In situ high-temperature X-ray diffraction was used to investigate the reaction mechanism and kinetics of CuGaSe2 formation from Cu-Ga precursors during selenization. The precursor films were deposited in a migration enhanced molecular beam epitaxial reactor on Mo-coated thin glass substrates. During the selenization CuSe forms in the temperature range of approximately 260 to 370 degrees C, and the onset of formation of CuGaSe2 occurred at approximately 300 degrees C. The kinetic analysis using a modified Avrami model suggests the formation of CuGaSe2 from selenization of Cu-Ga films follows a one-dimensional diffusion-controlled reaction with an apparent activation energy of 109 (+/- 7) kJ/mol. (C) 2006 Elsevier B.V. All rights reserved.