DESTABILIZATION OF GAAS(100) RECONSTRUCTIONS BY ADSORBED OXYGEN

The evolution of the morphology during heating of an oxygen-covered Ga As(100) surface is studied with thermal He-scattering. The accompanyin g desorption of oxygen is monitored with Auger electron spectroscopy a nd thermal desorption spectroscopy. The c(8 X 2) and the disordered (6 x 6) reconstruction of the GaAs(100) surface were investigated: oxyge n from a seeded nozzle beam (E(O-2)= 260 meV) is adsorbed on the surfa ce at room temperature. Upon heating the oxygen-covered surface both r econstructions are found to disorder above 150 degrees C. Above 380 de grees C desorption of molecular oxygen is observed, indicating that th e oxygen was molecularly adsorbed. As the desorption proceeds a comple x reordering process takes place in which areas with a 3 X n and/or n X 4 periodicity are formed. After the desorption is completed some fur ther reordering of the surface is observed before the transition to th e stable high temperature c(8 X 2) reconstruction takes place. The obs ervations can be explained by assuming that the oxygen molecules repla ce atoms in the outermost layer(s). The replaced atoms mimick an incre ase of the As-coverage.