Photoluminescence of porous silicon under pulsed excitation

Photoluminescence time resolved spectra (PL-TRS) and decay curves of photoluminescence (PL-DC) in the wavelength range 400-850 nm in micro and nanosecond time range at different temperatures (10K-room) on anodically etched boron doped porous silicon are presented. PL-TRS exhibit multiband structure and can be decomposed as a sum of few Gaussians. Positions of gaussian emission bands depend on temperature and change similar to thermal profile of the energy gap of the bulk silicon. PL-DC have multi exponential shape. Relaxation times depend on wavelength of the observation and temperature. At low temperature decay times dramatically increase (from few microsecond(s) at 300K to some hundred microsecond(s) ) and short component in nanosecond range has been observed. To explain our results we assumed model in which the multi barrier structure is formed by Si crystal (quantum well) surrounded by Si crystallites with diameters in the nanometer range (barrier region). The visible photoluminescence originates from radiative recombination between discrete energy levels in quantum well regions. Short component of decay at lowest temperatures is connected to non-radiative Auger relaxation inside porous silicon structures.