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Materials Science and Engineering R 58 (2008) 228–270
ate/mser
Current transport models for nanoscale semiconductor devices
V. Sverdlov *, E. Ungersboeck, H. Kosina, S. Selberherr
Institute for Microelectronics, TU Vienna, Gusshausstr. 27–29, A-1040 Vienna, Austria
Abstract
Due to the rapid decrease in device dimensions the well-established TCAD tools are pushed to the limits of their applicability.
Since conventional MOSFETs are already operating in the sub-100 nm range, new physical effects and principles begin to
determine the transport characteristics, and the validity of conventional current transport models is in question. The drift-diffusion
model, which has enjoyed a remarkable ess due to its relative simplicity, numerical robustness, and the ability to perform two-
and three-dimensional simulations on large unstructured meshes, must be generalized to include hot-carrier and classical non-local
effects. This motivated the development of higher order moments transport models such as the hydrodynamic, the energy-transport,
and the six-moments models. After the introduction of stress for device performance enhancement the demand for accurate carrier
mobility calculations based on full-band Monte Carlo algorithms has significantly increased, since they allow calibration of
phenomenological mobility models and thus justify closure relations for higher order moments equations.
The transport models based on the semi-classical Boltzmann transport equation already contain information which can only be
obtained from quantum-mechanical consideration. These are the band structure, expressions for the scattering rates, and the Pauli
exclusion principle reflecting the Fermi statistics of carriers. With scaling continuing, other quantum-mechanical effects begin to
affect transport properties. Quantum confinement in the direction orthogonal to transport in inversion layers makes the energy
spectrum discrete. For sufficiently long