Abstract:
Aluminum doped cadmium sulfide (Cd1-xAlxS) thin films for different values of x
(0.00- 0.18) have been prepared by spray pyrolysis technique on to glass substrates. In order
to prepare Cd1-xAlxS thin films the 0.1 M aqueous solution of [Cd(CH3COO)2.2H2O],
[Al(CH3COO)3.2H2O] and NH2CSNH2 were used as the precursor solution. The surface
morphology, structural, optical and electrical properties of the films is studied in details. The
SEM micrographs of film show uniform surface. The Energy Dispersive X-ray (EDX)
shows that films are stoichiometric. X-ray diffraction (XRD) study shows that the grain size
was varied from 22 nm to 29 nm with the increase in doping concentration of Al. Lattice
constant also calculated from XRD data. All the samples have Polycrystalline Hexagonal
crystal structure. The absorption coefficient (α) of the (Cd1-xAlxS) films was UV-VIS
transmission spectra. The optical spectra of Cd1-xAlxS ternary system exhibit high
absorbance near ultraviolet region and high transmission throughout the visible and nearinfrared
region (600-1100 nm). The direct band gap energies for the films of different
doping concentrations of Al were determined and found to be 2.29-2.44 eV. The various
optical parameters viz. Extinction coefficient (k), Refractive index (n), Dielectric constant
(ε), Dielectric loss (δ) and Optical conductivity (σ) have been measured from the optical
data. Electrical parameters like resistivity, conductivity, activation energy etc, of the Al
doped CdS films were measured by the four probe method. Resistivity of Cd1-xAlxS has been
measured for different doping concentrations in the temperature range of 320 to 430 K. The
resistivity of Cd1-xAlxS films is found to decrease up to 350 K and after that it’s become
saturated. This behavior indicates the semiconductor nature of the films. The variation of
conductivity of the films of different doping concentration with the increase in temperature
is studied. The Activation energy is found to be in the range of 0.245 to 0.368 for different
concentration of films. The experimental results show that Al incorporation into the CdS
enhances the photoconductivity and photosensitivity. The photoconductive Cd1-xAlxS thin
films deposited by the spray Pyrolysis technique is applicable for photodiodes, X-ray
detectors and FET transistor, etc. Cd1-xAlxS thin films regarded as a prime candidate for
solar cell fabrication because of large energy band gap, high refractive index, high optical
absorption and also suitability of these films for various optoelectronics applications.
