Localization in Semiconductor Heterostructures Studied by Charge Accumulation Imaging

本项目利用电荷积累成像（CAI）技术研究GaAs-AlGaAs异质结构中二维电子系统（2DES）的介观物理。CAI是一种扫描探针方法，允许在低温环境中以高空间分辨率定位微量电荷。虽然这项技术还处于起步阶段，但最初的实验表明，它可以测量其他探针无法测量的电荷结构。这些实验涉及介观物理学中一些更令人兴奋的话题，其中心主题是研究电子-电子相互作用及其与无序的相互作用。为此，我们将进行两项独立的研究。第一个系列的实验将研究外加磁场中的电子态。在较低的场域中，我们将探索量子霍尔体系的渗透模式。在更高的场中，我们将研究分数量子霍尔态和单个电子局域化态之间的竞争。第二系列实验研究了2DES进一步被微制栅电极限制以形成量子点。使用CAI，我们可以绘制出点的特征态的空间特征——本质上是成像电子波函数。因此，这项研究代表了在这些系统中发挥作用的量子力学的新测试。本研究应用一种新颖的扫描探针显微技术来探测半导体系统中局限于二维空间的电子的行为。通过绘制出从半导体表面发出的电场，我们的技术可以解析电子结构，尽管事实上电子层被埋在表面之下。该项目的目标是研究电子之间相互作用的本质，以及它们与半导体中缺陷和杂质的相互作用。该研究为研究生和本科生提供了一个具有挑战性的训练场地，因为他们掌握了先进的显微镜和半导体微加工技术

0075230Tessmer, S.This project exploits a novel technique, charge accumulation imaging (CAI) to investigate mesoscopic physics in two-dimensional electron systems (2DES) in GaAs-AlGaAs heterostructures. CAI is a scanning probe method that permits minute amounts of electrical charge to be located with high spatial resolution in a cryogenic environment. Although the technique is in its infancy, the initial experiments have shown that it can measure charging structures beyond the reach of other probes. The experiments address some of the more exciting topics in mesoscopic physics, with a central theme of studying electron-electron interactions and their interplay with disorder. To this end, we will perform two separate studies. The first series of experiments will investigate electronic states in an applied magnetic field. At lower fields, we will probe the percolation patterns of the quantum Hall regime. At higher fields, we will investigate the competition between fractional quantum Hall states and states in which individual electrons become localized. The second series of experiments investigates the 2DES further confined by microfabricated gate electrodes to form quantum dots. Using CAI, we can map-out the spatial characteristics of the dot's eigenstates -- essentially imaging electron wavefunctions. Hence, this study represents a new test of the quantum mechanics at play in these systems.%%%This research applies a novel scanning probe microscopy technique to probe the behavior of electrons confined to two dimensions in semiconductor systems. By mapping out the electric field emanating from the semiconductor's surface, our technique can resolve the electronic structure, despite the fact that the electron layer is buried beneath the surface. The goal of the project is to investigate the nature of interactions between electrons, and their interplay with defects and impurities within the semiconductor. The research provides a challenging training ground for graduate and undergraduate students, as they master advanced microscopy and semiconductor microfabrication techniques.***