LUMINESCENCE FROM A SI-SIO2 NANOCLUSTER-LIKE STRUCTURE PREPARED BY LASER-ABLATION

A photoluminescence study was made on thin films of Si-SO, nanoclusters prepared by reactive laser ablation of Si targets. The photoluminescence spectra were measured at ambient temperature and at liquid nitrogen temperature using 400 and 230 nm excitation from a dye laser driven by an excimer laser. A number of well-l mown (for Si-related materials) luminescence bands at 2.25, 2.7 and 4.3 eV were observed. The present results, however, strongly suggest that several bands (for example, at 2.7 eV) are composed of either more than one centre or a single centre in significantly different crystalline environments. For the first time we report a large luminescence band centred at 3.6 eV. Sample cooling leads to considerable enhancement of intensity of this band, which increases 4-5 times and reveals its structure as three adjacent bands with the maxima at approximately 3.54, 3.64 and 3.75 eV. All the other bands exhibit weak temperature dependence; their intensities are 1.5-2 times higher on cooling. The comparison of the luminescence time dependence to the excitation pulse indicates a luminescence lifetime tau less than or equal to 2 ns.