Red electroluminescence in Si+-implanted sol–gel-derived SiO2 films

Abstract

We report on a continuously emitting electroluminescent device fabricated by Si+-ion implantation and subsequent annealing of a SiO2 layer on a silicon substrate. The SiO2 layer with a thickness of 250 nm was prepared by the sol–gel technique. Four different Si+-ion energies and implantation doses were applied in order to obtain a flat Si+-ion profile across the SiO2 film thickness with an atomic Si excess of 5%. Electroluminescence (EL) occurs above a low-voltage threshold (∼5 V, 1 A/cm2) at one bias polarity only even if the device in fact does not exhibit rectifying properties. EL microscopy reveals that EL at 295 K is emitted from a small number of bright spots with diffraction-limited size. EL spectra of individual bright spots were measured using an imaging spectrometer. The wide EL emission band (situated in the red region ∼750 nm) obtained with spatial averaging over the semitransparent indium–tin–oxide contact represents the envelope of these individual contributions. We suggest that the EL is due to electron–hole injection into Si nanocrystals which create several conductive percolation paths across the SiO2 film. Shunting current paths due to defects exist in parallel and are probably the main factor responsible for low EL efficiency (10−5%).