Time-dependent characteristics and physical mechanisms of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors under different bias conditions

We experimentally investigate the time-dependent degradation of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors subjected to different bias conditions. By means of the combined performance under OFF/SEMI-ON/ON state bias conditions, the dependence of threshold voltage (V-th), maximum transconductance (g(m)) and saturation drain current (I-dsat) on stress mode are revealed. In the OFF-state, with the high temperature reverse bias stress, the main mechanism is the charge-trapping in the gate dielectric layer, leading to the recoverable negative shift of the V-th. In the SEMI-ON-state, because of the hot-carrier injection, the hot electrons could break the Si-H bonds, resulting in the generation of interface states and can also be captured by the trap states in the AlGaN barrier or GaN buffer. This effect will cause the decrease of saturation drain current and an unrecoverable V-th negative shift. In the ON-state, due to the attenuation of hot electrons effect, V-th hardly changes, while I-dsat has a dramatic decrease caused by the self-heating effect. Low frequency noise characteristics were used to extract the defect state density, which then increases by about three orders of magnitude after SEMI-ON-state stress.