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

在不久的将来，半导体器件的尺寸越来越小，将达到基本极限（~ 50纳米），低于该极限，器件将无法操作。另一方面，碳纳米管在1991年被发现，具有卓越的电子、结构、机械和导电性能，为利用这些大分子制造纳米器件打开了大门，其尺寸低于普通半导体器件的极限。根据它们的手性，碳纳米管既具有金属性质又具有半导体性质。通过将这些纳米管与金属引线接触，甚至接触不同的纳米管，可以制造出场效应晶体管、单电子晶体管或整流器等器件。然而，仍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对于低功耗快速器件的应用来说仍然太大。人们对其负责任的影响所知甚少，为了获得更多的了解，理论上的努力似乎是必要的。其他悬而未决的问题涉及纳米管结的传导、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，我们打算使用紧密绑定和从头算来解决其中的一些问题。虽然半经验的紧密结合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精确。因此，我们打算在这个项目的第二阶段进行从头算。

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.