Evolution of opto electronic properties during film formation of complex semiconductors

Optical and electrical properties of complex semiconducting alloys like Cu In,Ga Se2 CIGS are strongly influenced by the reaction pathways occurring during their deposition process. This makes it desirable to observe and control these properties in real time during the deposition. Here we show for the first time the evolution of the band gap and the sub band gap defect absorption of CIGS thin film as well as surface roughness during a three stage co evaporation process by means of an optical analysis technique, based on white light reflectometry WLR . By simultaneously recording structural information with in situ energy dispersive X ray diffraction and X ray fluorescence we can directly correlate the evolution of opto electronic material parameters with the structural properties of the film during growth. We find that the surface roughness and the sub gap light absorption can be correlated with the phase evolution during the transformation from In,Ga 2Se3 to Cu In,Ga Se2 by the incorporation of Cu into the film. Sub bandgap light absorption is found to be influenced by the Cusaturated growth phase and is lowered close to the points of stoichiometry, allowing for an advanced process desig