Raman-based mapping and depth-profiling of the relaxation state in amorphous silicon

Abstract

We show that the micro-scale variations in the relaxation state of amorphous silicon (aSi) can be well-identified by Raman mapping over hundreds or thousands of µm2 in 1-2 hours. Pure and relaxed a-Si is obtained by self-implantation in crystalline silicon (c-Si) followed by an anneal at 500°C. It is then locally re-implanted over micro-sized patterns to produce unrelaxed aSi zones. Raman mappings are obtained by pointwise confocal µ-Raman and Hyperspectral Raman Imaging (RIMA). We also measure depth profiles of the relaxation state in re-implanted a-Si by scanning the edge of a re-implanted sample. We infer from the depth profiles that the minimal damage dose to fully de-relax a-Si is 0.04 displacements per atoms, which is an order of magnitude smaller than the fluence needed to fully amorphize c-Si.