Chapter 1 Classical Device Modeling Thomas Windbacher, Viktor Sverdlov, and Siegfried Selberherr Abstract In this chapter an overview of classical device modeling will be given. The first section is dedicated to the derivation of the Drift–Diffusion Transport model guided by physical reasoning. How to incorporate Fourier’s law to add a dependence on temperature gradients into the description, is presented. Quantum mechanical effects relevant for small devices are approximately covered by quantum correction models. After a discussion of the Boltzmann Transport equation and the systematic derivation of the Drift–Diffusion Transport model, the Hydrodynamic Transport model, the Energy Transport model, and the Six-Moments Transport model via a moments based method out of the Boltzmann Transport Equation, which is the essential topic of classical transport modeling, are highlighted. The parame- ters required for the different transport models are addressed by an own section in conjunction with a comparison between the Six-Moments Transport model and the more rigorous Spherical Harmonics Expansion model, benchmarking the accuracy of the moments based approach. Some applications of classical transport models are presented, namely, analyses of solar cells, biologically sensitive field-effect transis- tors, and thermovoltaic elements. Each example is addressed with an introduction to the application and a description of its peculiarities. Keywords Classical device modeling · Drift–Diffusion · Six moments · Hydrody- namic transport · Energy transport · Solar cells · BioFET · Biologically sensitive field-effect transistor · Boltzmann transport · Thermoelectric · Figure of merit · Electrothermal transport · Spherical harmonics expansion 1 Heuristic Derivation of the Drift–Diffusion Transport Model Even though the method of moments, which will be presented in Sect. 5, is quite sophisticated and offers the possibility to extend a transport model to an arbitrary large and accurate set of equations, physically understanding of the model is not T. Windbacher (  ) Institute for Microelectronics, Gußhausstraße 27–29/E360, 1040 Vienna, Austria e-mail: Windbacher@iue.tuwien.ac.at D. Vasileska and S.M. Goodnick (eds.), Nano-Electronic Devices: Semiclassical and Quantum Transport Modeling, DOI 10.1007/978-1-4419-8840-9 1, c  Springer Science+Business Media, LLC 2011 1