SURFACE ORDERING ON GAAS(100) BY INDIUM-TERMINATION

The growth of indium-layers in the monolayer regime on As-rich (2X4)/c (2X8)- and Ga-rich (4X2)/c(8X2)-GaAs(100) surfaces has been investigat ed by scanning tunneling microscopy (STM), low-energy electron diffrac tion (LEED), Auger electron spectroscopy (AES) and reflectance anisotr opy spectroscopy (RAS). Clean (2X4)- and (4X2)-reconstructed surfaces were prepared in UHV by thermal desorption of a protective arsenic lay er deposited on top of GaAs(100) surfaces grown in a molecular beam ep itaxy (MBE)-system. For the (2X4) reconstruction, the STM images show As-dimer rows consisting mostly of two dimers per unit cell in the out ermost layer. Besides a large number of kinks in the dimer rows, a sur face roughness corresponding to about three bilayer steps (8.4 Angstro m) is observed due to multiple layer nucleation during MBE growth. Aft er deposition of indium and subsequent annealing to approximately 450 degrees C a well ordered reconstruction with c(8X2)-symmetry is establ ished. The STM images show a pattern consisting of kink free, alternat ing straight and broken rows oriented along the [110]-direction attrib uted to In-dimer rows. Remarkably, the surface roughness of these In-t erminated surfaces is strongly reduced. For the Ga-terminated (4X2) su rface reconstruction, STM results show a surface terminated with Ga-di mer rows, free of kinks, which appears flat over large areas similar t o the In-terminated surface. After deposition of indium and annealing to 450 degrees C, LEED, RAS and STM reveal a surface structure very si milar to that formed on the (2X4)-surface. Thus we conclude that in bo th eases a structure with In-dimer-rows on top of an As-layer (second layer) is formed. The smoothing of the surface roughness is a conseque nce of the larger mobility of the group III surface atoms, following t he As desorption. (C) 1995 American Vacuum Society.