Resonant Raman scattering and photoluminescence studies of porous silicon membranes

Raman scattering measurements as a function of excitation wavelength are conducted on a 55-mu m-thick porous silicon (PS) membrane of an approximate porosity of 70%. A narrowing of the Si-Si phonon peak with increasing excitation wavelength is observed. We attribute this to a resonance of the excitation energy with the electronic states of nanocrystallites in PS. We estimate the size of silicon particles from the shift and broadening of the phonon band. The absorption band edge is next blue shifted by annealing the sample at 300 and 500 degrees C. A collapse of the nanostructure with a decrease in particle size is observed. The photoluminescence (PL) spectra exhibit a red shift of the PL band upon annealing. We also estimate the size of silicon particles from the PL peak. (C) 1996 American Institute of Physics.