STABILITY AND INTERDIFFUSION OF SHORT-PERIOD SI/GE STRAINED LAYER SUPERLATTICES

Interdiffusion of Si/Ge short-period superlattices is studied in detail with Raman spectroscopy. Folded acoustic modes and alloy modes from the interface region are found to be very sensitive to intermixing and concentration profile. Annealing at elevated temperature first leads to indiffusion of Si into the Ge layers. The diffusion constant depends strongly on the Si content and consequently varies during the interdiffusion process. The experimental results are qualitatively understood on the basis of a simple atomistic diffusion model. In high quality samples with sharp interfaces the onset of intermixing is observed already at temperatures as low as 450-degrees-C.