An optical study of Ni induced crystallization of a-Si thin films

The optical properties of nanocrystalline silicon (nc-Si), formed by nickel (Ni) induced crystallization of amorphous silicon (a-Si) films, are presented. Growth of nc-Si was characterized by Raman spectroscopy and UV-vis-NIR spectrophotometry. Significantly, the onset of crystallization occurred at 600 deg C within 15 min of annealing, as evidenced from the Raman peak centered at 514 cm-1. It is demonstrated that the shape of the optical absorption spectrum is a function of thickness, substrate temperature, topological disorder and metal content in the films. Ni doping of the films results in optical inhomogeneity in the films and therefore anomalous dispersion in the behavior of the refractive index. It is further shown that these parameters also influence the position of the Urbach edges. The present study shows that metal induced crystallization of a-Si does not require extended durations of annealing and that the crystallization process is accompanied by structural, chemical and microstructural inhomogeneity in the films.