Description of anomalous centers in chlorine doped-CdTe by a non-purely electronic model

Abstract

In a study of chlorine-doped CdTe by capacitance techniques a new aspect to the “anomalous” effects associated with the incorporation of chlorine in CdTe as reported by several authors [4,5] has been discovered. There is evidence for the existence of an electron trap but there is a drastic disagreement between the result of thermostimulated capacitance measurements ( ΔE = 0.41 eV) and photocapacitance measurements (trap located at mid-gap approximately). Similar results were found on samples differing by the self-compensation ratio for the same chlorine content. The different models previously used to explain the behaviour of chlorine-doped CdTe were considered; namely the double-acceptor center and non-Γ donor models, but these models were ruled out and a new model proposed which is not a purely electronic model. In this, two chlorine atoms are involved in each anomalous center, one of the two atoms being able to occupy two sites in the lattice. To each configuration corresponds a given charge state of the center and a different electronic ionization energy. The thermally stimulated experiments are those associated with a change in the microscopic configuration of the center that leads to the freeing of the trapped electrons.