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

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0处不具左右对称性,且在化学势为±0.25 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.

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±0.25 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%.