LUMINESCENCE FROM PLASMA-DEPOSITED SILICON FILMS

We report the observation of room-temperature and low-temperature visi ble photoluminescence from nanocrystalline silicon (nc-Si) thin films produced by plasma-enhanced chemical vapor deposition (PECVD) through a gas discharge containing SiH4 diluted in Ar and H-2. The nanocrystal line silicon films were characterized using transmission electron micr oscopy, spectroscopic ellipsometry, infrared and Raman spectroscopy, a nd were examined for photoluminescence. Luminescent films consisted of dense silicon nanocrystals that grew in a columnar structure with app roximately 20%-30% void space dispersed inside the film. Aside from ha ving small crystalline silicon regions, the structure of the nc-Si fil ms is different than that of porous Si, another luminescent Si materia l generally produced by electrochemical anodization. Yet, the photolum inescence spectra of the thin nc-Si films were found to be similar to those observed from porous silicon. This similarity suggests that the same mechanism responsible for light emission from porous silicon may also be responsible for emission from nc-Si. The photoluminescence spe ctra are analyzed in terms of a simple quantum confinement model. Alth ough the mechanism of visible luminescence from porous Si is still a p oint of controversy, our results support the hypothesis that some of t he luminescence from porous silicon and nc-Si films is due to quantum confinement of electrons and holes in crystals with dimensions 2-15 nm . (C) 1997 American Institute of Physics.