We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiO x , 0Ͻ x Ͻ 2) films by high-vacuum annealing and dry oxidation. The SiO x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous-oxide/silane flow ratios. The physical and optical properties of the SiO x films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000°C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO 2 and elemental Si. This change indicates the phase separation of the SiO x into more stable SiO 2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. The size of Si NCs increases with increasing Si concentration in the films and increasing annealing temperature. Two photoluminescence (PL) bands were observed in the films after annealing. The ultraviolet (UV)-range PL with a peak fixed at 370-380 nm is independent of Si concentration and annealing temperature, which is a characteristic of defect states. Strong PL in red range shows redshifts from ϳ600 to 900 nm with increasing Si concentration and annealing temperature, which supports the quantum confinement model. After oxidation of the high-temperature annealed films, the UV PL was almost quenched while the red PL shows continuous blueshifts with increasing oxidation time. The different oxidation behaviors further relate the UV PL to the defect states and the red PL to the recombination of quantum-confined excitions.

SiO,, nanostructured films were formed by pulsed-laser deposition (PLD) of Si. The photoluminescence band at 1.6-2.1 eV shifts with ambient gas pressure, substrate temperature and post-deposition processing, which supports the quantum confinement effect theory. @2005 Optical Society of America OCIS codes: (310.6860) Thin films, optical properties; (140.3390) Laser materials processing Ever since visible photoluminescence (PL) was observed in Si nanostructures, Si nanocrystals (NCs) have attracted great interest in microelectronics and optoelectronics. They have opened up new opportunities for developing Si-based light emitting devices which are compatible with current electronic ultralarge-scale-integration (ULSI) technologies. In this study, we examined the structures and properties of SiOx nanostructured films formed by PLD and also the annealing and oxidation effects on the SiO, films. SiOx nanostructured films were deposited in

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