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

A photoluminescence study was made on thin films of Si-SO, nanocluster s prepared by reactive laser ablation of Si targets. The photoluminesc ence spectra were measured at ambient temperature and at liquid nitrog en 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 material s) luminescence bands at 2.25, 2.7 and 4.3 eV were observed. The prese nt results, however, strongly suggest that several bands (for example, at 2.7 eV) are composed of either more than one centre or a single ce ntre in significantly different crystalline environments. For the firs t time we report a large luminescence band centred at 3.6 eV. Sample c ooling leads to considerable enhancement of intensity of this band, wh ich increases 4-5 times and reveals its structure as three adjacent ba nds with the maxima at approximately 3.54, 3.64 and 3.75 eV. All the o ther 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.