Controlling the photoluminescence of ZnO:Si nano-composite films by heat-treatment

Nano-composite thin films of silicon and zinc oxide were deposited on glass substrates using thermal co-evaporation. On heating the films at different temperatures and different atmospheric pressures, the photoluminescence (PL) emission spectra become broad, giving emissions in UV-Blue, Green and Red region. Analyses reveal that defect-dominated structure of ZnO contributes to the broad PL spectra observed. X-ray diffraction and Raman spectra analysis show that the defects caused by oxygen vacancies decrease with heating which is accompanied by a competing process of decrease in grain size made possible by surrounding silicon reacting at the surface of the ZnO nano-cluster grains giving new bonds, possibly O-Si-Zn bonds. Crystallinity of nano-grains and defects contribute different emission peaks that depending on relative contributions can give comparable peaks resulting in broad emission spectra. The study shows that simple post-deposition process can lead to fabrication of white light emitting devices based on these nano-composites. Best emission spectra are obtained by heating at a temperature of 250 oC in low vacuum.