Reaction kinetics of CuInSe ₂ thin films grown from bilayer InSe/CuSe precursors

The reaction kinetics for the formation of CuInSe2 thin films from a stacked bilayer precursor consisting of InSe and CuSe was studied by means of in situ high-temperature x-ray diffraction. In particular, the isothermal phase evolution of the glass/InSe/CuSe precursor was observed at different temperatures. The pathway produces a CuInSe2 diffusion barrier layer that also functions as a nucleation barrier. Hence, amorphous and crystalline phases simultaneously grow during isothermal processing. The shape of the time-resolved fractional reaction curve exhibits a deceleratory behavior, consistent with the presence of a diffusion-controlled reaction mechanism. Analyses based on Avrami and parabolic-rate laws were conducted. The Avrami exponent for each isothermal reaction is in the range 0.5-0.8, which indicates that the growth reaction is dominantly one-dimensional diffusion controlled. The estimated apparent activation energy for this reaction is 66.0 kJ/mol. The results based on the parabolic rate model are consistent with the Avrami analysis, yielding a similar apparent activation energy value, and thus supporting the conclusion that the process is one-dimensional diffusion controlled.