Localization in Semiconductor Heterostructures Studied by Charge Accumulation Imaging

Michigan State University, East Lansing MI

Investigators

Abstract

0075230 Tessmer, 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. ***