Contributions of chemical potential to the diffusive Seebeck coefficient for bulk semiconductor materials

2020 ◽  
Vol 135 (6) ◽  
Author(s):  
Guangxi Wu ◽  
Xiong Yu
2013 ◽  
Vol 12 (06) ◽  
pp. 1350057 ◽  
Author(s):  
HSIU-YA TASI ◽  
CHAOYUAN ZHU

Dielectric constants and Seebeck coefficients for semiconductor materials are studied by thermodynamic method plus ab initio quantum density functional theory (DFT). A single molecule which is formed in semiconductor material is treated in gas phase with molecular boundary condition and then electronic polarizability is directly calculated through Mulliken and atomic polar tensor (APT) density charges in the presence of the external electric field. This electronic polarizability can be converted to dielectric constant for solid material through the Clausius–Mossotti formula. Seebeck coefficient is first simulated in gas phase by thermodynamic method and then its value divided by its dielectric constant is regarded as Seebeck coefficient for solid materials. Furthermore, unit cell of semiconductor material is calculated with periodic boundary condition and its solid structure properties such as lattice constant and band gap are obtained. In this way, proper DFT function and basis set are selected to simulate electronic polarizability directly and Seebeck coefficient through chemical potential. Three semiconductor materials Mg 2 Si , β- FeSi 2 and SiGe are extensively tested by DFT method with B3LYP, BLYP and M05 functionals, and dielectric constants simulated by the present method are in good agreement with experimental values. Seebeck coefficients simulated by the present method are in reasonable good agreement with experiments and temperature dependence of Seebeck coefficients basically follows experimental results as well. The present method works much better than the conventional energy band structure theory for Seebeck coefficients of three semiconductors mentioned above. Simulation with periodic boundary condition can be generalized directly to treat with doped semiconductor in near future.


2021 ◽  
Vol 81 (7) ◽  
Author(s):  
He-Xia Zhang ◽  
Jin-Wen Kang ◽  
Ben-Wei Zhang

AbstractThe Seebeck effect and the Nernst effect, which reflect the appearance of electric fields along x-axis and along y-axis ($$E_{x}$$ E x and $$E_{y}$$ E y ), respectively, induced by the thermal gradient along x-axis, are studied in the QGP at an external magnetic field along z-axis. We calculate the associated Seebeck coefficient ($$S_{xx}$$ S xx ) and Nernst signal (N) using the relativistic Boltzmann equation under the relaxation time approximation. In an isotropic QGP, the influences of magnetic field (B) and quark chemical potential ($$\mu _{q}$$ μ q ) on these thermoelectric transport coefficients are investigated. In the presence (absence) of weak magnetic field, we find $$S_{xx}$$ S xx for a fixed $$\mu _{q}$$ μ q is negative (positive) in sign, indicating that the dominant carriers for converting heat gradient to electric field are negatively (positively) charged quarks. The absolute value of $$S_{xx}$$ S xx decreases with increasing temperature. Unlike $$S_{xx}$$ S xx , the sign of N is independent of charge carrier type, and its thermal behavior displays a peak structure. In the presence of strong magnetic field, due to the Landau quantization of transverse motion of (anti-)quarks perpendicular to magnetic field, only the longitudinal Seebeck coefficient ($$S_{zz}$$ S zz ) exists. Our results show that the value of $$S_{zz}$$ S zz at a fixed $$\mu _{q}$$ μ q in the lowest Landau level (LLL) approximation always remains positive. Within the effect of high Landau levels, $$S_{zz}$$ S zz exhibits a thermal structure similar to that in the LLL approximation. As the Landau level increases further, $$S_{zz}$$ S zz decreases and even its sign changes from positive to negative. The computations of these thermoelectric transport coefficients are also extended to a medium with momentum-anisotropy induced by initial spatial expansion as well as strong magnetic field.


2011 ◽  
Vol 1314 ◽  
Author(s):  
Tsunehiro Takeuchi ◽  
Akio Yamamoto ◽  
Koto Ogawa

ABSTRACTThe relation between chemical potential and Seebeck coefficient was investigated by using high-resolution angle resolved photoemission spectroscopy. The temperature dependence of chemical potential was experimentally determined for the n-type TiS2 thermoelectric material and compared with the measured Seebeck coefficient. We found that the temperature dependence of chemical potential of TiS2 is significantly large, and its effect on Seebeck coefficient is not negligible. This fact strongly indicates that the temperature dependence of chemical potential has to be properly understood to construct the guiding principle for developing new, practical thermoelectric materials.


