Investigation of post-annealing effects for normally-off GaN metal-oxide semiconductor heterojunction field-effect transistors with thin AlN barrier layer

The effects of post-annealing processes for normally-off GaN metal-oxide semiconductor heterojunction field-effect transistors (MOS-HFETs) with a thin AlN barrier layer are investigated. These annealing processes are post-deposition annealing (PDA) after oxide deposition, post-metallization annealing (PMA) after gate metallization, and positive-bias annealing (PBA) after wafer processes. PMA and PBA are effective in enhancing the drain current density and threshold voltage shift. The most effective method is PBA and the obtained threshold voltage and drain current density are +3.0 V and 0.7 A mm, respectively. This is attributed to improvements in interfacial trap states which is confirmed by an investigation of the frequency dependence of capacitance-voltage characteristics.