Light emitting porous silicon from hydrogenated amorphous silicon

Light-emitting porous silicon layers have successfully been obtained from hydrogenated amorphous silicon (a-Si:H), by anodic dissolution in hydrofluoric acid. The maximum thickness of the porous layers is limited by an instability due to the high resistivity of a-Si:H. The high luminescence efficiency is well accounted for in a spatial confinement picture in which the microstructure of the porous material isolates the photogenerated electron-hole pairs from the non-radiative recombination centres. The temperature dependence of the photoluminescence efficiency and the dependence of the photoluminescence wavelength as a function of the microstructure typical size reveal that quantum confinement effects do not affect the luminescence, a feature consistent with the localized character of the electronic states. Finally, pushing light emission in the visible range has been achieved by making porous layers from hydrogenated amorphous silicon-carbon alloys.