Convergence of iron resonant level with heavy-hole valence band in Pb^sub 1-x^Sn^sub x^Te alloys

We synthesize a single-crystal Pb1-x-ySnxFeyTe (x = 0.08, y = 0.01) ingot and investigate the distributions of tin and iron along it, as well as the galvanomagnetic properties of samples cut from the ingot (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T). The scanning electron microscopy reveals microscopic inclusions with a reduced lead-tin content enriched with iron in a number of samples, indicating that the solubility limit of iron impurity is exceeded. In the main phase, the tin content rises monotonically along the ingot from x ≈ 0.06 to x ≈ 0.15 while the iron impurity concentration increases only slightly up to 0.6 mol. %. All samples exhibit the p-type metal conductivity. We find a monotonous increase in the free hole concentration at low temperatures with increasing tin content and an abnormal growth of the Hall coefficient with increasing temperature, indicating the pinning of the Fermi level by the resonant iron level lying in the valence band. Dependences of the hole concentration, of the Fermi energy, and of the Hall coefficient on the tin concentration and on the temperature are analyzed in the framework of the two-band Kane and six-band Dimmock dispersion relations. Compositional and temperature coefficients of deep iron level movement with respect to the band edges are determined and a diagram of the restructuring of the electronic structure with an increase of the tin concentration in alloys is build. The results indicate the possibility of crossing of the resonant iron level with the heavy-hole Σ band with increasing tin content in Pb1-x-ySnxFeyTe alloys and temperature.