Strong enhancement of porous silicon photoluminescence by dry photo-chemical surface treatment

Porous silicon has been subjected to NF₃/UV photochemical surface treatment in the range of 300-400°C. This treatment is found to enhance strongly the photoluminescence of porous silicon by couple orders of magnitude. The effect of photoluminescence enhancement has been observed only when the NF₃ treated porous silicon was exposed to ak environment. The photoluminescence intensity continued to grow with the aging time in air, even at the room temperature. Using atomic force microscope, scanning electron microscope and Auger measurements, it is found that the photoluminescence enhancement correlated with the formation of crystalline oxide layer at the porous silicon surface. This oxide layer S_iO_x (x≅2) is much more stoichiometric as compared to the native oxide S_iO_x (x≅1) covering the reference porous silicon surface (not treated by NF₃). The rapid growth of the S_iO₂ layer is supposed to be due to the NF₃/UV photo-thermal etching of the as-formed native oxide as well as to the cleaning and passivation of the porous silicon surface with fluorine.