Photoluminescence in Si/ZnO nanocomposites

Composite films of Si and ZnO were prepared by r.f. co-sputtering technique with different Si contents. Photoluminescence (PL) and Raman spectroscopy were used to characterize the films. Transmission electron microscopy revealed that the Si dispersed in the ZnO matrix form nano-particles of size ranging from 2 to 4 nm. On thermal annealing at and above 700 °C, the nano-particles aggregated to form micro-crystals. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that the Si in the composite films remain in the SiOX (0 < X < 2) state. With the increase of annealing temperature, the higher oxidation state of Si is revealed. A strong and broad PL peak revealed at around 2.24 eV along with the other emissions. The emission could involve a band-to-band recombination mechanism within Si cores and emission sensitive to surface and/or interface states. Evolution of PL emissions and Raman peaks are discussed on the basis of formation of nano-particles and micro-crystals in the films and variation of oxidation state of Si with annealing temperature.