A HIGH-RESOLUTION ELECTRON-ENERGY LOSS SPECTROSCOPY STUDY OF TRIMETHYLGALLIUM DECOMPOSITION ON GALLIUM RICH GAAS(100)

The adsorption and decomposition of trimethylgallium (TMGa) on the gallium rich (4 x 6) and (1 x 6) GaAs(100) surfaces have been studied by high resolution electron energy loss spectroscopy (HREELS), in conjunction with temperature-programmed desorption, x-ray photoelectron spectroscopy, and low energy electron diffraction. TMGa adsorbs molecularly at 108 K and dissociates above 200 K to form monomethylgallium (MMGa) and, possibly, some dimethylgallium surface species. Above 400 K, MMGa dominates. Surface MMGa remains stable until 650 K, above which temperature methyl radicals desorb. HREELS results showed unambiguously that methyl groups remain intact throughout the thermal decomposition of TMGa on GaAs(100). The effect of UV photons on both surface TMGa and MMGa has also been investigated, but no photochemistry was observed at wavelengths longer than 230 nm.