Faraday effect in epitaxial films of IV-VI semiconductors

The Faraday effect is a powerful method to obtain information on the spin splittings of semiconductors. We measured the Faraday rotation of the narrow gap semimagnetic lead salt IV-VI semiconductors Pb1-xEuxTe, Pb1-xEuxSe (x < 5%) with energy gaps in the mid infrared. An optical bridge technique recently published for Faraday effect measurements in the visible spectral region, was modified for use in the mid infrared. This allowed for the first time to observe Faraday rotation in epitaxial grown narrow gap semiconductor films with thicknesses down to 2 mu m. The experiments were performed in external magnetic fields up to 7 T and at various temperatures down to 1.7 K. The Faraday effect can be calculated in the framework of a k . p - theory. In the case of diluted magnetic semiconductors the exchange interaction between the localised paramagnetic ions and the band carriers is added to the original k . p - Hamiltonian. Each allowed transition between an occupied and an unoccupied state contributes to the total amount of rotation. The experimental results Mn be quantitatively reproduced by such a calculation, acting as verification for the used band parameters. Thus in future the method will allow to determine band and exchange parameters in thin films and superlattices.