Impact of layer structure on performance of unpassivated AlGaN/GaN HEMT

Improvement in AlGaN/GaN HEMT performance by using modulation doping and a thin GaN cap layer is described. Modulation doping (Si, 5×1018 cm−3) leads to ∼30% increase of the channel conductivity and a 3 nm thick undoped GaN cap layer reduced the gate leakage current in nearly two orders of the magnitude compared to conventionally used intentionally undoped AlGaN/GaN layer structure. The devices on doped GaN/AlGaN/GaN structure show improved DC and RF performance. The peak output power density of 7.7 W/mm at 7 GHz is obtained for unpassivated devices on optimized i.e. doped GaN/AlGaN/GaN structure, which is about twice of that resulting for devices on undoped AlGaN/GaN structure.