Optical and Electronic Propreties of GeSn and GeSiSn Heterostructures and Nanowires

Abstract

The first part of this work reports on detailed studies of the influence of both strain and composition on the band structure of GeSiSn ternary alloys. First, we developed a simple yet rigorous semi-empirical second nearest neighbors tight binding sp 3 s * method that incorporates the effect of substitutional disorder. We have found that the composition of α-Sn at the direct to indirect crossover of the ternary alloy decreases from 11% in a fully relaxed alloy to 7% in tensile strained alloy (for a strain value of 0.71%). In the latter case, we have considered a thin GeSiSn layer is epitaxialy grown on a thin Ge substrate. The last section of this work addresses the behavior of GeSn/Ge core-shell nanowires. Herein, we have solved the effective mass Hamiltonian in cylindrical coordinates using a finite difference technique for the core-shell nanowires where the core and the shell are made of different alloys. We have found that above a critical doping concentration of 5×10 16 cm -3 and below a core radius of 20 nm, the electron density is localized in the Ge shell for the Ge 0.9 Sn 0.1 /Ge core-shell nanowire system.