Graphene capped HEMT device
A graphene capped HEMT device and a method of fabricating same are disclosed. The graphene capped HEMT device includes one or more graphene caps that enhance device performance and/or reliability of an exemplary AlGaN/GaN heterostructure transistor used in high-frequency, high-energy applications, e.g., wireless telecommunications. The HEMT device disclosed makes use of the extraordinary material properties of graphene. One of the graphene caps acts as a heat sink underneath the transistor, while the other graphene cap stabilizes the source, drain, and gate regions of the transistor to prevent cracking during high-power operation. A process flow is disclosed for replacing a three-layer film stack, previously used to prevent cracking, with a one-atom thick layer of graphene, without otherwise degrading device performance. In addition, the HEMT device disclosed includes a hexagonal boron nitride adhesion layer to facilitate deposition of the compound nitride semiconductors onto the graphene.
1. A high electron mobility transistor (HEMT), comprising:
a substrate;
a heterostructure formed by top and bottom compound semiconductor layers sequentially deposited over the substrate;
a first graphene layer formed below the bottom compound semiconductor layer;
a second graphene layer formed above the top compound semiconductor layer;
source and drain contacts electrically coupled to the top compound semiconductor layer; and
a metal gate that modifies energy bands within the heterostructure in response to a voltage applied to the gate.
2. The HEMT of claim 1 , further comprising one or more adhesion layers in contact with the first or second graphene layers.
3. The HEMT of claim 2 wherein one or more of the adhesion layers includes hexagonal boron nitride.
4. The HEMT of claim 2 wherein one of the adhesion layers serves as a gate dielectric.
5. The HEMT of claim 1 wherein the substrate includes silicon covered with silicon dioxide.
6. The HEMT of claim 1 wherein the substrate includes silicon covered with silicon carbide.
7. The HEMT of claim 1 wherein the heterostructure includes one or more of GaN, AN, InP, AlGaN, GaAs, AlGaAs, InGaN, InGaP, InAlAs, InGaAs, AlGaSb, AlSb, or InAs.
8. The HEMT of claim 1 wherein the metal gate includes one or more of Ni, Ti, Pt, Al, Au, Cu, Ag, W, or combinations thereof.
9. The HEMT of claim 1 wherein the metal gate includes a liner material made of titanium or titanium nitride (TiN).
10. The HEMT of claim 1 wherein a switching speed of the HEMT exceeds 200 GHz.