Photoluminescence spectrum and dynamics in oxidized silicon nanocrystals: A nanoscopic disorder system

We have studied luminescence properties of nanometer-sized Si crystallites fabricated by laser breakdown of SiH4 gas. An exponential absorption tail is observed and red photoluminescence (PL) appears in the exponential tail. The PL decay behavior is characterized by a stretched exponential function. At higher temperatures, the effective PL decay rate tau(-1) depends exponentially on the monitored phonon energy h omega: tau(-1 alpha)exp(h omega/E(tau))here E(tau) is a constant depending on temperature. On the other hand, at low temperatures, the PL lifetime is almost independent of the PL wavelength and phonon-related structures in the PL spectrum are not clearly observed under resonance excitation. The order and disorder natures of Si nanocrystallites are discussed.