Band-Gap Engineering in ZnO Thin Films: A Combined Experimental and Theoretical Study

Abstract

Zinc oxide thin films are synthesized and characterized using x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and optical spectroscopy. Our results reveal that the structural, morphological, and optical properties are closely related to the stress of the sample provided that the texture of the film remains the same. The anomalous results are obtained once the texture is altered to a different orientation. We support this experimental observation by carrying out first-principles hybrid functional calculations for two different orientations of the sample and show that the effect of quantum confinement is much stronger for the (100) surface than the (001) surface of ZnO. Furthermore, our calculations provide a route to enhance the band gap of ZnO by more than 50% compared to the bulk band gap, opening up possibilities for wide-range industrial applications. © 2018 American Physical Society.