Solid phase crystallization of a-Si in Si/Ge multi-layer

We have investigated the effects of local Ge-insertion in a-Si films on solid-phase crystallization (SPC). Experiments were performed by using three types of stacked structures, i.e., (a) a-Si/a-Ge/a-Si/SiO₂, (b) a-Si/a-Ge/SiO₂, and (c) SiO₂/a-Ge/a-Si/SiO₂. These samples were annealed at 600°C. The results for the structure (a) with Ge films of 5 nm, Ge atoms were completely diffused into a-Si regions, and no-enhanced SPC was detected. However, if Ge thickness was increased to 15 nm, Ge atoms were localized. Such phenomena became significant by (b) and (c) structures even for samples with Ge films of 5 nm. In addition, significant enhancement of SPC of a-Si was found. These results indicated that crystal nucleation was initiated at Ge layers, and then propagated into a-Si layer. Therefore, interface nucleation driven SPC becomes possible by using the structures (b) and (c). It is expected that this process can be used to grow oriented Si crystals on SiO₂.