Optical study of thermally induced phase separation in evaporated SiOx films

Abstract

SiOx thin films (x ~1.3) have been prepared by thermal vacuum evaporation of silicon monoxide. A thermally stimulated (annealling temperatures – 700 and 1000°C) structural transformation of the Si-O phase in the SiOx layers, which leads to the formation of amorphous and crystalline Si nanoinclusions, was investigated using photoluminescence and infrared spectroscopy. It is demonstrated that the heat treatment leads to the decomposition of molecular complexes of slightly oxidized Si and the formation of both Si clusters and molecular clusters containing heavily oxidized Si. The transformations of the oxide phase are almost completed after 5 min. of the thermal treatment. The films annealed at 700°C contain amorphous Si nanoclusters embedded into homogeneous SiO₁.₇₅ matrix (the volume share of amorphous Si phase is equal to ~17 vol.%). The films annealed at 1000°C represent Si nanocrystals (the volume share is equal to ~20 vol.%) surrounded by SiOx interface layers and embedded into SiO₂. Both types of samples - the ones with Si nanocrystals and with amorphous Si nanoinclusions – exhibit photoluminescence in visible and near infrared spectral range. PL peak is blueshifted and is 5 to 10 time more intense for amorphous as compared with crystalline nano-Si. The origin of the light emission may be related to electron-hole pairs recombination in amorphous nanoinclusions and carrier recombination through double Si=O bonds at the nc-Si – oxide matrix interface. Remove selected