OBSERVATION OF TUNNELING PHENOMENA AND THE CHARGING EFFECT THROUGH SMALL CONSTRICTED REGIONS IN SEMICONDUCTORS FABRICATED WITH A FOCUSED ION-BEAM AT 4.2-K

Small tunnel barrier were formed on AlxGa1-xAs/GaAs by focused-ion-beam implantation. The samples were then measured with dc current at 4.2 K, and the I-V curves revealed two distinct regions depending on applied bias: a tunneling region at small bias voltage and a region where thermal current over the barrier is dominant at large bias voltage. A dip in the dI/dV curve was observed in the tunneling region in the source-drain voltage (V(SD)) range from - 5 to 5 mV. In a different sample, periodic and reproducible staircaselike steps with a periodicity DELTAV(SD) of 35 mV were observed. This phenomenon is related to he Coulomb staircase, which occurs when the capacitance of a quantum dot is very small.