ULTRAFAST CARRIER DYNAMICS IN POROUS SILICON

The carrier dynamics in porous silicon is investigated by two time-resolved techniques. The blue photoluminescence of oxidized porous silicon is measured with 100 ps time resolution as a function of the oxidation method, emission wavelength, excitation intensity, and measurement temperature. The blue luminescence has ii distinct origin from the well-studied red luminescence and is attributed to defects in the oxide. Femtosecond photoinduced absorption measurements are performed on thin red-emitting porous silicon films. The wavelength and intensity dependence of the recovery are interpreted in terms of trapping and of Auger recombination at high excitation intensity. It is shown that red-emitting porous silicon is not a direct-gap semiconductor.