The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1−xO/BexMgyZn1−x−yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1−xO and BexMgyZn1−x−yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ΔEV) of Mg0.15Zn0.85O ( Eg = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( Eg = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1−xO is lower by 0.03 eV with the enlargement of Eg from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the Eg of the alloy is 3.73 eV. The ΔEV of Mg0.11Zn0.89O ( Eg = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( Eg = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher ...