Hydrogen population on Ge-covered Si(001) surfaces

A series of isochronal annealing experiments have been performed using high resolution electron energy loss spectroscopy in order to probe the thermal decomposition of monohydride and dihydride species from Ge-covered Si(001) surfaces. The Ge coverage was varied from submonolayer until completely covering the silicon surface. The films were exposed to atomic hydrogen at room temperature and the intensities of the hydrogen vibrational features were monitored as a function of annealing temperature. Marked steps in the stretching mode intensities are observed, directly connected to monohydride decomposition. The existence of a desorption state specific to surface alloying is thus clearly identified in the Ge-H stretching intensity temperature dependence curve, interpreted as involving the recombinative desorption of two hydrogen atoms from mixed Ge-Si dimers. From the scissors mode intensity variation, it is deduced that both Ge and Si dihydride species decompose simultaneously at all coverages, and that it always occurs before monohydride desorption takes place. Furthermore, we observe the Ge-H-2 formation enhancement due to the presence of the neighboring silicon atoms. Finally, the desorption of all hydride species is shown to be boosted when increasing the Ge contents at the Si(001) surface. To summarize this study, the complete experimental desorption diagram of the hydrogen population, as functions of both stoichiometry and temperature, is presented. [S0163-1829(99)13131-X].