Modification of Optical Bandgap of Thin Silicon Films Induced by 94 MeV Xe Ion Irradiation

Key words: 
• silicon /
• thin film /
• heavy ion irradiation /
• optical bandgap

Abstract: Monocrystalline silicon(cSi), thin films of amorphous silicon(aSi) and nanocrystalline silicon(ncSi) were irradiated at room temperature(RT) by using 94 MeV Xeions at 1.0×10¹¹, 1.0×10¹² or 1.0×10¹³ Xeions/cm², respectively. All samples were analyzed at RT by an UV/VIS/NIR spectrometer (Lambda 900, PE, Germany), and then the uariation of the optical bandgap with the irradiation fluence was investigated systematically. The results show that the optical bandgap of the silicon samples irradiates by Xeion changed dramatically with different crystalline structures. For the aSi thin films, the optical bandgap values decreased gradually from ~1.78 to ~1.54 eV with increasing Xeion irradiation fluence. For the ncSi thin films, the optical bandgap values increased sharply from ~1.50 (origin) to ~1.81 eV(Φ=1.0×10¹²ions/cm²), and then decreased to ~1.67 eV(Φ=1.0×10¹³ ions/cm²). However, there is no observable change of the optical bandgap of the cSi after Xeion irradiations. Possible mechanism on the modification of the silicon thin films was briefly discussed.