Impurity bands in a magnetic field of arbitrary strength

On the basis of the self-consistentt-matrix approximation for a system of quasi free electrons interacting with randomly distributed attractive-potentials, we discuss impurity bands in the presence of a magnetic field of arbitrary strength. We compare the results with existing theoretical work on the limiting cases of weak and strong magnetic fields, which are shown to be partly incompatible, and with experimental work onn-type InSb in the magnetic freeze-out regime. Satisfactory agreement is obtained between the thermal ionisation energy, evaluated from experiments, and the calculated gap energy, separating impurity band and conduction band.