Defect structure of Sb2−xCrxTe3 single crystals

Abstract

Single crystals of Sb2Te3 doped with Cr (cCr=0–6×1020 cm−3) were prepared by the Bridgman method. The measurements of the Hall coefficient reveal a nonmonotonous dependence of hole concentrations on the Cr content in the crystal. The hole concentration decreases at low content of Cr, while at higher content of Cr it increases again. However, according to magnetic measurements, Cr atoms enter the structure and form uncharged substitutional defects CrSb×, which cannot affect the free carrier concentration directly. The observed dependence can be elucidated by means of a point defect model. The model is based on an assumption that defect structure of Sb2Te3 can be treated as hybrid Schottky and antisite defect disorder. Thus, we assume an interaction of CrSb× with the most populated native defects in the structure—antisite defects SbTe−1 and vacancies in the Te sublattice VTe+2.

Figure of Merit of (Sb0.75Bi0.25)2−x In x Te2.8Se0.2 Single Crystals

“…We note that the idea of interaction of impurity atoms with native defects of the host lattice was also used previously to describe free carrier changes in other tetradymitetype crystals. 8 From Fig. 3 it follows that, in the low-temperature region, the magnitude of the Seebeck coefficient S of all the doped samples (nominal x = 0.015 to 0.05) is higher compared with the magnitude for the undoped sample (x = 0).…”

Thermoelectric properties and nonstoichiometry of GaGeTe

“…Also, the pronounced decrease of both the Hall coefficient and the Seebeck coefficient can hardly support this idea. Thus, we suggest another scenario based on the presence of point defects rather like in tetradymite crystals, see e.g., [9,10].…”

Emergent surface superconductivity in the topological insulator Sb2Te3

“…From the detailed studies of these materials 17,50 we know that growth conditions using stoichiometric ratio starting materials result in slightly Te poor crystals, Sb 2 Te 3-x with xE0.03-0.05. Also, native concentrations of Sb antisites (contributing one hole each) and Te vacancies (contributing two electrons each) are B10 20 cm À 3 and 2 Â 10 19 cm À 3 , respectively, consistently accounting for the observed Hall number and other material properties 17,18 . As Te pressure during the growth is increased, a fully stoichiometric (2:3) crystalline material is obtained in which bulk carrier density is the lowest.…”

“…We note that such fine-tuned non-monotonic doping is not unprecedented; it has been also observed in Sb 2 Te 3 doped with Cr (ref. 17), in molecular-beam grown epitaxial TI films 51 , and upon stoichiometry variation in Bi-Sb-Te system grown by zone melting 52 .…”

“…Tellurium overpressure makes no detectable structural changes, yet results in a sharply localized and evidently non-monotonic doping effect 17,18 : in this process electrons are supplied to the system in a narrow range of Te vapour pressure (in the vicinity of B1.4 MPa), reducing free hole density by over two orders of magnitude, as compared with the samples grown at higher or lower vapour pressures. The net effect is an upshift of the Fermi energy from the bulk valence bands towards the vicinity of the Dirac point, with concurrent enhancement of carrier mobility from the typical mt200 cm 2 V À 1 s À 1 in the non-superconducting samples to the unprecedented value of \25,000 cm 2 V À 1 s À 1 in the superconducting phase.…”