Keldysh Greenʹs function approach to the noise properties of semiconductor superlattices

A Keldysh nonequilibrium Green function formalism is presented to study the superlattice shot noise behaviors. The peculiar device geometry of superlattices, such as the periodicity, is taken into account in this formalism. We emphasize that the role of each unit cell is actually twofold: It acts as not only a device region, but also as an emitter or a collector to its adjacent cells.