Phase Separation and Size Controlled Nanocrystal Formation in GeO

Semiconducting group IV nanocrystals (NC), such as Ge- and Si-NC, have drawn a lot of attention in recent years because of their potential use in new generations of light emitting diodes, fast and stable non-volatile flash memories or highly efficient solar cells. Although intensive research has been conducted regarding the photoluminescence and charge storage properties of readily produced oxide embedded NCs little is known about the phase separation and NC formation process. Here, we present in and ex situ X-ray absorption near edge structure (XANES) spectroscopy data of the temperature induced disproportionation, i.e phase separation of GeOx (x ≈ 1) into Ge and GeO2, which leads to the formation of Ge NCs embedded in a Ge oxide matrix. The formation of size controlled Ge NCs is achieved using a GeOx–SiO2 superlattice approach. The influence of reducing hydrogen in the annealing ambient on the phase separation process and resulting NC density is discussed.