wet etching.
11. The structure of HEMT according to claim 1 , wherein said first etch stop layer is formed of AlAs or InGaP.
12. The structure of HEMT according to claim 1 , wherein said Schottky layer is formed of Al x Ga 1-x As with an Al content, x, larger than 0.0 and smaller than 0.6, and the thickness of said Schottky layer is larger than 0 and smaller than 100 nm.
13. A high electron mobility transistor (HEMT) comprises sequentially:
a substrate;
a channel layer positioned above said substrate;
a spacing layer positioned above said channel layer;
a carrier supply layer positioned above said spacing layer;
a Schottky layer positioned above said carrier supply;
a first etch stop layer positioned above said Schottky layer;
a first n type doped layer positioned above said first etch stop layer;
a second n type doped layer positioned above said first n type doped layer;
a gate recess formed by using a multiple selective etching process and terminated the etching process at said Schottky layer;
a drain recess positioned at one end of said gate recess, which is formed by using a multiple selective etching process which is terminated at said Schottky layer, wherein the drain recess formed in the second n type doped layer is larger than the drain recess formed in the first n type doped layer;
a source recess positioned at the other end of said gate recess, which is formed by using a multiple selective etching process which is terminated at said Schottky layer, wherein the source recess formed in the second n type doped layer is larger than the source recess formed in the first n type doped layer;
a gate electrode positioned in said gate recess and formed Schottky contact to said Schottky layer;
a drain electrode positioned in said drain recess and said second n type doped layer surrounding said drain recess, which forms ohmic contact to said second n type doped layer and said Schottky layer; and
a source electrode positioned in said source recess and said second n type doped layer surrounding said source recess, which forms ohmic contact to said second n type doped layer and said Schottky layer.
14. The structure of HEMT according to claim 13 , wherein the material used for said first n type doped layer is GaAs, Al x Ga 1-x As, In x Al 1-x As, In x Ga 1-x As, or InAlGaAs, with an Al content x in Al x Ga 1-x As larger than 0.0 and smaller than 0.5, with an In content x in In x Al 1-x As larger than 0.0 and smaller than 0.5, with an In content x in In x Ga 1-x As larger than 0.0 and smaller than 0.5, and the thickness of said first n type doped layer is larger than 0 and smaller than 100 nm.
15. The structure of HEMT according to claim 13 , wherein the material used for said second n type doped layer is GaAs, Al x Ga 1-x As, In x Ga 1-x As, or InAlGaAs, with an Al content x in Al x Ga 1-x As larger than 0.0 and smaller than 0.5, with an In content x in In x Al 1-x As larger than 0.0 and smaller than 0.5, with an In content x in In x Ga 1-x As larger than 0.0 and smaller than 0.5, and the thickness of said second n type doped layer is larger than 0 and smaller than 100 nm.
16. The structure of HEMT according to claim 13 , wherein said drain electrode forms ohmic contact to said first n type doped layer and forms ohmic contact to said second n type doped layer in the meantime.
17. The structure of HEMT according to claim 13 , wherein said source electrode forms ohmic contact to said first n type doped layer and forms ohmic contact to said second n type doped layer in the meantime.
18. The structure of HEMT according to claim 13 , wherein a second etch stop layer is inserted between said first n type doped layer and said second n type doped layer.
19. The structure of HEMT according to claim 18 , wherein said second etch stop layer is formed of AlAs or InGaP.
20. The structure of HEMT according to claim 13 , wherein said etching process is dry etching or wet etching.
21. The structure of HEMT according to claim 13 , wherein said first etch stop layer is formed of AlAs or InGaP.
22. The structure of HEMT according to claim 13 , wherein said Schottky layer is formed of Al x Ga 1-x As with an Al content, x, larger than 0.0 and smaller than 0.6, and the thickness of said Schottky layer is larger than 0 and smaller than 100 nm.