Ge self-diffusion in isotopic(70Ge)n(74Ge)msuperlattices: A Raman study

Abstract

Ge self-diffusion is studied using Raman scattering by optical phonons in isotopic ${(}^{70}$Ge)${}_{n}$${(}^{74}$Ge)${}_{m}$ superlattices. Raman spectra of a series of isotopic ${(}^{70}$Ge)${}_{n}$${(}^{74}$Ge)${}_{m}$ superlattices with $n$ and $m$ equal to 8, 12, 16, and 24 monolayers are presented here for annealing at 500 $\ifmmode^\circ\else\textdegree\fi{}$C and various times. The results are compared with theoretical calculations based on a planar force constant model and the bond polarizability approach. The average value for the mass of an atom in each atomic plane is given by the diffusion profile, solving Fick's diffusion equation for the superlattices. The value obtained here for the self-diffusion coefficient at 500 $\ifmmode^\circ\else\textdegree\fi{}$C is 5.50$\ifmmode\times\else\texttimes\fi{}$10${}^{\ensuremath{-}24}$ m${}^{2}$ s${}^{\ensuremath{-}1}$ and compares very well with previous results.