The Pinch-Off Behaviour and Charge Distribution in AlGaN-GaN-AlGaN-GaN Double Heterostructure Field Effect Transistors

Abstract

AlxGa1—xN/GaN/AlyGa1—yN/GaN double heterojunction field effect transistors with bottom AlyGa1—yN barrier widths between 100 and 2000 Å and Al contents of y = 0.15–0.3 were grown by radio-frequency molecular beam epitaxy on both n+ and high resistivity GaN buffers on Al2O3. The charge distribution and pinch-off behaviour of the double heterojunctions grown on the n+ GaN layers were investigated in detail by capacitance–voltage profiling in conjunction with self-consistent Poisson-Schrödinger calculations. The electron densities and pinch-off voltages, deduced from capacitance–voltage measurements of the Schottky diodes are in excellent agreement with the theoretical values. We discuss the role of doping on the 2DEG density.