Sri Venkateswasra University

Tirupati, India

Sri Venkateswasra University

Tirupati, India
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Reddy V.R.M.,Yeungnam University | Reddy V.R.M.,Sri Venkateswasra University | Gedi S.,Yeungnam University | Gedi S.,Sri Venkateswasra University | And 5 more authors.
Science of Advanced Materials | Year: 2016

SnS films were grown on a variety of substrates, such as Al, Si, Mo, Ni, ITO, and glass, maintaining a constant sulfurization temperature of 350°C and time of 150 min using elemental sulfur via a two-stage process. The influence of the various types of substrates on the growth and physical properties was examined by Xray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, and electrical measurements. The XRD profiles indicated that the as-prepared films were in a polycrystalline nature with different planes as the preferred orientations and exhibited an orthorhombic crystal structure. The Raman spectra revealed bands at 95 cm-1, 189 cm-1 and 219 cm-1; and 163 cm-1, which were assigned to the Ag and B2g phonon modes of SnS, respectively. The surface morphology revealed complete coverage of the grains with good compactness. Electrical studies yielded interesting results in that the SnS films grown on glass substrates showed a higher electrical resistivity of 45 ω-cm compared to the other substrates but all the films exhibited p-type conductivity. © 2016 by American Scientific Publishers.

Gedi S.,Sri Venkateswasra University | Gedi S.,280 North | Minnam Reddy V.R.,Sri Venkateswasra University | Minnam Reddy V.R.,280 North | And 2 more authors.
Optical Materials | Year: 2015

A simple non-vacuum and cost effective wet chemical technique, chemical bath deposition was used to prepare tin sulphide (SnS) layers on glass substrates. The layers were formed by varying bath temperature in the range, 40-80 °C, keeping other deposition parameters as constant. An exhaustive investigation on their optical properties with bath temperature was made using the transmittance and reflectance measurements. The absorption coefficient was evaluated from the optical transmittance data utilizing Lambert's principle and is >104 cm-1 for all the as-prepared layers. The energy band gap of the layers was determined from the differential reflectance spectra that varied from 1.41 eV to 1.30 eV. Consequently, refractive index and extinction coefficient were obtained from Pankov relations and dispersion constants were calculated using Wemple-Didomenico method. In addition, other optical parameters such as the optical conductivity, dielectric constants, dissipation factor, high frequency dielectric constant and relaxation time were also calculated. Finally electrical parameters such as resistivity, carrier mobility and carrier density of as-prepared layers were estimated using optical data. A detailed analysis of the dependence of all above mentioned parameters on bath temperature is reported and discussed for a clean understanding of electronic characteristics of SnS layers. © 2015 Elsevier B.V. All rights reserved.

Minnam Reddy V.R.,Sri Venkateswasra University | Minnam Reddy V.R.,Yeungnam University | Gedi S.,Sri Venkateswasra University | Gedi S.,Yeungnam University | Park C.,Yeungnam University
Current Applied Physics | Year: 2015

Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (Ts) that varied in the range of 150-450 °C for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for Ts between 300 °C and 350 °C. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm-1, 189 cm-1 and 218 cm-1 are related to the Ag mode of SnS. AFM images revealed a granular change in the grain growth with the increase of Ts. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with Ts. The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 °C showed a low electrical resistivity of 64 ω-cm, a net carrier concentration of 2 × 1016 cm-3 and mobility of 41 cm2 V-1 s-1. With the use of sprayed Zn0.76Mg0.24O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%. © 2015 Elsevier B.V.

Gedi S.,Yeungnam University | Gedi S.,Sri Venkateswasra University | Minna Reddy V.R.,Yeungnam University | Minna Reddy V.R.,Sri Venkateswasra University | And 5 more authors.
Applied Surface Science | Year: 2016

Environment-friendly SnS based thin film solar cells with SnS2 as buffer layer were successfully fabricated from a facile inexpensive route, chemical bath deposition (CBD). Layer studies revealed that as-grown SnS and SnS2 films were polycrystalline; (1 1 1)/(0 0 1) peaks as the preferred orientation; 1.3 eV/2.8 eV as optical band gaps; and showed homogeneous microstructure with densely packed grains respectively. Ionization energy and electron affinity values were found by applying photoemission yield spectroscopy (PYS) to the CBD deposited SnS and SnS2 films for the first time. These values obtained as 5.3 eV and 4.0 eV for SnS films; 6.9 eV and 4.1 eV for SnS2 films. The band alignment of SnS/SnS2 junction showed TYPE-II heterostructure. The estimated conduction and valance band offsets were 0.1 eV and 1.6 eV respectively. The current density-voltage (J-V) measurements of the cell showed open circuit voltage (Voc) of 0.12 V, short circuit current density (Jsc) of 10.87 mA cm-2, fill factor (FF) of 39% and conversion efficiency of 0.51%. © 2016 Elsevier B.V. All rights reserved.

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