The mechanisms of the influence of illumination on the formation Of Po
rous silicon layers during anodization of p-type silicon has been anal
yzed. The stage of additional oxidation of silicon from the doubly cha
rge state to the quadruply charged state could involve participation o
f a solid phase, which was a light-sensitive catalyst of the process.
Uniform illumination of the substrate enhanced this process and as a c
onsequence it increased the porosity and the photoluminescence emitted
by such layers. Nonuniform illumination of the substrate resulted in
a redistribution of porous silicon over the surface area of a sample a
nd it altered its structure.