EFFECT OF IMPURITIES ON THE CONDUCTANCE OF NANOSTRUCTURES

The conductance G of narrow channels is calculated for the case that an impurity is present in the channels. The channels are modelled as the electron waveguides, and the impurity is assumed to be a barrier. The effect of impurities on G distorts the quantization of conductance in a quasi-one-dimensional constriction. The resonant tunnelling associated with bound states in a crossbar structure is reduced by the presence of the impurity. The sharp peaks in G associated with resonant tunnelling are still apparent for a crossbar structure containing an impurity. Weak impurity potentials do not have a pronounced effect on the conductance. For strong impurity potentials, however, both the magnitude and position of the peaks in G are affected by the presence of the impurity. The position of the impurity plays a role in reducing the resonant tunnelling in the crossbar constriction. In addition to the peaks in G associated with resonant tunnelling, there are deep anti-resonances that are insensitive to the presence of the impurity. The current density may be strongly affected by the impurity. A complex flow pattern containing vortices appears when the impurity is inserted.