蒙特卡罗方法模拟薄膜电致发光器件中碰撞离化的作用

Monte Carlo simulation of the effect of impact ionization in thin-film electroluminescent devices

基于经验赝势法得到的能带结构数据,采用分段多项式拟合获得ZnS能带结构的解析表达式,建立解析能带模型.使用建立的模型计算得到各能谷的态密度和总的散射速率,并与文献的计算结果进行了对比,验证该解析能带模型既具有非抛物型多能谷能带模型运算速度快、使用方便的优势,又具有与采用全导带模型相近的计算精度.进一步利用该模型进行蒙特卡罗模拟,得到第一导带和第二导带中电子数随电场强度的变化、不同电场中能量分布函数以及包含与不包含碰撞离化情况下电子能量随时间变化的曲线.讨论在外加电场下,电子在导带内各个能谷间和导带间的输运特性,揭示了谷间和带间散射在电子能量分布中的作用,特别是碰撞离化在电子能量分布和电流倍增中起到的重要作用.这些结论对研究提高薄膜电致发光器件的性能有一定的指导意义.

By fitting the empirical pseudopotential band structure data using piecewise polynomials, an analytical band model of ZnS is presented for thin-film electroluminescent devices. The density of states and scattering rates are calculated using the above model. As compared with the results from the full band model, we have shown that our model, which takes less time, has the same precision as that obtained from the full band model. Using Monte Carlo method, we simulated the field-dependent electron occupation functions of 1st and 2nd bands, electron energy distribution functions under four-electron fields and the dependence of electron energy on time with or without impact ionization. This shows that the inter-valley scattering, inter-band scattering and impact ionization are important for transporting electrons among valleys. Another important result is that the effect of impact ionization on current multiplication and electron energy distribution is also discussed.