Interfacial N Vacancies in GaN/(Al,Ga)N/GaN Heterostructures

Abstract

We show that N-polar GaN/(Al,Ga)N/GaN heterostructures exhibit significant N deficiency at the bottom (Al,Ga)N/GaN interface, and that these N vacancies are responsible for the trapping of holes observed in unoptimized N-polar GaN/(Al,Ga)N/GaN high electron mobility transistors. We arrive at this conclusion by performing positron annihilation experiments on GaN/(Al,Ga)N/GaN heterostructures of both N and Ga polarity, as well as state-of-the-art theoretical calculations of the positron states and positron-electron annihilation signals. We suggest that the occurrence of high interfacial N vacancy concentrations is a universal property of nitride semiconductor heterostructures at net negative polarization interfaces.