• Y N Mohapatra

      Articles written in Bulletin of Materials Science

    • Characterization of deep levels in semi-insulating gallium arsenide

      Y N Mohapatra N Balasubramanyam Vikram Kumar

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      Two traps with activation energies ofEc – 0·47 eV andEv + 0·79 eV have been detected in semi-insulating GaAs:Cr through optical transient current spectroscopy (otcs) in the temperature range 300–450 K. The latter trap gives rise to rising current transients which result in a negative peak in theotcs spectrum. The theoretical expressions for current transients have been derived.

    • Characterization of defects in gallium arsenide

      Vikram Kumar Y N Mohapatra

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      It is well-known that the properties of semiconductor materials including gallium arsenide are controlled by defects and impurities. The characterization of these defects is important not only for better understanding of the solid state phenomena but also for improved reliability and performance of electronic devices. We have been investigating the defects in gallium arsenide for several years using deep level transient spectroscopy, photoconductivity, transient photoconductivity, photoluminescence etc. Results drawn from our recent studies are presented here to illustrate some of the problems concerning transition metal impurities, process-induced defects, occurrence of intracentre transitions and metastability of deep levels in gallium arsenide.

    • Interfacial mechanisms controlling phase formation in sol-gel derived lead zirconate titanate thin films

      S B Majumder V N Kulkarni Y N Mohapatra D C Agrawal

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      An RBS study has been carried out to study the relative extent of Pb diffusion in the substrate from PZT films. It is found that extensive diffusion of Pb occurs into the quartz substrate making the film severely deficient in Pb. No such diffusion occurs in the case of PZT films on sapphire and the concentration of Pb is near stoichiometric, except for a small loss due to volatilization. Excessive Pb deficiency, rather than any epitaxial effect, has earlier been proposed by us to be the crucial factor responsible for the existence of the pyrochlore phase in PZT thin films on substrates such as Si, glass, quartz etc. The present results confirm this. The effects of other process variables such as thickness and chemical composition (Zr/Ti ratio) of the film can also be understood in terms of the same phenomenon.

    • Characterization of deep level defects in Si irradiated with MeV Ar+ ions using constant capacitance time analyzed transient spectroscopy

      P K Giri S Dhar V N Kulkarni Y N Mohapatra

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      An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC) mode has been used to characterize electrically active defects in the MeV Ar+ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault.

    • Ar ion induced copper germanide phase formation at room temperature

      S Dhar T Som Y N Mohapatra V N Kulkarni

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      The copper germanide phase Cu3Ge which is emerging as an alternative material for making contacts and interconnects for semiconductor industry has been produced across the interface of Cu/Ge bilayers by ion beam mixing at room temperature using 1 MeV Ar ions. The dose dependence of the thickness of the mixed region shows a diffusion controlled mixing process. The experimental mixing rate and efficiency for this phase are 5·35 nm4 and 10·85 nm5/keV respectively. At doses above 8 × 1015 Ar/cm2 the formation and growth of another copper rich phase Cu5Ge has been observed. The present theoretical models are inadequate to explain the observed experimental mixing rate.

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      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
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      Posted on July 25, 2019

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