IONOLUMINESCENCE OF POROUS SILICON

Ion-beam-induced luminescence of porous Si has been monitored during e xcitation with 40-250 keV H+, He+ and Ar+ beams. The spectra exhibit t hree bands, the positions of which do not depend on the type of ion sp ecies or energy. The blue band with a maximum at 2.64 eV is well known in luminescence of irradiated SiO2. Its identification is based on a characteristic intensity increase with ion dose for different ions. Th e red band at 1.92 eV is attributed to light emission from small Si cr ystallites of nanometer sizes, completely covered with SiO2 layers. Th e modification of electronic states, likely due to a quantum confineme nt effect, shifts the Si energy gap towards higher energies. The inten sity of the 1.92 eV band decreases with increasing ion dose. This beha vior, also observed in luminescence spectra, is associated with the in fluence of radiation defects.