Relation between surface and bulk electronic properties of Al doped ZnO films deposited at varying substrate temperature by radio frequency magnetron sputtering

Abstract

In this study, a qualitative relationship between the surface and bulk electronic states for Al-doped ZnO (AZO) thin films (thickness  373 K. Further, these films show two modes of electron tunneling, (a) direct tunneling at lower bias voltage and (b) FN tunneling at higher bias voltage, with transition voltage ( Vtrans ) shifting towards lower bias voltage (and thereby reducing the barrier height ( Φ )) with increasing T s. This is attributed to additional (local) density of states near the Fermi level of these AZO films because of higher carrier concentration ( ne ) at increased T s. Thus, qualitatively, the behavior in both the local surface electronic states and bulk state electronic properties for these deposited AZO films are found to follow similar trends with increasing T s. The variation in local barrier heights (indicative of the local surface electronic structures) across the AZO film surface is found to be smaller for the films deposited at T s ≤ 373 K, where semiconducting behavior is observed and wider for the semi-metallic AZO films deposited at higher T s > 373 K, indicating a larger inhomogeneity of local surface electronic properties at higher bulk carrier concentration.by Chetan Singh, Tvarit Patel and Emila Pand