Cathodoluminescence spectra recorded, to high spatial and wavelength resolutions, on tilted ZnO epitaxial layers permitted the identification of a very prominent emission peak at 3.314 eV as being due to a free electron to shallow acceptor (EA ≈ 130meV) transition. By cross-correlation with transmission microscopic cross-sectional images recorded for the same samples it was found that these acceptor states were located on basal-plane stacking faults. High concentrations of acceptor states were found locally. Since this spectral feature was often reported in the literature, especially after attempts to obtain p-type or transition metal doping, it was concluded that stacking faults were a common by-product when group-V or other extrinsic atoms were incorporated into ZnO layers or nanostructures.

The Role of Stacking Faults and Their Associated 0.13eV Acceptor State in Doped and Undoped ZnO Layers and Nanostructures. Thonke, K., Schirra, M., Schneider, R., Reiser, A., Prinz, G.M., Feneberg, M., Sauer, R., Biskupek, J., Kaiser, U.: Physica Status Solidi B, 2010, 247[6], 1464–8