Native point defects and low p-doping efficiency in Mg2(Si,Sn) solid solutions: A hybrid-density functional study

Ryu, Byungki; Choi, Eun–Ae; Park, Sungjin; Chung, Jaywan; Boor, Johannes de; Ziółkowski, Pawel; Müller, Eckhard; Park, Su-Dong

doi:10.1016/j.jallcom.2020.157145

Cited by 21 publications

(41 citation statements)

References 40 publications

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“…Indeed, Li doping is aimed at Mg sites in the Mg2X material; however, it was found that, although Li on Mg In order to verify if the same mechanism can explain our experimental results, hybrid-DFT calculations were performed to study the defect stability of Zn-related defects in Mg 2 Si and Mg 2 Sn. The possible formation of Zn-related point defects is confirmed by comparing the formation energies of the Zn-related point defects to those of intrinsic and extrinsic (Bi and Li) defects from previous papers [39,40]. As the samples of interest presented in this paper are Sn-rich Mg 2 (Si,Sn) solid solutions, only the results of Mg 2 Sn are shown in Figure 5, while the results for Mg 2 Si are shown in Figure S5 in SI.…”

Section: Resultsmentioning

confidence: 74%

“…For simplicity, only the most stable defects (with Eform < 1 eV) are presented in the figure below and discussed. Note that if the defect formation energy difference is larger than 1 eV, the defect number density is negligible due to its exponential dependence on the defect formation energy [40]. Figure 5a,b show the defect formation energies of Zn in p-and n-type, respectively, Mg-poor Mg2Sn.…”

Section: Resultsmentioning

confidence: 99%

“…where E tot [D q ] and E 0 are total energies with and without defects, subscript i indicates the atomic element, µ i is the atomic chemical potential, δn i is the change of number of i-th element in the defective supercell with respect to the pristine one, and E F is the Fermi level of the system. Detailed information can be found in our previous work [39][40][41].…”

Section: Methodsmentioning

confidence: 99%

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Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

et al. 2021

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Thermoelectric generators are a reliable and environmentally friendly source of electrical energy. A crucial step for their development is the maximization of their efficiency. The efficiency of a TEG is inversely related to its electrical contact resistance, which it is therefore essential to minimize. In this paper, we investigate the contacting of an Al electrode on Mg2(Si,Sn) thermoelectric material and find that samples can show highly asymmetric electrical contact resistivities on both sides of a leg (e.g., 10 µΩ·cm2 and 200 µΩ·cm2). Differential contacting experiments allow one to identify the oxide layer on the Al foil as well as the dicing of the pellets into legs are identified as the main origins of this behavior. In order to avoid any oxidation of the foil, a thin layer of Zn is sputtered after etching the Al surface; this method proves itself effective in keeping the contact resistivities of both interfaces equally low (<10 µΩ·cm2) after dicing. A slight gradient is observed in the n-type leg’s Seebeck coefficient after the contacting with the Zn-coated electrode and the role of Zn in this change is confirmed by comparing the experimental results to hybrid-density functional calculations of Zn point defects.

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Section: Resultsmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

et al. 2021

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“…The formation energies of all charged native defects of Mg 2 Si, which are calculated using DFT, are shown in Figure 11, in agreement with previous studies. 19,20 Some native defects have a single charge state corresponding to having all filled or unfilled molecular orbitals in the valence or conduction bands, while others have multiple charge states corresponding to the existence of a molecular orbital state in the band gap.…”

Section: Formation Energies Of Defects In Mg 2 Simentioning

confidence: 99%

Chemical Interpretation of Charged Point Defects in Semiconductors: A Case Study of Mg2Si

Toriyama¹,

Brod²,

Snyder³

2021

Preprint

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The number of excess charge carriers generated by a point defect, defined by the "charge state" of a defect, is oftentimes an important quantity used to engineer the electronic properties of semiconductors. Here, we develop a molecular orbital theory-based framework for interpreting the charge state(s) of a point defect, which is based on local chemical interactions between the defect and the atoms surrounding the defect site. We demonstrate how the framework can be applied to native defects in Mg2Si, such as interstitials, vacancies, and antisite defects, by utilizing symmetry principles and Density Functional Theory calculations. We anticipate that such an interpretive framework will guide efforts to engineer electronic and optical properties of semiconductors through manipulation of intrinsic and extrinsic defects.

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“…[1][2][3][4][5]12] Furthermore, Mg 2 X(X = Si, Ge, Sn) are chemically and thermally stable, nontoxic, resistive against oxidation, economically inexpensive, environmentally friendly, relatively light weight, and therefore have a great potential for large-scale production. [2,7,8] More importantly, they possess a high figure of merit and can serve as good solidstate thermoelectric materials for converting waste heat to electricity. These excellent characteristics have fuelled robust effort to explore various aspects of Mg 2 X and find ways to improve and optimize their favorable performance.…”

Section: Introductionmentioning

confidence: 99%

Machine-learned model Hamiltonian and strength of spin-orbit interaction in strained Mg2X (X = Si, Ge, Sn, Pb)

Alidoust,

Rothmund,

Akola

2022

Preprint

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We have developed multi-orbital tight-binding (MOTB) Hamiltonian models to describe the electronic characteristics of intermetallic compounds Mg2Si, Mg2Ge, Mg2Sn, and Mg2Pb subject to strain. We have incorporated spin-orbital mediated interactions and calibrated the MOTB models to the band structures of density functional theory (DFT) by a massively parallelized multi-dimensional Monte-Carlo search algorithm. The results show that a five-band tight-binding (TB) model reproduces the key aspects of the band structures in the entire Brillouin zone. The five-band TB model reveals that the compressive strain localizes the contribution of the 3s orbital of Mg to the conduction bands and the outer shell p orbitals of X to the valence bands. The tensile strain, in contrast, has a reversed effect and weakens the contribution of the 3s orbital of Mg and the outer shell p orbitals of X to the conduction bands and valence bands, respectively. We have found that the π bonding in the Mg2X compounds is negligible compared to the σ bondings, follow the hierarchy |σsp| > |σpp| > |σss|, and the largest variation against strain belongs to σpp. Moreover, the five-band TB model allowed for estimating the strength of SOC in Mg2X and obtaining its functionality with respect to the atomic number of X and strain. Additionally, the calculations find significant band gap tuning and band splitting due to strain. It is shown that a compressive strain of −10% can open a band gap at the Γ point in metallic Mg2Pb whereas a tensile strain of +10% closes the semiconducting band gap of Mg2Si. Also, +5% of tensile strain can remove the three-fold degeneracy of valence bands at the Γ point in semiconducting Mg2Ge. Our results and model approach can be useful in designing devices made of Mg2X more accurately.

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Native point defects and low p-doping efficiency in Mg2(Si,Sn) solid solutions: A hybrid-density functional study

Cited by 21 publications

References 40 publications

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

Chemical Interpretation of Charged Point Defects in Semiconductors: A Case Study of Mg2Si

Machine-learned model Hamiltonian and strength of spin-orbit interaction in strained Mg2X (X = Si, Ge, Sn, Pb)

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