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.
Energy calibration of x‐ray photoelectron spectrometers: Results of an interlaboratory comparison to evaluate a proposed calibration procedure
Results are reported of an interlaboratory comparison conducted to evaluate a proposed procedure for calibration of the binding energy (BE) scales on x-ray photoelectron spectrometers. The calibration was performed at two points on the BE scale (the Au 4f7/2 and Cu 2p3/2 lines) and checks were made of the assumption of BE-scale linearity from measurements on other lines. It is shown here that small offsets (up to ∼0.05 eV) can arise if peaks are located with assumed backgrounds of non-zero slope or if multipeak fits are made to Cu L3VV and Ag M4VV Auger spectra. The two parameters in the linear calibration equation could vary with analyzer pass energy and choice of x-ray source on a particular instrument. Check measurements of the calibrations were performed with the Ag 3d5/2 photoelectron line and the Cu L3VV and Ag M4VV Auger lines; difference between the corrected positions of these lines and the corresponding reference data were satisfactorily small in most cases. For Auger lines excited by monochromatized aluminum x-rays, however, the differences were significant and were interpreted in terms of different average x-ray energies for the monochromated and unmonochromated x-ray sources. The interlaboratory comparison was useful in testing the proposed calibration procedure and in providing guidance for some improvements.
X-Ray Photoelectron Study of the Valence Bands in I–III–VI2 Compounds
The X-ray photoelectron spectra of the valence bands in CuAIS 2 , CuGaS 2 , CuInS 2 , and AgGaS 2 have been measured. The spectra show that the upper parts of the valence bands in the Cu-compounds and the lower part of the valence band in the Ag-compound are mainly composed of d states of the monovalent metals. The spectra have been deconvoluted with a measured instrumental response function. The deconvoluted spectra of the Cu-compounds show almost d-like bands whose locations well agree with those obtained from the optical study by Shay et al. Resemblance between the valence bands of the Cu-compounds and those of cuprous halides is pointed out. In the deconvoluted spectra of CuAIS 2 and CuGaS 2 , peaks which may be due to the states of the trivalent ions are found in the high-binding-energy parts.