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  • 1
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    Fabrication and structural properties of AlN submicron periodic lateral polar structures and waveguides for UV-C applications (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-01
    Description: Periodically poled AlN thin films with submicron domain widths were fabricated for nonlinear applications in the UV-VIS region. A procedure utilizing metalorganic chemical vapor deposition growth of AlN in combination with laser interference lithography was developed for making a nanoscale lateral polarity structure (LPS) with domain size down to 600 nm. The Al-polar and N-polar domains were identified by wet etching the periodic LPS in a potassium hydroxide solution and subsequent scanning electron microscopy (SEM) characterization. Fully coalesced and well-defined vertical interfaces between the adjacent domains were established by cross-sectional SEM. AlN LPSs were mechanically polished and surface roughness with a root mean square value of ∼10 nm over a 90  μ m × 90  μ m area was achieved. 3.8  μ m wide and 650 nm thick AlN LPS waveguides were fabricated. The achieved domain sizes, surface roughness, and waveguides are suitable for second harmonic generation in the UVC spectrum.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Point defect reduction in wide bandgap semiconductors by defect quasi Fermi level control (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-11-15
    Description: A theoretical framework for a general approach to reduce point defect density in materials via control of defect quasi Fermi level (dQFL) is presented. The control of dQFL is achieved via excess minority carrier generation. General guidelines for controlling dQFL that lead to a significant reduction in compensating point defects in any doped material is proposed. The framework introduces and incorporates the effects of various factors that control the efficacy of the defect reduction process such as defect level, defect formation energy, bandgap, and excess minority carrier density. Modified formation energy diagrams are proposed, which illustrate the effect of the quasi Fermi level control on the defect formation energies. These formation energy diagrams provide powerful tools to determine the feasibility and requirements to produce the desired reduction in specified point defects. An experimental study of the effect of excess minority carriers on point defect incorporation in GaN and AlGaN shows an excellent quantitative agreement with the theoretical predictions. Illumination at energies larger than the bandgap is employed as a means to generate excess minority carriers. The case studies with C N in Si doped GaN, H and V N in Mg doped GaN and V M -2O N in Si doped Al 0.65 Ga 0.35 N revealed a significant reduction in impurities in agreement with the proposed theory. Since compensating point defects control the material performance (this is particularly challenging in wide and ultra wide bandgap materials), dQFL control is a highly promising technique with wide scope and may be utilized to improve the properties of various materials systems and performance of devices based upon them.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Interaction of elastocapillary flows in parallel microchannels across a thin membrane (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-10-04
    Description: We report the interaction of counter elastocapillary flows in parallel microchannels across a thin membrane. At the crossing point, the interaction between the capillary flows via the thin membrane leads to significant retardation of capillary flow. The drop in velocity at the crossing point and velocity variation after the crossing point are predicted using the analytical model and measured from experiments. A non-dimensional parameter J , which is the ratio of the capillary force to the mechanical restoring force, governs the drop in velocity at the crossing point with the maximum drop of about 60% for J  = 1. The meniscus velocity after the crossing point decreases ( J  
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 4
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    KOH based selective wet chemical etching of AlN, AlxGa1−xN, and GaN crystals: A way towards substrate removal in deep ultraviolet-light emitting diode (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-27
    Description: A controllable and smooth potassium hydroxide-based wet etching technique was developed for the AlGaN system. High selectivity between AlN and Al x Ga 1−x N (up to 12×) was found to be critical in achieving effective substrate thinning or removal for AlGaN-based deep ultraviolet light emitting diodes, thus increasing light extraction efficiency. The mechanism of high selectivity of AlGaN as a function of Al composition can be explained as related to the formation and dissolution of oxide/hydroxide on top of N-polar surface. Cross-sectional transmission electron microscopic analysis served as ultimate proof that these hillocks were not related to underlying threading dislocations.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
    Electronic Resource
    Electronic Resource
    Cation distribution of Li-Ti mixed ferrites (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6125-6125 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lithium-titanium mixed ferrites of different compositions have been prepared by the well known ceramic technique. Thermo power studies of these samples, after usual characterization by x-ray diffraction (XRD), bulk density, porosity, etc. have been measured by the differential method. Room temperature values of the Seebeck coefficient are found to vary from 2.3 to 114 μV/K. It is an established fact that the thermo power measurement would also be used to study the cation distributions on octahedral and tetrahedral sublattices of ferro spinel. This technique was successfully used in the study of cation distribution of Fe3O4, Fe3O4-TiFe2O4, etc. As such the cation distribution of Li-Ti mixed ferrites of P.I. has been arrived at using thermo-power data by assuming that small polorans rather than electrons/holes are responsible for the process of conduction. A knowledge of cation distribution among octahedral sites of a spinel ferrite is essential to understand the mechanism responsible for electrical properties like electrical conductivity, thermo power, dielectric properties, etc. Saturation magnetization of all the samples has also been obtained by the well known oscillation method. From the cation distribution it has been observed that the concentration of Ti4+ on octahedral sites is found to increase while those of Fe3+ and Fe2+ are found to decrease rapidly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355483
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  • 6
    Electronic Resource
    Electronic Resource
    Charge transport in Li-Ni ferrospinels (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3783-3785 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical conductivity (σ) and thermopower (Q) of Li-Ni mixed ferrites have been studied as a function of composition and temperature. The conduction mechanism in these ferrites has been explained with the help of carrier concentration (n) and charge carrier mobility (μ) calculated from the measured experimental values. The composition and frequency dependence of dielectric constant (ε') and dielectric loss tangent (tan δ) have also been studied at low frequencies. A relationship between dielectric constant (ε') and electrical resistivity (ρ) has been arrived at. A qualitative explanation for observing a maximum in the plots of dielectric loss tangent and frequency has also been given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340639
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  • 7
    Electronic Resource
    Electronic Resource
    Microprocessor-based boxcar signal averager (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1945-1947 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A boxcar signal averager using Intel 8085AH, an 8-bit microprocessor developed for processing free-induction decay (FID) signals from a pulsed nuclear-magnetic-resonance (NMR) spectrometer, is described. The boxcar signal averager works either in single-point mode or in scan mode. In addition to the software developed, the constructional features, circuit details, and the operation of the boxcar are discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139494
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  • 8
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    Magnetic, ferroelectric, and spin phonon coupling studies of Sr3Co2Fe24O41 multiferroic Z-type hexaferrite (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-08-04
    Description: The magnetic, Raman, ferroelectric, and in-field 57 Fe Mössbauer studies of polycrystalline multiferroic Sr 3 Co 2 Fe 24 O 41 are reported in this paper. From the magnetization studies, it is observed that the sample is soft magnetic in nature with low temperature magnetic spin transitions like longitudinal to transverse conical structure around 130 K and change in magnetic crystalline anisotropy from conical to planar structure at 250 K. Ferroelectric studies of the sample exhibit the spontaneous polarization at low temperature. Strong spin phonon and spin lattice coupling is observed through low temperature Raman spectroscopy. From the in-field 57 Fe Mössbauer spectroscopy, spin up and spin down site occupations of Fe ions are calculated in the unit cell.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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