Excitons in the layered insulators ZnI2 and CdI2:Zn

摘要: The fundamental electronic absorption spectra in the layered compounds ZnI2 and Zn-doped CdI2 are investigated spectral interval 3–5.9 eV. samples thin grain-oriented films deposited on quartz substrates. It is found that ZnI2, unlike CdI2, a direct-gap insulator, despite similarity of crystal structures these compounds. introduction Zn atoms into cation sublattice at concentrations x⩾1% leads to vanishing from indirect transitions appearance strong exciton band edge. parameters bands (spectral position, half-width Γ, oscillator strength f) measured temperature 80–330 K. dependence Γ both typical for three-dimensional excitons. In decreases with increasing T because Debye–Waller factor, while CdI2:Zn it increases. This last result evidence forbidden charact...