Abundant Acceptor Emission from Nitrogen-Doped ZnO Films Prepared by Atomic Layer Deposition under Oxygen-Rich Conditions

Nitrogen-doped and undoped ZnO films were grown by thermal atomic layer deposition (ALD) under oxygen-rich conditions. Low-temperature photoluminescence spectra reveal a dominant donor-related emission at 3.36 eV and characteristic acceptor-related emissions at 3.302 and 3.318 eV. Annealing at 800 °C in oxygen atmosphere leads to conversion of conductivity from n- to p-type, which is reflected in photoluminescence spectra. Annealing does not increase any acceptor-related emission in the undoped sample, while in the ZnO:N it leads to a considerable enhancement of the photoluminescence at 3.302 eV. The high resolution cathodoluminescence cross-section images show different spatial distribution of the donor-related and the acceptor-related emissions, which complementarily contribute to the overall luminescence of the annealed ZnO:N material. Similar area of both emissions indicates that the acceptor luminescence comes neither from the grain boundaries nor from stacking faults. Moreover, in ZnO:N the acceptor-emission regions are located along the columns of growth, which shows a perspective to achieve a ZnO:N material with homogeneous acceptor conductivity at least at the micrometer scale.