Etching or Stabilization of GaAs(001) under Alkali and Halogen Adsorption

Experimentally and by ab initio calculations it is shown that adsorption of electropositive cesium on the As-rich surface of GaAs(001) and, in a symmetric fashion, adsorption of electronegative iodine on the Ga-rich surface, induce a decrease of the surface stability, thus facilitating surface etching. Conversely, Cs adsorption on the Ga-rich surface and I adsorption on the As-rich surface lead to an increased surface stability. Etching occurs when adsorption-induced charge transfer weakens the backbonds of the top arsenic atoms for the case of Cs on the As-rich \uce\ub22(2 \uc3\u2014 4) surface and the lateral bonds in the topmost surface layer for I on the Ga-rich \uce\ub6(4 \uc3\u2014 2) surface. The possibilities of reversible transitions between the two reconstructed surfaces and of atomic layer etching with monolayer precision are demonstrated