Folded phonon spectra of progressively annealed amorphous Si/Ge superlattices

Abstract

Raman scattering from folded acoustic modes of amorphous Si/Ge superlattices has been employed to study thermally induced structural changes in samples of different periods. For a superlattice with 13.5-nm period, the position and intensity of the folded phonon doublet, obtained as a function of annealing temperature, reveal (i) the diffusion of Si into the Ge layers up to an anneal temperature of 500 °C without much effect on Si/Ge interfaces, (ii) a severe degradation of Si/Ge interfaces at an anneal temperature of 600 °C, followed by crystallization of the superlattice, and (iii) a nearly complete intermixing of the layers after the 700 °C anneal. A superlattice with a larger period (P=20.5 nm), on the other hand, retains its layered structure even after an anneal of 700 °C.