A diagram technique for nonequilibrium processes in semiconductor microstructures

The development of submicron semiconductor devices demands a clear and general description of nonequilibrium phenomena in micro structures. To describe electronic transport in these new submicron structures, in many cases we cannot resort to a classical Boltzmann description but must include the quantum-mechanical aspects of electronic transport. In the time-reversible Schroedinger equation for an electron state, the state does not change its eigenenergy during its temporal evolution. Accordingly, this is a pure state description, which cannot treat electron-phonon and electron-electron interaction. Due to the statistical nature of kinetic processes, a definite conserved Hamiltonian for the Schroedinger equation cannot be specified and quantum device should be considered as a statistical system, characterized by the density matrix or Green´s function. The objective of this work is to develop such based on general principles of gauge invariance.