First-Principles-Based Quantum Transport Simulations of Interfacial Point Defect Effects on InAs Nanowire Tunnel FETs

Abstract

The effects of a single point defect on InAs gate-all-around nanowire tunnel FETs (NW TFETs) are investigated. We considered two kinds of interfacial defects, the arsenic dangling bond (As-DB) and the arsenic antisite (As-In). The critical physics related to the point defects, which are the charge trapping (CT), the trap-assisted tunneling, and their interplay, are rigorously captured using the full quantum transport model with the physical defect Hamiltonian obtained from the density functional theory calculations. We found that both defects on the NW cause the bandgap states, which crucially affects the TFETs performances. Through nonequilibrium Green's function method self-consistently coupled with Poisson's equation, the characteristics of the point defects under finite bias conditions are analyzed. We found that the CT is strong in As-In, and thus the defect level, referenced to the valence band edge, is significantly changed by the gate bias. The strong CT leads to the screening of the gate field, which makes the defect level of As-In effectively pinned near the drain Fermi level. The radial distributions of the density of states (DOS) and the phase relaxation time are analyzed. As-In shows the strongly localized DOS at the defect center, while the DOS of As-DB is relatively delocalized due to the coupling with the valence bands. The impact of the defects on the TFET performances is examined as the gate length is scaled down. It is shown that As-In acts as a limiting factor for scaling down of the TFETs.