Resonant impurity level of Ni in the valence band of Pb1-xSnxTe alloys

The phase and elemental compositions and galvanomagnetic properties (4.2 K <= T <= 300 K, B <= 0.07 T) of samples from a single-crystal Pb1-x-ySnxNiyTe ingot (x = 0.08, y = 0.01) synthesized by the Bridgman-Stockbarger method were studied. Microscopic inclusions enriched in nickel were found. It is shown that in the main phase, the tin concentration increases exponentially along the ingot (x = 0.06-0.165), while the concentration of nickel impurity does not exceed 0.4 mol %. A significant increase in the concentration of holes along the ingot and an abnormal increase in the Hall coefficient with increasing temperature were found; both are due to the pinning of the Fermi level by the resonant nickel level located in the valence band. The dependences of the hole concentration and of the Fermi energy at T = 4.2 K on the tin concentration in alloys are calculated using the two-band Kane dispersion law. A qualitative model of electronic structure rearrangement is proposed. The model takes into account the movement of the nickel level into the depth of the valence band with an increase in tin concentration and the redistribution of electrons between the valence band and the level. The energy position of the nickel level and the speed of its movement relative to the top of the valence band with an increase in the tin content in Pb1-xSnxTe alloys are estimated.