FINITE-ELEMENT SOLUTION OF ELECTRON WAVE-GUIDE DISCONTINUITIES AND ITS APPLICATION TO QUANTUM-FIELD EFFECT DIRECTIONAL-COUPLERS

A numerical approach based on the finite element method is described f or the solution of electron waveguide discontinuities with arbitrary p otential and effective-mass distributions, Analytical solutions are in troduced for the uniform waveguide regions, The approach is applied to a quantum field effect directional coupler with finite coupling lengt h and longitudinal discontinuities. The effects of the longitudinal in terference due to the discontinuities and of the transverse interferen ce due to the even and odd supermodes in the coupling region are studi ed, The influence of the shape of the wire-tip on the transmission pro perties is also investigated.