C-induced Ge dots: enhanced light-output from Si-based nanostructures

Pre-deposition of a fraction of a monolayer of C on an Si (001) substrate causes the formation of extremely small islands after the growth of only 2 monolayers (ML) of Ge. We demonstrate that these CGe dots exhibit particularly intense photoluminescence (PL) compared to a variety of different but comparable structures. Although grown at low temperatures (460°C), the CGe islands show a ten times more intense PL signal than conventionally grown self-assembled Ge islands, grown at 700°C. We show that the initial stage of CGe dot formation is likely to be governed by strain compensation effects. In a series of samples, where we have kept the total C and Ge amounts constant but varied the deposition sequence, we show that the specific CGe dot growth order of pre-grown low surface mobility C, followed by high surface mobility Ge leads to a distinct nanostructure within the SiGeC material system, exhibiting typical `dot-like' and intense PL. An almost strain compensated 50 layer stack of CGe dots is shown to emit intense PL at 0.99eV.