Analytical Theory of Thin-Film Schottky Diodes

Thin-film electronics straddles the border between bulk electronics and the quantum realm. Though thin-film devices are increasingly prevalent, our understanding of their operation remains incomplete. Recent research has highlighted inconsistencies between the established theory and practical operation of thin-film Schottky junctions, a key constituent of many electronic devices. In thin-film devices, the entire semiconductor film can be depleted; thus, the standard depletion approximation no longer holds as the boundary conditions of Poisson’s equation are changed. The effects of these changes upon the current through the Schottky diode were investigated using both analytical theory and device simulations, with particular focus on the dependence of the reverse current upon semiconductor thickness. As thin-film electronics is increasingly geared toward the use of disordered materials and low-cost processing, it is of foremost importance to develop a theory of inhomogeneous thin-film Schottky junctions. A model was devised for a thin-film Schottky diode with a single inhomogeneity in the barrier height. Analytical theory and device simulations based upon this model were found to be in agreement about the thickness dependence of the effective barrier height in thin-film Schottky diodes with inhomogeneous barrier heights. Analytical theories were derived for both thermionic emission and diffusion currents and demonstrated good agreement with the results of device simulations. Finally, as practical devices contain a distribution of barrier heights, a multiple barrier height model for thin-film Schottky diodes was derived and used to fit an experimental result. Our results offer practical insight for device design, not just for Schottky diodes but also for p–n junctions, organic light-emitting diodes, and other heterostructure devices.