非简谐振动对半导体基外延石墨烯热电效应变化规律的影响

Effects of non-harmonic vibration on the thermoelectric properties of semiconductor-based epitaxial graphene

摘要:

本文建立了半导体基外延石墨烯的物理模型，考虑原子的非简谐振动，研究了它的杂化势以及热电势随化学势和温度的变化规律，探讨了原子非简谐振动对热电效应的影响. 对硅基外延石墨烯热电势的研究结果表明：简谐近似下，杂化势与温度无关；只考虑到第一非简谐项，杂化势随温度升高而增大；同时考虑到第一、第二非简谐项，则杂化势随温度升高而减小. 在给定温度下，外延石墨烯的热电势随化学势的变化在化学势为 处不具左右对称性，且在化学势为 eV附近有突变；给定化学势时，外延石墨烯热电势与单层石墨烯相似，均随温度升高而非线性减小，但外延石墨烯的值大于单层石墨烯的值；与简谐近似相比，非简谐效应会减小外延石墨烯热电势的值但减小量很小. 非简谐效应对热电势的影响随温度的升高而缓慢增大，大小在0.23%~0.25%之间.

Abstract:

In this paper, we establish the physical model of semiconductor-based epitaxial graphene. By considering the atomic non-harmonic vibration, we have the variations of the hybrid potential and thermoelectric potential of semiconductor-based epitaxial graphene with chemical potential and temperature are investigated, respectively. The influence of atomic non-harmonic vibration on the thermoelectric effect is also discussed. The results show that: 1) The hybrid potential is independent of temperature under the simple harmonic approximation. If the first non-harmonic term is considered, the hybrid potential increases with increasing temperature. However, if both the first and second non-harmonic terms are considered, the hybrid potential decreases with increasing temperature. 2) At a given temperature, the variation curve of thermoelectric potential of epitaxial graphene with chemical potential is left-right asymmetric at the chemical potential of zero, and there is a mutation near the chemical potential eV. 3) At a given chemical potential, the thermoelectric potential of epitaxial graphene is similar to that of single-layer graphene, namely that both decrease nonlinearly with increasing temperature, while the thermoelectric potential value of epitaxial graphene is larger than that of single-layer graphene. Compared with the simple harmonic approximation, the non-harmonic effect can reduce the thermoelectric potential value of the epitaxial graphene with a small amount. The influence of the non-harmonic effect on the thermoelectric potential increases slowly with increasing temperature, ranging from 0.23% to 0.25%.