Modification of Optical Band-gap of Si Films after Ion Irradiation

Amorphous silicon (a-Si), nanocrystalline silicon (nc-Si) and hydrogenated nanocrystalline silicon (nc-Si:H) films were fabricated by using chemical vapor deposition (CVD) system. The a-Si and nc-Si thin films were irradiated with 94 MeV Xe-ions at fluences of 1.0×1011, 1.0×1012 and 1.0×1013 ions/cm2 at room temperature (RT). The nc-Si:H films were irradiated with 9 MeV Xe-ions at 1.0×1012, 1.0×1013 and 1.0×1014 Xe/cm2 at RT. For comparison, mono-crystalline silicon (c-Si) samples were also irradiated at RT with 94 MeV Xe-ions. All samples were analyzed by using an UV/VIS/NIR spectrometer and an X-ray powder diffractometer. Variations of the optical band-gap (Eg) and grain size (D) versus the irradiation fluence were investigated systematically. The obtained results showed that the optical band-gaps and grain size of the thin films changed dramatically whereas no observable change was found in c-Si samples after Xe-ion irradiation. Possible mechanism underlying the modification of silicon thin films was briefly discussed.