Nanoelectronic Modeling Lecture 23: NEMO1D - Importance of New Boundary Conditions

One of the key insights gained during the NEMO1D project was the development of new boundary conditions that enabled the modeling of realistically extended Resonant Tunneling Diodes (RTDs). The new boundary conditions are based on the partitioning of the device into emitter and collector reservoirs which are assumed to be in local equilibrium with a local quasi Fermi level and a central non-equilibrium region. In the reservoirs the electrostatic potential generally varies spatially due to non-uniform doping and possibly heterostructures. The introduction of an empirical scattering relaxation rate in the reservoirs enabled the modeling of phase-breaking and relaxation in the equilibrium reservoirs and the elimination of un-realistically narrow resonance states. With these new boundary conditions one can reduce dramatically the spatial region in which the non-equilibrium problem is being computed. This allowed for the efficient simulation of scattering effects inside the central RTD under non-equilibrium conditions at low temperature, and avoided the need to compute explicitly the computation of the equilibrating scattering in the high electron density contacts.The presentation closes with the challenge that the boundary conditions alone are not sufficient to completely explain the valley current of resonant tunneling diodes. It leads into the discussion of incoherent scattering inside the central RTD for the next lecture.Learning Objectives:Comprehension of the major concept of device partition into reservoirs and central non-equilibrium regionConprehension of the associated reduction in computational cost due to device partitioningComprehension of the physical effects of relaxation in the reservoirs and the broadening of the resonance states