OBSERVATION OF (111) ORDERING AND [110] MODULATION IN MOLECULAR-BEAM EPITAXIAL GAAS1-YSBY LAYERS - POSSIBLE RELATIONSHIP TO SURFACE RECONSTRUCTION OCCURRING DURING LAYER GROWTH

Transmission electron diffraction (TED) was used to observe extra diffraction spots in the TED patterns of molecular beam epitaxial GaAs 1-y Sby layers with y=0.25, 0.50, and 0.71 grown at 520 °C on (001) GaAs substrates. Half-order diffraction spots in the TED patterns indicated ordering on the (1̄11) and (11̄1) planes of the Group V sublattice, and streaks with subsidiary spots indicated a modulation in the [110] direction with a periodicity of ∼4d110. Streaks in the [001] direction indicated monolayer disruptions of the {111} ordering and the [110] modulation in the [001] direction. As the composition parameter y varied, there were progressive changes in the {111} ordering, the [110] modulation, and the [001] disruptions, and these correlated with corresponding changes in the reconstruction of the dangling bonds at the growing layer surface, as determined by reflection high-energy electron diffraction. A model is proposed to explain the observed effects in terms of ordered atomic arrangements of the Group V atoms resulting from the surface reconstruction being incorporated into the bulk epitaxial layers.