High-temperature investigations of CdS single crystals. I. Electron concentration, Cd solubility, and charge of intrinsic defects

The electron concentration n in CdS single crystals was studied as a function of temperature (T = 300 to 1200 K) and Cd vapour pressure (pCd = 0.1 to 0.9 atm). It is found that at pCd = const the value of n non-monotonically depends on T and passes through a maximum. This points to a retrograde solubility of Cd in CdS; its dependence on pCd is determined. It is concluded that with decreasing temperature a part of the excess Cd forms agglomerates; the degree of dissociation of these agglomerates depends on T and is independent of pCd. The charge of the dominant electrically active defects changes within the investigated temperature range: these defects are singly charged at lower temperatures and doubly charged at higher temperatures.