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.