On the homogeneity region, growth modes and optoelectronic properties of chalcopyrite‐type CuInS₂

Abstract

Studying the pseudo‐binary phase diagrams of Cu2S–In2S3 and CuS–InS in the ternary system Cu–In–S showed that the CuInS2 compound semiconductor exhibits a melting point at T = 1093(±3) °C and a homogeneity region at room temperature ranging from 2 mol% in In2S3 to 1.5 mol% in the CuS direction. This material, which crystallizes in the chalcopyrite‐type structure, occurs in nature as the mineral roquésite. Investigating the influence of inert gas pressure on the crystallization of a stoichiometric melt, a disproportionation of the crystallized material into a Cu2S‐rich bulk material of composition Cu1.06In0.98S2 epitaxially intergrown with ∼1.5 µm thick lamellae of the thiospinel phase CuIn5S8 was observed. Structure and composition of the bulk material were characterized by applying scanning Auger microscopy (SAM) and scanning electron microscopy (SEM) as well as differential thermal analysis (DTA) and X‐ray diffractometry (XRD). In photoluminescence measurements (PL), Cu‐rich bulk material is distinguished by sharp emission lines representing excitons close to the band to band transition at 1.55 eV and a broadband emission in the range from 1.3 eV to 1.45 eV. Exciton peaks of highest intensity were found at a Cu:In ratio = 1.0524. Investigating the spectral response of thin film chalcopyrite solar cells, a significant change of the optical gap from 1.45 eV for a “Cu‐rich” to 1.37 eV for an “In‐rich” absorber layer was observed. The results show that the homogeneity region of the material can be varied in the percentage range. A shift of the optical band gap can be influenced by stoichiometry (at% sulphur: at% metal) and the crystallization conditions of the adamantine‐type structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In situ analysis of elemental depth distributions in thin films by combined evaluation of synchrotron x-ray fluorescence and diffraction

“…However, the widths of the homogeneity ranges for the phases observed in this work lie between 0 and 3 at.% (Refs. [18][19][20][21] and are up to 6 at.% for the case of the solid solution Cu 1Àx In x . In principle, the accuracy of the method can be increased by taking into account possible deviations from the stoichiometric compositions and by using more complex parameterizations of the depth distributions.…”

Quasi-Fermi-Level Splitting of Cu -Poor and Cu -Rich CuInS2Lomuscio1, Rödel2, Schwarz3 et al. 2019Phys. Rev. Applied315410View full textAdd to dashboardCite

“…More details are reported in Table I. The Cu:In values for the Cu-rich samples are referred to as the ratios before KCN etching, performed to remove the CuS x secondary phase(s) [23].…”

“…. These micrographs are obtained after etching the CuS x secondary phase, which is present in as-grown Cu-rich films [23]. For both Cu-rich films, the grain size is in the micrometer range, while the Cu-poor samples have a much smaller grain size.…”

Phonon coupling and shallow defects in CuInS2

“…After this cyanide treatment, the Cu/In ratio was close to 1, determined by EDX. In fact, concerning the final compositions of the Cu-rich as grown films, they all reflect a stoichiometric CIS layer together with the CuS x phase [22]. As the Cu/In ratio is tuned above 1 during the depositions, the CIS layers are not grown off-stoichiometric, but the Cu excess translates into a thicker layer of CuS x phase.…”

“…The indium amount evaporated has been tuned to obtain different compositions in the final absorbers, described by the Cu/In ratio. It is worth mentioning for samples grown under Cu excess, thus Cu/In > 1, the final films include both a stoichiometric chalcopyrite phase and a secondary CuS x phase [22].…”