Ordering of amorphous germanium prior to crystallization

Abstract

We present the results of Raman and extended x-ray-absorption fine-structure (EXAFS) experiments performed on sputtered amorphous germanium for both as-deposited and postdeposition annealed samples. From the Raman results, shifts in TO-phonon frequency and linewidth associated with relatively low-temperature annealing are interpreted as indications of ordering prior to crystallization. For annealing at 400\ifmmode^\circ\else\textdegree\fi{}C, we determine from the Raman results that the volume fraction of crystallinity is \ensuremath{\le}${10}^{\ensuremath{-}3}$. From EXAFS results performed on the same samples, indications of ordering prior to crystallization are manifest in the appearance of a second-nearest-neighbor peak. A bond-angle variation of $\ensuremath{\Delta}\ensuremath{\theta}=7\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}1\ifmmode^\circ\else\textdegree\fi{}$ was found for the 400\ifmmode^\circ\else\textdegree\fi{}C-annealed sample. This value of $\ensuremath{\Delta}\ensuremath{\theta}$ was determined by comparing the EXAFS data for this sample with models of the amorphous material generated by adding bond-angle distortion to the crystalline data.