Investigation of Nonlocal Conduction in Two Dimensional Electron System Controlled by Various Gate

我们研究了不同栅极结构的半导体中的2DES，得到了以下结果：(1)量子霍尔体系中的磁电容我们测量了量子霍尔体系中2DES和栅极GaAs/AlGaAs之间磁电容最小值的温度和频率依赖性。我们发现可以分离出与边缘状态面积成正比的电容和与体状态面积成正比的电容，而体状态面积是sigma_<xx>的函数。(2) GaAs/AlGaAs和Si-MOSFET的非局域磁阻和边缘态从QHE态的非局域磁阻可以确定GaAs/AlGaAs和Si-MOSFET边缘态的能量弛豫长度分别为几cm和几百微米。磁电子聚焦效应中额外探针的反射我们发现，在MEFE中，额外探针的电子明显反射，反射电子来自额外探针的发射电子，其电势由于电子的堆积而增大。(4)斜导线上电子的角分布我们用低磁场下的弹道电子输运测定了斜导线上电子的角分布。发现发射分布取决于出口的结构而不是导线方向。(5)人工反点超晶格中的相应振荡研究了电流方向和超晶格的各向异性对反点超晶格中相应振荡的影响。结果表明，除与电流平行的最近邻方向外，振荡的峰值位置由最近邻距离决定。(6)多晶硅TFT中的电子局域化效应通过对多晶硅TFT的低温电测量发现，TFT样品表现出从二维弱局域化到强局域化引起的变程跳变的多种安德森局域化现象。

We have investigated 2DES in semiconductor with various gate structures and obtained the following results.(1) Magnetocapacitance in the Quantum Hall RegimeWe have measured the temperature and frequency dependence of the magnetocapacitance minima between 2DES and the gate GaAs/AlGaAs in QHE regime. It is found that we can separate the capacitance which is prportional to the area of the edge state and that from the bulk state, which is a function of sigma_<xx>.(2) Nonlocal Resistance and Edges State in GaAs/AlGaAs and Si-MOSFETFrom the nonlocal magnetoresistance in QHE regime, it is determined that energy relaxation lengh of edge state in GaAs/AlGaAs and Si-MOSFET is several cm and several hundred of microns.Reflection from Extra Probes in Magnetic Electron Focusing EffectWe have found that the electron in apparently reflected from the extra probe in MEFE and the reflected electron comes from the remitted electron from the extra probe, whose potential increases due to the pile of electrons.(4) Angular Distribution of Electron from Oblique WireWe have determined the angular distribution of electron from the oblique wire by the ballistic electron transport at low magnetic fields. The emitted distribution is found to depend on the structure at the outlet rather than the wire direction.(5) Commensutate Oscillations in Artificial Antidot SuperlatticeWe have investigated the influence of current direction and the anisotropy of superlattice on the commensurate oscillations in antidot superlattice. It is found that the peak position of the oscillations is determined by the nearest neighbor distance except for the direction of nearest neighbor parallel to the current.(6) Electron Localization Effect in poly-Si TFTFrom the low temperature electrical measerement of poly-Si TFT,it is found that the TFT samples show various Anderson localization phenomena from the 2D weak localization to the variable range hopping due to the strong localization.