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  • 1.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy2012Conference paper (Refereed)
    Abstract [en]

    In this study deep level transient spectroscopy has been performed on boron-nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N-A-N-D)similar to 3 x 10(17) cm(-3). We observed a hole H-1 majority carrier and an electron E-1 minority carrier traps in the device having activation energies E-nu + 0.24 eV, E-c -0.41 eV, respectively. The capture cross-section and trap concentration of H-1 and E-1 levels were found to be (5 x 10(-19) cm(2), 2 x 10(15) cm(-3)) and (1.6 x 10(-16) cm(2), 3 x 10(15) cm(-3)), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H-1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E-1 defect to a nitrogen donor.

  • 2.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia Municha
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method2012Conference paper (Refereed)
    Abstract [en]

    Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N-D-N-A) similar to 2.0 x 10(12) cm(-3), 2 x 10(16) cm(-3) and 9 x 10(15) cm(3), respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E-c - 0.39 eV, E-c - 0.67 eV and E-c - 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen-boron complex. A comparison with the published data revealed A, B and C to be E-1/E-2, Z(1)/Z(2) and R levels, respectively.

  • 3.
    Ashraf, H.
    et al.
    Radboud University Nijmegen.
    Imran Arshad, M.
    Islamia University Bahawalpur.
    Muniza Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hageman, P. R.
    Radboud University Nijmegen.
    Asghar, M.
    Islamia University Bahawalpur.
    Study of electric field enhanced emission rates of an electron trap in n-type GaN grown by hydride vapor phase epitaxy2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed)
    Abstract [en]

    Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from E-c -0.48 +/- 0.02 eV to E-c-0.35 +/- 0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55 +/- 0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data.

  • 4.
    Muniza Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Physical simulation, fabrication and characterization of Wide bandgap semiconductor devices2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wide band gap semiconductors, Zinc Oxide (ZnO), Gallium Nitride (GaN) and Silicon Carbide (SiC) have been emerged to be the most promising semiconductors for future applications in electronic, optoelectronic and power devices. They offer incredible advantages in terms of their optical properties, DC and microwave frequencies power handling capability, piezoelectric properties in building electromechanical coupled sensors and transducers, biosensors and bright light emission. For producing high quality devices, thermal treatment always plays an important role in improving material structural quality which results in improved electrical and optical properties. Similarly good quality of metal–semiconductor interface, sensitive to the semiconductor surface, is always required.

    In this thesis we report the study of the interface states density for Pd/Ti/Au Schottky contacts on the free-standing GaN and post fabrication annealing effects on the electrical and optical properties of ZnO/Si hetero-junction diodes. The determination of interface states density (NSS) distribution within the band gap would help in understanding the processes dominating the electrical behavior of the metal–semiconductor contacts. The study of annealing effects on photoluminescence, rectification and ideality factor of ZnO/Si hetero-junction diodes are helpful for optimization and realization to build up the confidence to commercialize devices for lightening. A comparison of device performance between the physical simulations and measured device characteristics has also been carried out for pd/ZnO Schottky diode to understand the behavior of the devices.

    This research work not only teaches the effective way of device fabrication, but also obtains some beneficial results in aspects of their optical and electrical properties, which builds theoretical and experimental foundation for much better and broader applications of wide band gap semiconductor devices.

    List of papers
    1. Interface state density of free-standing GaN Schottky diodes
    Open this publication in new window or tab >>Interface state density of free-standing GaN Schottky diodes
    Show others...
    2010 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 25, no 9, p. 095008-Article in journal (Refereed) Published
    Abstract [en]

    Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance-voltage (C-V) measurement, the net doping concentration of n-GaN is 4 x 10(17) cm(-3), resulting in a lower reverse breakdown of around -12 V. The interface state density (N-SS) as a function of E-C-E-SS is found to be in the range 4.23 x 10(12)-3.87 x 10(11) eV(-1) cm(-2) (below the conduction band) from Ec-0.90 to E-C-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.

    Place, publisher, year, edition, pages
    Iop Publishing Ltd, 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-59253 (URN)10.1088/0268-1242/25/9/095008 (DOI)000281221200009 ()
    Available from: 2010-09-10 Created: 2010-09-10 Last updated: 2017-12-12Bibliographically approved
    2. Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes
    Open this publication in new window or tab >>Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Annealing effects on optical and electrical properties of n-ZnO/p-Si heterojunction diodes are studied. ZnO nanorods are grown on p-Si substrate by aquous chemical growth technique. As grown samples were annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. Structural, optical and electrical characteristics are studied by Scanning Electron Microscopy (SEM), Photoluminescence (PL), Current–Voltage (I-V) and Capacitance-Voltage (CV) measurements. Well aligned hexagonal–shaped vertical nanorods are revealed in SEM. PL spectra indicated higher ultraviolet to visible emission ratio with a strong peak ofnear band edge emission (NBE) and weak broad deep-level emissions (DLE). For device fabrication Al/Pt non-alloyed ohmic contacts have been evaporated. I-V characteristics indicate that annealing in air and oxygen resulted in better rectifying behavior as well as decrease in reverse leakage current. An improvement in PL intensity has been shown by the samples annealed at 400 oC.

