Thermoelectric properties of semimetals
Thermoelectric properties of semimetals
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DOI：
10.1103/physrevmaterials.3.095401
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发表时间：
2019-09-03
影响因子：
3.4
通讯作者：
Zebarjadi, Mona
中科院分区：
文献类型：
--
作者：
Markov, Maxime;Rezaei, S. Emad;Zebarjadi, Mona
在过去的几十年里，重掺杂半导体是迄今为止研究最多的一类热电应用材料。它们具有比金属高2-3个数量级的塞贝克系数值，使得它们对于热电应用具有吸引力。传统观点认为，实现最大功率因数的半导体的最佳带隙应该在6到10 kBT之间，但迄今为止已知的最高功率因数材料没有带隙。在本文中，我们表明，半金属具有非常小的或没有带隙，但其导带和价带之间的高度不对称性，也可以有大的塞贝克系数值的顺序为200亩V/K，这是接近热电应用的最佳值。我们用第一性原理计算方法研究了一类18种半金属的能带结构，并用线性化的Boltzmann方程在常数弛豫时间近似下计算了它们的Seebeck系数。我们的结论是，尽管没有带隙，带不对称的半金属可以有良好的热电性能。我们分析了经常用来描述材料的热电性能的指标，并表明电子和空穴的状态密度的质量比是一个关键参数，导致高塞贝克系数值的半金属。因此，这项工作表明一些高热电性能材料可能具有半金属性质。
Heavily doped semiconductors are by far the most studied class of materials for thermoelectric applications in the past several decades. They have Seebeck coefficient values which are 2-3 orders of magnitude higher than metals, making them attractive for thermoelectric applications. Conventional wisdom suggests that the optimal band gap of a semiconductor to achieve the largest power factor should be between 6 and 10 kBT , yet the highest power factor materials known up to now do not have a band gap. In this paper, we show that semimetals with very small or no band gap, but high asymmetry between their conduction and valence bands, can also have large Seebeck coefficient values on the order of 200 mu V/K, which is near the optimum value for thermoelectric applications. We have studied the band structure of a class of 18 semimetals using first principles calculations and calculated their Seebeck coefficient using the linearized Boltzmann equation within the constant relaxation time approximation. We conclude that despite the absence of the band gap, semimetals with band asymmetry can have good thermoelectric performance. We analyze the metrics often used to describe thermoelectric properties of materials and show that the ratio of electron and hole mass of density of states is a key parameter resulting in high Seebeck coefficient values in semimetals. This work is therefore suggesting some high thermoelectric performance materials could be of semimetallic nature.