CORRELATION OF SIZE AND PHOTOLUMINESCENCE FOR GE NANOCRYSTALS IN SIO2MATRICES

Synthesis and size-dependent photoluminescence has been performed for Ge nanocrystals in SiO2 matrices with average diameters between 2 and 9 nm, formed by room-temperature ion implantation into SiO2 followed b y precipitation during vacuum thermal anneals. Nanocrystal size distri butions obtained from electron microscopy data were used in conjunctio n with a quantum-confined exciton recombination model [T. Takagahara a nd K. Takeda, Phys. Rev. B 46 (1992) 15578] to generate calculated pho toluminescence spectra, which were compared with experimental spectra. Qualitative agreement between calculated and observed spectra could b e obtained when: (i) the non-radiative and radiative carrier recombina tion rates were approximately equal for nanocrystal sizes correspondin g to visible emission, (ii) the spatial extent of the nanocrystal conf inement potential is assumed to be slightly smaller than the measured size of the nanocrystal, and (iii) coalescence of individual nanocryst als produces electronic states corresponding to single nanocrystals wi th larger volume.