Conduction anisotropy in layered semiconductors.

We present a simple theoretical model for the diffusion of free carriers in layered semiconducting compounds, for which a small concentration of dopants (guest layers) disturb the system conductance, resulting in a strong anisotropy across and along the layers, which depends on the temperature of the system, as well as on the barrier lowering caused by the applied voltage. This model is based on diffusion via random walks of free particles, with the guest layers acting as barriers hindering free motion. By considering the probability of overcoming the barriers, we derive a formula for the current in terms of the guest concentration, barrier height, and temperature. Experimental results from previous studies for the system ZnIn&S4..Zn&In&SS concerning the anisotropic conductivity, its temperature and voltage dependence, as well as computer simulations are in excellent agreement with this model.