Cathodoluminescent imaging of ZnO:N films. Study of annealing processes leading to enhanced acceptor luminescence

A worldwide effort is under way to understand the activation of acceptor states in ZnO with the motivation to achieve persistent p-type conductivity. In this study, cathodoluminescent (CL) imaging, electron microscopy (SEM), secondary-ions mass spectrometry (SIMS), and X-ray diffraction (XRD) are used to compare ZnO:N films subjected to a rapid thermal annealing process (RTP) in N${}_2$ and O${}_2$ atmosphere at 400-900 °C. The study, performed for ZnO:N films with nitrogen concentration of 2 × 10${}^{18}$ at cm${}^{-3}$ grown under O-rich conditions is directed to establish the optimal atmosphere and temperature at which acceptor-related CL is enhanced and correlated with structural properties. XRD shows that crystallite size increases from ≈100 to ≈250 nm with increasing annealing temperature up to 800 °C. The low-temperature (LT) CL maps reveal that the acceptor- and donor-related CL mostly derives from different crystallites. Both annealing medium and temperature influence acceptor-related CL intensity, which is higher under oxygen annealing. It is observed that the intensity of acceptor-related CL increases with annealing temperature up to 800 °C and then decreases. Noticeable donor-related emission appears only after RTP at 700 °C and becomes prominent for RTP at 900 °C (© 2022 Wiley‐VCH GmbH)