The formation of germanium nanocrystals by thermal annealing of a‐SiOx: H/a‐GeOx: H multilayers

Multilayer films consisting of alternating sublayers of hydrogenated amorphous silicon oxide and germanium oxide were prepared by dual magnetron sputtering of silicon and germanium targets in an argon/water vapor atmosphere. The number and thickness of the a‐GeOx: H sublayers ranged from one to eight and from 80 to 7 nm, respectively. The structure of the multilayers and their components were investigated by means of optical transmission and reflection, infrared spectroscopy, wide‐angle X‐ray scattering, and X‐ray reflectometry. Upon annealing, first an ordering of the amorphous germanium oxide network connected with an outdiffusion of oxygen and an increase of the surface roughness are observed. Depending on sublayer thickness, the onset of the formation of Ge nanocrystals is observed around 700 K. Crystallization of the germanium oxide sublayers is nearly completed at 870 K, and the crystallite diameter ranges from 4 to 13 nm depending on sublayer thickness. With crystallization the surface roughness decreased and the structure of the silicon oxide was improved.