Confinement potential at sample edge in low-dimensional electron system investigated by maghetocapacitance measurement

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In low dimensional confined electron systems, such as two-dimensional electron systems and quantum wires in semiconductor, the spatial profile of electron confinement potential at the sample boundary is very important information to understand the properties of electron transport and the energy levels. In this study, the information of spatial profile of edge states in quantum Hall effect is applied to investigate the local electron density profiles in two dimensional electron systetems and in thin wires. In GaAs/AlGaAs wires, the profile of confinement potential becomes steep when the wire width is less than 1micron meter. After brief illumination to the GaAs/AlGaAs wires, the shrinkage of depletion region near the sample edge and the change of confinement potential profile are studied in detail. The relation between local electron density and the confinement potential at the sample boundary is investigated by using side gate structures, whose confinement potential can be tuned by the gate voltage.We also investigated the breakdown of quantum Hall effect whose critical current shows sub-linear dependence on the channel width. We found that the breakdown current is not affected by the confinement potential from the experimental results of by side gated samples. The sub-linear type breakdown can not be understood by the model that the current concentration near the sample edge. The bulk properties of two dimensional electron system, potential fluctuation for example, may be closely related to the sub-linear type quantum Hall breakdown. These above mentioned results were presented in 26th ICPS (Edinburgh UK, 2002) and will be presented EP2DS-15 (Nara Japan, 2003).Note : Head investigator of this study, K.Oto, moved to Chiba University from Osaka university on January 1st (2003) and continued the research project.