Thermal Conductivity and Natural Cooling Rate of Excimer-Laser Annealed SI: A Molecular Dynamics Study
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0910-A05-05
THERMAL CONDUCTIVITY AND NATURAL COOLING RATE OF EXCIMER-LASER ANNEALED SI: A MOLECULAR DYNAMICS STUDY Byoung Min Lee1, Baek Seok Seong1, Hong Koo Baik2, Shinji Munetoh3, and Teruaki Motooka3 1 Neutron Physics Department, Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong, Daejeon, 305-600, Korea, Republic of 2 Dept. of Metallurgical Engineering, Yonsei University, 134 Shinchon-dong, Seodaemoon-ku, Seoul, 120-749, Korea, Republic of 3 Dept. of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan ABSTRACT To investigate the relationship between the thermal conductivity and the cooling rate, we have performed molecular-dynamics (MD) simulations based on a combination of the Langevin and Newton equations to deal with a heat transfer from l-Si to c-Si. The thermal conductivity of c-Si was measured by the direct method. In order to deal with finite-size effects, different cell sizes perpendicular to the direction of the heat current were used. The values of the thermal conductivity of 58 W/mK and 35.7 W/mK in the Tersoff potential were obtained at 1000 K and 1500 K, respectively. A MD cell with a length of 488.75 Å in the direction of a heat flow was used for estimating the natural cooling rate. The initial c/l interface systems were obtained by setting the temperatures of the MD cell at 1000 K and 1500 K, respectively, for Z ≤ 35 Å and 3800 K for Z > 35 Å. During the natural cooling processes, the temperature of the bottom 10 Å of the MD cell was controlled. The cooling rates of 7.4×1011 K/sec for 1000 K and 5.9×1011 K/sec for 1500 K were obtained, respectively.
INTRODUCTION The thermal conductivity of substrate materials is a key factor to determine the cooling rate of excimer-laser annealed Si. MD simulations are suitable for interpreting the experimental results, and they have been used as a good technique in obtaining the time-averaged atomic quantities and their fluctuations that are needed for calculating the thermal conductivity [1,2]. Experimentally, the thermal conductivity is determined by measuring the stationary heat flux necessary to maintain a temperature gradient. One fundamental problem during an experiment is the heat loss to the surroundings. But in a computer simulation, this problem can be avoided by imposing periodic boundary conditions. The two commonly applied methods for computing a thermal conductivity are the direct method and the Green-Kubo method [3-5]. The direct method is a nonequilibrium MD method that relies on imposing a temperature gradient across the MD cell. Therefore, it is similar to the experimental conditions. For the direct method, it is important to establish a steady-state heat current. This is done by scaling the velocity of the atoms lying in the heat source and the heat sink layer at each time step so that the desired temperature difference is obtained between the heat source and the heat sink layer of the system. The thermal conductivity is given by
κ =−
J , ∂T ∂x
where ∂T ∂x is the temperature
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