Increase in breakdown voltage of AlGaN/GaN HEMTs with a high-k dielectric layer

A two-dimensional analysis of breakdown characteristics in AlGaN/GaN high-electron-mobility transistors (HEMTs) is performed by considering a deep donor and a deep acceptor in a buffer layer. The dependence of an off-state breakdown voltage on the relative permittivity of the passivation layer ε_r is studied. It is shown that as ε_r increases, the off-state breakdown voltage increases. This is because the electric field at the drain edge of the gate is weakened as ε_r increases. This occurs because in the insulator the applied voltage tends to drop uniformly in general, and hence when the insulator is attached to the semiconductor, the voltage drop along the semiconductor becomes smoother at the drain edge of the gate if ε_r of the insulator is higher and the effect of the insulator becomes more significant. It is concluded that AlGaN/GaN HEMTs with a high-k passivation layer should have high breakdown voltages.