Comparison of MOS capacitors on n- and p-type GaN

Abstract

The electrical characteristics of both n- and p-type GaN metal-oxide semiconductor (MOS) capacitors utilizing plasma-enhanced CVD-SiO2 as the gate dielectric were measured. Both capacitance and conductance techniques were used to obtain the MOS properties (such as interface state density). Devices annealed at 1000°C/30 min. in N2 yielded an interface state density of 3.8×1010 cm−2 eV−1 at 0.19 eV from the conduction band edge, and it decreased to 1.1×1010 cm−2 eV−1 deeper into the band gap. A total fixed oxide charge density of 8×1012 q cm−2 near the valence band was estimated. Unlike the symmetric interface state density distribution in Si, an asymmetric interface state density distribution with lower density near the conduction band and higher density near the valence band was determined.