Models of donor impurity compensation in cadmium telluride

A review is presented of the various models proposed to explain electric compensation of donors in CdTe. These models differ by the strength of interaction between impurities and cadmium vacancies : non interacting donor ions and charged defects ; formation of complexes by association of defects and impurities ; chemical compensation between donors and native defects. These analysis postulate the presence of a large number of ionized free vacancies. Results of high temperature measurements are discussed which set certain limits to the concentration of ionized vacancies under specified conditions. Starting from these values it appears difficult to account for compensation of donor impurities in the range 1017 cm-3. A tentative model is then presented which assumes the existence of neutral cadmium vacancies in a large concentration and describes the compensation process by a donor-neutral vacancy interaction, such complexes being stabilized by electron trapping. From this point of view, the electronic perfection of presently grown CdTe is limited by the residual impurities content.