I. K. Shmagin

North Carolina State University, Raleigh, North Carolina, United States

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Publications (23)33.07 Total impact


  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Up to 3 mm long GaN single crystals were grown by sublimation of cold pressed GaN pellets or evaporation of gallium (Ga) metal under an ammonia (NH3) flow in a dual heater, high-temperature growth system. A growth rate of 500 μm/h along the [0 0 0 1] direction was achieved using a source temperature of 1200°C, a total pressure of 760 Torr, and an NH3 flow rate of 50 sccm. The resulting crystals were transparent, possessed low aspect ratios and well-defined growth facets. The only impurity present at high concentrations was oxygen (3×1018 atoms/cm3). Photoluminescence studies conducted at 77 K showed a sharp emission peak centered at 359 nm. Time-dependent photoluminescence measurements revealed optical metastability in bulk GaN. Raman spectroscopy yielded narrow peaks representing only the modes allowed for the wurtzite structure. All characterization studies confirmed excellent crystalline and optical quality of the obtained single crystals.
    No preview · Article · Jan 2000 · Journal of Crystal Growth
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    ABSTRACT: We report on the investigation of the effect of growth temperature on point defect density of unintentionally doped GaN grown by atmospheric pressure metalorganic chemical vapor deposition and hydride vapor phase epitaxy. A correlation between photoluminescence (PL) spectra and the concentration of donors and acceptors in unintentionally doped GaN is presented. The effects of oxygen and native acceptors on the electrical and optical properties of GaN epitaxial layers are discussed and a classification of PL data is presented. On this basis we show that oxygen creates a shallow donor in GaN with an activation energy of about 23.5+/-1 meV. We determine that the concentration of native acceptors in GaN increases with an increase in growth temperature. These native acceptors, probably gallium antisites (Ga-N) and/or gallium vacancies (V-Ga), are nonradiative defects. We show that a second donor level in GaN has an activation energy of about 52.5+/-2.5 meV and produces a PL peak with an energy of about 3.45 eV at low temperatures. From Hall investigations we show that a third donor in GaN has an activation energy of 110+/-10 meV. (C) 1999 American Institute of Physics. [S0021-8979(99)05405-5].
    No preview · Article · Jul 1999 · Journal of Applied Physics
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    ABSTRACT: We report novel GaN detectors grown by molecular beam epitaxy on Si(111) substrates. Wurtzite structure epitaxial GaN exhibits room-temperature photoluminescence with a band-edge-related emission width as narrow as 7 nm and intensities comparable to high quality layers grown on sapphire by metalorganic chemical vapor deposition. Spectral response of lateral geometry Schottky detectors shows a sharp cutoff at 365 nm with peak responsivities of approximate-to 0.05 A/W at 0V, and approximate-to 0.1 A/W with a -4V bias. The dark current is approximate-to 60 nA at -2V bias. the noise equivalent power is estimated to be 3.7x10(-9)W over the responsible bandwidth of 2.2 MHz.
    No preview · Article · Feb 1998 · Applied Physics Letters
  • R M Kolbas · I K Shmagin · J F Muth
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    ABSTRACT: Applications of m-V nitride materials, such as GaN, AIN, InN and their:ir alloys include blue-green light emitting devices, solar blind photodetectors, and high power/frequency electronics. A number of unique and potentially useful optical phenomena have been observed in high quality thin films and heterostructures of AlGaN, GaN, and InGaN. These include: 1) persistent optical effects such as optical metastability in bulk GaN single crystals; 2) tunable emission from InGaN multiple quantum wells, (MQW) and; 3) reconfigurable optical properties in InGaN/GaN heterostructures.
    No preview · Book · Jan 1998
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    ABSTRACT: — Nanosize phosphor particles of Eu-doped Y2O3 were synthesized at room temperature by an organometallic vapor-phase microwave plasma-synthesis technique. These particles were selectively deposited downstream of the plasma reaction region to form thin layers on biased regions of a substrate. Particles were characterized using x-ray diffraction and transmission electron microscopy. The morphologies of the thin phosphor layers were studied using field-emission scanning electron microscopy. Results indicate that the particles form a fibrous structure with good selectivity for thicknesses less than 100 nm. The nanoparticle-phosphor optical characteristics were analyzed using absorption and photoluminescence spectroscopy. These results indicate that the particles have absorption and luminescence spectra similar to the bulk. This study demonstrates that the microwave plasma-synthesis technique may provide an effective method for producing phosphor screens that meet many of the needs of advanced cathodoluminescent low-voltage devices.
