Ellipsometry, reflectance, and photoluminescence of nanocrystalline CuCl thin films on silicon

The authors have used sequential pulsed vapor deposition to prepare thin films of copper(I) chloride (CuCl) on silicon. The films are nanocrystalline and show a very strong ultraviolet luminescence. The excitonic response and corresponding luminescent properties make these films promising for new short-wavelength photonic/photoelectronic devices. The authors have undertaken systematic studies of these films, using the potential of multiple-angle-of-incidence spectroellipsometry with a rotating compensator, normal-incidence reflectance with small illuminated spots, and photoluminescence with high spatial resolution. The silicon substrate presents specific problems in the interpretation of the ellipsometric and reflectance spectra, as the excitonic multiplets of CuCl are close to the E₁ interband spectral structure of Si. The authors discuss appropriate procedures to isolate the response of the thin films. In addition, since the coverage of the substrates typically shows inhomogeneity, care has to be taken in accounting for its presence. A consistent picture of the passive and active excitonic response of the films results from the multitude of experimental techniques used.