SURFACE REFLECTANCE ANISOTROPY OF INDIUM-TERMINATED GAAS(100) SURFACES

The growth of thin indium-layers on the GaAs(100) As-rich (2 x 4)/c(2 x 8) surface has been investigated by reflectance anisotropy spectrosc opy (RAS), LEED and AES. Clean surfaces of the (2 x 4)/c(2 x 8) recons truction were prepared in UHV by thermal desorption of a protective ar senic layer deposited on homoepitaxially grown MBE layers. Room temper ature deposition of indium on the (2 x 4)/c(2 x 8) surface and subsequ ent annealing at 450 degrees C leads to a 90 degrees rotation of symme try in the LEED pattern at a threshold coverage of 0.5 monolayers, i.e . a change from the (2 x 4)/c(2 x 8) to the (4 x 2),/c(8 x 2) reconstr uction. The RAS spectra show the evolution of a distinct negative feat ure at 1.8 eV, that shifts to 2.1 eV after annealing, corresponding to optical transitions attributed to In-dimers orientated along the [011 ]-direction. AES analysis shows a change in growth mode beyond 0.5 ML indicating saturation of all available adsorption sites at this covera ge and RAS spectra show a contribution from additional disordered In. The AES spectra display no evidence of a surface exchange reaction bet ween gallium and arsenic atoms, thus indicating a surface termination by In-dimers adsorbed on a layer of As.