Comparative Mossbauer spectroscopic study of iron impurities in ZnSe

An anomalous spectral doublet attributed to Fe2+ impurity pairs is observed in Mossbauer absorption spectra of (Fe0.01Zn0.99Se)-Fe-57 below room tempe rature. Tn Mossbauer emission experiments, ZnSe:Co-57 polycrystal and powde r sources exhibit below 45 K the nucleogenic Fe1+ valence state born as an after effect of the electron-capture decay of Co-57. Above 8 K, the proport ion of the nucleogenic Fe1+ decreases under the effect of the thermally act ivated Fe1+ --> Fe2+ relaxation. The activation energy is estimated to 0.00 4 eV. While nucleogenic Fe1+ is absent in ZnSe:Co-57 single crystal spectra , increasing proportions are detected in samples with an enhanced specific surface. The formation model of the nucleogenic Fe1+ is extended to other z inc chalcogenides and a tentative model is developed, which shows the role of the surface electric field in limiting the formation of nucleogenic Fe1 in well crystallised source samples. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.