Temperature dependence of the transient and AC electrical conductivity of porous silicon thin films M. Theodoropoulou a , C.A. Krontiras a, *, N. Xanthopoulos a , S.N. Georga a , M.N. Pisanias a , C. Tsamis b , A.G. Nassiopoulou b a Department of Physics, University of Patras, 26500 Patras, Greece b IMEL/NCSR Demokritos, PO Box 60228, 153 10 Athens, Greece Abstract 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 /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. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Porous silicon; Electrical conductivity; Tunneling; Ohmic; Poole /Frenkel PACS numbers: 68.55a 1. Introduction Porous Silicon (PS) is a material with many interest- ing applications. The strong photoluminescence that exhibits is extensively studied. It is common agreement that the excitation of photoluminescence is connected with the quantum confinement in the Silicon crystallites [1,2]. On the other hand there is no agreement concerning the electrical conduction mechanisms on PS thin films. Resent suggestions for the electrical properties vary from electrical transport in the Silicon crystallites [3], diffusion [4] or tunneling [5], Schottky rectification, Poole  /Frenkel conduction [6], injection Power Law conduction and hopping transport [7 /9]. Reshotko et al. [10] have proposed that the prevailing conduction mechanism, at low temperatures, is tunneling between adjacent conducting grains, under Coulomb blockade conditions. Also Axelrod et al. [11,12] have proposed an energy-band diagram of the metal/PS/Si structure based on dielectric spectroscopy measurements. The aim of the present work is to clarify the time evolution of the conduction mechanisms responsible for the electrical properties of porous silicon thin films as a function of temperature and applied voltage. This work follows the previously published one [13], concerning the time evolution of the conduction mechanisms of PS at room temperature. 2. Experimental details Porous silicon layers have been obtained on p-type (100) silicon wafers with resistivity 1  /10 V cm. Boron * Corresponding author. E-mail address: krontira@physics.upatras.gr (C.A. Krontiras). Materials Science and Engineering B101 (2003) 334  /337 www.elsevier.com/locate/mseb 0921-5107/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-5107(02)00753-5