STOICHIOMETRY-DEPENDENT SCATTERING OF TRIMETHYLGALLIUM FROM GAAS(100) SURFACE

We examined the scattering of pulsed trimethylgallium (TMG) beams from GaAs surfaces with c(4 x 4), (2 x 4) and (1 x 6) reconstructions in order to obtain dynamical information concerning surface chemical reactions in metalorganic molecular beam epitaxy (MOMBE). The time-of-flight (TOF) spectra for scattered TMG were analyzed by taking into account the change in velocity distribution and the finite surface residence. We also investigated the sticking of TMG on these surfaces as a function of the TMG dosage. For the (2 X 4)-reconstructed surface, we observed no permanent sticking of TMG, although incident TMG molecules were dominantly desorbed after a long surface residence (900 mus at 546 K). This result indicates that the (2 x 4)-reconstructed surface is highly stabilized, although it has a deep trapping potential, which is consistent with the strong stoichiometry dependence of the TMG decomposition rate. On the other hand, clean c(4 x 4)- and (1 x 6)-reconstructed surfaces were considered to be rather reactive because of the high sticking coefficients. However, these surfaces were inactivated by TMG exposure. After about one monolayer of TMG exposure, most of the incident TMG molecules were scattered without any observable surface residence.