Large bandgap tunability of GaN/ZnO pseudobinary alloys through combined engineering of anions and cations

Abstract

Bandgap engineering of gallium zinc oxynitride (GaZnON) thin films has been performed by the GaN/ZnO pseudobinary alloying in a periodical superlattice order through the pulsed laser deposition technique. By tuning the growth temperature, the combined engineering of anions and cations in GaZnON quaternary alloys leads to a large tunability of the optical bandgap from 1.80 to 4.34 eV. In terms of the enthalpy of formation and kinetic dynamics of reactant species, nitrogen incorporation is effective to form Zn3N2-rich GaZnON quaternary alloys at low-temperature (<100 °C) conditions far from the equilibrium, while amorphous nitrogen deficient GaZnON is formed at high temperatures with ZnGa2O4 and β-Ga2O3 nanocrystalline structures embedded. The conduction band (CB) and valence band (VB) of GaZnON are determined by Zn 4s orbital electrons and the hybridization of N 2p and O 2p electrons, respectively, while the Ga 4s and O 2p are predominant to construct the CB and VB of O-rich GaON due to the low solubility of N at high temperature. The asymmetric band bowing effect of GaZnON quaternary alloy demonstrates a large bandgap tunability down to the visible spectral range, which provides significant potential applications in the harvest of solar energy technologies.