Optical Properties of GaN/ZnO solid solutions studied by Density Functional Calculations

Semiconducting alloys of GaN/ZnO are promising hosts for solar photo-catalysis. The aqueous interface has been shown by Domen and collaborators\footnote{K. Maeda {\it et al.}, Nature {\bf 440}, 295 (2006).} to catalyze water oxidation, a key half- reaction in water splitting. We calculate by DFT, the energetics of many (GaN)$_{1-x}$(ZnO)$_x$ supercell configurations. Results show that significant short-range order should be expected. A phase diagram is suggested from free energies calculated versus temperature and concentration. The mechanism of band gap bowing is examined. The DFT+U method and hybrid functionals are used to reduce the problems of band gap underestimation. Oscillator strengths near the band gap are calculated, and an ensemble-averaged dielectric function is constructed, with an aim to learn how to optimize solar light absorption.