The effects of cap layers on electrical properties of indium nitride films

The unintentional n-type doping in the indium nitride thin films was investigated. The electron density decreases from 3.5×1019 to 9×1018 cm−3 and the mobility increases from 4 to 457 cm2 V−1 s−1 when the thickness increases from 50 to 350 nm. This can be explained by assuming the film consists of a surface accumulation layer and a bulk layer. It was found that the accumulation layer can be eliminated by capping the surface with silicon nitride, GaN or zinc nitride of 2 nm each, respectively; while an AlN cap layer will cause the formation of two-dimensional electron gas at the AlN/InN interface.