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

在低维受限电子系统中，如二维电子系统和半导体中的量子线，样品边界处的电子约束势的空间分布是理解电子输运和能级性质的重要信息。本研究利用量子霍尔效应中边缘态的空间分布信息，研究了二维电子系统和细导线中的局域电子密度分布。在GaAs/AlGaAs线中，当线宽小于1微米时，约束电位曲线变得陡峭。在对GaAs/AlGaAs金属丝进行短暂照射后，详细研究了样品边缘附近耗尽区的收缩和约束势分布的变化。利用可以通过栅极电压调节约束势的边栅结构，研究了样品边界处局部电子密度与约束势的关系。我们还研究了量子霍尔效应的击穿，其临界电流与通道宽度呈亚线性关系。从侧面门控样品的实验结果中发现，击穿电流不受约束电位的影响。电流浓度在样品边缘附近的模型不能理解亚线性击穿。二维电子系统的体性质，如势涨落，可能与亚线性型量子霍尔击穿密切相关。上述结果已在第26届ICPS（英国爱丁堡，2002年）上发表，并将在EP2DS-15（日本奈良，2003年）上发表。注：本研究的首席研究员k.o oto于2003年1月1日从大阪大学转至千叶大学，继续本研究项目。

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.