Photoluminescence of silicon nanocrystals embedded in silicon oxide

The bonding structure and the optical properties of silicon-rich silicon oxide films which were prepared using plasma-enhanced chemical vapor deposition (PECVD) with thermal oxidation were studied in detail. The composition and bonding structures were explored using X-ray photoelectron spectroscopy (XPS). The luminescent properties were studied using Raman spectroscopy and photoluminescence (PL) measurements. Results show that high-temperature (approximately 1000 degrees C) annealing of as-deposited Si-rich silicon oxide gives rise to phase separation and formation of crystalline Si phases in the oxide films. Upon high temperature annealing, the PL (550-900 nm) intensity was significantly reduced in stoichiometric oxide or in low Si-content (prepared with [N2O]/[SiH4] gas flow ratio > 2.5) films whereas an opposite trend was found in higher Si-rich samples. Particularly, for the red band (650 nm) and the infrared band (750 nm), the PL intensity was significantly enhanced by annealing slightly Si-rich samples ([N2O] / [SiH4] = 2.5) at 1100 degrees C. This observation was explained by the formation of Si nanocrystallites via phase separation reaction and the removal of defect-related absorption centers during annealing.