Photoconductivity and photoluminescence in chemically deposited (Cd‐Zn)S:CdCl₂,Tb films

Abstract

Results of SEM, EDX and XRD studies, Optical Absorption spectra, Photoconductivity (PC) rise and decay, PC excitation spectra and Photoluminescence (PL) emission spectra are presented for (Cd-Zn)S:CdCl 2 , Tb films prepared by chemical deposition method on glass substrates either at room temperature (RT) or at 60 ο C in a water bath (WB). SEM studies show ball type structure which is related to layered growth. EDX measurements show excess of Cd in such preparations along with the presence of Tb. XRD studies show prominent diffraction lines of CdS and ZnS along with lines of CdCl 2 and impurity. The values of strain (ε), grain size (D), and dislocation density (δ) are evaluated from XRD studies and the nature of crystallinity of the films are discussed. Optical Absorption spectra also show the presence of Tb in the lattice corresponding to the transition 7 F 6 (4f) of Tb 3+ ions. From results of optical absorption spectra, the band gaps are determined, whose values are quite similar to those obtained from PC excitation spectra. Sufficiently high photo current (I pc ) to dark current (I dc ) ratios with a maximum value of the order of 10 6 are observed. This high photosensitisation is related to increase in mobility and lifetime of carriers due to photo excitation. PL emission spectra consist of peaks due to transitions in Tb levels.

Optimization of Zn concentration in chemically deposited (Cd x –Zn1−x )S nanocrystalline films for solar cell applications

“…Actually, in nanocrystalline thin films, with the increase in particle sizes, the strain and dislocation densities decrease. It happens so because when particles are of nanosize; the corresponding surface area is large and there are bright chances of introducing impurity and artifacts in the material [43]. This can be explained by the fact that when the number of particles in a particular volume is small, greater interaction is probable among them leading to more strains.…”