Band gap of Ge rich Si1−<i>x</i>−<i>y</i>Ge<i>x</i>C<i>y</i> alloys

Abstract

Si1−x−yGexCy films ( x≊0.90, y⩽0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x-ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C-resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions.