P-GaN/AlGaN/AlN/GaN enhancement-mode field effect transistor

1. A nitride based enhancement mode High Electron Mobility Transistor (HEMT), comprising:

(a) a III-nitride channel layer having a channel potential energy for containing a two dimensional electron gas (2DEG), wherein the 2DEG has a resistance;

(b) a III-nitride barrier layer positioned for, and having a barrier potential energy for, confining the 2DEG in the channel layer, wherein a polarization coefficient of the barrier layer is larger than a polarization coefficient of the channel layer;

(c) a III-nitride interlayer between the barrier layer and the channel layer, wherein the III-nitride interlayer has a polarization coefficient higher than the polarization coefficient of the barrier layer;

(d) a source for supplying a current to the 2DEG;

(e) a drain for supplying an output current, wherein the current flows from the source, through the 2DEG and then to the drain to produce the output current;

(f) a gate for controlling the current's flow through the 2DEG; and

(g) a p-type III-nitride layer between the III-nitride barrier layer and the gate for depleting the 2DEG under the gate at zero bias.

2. The HEMT of claim 1 , further comprising a thickness and material composition of the III-nitride barrier layer, wherein the thickness and the material composition is selected to obtain a desired threshold voltage of the HEMT.

3. The HEMT of claim 2 , further comprising a thickness of the p-type III-nitride layer, wherein the thickness of the p-type III-nitride layer is selected to obtain a turn-on voltage of the gate of 3 V or greater.

4. The HEMT of claim 2 , wherein the thickness of the III-nitride barrier layer does not substantially reduce an on-resistance of the HEMT or resistance of the 2DEG.

5. The HEMT of claim 2 , wherein the thickness and the material composition of the III-nitride barrier is selected to obtain the threshold voltage of at least 1V and a charge density of the 2DEG in excess of 7×10 12 cm −2 or a current density in the 2DEG is in excess of 0.3 A/mm.

6. The HEMT of claim 2 , further comprising:

(a) a first access region between the source and the gate and a second access region between the drain and the gate, wherein the p-type III-nitride layer is not present under the source, drain, first access region and second access region; and

(b) the thickness of the III-nitride barrier layer which is smaller than a thickness of the III-nitride barrier layer in a HEMT without the III-nitride interlayer.

7. The HEMT of claim 2 , wherein the III-nitride barrier layer is AlGaN, the material composition is an Al content, and the III-nitride interlayer is AlN.

8. The HEMT of claim 7 , wherein a thickness of the AlN is thin enough such that the AlN is not relaxed but is strained, due to a lattice mismatch with the barrier layer and the channel layer, or is less than 20 nm.

9. The HEMT of claim 2 , wherein the III-nitride interlayer interfaces the III-nitride barrier layer and the III-nitride channel layer.

10. The HEMT of claim 2 , wherein the channel layer is GaN and the p-type III-nitride layer is GaN.