Gate control, surface leakage currents, and peripheral charging in AlGaN/GaN heterostructure field effect transistors having nanometer-scale Schottky gates

Gate control properties together with gate leakage currents in AlGaN/GaN heterostructure field effect transistors (HFETs) with nanometer-scale Schottky gates were investigated, focusing on the effects of AlGaN surfaces at the gate periphery. Fabricated AlGaN/GaN HFETs showed unexpectedly small gate length (L-G) dependence of transconductance, g(m). Comparing the transfer characteristics from theory and experiment, effective L-G values in the fabricated devices were found to be much longer than the geometrical size on the order of 100 nm, indicating the formation of virtual gates. Detailed analysis of the gate leakage current behaviors based on a thin surface barrier model showed the presence of a strong electric field at the gate periphery. The mechanism of the virtual gate formation was discussed based on the obtained nanometer-scale Schottky gate behaviors.