Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurem
ents after Ge chemical vapor deposition on Si(111)-(7 x 7) show that no mor
e than 2.5 bilayers of Ge can be deposited upon GeH4 exposure at 730 K [p(G
eH4) = 7 x 10(-5) mbar], and that the surface remains atomically flat with
a high quality(5 x 5) reconstruction. If, however, the Si substrate is expo
sed to Al K alpha radiation prior to GeH4 exposure, Ge growth does not stop
and three-dimensional islands form on top of the initial Ge wetting layers
. Photoluminescence measurements show that defects are created in the Si su
bstrate during X-ray irradiation, which may account for the different growt
h behavior of Ge on irradiated and non-irradiated Si surfaces. (C) 2000 Els
evier Science B.V. All rights reserved.