Improvement of Breakdown Voltage in Quaternary in AlGaN HEMT with Different High-K Passivation Layer for Power Switching Applications

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 εr and the thickness of the passivation layer d are studied. It is shown that as εr increases, the OFF-state breakdown voltage increases. This is because the electric field at the drain edge of the gate is weakened as εr 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 εr 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. . It is well known that the introduction of a field plate enhances the power performance of AlGaN/GaN HEMTs because the socalled current collapse is reduced and the OFF-state breakdown voltage is increased. This increase in the OFF-state breakdown voltage occurs because the field plate reduces the electric field at the drain edge of the gate. However, the introduction of the field plate increases the parasitic capacitance and may degrade the high-frequency performance.