Impact of band-gap graded structures artificially implemented in Mg–ZnO epitaxial films on photoelectrochemical properties

Abstract

The impact of band gap-graded structures artificially implemented in a photocatalyst on the photoelectrochemical properties was investigated in a model system of epitaxial thin film Mg–ZnO. The band gap-graded Mg–ZnO films were fabricated by introducing nanoscale modulation of the Mg composition during pulsed laser deposition. The Mg composition was designed to continuously change between 0 at% and 20 at% or more along the growing direction within a single 100 nm-thick Mg–ZnO film, in accordance with which the band-gap varies between 3.3 eV and 3.9 eV. As a result, it was found that the down-graded film with the Mg composition decreasing from the substrate to the film surface exhibited a larger photoanodic current density and a higher photooxidation ability than the up-graded film with the opposite Mg gradient. The different photochemical properties between them are discussed in terms of their graded band structures.