Anomalous mobility behavior in CdS and CdTe: Electrical evidence for impurity pairs

An anomalous mobility behavior in certain n-type CdS and CdTe samples has been observed. This behavior is characterized by low-temperature-Hall-mobility maximums which are much higher than can be understood on the basis of simple impurity-charge scattering. The anomaly correlates with the level depth of the hydrogenic-donor defects controlling the conductivity, the degree of compensation, and with the thermal annealing history of the sample. It is suggested that the effect is due to defect pairing.