AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS+EL-ThM

Paper SS+EL-ThM4
First Atomic-Resolution Ultrahigh Vacuum Scanning Tunneling Microscopy Study of GaSe/Si(111) Ultrathin Films

Thursday, November 7, 2002, 9:20 am, Room C-110

Session: Structure of Semiconductor Surfaces & Interfaces
Presenter: T. Ohta, University of Washington
Authors: T. Ohta, University of Washington
A. Klust, University of Washington
J.A. Adams, University of Washington
Q. Yu, University of Washington
M.A. Olmstead, University of Washington
F.S. Ohuchi, University of Washington
Correspondent: Click to Email
Gallium-selenide thin films deposited on Si(111) are of increasing interest for applications, both in their own right as optoelectronic structures, and as non-reactive, low surface energy, high band gap buffer layers for subsequent nanostructure formation. Gallium selenide crystallizes into two crystal structures, layered GaSe and cubic Ga@sub 2@Se@sub 3@ with bandgaps of 2.0 and 2.6eV, respectively. Crystal structure and stoichiometry of the deposited Ga@sub x@Se@sub y@ can be controlled by the substrate temperature during deposition. We present the first atomic-resolution ultrahigh vacuum scanning probe microscopy study of GaSe/Si(111) ultrathin films. When GaSe thin films are deposited at substrate temperature 520°C, atomically flat surfaces consisting of a single molecular layer of GaSe with altered step structures of 7*7-Si(111) were observed. These surfaces have no dangling bonds to react with residual gases, or to provide nucleation sites for subsequent growth. We also observed occasional point defects causing long-range alterations of the local band bending, but no sharp states revealed by the tunneling spectroscopy. At lower substrate temperatures, Ga@sub x@Se@sub y@ multilayers with flat surface and triangle features with 3-4nm sides were formed. Height difference of the atomic steps suggests that the multilayers have a cubic structure. These triangles are likely associated with Ga or Se vacancies in the Ga@sub 2@Se@sub 3@. @FootnoteText@This work was partially supported by the M. J. Murdock Charitable Trust and NSF Grant DMR 0102427.