Acceptor-related luminescence at 3.314Â eV in zinc oxide confined to crystallographic line defects

The 3.314 eV emission band characteristically appearing in bulk, epitaxial, and nano-structured ZnO samples is studied by photoluminescence (PL) and spatially resolved cathodoluminescence (CL) at cryogenic temperatures along with SEM and TEM. We show that the band originates from a free electron transition to a neutral acceptor (e, A0) with ionization energy of 130±2 meV. Our TEM data reveal that the acceptor is a complex defect related with basal plane stacking faults. We also conclude that it is unrelated with elemental impurities such as group V elements used for nominal ZnO doping to achieve p-type conductivity.