Experimental evidence of Si nanocluster δ-layer formation in the vicinity of ion-irradiated SiO2–Si interfaces

Abstract

Predictions on formation and self-alignment of Si nanocrystals (NCs) at ion-irradiated SiO2–Si interfaces have been verified by cross-section transmission electron microscopy (TEM). The model is based on ion-mixing of SiO2–Si interfaces resulting in a region of SiOx (x<2). During annealing, the interface restores and in the tail of the mixing profile Si excess precipitates and forms a self-aligned layer of Si NCs in SiO2. This Si NC δ-layer structure can hardly be observed by conventional TEM techniques due to the very low mass contrast of tiny Si NCs embedded in SiO2. Here, a contrast enhancing method is presented based on alloying these Si NCs with Ge. For this purpose, a thin Ge layer is embedded into the oxide sufficiently far from the interface mixing range, thus, preventing interference with the Si precipitate formation. During annealing, diffusing Ge monomers attach to the Si NCs, mainly due to the energetically favored Si–Ge bond, resulting in Si1−xGex NCs with an enhanced mass contrast in TEM.