Adsorption of [(Bu-t)GaS](4) on the GaAs(001)-(4 x 2) surface

We have studied the adsorption of [(Bu-t)GaS](4) in ultrahigh vacuum on the single-domain Ga-rich GaAs(0 0 1)-(4 x 2) surface using scanning tunneling microscopy (STM), Auger electron spectroscopy, and low-energy electron dif fraction (LEED). This study has focused on deposition at 650 K where adsorp tion is carbon-free. For submonolayer coverages, STM images show the presen ce of protrusions on the surface. The height distribution of these protrusi ons (which is insensitive to bias voltage) is peaked between 0.7 and 1.4 An gstrom. Since the expected height of an intact Ga4S4 cubic core of the [(Bu -t)GaS](4) precursor residing on the surface is expected to be between 3 an d 4 Angstrom, our data suggest that the Ga(4)S4 cubic core dissociates upon adsorption on the (4 x 2) surface. Adsorption of a GaS overlayer by exposu re of [(Bu-t)GaS](4) at 650 K, results in a reasonably ordered surface exhi biting a (2 x 1) reconstruction, as judged by LEED and STM. Unlike adsorpti on on the As-rich GaAs(0 0 1)-(2 x 4) surface, post-deposition annealing to temperatures in excess of 650 It is not necessary for the fabrication of a n ordered GaS overlayer. Possible structural models for the (2 x 1) surface are discussed along with the practical implications of these results. (C) 2000 Elsevier Science B.V. All rights reserved.