The electrical properties and growth conditions of CdS crystals

Large crystals of cadmium sulphide have been grown in various partial pressures of cadmium and sulphur vapour. The concentration and ionisation energy of the shallow donors in the different crystals have been determined by measuring the Hall coefficient and electrical conductivity of semiconducting samples, and by comparing the magnitudes of the drift and Hall mobilities in photoconducting (semi-insulating) samples. The variation of the donor and acceptor content can be explained in broad terms in relation to the parameters of crystal growth. Hall measurements indicate that the ionisation energy of the shallow donors is 0·021 ± 0·002eV. The drift mobility experiment suggests that two shallow traps are present with energy depths of 0·015 and 0·037 eV. The variation of Hall mobility with temperature over the range 30–300°K can be explained in terms of polar optical mode, piezoelectric and ionised impurity scattering. The best value of effective mass obtained was 0·19m.