Ozone passivation of slow transient current collapse in AlGaN∕GaN field-effect transistors: The role of threading dislocations and the passivation mechanism

Current collapse in AlGaN∕GaN field-effect transistors subjected high rf drive levels and/or to bias stresses is attributed to the presence of surface trapping levels whose nature remains to be identified. Although current collapse manifestations can be alleviated with various surface films, the exact passivation mechanism remains a matter of debate. We show that slow transient current collapse can be eliminated by a short ozone exposure, unambiguously tying current collapse to the sample surface, without invoking strain or dielectric encapsulation arguments. We assert that the surface states responsible for slow collapse arise where dislocations intersect the sample surface, and propose an alternative current collapse mechanism wherein individual dislocation lines result in multiple discrete virtual gates that locally deplete the transistor channel access regions.