The structure of Sb-terminated GaAs(001) surfaces

We have studied the structure of Sb-terminated GaAs(001) surfaces using ref lection high energy electron diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy (STM). Clean, As-terminated (2 x 4) surf aces were prepared by molecular beam epitaxy and then exposed to Sb-4 at 49 0 degrees C, producing a (2 x 8)-reconstructed surface terminated with simi lar to 1 ML of Sb. Re-heating such a surface to 460 degrees C in vacuum ret urns the surface to a (2 x 4) reconstruction with approximately 0.5 ML Sb r emaining. STM reveals a complex, but well-ordered structure on the (2 x 8) surface for which a tentative model is proposed. On the (2 x 4) surface, ou r results clearly show that each unit cell is terminated by three dimers, w ith two-thirds Sb dimers and one-third As dimers. These results contrast wi th previous proposals that the Sb-induced (2 x 4) surface is terminated sol ely by one or two Sb dimers. (C) 1999 Elsevier Science B.V. All rights rese rved.