Enhanced visible light absorption in ZnO/GaN heterostructured nanofilms
  ZnO/GaN alloys exhibit exceptional photocatalyst applications owing to the flexibly tunable band gaps that cover a wide range of the solar spectrum, and thus have attracted extensive attentions over the past few years. In this study, first-principles calculations were employed to investigate structural stabilities and electronic properties of (1-100) and (11-20) ZnO/GaN heterostructured nanofilms. The effects of nanofilm thickness and GaN ratio were explored. It was found that all studied heterostructured nanofilms were less stable than the corresponding pure ZnO film but more stable than pure GaN one, exhibiting a much thicker film with better stability. Electronic band structures displayed that both two types of (1-100) and (11-20) heterostructured nanofilms were semiconductors with band gaps strongly depending on the GaN ratios as well as the thicknesses. Of particular interesting is that the band gaps decreased firstly, and then increased with the increasing GaN ratio. Furthermore, electronic contribution to the valence band maximum and the conduction band minimum, and optical absorption were discussed. Our results of ZnO/GaN heterostructured nanofilms with spatial separation of electrons and holes, and flexibly tunable band gaps hold great promise for applications in visible-photovoltaic field. 
Yang Zhang, Zhi-Feng Wu, Peng-Fei Gao, Dang-Qi Fang and Sheng-Li Zhang
cond-mat.mtrl-sci