Current Flow in Thin Solid Films: Thermionic Emission and Tunneling.

Abstract

Current flow in metal-GaSe-metal sandwiches is investigated. These structures are particularly well suited to the study of current flow mechanisms because sandwiches containing uniform, single crystal films of gallium selenide can be easily fabricated. The well-defined nature of these structures allows sufficient a priori knowledge of their properties to make quantitative calculation of the predictions of appropriate models of current flow meaningful. As discussed in Part I, for gallium selenide films between 200 A and 1000 A thick, experimentally observed currents are in excellent agreement with a simple model of thermionic contact-limited current flow. This investigation presents the first unequivocal evidence for contact-limited thermionic currents in solids. In Part II films less than 100 A thick are studied. For this thickness range, direct, inter-electrode tunneling is shown to be the dominant mechanism of current flow and an accurate energy-momentum dispersion relation within the forbidden gap of GaSe is obtained. This work represents the first quantitative calculation of tunneling currents in a metal-insulator-metal structure with all parameters relevant to the experiment independently determined.