Band bending at metal-semiconductor interfaces, ferroelectric surfaces and metal-ferroelectric interfaces investigated by photoelectron spectroscopy

Abstract

X-ray photoelectron spectroscopy is nowadays a well-established technique for the determination of chemical compounds with surface sensitivity. To the atomic and chemical specificity and surface sensitivity, recently a new functionality was added to this technique, the ability to identify energy band bendings near surfaces and interfaces. Two standard cases are represented by Schottky metal–semiconductor structures and by ferroelectric surfaces exhibiting out-of-plane polarization. The case of metal–ferroelectric interfaces is more difficult to assess, but elements of a suitable theory start to be sketched nowadays and in short time a consistent model is expected to emerge. This chapter analyzes the recent progresses in the derivation of band bendings at surfaces and interfaces by X-ray photoelectron spectroscopy. A critical review of the literature will be presented, together with basic aspects of the theory of band bending. The experimental section will review some quite recent results, going from “standard” cases of Schottky contacts to usual semiconductors and to free ferroelectric surfaces, analyzing also the preferential adsorption of dipole molecules on some ferroelectrics, and ending with metal–ferroelectric cases, where sometimes unexpected phenomena occur, connected to a competition between Schottky barrier formation and loss of ferroelectric out-of-plane polarization by the grounding of the surface due to the deposited metal layer.