Transient current through a single germanium quantum dot

We have experimentally investigated time-dependent charge transportation through a single germanium (Ge) quantum dot (QD), which weakly couples to adjacent semiconductor electrodes via SiO₂ tunnel barriers, under a voltage pulse excitation at room temperature. The time-dependent current arises from a tunneling current through the Ge QD's resonant energy levels as well as displacement currents due to the charge accumulation or depletion within the QD. We find that the displacement current dominates in the pulse transition regimes, while the tunneling current dominates as the pulse reaches steady state. The charge absorption and emission processes are experimentally observed and theoretically analyzed.