Transport Processes in Metal-Insulator Granular Layers

TL;DR

This paper develops a mean-field kinetic theory for tunnel transport in metal-insulator granular layers, revealing different charge and current behaviors in free and contact areas, and compares results with experimental data.

Contribution

It introduces a new kinetic model accounting for charging states and processes in granular layers, explaining charge distribution and conduction mechanisms.

Findings

Charge accumulation causes non-ohmic behavior in contact areas.

Steady state transport requires zero charge density in free areas.

Analytic solutions describe low and high charge density regimes.

Abstract

Tunnel transport processes are considered in a square lattice of metallic nanogranules embedded into insulating host to model tunnel conduction in real metal/insulator granular layers. Based on a simple model with three possible charging states ($\pm$, or 0) of a granule and three kinetic processes (creation or recombination of a $\pm$ pair, and charge transfer) between neighbor granules, the mean-field kinetic theory is developed. It describes the interplay between charging energy and temperature and between the applied electric field and the Coulomb fields by the non-compensated charge density. The resulting charge and current distributions are found to be essentially different in the free area (FA), between the metallic contacts, or in the contact areas (CA), beneath those contacts. Thus, the steady state dc transport is only compatible with zero charge density and ohmic resistivity in FA, but charge accumulation and non-ohmic behavior are \emph{necessary} for conduction over CA. The approximate analytic solutions are obtained for characteristic regimes (low or high charge density) of such conduction. The comparison is done with the measurement data on tunnel transport in related experimental systems.