Modification of Optical Band-Gap of Si Films After Ion Irradiation

Amorphous silicon (a-Si),nanocrystalline silicon (nc-Si) and hydrogenated nanocrys-talline 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 1.0×10 11 ions/cm-2,1.0×10 12 ions/cm-2 and 1.0×10 13 ions/cm-2 at room temperature (RT).The nc-Si:H films were irradiated with 9 MeV Xe-ions at 1.0×10 12 Xe/cm-2,1.0×10 13 Xe/cm-2 and 1.0×10 14 Xe/cm-2 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 (E g) 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.