硅晶体热导率及点缺陷散射影响的分子动力学模拟

Thermal conductivity of silicon crystal and effects of point defect scatter by molecular dynamics

摘要:

由于材料中存在的缺陷结构会对材料的导热性能造成影响,本文应用逆非平衡分子动力学方法对硅材料的热导率及空位缺陷、间隙原子两种点缺陷结构对材料热导率的影响进行模拟研究. 模拟结果表明:由于点缺陷存在时声子与缺陷间的散射作用,材料热导率随两种点缺陷浓度的增加逐渐减小,低缺陷浓度使得材料热导率有更大幅度的降低,随缺陷浓度增加,热导率降低的幅度逐渐平缓; 当材料中存在相对较高缺陷浓度时,温度对热导率不再具有显著影响. 通过对热阻的分析得出,各温度下含两种点缺陷结构时的相对热阻增量均与所考虑的点缺陷浓度呈线性关系. 进一步由此宏观量间的线性关系揭示出微观层面声子、缺陷散射的平均自由程与点缺陷浓度间的反比关系. 以线性关系的斜率作为衡量点缺陷对材料热阻（热导率）影响程度大小的影响因子,两种点缺陷的影响因子均随温度的升高而降低,而间隙原子对材料热导率有相对更大的影响.

Abstract:

For the existence of defects in material can affect thermal conductivity, we calculate the thermal conductivity of perfect crystalline silicon and exam the effects of two types of point defect of vacancy and interstitial on the thermal conductivity of bulk crystalline silicon by molecular dynamics simulation applying reverse non-equilibrium method. The simulation results demonstrate that for scatter between phonon and defect, the thermal conductivity decreases with the increasing concentration of both types of the point defect and it decreases rapidly at low concentration condition and gradually gets flat with the increasing defect concentration. The loss of temperature sensitivity to thermal conductivity is observed at relative high concentration condition. In terms of thermal resistivity, the relative additional thermal resistivity is proportional to both types of point defect concentration considered. Furthermore, considering the microcosmic aspect, the inverse relationship between the concentration of point defect and the mean free path of scattering interacted by phonon and defect is deduced from this macroscopic proportional relationship. Taking the slope of the proportional relationship as impact factor to judge the extent of point defect effect on thermal resistivity (thermal conductivity), it is found by comparing the impact factor that the effects of both types of point defect on the thermal conductivity reduce with the increasing of temperature, and the interstitial has a rather more decreasing effect on the thermal conductivity than the vacancy.