Threshold voltage controlled by gate area and gate recess in inverted trapezoidal trigate AlGaN/GaN MOS high-electron-mobility transistors with photoenhanced chemical and plasma-enhanced atomic layer deposition oxides

Abstract

An enhancement-mode AlGaN/GaN inverted-trapezoid trigate MOS high-electron-mobility transistor (HEMT), featuring double-layer oxides formed by photoenhanced chemical oxidation and plasma-enhanced atomic layer deposition (PEALD) oxide deposition, was shown to support the threshold voltage (Vth) with linear slopes of 0.36 V/nm and −0.32 V/µm2 scaled with recess depth and device area, respectively. The proposed device exhibited Vth of 1.2 V, current on/off ratio of 108, and fT/fmax of 9/36 GHz at a gate length/width of 250/360 nm. These observations can be ascribed to the combined effects of (a) an interfacial negative space charge of 3.2 µC/cm2 in the gate-recessed device that partially compensates for the spontaneous charge and (b) side-wall passivation that preserves the high-mobility channel.