超短脉冲激光辐照硅膜升温效应的模拟研究

Simulation study on thermal effect of Si film irradiated by ultra-short pulse laser

考虑到载流子和晶格的热容、热导率、弛豫时间等热力学参数随温度非线性变化因素的影响,利用有限差分算法,数值求解了半导体材料自相关热传导模型,讨论了2μm厚硅膜在波长和脉宽分别为775 nm和500 fs的脉冲激光辐照下的升温规律。数值结果表明:硅膜前表面载流子温度在激光辐照过程的0.69 ps时刻达到最大值,在4.8 ps时刻以后硅膜基本趋于总体热平衡;载流子热容的快速变化以及单光子吸收和由载流子浓度变化而引起的载流子能流变化是导致载流子温度变化的主要原因;超短脉冲激光辐照时,激光作用时间短,各扩散项及传导项不起主要作用,因此硅膜内各主要计算参数与硅膜的厚度及基体材料类型等的关系不大。

Using the model of self-consistent for transport dynamics in semiconductors, taking the silicon film as example, the temperature effects on the heat capacity of carrier and lattice, thermal conductivity, relaxation time have been studied with a finite difference method. The primary researches in this paper are on the thermal response of 2 μm Si film irradiated by 500 fs laser pulse. The numerical results indicate that after having been heated for 0.69 ps, the maximum electron temperature at the front surface occurs, after about 4.8 ps the temperature is nearly thermally equilibrated. The temperature of carriers change is rapidly because the heat capacity of carrier changes rapidly. The linear absorption and the rate of change of the carrier energy density due to the changes of the carrier density are the two critical factors that influence the temperature of carriers.