AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM7
Halogens Adsorbed on the Ga-rich c(8x2) GaAs(001) Surface: Adsorbtion Sites, Mobility and Overlayer Structure

Tuesday, November 3, 1998, 10:20 am, Room 308

Session: Semiconductor Surface Structure
Presenter: J.G. McLean, University of California, San Diego
Authors: J.G. McLean, University of California, San Diego
P. Kruse, University of California, San Diego
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Chlorine is commonly used to etch the As-rich c(2x8) Gallium Arsenide (001) surface. However, on the well-ordered Ga-rich c(8x2) reconstruction of GaAs(001) at 300 K, Cl@sub 2@ has been found to form an overlayer which passivates the surface against attack by atmospheric gases. Although the clean surface always reconstructs, the Cl@sub 2@ passivated surface yields a sharp (1x1) LEED pattern. A more complete understanding of the Cl chemisorption is desirable both for better control of the etching process and to understand the properties of the passivating overlayer. We have used scanning tunneling microscopy to study the adsorption sites of Cl@sub 2@ on the Ga-rich c(8x2) surface of GaAs(001). The Cl bonds exclusively to the Ga atoms, consistent with expectations based on molecular bonding theory. At low coverage the Cl is mobile along the Ga rows, which is surprising given the strength of the Ga-Cl bond. We have also investigated the overlayer at high coverages, for which STM revealed both c(2x6) and (1x1) structures. In both cases, the structures are inconsistent with the Ga/As ratio of the initial clean c(8x2) reconstruction. This shows that long-range rearrangement of surface atoms has taken place, allowing a bulk terminated surface to form in the case of the (1x1) structure. Tunneling spectroscopy will be used to determine whether this surface rearrangement results in a modified electronic structure, allowing electronic as well as chemical passivation.