Ionoluminescence of porous silicon

Abstract

Ion-beam-induced luminescence of porous Si has been monitored during excitation with 40–250 keV H +, He + and Ar + beams. The spectra exhibit three bands, the positions of which do not depend on the type of ion species or energy. The blue band with a maximum at 2.64 eV is well known in luminescence of irradiated SiO 2. Its identification is based on a characteristic intensity increase with ion dose for different ions. The red band at 1.92 eV is attributed to light emission from small Si crystallites of nanometer sizes, completely covered with SiO 2 layers. The modification of electronic states, likely due to a quantum confinement effect, shifts the Si energy gap towards higher energies. The intensity of the 1.92 eV band decreases with increasing ion dose. This behavior, also observed in luminescence spectra, is associated with the influence of radiation defects.