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

The valence band offsets (ΔEV) of the a-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 ΔEV are determined to be −0.02 eV, −0.02 eV, −0.03 eV, and the related conduction band offsets (ΔEC) are deduced to be 0.06 eV, 0.10 eV, 0.17 eV for x=0.05,0.08and0.13, 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 − xMgxO 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.