  The band alignment in ZnO/GaN and related heterostructures are crucial for
the uses in solar harvesting technology. Here, we report our density functional
calculations of the band alignment and optical properties of ZnO/GaN and
ZnO/(Ga1-xZnx)(N1-xOx)/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
(Ga1-xZnx)(N1-xOx) 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/(Ga1-xZnx)(N1-xOx)/ZnO core-shell solar cell model is presented to improve
the visible light adsorption ability and carrier collection efficiency.
