Optical and structural characterization of Si nanocrystals ion beam synthesized in SiO2: correlation between the surface passivation and the photoluminescence emission

We present in this paper a systematic study of the evolution of photolumine scence (PL) emission of Si nanocrystals embedded in SiO2 with elaboration c onditions. Si nanocrystals have been synthesized in SiO2 by ion implantatio n with doses that cover from 1 x 10(16) to 10(17) ions/cm(2). This correspo nds to a Si super-saturation of 1-10 at.% at the projected range. The annea ling process was performed at 1100 degreesC. These samples show a wide (0.2 6 eV) and very intense PL emission centered at about 1.72 eV. The intensity of this emission shows a typical behavior with annealing time, with a fast transitory increase that bends over to reach asymptotic saturation. There is a linear increase of the PL intensity with the implantation dose at this saturation stage. The structural characterization has been performed by tr ansmission electron microscopy and electron spin resonance. Based on these results, the kinetic evolution of the volume fraction of precipitates and t heir surface rearranging have been correlated with the time evolution of PL intensity. The band gap of nanocrystals has been determined to be 1.85 eV from PL excitation measurements. All the results indicate that the radiativ e recombination process is related with recombination at a Si-O bond of nan ocrystal-matrix interface, together with the emission of a phonon (a local vibration of the Si-O bond). (C) 2001 Elsevier Science Ltd. All rights rese rved.