Band gap of Ge rich Si1-x-yGexCy alloys

Si1-x-yGexCy films (x approximate to 0.90, y less than or equal to 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. (C) 1996 American Institute of Physics.