Structure of GaAs(0 0 1)-c(4 × 4): Comparison of X-ray diffraction and first-principles calculation

The surface structure of GaAs(0 0 1)-c(4 × 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 × 4 to the c(4 × 4) structures.