In general, carrier transport can be divided into three
regimes: diffusive transport, ballistic transport, and quantum transport. When the gate length is much greater than the carrier mean free path, the carriers transit within the diffusive transport regime where scattering dominates. Carriers can reach their equilibrium states through sufficient scattering
events and thus DD (Drift-Diffusion) model can capture well this equilibrium carrier transport property. When the gate length is shorter than de Broglie wavelength, the carriers transit within the quantum transport regime, where the full quantum transport approach such as non-equilibrium Green’s function (NEGF) is suitable to simulate strong quantum confinement and significant source-to-drain tunneling. In the range between these two regimes, the carriers transit from quasi-ballistic to ballistic transport regime. The semi-classical approach Monte Carlo simulator incorporated with full band structure is able to capture the non-equilibrium transport effects.