Polarization retention in the visible photoluminescence of porous silicon

The polarization state of the visible photoluminescence of porous silicon excited with linearly polarized light has been examined. The photoluminescence was linearly polarized in the same direction as the excitation light, independent of the crystallographic orientation of the sample. The degree of linear polarization decreased significantly with increasing emission wavelength. However, no definite trend of its excitation-wavelength dependence was observed. An interesting correlation was found to exist between the photoluminescence efficiency and the degree of linear polarization, where polarized photoluminescence was more prominent in photoluminescence-inefficient samples. Furthermore, the polarization retention phenomenon was found to be independent of temperature. These experimental results can be explained by the radiative recombination of excitons localized within optically anisotropic and randomly distributed Si nanocrystallites.