Abstract
A luminescence study is carried out on as-grown and Cd-annealed samples towards a systematic analysis of V-doped CdTe and CdZnTe crystals. PL spectra of as-grown V-doped crystals show a series of sharp high energy lines which are associated with free excitons and excitons bound to neutral shallow donors (unknown) and acceptors (possibly Li Cd0). These shallow impurities are also involved in a donor-acceptor pair (DAP) recombination band. More remarkable is the presence of a wide band around 1.1 eV whose intensity is particularly high in CdZnTe samples codoped with vanadium and arsenic. Annealing under Cd-overpressure produces a number of changes: the shallow DAP disappears and a deeper structured band appears around 1.42 eV; furthermore the intensity of the 1.1 eV band is strongly reduced. Cathodoluminescence experiments (CL) performed at 100 K on some of these crystals show transitions similar to the above except the high energy exciton lines which are not observed. These results are examined with the object to understand the involvement of vanadium in the observed transitions. The band at 1.1 eV is discussed in terms of recombination between a V 2+ excited state and the valence band. On the other hand, the structured band around 1.42 eV could be an indication of a new A-centre including a vanadium atom and a cadmium vacancy.
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