Modeling of crystal impurities in III-V ultra-thin body field-effect transistors within the empirical tight-binding framework

In this paper, we present a novel technique to model crystal impurities in III-V semiconductors at the material level, within the empirical sp³d⁵s* tight-binding (TB) framework. Regular semiconductor atoms are replaced by so-called “impurity atoms” whose TB parameters are adjusted to create single trap states characterized by a flat E-k dispersion. With the help of two dimensionless parameters, the energy level of a trap state can be continuously adjusted from deep inside the band gap to well inside the conduction band. To increase trap volume and model more complex defect structures, two or more impurity atoms can be clustered together. Coupled to a Poisson-Schrödinger device simulator, the model accounts for both electrostatic screening caused by free charge carrier trapping and trap-assisted tunneling. In particular, the impact of trap energy and volume on the coherent drive and leakage currents of an ultra-scaled double-gate In_0.53Ga_0.47As MOSFET is investigated. It has been found that conduction band traps substantially lower the device ON-current, while source-to-drain tunneling assisted by band gap traps significantly increases the subthreshold slope.