Scaling of current collapse in GaN/AlGaN HEMT for microwave power applications

This study reports the scaling of current collapse in GaN/AlGaN HEMTs with respect to the un-passivated gate drain distance on the gate edge. The source drain current reduction increased from 4mA to 28mA, when un-passivated gap increased from 200nm to 600nm respectively. This reduction in current is mainly due to virtual gate formation at gate edge as a result of applied large reverse bias between the gate and drain electrodes. The length of virtual gate is a function of un-passivated gap and results in variable current reduction due to variation in available traps with gap. Similarly knee voltage shifted from 0.5 V to 1.2 V when gap is increased from 200nm to 600nm respectively. This is due to increase in device on resistance (Ron) due to electron trapping in the un-passivated gap. This current collapse resulted in reduction of device saturated RF power to 1.2W/mm at 2.2GHz for HEMT with an un-passivated gap of 600nm.