Abstract: Two electron transition processes between channel and surface states in GaN HFET:hot electron tunneling and surface to band edge transition are investigated.Based on the tunneling between channel hot electrons and surface states,a new microscope mechanism of current collapse is proposed.Various experimental behaviors of photoionization spectroscopy,DLTS,transient current, and current collapse are explained by this microscopic mechanism.The different current collapse behaviors are investigated for various heterostructures,from which the optimized design of GaN HFET without current collapse is discussed.

Key words: current collapse,  transient current,  hot electron tunneling,  GaN HFET