Optical investigation of Si1−yCy alloys (0 ⩽ y ⩽ 0.015)

IR absorption was used to study the vibrational modes of substitutional carbon in strained layers of Si1−yCy (0 ⩽ y ⩽ 0.015) alloys, which were grown by molecular beam epitaxy on Si (100) substrates. Satellite peaks that appear in the absorption spectrum close to the vibrational mode of substitutional carbon in the alloy are explained by a recently developed anharmonic Keating model. The interaction of substitutional carbon atoms gives rise to these peaks which can also be observed in Raman spectra. We observe a shift of the absorption onset below the fundamental silicon band gap to lower energy with rising carbon concentration.