Phonons as a probe of short-range order in Si1-xCx alloys

This paper shows that by combining theoretical and experimental results for local Si-C phonon modes in dilute Si1-xCx alloys, information concerning the short-range order can be obtained. Calculations using an anharmonic Keating model predict satellite peaks near the vibrational frequency of an isolated C impurity which are associated with second-, third-, etc., nearest-neighbor C-C pairs. By comparing theoretical spectra with those obtained by Raman and infrared absorption spectroscopy, we conclude that the probability for a third-nearest-neighbor coordination of the C atoms is considerably above that fora purely random alloy. This confirms earlier work predicting an attractive third-nearest-neighbor interaction of the C impurities due to elastic interactions.