Incorporation of Cd‐Interstitial Double Donors into CdS Single Crystals

Abstract

Abstract The incorporation of excess Cd into CdS crystals in a Cd atmosphere is studied experimentally. During the heat treatment in Cd vapour the conductivity (ν) of the crystals is measured as a function of Cd pressure ( p Cd) and temperature, between 400 and 730 °C. The relaxation of σ after a step‐like increase in p Cd is also investigated. It is shown that excess Cd is incorporated in the form of doubly ionised Cd interstitials (Cd ○ 2+ ), and this leads to a transition from “pure” Frenkel disorder to interstitial disorder. The energy required for the incorporation of a neutral Cd atom on an interstitial site (Cd gas → Cd ), the migration energy of Cd , and the first ionisation energy of Cd ○ are found to be 1.0 eV, 0.62 eV, and 0.05 eV, respectively. The formation energy of a Frenkel defect (Cd + Cd ) is estimated to be about 2.5 eV. The temperature dependence of the conductivity of crystals quenched after heat treatment in Cd vapour is also measured and is found to be determined by the first ionisation of Cd ○ at low temperatures. It is shown that large concentrations of Cd interstitials and Cd vacancies can be frozen in by quenching.