Influence of layer structure on performance of AlGaN/GaN high electron mobility transistors before and after passivation

Intentionally undoped and three different, doped layer structures are used to investigate properties of AlGaN/GaN high electron mobility transistors (HEMTs) before and after SiN passivation. For unpassivated devices, the drain current, transconductance, cutoff frequency, and microwave output-power increase with increased doping level, in spite of an increase in the gate-leakage current. After passivation, an overall performance improvement of all devices occurs. The passivation-induced sheet charge decreases from 2 X 10(12) cm(-2) in undoped structures to similar to0.7 X 10(12) cm(-2) in higher doped structures and performance improvement with passivation is less pronounced for higher doped devices. However, the output power of unpassivated and passivated devices on higher doped structures is much higher than that on the undoped-passivated counterpart. These results underline an advantage of the doped layer structure for the preparation of high-performance AlGaN/GaN HEMTs.