Infrared absorption of Al-Li defect pairs in ZnSe and CdTe

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Abstract
Infrared localised vibrational mode absorption bands have been measured for Li-diffused, Al-doped ZnSe and CdTe. Except for one band, the results for ZnSe are largely in agreement with previously reported measurements, and these results indicate that the prior assignments of the bands on the basis of a weakly coupled Al-Li pair model are questionable. There are no previous results for CdTe, but the present measurements indicate a behaviour very similar to that of ZnSe. The results are approximated by a 'strongly coupled' model in which the Li acts as a substitutional acceptor, LiZn, at a second-nearest-neighbour site to the AlZn donor. Some of the observed bands are due to the coupled modes and hence show only partial Li isotopic shift. The band positions are calculated and a comparison with the experimental results gives satisfactory agreement. Extensions of the estimates obtained from this model are in agreement with the measured results reported here for Li-diffused, Ga-doped ZnSe.
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