Effects of gate recess depth on pulsed I-V characteristics of AlGaN/GaN HFETs

This paper reports pulsed I-V characteristics of AlGaN/GaN HFETs fabricated with gate regions recessed into the AlGaN barrier layer with different recess geometries. Pulsed I-V characteristics are known to correlate with rf ouput power measurements vs bias, and are an important estimator of "knee voltage walkout" and "current slump" effects in the nitride HFETs. Our measurements indicate that the knee voltage walkout is strongly dependent on the depth of the recessed region, and that the walkout is minimized in devices with shallower recess depth. The results strongly support the model that current slump is due to surface traps. An effective trap time constant of 10 μsec is extracted for these devices.