Anion vacancies in II–VI chalcogenides: Review and critical analysis

• A comprehensive and critical review of the existing experimental data is presented.
• Energy levels of anion vacancies for Zn- and Cd-related II–VI materials are discussed.
• Recombination schemes explain photo-EPR, absorption, luminescence, and photoconductivity.
• The level of singly charged anion vacancy for all Zn-related II–VI materials is at EC−1.0 eV.
• For all Cd related compounds this level is at EC+0.8 eV.

We performed critical analysis and comparison of all EPR, photo-EPR, photosensitive optical absorption, photoluminescence, and photoconductivity data taken on various Zn- and Cd-related II–VI chalcogenides compounds, such as ZnO, ZnS, ZnSe, and ZnTe, and CdS, CdSe, and CdTe. We developed a scheme for the electronic transitions and recombination associated with anion vacancies that is common for all these materials. This scheme explains all known facts obtained to date on quenching and excitation of the EPR signal, optical absorption, photoluminescence and photoconductivity. Based on these data we determined that the location of the energy level of the singly charged anion vacancy, VA+, is nearly equal for Zn-related II–VI materials (EC−1.0 eV) and EC+0.8 eV for Cd-related materials. For Cd-related chalcogenides most of the data were derived only from photoluminescence- and photoconductivity-spectra, so based on the available data, the position of the energy level of a singly charged anion vacancy in these materials was determined not so convincingly. Nonetheless, these materials have attracted much interest for decades because of their industrial applications as luminescent devices, laser filters and other optical elements, infrared, visible- and (X) γ-ray-detectors, solar cells, and the like.