Thermodynamic Properties of Nonstoichiometric Cadmium Telluride and Defect Chemistry Analysis

CdTe is one of the most important electrooptical materials for many kinds of radiation detectors because it has very advantageous properties as compared to other semiconductor chalcogenides of cadmium, such as comparatively great mobility, a simple controllability of the conductivity from n- top-type, and conversely, as well as the availability of higher quality and low cost crystal growth technique. The nonstoichiometric CdTe is used to make semi-insulator (or high resistivity) CdTe crystal for the X-ray detector. The thermodynamic properties and the defect chemistry analysis of CdTe is crucial to obtain the controllability of electronic properties in crystal growth or post-growth annealing. In this investigation the partial pressure of Te2(g) is measured over CdTe inside and on the limits of the homogeneity range and the atomic fraction of Te determined. A statistical thermodynamic analysis has been carried out for a model of Te-rich CdTe in which doubly ionizable Cd-vacancy acceptor and singly ionizable Te on Cd-site donor are assumed. The enthalpies and excess entropies of neutral Cd-vacancy and Te antistructure defect have been obtained. A foreign gas (Te,(g)) broadening coefficient of atomic absorption line profile of Cd(g) is determined using measured PT, 2 and optical density of Cd(g) at 2288 A as well as a well established model of Cd(g) absorption line