Observation of zinc-blende to diamond transition in metastable (GaAs)1-x(Ge2)x alloys by Raman scattering

Epitaxial metastable (GaAs)(1-X)(Ge-2)(X) thin films throughout most of the full compositional x range were studied by Raman scattering. Two optical modes were present near the allowed longitudinal optic (LO) and forbidden transverse optical (TO) modes of GaAs. We get direct evidence for the zinc-blend to diamond structural transition (ZB-D transition), which is observed to occur at x approximate to0.35, from the features observed in the compositional dependence of the ratio of the Gamma (a) lower energy to rh higher energy half widths at half maximum intensities Gamma (a/) Gamma (b) of the LO like-mode and those of the integrated intensities of the forbidden TO like-mode and the allowed LO like-mode. Raman scattering data combined with X-ray diffraction results imply that the macroscopically averaged ZB-D transition has manifestation in microscopic sizes at the same concentration.