Interface Electron Traps as a Source of Anomalous Capacitance in AlGaN/GaN Heterostructures

Abstract

We studied by modeling and simulation how deep traps at the AlGaN/GaN heterostructure interface influence the shape of capacitance–voltage (C–V) curves of the heterostructure. Assuming donor and acceptor type of traps, we found differences in the C–V curves for sharp energy interface states or continuously distributed states with the same total concentration for the acceptor-type interface states. The background doping concentration of GaN had only a marginal influence on the shape of the C–V curves. We observed that an anomalous capacitance peak occurred for the continuous distribution of traps in the bandgap; a similar peak had been observed in experiment. We also saw that the capacitance curves shifted slightly to the right or to the left depending on the GaN doping concentration. A remarkable difference was found between the capacitance curves for the structures with the sharp acceptor trap level and continuous distribution of traps. For donor-type interface states, we found practically no influence on C–V curves since they remain populated and charge neutral during the measurement.