Improvement of electrical characteristics in regrown AlGaN/GaN MOSFETs by suppression of the residual interface charge

•Electron mobility of 2DEG on AlGaN/GaN was degraded by regrown interface.•Regrown interface of GaN had Si impurities and unintentional carrier.•Contamination of GaN surface by Si compounds was caused to exposure of air.•Cleaning of regrown interface improve device properties of AlGaN/GaN FET.