Transport properties of carbon-nanotube devices studied by tight-binding and ab-initio calculations

在不久的将来，半导体器件缩小到越来越小的尺寸将达到基本极限(~50 nm)，低于该极限，器件将无法工作。另一方面，1991年发现的碳纳米管具有显著的电子、结构、机械和导电性能，为用这些尺寸低于普通半导体器件极限的大分子制造纳米器件打开了大门。根据它们的手性，碳纳米管既具有金属性质，也具有半导体性质。通过将这种纳米管与金属导线接触，甚至与不同的纳米管接触，就产生了场效应晶体管、单电子晶体管或整流器等设备。然而，仍然有一些严重的问题需要解决。例如，金属引线和纳米管之间的接触电阻仍然太大，不适合作为低功耗的快速器件的预期应用。人们对负责任的影响知之甚少，似乎有必要在理论上做出努力，以获得更多的洞察。其他悬而未决的问题涉及纳米管结中的传导、纳米管的电阻、电迁移以及外场对器件的操作和控制。在这个项目中，我们打算使用紧束缚和从头计算来解决其中一些问题。尽管半经验的紧束缚计算将允许大规模系统，并揭示主要的潜在物理原理，但它们在细节上可能不够准确。因此，我们打算在这个项目的第二阶段进行从头计算。

In the near future, the scaling down of semiconductor devices to smaller and smaller sizes will reach fundamental limits (~ 50 nm) below which the devices become inoperable. On the other hand, the discovery of carbon nanotubes in 1991 with their remarkable electronic, structural, mechanical and conductive properties has opened the door to build nanodevices from these large molecules with sizes below the limits for common semiconductor devices. Depending on their chirality carbon nanotubes show metallic as well as semiconducting properties. By contacting such nanotubes to metal leads or even contacting different nanotubes, devices like field-effect transistors, single electron transistors, or rectifiers have been created. However, there are still a number of serious problems to be solved. For example contact resistances between the metal leads and the nanotubes are still too large for the desired application as fast devices with low power dissipation. Little is known about the responsible effects and theoretical effort seems necessary to gain more insight. Other open questions concern the conduction in nanotube junctions, the resistance of nanotubes, electromigration as well as the operation and control of devices by external fields. In this project we intend to tackle some of these problems using tight-binding as well as ab-initio calculations. While the semi-empirical tight-binding calculations will allow large-scale systems and reveal the main underlying physical principles they may be insufficiently accurate in details. Therefore, we intend to perform ab-initio calculations in the second stage of this project.