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Isotope-Dependent Phonon Trapping at Defects in Semiconductors

Unexpectedly large isotope effects have been reported for the vibrational lifetimes of the H-C stretch mode of the CH2* defect in Si and the asymmetric stretch of interstitial O in Si as well. First-principles theory can explain these effects. The results imply that defects trap phonons for lengths of time that depend on the defect and sometimes on its isotopic composition. Some consequences of phonon trapping are discussed.