Nanocrystalline CdS thin films deposited by sol-gel spin coating method: Effect of aging and doping on structural, optical, and electrical properties

This work deals with the synthesization of pristine and Fe-doped CdS nanocrystalline thin films by the sol-gel spin coating method with the freshly prepared solution (Set-A) and 24 h aged solution (Set-B). The XRD patterns of pristine and Fe-doped nanocrystalline CdS thin films (Set-A) reveal hexagonal structure and the other films of set-B exhibit cubic structure. The average crystallite size of all pristine and Fe-doped nanocrystalline CdS thin films (Set-A and Set-B) was found to be lying in the range of 4.997-17.142 nm. The particle size calculated from TEM studies was found to be 11.14 nm, 10.74 nm and 8.74 nm for pristine, 2 ml Fe doped, and 5 ml Fe doped CdS thin films. The average surface roughness of the films was found to be 0.1518 nm, 4.2216 nm, and 0.1471 nm for Fe_00, Fe_01, and Fe_05 samples of Set-A, while it was found to be 0.2055 nm, 4.839 nm and 0.1803 nm for Fe_00, Fe_01 and Fe_05 samples of Set-B respectively. PL spectra reveal the occurrence of cyan emission for both sets of samples. The band gap values for the nanocrystalline thin films (Set-A) were 2.46-2.71 eV and for Set-B were in the range of 2.47-2.75 eV, which is higher than that of bulk CdS (2.42 eV). The low-temperature resistivity of the deposited films of both sets was obtained in the range of 105 to 103 omega cm, and also found to decrease with increasing Fe concentration in CdS.