Control of surface composition on Ge/Si(001) by atomic hydrogen irradiation

The surface composition of Ge/Si(001)2 x 1 surfaces after atomic hydrogen ( H) irradiation was investigated using IR reflection spectroscopy in UHV. It was confirmed that an extremely high dose of H at room temperature causes an etching reaction of the surface Ge layer. However, when H is irradiated at a temperature higher than 150 degrees C, the etching reaction does not o ccur; instead, Ge segregated at the surface is observed to move into a subs urface and Si tends to exist on the topmost surface as a hydride in mixed G e-Si and pure Si-Si dimers. This is in remarkable contrast to the Ge/Si(001 ) surface in the absence of hydrogen, where Ge is segregated at the surface and forms Ge-Ge pure dimers. The phenomenon of 'reverse segregation' by H irradiation may be understood by the thermochemical consideration that Si-H bonds are much more stable than Ge-H bonds. The result of the first-princi ples total energy calculations in which the presence of hydrogen changes th e stable composition at the surface from Ge to Si is also consistent with t he phenomenon. (C) 1999 Elsevier Science B.V. All rights reserved.