Sol-Gel Derived Cds Nanocrystalline Thin Films: Optical and Photoconduction Properties

Abstract

High-quality CdS nanocrystalline thin films were grown by sol-gel spin coating method at different solution temperatures on glass substrates. As-deposited films exhibited nanocrystalline phase with hexagonal wurtzite structure and showed good adhesion and smooth surface morphology. It was clearly observed that the crystallinity of the thin films improved with the increase in solution temperature. Crystallites sizes of the films also increased and were found to be in the range of 10 mm to 17 nm. The influence of the growth mechanism on the band and sub-band gap absorption of the films was investigated using UV-Vis and photothermal deflection spectroscopy (PDS). The band gap values were calculated in the range of 2.52 eV to 2.75 eV. The band gap decreased up to 9 % with the increase in solution temperature from 45 °C to 75 °C. Absorption coefficients estimated by PDS signal showed the significant absorption in low photon energy region of 1.5 eV to 2.0 eV. The dark and illuminated I-V characteristics revealed that the films were highly photosensitive. The results demonstrated the potential applications of sol-gel grown CdS nanocrystalline thin films as photoconductors and optical switches.

An in-depth analysis of nucleation and growth mechanism of CdS thin film synthesized by chemical bath deposition (CBD) technique

“…This further increases the kinetic energy of all molecules, which increases the interaction between the ions. This can increase / decrease the terminal thickness of the films, based on the level of supersaturation of the reaction solution 69 . Based on the modern complexity theory, when ammonium is used in the reaction, the common Cd 2+ complex structural geometries noted in the crystals are the tetrahedral, square planar, and octahedral geometries 70 .…”

Surface charge doping induced carrier type reversal in spin coated CdS/rGO layered nanohybrid films

“…Structure analysis Figure 1 shows the x-ray diffractogram for CdS/rGO nanohybrid films. The broad diffraction peak for cubic phase of CdS was observed at ∼26.68°(JCPDS No: 42-1411), indicating the growth of nanoparticle [7,8]. The formation of shoulder at lower diffraction angle (24.5°peak can be assigned to rGO) than CdS phase confirm the incorporation of rGO in CdS/rGO composites [9][10][11][12].…”

“…Figure 4(b) shows the variation of (αhν) 2 versus hν for CdS/rGO nanohybrid films. The value of optical gap is 2.21 eV for CdS films [7,8] and the values as 1.97 eV, 2.12 eV and 1.78 eV for the increasing rGO (1, 3 and 5 wt.%) contents in CdS/ rGO films [19,21]. The small content of rGO, the increase in nanoparticle size can be related to decrease in optical gap due to agglomeration of CdS nanoparticles or the rGO act as structure directing units.…”

“…CdS films were deposited on very well cleaned glass substrates by sol-gel spin coating method [7]. Firstly, the CdS solution was prepared for spin coating by dissolving 1.0 M cadmium acetate (CH 3 COO) 2 Cd.2H 2 O and 1.0 M thiourea (NH 2 CSNH 2 ) in 2-methoxyethanol separately and kept them under constant stirring for 1 h. Then, both the solutions were mixed and stirred magnetically for half an hour at 70°C.…”

“…unipolar electrical conductivity, that is, n-type conductivity for ZnS, ZnSe, CdS, and CdSe and p-type conductivity for ZnTe and CdTe [6]. Among these, cadmium sulfide (CdS) is n-type semiconductor with direct band gap (2.42 eV) have promising candidate for efficient light harvesting media and excellent charge separation properties for their applications in photocatalytic degradation, sensor, bio imaging, solar cell, water splitting, photochemical catalysts and luminescence devices etc [7,8].…”