Study on Nanofabrication and One-Dimensional Quantum Effects

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The present project is to establish the basis of nanofabrication technology and to investigate mesoscopic effects and their control by external fields in nanostructures, which are important for future quantum devices. The results are summarized as follows.1) It was demonstrated that SiO_2 and Si_3N_4 are effectively patterned by ion beam assisted etching with high etching rate, more than 100 times faster than the physi-cal sputter etching. Reduction of process induced damage in GaAs was also demonstrated by using low energy focused ion beams. These results are important for maskless etching or deposition using focused ion beams.2) We, first, observed universal conductance fluctuations in GaAs which comes from interference of electron waves in mesoscopic structures. In addition, we also found nonlocality and asymmetry of magnetoresistance. This was realized by using nanofabrication technology which we have established.3) We, first, observed a clear Aharanov-Bohm effect in GaAs/GaAlAs heterostructure submicron ring devices. This indicates the possibility of controlling the inter-ference effects by an external fields, which is important for device applications.4) We observed various ballistic transport effects in GaAs/GaAlAs heterostructure quantum wires. We, first, demonstrated that a large negative resistance appears at bents or interconnects of current path becouse electrans travel straightforward in ballistic region.5) We observed one dimensional quantum size effect in narrow GaAs/GaAlAs wires.