Structure and optical properties of amorphous silicon oxide thin films with different porosities

Amorphous silicon oxide thin films were prepared by evaporation of a silicon oxide powder. Samples were prepared under ultrahigh vacuum, under a flow of hydrogen ions or under it molecular hydrogen atmosphere. Two others sets of samples were prepared Using deuterium instead of hydrogen. These five groups of samples were then annealed to different temperatures up to 950 degreesC and were exposed to the ambient air, The samples present different densities and microstructures. The sample prepared under ultrahigh vacuum is dense. hydrogen free and Off-bond free. Samples prepared under atomic hydrogen and deuterium flows contain Si H and Si D bonds. respectively, and are OH-bond free. The sample prepared under a molecular hydrogen atmosphere is very similar to that prepared under a molecular deuterium atmosphere. Both samples are porous and contain Si-H bonds and OH-groups coming from the exposure to the air. All the samples show visible photoluminescence attributed to isolated silicon clusters. The photoluminescence intensity increases with thermal annealing post-treatments up to an optimal annealing temperature. This maximum value is equal to 650 degreesC for the unhydrogenated sample and the sample prepared under an atomic hydrogen flow and to 800 degreesC for the sample prepared under a molecular hydrogen atmosphere. This difference is correlated to the different microstructures of the samples. Moreover the strongest photoluminescence intensity is obtained for the porous sample. (C) 2003 Elsevier Science B.V. All rights reserved.