Numerical Analysis of Breakdown Voltage Enhancement in AlGaN/GaN HEMTs With a High- $k$ Passivation Layer

2-D 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 the OFF-state breakdown voltage on the relative permittivity of the passivation layer ε_r and the thickness of the passivation layer d are 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 the ε_r of the insulator is higher. It is also shown that the OFF-state breakdown voltage increases as d increases because the electric field at the drain edge of the gate is weakened as d increases. It is concluded that AlGaN/GaN HEMTs with a high- k and thick passivation layer should have high breakdown voltages.