Experimental evidence of the self-compensation mechanism in CdS

Microscopic origin of full electrical compensation of donor doped CdS was analyzed with perturbed angular correlation and I-fall-effect measurements. Single crystals were implanted with radioactive In-111 and stable In-115 ions. Total In concentration ranged from 10(16) to 10(20)/cm(3). A strong correlation was observed between electrical self-compensation and the formation of(In-Cd-V-Cd) pairs (A centers) as a result of thermal annealings. It is shown that the presence of In donors during thermal treatment under the S pressure provokes spontaneous formation of (doubly) ionized cation vacancies [V-Cd] During cooling, these vacancies form pairs with In donors (A center), which compensate the rest of the donors, leading to highly resistive material. The experiments presented provide direct evidence for self-compensation: doped crystals spontaneously create just a matching concentration of native point defects needed to compensate foreign doping atoms electrically. This holds for over four orders of magnitude of In concentrations. (C) 1999 Elsevier Science B.V. All rights reserved.