• Mukul Gupta

      Articles written in Bulletin of Materials Science

    • Influence of annealing temperature on ZnO thin films grown by dual ion beam sputtering

      Sushil Kumar Pandey Saurabh Kumar Pandey Vishnu Awasthi Ashish Kumar Uday P Deshpande Mukul Gupta Shaibal Mukherjee

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      We have investigated the influence of in situ annealing on the optical, electrical, structural and morphological properties of ZnO thin films prepared on 𝑝-type Si(100) substrates by dual ion beam sputtering deposition (DIBSD) system. X-ray diffraction (XRD) measurements showed that all ZnO films have (002) preferred orientation. Full-width at half-maximum (FWHM) of XRD from the (002) crystal plane was observed to reach to a minimum value of 0.139° from ZnO film, annealed at 600 °C. Photoluminescence (PL) measurements demonstrated sharp near-band-edge emission (NBE) at ∼ 380 nm along with broad deep level emissions (DLEs) at room temperature. Moreover, when the annealing temperature was increased from 400 to 600 °C, the ratio of NBE peak intensity to DLE peak intensity initially increased, however, it reduced at further increase in annealing temperature. In electrical characterization as well, when annealing temperature was increased from 400 to 600 °C, room temperature electron mobility enhanced from 6.534 to 13.326 cm2/V s, and then reduced with subsequent increase in temperature. Therefore, 600 °C annealing temperature produced good-quality ZnO film, suitable for optoelectronic devices fabrication. X-ray photoelectron spectroscopy (XPS) study revealed the presence of oxygen interstitials and vacancies point defects in ZnO film annealed at 400 °C.

    • Negative capacitance effect of Cu–TiC thin film deposited by DC magnetron plasma


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      The quest for low power consumption devices with new functionalities has made the negative capacitance (NC) effect, the most captivating and studied phenomenon. The NC effect is observed in Cu–TiC thin film at a low frequencyrange between 112.9 Hz and 2 kHz. The Cu–TiC thin film was deposited on Si (100) substrate by DC magnetron co-sputtering process and then annealed in a vacuum at different temperatures (100–600$^{\circ}$C). The magnitude ofNC increased from $-$0.016 to $-$27.5 lF after annealing. The NC behaviour is also observed in the forward biased region of the capacitance–voltage ($C–V$) characteristics. The current–voltage ($I–V$) characteristics reveal the decreasing static and dynamic resistance for higher annealed films. An improved electrical conductivity ($27.70 \times 10^3$ to $384.62 \times 10^3$ S m$^{-1}$)is evidenced with decreasing ideality factor (2.01–0.55) in the post-annealed films. The films were found to be polycrystalline from X-ray diffraction patterns with Cu and TiC phases. Raman studies have also confirmed the presence of Cuand TiC vibrational modes in all films. The intensity of C peaks detected at 1359 cm$^{-1}$ (D peak) and at 1590 cm$^{-1}$ (G peak) in the as-deposited film decreased after annealing. The annealing effect reduced the amount of unreacted carbon and contributed to form stoichiometric TiC from non-stoichiometric TiC.

    • Influence of AlN buffer layer on molecular beam epitaxy growth of wurtzite Al$_{1-x}$Sc$_x$N thin films


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      Wurtzite–Al$_{1-x}$Sc$_x$N thin films deposited by solid-state alloying of AlN with ScN exhibit high piezoelectric coefficient and large band gap that makes it a promising material for a variety of applications in piezo-electronics, electronic, acoustoelectric devices, etc. Research on epitaxial Al$_{1-x}$Sc$_x$N growth in wurtzite crystal structure is still at an early stage and achieving high scandium (Sc) concentrations in epitaxial films without any phase separation or secondaryphase formation is still a critical challenge. Moreover, as most of the reports of wurtzite–Al$_{1-x}$Sc$_x$N growth thus far relies on low-vacuum growth techniques, such as magnetron sputtering that are prone to large impurities and contaminants detrimental for device applications, high-vacuum deposition techniques, such as molecular beam epitaxy method needs to be developed. In this paper, we report the epitaxial growth of wurtzite–Al$_{1-x}$Sc$_x$N on sapphire (Al$_2$O$_3$) substrates under different Sc fluxes using ultra-high vacuum plasma-assisted molecular beam epitaxy. To prevent ScN phase separation, a 30 nm AlN buffer layer is deposited in situ on GaN epilayers as well as Al$_2$O$_3$ substrates that result in phase-pure wurtzite–Al$_{1-x}$Sc$_x$N thin films without any phase separation or secondary phase formation. The structural and compositional analyses performed with high-resolution X-ray diffraction (HRXRD) and secondary ion mass spectroscopy(SIMS), reveal epitaxial wurtzite–Al$_{1-x}$Sc$_x$N growth with 0001 orientations on (0001) Al$_2$O$_3$ substrates and the presence of cubic ScN. Demonstration of phase-pure Al$_{1-x}$Sc$_x$N on AlN buffer layers will enable the development of devices with improved efficiencies.

  • Bulletin of Materials Science | News

    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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