Irradiation-induced Ge multilayer growth from GeH4 on Si(111)

Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements after Ge chemical vapor deposition on Si(111)-(7×7) show that no more than 2.5 bilayers of Ge can be deposited upon GeH4 exposure at 730 K [p(GeH4)=7×10−5 mbar], and that the surface remains atomically flat with a high quality (5×5) reconstruction. If, however, the Si substrate is exposed to Al Kα 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 substrate during X-ray irradiation, which may account for the different growth behavior of Ge on irradiated and non-irradiated Si surfaces.