Small valence band offsets of non-polar ZnO/Zn1-xMgxO heterojunctions measured by X-ray photoelectron spectroscopy

The valence band offsets (Delta E-V) of the alpha-plane non-polar ZnO/Zn1-xMgxO heterojunctions grown by plasma-assisted molecular beam epitaxy were investigated by X-ray photoelectron spectroscopy. Excluding the strain effect, the Delta E-V are determined to be -0.02 eV, -0.02 eV, -0.03 eV, and the related conduction band offsets (Delta E-C) are deduced to be 0.06 eV, 0.10 eV, 0.17 eV for x = 0.05, 0.08 and 0.13, respectively. The heterojunctions form in the type-I straddling alignment and the Mg composition dependent band alignment is revealed. Our results show important polarity dependence for ZnO/Zn1-5MgxO heterojunctions. The accurate determination of the band alignment of non-polar ZnO/Zn1-xMgxO heterojunctions is valuable for designing non-polar ZnO-based optoelectronic devices. @ 2014 Elsevier B.V. All rights reserved.