| Research Abstract |
We have developed a technique to form position-and size-controlled quantum wires (QWRs) and quantum dots (QDs) by selective area metalorganic vapor phase epitaxial (SA-MOVPE) growth. The technique is applied for the direct fabrication of single electron transistors and circuits using QD-QWR coupled structures. Main results of the project are summarized below.
(1) We investigated the mechanism of SA-MOVPE for the fabrication of high-density QD arrays with extreme uniformity. We have found and clarified the self-limited mechanism in SA-MOVPE where the top size and shape of the GaAs pyramidal structures and ridge structures are maintained after the formation of such 3-dimensional structures. This self-limited growth mode is utilized to achieve size uniformity in QDs. We also have clarified that the top size of the GaAs pyramid is determined by the balance between the adsorption and desorption of adatoms at the step edges and can be controled by the growth conditions.
(2) Based on the fabric
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ation technique of QD arrays, we have proposed and succes sfully fabricated a two-dimensional coupled array of QDs and QWRs by SA-MOVPE.The optical characterization has confirmed the formation of network-like array of QDs and QWRs. The results indicate that our proposed fabrication method is effective to realize high-density integration of quantum devices, such as single electron transistors, for future electronics.
(3) Single electron transistors have successfully been fabricated by the combination of coupled structures of QWR-QD-QWR formed by SA-MOVPE technique and Schottky gate technology. We have succeeded in the demonstration of the circuit operation of single electron inverters, which integrates quantum wire transistor and single electron transistors fabricated by one-step growth on designed masked substrate for SA-MOVPE.Our quantum dot devices also have shown to exhibit strong lateral confinement that are beneficial to explore the physics of nanostructures, such as Kondo effect in QDs. Less
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