BAND-GAP OF GE RICH SI1-X-YGEXCY ALLOYS

Si1-x-yGexCy films (x approximate to 0.90, y less than or equal to 0.0 2) were grown by molecular beam epitaxy on Si substrates. Infrared opt ical absorption was used to obtain the band gap energy at room tempera ture, Biaxial strain obtained from x-ray diffraction measurements veri fied the presence of nearly relaxed films, and the total and substitut ional C contents were obtained from channeling C-resonance backscatter ing spectrometry. We show by direct measurements that interstitial C h ad a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1-xG ex alloys. While strain decreases the band gap, the effect of substitu tional C on the band gap depends on the Si and Ge fractions. (C) 1996 American Institute of Physics.