Reconstructed-structure-dependent surface reaction in metal-organic molecular beam epitaxy of GaAs

The initial stage of the surface reaction during metalorganic molecular beam epitaxy (MOMBE) is discussed as a function of relaxed or reconstructed GaAs surface structure on the basis of the scattering of continuous and pulsed trimethylgallium (TMG) beams from structure-controlled GaAs(100), (110) and (111)B surfaces. The results of TMG scattering are interpreted within the framework of the precursor-mediated adsorption mechanism, where TMG molecules are trapped in the precursor states in the initial stage of the scattering. In the case of the scattering from highly stabilized GaAs surfaces, we find that TMG molecules are desorbed after a long surface residence time without decomposition, while, in the case of the scattering from less stabilized surfaces, the trapped TMG molecules are efficiently chemisorbed with dissociation. The surface structure dependence of the precursor state suggests that the precursor states are attributed to the charge distribution in the relaxed or reconstructed surface. This is supported by the result that the surface residence time on the GaAs(100)-(2 × 4) surface decreases when metallic Ga is deposited onto the surface, resulting in the decrease in the number of AsGa pairs generating electric field.