应变影响下单晶Ge薄膜热导率分析

Strain effect analysis on thermal conductivity of Ge thin films

摘要:

利用非平衡态分子动力学模拟方法研究了应变对Ge薄膜热导率的影响。结果表明系统应变对单晶Ge薄膜热导率产生明显影响,热导率随着拉伸应变的增大而减小,随着压缩应变的增大而增大,得出声子速率降低以及薄膜表面重构是产生该模拟结果的内在原因。同时,采用修正的Callaway模型对NEMD结果进行理论验证,两种方法得到的结果吻合得较好。理论结果表明应变弛豫时间对Ge单晶薄膜的热导率产生了重要影响。

Abstract:

Nonequilibrium molecular dynamics (NEMD) simulations are investigated to obtain an understanding of the effect of strains on the thermal conductivity of Ge thin films. The results show that the strains have an appreciable influence on the thermal conductivity of Ge thin films. The thermal conductivity decreases as the tensile strain increases and increases as the compressive strain increases. It is explained by the fact that the decrease of the phonons velocities and the surface reconstructions. Meanwhile, a theoretical calculation basing on Modified-Callaway model under different strains is performed to assess our NEMD simulation results. We find that the theoretical results closely match the molecular dynamics results. The theoretical analysis reveals that the contributions of the relaxation time on strains are very important to the thermal conductivity of Ge thin films.