碳纳米管交流输运特性研究

AC Transport Properties of Carbon Nanotube

提出了一种新型的研究半导体低维系统的含时输运特性的数值模拟方法。基于紧束缚模型,直接在时域采用迭代法计算含时的非平衡格林函数(NEGF),求解出交流信号作用下的响应电流。将该方法应用于低维碳纳米管系统的交流输运性质的研究,并对载流子含时输运的物理机制进行了阐述。结果表明:在外加电压作用的瞬间,电流值突然变得很大,类似于传统CMOS器件的过冲效应。当输入电压为单个方波,随着时间的推移,电流呈现出平滑的逐步振荡衰减,最终趋于稳态。当输入电压为连续方波,响应电流的振荡幅度和频率随电压幅度的增加而增加。仿真结果有助于对低维材料电学特性的评估,并且为将来工作在交流信号下的低维纳米电子器件的设计和制作提供初步的理论依据。

In this paper, we present a novel numerical approach to study time-dependent transport in lowdimensional systems of semi-conductor. Due to tight-binding approximation, this method directly computes the time-dependent non-equilibrium Green＇ s functions by recursive method in the time domain, obtains the current in response to an ae signal. Then we apply it to explore the ae transport properties of carbon nanotuhes. The results show that： when a voltage is applied to one electrode, the instantaneous current suddenly increases, similar to the overshoot effect in traditional CMOS devices. When the voltage is a sin- gle square pulse, the current shows smooth damping oscillation attenuation versus time, and reaches a steady state in the end. When the input voltage is a continuous square pulse, the amplitude and oscillation frequency of the current increase with the increasing amplitude of the voltage. Simulated results may be useful to evaluate the electrical properties of low-dimensional materials, and provide a preliminary theoretical basis for designing and making the low-dimensional nanoelectronic devices which will operate under ac signals in the future.