Growth and characterisation of thin films of CuCl and related materials
Foy, Barry (2012) Growth and characterisation of thin films of CuCl and related materials. PhD thesis, Dublin City University.
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CuCl thin films grown on (100) Si by thermal evaporation are studied by means of low temperature photoluminescence (PL) and reflectance spectroscopies. Spatially and wavelength resolved room temperature cathodoluminescence (CL) imaging of the surface of the CuCl samples in a scanning electron microscope (SEM) has also been performed.
Investigation of the effect of mixing KCl with the CuCl has been performed. The samples produced by the liquid phase epitaxy (LPE) machine use this element to lower the boiling point of CuCl so it is important to understand the effect they have on the resultant thin films. P-type doping has also been performed with oxygen.
Characterisation of these doped and undoped γ-CuCl samples has been performed. Reflectance and X-ray diffraction measurements show the effect the oxygen doping has on the structural and optical properties of the material. The exciton positions in the undoped samples have been repeatable, but deteriorate as oxygen doping levels increase. A suitable capping method for use in x-ray diffraction has been found. Nail varnish applied to the samples was shown to prevent structural decay of the
CuCl thin films due to their hygroscopic nature.
Cathodoluminescence work on undoped and doped samples (doped with both oxygen and KCl) has been performed showing the effect of these techniques on the electrical properties. Digital CL has also been performed, but with limited results due to the low resolution of the digital CL camera.
EDX has been used to analyse the atomic structure of the thin film samples. Traces of K were found in the KCl-CuCl samples with little change in the Cl levels. This gives further credence to the idea that the K+ atom within the material is responsible for the increase in conductance produced by KCl doping.
The Reflectance of the various CuCl samples was tested at different angles of incidence using a Deuterium light source. The reflectance spectra are modelled using a dielectric response function with various models involving dead layers and reflected waves in the thin film and the exciton-polariton structure obtained is compared to other
studies of CuCl. The modelling is shown to match the experimental data quite well with the dead layer having little effect on the modelled spectra. KCl-CuCl samples prove to have a consistently higher reflectance signal than undoped CuCl.
Photoluminescence (PL) tests of doped CuCl reveal the emergence of an unknown peak centred at 3.187 eV. This peak has not been previously identified to the best of our knowledge and steadily increases to become the maximum in the PL spectrum as doping levels are increased. A combination of PL and reflectance scans have been used to locate an ideal doping level which provides p-type doping attribute of CuCl without a corresponding significant decrease in the optical properties. This ideal region is between 3-4 minutes of exposure at the settings detailed herein.
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