Electrical behaviour of fresh and stored porous silicon films

Abstract

We have measured I–V and C–V characteristics, the temperature dependence of dark currents, and thermally stimulated depolarisation currents on fresh and stored samples of photoluminescent porous silicon. By storage in ambient, the low rectifying I–V curves become strong rectifying, and C–V curves become MIS-like. I–T characteristics for fresh samples have only one activation energy, in the 0.49–0.55 eV range. After storage, a slightly modified value, of about 0.50–0.60 eV is observed at low temperatures only. At about 280 K, the activation energy suddenly changes to 1.20–1.80 eV. Also, both the number and the positions of maxima in thermally stimulated depolarisation currents change by storage. The annealing at about 50°C induces small reversible changes in I–T characteristics and strong irreversible ones in thermally stimulated depolarisation currents, both for fresh and stored samples. A simplified quantum confinement model is proposed to explain the main aspects of the electrical behaviour of porous silicon films. The surface and/or interface contributions are observed especially in thermally stimulated depolarisation currents. The changes induced by storage are attributed to the oxidation process of the internal surface of porous silicon films.