Chemisorption and decomposition of trimethylgallium on GaAs(100)

Abstract

The chemisorption and decomposition of trimethylgallium on the gallium-rich (4 × 6) and (1 × 6) GaAs(100) surfaces have been studied by temperature-programmed desorption, LEED, and Auger electron spectroscopy. Upon adsorption and subsequent heating, a fraction of a monolayer ((1.6 ± 0.7) × 10 14 molecules cm −2) of trimethylgallium irreversibly dissociates into monomethylgallium surface fragments. Upon heating, methyl radicals are observed desorbing from the surface with a narrow peak at 710 K. The desorption parameters (activation energy and pre-exponential factor) of the methyl radicals depend on surface coverage, indicating significant adsorbate-adsorbate interactions. The zero coverage limit desorption parameters are: E = 46.1 ± 0.5 kcal mol and v = 1.6 × 10 14±0.2 s −1. Higher coverages of trimethylgallium desorb molecularly in peaks at 500 and 350 K. After desorption of all hydrocarbon fragments the surface immediately converts into the (1 × 6) reconstruction. The excess gallium released from trimethylgallium decomposition is not incorporated in the GaAs surface and apparently resides in gallium droplets. We present structural models for the gallium-rich GaAs(100) surfaces before and after TMGa chemisorption which are consistent with all of our observations.