THE ROLE OF QUANTUM-CONFINED EXCITONS VS DEFECTS IN THE VISIBLE LUMINESCENCE OF SIO2-FILMS CONTAINING GE NANOCRYSTALS

Synthesis of Ge nanocrystals in SiO2 films is carried out by precipita tion from a supersaturated solid solution of Ge in SiO2 made by Ge ion implantation. The films exhibit strong room-temperature visible photo luminescence. The measured photoluminescence peak energy and lifetimes show poor correlations with nanocrystal size compared to calculations involving radiative recombination of quantum-confined excitons in Ge quantum dots. In addition, the photoluminescence spectra and lifetime measurements show only a weak temperature dependence. These observatio ns strongly suggest that the observed visible luminescence in our samp les is not due to the radiative recombination of quantum-confined exci tons in Ge nanocrystals. Instead, observations of similar luminescence in Xe+-implanted samples and reversible PL quenching by hydrogen or d euterium suggest that radiative defect centers in the SiO2 matrix are responsible for the observed luminescence. (C) 1996 American Institute of Physics.