Effect of thermal oxidation on charge carrier transport in nanostructured silicon

The effect of short-time annealing in air on the conductivity of porous silicon in two different directions (parallel and orthogonal to the sample surface) is studied. The samples under study are produced by electrochemical etching of single-crystal silicon wafers with (100)-oriented surfaces. It is found that thermal oxidation of the resulting porous silicon layers has different effects on the conductivity measured normally and parallel to the sample surface. For the oxidized samples, the conductivity in the direction orthogonal to the surface is noticeably higher than the conductivity in the direction parallel to the surface. The results are interpreted in the context of the model of charge carrier transport with consideration for potential barriers at the boundaries of silicon nanocrystals.