In Situ thickness measurements of chemical bath-deposited CdS

Chemical bath-deposited (CBD) cadmium sulfide has been a component in some of the most efficient Cu(In,Ga)Se2-based solar cell devices. While accurate in situ measurements of the thicknesses of vacuum-based depositions can be accomplished with quartz crystal monitors, solution-based growth rates of CdS vary greatly on different substrates and are therefore difficult to measure. This work discusses the effectiveness of using an optical reflectance-based measurement of the growing film to determine the film’s thickness. On specular molybdenum films the measurement is accurate, while on the rough, poorly reflecting Cu(In,Ga)Se2 (CIGS) films, the measurement is hampered.