Raman scattering of α-Sn/Ge superlattices on Ge (001)

Abstract

A Raman scattering study on short-period single-crystal α-Sn/Ge superlattices grown by low-temperature molecular beam epitaxy pseudomorphically on Ge (001) substrate is presented herein. The phonon spectra exhibit distinct superlattice effects, such as narrow first, second, and third order folded-acoustic modes showing a doublet splitting, which is evidence for the proper periodic compositional modulation of the structure. A peak at 260 cm−1 is attributed to a Sn–Ge vibrational mode. The Raman cross section resonance of this mode is redshifted compared to that of the Ge optical mode. There are also Ge bulklike contributions from two-phonon scattering and disorder activated modes present in the spectra. Annealing experiments show that, despite the negligible solid solubility of Sn and Ge, layer intermixing occurs up to complete alloying, while the crystal quality is preserved.