    No preview · Article · Jan 1998
  • R. M. Kolbas · I. K. Shmagin · J. F. Muth
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    ABSTRACT: Applications of III-V nitride materials, such as GaN, AlN, InN and their alloys include blue-green light emitting devices, solar blind photodetectors, and high power/frequency electronics. A number of unique and potentially useful optical phenomena have been observed in high quality thin films and heterostructures of AlGaN, GaN, and InGaN. These include: (1) persistent optical effects such as optical metastability in bulk GaN crystals; (2) tunable emission from InGaN quantum wells, (MQW) and; (3) reconfigurable optical properties in InGaN-GaN heterostructures
    No preview · Article · Jan 1998
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    ABSTRACT: The absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for the A and B excitons was obtained. The A, B, and C excitonic features are clearly defined at 77 K. At room temperature, an energy gap Eg=3.452±0.001 eV and an exciton binding energy ExA,B=20.4±0.5 meV for the A and B excitons and ExC=23.5±0.5 meV for the C exciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constant B=1.1×10−8 cm3/s was obtained.
    Full-text · Article · Nov 1997 · Applied Physics Letters
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    ABSTRACT: Optical metastability was studied in an InGaN/GaN single heterostructure. It was observed that an exposure to a high intensity ultraviolet (UV) light temporarily changes the optical properties of the InGaN/GaN epitaxial layer. The photo-induced changes were used to create high contrast optical patterns on the sample at room temperature and 77 K. The photo-induced patterns were viewed under low-intensity illumination with UV light from the same light source
    No preview · Conference Paper · Oct 1997
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    ABSTRACT: Optical storage data was realized using an InGaN/GaN single heterostructure. It was observed that exposure to a high power density ultraviolet light temporarily changes the optical properties of the InGaN epitaxial layer. The photo-induced changes can be observed under an optical microscope with low intensity ultraviolet excitation. This effect was used to create high contrast optical patterns on the sample at room temperature and 77 K. The photo-induced changes completely disappear in about four hours at room temperature. After the recorded pattern is erased, the information can be rewritten without a change in efficiency or retention time. © 1997 American Institute of Physics.
    No preview · Article · Oct 1997 · Applied Physics Letters
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    ABSTRACT: Reconfigurable optical properties were studied in InGaN/GaN multiple quantum well (MQW) structures. It was observed that a short time exposure to a high intensity ultraviolet light results in long term, but reversible changes of the optical properties of InGaN/GaN MQW samples. The photoinduced changes can be observed using an optical microscope under low intensity ultraviolet light and are visible as a high contrast pattern. The retention time at room temperature for 12 and 20 MQW samples was longer than five days and four weeks, respectively. The effect was studied at room and cryogenic temperatures. (C) 1997 American Institute of Physics.
    No preview · Article · Sep 1997 · Applied Physics Letters
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    ABSTRACT: Summary form only given. Single crystals of AlN to 1 mm thickness were grown at 1950-2250°C on 10×10 mm<sup>2</sup> 6H-SiC substrates via sublimation-re-condensation. Most crystals were 0.3 mm-1 mm thick transparent layers completely covering the substrates. Raman, optical and TEM results will be presented. Single crystals of GaN were grown by subliming powders of this material under NH<sub>3</sub>. Raman and photoluminescence results will be shown
    No preview · Conference Paper · Sep 1997
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    ABSTRACT: High-quality III-V nitride epitaxial films and heterostructures are of great importance for a wide variety of electronic and optoelectronic devices. In this talk, data are presented on the optical and structural properties of InGaN-GaN heteroepitaxial films and InGaN-InGaN heterostructures and quantum wells grown by low-pressure metalorganic chemical vapor deposition (MOCVD). The films have been characterized by room-temperature (300K) and low temperature (77K and 4.2K) photoluminescence (PL), cathodoluminescence (CL), high resolution X-ray diffraction, secondary-ion mass spectrometry, and transmission electron microscopy
    No preview · Conference Paper · Sep 1997
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    ABSTRACT: Bulk GaN single crystals were grown from cold pressed GaN powder by sublimation in flowing ammonia. Optical transmission measurements indicated that the absorption coefficient for the transparent samples is 50 cm(-1) in the wavelength region from 650 to 400 nm. Optical metastability in bulk GaN crystals was studied through time dependent photoluminescence both at room and liquid-nitrogen temperatures. The observation included decreasing output intensity of the ultraviolet emission attributed to the band edge and increasing output intensity of a new emission band centered at 378 nm at room temperature. At liquid-nitrogen temperature, the photoinduced emission band consisted of at least one LO-phonon replica of the zero-phonon line centered at 378 nm. The ratio of output intensities of the photoinduced band to the band edge increased by a factor of 10 during 27 min of exposure time. The photoinduced effect is attributed to the metastable nature of traps in bulk GaN. (C) 1997 American Institute of Physics.
