Backward Reconstructions on GaAs(001) Surface Induced by Atomic Hydrogen Reactions: Surfactant-Assisted Low-Temperature Surface Ordering

The sequence of surface reconstructions on GaAs(001), usually observed under As desorption in the temperature range from 450 to 580 degrees C, was obtained by atomic hydrogen (AH) reaction with the oxide-covered GaAs(001) surfaces in the temperature range from 420 to 280 degrees C. With the decrease in annealing temperature under AH treatment of oxide-covered GaAs(001) surfaces, the reconstructions changed from As-rich (2 x 4)/c(2 x 8) at 420 degrees C through the intermediate (2 x 6)/(3 x 6) at 380 degrees C, Ga-stabilized (4 x 2)/c(8 x 2) at 350 degrees C and (4 x 6) at 330 degrees C, to a very Ga-rich (4 x 4) at 280 degrees C, in the order of Ga/As ratio increase. The observed backward reconstructions on the GaAs(001) surface are explained by AH-induced Ga accumulation on the surface and by surfactant activities of AH allowing low-temperature ordering. The Ga-rich (4 x 4) surface structure covered by Theta(Ga) approximate to 0.8 ML was reconstructed to a new Ga-terminated structure with the symmetry of As-rich (2 x 4)/c(2 x 8) surface under vacuum annealing at the temperature higher than 560 degrees C. DFT calculations support the existence of the energetically favored Ga-rich (2 x 4) reconstruction described by the mixed-dimer model, developed for InP(001)-(2 x 4) surface, and predict the coexistence of (2 x 4) and (4 x 4) reconstructions on GaAs(001) at the Ga-rich limit.