Surface ordering on GaAs(100) by indium-termination

Abstract

The growth of indium-layers in the monolayer regime on As-rich (2×4)/c(2×8)- and Ga-rich (4×2)/c(8×2)-GaAs(100) surfaces has been investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and reflectance anisotropy spectroscopy (RAS). Clean (2×4)- and (4×2)-reconstructed surfaces were prepared in UHV by thermal desorption of a protective arsenic layer deposited on top of GaAs(100) surfaces grown in a molecular beam epitaxy (MBE)-system. For the (2×4) reconstruction, the STM images show As-dimer rows consisting mostly of two dimers per unit cell in the outermost layer. Besides a large number of kinks in the dimer rows, a surface roughness corresponding to about three bilayer steps (8.4 Å) is observed due to multiple layer nucleation during MBE growth. After deposition of indium and subsequent annealing to approximately 450 °C a well ordered reconstruction with c(8×2)-symmetry is established. The STM images show a pattern consisting of kink free, alternating straight and broken rows oriented along the [110]-direction attributed to In-dimer rows. Remarkably, the surface roughness of these In-terminated surfaces is strongly reduced. For the Ga-terminated (4×2) surface reconstruction, STM results show a surface terminated with Ga-dimer rows, free of kinks, which appears flat over large areas similar to the In-terminated surface. After deposition of indium and annealing to 450 °C, LEED, RAS and STM reveal a surface structure very similar to that formed on the (2×4)-surface. Thus we conclude that in both cases a structure with In-dimer-rows on top of an As-layer (second layer) is formed. The smoothing of the surface roughness is a consequence of the larger mobility of the group III surface atoms, following the As desorption.