We studied nitrided surfaces and the kinetics of nitridation with tertiarybutylhydrazine (tBHy) in metal organic vapor-phase epitaxy (MOVPE). Reflectance anisotropy spectroscopy (RAS) and X-ray diffraction (XRD) were used for in situ and ex situ analysis. By comparing RAS spectra with molecular beam epitaxy (MBE) results we found a (3 x 3)-like reconstruction of the nitrided surfaces. The kinetics of the nitrogen-arsenic exchange were studied by RAS transients. An activation energy of E-a similar or equal to 1.7 eV was calculated for the exchange process. This value was independent from the tBHy partial pressure. Incorporation of nitrogen into GaAs up to six monolayers was further demonstrated by ex situ XRD for samples grown between 460 and 560degreesC. (C) 2004 Published by Elsevier B.V.