The pinch-off behaviour and charge distribution in AlGaN-GaN-AlGaN-GaN double heterostructure field effect transistors

Al x Ga 1-x N/GaN,/Al y Ga 1-y N./GaN double heterojunction field effect transistors with bottom Al y Ga 1-y N barrier widths between 100 and 2000 A 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 Al 2 O 3 . 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-Schrodinger 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.