Transport studies of Al_xGa_1-x As/GaAs quantum heterostructures using BEEM

Abstract

In 1988, Kaiser and Bell first demonstrated the unique capability of Ballistic Electron Emission Microscopy (BEEM) not only to perform microscopy studies with nanometer resolution, but also to spectroscopically probe metal/semiconductor (M/S) interfaces on a local scale. The majority of BEEM studies to date have focused on transport across M/S interfaces. We have explored the novel application of BEEM to study charge transport across spatially buried quantum structures. Unlike conventional transport measurement techniques, BEEM allows the injected electron energy to be precisely varied independent of the band profile. We have shown that BEEM can be used as a powerful spectroscopic tool to study transport in GaAs/Al_xGa_1-x As single barrier structures and a GaAs/Al_xGa_1-x As double barrier resonant tunneling structure spatially buried beneath the Schottky barrier. We will present band-offset measurements of buried single barrier GaAs/Al_xGa_1-x As heterostructures as a function of the Al mole fraction (x) and temperature. We will discuss the observation of quasi-bound states and band-structure effects in the double barrier resonant tunneling structure as deduced from the systematic temperature evolution of the BEEM Spectra. We will show that BEEM can potentially be used to study charge transport in low-dimensional quantum structures such as quantum wires and quantum dots, and also to characterize newly-developed and exotic compound semiconductor materials.