Modification of the surface termination of GaAs(001) using photon-activated electron-transfer reactions

We report the use of a photon-activated electron-transfer chemical reaction to modify the surface termination of the (001) face of single-crystal GaAs . The technique involves the extraction of surface Ga atoms as a result of reaction with bromine. The bromine is produced at the surface by photoiniti ated dissociative electron attachment to methyl bromide molecules in a sing le monolayer physisorbed at similar to 80 K. Subsequent to the photoinduced surface reaction, the gallium is removed by annealing to desorb a gallium halide product. We have demonstrated that variation in photon exposure and thermal treatment allows the surface reconstruction to be controllably adju sted from the Ga-rich c(8 x 2) to the (4 x 6), (3 x 1) and As-rich c(2 x 8) terminations. A comparison of the results obtained with several surface di agnostics, including low energy electron diffraction, temperature programme d desorption and energy-resolved photofragment angular distribution measure ments, indicates that the most As-rich surface obtained by our technique is identical in structure to that of a control surface prepared using the sta ndard thermal reaction technique. In principle, the use of this photon-acti vated reaction, and others like it, allows precise adjustment and patternin g of the surface structure based on control of photon or electron exposure, molecular coverage, thermal treatment and lateral patterning of the incide nt photon or electron beam. (C) 2000 Elsevier Science B.V. All rights reser ved.