AVS 45th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM1-WeA

Paper EM1-WeA3
Structure of a Passivated Ge Surface Prepared from Aqueous Solution

Wednesday, November 4, 1998, 2:40 pm, Room 314/315

Session: Si Surface Chemistry
Presenter: P.F. Lyman, Northwestern University
Authors: P.F. Lyman, Northwestern University
D.T. Keane, Northwestern University and DND CAT
D.L. Marasco, Northwestern University
T.-L. Lee, Northwestern University
M.J. Bedzyk, Northwestern University and Argonne National Lab
Correspondent: Click to Email
We investigated the local structure and order of a aqueously sulfided Ge(001) surface using x-ray standing waves. The adsorption of a group VI element on the Ge(001) surface could satisfy all of the substrate dangling bonds by occupying a bridge site. Such a surface would be expected to be both chemically and electronically passivated, perhaps suppressing surface carrier recombination. In the present study, S/Ge(001) surfaces prepared in aqueous (NH@sub 4@)@sub 2@S solution (diammonium sulfide) exhibited a S coherent position P@sub 004@ of 0.90 ± 0.01, implying that the S adsorption height is 1.27 Å ± 0.01 Å. This closely corresponds to the expected adsorption height for S residing in a bridge site. This finding supports the local geometry inferred for aqueously sulfided Ge(001) by previous workers.@footnote 1@ That study concluded that a single atomic layer of S binds to the surface, residing in the a (1x1) bridge-bonded configuration. However, the present studies showed a low, repeatable value of 0.15 for the coherent fraction. The simplest explanation for these observations is that, in addition to an ordered S monolayer at the interface, a ~5 ML sulfided Ge layer is formed during the chemical passivation treatment. Although this model conflicts with the conclusions of Ref. 1, such an interface is not unlike the native oxide of Si, where several atomic layers of passivating silicon oxide readily form. We are presently conducting other tests of the S/Ge(001) surface to determine the nature of this interface more completely. @FootnoteText@ @footnote 1@G. W. Anderson, et al., Appl. Phys. Lett. 66, 1123 (1995).