The reaction pathway and kinetics of CuGaSe2 formation were investigated by monitoring the phase evolution of temperature ramp annealed or isothermally soaked bilayer glass/GaSe/CuSe precursor film using time-resolved, in situ high-temperature X-ray diffraction. Bilayer GaSe/CuSe precursor films were deposited on alkali-free thin glass substrates in a migration-enhanced epitaxial deposition system. The initial CuSe phase begins to transform to beta-Cu2-xSe at around 230 degrees C, followed by CuGaSe2 formation accompanied by a decrease in the beta-Cu2-xSe peak intensity at around 260 degrees C. Both the parabolic and Avrami diffusion-controlled reaction models represented the experimental data very well over the entire temperature range (280-370 degrees C) of the set of isothermal experiments with estimated activation energies of 115(+/- 16) and 124( +/- 19)kJ/mol, respectively. Transmission electron microscopy-energy-dispersive X-ray spectrometry (TEM-EDS) analysis suggests that CuGaSe2 forms at the interface of the initial GaSe and CuSe lacers. (c) 2008 Elsevier B.V. All rights reserved.