Multiple sharp peaks were observed in the visible photoluminescence spectra of amorphous silicon thin films, prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxidized silicon substrates. The angular dependence of the photoluminescence, measured by a home-built fiber-optics device, revealed that the origin of these sharp features was due to Fabry-Pérot cavity interference effects. The interference is enhanced by deposition on thermally grown oxide layers with relatively smooth surfaces. We also consider how thin-film interference effects can add to the already existing confusion regarding the photoluminescence (PL) mechanism of porous and other luminescent forms of silicon and propose angle-dependent PL spectroscopy as a remedy for identifying spectral features due to interference effects.
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