AVS 51st International Symposium
    Nanometer-scale Science and Technology Friday Sessions
       Session NS-FrM

Paper NS-FrM5
Cross-sectional Ballistic Electron Emission Microscopy Studies of Molecular Beam Epitaxy Grown Quantum Wells

Friday, November 19, 2004, 9:40 am, Room 213D

Session: Nanometer-scale Structures
Presenter: C. Tivarus, The Ohio State University
Authors: C. Tivarus, The Ohio State University
J.P. Pelz, The Ohio State University
M.K. Hudait, The Ohio State University
S.A. Ringel, The Ohio State University
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Schottky diodes formed on GaAs quantum wells grown by Molecular Beam Epitaxy are studied using Cross-sectional Ballistic Electron Emission Microscopy (XBEEM), in order to determine the influence of quantum confinement and pinning effects on Schottky barrier (SB) formation. The diodes were formed by both in-situ and ex-situ gold deposition on cleaved sides of heterostructures composed of a sequence of GaAs quantum wells (QW) separated by AlGaAs barrier layers. Using this technique, we were able to determine the local SB height for each QW. We found that the SB height increases with decreasing the QW thickness d@sub QW@ , varying from ~0.91 eV for d@sub QW@ @>=@ 9 nm to ~1.04eV for d@sub QW@=1 nm. This dependence will be discussed in terms of the QW confinement energy as well as reduced pinning effects at the QW/metal interface. We will also compare XBEEM samples made by in-situ vs. ex-situ metal deposition to clarify the role of chemical treatment and of an interfacial oxide layer on the SB formation. Additionally, the cross sectional configuration offered a direct measure of electron beam spreading due to scattering inside the metal film, as a function of film thickness. This spreading was surprisingly large, with full width at half maximum spreading of ~16 nm (~23 nm) for a 4 nm (7nm) thick Au film. The measurements will be compared with model simulations to quantify inelastic and elastic hot-electron scattering processes in the bulk and at the interfaces of the metal film, and to gain insight into the controversial issue of whether lateral momentum is conserved during hot electron transport over a metal/semiconductor interface. Work was supported by NSF and Office of Naval Research.