Origin of forbidden modes in Raman spectraof Ge isotope superlattices

摘要

Raman investigations of Ge isotope heterostructures and superlattices arereported. A comparison of Raman spectra of Ge isotope heterostructuresrecorded at low temperatures (10-80K) using 488 nm and 514.5 nmexcitations shows differences due to change in the laser penetrationdepths. Raman forbidden (inactive) modes have been observed clearlyin the spectra excited by 488 nm and its origin is discussed in terms ofthe penetration depth of the laser which is anomalously small.