The effect of NO2 adsorption on optical and electrical properties of porous silicon layers

The Raman spectra and current-voltage characteristics of porous silicon layers are studied before and after exposure to NO2. It is shown that spherical nanocrystallites with the diameter of approximately 6–8 nm are present in the samples’ structure. The effect of NO2 brings about a decrease in the resistance of porous Si by two-three orders of magnitude. An increase in the conductance of the structures at gas concentrations as high as 2000 ppm and a drastic decrease in this conductance if the concentration exceeds the above value are observed. This effect is explained in the context of the model that implies the formation of additional defects of the type of dangling silicon bonds at the Si/SiO2 interface as a result of oxidation of the porous silicon surface. These defects are traps for holes and reduce the increase in the hole concentration.