Electronic structure and band gap of zinc spinel oxides beyond LDA: ZnAl2O4, ZnGa2O4and ZnIn2O4

We examine the electronic structure of the family of ternary zinc spinel oxides ZnX 2 O 4 (X=Al, Ga and In). The band gap of ZnAl 2 O 4 calculated using density functional theory (DFT) is 4.25 eV and is overestimated compared with the experimental value of 3.8–3.9 eV. The DFT band gap of ZnGa 2 O 4 is 2.82 eV and is underestimated compared with the experimental value of 4.4–5.0 eV. Since DFT typically underestimates the band gap in the oxide system, the experimental measurements for ZnAl 2 O 4 probably require a correction. We use two first-principles techniques capable of describing accurately the excited states of semiconductors, namely the GW approximation and the modified Becke–Johnson (MBJ) potential approximation, to calculate the band gap of ZnX 2 O 4 . The GW and MBJ band gaps are in good agreement with each other. In the case of ZnAl 2 O 4 , the predicted band gap values are >6 eV, i.e. ∼2 eV larger than the only reported experimental value. We expect future experimental work to confirm our results. Our calculations of the electron effective masses and the second band gap indicate that these compounds are very good candidates to act as transparent conducting host materials.