Influence of deep levels on capacitance-voltage characteristics of AlGaN/GaN heterostructures

We studied the influence of deep levels in GaN buffer and AlGaN barrier layer on capacitance–voltage characteristics of the AlGaN/GaN structure. Deep level states were assumed to be both donor and acceptor type and were modeled with discrete peak distribution in energy with certain energy distance from the conduction-band minimum for acceptor-type states or valence-band maximum for donor states. For all the cases studied, the presence of the deep levels in the structure influenced mainly the capacitance plateau of the curves and caused the appearance of the capacitance valley. In addition, the deep levels in AlGaN shifted the capacitance curves to more negative voltages, and the deep levels in GaN changed the slope of capacitance decrease after two-dimensional electron-gas depletion.