Growth of Europium-Doped Magnesium Selenide Films by Electric Field-Assisted Spray Pyrolysis: Optical and Structural Analysis

Abstract

Europium-doped MgSe films were deposited via electric field-assisted spray pyrolysis. The dopant concentration of the bulk solution of europium trioxide was 5wt. %. However, for doping the films at different substrate temperatures, volume percentage (vol. %) was employed at each instance of variation. Variation of spray temperature was around 573K and 673K (±0.3). Deposition occurred at optimized conditions. Spectra of absorption indicate poor absorption characteristics demonstrated by Europium-doped MgSe films in the ultra-violet region and very low absorption characteristics in the visible section. Absorption peaks were evident around 230nm, 240nm, 350nm and 365nm which confirmed defect states are inherent inside the crystal structure of the films. The films displayed high transparency and low reflection in the visible section at varying substrate temperatures. The high transparency revealed by the MgSe:Eu films in the visible section of the electromagnetic spectrum makes the material applicable as a coating layer in the manufacturing of transparent products. Band gap energies within the range of 2.49eV to 2.95eV corresponding to varying substrate temperatures (573K, 598K, 623K, 648K and 673K) and film thicknesses (2900nm, 2750nm, 2500nm, 2100nm and 200nm) were determined for the MgSe:Eu films. However, a clear observation shows that the band gaps of MgSe:Eu films are mainly dependent on thickness such that the obtained band gaps decreased with increasing thickness (band gap increases with thickness reduction). Structural analysis (XRD) studied at 10% and 40% Eu concentrations reveals a hexagonal (or wurzite) structure for the films with a distortion in crystallinity at higher dopant concentration (40 vol. %) and a resultant blue shift in the lattice constant from the bulk value. Multiple planes of reflection from XRD pattern of the deposited MgSe:Eu films indicate clearly that the films are polycrystalline. Surface morphology (SEM) confirms the highly strained nature and the presence of defect states within the crystal lattice of the Europium-doped MgSe films. Composition of MgSe:Eu films obtained by energy dispersive analysis x-ray (EDAX) confirms the growth of MgSe:Eu films.