  Due to random dopant fluctuations, the device-to-device variability is a
serious challenge to emerging nanoelectronics. In this work we present
theoretical formalisms and numerical simulations of quantum transport
variability, based on the nonequilibrium Green's functions and the multiple
scattering theory. We have developed a general formalism using the diagrammatic
technique within the coherent potential approximation (CPA) that can be applied
to a wide range of disorder concentrations. In addition, we have developed a
method by using a perturbative expansion within the low concentration
approximation (LCA) that is extremely useful for typical nanoelectronic devices
having low dopant concentration. Applying both formalisms, transport
fluctuations due to random impurities can be predicted without lengthy brute
force computation of ensemble of devices structures. Numerical implementations
of the formalisms are demonstrated using both tight-binding models and first
principles models.
