Carrier trapping and current collapse mechanism in GaN metal–semiconductor field-effect transistors

Abstract

A mechanism for current collapse in GaN metal–semiconductor field-effect transistors is proposed, which assumes the existence of acceptor traps with multiple states in the band gap. Current collapse has been experimentally observed in the current–voltage characteristic after the drain voltage sweep had exceeded the threshold for impact ionization in a previous measurement. In the proposed model, electrons generated by impact ionization are captured by neutral acceptor trap states in the substrate located above the valence band. The charged trap states move to an energy level located near midgap, creating a positively charged depletion region in the channel, and causing current collapse. With increasing drain bias, the quasi-Fermi level approaches the charged trap states at the drain end of the gate, initiating detrapping of the electrons and restoring the current. The calculated results show good agreement with published experimental data.