Modified Becke-Johnson Research Articles

Electronic structure and band gap of zinc spinel oxides beyond LDA: ZnAl2O4, ZnGa2O4 and ZnIn2O4

We examine the electronic structure of the family of ternary zinc spinel oxides ZnX2O4 (X=Al, Ga and In). The band gap of ZnAl2O4 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 ZnGa2O4 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 ZnAl2O4 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 ZnX2O4. The GW and MBJ band gaps are in good agreement with each other. In the case of ZnAl2O4, 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.

Band gap of InxGa1−xN: A first principles analysis

We report first principles analysis of the band gap Eg of ternary group-III nitride InxGa1−xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method. We have implemented the semilocal modified Becke–Johnson (MBJ) exchange potential to accurately determine the band gap. The doping of In atoms into the GaN crystal is handled by the InxGa1−xN alloy model within the coherent potential approximation (CPA). The LMTO-CPA-MBJ approach allows us to predict Eg as a function of arbitrary In concentration x. Quantitative comparison to the experimental data is made.