THE ADSORPTION AND THERMAL-DECOMPOSITION OF TRIMETHYLALUMINUM AND DIMETHYLALUMINUM HYDRIDE ON GAAS(100)

The adsorption and thermal decomposition of the aluminium precursors trimethylaluminium (TMAl) and dimethylaluminium hydride (DMAlH) on GaAs(100) surfaces has been studied by high resolution electron energy loss spectroscopy (HREELS). In both cases the dominant surface species at room temperature is based on intact methyl groups, with a dimethylaluminium species formed through either loss of a methyl group from TMAl, or hydrogen from DMAlH. As the temperature is raised the vibrational bands associated with the CH3 groups decrease in intensity consistent with the loss of methyl groups from the surface. A surface methylene (CH2) group is also identified at higher temperatures suggesting a competing decomposition pathway involving hydrogen abstraction from a surface methyl group. This minority decomposition pathway is the likely cause of the high carbon incorporation levels found in the epitaxial growth of GaAs using these precursors. The similarity of the results obtained with TMAl and DMAlH indicates that the hydrogen present in DMAlH plays a relatively insignificant role in influencing the decomposition process at the surface.