The valence band offsets (ΔEV) of Zn(1-x)Mg(x)O/ZnO heterojunctions grown by plasma-assisted molecular beam epitaxy were measured by photoelectron spectroscopy. From the directly obtained ΔEV values, the related conduction band offsets (ΔEC) were deduced. All the Zn(1-x)Mg(x)O/ZnO heterojunctions exhibit a type-I band alignment with the ΔEC/ΔEV estimated to be 1.5, 1.8, 2.0 for x = 0.10, 0.15 and 0.20, respectively. The band offsets of Zn(1-x)Mg(x)O/ZnO heterojunctions depend on Mg composition. The accurate determination of energy band alignment of Zn(1-x)Mg(x)O/ZnO is helpful for designing ZnO based optoelectronic devices.

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 VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the Eg of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1−xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

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