The valence-band offset of ZnO / MgO ͑111͒ heterojunction has been directly measured by x-ray photoelectron spectroscopy. Excluding the strain effect, the valence-band offset is determined to be 0.87Ϯ 0.20 eV, and the conduction-band offset ⌬E C is deduced to be −3.59Ϯ 0.20 eV, indicating that ZnO / MgO heterojunction has a type-I band alignment. The conduction-band and valence-band offset of MgO / ZnO is used to interpret the origination of p-type conduction in undoped Mg x Zn 1−x O alloy and deeper acceptor level in undoped and N-doped p-type Mg x Zn 1−x O alloy than in ZnO.

This work reports on the fabrication and characteristics of n-ZnO/p-GaN and n-ZnO/n-MgZnO/n-ZnO/p-GaN heterojunction light emitting diodes (LEDs). Both devices exhibited diode-like rectifying current-voltage characteristics. Room temperature electroluminescence (EL) spectra for both LEDs consisted of dominant emission at 375 nm and two weaker bands centred at 415 nm and 525 nm, which were attributed to ZnO excitonic transition and defect-related emissions from GaN and ZnO, respectively. Moreover, it was demonstrated that the single heterojunction required a higher injection current to obtain an excitonic EL than that for the n-ZnO/n-MgZnO/n-ZnO/p-GaN LEDs. This indicated that the insertion of the MgZnO layer confined the injection carriers and thus increased the intensity of excitonic emission in the ZnO active region.

We report on the fabrication of an n-Mg0.12Zn0.88O/p-GaN heterojunction light-emitting diode with an MgO dielectric interlayer by plasma-assisted molecular beam epitaxy. The current−voltage curve of the heterojunction diode showed obvious rectifying characteristics with a threshold voltage of about 8 V. Under forward bias, an ultraviolet electroluminescence (EL) emission located at about 374 nm coming from the Mg0.12Zn0.88O layer was observed at room temperature. This is one of the shortest EL emissions observed in ZnO-based pn junctions to the best of our knowledge. The origin of the EL emission was elucidated in terms of the carrier transportation process modulated by the MgO interlayer in the heterojunction.

Nitrogen doped zinc oxide (ZnO) films have been prepared by molecular beam epitaxy. The as-grown samples show n-type conduction, but they convert to p-type after being annealed in O2 atmosphere. X-ray photoelectron spectroscopy reveals that the conversion is mainly caused by the escaping of substituted N molecule (N2)O donors from the films, and photoluminescence spectroscopy confirms the extraction of (N2)O. The work shown in this paper reveals experimentally that the main compensation source in nitrogen doped ZnO is (N2)O donors instead of intrinsic donors or background impurities, and annealing in oxygen may be a promising route to p-ZnO.