Evidence was presented which supported the suggested occurrence of a new 2 x 8 surface reconstruction on Si1-xGex alloys which had been grown onto (100)Si substrates by means of molecular beam epitaxy. The reflection high-energy electron diffraction patterns from samples with x-values ranging from 0.1 to 0.3 (which were grown at temperatures of between 350 and 550C) exhibited n/8 fractional-order diffraction streaks; in addition to the 2 x 1 pattern which was normally seen on (100) Si surfaces. The presence of fractional-order diffracted beams indicated an 8-fold periodic modulation of the electron scattering factor across the alloy surface. Low-energy electron diffraction patterns supported the conclusion that the modulation occurred in the direction of the dimer chains of a 2 x 1 reconstruction. The thermal stability of the 2 x 8 reconstruction was

investigated, and it was found that it changed to 2 x 1 upon annealing at 700C. It reappeared when the sample temperature was decreased to below 600C. It was concluded that the reconstruction was a stable ordered phase in which the pair-correlation function of surface Ge atoms exhibited an 8-fold periodicity in the '1-direction' of a 2 x 1 Si-like reconstruction.

E.T.Croke, R.J.Hauenstein, T.C.Fu, T.C.McGill: Journal of Vacuum Science and Technology B, 1991, 9[4], 2301-6