Structure of a pHEMT transistor capable of nanosecond switching
View Patent ↗A method for fabricating a transistor and the resulting transistor is disclosed. The method generally includes steps (A) to (E). Step (A) may form a high mobility layer. The high mobility layer is generally configured to carry a two-dimensional electron gas. Step (B) may form a planar layer on the high mobility layer. Step (C) may form a barrier layer on the planar layer. Step (D) may form a doped layer on the barrier layer. The doped layer is generally a low bandgap III-V semiconductor. Step (E) may form a gate in contact with the doped layer. The gate may be separated from both a source and a drain by corresponding ungated recess regions. The high mobility layer, the planar layer, the barrier layer, the doped layer, the source, the gate and the drain are generally configured as a pseudomorphic high electron mobility transistor.
1. A method for fabricating a transistor, comprising the steps of:
(A) forming a high mobility layer, wherein said high mobility layer is configured to carry a two-dimensional electron gas;
(B) forming a planar layer in contact with said high mobility layer, wherein said planar layer has a uniform composition;
(C) forming a barrier layer in contact with said planar layer;
(D) forming a doped layer in contact with said barrier layer, said doped layer (i) comprising a low bandgap III-V semiconductor and (ii) having a first surface that is doped;
(E) forming a source and a drain in contact with said first surface of said doped layer; and
(F) forming a gate in contact with said first surface of said doped layer, wherein (i) said gate is separated from both said source and said drain by corresponding ungated recess regions on said first surface of said doped layer and (ii) said high mobility layer, said planar layer, said barrier layer, said doped layer, said source, said gate and said drain are configured as a pseudomorphic high electron mobility transistor.
2. The method according to claim 1 , wherein said doped layer has a dopant which establishes an on resistance that conducts (i) ungated surface charges in said ungated recess regions and (ii) channel charges adjacent a depletion region proximate said gate such that a gate lag time is less than 110 nanoseconds.
3. The method according to claim 2 , wherein said gate lag time comprises a delay between at least one of (i) a rise from 90% to 98% of a radio frequency envelope and (ii) a fall from 10% to 2% of said radio frequency envelope.
4. The method according to claim 1 , further comprising the step of:
forming at least one semiconductor layer in contact with said doped layer, wherein said source and said drain are formed in said semiconductor layer.
5. The method according to claim 4 , further comprising the step of:
etching said semiconductor layer to form a channel recess, wherein said gate is disposed in said channel recess.
6. The method according to claim 1 , further comprising the steps of:
cleaning said first surface of said doped layer in said ungated recess regions after said forming of said gate; and
forming a passivation layer in contact with said first surface of said doped layer in said ungated recess regions after said cleaning.
7. The method according to claim 1 , wherein said gate is formed as a T-shaped gate.
8. The method according to claim 1 , wherein said doped layer comprises an n-type InGaP layer.
9. The method according to claim 1 , wherein said doped layer ranges from approximately 30 to 60 angstroms thick.
10. The method according to claim 1 , wherein said doped layer comprises a concentration of at least 5×10 16 donors per cm 3 .
11. An apparatus comprising:
a high mobility layer, wherein said high mobility layer is configured to carry a two-dimensional electron gas;
a planar layer formed in contact with said high mobility layer, wherein said planar layer has a uniform composition;
a barrier layer formed in contact with said planar layer;
a doped layer formed in contact with said barrier layer, said doped layer (i) comprising a low bandgap III-V semiconductor and (ii) having a first surface that is doped;
a source formed in contact with said first surface of said doped layer;
a drain formed in contact with said first surface of said doped layer; and
a gate formed in contact with said first surface of said doped layer, wherein (i) said gate is separated from both said source and said drain by corresponding ungated recess regions on said first surface of said doped layer and (ii) said high mobility layer, said planar layer, said barrier layer, said doped layer, said source, said gate and said drain are configured as a pseudomorphic high electron mobility transistor.
12. The apparatus according to claim 11 , wherein said doped layer has a dopant which establishes an on resistance that conducts (i) ungated surface charges in said ungated recess regions and (ii) channel charges adjacent a depletion region proximate said gate such that a gate lag time is less than 110 nanoseconds.
13. The apparatus according to claim 12 , wherein said gate lag time comprises a delay between at least one of (i) a rise from 90% to 98% of a radio frequency envelope and (ii) a fall from 10% to 2% of said radio frequency envelope.
14. The apparatus according to claim 11 , further comprising at least one semiconductor layer formed in contact with said doped layer, wherein said source and said drain are formed in said semiconductor layer.
15. The apparatus according to claim 14 , further comprising a channel recess formed in said semiconductor layer, wherein said gate is disposed in said channel recess.
16. The apparatus according to claim 11 , further comprising a passivation layer formed in contact with said first surface of said doped layer in said ungated recess regions.
17. The apparatus according to claim 11 , wherein said gate is formed as a T-shaped gate.
18. The apparatus according to claim 11 , wherein said doped layer comprises an n-type InGaP layer.
19. The apparatus according to claim 11 , wherein said doped layer ranges from approximately 30 to 60 angstroms thick.
20. An apparatus fabricated in accordance with the method of claim 1 .