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 electrical properties of polar and non-polar ZnMgO:Na films that have been fabricated on c-plane and r-plane sapphire substrates using intervened ZnO layers (10–30 nm thick) by pulsed laser deposition. Hall-effect measurements indicate that the a-plane ZnMgO:Na film exhibits p-type conductivity with a carrier concentration of about 3.5 × 1016 cm−3, while the polar film shows a compensatory conductivity. Meanwhile, the dependence of the band alignment on the orientation of the ZnMgO/ZnO heterojunctions has been investigated using photoelectron spectroscopy. The heterojunctions form in the type-I straddling alignment with valence band offsets of 0.07 (0.02) eV for the (non-)polar heterojunction. The difference in valence band offsets is primarily attributed to the spontaneous polarization effect. We propose that the smaller valence band offsets and larger conduction band offsets would reduce the NaZn acceptor level and enhance the relative intrinsic donor levels. Such effects consequently lead to p-type conductivity in non-polar ZnMgO:Na films. The band alignment of non-polar ZnMgO/ZnO can be used to facilitate p-type doping with a shallower acceptor state in the ZnO-like alloy.

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