Multi-terminal nano-electronic device simulations with atomistic details

Abstract

Miniaturization of electronics is an unstoppable trend in the semiconductor industry. Moore’s Law has been the driving force to the advancement of the industry for half a century; and will continue to be the indicator for technology developments. As the feature size of an electronic device is reducing to the nano-scale level, quantum mechanics and atomistic details will become more and more important. In addition, simulations on devices with two or more terminals, such as transistors or junctions, are essential for design of electronics. Thus, Quantum mechanics based method with atomistic details for simulations of nano-electronic devices with two or more terminals is proposed and demonstrated. Similar studies can be found in the literature. However, most work was focusing on static / steady state problems, only few had looked into the dynamics. On the other hand, most methods being used in previous work can only handle two-terminal devices, while those few methods which can be applied for multi-terminal devices can only deal with steady state problems. Therefore, there is a research gap lies in multi-terminal time-dependent device simulations; and this gap will be filled by the work in this thesis.

Quantum mechanics based method for open system has been used to simulate the electrical response through nano-electronic devices. Nearest neighbor tight binding models and carbon based models are the systems of interests. The core part of the structures of the systems of interest is a hexagonal ring. This is essentially a benzene ring based structure in our studies. Several situations for electrodes connecting the benzene ring at para- and metapositions are considered. Two-terminal cases and three-terminal cases for the mentioned systems have been studied. The third terminal in the three-terminal case is basically being viewed as a probe to the corresponding two-terminal case. For all the cases, steady state currents have been calculated; and currentvoltage curves of the systems have been obtained. Transient currents have also been calculated, so that dynamic responses of the systems are revealed. Different magnitudes of bias voltages have been applied to the systems. Linear response of the currents through the devices with respect to the bias voltage is observed for most cases. The para-position case can be taken as a reference to the meta-position case, due to simple structure and well-behaved responses. Interesting electric responses from the meta-position case is observed. The possibility for the meta-position system to be used as a transistor or other devices is briefly discussed.