Experimental Evidence of Multiple Diffusion Mechanisms in Thin-Film Cu(In,Ga)Se2

Lattice and grain boundary diffusions of cadmium in copper indium gallium diselenide (Cu(In,Ga)Se2 or CIGS) thin films were investigated by annealing cadmium into samples of 700-nm CIGS thickness at temperatures between 250 and 300 °C. Diffusion profiles of cadmium were analyzed by dual-beam time-of-flight secondary ion mass spectroscopy (TOF-SIMS). In addition to fast cadmium grain boundary diffusion, experiments revealed cadmium diffusion profiles with two distinct lattice diffusion stages, which could be indicative of simultaneous vacancy and dissociative diffusion mechanisms.