Relaxation-time approximations of quasi-hydrodynamic type in semiconductordevice modelling

We analyse mathematical models for the description of carrier transport in semiconductors as a hierarchy of models constructed on the basis of the the relaxation-time concept. In this hierarchy we focus on a reasonable compro mise between drift-diffusion, hydrodynamic, and kinetic models, This compro mise is provided by non-local quasi-hydrodynamic mathematical models descri bing non-equilibrium physical processes in semiconductor devices. Details o f the normalization procedure for the quasi-hydrodynamic system will be giv en along with a transformation of the energy-balance equations to provide c omputationally convenient forms.