Mechanism of radio-frequency current collapse in GaN-AlGaN field-effect transistors

The mechanism of radio-frequency current collapse in GaN-AlGaN heterojunction field-effect transistors (HFETs) was investigated using a comparative study of HFET and metal-oxide-semiconductor HFET current-voltage (I-V) and transfer characteristics under dc and short-pulsed voltage biasing. Significant current collapse occurs when the gate voltage is pulsed, whereas under drain pulsing the I-V curves are close to those in steady-state conditions. Contrary to previous reports, we conclude that the transverse electric field across the wide-band-gap barrier layer separating the gate and the channel rather than the gate or surface leakage currents or high-field effects in the gate-drain spacing is responsible for the current collapse. We find that the microwave power degradation in GaN-AlGaN HFETs can be explained by the difference between dc and pulsed I-V characteristics. (C) 2001 American Institute of Physics.