Formation of Ge nanocrystals in amorphous GeOx, and SiGeOx alloy films

Abstract

We present a systematic analysis of the conditions for the formation of Ge nanocrystals in GeOx and SiGeOx alloy films during annealing. Amorphous SiOx, GeOx and SiGeOx alloy films prepared by d.c. magnetron sputtering were subsequently annealed for times between 10 min and 60 min and at annealing temperatures ranging from 350 °C up to 800 °C. The formation of nanocrystals is analysed by X-ray scattering under grazing incidence. No crystallisation is found for the SiOx films under any annealing conditions. On the other hand, clear evidence for the formation of Ge nanocrystals is found in the GeOx as well as in the SiGeOx films. For the GeOx films the particle diameter ds linearly decreases with increasing oxygen content yielding values of ds = 40 nm down to 10 nm. The as-prepared amorphous SiGeOx films were found to always consist of nanoamorphous Ge clusters in an amorphous SiOx matrix determining the size of the resulting Ge nanocrystal after annealing. A Ge nanocrystal diameter of around ds = 6.0 nm is found for all SiGeOx alloy films independent of the annealing time and temperature.