Structural properties of Silicon-Germanium and Germanium-Silicon Core-Shell Nanowires

Abstract

Core-shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core-shell nanowires aligned along the $[110]$ direction, with diameters up to 10.2~nm and varying core to shell ratios, using linear scaling Density Functional Theory (DFT). We show that Vegard's law, which is often used to predict the axial lattice constant, can lead to an error of up to 1\%, underlining the need for a detailed \emph{ab initio} atomistic treatment of the nanowire structure. We analyse the character of the intrinsic strain distribution and show that, regardless of the composition or bond direction, the Si core or shell always expands. In contrast, the strain patterns in the Ge shell or core are highly sensitive to the location, composition and bond direction. The highest strains are found at heterojunction interfaces and the surfaces of the nanowires. This detailed understanding of the atomistic structure and strain paves the way for studies of the electronic properties of core-shell nanowires and investigations of doping and structure defects.

arXiv comment9 pages, 9 figures, submitted to J. Phys.:Condens. Matter

References in corpus (7)

• The SIESTA method for ab initio order-N materials simulation
• Efficient index handling of multidimensional periodic boundary conditions
• O(N) methods in electronic structure calculations
• One-Dimensional Hole Gas in Germanium/Silicon Nanowire Heterostructures
• Calculations on millions of atoms with DFT: Linear scaling shows its potential
• Electronic Properties of Strained Si/Ge Core-Shell Nanowires
• Band structure of Si/Ge core-shell nanowires along [110] direction modulated by external uniaxial strain

Cited by in corpus (2)

• Large scale and linear scaling DFT with the CONQUEST code
• DFT study of undoped and As-doped Si nanowires approaching the bulk limit