Composition of dimers on Ge/Si(001)2×1 surfaces analyzed by infrared (IR) reflection spectroscopy of surface hydrogen vibration

The composition of dimer structures formed on a Ge/Si(001)2×1 surface was investigated under various conditions of Ge coverage and annealing temperature using surface infrared (IR) spectroscopy on Si substrates with a buried metal layer (BML). Dimer structures were modified by atomic hydrogen to visualize the surface species in the IR spectra, where the signals from the mixed Ge–Si and pure Si–Si/Ge–Ge dimers as well as the non-dimer structures have different frequencies and thus are distinguishable from each other. These surface modes can be assigned to specific dimer structures on the basis of the surface selection rule on the BML substrate. Ge grows as mixed Ge–Si dimers for 0.2 monolayer (ML) of initial Ge coverage, as a mixture of the mixed and pure dimers for 0.6 ML, and as the pure Ge–Ge dimers for 1.2 ML. On annealing, Ge in the Ge–Ge and Ge–Si dimers diffuses into the second or deeper layers of Si and the dimers converted into pure Si–Si dimers at 810°C, through the formation of the mixed dimer from the pure Ge–Ge dimer at medium annealing temperature. These results show the potential of IR spectroscopy as a sensitive probe for evaluating the composition of semiconductor surfaces.