Cr-related energy levels and mechanism of Cr2+ ion photorecharge in ZnS:Cr



It is shown that published data and interpretation concerning the energy and origin of Cr-related defects in ZnS:Cr as well as the mechanism of the Cr2+ → Cr+ photorecharge are ambiguous and contradictory. New data concerning these questions obtained by means of photodepolarization (PDP) spectroscopy methods for the first time are given. Several peaks of the impurity photocurrent are revealed in the PDP spectrum of ZnS:Cr thin-film structures, which was measured from 0.7 eV to 3.9 eV. Two peaks are due to the photoionization of Cr2+ and Cr+ ions (2.8–3 eV and 1.3–1.5 eV, respectively). Three peaks are attributed to Cr-related lattice defects, namely, a equation image isovalent trap (∼3.5 eV) and a equation image acceptor isolated (∼2.7 eV) and associated with a donor (1.8–2.2 eV). A new interpretation of the mechanism of the photorecharge of Cr2+ ions is also proposed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)