Formation of Ge NC’s out of (GeOx-SiO2) superlattice structures

Semiconductor Nanocrystals (NC), consisting only of a few hundred of atoms, are of great interest for new generations of light emitters, nonvolatile memories or high efficiency solar cells [1]. However, it remains a remarkable challenge to achieve a high density (>10¹²cm^-2) of equalsized, small (<5 nm) NC’s of Ge or Si embedded in dielectric films. In this study we present the fabrication of Ge-NC’s by decomposition of GeOx (1< x <2) out of a (GeOx -SiO2) superlattice structure (SL). The SL was grown by dual reactive DC magnetron sputtering from elemental targets. Different Ge/O ratios in the SL structures were realized by the variation of oxygen flow and deposition temperature. Using in-situ x-ray reflectivity and grazing incidence diffraction at the CRG Beamline ROBL at ESRF we studied the deposition of the SL and the Ge NC’s evolution during subsequent annealing. Depending on the GeOx stoichiometry closed nanocrystalline films or separated Ge NC’s with grain or particle sizes between 2-5 nm have been obtained with grazing incidence x-ray diffraction. The size of the NC’s can be tuned with thickness of the GeOx sublayer, its density exceeds 10¹²cm^-2.
[1] A.Rogach (ED.), Semiconductor nanocrystal quantum dots, Springer, Wien 2008, ISBN 978-3211752357