High thermoelectric potential of Bi{sub 2}Te{sub 3} alloyed GeTe-rich phases

• Published in: Journal of applied physics 2016-07, Vol.120 (3)
• Main Authors: Madar, Naor, Givon, Tom, Mogilyansky, Dmitry, Gelbstein, Yaniv
• Format: Article
• Language: English
• Subjects: BISMUTH TELLURIDES; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONCENTRATION RATIO; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DOPED MATERIALS; FERMI LEVEL; GERMANIUM ALLOYS; GERMANIUM TELLURIDES; HOLES; OPTIMIZATION; SOLUBILITY; TELLURIUM ALLOYS; TEMPERATURE RANGE; THERMOELECTRIC PROPERTIES
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4958973

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe){sub 1−x}(Bi{sub 2}Te{sub 3}){sub x} alloys, with x values of up to 20%. Higher solubility limit of Bi{sub 2}Te{sub 3} in GeTe, than previously reported, was identified around ∼9%, extending the doping potential of GeTe by the Bi{sub 2}Te{sub 3} donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ∼1.55 at ∼410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%–17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge{sub 8}Bi{sub 2}Te{sub 11} and Ge{sub 4}Bi{sub 2}Te{sub 7} phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi{sub 2}Te{sub 3}), was suggested for further electronic optimization of the thermoelectric properties.