LOCAL STRAINS IN SI1-X-YGEXCY ALLOYS AS DEDUCED FROM VIBRATIONAL FREQUENCIES

Raman spectroscopy has been used to study the bond structure of Si1-x- yGexCy alloys. An anharmonic model for the force constants is applied to interpret the results. It is well established that the Ge and C con centrations in these alloys can be chosen so that their average lattic e constants may be equal to, or even smaller than that of the Si latti ce, Our Raman results show that the C local mode vibrational energy in creases rapidly with increasing C concentration, al a rate of 3.2 cm(- 1)/at%. Additional fine structure is observed near the Si-C main peak in samples grown by rapid thermal chemical vapor deposition (RTCVD). T his fine structure is absent in samples grown by pulsed laser induced epitaxy (PLIE). In agreement with previous studies, the satellite stru cture of the Si-C peak is interpreted as an indication for short-range order. Our analysis shows that pronounced differences exist in the mi croscopic structures of SiGeC alloys grown by different growth techniq ues.