AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM6
Chemically Resolved STM Imaging of Al on Al@sub 0.1@Ga@sub 0.9@As(001)-c(2x8)/(2x4)

Wednesday, November 5, 2003, 10:00 am, Room 328

Session: Adsorption on Semiconductor Surfaces
Presenter: M.J. Hale, University of California, San Diego
Authors: M.J. Hale, University of California, San Diego
D.L. Winn, University of California, San Diego
A.C. Kummel, University of California, San Diego
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It has been proposed that growing an oxide/AlGaAs/GaAs stack will prevent interface roughness from interfering with carrier mobility within the channel when attempting to create a GaAs-based MOSFET. Before attempting to grow an oxide/AlGaAs interface, one must first characterize the AlGaAs(001) surface. We will present STM images of the AlGaAs(001) surface in which Al and Ga can be distinguished. Al atoms in the second layer of Al@sub 0.1@Ga@sub 0.9@As(001)-c(2x8)/(2x4) cause the adjacent As atoms in layer one to be brighter than As atoms bonded to Ga atoms in STM images. Al is a stronger charge donor than Ga, which makes the As atoms in layer one bonded to Al atoms in layer two to have a greater charge density than As atoms bonded to Ga. This affect was only seen for p-type AlGaAs grown on a p-type GaAs substrate. Scanning tunneling spectroscopy (STS) measurements show that the excess charge transferred to the first layer As atoms from the second layer Al atoms causes electrical inversion to occur on the surface. For n-type Al@sub 0.1@Ga@sub 0.9@As(001)-c(2x8)/(2x4) grown on an n-type GaAs substrate, the ability to differentiate Al from Ga atoms in STM images is not possible. STS spectra show that the Fermi level resides near the conduction band, typical of a non-inverted n-type sample. This result is consistent with our model of a strong charge donation by Al since excess charge would not affect the position of the surface Fermi level in n-type material. The ability to differentiate between second layer Al and Ga atoms on p-type AlGaAs(001) with STM will enable further studies to understand the oxide/AlGaAs(001) interface.