Y.P. Venkata Subbaiah

Thickness effect on the microstructure, morphology and optoelectronic properties of ZnS films

Thin films of ZnS with thicknesses ranging from 100 to 600 nm have been deposited on glass substrates by close spaced thermal evaporation. All the films were grown at the same deposition conditions except the deposition time. The effect of thickness on the physical properties of ZnS films has been studied. The experimental results indicated that the thickness affects the structure, lattice strain, surface morphology and optoelectronic properties of ZnS films significantly. The films deposited at a thickness of 100 nm showed hexagonal structure whereas films of thickness 300 nm or more showed cubic structure. However, coexistence of both cubic and hexagonal structures was observed in the films of 200 nm thickness. The surface roughness of the films showed an increasing trend at higher thicknesses of the films. A blue-shift in the energy band gap along with an intense UV emission band was observed with the decrease of film thickness, which are ascribed to the quantum confinement effect. The behaviour of optical constants such as refractive index and extinction coefficient were analysed. The variation of refractive index and extinction coefficient with thickness was explained on the basis of the contribution from the packing density of the layers. The electrical resistivity as well as the activation energy were evaluated and found to decrease with the increase of film thickness. The thickness had a significant influence on the optical band gap as well as the luminescence intensity.

Influence of sulfurization temperature on physical properties of Cu2ZnSnS4 thin films

Copper Zinc Tin Sulfide (Cu2ZnSnS4 or CZTS) is gaining much attention recently as a potential light absorber alternative to CuInGaSe2 due to its suitable energy band gap ∼1.5u2009eV with p-type conductivity, high optical absorption coefficient of ∼105u2009cm−1. Moreover, all its constituents are abundant in the crust of the earth and environmentally harmless. In the present investigation, CZTS thin films were prepared using simple two step process of, sulfurization of sequentially sputtered stack, Glass/Zn/Sn/Cu (hereafter CTZ) metallic precursors on soda lime glass substrate held at temperature 200u2009°C. The sputter power was optimized individually for Zn, Sn, and Cu layers. The sputtered CTZ precursors were annealed at different temperatures in the range, 300–550u2009°C with an increment of 50u2009°C for 2 h in the ambience of vaporized elemental sulfur. The XRD pattern revealed that the films sulfurized in the temperature range 300–400u2009°C showed various spurious (binary and ternary) phases and the films sulfurized at 45...

Growth and properties of Cu2ZnSnS4 thin films prepared by multiple metallic layer stacks as a function of sulfurization time

In this paper, we report the two stage growth of Cu2ZnSnS4 (CZTS) thin films as a function of sulfurization time. First, magnetron sputtered metallic precursors were deposited sequentially (Zn/Cu/Sn/Cu) over rotating glass substrates held at 230u2009°C. Later, the sputtered precursors were heat treated at 500u2009°C in the ambiance of sulfur for various time durations in the range, 10–120xa0min. The sulfur treated samples were examined using various analytical tools to understand the role of sulfurization time on the CZTS growth and properties. From composition and structural analysis, Zn/Cu/Sn/Cu precursors sulfurized for shorter duration (10 and 20xa0min) revealed severe deficiency of sulfur that resulted in several metallic, bi-metallic and metal sulfide phases. With the increase of sulfurization time to 30xa0min, sulfur incorporation was enhanced and reached stoichiometric ratio (~50% S) for CZTS growth, however, samples were poorly crystalline in nature and consisted of prominent Cu2−xS phase as well. The Zn/Cu/Sn/Cu precursors sulfurized for 60xa0min exhibited prominent CZTS phase without Cu2−xS phase. Further, rise in sulfurization time to 120xa0min enabled drastic improvement in crystallinity of CZTS phase. Raman mapping over 60xa0µmxa0×xa060xa0µm for these films confirmed the homogeneous phase growth of CZTS. XPS study revealed the oxidation states of Cu1+, Zn2+, Sn4+ and S2− in CZTS films. The optimized films showed high absorption coefficient of 105xa0cm−1 with an optical band gap of 1.51xa0eV. These films showed leaf like grain morphology with high mobility and low resistivity of 18.2xa0cm2/V-s and 0.7xa0Ω-cm, respectively.

Low temperature crystallization of Cu2ZnSnSe4 thin films using binary selenide precursors

In the present paper, a novel process for synthesis of Cu2ZnSnSe4 thin films via low temperature selenization (350xa0°C) of multiple stacks of binary selenides has been reported. Further, the influence of selenization temperature (250–450xa0°C) on the physical properties of Cu2ZnSnSe4 thin films was studied and discussed herein. The Rietveld refinement from X-ray diffraction data of Cu2ZnSnSe4 films grown at a selenization temperature of 350xa0°C was found to be single phase with kesterite type crystal structure and having lattice parameters au2009=u20095.695xa0Å, cu2009=u200911.334xa0Å. Raman spectra recorded using multi excitation wavelength sources under non-resonant and near resonant conditions confirms the formation of single phase Cu2ZnSnSe4 films. Secondary ion mass spectroscopic (SIMS) analysis demonstrated that composition of elements across the thickness is fairly uniform. Energy dispersive X-ray analysis measurement reveals that the obtained films are Cu-poor and Zn-rich. The scanning electron micrographs of binary selenide stacks selenized at a temperature of 350xa0°C shows randomly oriented cylindrical grains. The optical absorption studies indicated a direct band gap of 1.01xa0eV. The films showed p-type conductivity with electrical resistivity of 4.66xa0Ωxa0cm, Hall mobility of 15.17xa0cm2 (Vs)−1 and carrier concentration of 8.82u2009×u20091016xa0cm−3.

A Facile and TGA Free Hydrothermal Synthesis of SnS Nanoparticles

In this paper, we employed a simple and cost-effective thioglycolic acid (TGA) free hydrothermal method, based on thiourea hydrolysis of stannous chloride dihydrate [SnCl2.2H2O] at 160∘C–190∘C for 6h, for the synthesis of SnS nanoparticles. The effect of hydrothermal autoclave reaction temperature on various properties of SnS nanoparticles have been examined at length using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy attached with EDAX (FE-SEM), transmission electron microscopy (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. The results suggest that the crystallization of orthorhombic SnS nanoparticles, with size varying from 3nm to 5nm, formed at RT=160∘C. Further, the formation of SnS phase was confirmed by an IR Sn-S characteristic bands around 2350cm−1, 1041cm−1 and 570cm−1, and four distinguished Raman peaks at 95cm−1, 160cm−1, 189cm−1 and 220cm−1. The mechanism for the formation of SnS nanoparticles have been proposed and discussed. The SnS nanoparticles have exhibited reaction temperature dependent morphological features like nanoflowers, nanoflakes, spherical nanoparticles and nanogranules. The absorbance studies indicated both strong direct and weak indirect allowed transitions for SnS nanoparticles and the associated band gaps were found to be 1.5eV and 1.19eV, respectively. The dual band gap combination of SnS would favor strong direct absorption of carriers and improved minority carrier life time due to indirect nature, which means the grown particles are suitable for ideal absorber material for solar cell applications.