Structural stability and band alignment in the c-plane ZnO/GaN heterostructure

The structural stability and electronic properties of ZnO on c-plane GaN substrates with and without a Ga-adlayer or Ga-bilayer are studied by first-principles calculations. The ZnO/GaN heterostructures are determined by a layer-by-layer mode from the initial adsorption of the alternative Zn and oxygen atomic layers of the first ZnO unit cell on c-plane GaN surfaces. The Ga-adlayer occupies the T₄ sites of GaN (0001) substrates and improves the ordered structure of the grown ZnO. The atomic and the electronic structures are systematically analyzed for the optimized ZnO/GaN heterojunction. The perfect Zn-terminated ZnO/GaN (000$\overline{1}$) heterostructure has a band gap 2.57 eV and small band offset values, which is a potential candidate for GaN-based semiconductor heterojunction field-effect transistors devices. The Ga-adlayer induces in-gap states and causes a decrease of the band offsets for the Zn-terminated ZnO/GaN (000$\overline{1}$) heterojunction. (paper)