Nonlinear behavior of the energy gap in Ge1-x Snx alloys at 4 K

Abstract

The optical energy gap of Ge1-x Snx alloys (x≤0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4 K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1-x Snx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT =2.30±0.10 eV and b0 4 K =2.84±0.15 eV, at room temperature and 4 K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%. © 2007 American Institute of Physics.