Piezoelectric enhancement of Schottky barrier heights in GaN-AlGaN HFET structures

We describe here the design, experimental characterisation, and analysis of GaN-Al/sub x/Ga/sub 1-x/N HFET structures in which the piezoelectric effect is employed to achieve a marked enhancement of the effective Schottky barrier height. Specifically, a two-layer GaN-Al/sub x/Ga/sub 1-x/N barrier is employed, within which the piezoelectrically induced polarization charge acts to increase the electrostatic potential, and consequently the barrier height for gate leakage current in the HFET. This can be accomplished with no increase in barrier thickness, and consequently little if any change in gate capacitance, and with only a minor impact on carrier concentration in the channel. It is anticipated that this will allow gate currents to be significantly reduced in nitride HFETs with little if any penalty exacted in terms of channel conductance, transconductance, and other device properties.