ANNEAL-INDUCED STRUCTURAL-CHANGES IN AMORPHOUS SI/GE SUPERLATTICES

The thermal stability of amorphous Si/Ge (a-Si/Ge) superlattices has been studied using Raman and optical spectroscopy techniques. The annealing of the short period samples (period, P = 3.9 and 5.8 nm) causes the diffusion of Si into the Ge layers well before the crystallization of superlattices occurs. Further annealing beyond the crystallization temperature leads to a near complete intermixing of the individual layers. The long period superlattice samples (P = 9.2 and 18.5 nm) show a little diffusion of Si into the Ge layers before crystallization and a continued interdiffusion after crystallization. The long period samples retain their layered structure even after an anneal of 660-degrees-C.