Defects responsible for abnormal n-type conductivity in Ag-excess doped PbTe thermoelectrics

Journal Article · Tue Jul 07 04:00:00 EDT 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4923391· OSTI ID:22490767

Ryu, Byungki; Lee, Jae Ki; Lee, Ji Eun; Joo, Sung-Jae; Kim, Bong-Seo; Min, Bok-Ki; Lee, Hee-Woong; Park, Su-Dong ^[1]; Oh, Min-Wook ^[2]

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1. Thermoelectric Conversion Research Center, Korea Electrotechnology Research Institute (KERI), 642-120 Changwon (Korea, Republic of)
2. Department of Advanced Materials Engineering, Hanbat National University, 305-719 Daejeon (Korea, Republic of)

Density functional calculations have been performed to investigate the role of Ag defects in PbTe thermoelectric materials. Ag-defects can be either donor, acceptor, or isovalent neutral defect. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect at Pb-site is formed and the environment changes to the Pb-rich/Te-poor condition. Under Pb-rich condition, the ionized Ag-interstitial defect (Ag{sub I}{sup +}) becomes the major donor. The formation energy of Ag{sub I}{sup +} is smaller than other native and Ag-related defects. Also it is found that Ag{sub I}{sup +} is an effective dopant. There is no additional impurity state near the band gap and the conduction band minimum. The charge state of Ag{sub I}{sup +} defect is maintained even when the Fermi level is located above the conduction band minimum. The diffusion constant of Ag{sub I}{sup +} is calculated based on the temperature dependent Fermi level, formation energy, and migration energy. When T > 550 K, the diffusion length of Ag within a few minutes is comparable to the grain size of the polycrystalline PbTe, implying that Ag is dissolved into PbTe and this donor defect is distributed over the whole lattice in Ag-excess doped polycrystalline PbTe. The predicted solubility of Ag{sub I}{sup +} well explains the increased electron carrier concentration and electrical conductivity reported in Ag-excess doped polycrystalline PbTe at T = 450–750 K [Pei et al., Adv. Energy Mater. 1, 291 (2011)]. In addition, we suggest that this abnormal doping behavior is also found for Au-doped PbTe.

• OSTI ID: 22490767
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 1 Vol. 118; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CHARGE STATES
DENSITY FUNCTIONAL METHOD
DIFFUSION LENGTH
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
FERMI LEVEL
FORMATION HEAT
GRAIN SIZE
LEAD TELLURIDES
POLYCRYSTALS
THERMOELECTRIC MATERIALS