The anisotropic Voigt effect in cubic semiconductors, with particular reference to the infra-red approximation

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Abstract
A formal treatment of the free carrier Voigt effect, valid for all frequencies and magnetic field strengths, and taking into account multiple reflections, is developed for cubic semiconductors with anisotropic effective masses. The behaviour of the Voigt rotation and ellipticity is considered in detail for multi-ellipsoidal band structures, and with the magnetic field confined to the (100) or (110) plane. A critical examination is made of the assumption, generally applied to the infra-red region, that the relaxation and cyclotron frequencies can be neglected in comparison to the frequency of the incident radiation. The so-called `plasma' corrections are analysed and it is shown that only one such term (which is isotropic) is important, and can be incorporated systematically into the theory. The approximate expressions for the rotation and ellipticity are compared with the exact treatment by detailed numerical calculations, based on representative data for n-type germanium. It is shown that the relaxation time correction may be significant and a simple form is obtainable for any isotropic scattering mechanism.