Single-electron tunneling in nanometer-scale double-barrier heterostructure devices

We report a systematic experimental study of charge transport in nanometer-scale double-barrier resonant-tunneling devices. Asymmetric heterostructure material was used so that one barrier is substantially less transparent than the other. Resonant tunneling through size-quantized well states and single-electron charging of the well are thus largely separated in the two bias polarities. When the emitter barrier is more transparent than the collector barrier, electrons accumulate in the well; incremental electron occupation of the well, starting from zero, is accompanied by Coulomb blockade, which leads to sharp steps of the tunneling current. The voltage extent of the steps is affected by the intrawell electron-electron interaction. When the emitter barrier is less transparent, the current reflects resonant tunneling of just one electron at a time through size-quantized well states; the current peaks and/or steps (depending on experimental parameters) appear in current-voltage characteristics. Experimental results on magnetic field and temperature dependence of the current-voltage curves are also reported. Good agreement is achieved in comparison of many features of the experimental data with simple theoretical models.