Hybrid density functional study of band alignment in ZnO-GaN and ZnO-(Ga _1-xZn _x)(N _1-xO _x)-GaN heterostructures

The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga _1-xZn _x)(N _1-xO _x)-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga _1-xZn _x)(N _1-xO _x) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga _1-xZn _x)(N _1-xO _x)-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.