Room temperature oxidation of porous silicon in air

The changes in the chemical composition calculated from infrared spectra and photoluminescence spectra of p-type porous Si layers having 60–80% porosity were investigated over 1.5 years storage in air. The main changes of oxygen concentration (NO) take place in the linear range of the kinetic dependence. This means that in this range the oxidation is reaction-limited with the cleavage of Si–Si bonds. For extended storage the linear dependence of NO(t) transforms to the weak dependence that is caused by oxygen diffusion into crystallites. At the beginning of the oxidation process the character of NO(t) depends on the postanodization treatment. All stages of aging are photostimulated. The hydrogen concentration is practically unchanged over about 60 weeks. The infrared absoption bands at 840 and 880 cm−1 apparently belong to Si–Hx deformation mode with oxidized Si backbonds. During storage in air the initial photoluminescence peak intensity decreases and after extended storage this peak disappears but simultaneously the new band with a maximum at about 0.75 μm appears, probably due to oxide related luminescence and its intensity increases.