SYSTEMATIC STEPS TOWARDS EXACTLY STOICHIOMETRIC AND UNCOMPENSATED CDTE BRIDGMAN CRYSTALS

A modified vertical Bridgman arrangement with Cd extra source and vari able CdTe melt surface temperature is used to find out conditions for the growth of near stoichiometric CdTe crystals. Growth experiments we re carried out with different temperature courses according to predict ions for the optimum temperature program obtained from thermodynamic c alculations. The transition point from p- to n-type conductivity for i nclusion-free crystals was observed at a CdTe melt surface temperature of 1118-degrees-C and a Cd source temperature of 850-degrees-C. The i ncorporation of shallow acceptors (Ag, Cu) as a function of the deviat ion from stoichiometry during the growth was analysed by photoluminesc ence, mass spectroscopy and atomic absorption spectrophotometry. The i ncorporation coefficients of atoms substituting Cd were deduced in dep endence on their total concentration in the melt and the Te excess. Th e maintenance of nearly stoichiometric growth conditions drastically r educes the substitutional impurity fraction, acting as shallow accepto rs, and therefore the carrier concentration.