Order and structure of semiconductor surfaces: An assessment with He diffraction.

The capability of He diffraction to monitor the topography and the detailed ordering of crystal surfaces will be discussed using the reconstructed Ge(100) and Si(100) surfaces as examples. We find the nature of disorder and the topography of both surfaces to be similar. In each case, the room temperature reciprocal net is two-domain (2x1) with strong additional intensity streaks characteristic of a disordered c(4x2) structure. In contrast, with LEED we observe only a (2x1) reconstruction for Si(100) and relatively weak extra intensity for Ge(100). At low temperatures these surfaces contaminate easily and the extra intensity disappears quickly at 10(-10) torr. Pulsed laser annealing is examined as a technique to enable observation of the ordering of the Ge(100) surface at low temperatures. The ordering of the Ge (100) c(4x2) surface will be described as well as the complications of additional laser-induced disorder.