A semi-analytical, two-dimensional model for AlGaN/GaN high-electron-mobility-transistor Schottky currents at high reverse voltages

A semi-analytical model is derived for the reverse Schottky gate current in AlGaN-GaN high-electron-mobility-transistors (HEMTs) in off-state at high drain voltage. At elevated drain voltages, the depletion of the two-dimensional electron gas (2-DEG) not only exists directly underneath the gate contact but also extends from the gate towards the drain. This increases the electric fields at the gate edge on the drain side, which causes an increase in the gate leakage current. In this paper, a new method is proposed to calculate the electric fields at the gate edge using conformal mapping of the charge configuration in the device. This method also allows calculation of the influence of charges trapped at the interface between the semiconductor and the passivation layer next to the gate. It is shown that direct tunneling is the dominant current mechanism at high drain voltages, such that the current becomes insensitive to temperature variation. Interface charges next to the gate exert a large influence on the high voltage leakage current. It is argued that temperature variations of the high voltage leakage current are caused by temperature dependent changes in trapped charge