Origin of visible photoluminescence from arrays of vertically arranged Si-nanopillars decorated with Si-nanocrystals

Arrays of vertically aligned Si-nanopillars, with average diameters of 100 nm and 5 mu m length, have been prepared by wet chemical etching of crystalline silicon in a special manner. Samples with smooth-and porous-walled nanopillars have been studied. In the case of the latter, Si-nanocrystals, passivated with SiOx, decorating the surface of the nanopillars are identified by the means of TEM and FTIR. When excited by UV-blue light, the porous-walled Si-nanopillars are found to have a strong broad visible emission band around 1.8 eV with a nearly perfect Gaussian shape, mu s luminescence lifetimes, minor emission polarization and a non-monotonic temperature dependence of luminescence. The Si-nanocrystal surface is found to be responsible for the luminescence. The red-shift of the emission maximum and the luminescence quenching induced by oxidation in UV-ozone confirm this assumption. A model of luminescence involving UV photon absorption by Si-nanocrystals with subsequent exciton radiative recombination on defect sites in SiOx covering Si-nanocrystals has been proposed. Possible applications of the nanopillar arrays are discussed.