Electronic properties calculation of Ge1 − x − ySixSny ternary alloy and nanostructure

Abstract

The band structure of Ge1−x−ySixSny ternary alloys, which are easier to grow than binary Ge1-xSnx alloys, and clearly offer a wider tunability of their direct band-gap and other properties, was calculated and investigated by using the empirical pseudo-potential plane wave method with modified Falicov pseudo-potential formfunction. The virtual crystal approximation (VCA) and 2×2×2 super-cell (mixed atoms) method were adopted to model the alloy. In order to calculate all of these properties, the empirical pseudo-potential code was developed. The lattice constant of the alloy varies between 0.543 to 0.649nm. The regions in the parameter space that corresponds to a direct or indirect band gap semiconductor are identified. The Ge1−x−ySixSny ternary alloy shows the direct band gap for appropriate composition of Si, Ge and Sn. The direct energy gap is in the range 0–1.4eV (from the VCA calculation), and 0–0.8eV (from the super-cell calculation), depending on the alloy composition. Therefore, this alloy is a promising material for optoelectronic applications in both visible and infrared range, such as interband lasers or, solar cells. Furthermore, strain-free heterostructures based on such alloys are designed and, using the effective-mass Hamiltonian model, the electronic structure of GeSiSn quantum wells with arbitrary composition is investigated, in order to understand their properties and the potential of their use in devices.