Wide bandgap tunability of N-alloyed ZnGa2O4 thin films

Abstract ZnGa 2 O 4 films with different nitrogen impurity concentrations were deposited using radio frequency magnetron sputtering in an ammonia (NH 3 )/Ar gas mixture and were post-annealed at different temperatures, ranging from 600 °C to 900 °C, in NH 3 atmosphere. The influence of ammonia partial pressure ratio and nitridation temperature on the microstructure, surface morphology, nitrogen doping profile, and optical properties has been investigated. The optical band gap of ZnGa 2 O 4 , under in-situ nitrogen-doping, decreases from 4.6 to 4.1 eV but the primitive ZnGa 2 O 4 crystalline structure does not change. On nitridation, the optical band gap gradually decreases from 4.6 to 2.1 eV and the ZnGa 2 O 4 changes into a zinc gallium oxynitride quaternary alloy structure. Secondary ion mass spectrometry analysis revealed that nitrogen atoms were uniformly distributed in the film. The narrowing, by more than 40%, of the optical band gap is attributed to the hybridization of Zn3d and N2p orbits promote p-d repulsion in the top of the valence band, and the formation of hexagonal wurtzite phase.