RAMAN-SCATTERING FROM TRIMETHYLALUMINUM (TMA) - FREE AND ADSORBED MOLECULES ON GAAS(100)

We have measured the Raman scattering from an adsorbed layer of trimet hylaluminum (TMA) on GaAs(100) as a function of coverage down to 17 mo nolayers. The absolute scattering cross-section of the CH3-symmetric s tretching mode of TMA was found to be 8.0 x 10(-29) cm(2)/dimer sr lin e. The corresponding cross-section in the gaseous state is 2.6 x 10(-2 9) cm(2)/dimer sr line. The observed enhancement of the cross-section in the multilayer is due to the effect of the molecular field. The sca ttering cross-section of the CH3-symmetric stretching mode of gaseous trimethylgallium (TMG) is 1.3 x 10(-29) cm(2)/molecule sr line. Based on these data on the absolute Raman cross-sections, we expect that the monolayer of these molecules on GaAs would be extremely difficult to observe by Raman scattering in a crystal growing environment.