Performance evaluation of Cascode GaN HEMT

GaN devices are rapidly replacing silicon based MOSFETs and IGBTs in industry due to its high switching speed, lower conduction loss and no reverse recovery phenomenon. One of undesirable characteristics of GaN devices is temporary increase in on-resistance known as dynamic Rdson caused by electron trapping in surface traps in the gate-to-drain access region and in buffer traps beneath the two-dimensional electron gas (2DEG) channel. Depletion mode GaN which are “normally on” devices are easier to fabricate and have better performance compared to enhancement mode devices. To make depletion mode a normally off device, a Cascode structure with low voltage FET is introduced. However, Cascode GaN devices have limited reverse switching current due to electron trapping phenomenon which in turn increases dynamic Rdson. Performance of Cascode GaN HEMT for different rate of current change di/dt has been evaluated and a solution has been proposed to increase reverse di/dt and thus maximum switching current capability.