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Thermal conductivity of silicon: theoretical first principles study DOI:10.15199/48.2016.09.25

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New version of the first principles molecular dynamics calculations of thermal conductivity of materials has been proposed and applied to the silicon crystals. The method proposed is based on the kinetic theory of phonon thermal conductivity and permits to calculate several material properties (specific heat, elastic constant, acoustic velocity, mean phonon relaxation time and coefficient of thermal conductivity) at certain temperature. The method has been applied to the silicon crystal and the results obtained have been found to be in satisfactory agreement with corresponding experimental data. The method proposed is promissing for the ab initio calculations of thermal conductivity of pure and doped semiconductors. Streszczenie. Zaproponowano nowy sposób obliczeń metodą dynamiki molekularnej z pierwszych zasad współczynnika przewodności cieplnej materiału i zastosowano go do kryształów krzemu. Metoda bazuje na kinetycznej teorii fononowej przewodności cieplnej i daje możliwość obliczenia szeregu własności materiałowych (ciepła właściwego, współczynnika elastyczności, prędkości akustycznej, średniego czasu relaksacji fononów i współczynnika przewodności cieplnej) w określonej temperaturze. Metoda została zastosowana do kryształów krzemu a obliczone wielkości okazały się być zadowalająco bliskie do odpowiednich wartości eksperymentalnych. Zaproponowana metoda może być wykorzystana do obliczeń z pierwszych zasad przewodności cieplnej doskonałych i domieszkowanych półprzewodników. (Przewodność termiczna krzemu: badania teoretyczne z pierwszych zasad). Keywords: silicon, coefficient of thermal conductivity, molecular dynamics. Słowa kluczowe: krzem, współczynnik przewodności cieplnej, dynamika molekularna. Motivation The silicon (Si) based materials and other wide band gap semiconductors remain the most frequently used substances for the fabrication of different electronic devices. Thermal characteristics of these materials and interfaces b[...]

Ab initio molecular dynamics calculations of heat conductivity for silicon related materials DOI:10.15199/48.2017.08.16

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Thermal effects occurring in the active electronic elements and devices lead to their temperature increase and may change their functional characteristics. To keep these characteristics within the determined frameworks, one has to construct the corresponding devices taking into account the heat conductivity characteristics of the corresponding active and neighboring materials. Because of the large variety of these materials in modern electronics the problem of their heat characteristics determination is extremely important [1]. There are several theoretical techniques reported in the literature [2], which are used for determination of the phonon thermal conductivity. One of the often applied techniques is the molecular dynamics (MD), which can be separated into two main groups: (1) equilibrium and (2) nonequilibrium methods. In an equilibrium MD simulation, the system under investigation has a constant average temperature and an average heat flux of zero [2]. However, at each instant of time a finite heat flux exists due to instantaneous fluctuations of temperature. The popular Green-Kubo method [3, 4], based on the general fluctuation-dissipation theorem [5], relates the lattice thermal conductivity of the system to the time required for such fluctuations to dissipate. The corresponding algorithms however are not implemented in the more popular ab initio packages, for example in VASP code [6]. In the present study, we propose a new approach for the theoretical first-principles calculations of the phonon lifetime  and thermal diffusivity D of a material on the basis of the standard ab initio molecular dynamics (AMD) study. This approach has been applied to the study of heat conductivity in pure silicon and phosphorus doped silicon crystals. Some subsidiary calculations of this type were performed with diamond, sapphire (Al2O3) and silver. On the basis of the calculated thermal diffusivity D one can obtain the corr[...]

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