We have investigated the formation of Cu(In,Ga)Se2 thin films by real-time X-ray diffraction (XRD) experiments while annealing differently deposited and composed stacked elemental layer (SEL) precursors.
The in-situ measurements during the selenization of bi-layered Cu/In precursors reveal, that the semiconductor formation process is similar for precursors with thermally evaporated or sputtered indium. In both cases, the formation of binary copper and indium selenides is observed at temperatures around the melting point of selenium. After subsequent selenium transfer reactions, the chalcopyrite CuInSe2 is formed from the educt phases Cu2-xSe and InSe.
The addition of gallium leads to the formation of the intermetallic precursor phase Cu9Ga4, which reduces the overall amount of copper and gallium selenides at process temperatures above 500 K. This causes an ongoing selenization in the indium selenium subsystem, which results in the formation of CuInSe2 from the educt phases Cu2-xSe and the selenium richest indium selenide g-In2Se3.