Analysis and modeling of quantum waveguide structures and devices

A complete description of the numerical analysis of quantum waveguide structures and devices is given. Modal expansions of the wave function together with a mode-matching technique are utilized to calculate the generalized scattering matrices (GSMs) of junctions or discontinuities and uniform waveguide sections. The different GSMs are combined via an extended generalized scattering-matrix technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right-angle bends and periodic multiwaveguide structures in a split-gate configuration are presented. A sharp transition to a plateau of zero conductance is observed for the double-bend configuration. For the periodic multiwaveguide structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current-voltage characteristics for the special case of a double constriction are shown, exhibiting a region of negative-differential resistance (NDR) for temperatures up to approximately 10 K with a peak-to-valley ratio of about 2.5:1 at zero temperature. Using a simple design procedure, the temperature range with achievable NDR is extended to up to approximately 60 K with a peak-to-valley ratio of over 80:1 at zero temperature.