A luminescence versus temperature study of fresh and oxidized porous silicon layers under different atmospheres

Continuous and time resolved photoluminescence measurements of respectively oxidized and fresh porous silicon layers versus the temperature have been performed. Oxidized samples show an increase of both photoluminescence intensities and lifetimes when the temperature decreases, usually attributed to the reduction of the recombination rate on nonradiative centers at low temperatures. A drastically opposite behavior is observed on fresh samples which show correlated decreases of the photoluminescence intensities and of the lifetimes. Between the ambient and the liquid nitrogen temperatures, the luminescence signal is divided by 70. Moreover, the quenching is observed under nitrogen, helium and vacuum, but is totally inefficient when a film of pentane recovers the surface of the layer. We explain those experimental results by the nonradiative energy transfer from confined photocreated carriers in the silicon crystallites to Si-H surface vibrations which cannot happen when the oscillators are caged by pentane or isolated by the oxide layer. (C) 1998 American Institute of Physics. [S0021-8979(98)03214-9].