Exploration of Zn Resonance Levels and Thermoelectric Properties in I-Doped PbTe with ZnTe Nanostructures

Abstract

Motivated by the theoretically predicted Zn resonant states in the conduction band of PbTe, in the present work, we investigated the effect of Zn substitution on the thermoelectric properties in I-doped n-type PbTe. The room temperature thermopower values show good agreement with the theoretical Pisarenko plot of PbTe up to a carrier concentration of 4.17 × 10(19) cm(-3); thus, the presence of Zn resonance levels is not observed. Because of the low solubility of Zn in PbTe, a second phase of coherent ZnTe nanostructures is observed within the PbTe host matrix, which is found to reduce the lattice thermal conductivity. The reduced lattice thermal conductivity in PbTe by ZnTe nanostructures leads to notable enhancement in the figure of merit with a maximum value of 1.35 at 650 K. In contrast to the recent literature, the carrier mobility is not found to be affected by the band offset between ZnTe nanostructures and PbTe. This is explained by the quantum tunneling of the charge carrier through the narrow offset barrier and depletion width and coherent nature of the interface boundary between the two phases, i.e., ZnTe and PbTe.

Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

“…0.8 [2,3], which can approach ca. 2.0 owing to doping and nanostructuring [4][5][6]. The lattice thermal conductivity of PbTe is typically 2.2 Wm −1 K −1 at room temperature [7,8], which is yet far away from the theoretical alloy limit [9].…”

Preparation and low temperature stability of PbTe nanocrystals embedded in ZnTe matrix by hot-wall deposition

“…The composite has a strict hetero-interface between PbTe and ZnTe, without forming a ternary solid solution such as Zn 1-x Pb x Te. Hence, PbTe nanocrystal is expected to form a steep energy potential barrier with type-I band offset [19]. According to Brus model [28], the ground state transition of electron-hole pairs in PbTe nanocrystal is calculated to be 0.38 eV with a mean grain size of 13 nm at 290 K, which is the smallest size thus obtained in the present study.…”

“…This system phase-separates at temperatures below 1160 K in bulk phase diagram [15]. Also, a nanocomposite thin film of PbTe nanocrystal embedded in a ZnTe matrix is capable of exhibiting quantum size effects because of the relatively large exciton Bohr radius of 46 nm in PbTe [16], and the relatively large band-gap difference between ZnTe (2.25 eV) [17] and PbTe (0.31 eV) [18] with type-I band offset [19]. Also, vapor pressure of PbTe [20] is similar to that of ZnTe [21].…”

A Practical Approach to Evaluate Lattice Thermal Conductivity in Two-Phase Thermoelectric Alloys for Energy Applications

“…There are many studies dealing with effects of second-phase precipitation on thermal conductivity of TE compounds, in particular for PbTe-based compounds [22,26,32,44,45,46,47,70,71,72,73]. First, our room temperature value of calculated lattice thermal conductivity, ca.…”

“…These are narrow-gap semiconductors offering the unique combination of high Seebeck coefficient with relatively high electrical conductivity and low thermal conductivity. Owing to this combination, single-phase PbTe exhibits a maximum ZT value of ~0.8 [18], which can normally reach ~1.3 or surpass the limit of 2.0 under certain conditions, owing to doping and nanostructuring [22,44,45]. The lattice thermal conductivity of PbTe is ca.…”