Growth and characterisation of Pb1-xEuxTe

Abstract

Pb_1-xEu_xTe single-crystalline epitaxial films were prepared by a modified hot-wall technique. The structural properties were checked by X-ray diffractometry and microprobe analysis. Single-phase material with up to 5% Eu content was produced. Transport properties were investigated between 5 and 300K yielding electron concentrations and mobilities comparable with those of PbTe epitaxial layers. The direct energy gap and its dependence on Eu content as well as on temperature were determined by optical absorptance and reflectance measurements using Fourier transform spectroscopy. This technique also yielded the phonon and free-carrier contributions to the dielectric function in the far-infrared region. Intraband magneto-optical experiments were carried out in Faraday and Voigt geometries in order to obtain information on the effective masses and their anisotropies. For the interpretation of these reflectance and transmittance data as a function of frequency and magnetic field, a Drude model calculation for this many-valley system was performed. For the Voigt geometry in particular, the dielectric tensor and the appropriate complex refractive indices for the ordinary and extraordinary modes are treated in detail. The Shubnikov-de Haas data reveal that the L valleys are not occupied by the carriers equally. Magneto-optical studies between 5 and 50K confirm these findings. Possible sources for the carrier repopulation and its change with temperature are discussed.