    Full-text · Article · Jul 1997 · Applied Physics Letters
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    ABSTRACT: Photoluminescence (PL) characteristics of GaN/InGaN/GaN single quantum wells (QWs) and an InGaN/GaN single heterojunction were studied using continuous wave (CW) and pulsed photoluminescence in both edge and surface emitting configurations. Samples were grown on c-plane sapphire substrates by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Room temperature and 77K PL measurements were performed using a CW Ar-ion laser (305 nm) and a frequency tripled (280 um), pulsed, mode-locked Ti: sapphire laser. CW PL emission spectra from the quantum wells (24, 30, 80Å) were all blue shifted with respect to the reference sample. The difference (i. e., the blue shift) between the measured value of peak emission energy from the QW and the band-edge emission from the reference sample was attributed to quantum size effects, and to strain arising due to a significant lattice mismatch between InGaN and GaN. In addition, stimulated emission was observed from an InGaN/GaN single heterojunction in the edge and surface emitting configuration at 77K. The narrowing of emission spectra the nonlinear dependence of output emission intensity on input power density, and the observation of a strongly polarized output are presented.
    No preview · Article · Mar 1997 · Journal of Electronic Materials
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    ABSTRACT: The photoluminescence (PL) in as-received and milled Si and SiO2 powder is reported. The Si and SiO2 powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous SiO2 component is formed by milling crystalline SiO2 . The PL spectra for as-received Si, milled Si, and SiO2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO2 powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled SiO2 can be related to both the increased volume fraction of the amorphous SiO2 component and the increased density of defects introduced in the amorphous SiO2 upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled SiO2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or SiO2 components existing in these powder samples. The PL measurement for milled SiO2 is dependent on air pressure whereas that for as-received SiO2 is not, suggesting that new emitting centers are formed by milling.
    Full-text · Article · Mar 1997 · Physical Review B
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    ABSTRACT: Optically pumped lasing from InGaN/GaN single heterojunctions (SH) was observed in an edge emitting configuration at 77 K. The heterojunctions were grown by atmospheric pressure metalorganic chemical vapor deposition on c-plane sapphire substrates. The frequency tripled output of a mode-locked titanium:sapphire laser with a pulse width of 250 fs, operating at 280 nm, was used as the photoexcitation source. The nonlinear dependence of output emission intensity on input power density, the observations of a strongly polarized output emission, and distinct Fabry–Perot modes are discussed.
    No preview · Article · Feb 1997 · Journal of Applied Physics
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    ABSTRACT: Photoluminescence (PL) characteristics of GaN/lnGaN/GaN single quantum wells (QWs) and an InGaN/GaN single heterojunction were studied using continuous wave (CW) and pulsed photoluminescence in both edge and surface emitting configurations. Samples were grown on c-plane sapphire substrates by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Room temperature and 77K PL measurements were performed using a CW Ar-ion laser (305 nm) and a frequency tripled (280 nm), pulsed, mode-locked Ti: sapphire laser. CW PL emission spectra from the quantum wells (24, 30, 80Å) were all blue shifted with respect to the reference sample. The difference (i. e., the blue shift) between the measured value of peak emission energy from the QW and the band-edge emission from the reference sample was attributed to quantum size effects, and to strain arising due to a significant lattice mismatch between InGaN and GaN. In addition, stimulated emission was observed from an InGaN/GaN single heterojunction in the edge and surface emitting configu-ration at 77K. The narrowing of emission spectra, the nonlinear dependence of output emission intensity on input power density, and the observation of a strongly polarized output are presented.
    No preview · Article · Jan 1997 · Journal of Electronic Materials
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    ABSTRACT: InGaN/GaN Heterostructures were deposited on c-plane sapphire substrates by atmospheric pressure Metalorganic Chemical Vapor Deposition (MOCVD). A frequency tripled modelocked Ti-sapphire laser with a 250 fs pulse operating at 280 nm was used for photoexcitation. Photopumped stimulated emission was observed from InGaN/GaN single heterostructures (SH's) in both edge and surface emitting configurations. A sharp threshold at the onset of stimulated emission and a strong nonlinear dependence of output emission on input power density was observed. Distinct Fabry-Perot modes corresponding to both cavity configurations were also observed. Gain coefficients were measured from an In0.14Ga0.86N film using the method developed by Shaklee and Leheny for the edge emitting configuration.
    No preview · Chapter · Jan 1997
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    ABSTRACT: InGaN bulk layers and single quantum wells were grown on 1.4 to 2.4 μm thick GaN on sapphire films by atmospheric pressure metalorganic chemical vapour deposition (AP-MOCVD). The morphology of the epitaxial layers was strongly affected by the VIII ratio in the gas phase. The incorporation efficiency of indium was observed to increase with higher growth rates and decreasing temperature, but was independent of the VIII ratio in the investigated parameter range. In0.16Ga0.84N single quantum wells showed intense quantum well related luminescence at room temperature, with a full width at half maximum of 7.9 nm at a thickness of 50 Å. Single quantum wells embedded in InGaN of graded composition showed superior properties compared to quantum wells with In0.04Ga0.94N barriers of constant composition.
    No preview · Article · Jan 1997 · Journal of Crystal Growth