Geometric effects of scattering in microstructures

Transfer Matrix techniques are used to study elastic scattering by point defects embedded in quasi-one-dimensional microstructures. This makes possible an exact analysis of phenomena that arise from breaking of transverse translation invariance. The dependence of transmission probability on scatterer position is studied for parallel transport in quantum wells and for perpendicular transport across single and double barrier structures. It is found that in laterally confined structures, delta-function and other extremely sharp models of a single defect lead to sharp resonances when such defects are well isolated. Such features are associated with multiple reflections between the lateral confining potential and the defect potential. In single-barrier structures with a single nearby defect, an approximate scaling behavior is found that relates transmission for defects at different distances to that at a fixed distance with different energy scales. In double-barrier resonant tunneling diodes (DBRTDs), the position of the transmission peak is affected primarily by defects within the quantum well region. The height of the transmission peak is very sensitive to the positions of defects within that region, acting essentially as a probe of the resonance wave function. Defects in front of a DBRTD also affect the valley current by modifying the longitudinal component of the incident momentum.