Composition dependent optical, structural and photoluminescence behaviour of CdS:Al thin films by chemical bath deposition method

Undoped and Al doped CdS thin films were deposited successfully on glass plates using chemical bath deposition method at 80 °C with different Al concentrations between 0 and 8%. X-ray diffraction spectra revealed that undoped CdS thin film had cubic structure which was turned to mixed phase of cubic and hexagonal by Al doping. The noticed decrease in d-value, cell parameters, bond length and volume up to 4% of Al is due to the substitution of Al3+ into Cd–S lattice whereas the increase of these parameters beyond 4% is due to the formation of defects. Structural, optical and photoluminescence properties of Al doped CdS thin films were studied using X-ray diffraction, energy dispersive X-ray, scanning electron microscopy, UV–Vis absorption, Fourier transform infra red spectroscopy and photoluminescence spectra. The enhanced crystal size at lower Al concentrations is due to the proper substitution of Al3+ and the reduced crystal size after Al=4% is due the interstitial defects of Al3+ in Cd–S lattice. The continuous red shift of energy gap from 2.18 eV (Al=0%) to 1.96 eV (Al=8%) is elucidated by increasing amount of sulfur deficiency by Al doping. The presence of functional groups and chemical bonding were confirmed by FTIR spectra. Room temperature photoluminescence spectra showed the two well distinct and strong bands; blue band around 409 to 415 nm and green band around 538 to 547 nm. The change in intensity and their shift were discussed in detail.