The analsis of in-plane lattice thermal conductivity of thin-film superlattices
Date Issued
2006
Date
2006
Author(s)
Liu, Yu-Wei
DOI
zh-TW
Abstract
It is known that the thermal conductivity of a thin-film superlattices semiconductor has a larger figure-of-merit, mainly because its thermal conductivity is significantly reduced by the size effects. The goal of this study is to re-establish a theory for calculating/predicting the in-plane lattice thermal conductivity of a thin-film superlattices semiconductor. The theory is particle-based for the thickness of each layer still being larger than the phonon coherent length scale. The phonon Boltzmann transport equation is thus solved under the single relaxation-time approximation and proper boundary conditions. From the calculation results of the present model, it is found that the phonon heat flow rate is largely decreased due to the infinitely many interactions between phonons and the partially specular and partially diffuse interfaces through reflections and refractions. Moreover, the thinner each layer, the stronger the interface scattering effect is. An optimum thickness ratio resulting in a minimum lattice thermal conductivity is also found due to a balance between the difference of the intrinsic thermal conductivities and the boundary scattering effect. It is also shown that the predicted thermal conductivities also agree well with the experimental measurements. Finally, the temperature-memory effect on the lattice thermal conductivity is found to be negligible at room temperature.
Subjects
超晶格薄膜
聲子波茲曼方程式
晶格熱傳導係數
溫度記憶效果
Thin-film superlattice
Phonon Boltzmann transport equation
Lattice thermal conductivity
temperature-memory effect
Type
thesis
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