Temperature dependence of the transient and AC electrical conductivity of porous silicon thin films

In order to investigate the prevailing conduction mechanisms of porous silicon (PS) thin films AC impedance spectroscopy measurements, as well as transient current measurements, as a function of voltage, were performed in the temperature range from 170 to 350 K. The frequency span was 1 Hz up to 1 MHz and the time range 5 x 10(-5)-10 s. The analysis of the experimental results involved correlation between AC and transient conductivity. The AC and transient conductivity measurements obey the Power Law of Dielectric Universal Response. The analysis shows that, within the range of the frequency span and time range of the measurements, the electrical conductivity is governed by three conduction mechanisms: In the low temperature region, specifically from 170 to 230 K, tunneling is the prevailing conduction mechanism. In the temperature range from 230 to 350 K two more thermally activated mechanisms contribute to the conductivity of PS thin films. The Ohmic conduction mechanism follows tunneling and precedes the Poole-Frenkel conduction mechanism. The time interval within each of these mechanisms is the prevailing one depends on temperature and applied voltage. The activation energy of Ohmic conduction as well as the exponential factor of Poole-Frenkel mechanism have been calculated. (C) 2003 Elsevier Science B.V. All rights reserved.