Low-temperature magnetotransport properties of PbTe fims doped with Thallium grown by Molecular Beam Epitaxy

PbTe is a narrow gap semiconductor that crystallizes in the rock-salt structure. PbTe is also an important thermoelectric material with figure of merit (ZT) exceeding 2.0. Thallium is the only impurity known to cause superconductivity in PbTe, even though it can be doped with other impurities to similar carrier concentrations. We have grown PbTe films on single crystal CdTe(211)B substrates by Molecular Beam Epitaxy. The films are doped with Thallium (Tl) acting as an acceptor, the only impurity known to cause superconductivity in PbTe, even though it can be doped with other impurities to similar carrier concentrations levels. We investigate the low temperature magnetotransport properties of PbTe films doped Tl. The PbTe films are 150 nm or 650 nm thick and we measure hole carrier concentrations 10¹⁴-10¹⁵ cm^-2. We find evidence of a Kondo effect below 20 K for high Tl doping with hole carrier concentrations ranging from 10¹⁴ to 10¹⁵ cm^-2.