First principles study of size and external electric field effects on the atomic and electronic properties of gallium nitride nanostructures

A comprehensive density functional theory study of atomic and the electronic properties of wurtzite gallium nitride (GaN) nanostructures with different sizes and shapes is presented and the effect of external electric field on these properties is examined. We show that the atomic and electronic properties of [101¯0] facet single-crystal GaN nanotubes (quasi-1D), nanowires (1D) and nanolayers (2D) are mainly determined by the surface to volume ratio. The shape dependent quantum confinement and strain effects on the atomic and electronic properties of these GaN nanostructures are found to be negligible. Based on this similarity between the atomic and electronic properties of the small size GaN nanostructures, we calculated the atomic and electronic properties of the practical size (28.1 A wall thickness) single-crystal GaN nanotubes through computational much economical GaN nanoslabs (nanolayers). Our results show that, regardless of diameter, hydrogen saturated single-crystal GaN tubes with the wall thickness of 28.1 A are energetically stable and they have a noticeably larger band gap with respect to the band gap of bulk GaN. The band gap of unsaturated single-crystal GaN tubes, on the other hand, is always smaller than the band gap of the wurtzite bulk GaN.;In a separate study, we show that a transverse electric field induces a homojunction across the diameter of initially semiconducting GaN single-crystal nanotubes and nanowires. The homojunction arises due to the decreased energy of the electronic states in the higher potential region with respect to the energy of those states in the lower potential region under the transverse electric field. Calculations on single-crystal GaN nanotubes and nanowires of different diameter and wall thickness show that the threshold electric field required for the semiconductor-homojunction induction increases with increasing wall thickness and decreases significantly with increasing diameter.