Effect of a Nickel Impurity on the Galvanomagnetic Properties and Electronic Structure of PbTe
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TRONIC PROPERTIES OF SEMICONDUCTORS
Effect of a Nickel Impurity on the Galvanomagnetic Properties and Electronic Structure of PbTe E. P. Skipetrova,b,*, B. B. Kovaleva, I. V. Shevchenkoa, A. V. Knotkob,c, and V. E. Slynkod a Moscow
State University, Faculty of Physics, Moscow, 119991 Russia State University, Faculty of Materials Science, Moscow, 119991 Russia c Moscow State University, Faculty of Chemistry, Moscow, 119991 Russia d Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Chernivtsi, 58001 Ukraine *e-mail: [email protected] b Moscow
Received April 15, 2020; revised April 20, 2020; accepted April 27, 2020
Abstract—The phase and elemental composition and galvanomagnetic properties of the Pb1 – yNiyTe alloys at temperatures of 4.2 K < T < 300 K in magnetic fields of B < 7 T are investigated upon a variation in the nickelimpurity concentration along a single-crystal ingot synthesized by the Bridgman–Stockbarger technique. The solubility of nickel is shown to be no more than 0.35 mol %. The anomalous temperature dependences of the Hall coefficient and temperature and field dependences of the magnetoresistance are established. The results obtained are explained under the assumption of the formation of an inversion layer with n-type conductivity on the sample surface and the existence of several competing conductivity mechanisms in the samples. A model of the Pb1 – yNiyTe electronic structure is proposed that suggests Fermi-level pinning within the Ni impurity band located at the edge of the valence band and moving deeper into it with increasing temperature. Keywords: Pb1 – yNiyTe alloys, galvanomagnetic effects, electronic structure, nickel-impurity band DOI: 10.1134/S1063782620100279
1. INTRODUCTION The doping of lead telluride-based alloys with 3d transition metals evokes the occurrence of mainly resonance donor-impurity levels in the electronic spectrum of these materials [1]. In the PbTe compound, the levels of impurities from the first half of the series (Sc, Ti, V, Cr) are localized in the vicinity of the bottom of the conduction band [2–5]. The first of the levels of variable-valence 3d impurities located in the valence band of the PbTe compound (the Fe level) appears under its very top [6]. With an increase in the content of tin in Pb1 – xSnxTe alloys, it moves into the light valence band with extrema at points L of the Brillouin zone and can reach the top of the heavy valence Σ band at a certain temperature-dependent critical tin content (x = 0.60–0.65 at a temperature of T = 4.2 K) [7, 8]. This is interesting for enhancing the thermoelectric figure of merit of IV–VI semiconductor-based materials by band engineering methods [9–19]. In particular, one can hope to achieve the maximum synergistic effect in Pb1 − x − ySnxFeyTe alloys due to a combination of the advantages of its two main directions: crossing of the extrema of the light- and heavy valence bands in the electronic spectrum [9–15] and the existence of a resonance level near the Fermi level [1
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