Influence of hydrogen on thermally induced phase separation in GeO/SiO2 multilayers

The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeOx/SiO2 multilayers (x∼1), leading to size controlled growth of Ge nanocrystals, is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing complete phase separation at approximately 450 deg. C using inert N2 ambient. The use of reducing H2 in the annealing atmosphere influences the phase separation even at an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50 deg. C. At temperatures above 400 deg. C the sublayer composition, and thus the density of the Ge nanocrystals, can be altered by making use of the reduction of GeO2 by H2.