Systematics of conduction in a band tail

Systematic trends in the transport properties of a series of slightly Eu-rich EuS crystals, which strongly suggest that conduction occurs in a band tail, are reported and analyzed. A quantitative model for transport in band tails is developed. The model achieves good agreement with the high-temperature resistivity and Hall coefficient of our samples, and gives accurate predictions of their low-temperature properties. © 1972 The American Physical Society.