Atomic displacements and the nature of band edge radiative emission in cadmium telluride

Abstract

By combining low temperature luminescence measurements on electron-irradiated samples with reported luminescence data on non-stoichiometric specimens it has been possible to identify the luminescence role and energy levels of a number of defects in cadmium telluride. Cadmium and tellurium vacancies are shown to produce energy levels 0·036 ev and 0·46 ev above the valence band respectively. Using electrons from a Van de Graaff accelerator and observing photoluminescence and cathodoluminescence emission spectra at liquid helium temperatures the displacement energies of tellurium and cadmium have been found to be 7·8 ev and 5·6 ev respectively. The defects introduced by low temperature electron irradiation have been shown to produce emission characteristics which are not observed in specimens grown from the melt. It is suggested that this is the result of the strong perturbation of the electronic wave functions of a cadmium vacancy by the displaced cadmium atom at a nearby interstitial site.