Author(s):  
V. N. Davydov

Singularities of thermopower (the Seebeck coefficient) are considered at the Lifshitz topological transitions (LTT) in bilayer graphene (BLG) and multilayer graphene (MLG) due to stacking change from AB to AA . The dependence of singularities on μ , γ 1 and Δ is investigated ( μ is the chemical potential, γ 1 is the interlayer hopping parameter and Δ is the gap value) for the gapped graphene, as well as for the gapless one. The present paper results indicate that effects of the thermopower singularities are appreciable and can be used to observe the LTT, and to explore the degree of stacking change from AB to AA in graphene. Therefore, the thermopower singularities at LTT due to stacking change from AB to AA can be used as a powerful tool to control electronic properties of BLG- and MLG-based structures.


2001 ◽  
Vol 681 ◽  
Author(s):  
J. Bagdahn ◽  
D. Katzer ◽  
M. Petzold ◽  
M. Wiemer ◽  
M. Alexe ◽  
...  

ABSTRACTDirect waferbonding is an appropriate technology to join two or more wafers of the same or of different materials. Waferbonding can be used to stiffen thin wafers during fabrication. However, conventional fabrication processes lead to an increase of the bond strength, which inhibits the required de-bonding. The propagation of cracks, which is based on a subcritical crack growth in the bonded interface, was used to cleave the bonded wafers. The subcritical crack growth is limited to the bonded interface, since the adjacent bulk semiconductor materials are inherently resistant to subcritical crack growth. The process allows the separation of Si-Si and Si-GaAs wafers after annealing. Wafer-bonded SOI wafers can also be separated with this technology even if they were annealed at 1100°C. The first examples for wafer stiffening during fabrication and wafer transfer using the developed approach will be presented.


2016 ◽  
Vol 78 (3) ◽  
Author(s):  
Muhammad Azim Izzuddin Mohd Amin ◽  
R. Ahmed ◽  
A. Shaari ◽  
Bakhtiar Ul-Haq ◽  
Mazmira Mohamad ◽  
...  

Linearized augmented plane wave plus local orbitals (LAPW + lo) method designed within density functional theory (DFT) has been used in this study to calculate the structural, electronic and thermoelectric properties of XCuOTe (X=Bi, Ce, La). Generalized gradient approximation, Wu-Cohen (GGA-WC) parameterized exchange correlation functional, was used. The structural and electronic calculations have a good agreement with previous study. For thermoelectric calculation, semi empirical Boltzmann approach implemented in BoltzTraP package was used to calculate Seebeck coefficient, electronic conductivity as well as thermal conductivity. By referring to previous studies, the results have good agreement with them. In addition, the Seebeck coefficient of these materials was calculated as a function of the chemical potential at temperatures 300K, 600K, and 900K. Our calculations highlight suitability of these materials for applications in thermoelectric devices.


2011 ◽  
Vol 71-78 ◽  
pp. 3741-3744
Author(s):  
Ke Gao Liu ◽  
Jing Li

For investigating the thermoelectric properties, bulk FeSb2and the composite of CoSb3:FeSb2=7:3 was prepared via sintering. The phases of samples were analyzed by X-ray diffraction and their thermoelectric properties were tested by electric constant instrument and laser thermal constant instrument. Experimental results show that, bulk FeSb2and the composite of CoSb3:FeSb2=7:3 are P-type semiconductor materials. The electric resistivity of bulk FeSb2sample increases with temperature rising while that of the composite (CoSb3:FeSb2=7:3) decreases with temperature rising. The Seebeck coefficient of the composite (CoSb3:FeSb2=7:3) is evidently higher than that of bulk FeSb2. The thermal conductivities of the composite (CoSb3:FeSb2=7:3) are relatively lower than those of bulk FeSb2. TheZTvalues of bulk FeSb2sample are lower than those of the composite (CoSb3:FeSb2=7:3), that of the later increases with temperature rising at 100~500°C, the maximum value is up to 0.1647.


Author(s):  
E.D. Boyes ◽  
P.L. Gai ◽  
D.B. Darby ◽  
C. Warwick

The extended crystallographic defects introduced into some oxide catalysts under operating conditions may be a consequence and accommodation of the changes produced by the catalytic activity, rather than always being the origin of the reactivity. Operation without such defects has been established for the commercially important tellurium molybdate system. in addition it is clear that the point defect density and the electronic structure can both have a significant influence on the chemical properties and hence on the effectiveness (activity and selectivity) of the material as a catalyst. SEM/probe techniques more commonly applied to semiconductor materials, have been investigated to supplement the information obtained from in-situ environmental cell HVEM, ultra-high resolution structure imaging and more conventional AEM and EPMA chemical microanalysis.


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