SPECTROSCOPIC ANALYSIS OF THE BLUE-GREEN EMISSION FROM OXIDIZED POROUS SILICON - POSSIBLE EVIDENCE FOR SI-NANOSTRUCTURE-BASED MECHANISMS

The mechanism of the blue-green emission from oxidized porous silicon has been investigated in terms of the excitation energy dependencies o f photoluminescence spectra and polarization memory (PM) effects. Unli ke the orange-red band, the blue-green band shows wide inhomogeneous b roadening, a significantly small Franck-Condon shift and large PM. The high degree of PM is maintained even when the difference between the excitation and emission energies (i.e. the Stokes shift) is sufficient ly larger than the Franck-Condon shift. The implication is that photog enerated radiative excitons relax over a wide energy range without def orming their wavefunctions significantly. This is most consistently ex plained by Si-nanostructure-based mechanisms. (C) 1997 Elsevier Scienc e Ltd.