We report the identification of reflectance difference (RD) spectra for GaAs (001) surfaces in the presence of small quantities of trimethylbismuth (TMBi) vapor under organometallic vapor phase epitaxy (OMVPE) conditions. Ail RD spectrum similar to that observed from the previously reported (3 x 8) Sb-terminated surface of GaAs is reported, suggesting strong similarities between the Bi and Sb terminated surfaces. Because of the low vapor pressure of Bi, it is stable under extended hydrogen purges at growth temperatures of 450 degrees C. Whereas As or Sb coverage typically saturates at 1-2 monolayers oil the GaAs (001) surface under OMVPE conditions, no saturation of the Bi coverage is observed in this work. Extended exposure to TMBi results in the formation of Bi islands whose size increase with exposure time and TMBi concentration. (c) 2005 Elsevier B.V. All rights reserved.