Thermodynamically driven Ge/Si place exchange induced by hydrogen on Ge-covered Si(001) surfaces

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Abstract
Recently, hydrogen induced Si segregation on 1.4 monolayer Ge-covered Si(001) surface has been observed by means of Fourier transform infrared-attenuated total reflectance spectroscopy [E. Rudkevich et al., Phys. Rev. Lett. 81, 3467 (1998)]. We confirm these results independently, using x-ray photoelectron diffraction and high-resolution electron-energy-loss spectroscopy. We demonstrate that the Ge/Si place exchange already takes place, but to a limited extent, at room temperature. Moreover, we observe that increasing the H-exposure temperature intensifies Si surface segregation, which we correlate to Ge-H decomposition. From that, we deduce that the creation of free Ge surface dangling bonds strongly modifies the energetic balance at the surface and in turn favors Si segregation. We propose that the driving force for H-induced Si/Ge site exchange is mostly the thermodynamics involved in the modification of hydrogen populations with temperature.