PYROLYSIS OF TRIMETHYLGALLIUM ON (001) GAAS SURFACE INVESTIGATED BY SURFACE PHOTOABSORPTION

We directly observe the process of CH3 desorption from a GaAs surface reacted with trimethylgallium (TMG), using the surface photo-absorption method. After supply of TMG onto the As-stabilized (001) GaAs surface in H2 carrier gas, the reflectivity increases and saturates during H2 purging at substrate temperatures below 500-degrees-C. The observed reflectivity change corresponds to the formation of the Ga metal surface caused by CH3 desorption from the CH3-terminated surface. The CH3 desorption can be described by first-order kinetics, and the desorption rate constant is 2 x 10(-2) s-1, i.e., a lifetime of 50 s at 485-degrees-C. This is long enough to support the well-accepted mechanism of atomic layer epitaxy, i.e., the inability of the excess TMG to adsorb when supplied to the CH3-terminated surface.