Real-time analysis of adsorption processes of Zn on the GaAs(001)-(2 x 4) surface

We have studied adsorption processes of Zn on the GaAs(001)-(2x4) surface u sing reflection high-energy electron diffraction (RHEED) and total-reflecti on-angle x-ray spectroscopy in real time. A rocking-curve analysis of RHEED has been used;to determine the atomic coordinates of both clean and Zn-ads orbed 2x4 surfaces. The analysis for the clean 2x4 surface (beta 2 phase) h as shown that both As dimers in the outermost and third atomic layers are d isplaced upward from their bulk positions. When the 2x4 surface was exposed to a Zn beam, the Zn atoms are preferably adsorbed at Ga-vacancy sites in the missing dimer trenches of the 2x4 unit cell with site occupancies of si milar to 100% and similar to 50% at 200 and 250 degrees C, respectively.