DIRECT IMAGING OF CDTE(001) SURFACE RECONSTRUCTIONS BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

Novel reconstructions of the CdTe(001) surface have been directly observed using high-resolution electron microscopy in the profile-imaging geometry. The CdTe(001) surface, obtained by in situ annealing under ultrahigh vacuum conditions, is found to have a (2 x 1) structure at temperatures of less than about 200-degrees-C, but it transforms reversibly into a (3 x 1) structure at temperatures above 200-degrees-C. Structural models for the reconstructions have been proposed and confirmed by extensive computer simulations. The (2 x 1) reconstruction, stabilized by Cd atoms, consists of a 1/2 monolayer of Cd vacancies and a large inward relaxation of the remaining surface Cd atoms, similar to the (2 x 1) reconstruction previously proposed for the GaAs(001) surface. The (3 x 1) reconstruction, stabilized by Te atoms, involves formation of surface dimers and the presence of vacancies. In both reconstructions, atomic displacements are observed that extend a few layers into the bulk and serve to reduce the strain energy.