Infrared Absorption Studies of Aluminum, Lithium and Aluminum + Lithium Related Defects in Zinc-Selenium and Cadmium-Tellurium

The experimental work presented here is a detailed investigation of the defect structure of the Al and/or Li-related defects in ZnSe and CdTe. Three essentially independent but closely related studies are reported and discussed. The first study reports the infrared absorption measurements of Li-diffused, Al-doped ZnSe and CdTe. The experimental results are largely in agreement with previously reported measurements for Al+Li-doped ZnSe. The 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 behavior very similar to that of ZnSe. The experimental results can be approximated by a "strongly -coupled" Al-Li pair model. 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. The second study is to determine results of Al -related defects in ZnSe. Through a systematic study of the annealing behavior, it is suggested that the infrared absorption spectrum of the localized vibrational modes of Al-doped ZnSe can be explained by two Al defects: Al(,Zn) and an Al dimer, possibly 2Al(,Zn)-V(,Zn), where the two Al(,Zn) and V(,Zn) are all mutually second nearest neighbors to one another. A simple molecular model is used to calculate the local frequencies and the results show the observed band frequencies can be accounted for the model. The last work is a detailed study of Li-related defects in ZnSe and CdTe. The results are completely different from those previously reported. In the ZnSe:Li system, the reproducibility of all of these bands observed here for samples from different sources and the prescence of a full Li isotopic shift indicate that our results are indeed due to Li modes in ZnSe. In CdTe:Li our results demonstrate that the previous report was preliminary and incomplete. It is also shown here that prolonged diffusions of Li in both ZnSe and CdTe lead to the formation of new phases.