Abstract
beta-In2S3 is of great interest in photovoltaic applications and presents a certain number of vacant sites allowing the displacement of indium atoms by hopping from one site to another. Recently, it has been shown that it exhibits ionic behavior. Experimental works have been carried out in order to study the alternating current (AC) conductivity in beta-In2S3, showing the validity of the hopping model (correlated barrier hopping; CBH) in the frequency range not exceeding omega = 10(4) Hz. For omega > 10(4) Hz, the transport mechanism was dominated by small polaron tunneling (SPT). The theoretical model developed in this work in order to study the AC conductivity is based on the hopping model adapted to the case of beta-In2S3 by considering the jump of indium ions from one site to another. We report the frequency and temperature dependence on beta-In2S3 AC conductivity. An examination of the experimental results shows a qualitative compatibility of our model. Indeed, our theoretical simulations are in agreement with the experimental data in the same frequency range where the CBH model was dominant. A quantitative discrepancy between theory and experiment has been observed beyond this frequency range where the SPT has been dominant. This discrepancy increases by raising the temperature. A FORTRAN program based on the Lenvenberg-Marquardt method was established to determine the fitting curve of the theoretical model to the experimental. This program allowed us to deduce the vibration frequencies about the equilibrium of indium atoms in the case of beta-In2S3 which are parameters of fundamental importance in solid-state physics. The vibration modes obtained from the numerical simulation are in agreement with the orders of magnitude found in the literature.