PHOTOLUMINESCENCE AS A SURFACE-EFFECT IN NANOSTRUCTURES

Nanocrystalline Si powder prepared by Laser Induced CVD (LCVD) showed photoluminescence (PL) at wavelengths of 400-900 nm when excited at 48 8 nm and 330 nm. The powder consists of spherical grains with an avera ge diameter of 25 nm and log-normal size distribution. In this study w e present a model which explains the origin of the photoluminescence: the latter is generated by electrons which jump from the regular bulk- states into the surface-states of the nanocrystals, which in turn are not populated after being Excited by the illuminating photons. We pres ent the effect of the surface potential on the surface states and, thu s, on the possible transitions. The model is tested against experiment al results which cannot be explained by the quantum size confinement e ffect such as photoluminescence from particles bigger than 10 rim and shift in the PL emission wavelength due to oxygen and nitrogen bonds a t the surface of the particles. The tools presented here can be applie d also to porous silicon.