TECHNOLOGY OF CdTe MONOGRAIN POWDERS

Abstract

Monograin CdTe powders were grown by recrystallisation in isothermal ampoules in the presence of CdCl, or CdCl,~NaCl liquid phases. We found that NaCl in CdCl, flux inhibits crystal growth and dopes CdTe with Na, which acts as an effective acceptor impurity in CdTe. Te in the flux enabled us to convert the n-type conductivity to p-type. The cooling rate was found to be the most important technological factor to control electrical parametres of powders. The highest values of p-conductivity (~10 €2 cm) in undoped CdTe were achieved in the CdCl,-Te flux by combined cooling: quenching from 650°C to the room temperature and additional annealing at 400°C followed by slow cooling. Nearly the same results were obtained in samples lightly doped with Na ([Na]yos =5 X 10'7 ¢m™) and Te in the flux and quenched from 750°C or slowly cooled from 510°C. The prerequisites for the high conductive n-CdTe monograin powders are the lowest possible recrystallisation temperature and the use of unmodified CdCl,.