• S C GADKARI

      Articles written in Bulletin of Materials Science

    • Development of a silicon photodiode-based compact gamma spectrometer using a Gd$_3$Ga$_3$Al$_2$O$_{12}$:Ce,B single crystal scintillator

      PRATIP MITRA SAURABH SRIVASTAVA MOHIT TYAGI A VINOD KUMAR S C GADKARI

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      A compact gamma spectrometer was developed by employing an in-house grown single crystal of Gd$_3$Ga$_3$Al$_2$O$_{12}$:Ce,B scintillator optically coupled with a silicon photodiode. The performance of the detector was characterized in detail. The detector setup works with a low bias voltage of 9 V, drawn from a single battery. Power to the electronic components of the entire system is derived from a single universal serial bus port by employing required DC–DC converters. In addition to the low voltage operation, this developed spectrometer is very compact in size compared to the one developedby employing photo-multiplier tubes. The system offers excellent linearity over the gamma energy range of 344–1408 keV and an optimum energy resolution of about 13% at 662 keV.

    • Impurity concentration dependent electrical conduction in germanium crystals at low temperatures

      MANORANJAN GHOSH SHREYAS PITALE S G SINGH SHASHWATI SEN S C GADKARI

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      A germanium single crystal of 7 N$+$ purity with a diameter of 45 mm and a length of 100 mm has been grown by the Czochralski method. The structural quality of the crystal has been characterized by Laue diffraction. Electrical conduction and Hall measurements are carried out on samples retrieved from different parts of the crystal along the growth axis. The top part of the crystal exhibits the lowest impurity concentration ($\sim$10$^{12}$ cm$^{−3}$) that gradually increases towards the bottom (10$^{13}$ cm$^{−3}$). The crystal is n-type at room temperature and the resistivity shows a non-monotonic temperature dependence. There is a transition from n-type to p-type conductivity below room temperature at which bulk resistivity shows a maximum and dip in carrier mobility. The intrinsic to extrinsic transition region shifts towards room temperature as the impurity concentration increases and it reflects the purity level of the crystal. A similar trend is observed in the boron-implanted high purity germanium (HPGe) crystal at different doping levels. The phenomena can be understood as a result of interplay between a temperature dependent conduction mechanism driven by an impurity band and an intrinsic carrier in Ge crystalshaving fairly low acceptor concentrations (<10$^{12}$ cm$^{−3}$).

    • Elucidation of structural, morphological, optical and photoluminescence properties of single and (In, Ga) co-doped ZnO nanocrystalline thin films

      M SHAHEERA K G GIRIJA MANMEET KAUR V GEETHA A K DEBNATH R K VATSA K P MUTHE S C GADKARI

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      Single and co-doped ZnO thin films are currently under intense investigation and development for optoelectronic applications. Here in this study, pristine, indium-doped (IZO), gallium-doped (GZO) and co-doped (IGZO) ZnO thin filmswere deposited on a glass substrate using radio frequency magnetron sputtering. A comparative study of all the films was carried out on the basis of their various properties. The effect of single and co-doping on the structural (X-ray diffraction(XRD) studies and Raman studies), morphological (field emission scanning electron microscopy and energy dispersiveX-ray spectroscopy studies) and optical properties (ultraviolet–visible (UV–Vis) and photoluminescence (PL)) of the deposited films was investigated. X-ray photoelectron spectroscopy (XPS) characterization was employed to analyse the surface chemical composition and bonding of the deposited film. From the XRD patterns, it was found that the films were highly crystalline in nature and preferentially oriented along the (002) direction with a hexagonal wurtzite structure, consistent with Raman analysis. IGZO films displayed a dramatic improvement in the surface morphology as compared with the single dopant films due to the compensation effect of gallium and indium doping which reduced the lattice strain. The XPS analysisconfirmed the presence of the oxidized dopants in each film. All thin films have shown excellent optical properties with more than 90% transmission in the visible range of light. The blue-shift of the absorption edge accompanied by the increase of the optical band gap confirmed the Burstein–Moss effect. The UV PL peak originated from the near band edge emission of crystalline ZnO, while the visible PL was associated with the radiative transition related to oxygen interstitial (Oi) defects in the ZnO structure.

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