Modeling of Nano-Scale Semiconductor Devices

本工作的目的是改进超小尺寸半导体器件的器件模拟模型。本文试图改进能量输运模型，以处理纳米器件中的非平衡载流子输运，异质结双极型晶体管（HBT）是非平衡载流子输运特别显著的半导体器件，并利用能量输运模型进行了一些分析。然而，给出输运参数的方法过于粗暴。例如，输运参数的组成和掺杂依赖性常常被忽略，并且它们的能量依赖性没有被充分纳入。因此，在这项工作中，我们已经开发出一种新的方法来给任何组合物，掺杂浓度和载流子能量的输运参数（如能量弛豫时间，载流子迁移率，和上谷分数）。这是通过使用蒙特卡罗方法和线性外推方法实现的。该方法被应用于AlGaAs/GaAs HBT的模拟。因此，我们已经发现，简化的传统方法导致高估或低估的速度过冲效应和不准确的评估的截止频率特性，这表明了适当的传输参数的重要性。该方法可以很容易地应用到其他具有位置相关能带结构的器件中。

The purpose of this work is to refine the device simulation model for ultra-small-sized semiconductor devices. We have tried to refine the energy transport model that can be used to treat the nonequilibrium carrier transport in nano-scale devices.Heterojunction bipolar transistors (HBTs) are the semiconductor devices where the nonequilibrium carrier transport becomes particularly remarkable, and some analyzes by the energy transport model have been made. However, the methods of giving transport parameters were too rude. For an example, the composition- and doping-dependences of transport parameters were often neglected, and their energy dependence was not adequately incorporated. Therefore, in this work, we have developed a new method to give transport parameters (such as energy relaxation time, carrier mobility, and upper-valley fraction) for any composition, doping density and carrier energy. This is realized by using the Monte Carlo method and the linear extraporation method. This approach is applied to the simulation of AlGaAs/GaAs HBTs. As a result, we have found that the simplified conventional approaches lead to overestimation or underestimation of the velocity overshoot effects and to the inaccurate evaluation of the cutoff frequency characteristics, indicating the importance of giving adequate transport parameters. The method developed here can be easily applied to other devices that have position-dependent band structures.