THEORETICAL-STUDY OF THE LUMINESCENT SUBSTOICHIOMETRIC SILICON-OXIDES(SIOX)

Density-functional based tight-binding molecular-dynamics and semi emp irical molecular orbital calculations are applied to identify the 1.9 eV luminescence center in SiOx. The identification is made possible by an 890 cm(-1) vibrational line that is correlated to the luminescence peak. Two possible models are examined: (i) Si-6 rings in substituted siloxenes are known to show 1.8 eV emission. A model SiO crystal is b uilt based upon Si rings interconnected by bridging O atoms. The struc ture is found to be stable up to 1000 K, but the correlated vibration is not observed. (ii) a-SiO is exposed to simulated annealing and the quenched amorphous structure is analysed for occurance of Si rings and the previously proposed nonbridging oxygen hole centers (NBOHCs). Loc alized stretching vibrations of the NBOHCs are found to be in the expe rimentally detected frequency range, thus explaining the correlation w ith the observed and calculated photoluminescence peak. (C) 1998 Elsev ier Science Ltd. All rights reserved.