Strongly nonlinear luminescence in oxidized porous silicon films

Abstract

Partially oxidized free-standing porous silicon films show a strongly superlinear increase in photoluminescence (PL) intensity above a threshold cw excitation intensity of ∼10 W/cm 2. The PL-intensity increase can be expressed by a power law with n∼9 as a function of the excitation intensity. The PL-peak wavelength of this emission is slightly redshifted from that at low-excitation levels. These changes are fully reversible and reproducible, but not observed in samples on substrate. We attribute this behavior to thermal reexcitation of carriers trapped at the dangling bond states in initially nonluminescent Si nanocrystallites.