Gate structure dependent normally-off AlGaN/GaN heterostructure field-effect transistors with p-GaN cap layer

In this study, the influences of a p-GaN gate structure on normally-off AlGaN/GaN heterostructure field-effect transistors were evaluated. It is demonstrated that a metal-insulator-semiconductor (MIS) gate structure can effectively suppress the gate leakage current and shift the threshold voltage positively, as compared with the Schottky and ohmic gate structures. To further improve the device performance, a novel gate-first MIS gate structure was proposed by combining the self-alignment gate and low-temperature ohmic. Good ohmic contact with a contact resistance of 1.45 Ω mm was achieved after annealing at 500 °C. For the self-aligned gate structure, a threshold voltage of 2.5 V, gate swing of 16 V, and drain current density of 50 mA mm⁻¹ were observed. Besides, the gate leakage current was reduced to a very low level in both positive and negative bias regions. (paper)