Electronic and structural properties of InAs/InP core/shell nanowires: A first principles study

Abstract

The one-dimensional character of the nanowires (NWs), with large surface to volume ratios, allows one to accommodate internal strains that would not be achieved in composite bulk materials with large mismatches. This opens a vast field to explore new materials with specific properties. One of the ways to efficiently exploit this characteristic feature of the NWs is through composition modulation. Using first principles calculations, we investigate the structural and electronic properties of core/shell modulated [111] zinc-blende InAs/InP NWs with different core/shell ratios and diameters (from 1.0 to 2.0 nm). Basic properties of these systems like the lattice parameter and the band gaps are seen to vary non-linearly with the core/shell ratio. The presence of an external InP shell is shown to improve the electronic mobility when compared with pure InAs NWs by eliminating the pinning of the Fermi level at InAs-derived surface states, while keeping the electron effective mass as low as in pure InAs NWs with similar diameters. We determine a type-I like band alignment, with a valence band offset depending on the core/shell ratio and a vanishing conduction band offset. We discuss the consequences of these results to the p-type conduction in the InAs core due to remote p-type doping at the InP shell region.