Photophysical processes stimulated in nanoporous silicon by high-power laser radiation

Photoprocesses initiated on the surface of porous silicon irradiated with l aser radiation with various wavelengths (lambda = 266, 337, and 532 nm) in a wide range of intensities (up to 2 x 10(7) W/cm(2)) were investigated. La ser-induced luminescence and laser mass-spectrometry were used as experimen tal procedures. X-ray reflection was used to determine the parameters of th e porous silicon films. The photoluminescence spectra obtained at different wavelengths and low intensities were analyzed. This analysis showed that f or an optically thin layer of porous silicon the luminescence spectrum does not depend on the wavelength of the exciting radiation. This indicates the existence of a separate system of levels in porous silicon that are respon sible for the luminescence. The behavior of the photoluminescence spectra a s a function of the intensity q of the exciting radiation was investigated. It was shown that the luminescence intensity is a nonlinear function of q. At high intensities of the exciting radiation, the luminescence intensity saturates and a short-wavelength shift of the spectra is observed; this is due to the high concentrations of photoexcited carriers. This increases the probability of the experimentally observed nonequilibrium photodesorption of H-2 and Si from the surface of porous silicon. (C) 2000 MAIK "Nauka/Inte rperiodica".