    Keywords
    heterojunction diodes, ZnO on Si, electrical properties, ZnO nanorods
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-68074 (URN)
    Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2014-10-08Bibliographically approved
    3. Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements
    Open this publication in new window or tab >>Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements
    Show others...
    2009 (English)In: Advanced Materials Research, ISSN 1662-8985, Vol. 79-82, p. 1317-1320Article in journal (Refereed) Published
    Abstract [en]

    Modeling of Pd/ZnO Schottky diode has been performed together with a set of simulations to investigate its behavior in current-voltage characteristics. The diode was first fabricated and then the simulations were performed to match the IV curves to investigate the possible defects and their states in the bandgap. The doping concentration measured by capacitancevoltage is 3.4 x 1017 cm-3. The Schottky diode is simulated at room temperature and the effective barrier height is determined from current voltage characteristics both by measurements and simulations and it was found to be 0.68eV. The ideality factor obtained from simulated results is 1.06-2.04 which indicates that the transport mechanism is thermionic. It was found that the recombination current in the depletion region is responsible for deviation of experimental values from the ideal thermionic model deployed by the simulator.

    Keywords
    ZnO, Schottky contact, Barrier height
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-68075 (URN)10.4028/www.scientific.net/AMR.79-82.1317 (DOI)
    Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2014-01-15Bibliographically approved
  • 5.
    Muniza Faraz, Sadia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Alvi, Naveed ul Hassan
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Henry, Arne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Wahab, Qama ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodesManuscript (preprint) (Other academic)
    Abstract [en]

    Annealing effects on optical and electrical properties of n-ZnO/p-Si heterojunction diodes are studied. ZnO nanorods are grown on p-Si substrate by aquous chemical growth technique. As grown samples were annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. Structural, optical and electrical characteristics are studied by Scanning Electron Microscopy (SEM), Photoluminescence (PL), Current–Voltage (I-V) and Capacitance-Voltage (CV) measurements. Well aligned hexagonal–shaped vertical nanorods are revealed in SEM. PL spectra indicated higher ultraviolet to visible emission ratio with a strong peak ofnear band edge emission (NBE) and weak broad deep-level emissions (DLE). For device fabrication Al/Pt non-alloyed ohmic contacts have been evaporated. I-V characteristics indicate that annealing in air and oxygen resulted in better rectifying behavior as well as decrease in reverse leakage current. An improvement in PL intensity has been shown by the samples annealed at 400 oC.

  • 6.
    Muniza Faraz, Sadia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ashraf, H
    Applied Material Science, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalsweg 135, 6525AJ Nijmegen, The Netherlands.
    Imran Arshad, M
    Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan.
    Hageman, P R
    Applied Material Science, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalsweg 135, 6525AJ Nijmegen, The Netherlands.
    Asghar, M
    Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Interface state density of free-standing GaN Schottky diodes2010In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 25, no 9, p. 095008-Article in journal (Refereed)
    Abstract [en]

    Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance-voltage (C-V) measurement, the net doping concentration of n-GaN is 4 x 10(17) cm(-3), resulting in a lower reverse breakdown of around -12 V. The interface state density (N-SS) as a function of E-C-E-SS is found to be in the range 4.23 x 10(12)-3.87 x 10(11) eV(-1) cm(-2) (below the conduction band) from Ec-0.90 to E-C-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.

  • 7.
    Muniza Faraz, Sadia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Noor, Hadia
    Department of Physics, Islamia University of Bahawalpur, Pakistan.
    Asghar, M.
    Department of Physics, Islamia University of Bahawalpur, Pakistan.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Wahab, Qamar ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Modeling and simulations of Pd/n-ZnO Schottky diode and its comparison with measurements2009In: Advanced Materials Research, ISSN 1662-8985, Vol. 79-82, p. 1317-1320Article in journal (Refereed)
    Abstract [en]

    Modeling of Pd/ZnO Schottky diode has been performed together with a set of simulations to investigate its behavior in current-voltage characteristics. The diode was first fabricated and then the simulations were performed to match the IV curves to investigate the possible defects and their states in the bandgap. The doping concentration measured by capacitancevoltage is 3.4 x 1017 cm-3. The Schottky diode is simulated at room temperature and the effective barrier height is determined from current voltage characteristics both by measurements and simulations and it was found to be 0.68eV. The ideality factor obtained from simulated results is 1.06-2.04 which indicates that the transport mechanism is thermionic. It was found that the recombination current in the depletion region is responsible for deviation of experimental values from the ideal thermionic model deployed by the simulator.

  • 8.
    Noor, Hadia
    et al.
    Islamia University Bahawalpur.
    Klason, P
    University of Gothenburg.
    Faraz, Sadia Muniza
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Asghar, M
    Islamia University Bahawalpur.
    Influence of background concentration induced field on the emission rate signatures of an electron trap in zinc oxide Schottky devices2010In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979, Vol. 107, no 10Article in journal (Refereed)
    Abstract [en]

    Various well-known research groups have reported points defects in bulk zinc oxide (ZnO) [N-D (intrinsic): 10(14)-10(17) cm(-3)] naming oxygen vacancy, zinc interstitial, and/or zinc antisite having activation energy in the range of 0.32-0.22 eV below conduction band. The attribution is probably based on activation energy of the level which seems not to be plausible in accordance with Vincent et al., [J. Appl. Phys. 50, 5484 (1979)] who suggested that it was necessary to become vigilant before interpreting the data attained for a carrier trap using capacitance transient measurement of diodes having ND greater than 10(15) cm(-3). Accordingly the influence of background free-carrier concentration, ND induced field on the emission rate signatures of an electron point defect in ZnO Schottky devices has been investigated by means of deep level transient spectroscopy. A number of theoretical models were tried to correlate with the experimental data to ascertain the mechanism. Consequently Poole-Frenkel model based on Coulomb potential was found consistent. Based on these investigations the electron trap was attributed to Zn-related charged impurity. Qualitative measurements like current-voltage and capacitance-voltage measurements were also performed to support the results.

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