Nanoelectronic Devices Based on Low-Dimensional Semiconductor Structures
Sammanfattning: The present thesis reports on results from the fabrication technology development and the corresponding electrical transport measurements of low-dimensional semiconductor structures. The focus of the work has been directed towards two parts: the ballistic transport in nanostructure devices at room temperature, and the development of a charge-sensing technique for quantum dots (QD) in nanowires. Ballistic transport is interesting since it introduces many electrical non-linear effects that cannot be expected from diffusive transport. One example of a ballistic device is the three-terminal ballistic junction (TBJ), where three branches are connected in a small nanojunction. Within the scope of this work, the non-linear transport properties of such a TBJ were studied and the size limitations of the device for ballistic transport were investigated. Additionally, in order to demonstrate the potential of the TBJ as a candidate for future electronics, components such as logic gates and frequency mixers were realized. When a QD is weakly coupled to source and drain contacts, it is difficult to detect its state by direct transport measurements. In such cases, a quantum point contact (QPC) can be employed as a sensitive charge sensor so as to obtain further information with regard to the QD state. A charge sensor scheme was developed for QDs defined in InAs nanowires, either by heterostructure growth of InP barrier segments or by local top finger gates. Such charge sensors for QDs are interesting for possible use as future read-out schemes for QD-based solid state qubits.
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