Thinning down of thermal conductivity in ultrashort period superlattices
Thinning down of thermal conductivity in ultrashort period superlattices
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DOI：
10.1103/physrevb.88.115207
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发表时间：
2013-09
影响因子：
3.7
通讯作者：
I. O. Thomas;G. P. Srivastava
中科院分区：
文献类型：
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作者：
I. O. Thomas;G. P. Srivastava
给出了超短周期（Si）n（Ge）n[001]超晶格中晶格热导率张量分量{κα，β}约化的数值结果，其中n为原子双层的数目.计算是在单模弛豫时间近似，占原子间键长弛豫和采用声子色散关系从密度泛函微扰理论，模型非谐哈密顿量处理三声子相互作用，涉及声学以及光学声子在两种材料的超晶格结构，和一个改进的计划，由于在界面处的质量弄脏的声子散射。在室温下，对于n = 8的情况，电导率的交叉平面分量比平面内分量小约4.1倍，并且界面质量混合（IMS）散射强度为0.05。当IMS散射强度保持不变时，电导率的面内和跨面分量都随超晶格周期的增加而急剧减小。将物理因素考虑到IMS散射的行为中，我们预测了n = 4时热导率的最小值。我们估计，少量的界面质量污迹的结果在100至700 K的温度时，边界散射相对较弱的ZZ电导率分量约3%-14%的减少。我们估计相关的声子散射率，以解释现有的实验电导率测量系统的大小可比的（8，8）超晶格。
We present numerical results for the reduction of the lattice thermal conductivity tensor components {κα,β} in ultrashort period (Si)n(Ge)n[001] superlattices, with 1 n 8, where n represents the number of atomic bilayers. The calculations are made within the single-mode relaxation-time approximation, accounting for interatomic bond length relaxation and employing phonon dispersion relations obtained from density functional perturbation theory, a model anharmonic Hamiltonian to deal with three-phonon interactions involving acoustic as well as optical phonons in a two-material superlattice structure, and an improved scheme for phonon scattering due to mass smudging at interfaces. The cross-plane component of the conductivity is around 4.1 times smaller than the in-plane component for the n = 8 case at room temperature and an interface mass mixing (IMS) scattering strength of 0.05. Both the in-plane and cross-plane components of the conductivity decrease sharply with the superlattice period when the strength of the IMS scattering is kept constant. Incorporating physical considerations into the behavior of the IMS scattering, we predict a minimum of the thermal conductivity for n ≈ 4. We estimate that a small amount of interface mass smudging results in a reduction of around 3%–14% in the zz conductivity component for temperatures of 100 to 700 K when boundary scattering is relatively weak. We estimate relevant phonon scattering rates to explain available experimental conductivity measurements on a system comparable in size to the (8,8) superlattice.