Trapping mechanisms in insulated‐gate GaN power devices: Understanding and characterization techniques

Abstract

In addition to surface‐ and buffer‐trapping, interface/border trapping and the consequent VTH shift in insulated‐gate GaN power transistors could also cause RON increase, due to the reduced gate overdrive. This work reports on a systematic study of the trapping mechanisms in normally‐on/off insulated‐gate GaN transistors subjected to dynamic (AC) and static (DC) gate stress. The fast dynamic characterizations featuring an ultrashort measurement delay of 10−7 s minimize the recovery during measurement and enable a quantitative evaluation of VTH shift‐induced RON increase. By analyzing the time‐resolved instability in normally‐on MIS‐HEMT and normally‐off MIS‐FET with fully recessed barrier, we elucidate several key mechanisms including: (i) recessing the polarized III‐nitride barrier layer can suppress VTH shift during ON/OFF switching; (ii) AC stress, which has more practical implication for lifetime projection for power switching applications, produces smaller VTH shift and RON increase comparing to DC stress; (iii) Sufficient gate overdrive at ON state and lower channel resistance in normally‐on MIS‐HEMT allow a better tolerance to VTH shift.Primary trapping effects in an insulated‐gate GaN power transistor.