Synchrotron X-ray Diffraction Study of the Disordering of the Ge(111) Surface atHigh Temperatures

摘要

Currently, experimental information on the morphology of semiconductor surfacesnear the bulk melting point is very limited, in spite of its evident importance in many growth processes. The Ge(111) surface has been reported to undergo a phase transition at a crystal temperature of about 1050 K, which is 160 K below bulk melting temperature Tm (1210 K). The nature of the transition remains controversial. We have studied the Ge(111) surface using synchrotron x-ray scattering techniques with a glancing-angle scattering geometry. Our observations do not conform to any standard model of surface disordering. We believe that the structural change is not due to a phase transition, but rather reflects a continuous changes of the surface morphology. We propose a model in which disorder is induced by surface vacancies which become abundant at about 160 K below Tm. The surface diffraction data can be understood quantitatively by use of kinematical diffraction theory,