Tunneling current through a single germanium quantum dot

The tunneling current through a germanium quantum dot (Ge QD) of nanometer size is studied theoretically. The energy levels and Coulomb interactions of electrons in a Ge QD are calculated using an effective mass model. In small Ge QDs, the interlevel Coulomb interactions as well as the intralevel Coulomb interactions are important in the calculation of tunneling current. The Anderson model with two energy levels is used to simulate the carrier transport in a single-electron transistor (SET) composed of a single Ge QD embedded in a SiO₂ matrix. The tunneling current of the Ge SET is derived by the Keldysh-Green's function technique. It is found that the differential conductance displays multipeaks for the tunneling current through an isolated QD with the two energy levels, which is due to the statistical nature of the open system. Finally, the bistable current arising from the fourfold degeneracy state of Ge QD is discussed.