Cathodoluminescence studies of the 1.4 eV bands in CdTe

Abstract

Using cathodoluminescence at 80 K, we have studied the 1.4 eV luminescence bands in nominally undoped, nominally stoichiometric CdTe and in donor-compensated, Te-rich CdTe. The present work represents the first combined measurements of injection level dependence, transition response and thermal quenching for these materials. We find that the 1.4 eV luminescence has the following characteristics : 1) the band shape and peak position are independent of injection level, except for those samples having overlapping bands, 2) the transition is slow, with characteristic times on the order of 1-5E-6 s, 3) the transition response time is approximately constant over three orders of magnitude in doping level, 4) the luminescence intensity increases with donor doping level, and 5) the luminescence shows thermal quenching with a relatively large activation energy. This combination of characteristics is not explicable in terms of well-understood transition mechanisms. While the results of our individual measurements are similar to results from corresponding measurements in the literature, it is clear from the present work that the contradictory conclusions of previous investigators regarding the nature of the 1.4 eV transitions in CdTe arose from the fact that this transition is of a more complex nature than generally appreciated rather than from the appearance of different types of transitions in different CdTe samples