In situ passivation of GaAs surface subsequent to the growth in a metalorganic vapor phase epitaxy (MOVPE) reactor has been made possible using trimethylaluminum (TMAl). The adsorption layer on GaAs, presumably consisting of aluminum and the decomposition product of TMAl, was oxidized upon exposure to air to form thin AlOx layer. TMAl supply of only 0.5 monolayer completely prevented the oxidation of As on the surface, as confirmed by XPS. The passivation layer mostly prevented the oxidation of As upon O-2 annealing for 5 min at 250 degrees C. For the successful passivation, complete desorption of excess As on the GaAs surface was essential prior to the injection of TMAl Otherwise, AlAs layer was formed and arsenic oxide was inevitably formed. The optimum length of H-2 purge to desorb As was determined to be 2 min with in situ surface monitoring using reflectance anisotropy spectroscopy (RAS). This passivation method, combined with the succeeding deposition of Al2O3 as a gate dielectric in a different reactor, provides the GaAs/gate interface without As-oxide. The method is applicable to the MOVPE growth of electron channel layers containing As for III-V metal-insulator-semiconductor field effect transistors (MISFETs). (C) 2008 Elsevier B.V. All rights reserved.