THERMAL-CONDUCTIVITY OF ISOTOPICALLY ENRICHED SI

We have used an optical pump-and-probe technique to measure the temper ature dependence of the thermal conductivity, kappa(T), of isotopicall y pure Si. The sample was made from 99.7% Si-28 by liquid phase epitax y. Measurements were performed over the temperature range of 100-375 K . We found an increase in the thermal conductivity of isotopically pur e Si, as compared to Si of natural isotopic abundance, throughout the entire temperature range. The results were theoretically reproduced by appropriately scaling the parameters used recently to fit the thermal conductivity of Ge samples with different isotopic compositions. A ma ximum in kappa(T) of similar to 4X10(14) W m(-1) K-1 is predicted for Si-28 at T similar or equal to 33 K. (C) 1997 American Institute of Ph ysics.