ELECTRICAL BEHAVIOR OF FRESH AND STORED POROUS SILICON FILMS

We have measured I-V and C-V characteristics, the temperature dependen ce of dark currents, and thermally stimulated depolarisation currents on fresh and stored samples of photoluminescent porous silicon, By sto rage in ambient, the low rectifying I-V curves become strong rectifyin g, and C-V curves become MIS-like. I-T characteristics for fresh sampl es have only one activation energy, in the 0.49-0.55 eV range. After s torage, a slightly modified value, of about 0.50-0.60 eV is observed a t low temperatures only. At about 280 K, the activation energy suddenl y changes to 1.20-1.80 eV. Also, both the number and the positions of maxima in thermally stimulated depolarisation currents change by stora ge. The annealing at about 50 degrees C induces small reversible chang es in I-T characteristics and strong irreversible ones in thermally st imulated 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 surfa ce and/or interface contributions are observed especially in thermally stimulated depolarisation currents. The changes induced by storage ar e attributed to the oxidation process of the internal surface of porou s silicon films. (C) 1998 Elsevier Science S.A. All rights reserved.