Structure of GaAs(001)-c(4 x 4): Comparison of X-ray diffraction and first-principles calculation

The surface structure of GaAs(001)-c(4 x 4) was investigated by synchrotron surface X-ray diffraction which is sensitive to both in-plane and out-of-plane structures. The atomic coordinates and Debye-Waller factors for up to the sixth layer from the surface are given. The resultant atomic coordinates were compared with those given by a first-principles calculation. Among a variety of heterodimer models that were examined by theoretical calculation, our data fit best a three-heterodimer model where three Ga-As heterodimers are present in one unit cell. The preference for the formation of heterodimers is discussed in relationship to the transition process from the 2 x 4 to the c(4 x 4) structures. (c) 2006 Elsevier B.V. All rights reserved.