XPS AND UPS investigation of NH/sub 4/OH-exposed Cu(In,Ga)Se/sub 2/ thin films

Photoelectron spectroscopy was used to determine the compositional and electronic changes occurring in Cu(In,Ga)Se/sub 2/ thin films as a result of immersion in aqueous ammonia solution. We find that NH/sub 4/OH-treated CIGS surfaces are preferentially etched of indium and gallium, resulting in the formation of a thin layer of a degenerate Cu-Se compound that we tentatively identify as Cu/sub 2/Se. The work function of ammonia-treated samples is found to increase by 0.6 eV relative to as-grown CIGS thin films. The uniformity of chemical bath effects (etching & deposition) was found to be improved by the addition to the bath of a non-ionic surfactant. Initial device results show that the new surfactant-based chemical bath deposition (CBD) method may lead to better and thinner CdS buffer layers.