SOURCE:

Faculty: Physical Sciences
Department: Physics And Industrial Physics

CONTRIBUTORS:

Jeroh, D. M.
Ekpunobi,A. J.
Okoli, D. N.

ABSTRACT:

Pure II-VI (ZnSe) and europium doped II-VI (ZnSe:Eu, CdSe:Eu and MgSe:Eu) semiconductor films were deposited on glass substrates at different variations using electrostatic spray pyrolysis. For the deposition of ZnSe films, two variations (substrate temperature and volume of spray solution) were considered while for the deposition of ZnSe:Eu, CdSe:Eu and MgSe:Eu films, three variations (substrate temperature, flow rate and dopant concentration) were considered. All the films were characterized accordingly and their optical, structural, surface morphology and elemental composition analyses were studied for possible applications of the films. Optical analysis of ZnSe films for the different variations considered show that absorbance values were between 4.69% and 55.17% in the ultra-violet (UV) region while absorption values ranging from 4.09% to 14.94% in the visible (VIS) region were obtained. Optical transmission for the ZnSe films is within the range of 28.07% to 78.11% in the UV region while the VIS region recorded transmission values of 76.37% to 91.01%. Band gap study of the ZnSe films at different substrate temperatures reveal the band gaps values are within the range of 2.68 eV to 2.79 eV. For the ZnSe:Eu films, optical study reveal absorption values between 1.85% to 68.12% in the UV region while absorption values between 0.65% and 6.02% were observed in the VIS region for all deposition conditions. Transmission values ranging from 20.84% to 95.83% in the UV region and 87.06% to 98.52% in the VIS region were obtained for the ZnSe:Eu films for all deposition conditions. Optical band gap obtained for the ZnSe:Eu films ranged between 3.01 eV to 3.12 eV for different substrate temperatures. The CdSe:Eu films recorded poor absorption from about 1.17% to 30.27% in the UV region and 0.49% to 8% in the VIS region for the different variations considered. Transmission in the UV region was estimated to be between 49.81% and 97.34% while high transmission between 77.20% and 98.88% was observed for the CdSe:Eu films in the VIS region. Band gap analysis reveal band gaps values for CdSe:Eu films from 2.40 eV to 2.84 eV depending on the substrate temperature. In the case of MgSe:Eu films, optical results indicates poor absorption values within 2.73% to 30.53% in the UV region and 0.23% to 25.60% in the VIS region in all cases of variation. Band gap estimated for the MgSe:Eu films at different deposition temperature is within the range of 2.49 eV to 2.95 eV. X-ray diffraction (XRD) analysis conducted on the ZnSe film obtained at substrate temperature of 300 oC indicates amorphous structure. However, the ZnSe film deposited at substrate temperature of 350 oC appears to be polycrystalline. For the ZnSe:Eu films deposited at substrate temperature of 350 oC (10% and 20% dopant concentrations), polycrystalline nature was also observed. However, the film obtained at 20% dopant concentration had less sharp diffraction peaks. The XRD pattern of CdSe:Eu film obtained at deposition temperature of 360 oC and dopant concentrations of 10% and 15% respectively are crystalline in nature. XRD study of MgSe:Eu film at 350 oC (10% dopant concentration) reveal multiple planes of diffraction indicating clearly the polycrystalline nature of the film. Scanning electron microscopy (SEM) study performed on the ZnSe film shows smooth and homogeneous film. SEM image of ZnSe:Eu film obtained at 350 oC and 10% dopant concentration reveal cotton-like morphology while the SEM image of ZnSe:Eu film obtained at 375 oC and 10% dopant concentration indicates fibre-type nature. For the CdSe:Eu film obtained at 340 oC and 15% dopant concentration, SEM image shows the film has a smooth surface. SEM images of MgSe:Eu films obtained at 300 oC (10% dopant concentration) and 350 oC (40% dopant concentration) show cracks and strains all over the surface of the films. Energy dispersive x-ray (EDX) analysis conducted on all the films confirmed their formation