  We theoretically investigate the electron transport properties for a
semiconductor quantum wire containing a single finite-size attractive impurity
under an external terahertz electromagnetic field illumination in the ballistic
limit. Within the effective mass free-electron approximation, the scattering
matrix for the system has been formulated by means of a time-dependent mode
matching method. Some interesting properties of the electron transmission for
the system have been shown through a few groups of numerical examples. It is
found that in the case of the comparative stronger field amplitude and the
frequency resonant with the two lowest lateral energy levels in the impurity
region, the field-induced intersubband transition dominates the process as if
without the impurity. And there is a step-arising on the transmission as a
function of the incident electron energy. However, in the case of lower field
amplitude and the non-resonant frequencies both multiple symmetry Breit-type
resonance peaks and asymmetry Fano-type dip lines appear in the electron
transmission dependence on the incident energy due to the presence of the
impurity and the external field. Therefore, within certain energy range the
transmission as a function of the field frequency and/or field amplitude shows
a rich structure. Moreover, the transmission dependence on the strength and
size of the impurity is also discussed. It is suggested that these results
mostly arise from the interplay effects between the impurity in a quantum wire
and the applied field.
