Hydrogen evolution from strained Si_xGe_1-x(100)2×1:H surfaces

The evolution of hydrogen from a series of strained Si_xGe_1-x(100)2×1:H surfaces were studied with angle resolved ultraviolet photoemission spectroscopy (ARUPS). A series of strained Si_xGe_1-x alloys were grown on Si(100) wafers using electron beam evaporation in an ultra-high vacuum molecular beam epitaxy chamber. The growth was followed by an situ H-plasma exposure. After the in situ H-plasma exposure, a diffuse double domain 2×1 reconstructed surface was obtained, which indicates a Si(Ge)-H monohydride surface termination. ARUPS spectra of the series of H-terminated Si_xGe_1-x alloys were obtained as a function of annealing temperature. Hydrogen induced surface states/resonances were observed from the H-terminated surfaces of all samples, and as the annealing temperature was increased the states were gradually extinguished. The ARUPS spectra of the H-terminated alloy surfaces indicated that the monohydride started to dissociate at annealing temperatures ≤250°C. The results show that, for all H-terminated Si_xGe_1-x alloys and Ge, the surface state attributed to the dangling bond was visible after annealing at ∼250°C. In contrast, annealing to >400°C was required to desorb H from a pure Si surface. It is proposed that the hydrogen starts to desorb preferentially from the Ge sites on the strained Si_xGe_1-x alloy surfaces.