Magnetic Field Dependence of the Cyclotron-Resonance Linewidth at Infrared Frequencies

We have derived expressions for the cyclotron-resonance line-shape parameters by means of a new formalism. The formalism is based on a "damping iteration" for the exact expression of the conductivity tensor in the presence of static impurities. We have applied this theory to the case of a nondegenerate semiconductor in the quantum limit and have obtained an expression of the cyclotron-resonance linewidth for the case of dilute and weak scatterers. We have considered electron-impurity interactions with a screening radius, separately, of Gaussian and isotropically screened Coulomb forms. In both cases we have found that the cyclotron absorption line broadens and approaches a constant value with increasing magnetic field, in the limit of a strong enough field so that the screening radius is much larger than the cyclotron radius. This result is in contradiction to earlier theoretical calculations and a recent interpretation of some experiments. A discussion of the earlier theoretical works as well as of the experimental work of Apel et al. is given.