Development of Tight-binding-based band structure simulator and its application to device simulation

Abstract

As devices scale down continuously to a few nanometers, alternative device structures become highly desirable to enhance the performance of nanoscale metal-oxide-semiconductor field-effect transistors (MOSFETs). Consequently, dual gate ultra-thin-body (UTB) devices, multi gate FinFETs, and gate all around nanowire devices are considered as possible candidates for the next generation devices due to their better electrostatic controllability over the channel than that of planar MOSFETs. Furthermore, new channel materials such as Ge and III-V semiconductors incorporated with strain engineering are also contemplated to improve the transport properties in nanoscale devices. As a consequence of these trends, to provide insight into the device operation, it becomes essential to describe not only the electronic band structure but also the carrier transport properties of the devices with including quantum mechanical effects in computational electronics. In this thesis, we introduce the semi-empirical tight-binding (TB) methods to accurately describe the band structure of bulk, nanowire, and UTB structures at the atomic level which has its origin in linear combination of atomic orbitals (LCAO) method. It is shown that appropriate boundary condition, namely surface passivation, should be applied in the TB Hamiltonian to remove spurious states in the calculation of the band structure of abruptly truncated systems such as nanowires and UTBs. Moreover, implementation of spin-orbit (SO) interactions is also addressed, and it can be seen that the effect of SO interactions is almost negligible in the case of Si which has a relatively small SO splitting energies. Since the semi-empirical TB method computes the band structure at the atomic level, strain effects can be directly incorporated by the displacement of atoms which is determined based on elasticity theory. By employing the developed semi-empirical TB band structure simulator, an in-depth systematic analysis of band stru...