Thermal annealing effect on the structure, bandgap, and optical constants of Er-Mn oxide thin films

Thin films of erbium-manganese oxide were grown on glass and p-type Si substrates. The films were thermally pre-annealed at different temperatures ranging from 400 to 1000 degrees C to produce different crystalline structures and agitate a solid-state reaction. The structural characterisation of the films was carried out by X-ray diffraction (XRD) and energy dispersion X-ray fluorescence (XRF). The XRD investigation shows that the films annealed at 400 degrees C were amorphous and nanocrystals of ErMnO3 appear under pre-annealing at about 800 degrees C or more. Mn oxide and Er oxide prevent each other from crystallising alone. The optical properties of the films pre-annealed at different temperatures were studied in the fundamental absorption region of the spectrum in wavelength range 230-800 nm. The spectral complex refractive index, complex optical dielectric constant, and optical bandgap were determined. A modified single-oscillator Forouhi-Bloomer (FB) technique, Wemple-Didomenico (WD) equation, Urbach's relation, Tauc et al. relation, and pointwise unconditioned minimisation approach (PUMA) were used in the analysing of the obtained spectral data. (c) 2007 Elsevier Ltd. All rights reserved.