A two-dimensional lattice is considered with a linear charge-density gradient produced by a charge source at one end and a sink at the opposite end. A fraction p of the lattice sites are occupied by mobile particles that interact only with neighboring particles and empty sites (the substrate) and carry charges from source to sink; the charge neutrality of the whole lattice is maintained. The root-mean-square (rms) displacement of the particles (i.e., the tracers) and their effective conductivity for the charge transport are studied as a function of temperature and concentration p. The rms displacement shows a crossover from diffusion (at short time) to driftlike behavior (in the long-time regime). The effective conductivity depends nonmonotonically on the carriers’ concentration, in which two maxima peaks are observed; the peak at the higher concentration seems to characterize the onset of static percolation. At a fixed concentration, the conductivity remains almost constant at low temperatures and increases before it saturates to a higher value in the high-temperature regime. In the intermediate-temperature range, an Arrhenius dependence seems valid at high concentrations; however, a deviation on varying the concentration cannot be ruled out at low concentration. We find that the activation energy depends on carrier concentration and temperature.

• Received 21 December 1990

DOI:https://doi.org/10.1103/PhysRevA.43.4365