Abstract
In the beginning of the New Age, the development of technology was more rapid than the other ages, specifically the semiconductor technology. Today, nonstop scale-down devices are approaching the limit of thermodynamics. It implies that researchers need to search new transistors which have innovative structure. These innovative transistors could replace MOS-transistors, like MOS replaced vacuum tubes. The study of electron transport through single molecules has evolved thanks to C. Joachim et al, who measured the current through C60[1], and M. A. Reed et al who fabricated molecule that are suspended on metal contacts[2]. In the following year, first carbon nanotube field-effect transistors (CNTFETs) had been fabricated [3][4]. Therefore, the molecular transistor is one among several of the next generation transistors. At the same time theoretical efforts have been made to describe and understand the experiments. Actually, theoretical and experimental results had showed errors. Furthermore, some theories which talk about transport have provoked a great deal of controversy. Consequently, if researchers want to improve nanotransistors, they would need to understand the transport theory. In this thesis, I have simulated the properties of hydrogen molecular junction and CNTFETs ab initio. In addition to this, I attempt to understood their transport mechanism.