Co-evaporation of Cu(In, Ga)Se2 at low temperatures: An In-Situ x-ray growth analysis

Cu(In, Ga)Se₂ thin films have been coevaporated onto Mo coated soda-lime glass using a multi-stage approach and two different maximum growth temperatures (420°C and 530°C). In order to investigate principal differences in the growth dynamics for the two temperature regimes, the growth has been monitored by in-situ energy dispersive X-ray diffraction, performed at the EDDI beamline at the Helmholtz-Zentrum Berlin´s BESSY II synchrotron facility. During the in-diffusion of Cu-Se into the In-Ga-Se precursor a signature that points towards a possible Cu-deficient defect phase or a chalcopyrite phase that incorporates stacking faults in the [221] direction is observed to be visible throughout a wider compositional range for the low temperature process. It disappears once the film becomes Cu-rich and thus highlights the critical role of Cu-excess for the growth of chalcopyrite thin films, particularly at low growth temperatures.