Modification of structure and optical band-gap of nc-Si:H films with 30 and 196 MeV Kr-ions

In the present work, experimental results on irradiation effects of 30 and 196 MeV Kr-ions on nc-Si:H films are presented. The irradiation fluences are 5.0 × 1013, 1.0 × 1014 and 2.0 × 1014 Kr-ions/cm2, respectively. Irradiation induced modification on microstructure and optical properties of nc-Si:H films are studied by X-ray diffraction, Raman scattering and UV–Vis-NIR spectroscopy. The analyses results indicate that the irradiations lead to the decrease of crystalline fraction and crystallite size, as well as the increase of bond angle variation of amorphous network. The structural changes become more obvious with the nuclear energy loss increases. Moreover, with the ion fluence increases, the optical band-gap for samples irradiated with 30 MeV Kr-ions decreases gradually, while it for samples irradiated with 196 MeV Kr-ions decreases significantly at first and then remains nearly constant. It is considered that the irradiation induced atomic displacements in the films lead to the amorphization of crystalline phase and the decrease of short-range order in amorphous phase, and then result in the reduction of optical band-gap.