Correlation between quantum nanocrystal particle size and photoluminescence using Raman scattering

The PL (photoluminescence) and EL (electroluminescence) demonstrated for porous silicon and silicon rich SiO₂ films have provided exciting opportunities for the integration of optoelectronics and Si digital electronics. Recent work has suggested that the porous silicon luminescence results from either quantum size or surface state effects. In this report, we review PL demonstrated in the visible spectral range from quantum nanocrystals (QNC) formed from Si embedded in an SiO₂ matrix. We used Raman scattering to estimate the QNC particle size and correlated the shift in the luminescence spectra to the observed change in the Raman spectra. The PL spectrum peak shifted from 7000 to 8000 angstrom as the average particle size increased from approx.50 to 70 angstrom, measured from Raman scattering. Further, High Resolution Transmission Electron Microscopy, HRTEM, and X-ray Diffraction, XRD, measurements confirmed the particle size range. PL lifetime measurements and excitation intensity studies are also presented. The stable nature of the QNC embedded in an insulating or semiconducting matrix offers further advances towards the integration of optoelectronics with Si devices.