Device simulation is a branch of Technology Computer Aided Design (TCAD) and has become an indispensable tool within the semiconductor industry. TCAD sheds light on many phenomena in semiconductor devices otherwise not known and unable to be studied by characterization alone. Applications of device simulation are manifold, and include strain and band-gap engineering, variability studies, as well as degradation modeling and life-time prediction.
The electrical operation of a semiconductor device is based on the flow of charge carriers as a response to the voltages applied to the device terminals. The fundamental equations describing carrier transport are in general complex, and an active research field is the development of suitable models of reduced complexity which retain enough physical accuracy at moderate numerical costs. In the semi-classical transport picture, electrons and holes are treated as point-like particles whose collective behavior is described by the Boltzmann equation. Particularly for nano-scale devices, a complete solution of the BE must be sought. Spherical harmonics expansion of the distribution function and the Monte Carlo method are the numerical methods of choice. In particular, full-band effects and a variety of scattering mechanism, including impact ionization and carrier-carrier scattering, can taken into account. 

Effects originating from the quantum mechanical nature of carriers play an important role in contemporary technology nodes and require appropriate modeling. The non-equilibrium Green’s function (NEGF) method has become the de facto standard for device simulation at the nanoscale. It owes this prominence to both its entirely quantum mechanical formulation of carrier transport and its expandability to a variety of interaction effects such as carrier scattering with phonons and defects, interaction with radiation, or spin polarization. Carrier tunneling, quantum confinement, and Fermi-Dirac statistics are intrinsically included. This high level of physical modeling accuracy, however, comes at the expense of high computational cost. Research is focusing on the development of efficient algorithms for dissipative quantum transport, parallel algorithms, and high-performance computing methods. On the other hand, the Wigner formalism extends many classical concepts and provides a phase space formulation of quantum mechanics. A transport equation which combines the coherent Wigner equation with the Boltzmann scattering operator describes the decoherence effects caused by the environment. This equation bridges the gap between full quantum transport and classical transport.