Surface Structures and Properties of Diamond-Structure Semiconductors

Low-energy electron-diffraction and secondary electron-emission measurements have been made on (111) and (111) surfaces of GaSb and (100) surfaces of InSb. To account for the diffraction patterns observed both for these materials and previously for Ge and Si, a general model for (111) surfaces of diamond-structure semiconductors is proposed. Every second atom, counting along alternate close-spaced rows is raised with respect to its neighbors, being bonded to the sublayer by three p bonds while the "dangling bond" is s type. The remaining three-fourths of the surface atoms have dangling p bonds and are bonded to the sublayer by trigonal sp^2-type bonds. The Ga or (111) face of GaSb has maximum sticking coefficients of 10^-5 and 10^-4 for oxygen and CO₂, respectively, these values being 10 times greater than those found for the Sb or (111) face. Multilayer adsorption of oxygen takes place on all the surfaces measured. The oxygen can be removed by heat treatment alone. Evidence is presented to show that diffusion of oxygen into the bulk is an important mechanism for regenerating the clean surfaces by heat treatment. Carbon dioxide adsorbs on GaSb so as to show structure. It apparently deposits as an unbroken molecule, and, unlike oxygen, does not build up several layers.