Cation sublattice stacking faults in Cu-rich chalcopyrite CuInSe₂

Using transmission electron microscopy, we investigate the microstructure of CuInSe₂ films grown by molecular beam epitaxy on GaAs substrates under Cu-rich conditions. We find both a transition towards c-axis oriented growth as the film gets thicker, and a significant density of stacking faults on the cation sublattice in the chalcopyrite structure. These stacking faults are found to extend large distances in the plane of the film, and are not found to be present in samples not grown in Cu-rich conditions.