Nanotechnology Research Center (NANOTAM)

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Browsing Nanotechnology Research Center (NANOTAM) by Author "Acar, S."

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    Determination of two-dimensional electron and hole gas carriers in AlGaN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition
    (Elsevier BV, 2008-02-29) Acar, S.; Lisesivdin, S. B.; Kasap, M.; Özcelik, S.; Özbay, Ekmel
    Resistivity and Hall effect measurements on nominally undoped Al0.25Ga0.75N/GaN/AlN heterostructures grown on sapphire substrates prepared by metal organic chemical vapor deposition have been carried out as a function of temperature (20-300 K) and magnetic field (0-1.4 T). Variable magnetic field Hall data have been analyzed using the improved quantitative mobility spectrum analysis technique. The mobility and density of the two-dimensional electron gas at the AlGaN/GaN interface and the two-dimensional hole gas at the GaN/AIN interface are separated by quantitative mobility spectrum analysis. The analysis shows that two-channel conduction is present in nominally undoped Al0.25Ga0.75N/GaN/AlN heterostructures grown on sapphire substrate.
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    The effect of strain relaxation on electron transport in undoped Al0.25Ga0.75N/GaN heterostructures
    (Elsevier BV * North-Holland, 2007-11-01) Lişesivdin, S. B.; Yıldız, A.; Acar, S.; Kasap, M.; Özçelik, S.; Özbay, Ekmel
    The two-dimensional electron gas (2DEG) transport properties of two-step growth undoped Al0.25Ga0.75N/GaN heterostructures with semi-insulating buffer, grown by MOCVD, were investigated in a temperature range of 20–350 K. Using the quantitative mobility spectrum analysis (QMSA) method, it was shown that significant parallel conduction does not occur in worked structures. In-plain growth axis strains are calculated using the total polarization-induced charge density taken as the sheet carrier density measured from the Hall effect. It was found that the calculated strain values are in good agreement with those reported. Influences of the two-step growth parameters such as growth ramp time, the annealing temperature of the GaN nucleation layer on the mobility, and density of the 2DEG are also discussed.
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    Electronic transport characterization of AlGaN∕GaN heterostructures using quantitative mobility spectrum analysis
    (AIP Publishing LLC, 2007-09-06) Lisesivdin, S. B.; Yildiz, A.; Acar, S.; Kasap, M.; Ozcelik, S.; Özbay, Ekmel
    Resistivity and Hall effect measurements in nominally undoped Al0.25Ga0.75N/GaN heterostructures grown on sapphire substrate by metal-organic chemical vapor deposition are carried out as a function of temperature (20-350 K) and magnetic field (0-1.5 T). The measurement results are analyzed using the quantitative mobility spectrum analysis techniques. It is found that there is strong two-dimensional electron gas localization below 100 K, while the thermally activated minority carriers with the activation energies of similar to 58 and similar to 218 meV contribute to the electron transport at high temperatures.
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    ItemOpen Access
    Scattering analysis of 2DEG carrier extracted by QMSA in undoped Al0.25Ga0.75N/GaN heterostructures
    (Institute of Physics Publishing Ltd., 2007) Lisesivdin, S. B.; Acar, S.; Kasap, M.; Ozcelik, S.; Gokden, S.; Özbay, Ekmel
    Hall effect measurements on undoped Al0.25Ga0.75N/GaN heterostructures grown by a metalorganic chemical vapour deposition (MOCVD) technique have been carried out as a function of temperature (20-350 K) and magnetic field (0-1.5 T). Magnetic field dependent Hall data were analysed using the quantitative mobility spectrum analysis (QMSA) technique. The mobility and density within the two-dimensional electron gas (2DEG) at the Al 0.25Ga0.75N/GaN interface and within the underlying GaN layer were successfully separated by QMSA. Mobility analysis has been carried out using both the measured Hall data at a single field and the extracted data from QMSA. Analysis of the temperature-dependent mobility of 2DEG extracted from QMSA indicates that the interface roughness and alloy disorder scattering mechanisms are the dominant scattering mechanisms at low temperatures while at high temperatures only polar optical phonon scattering is the dominant mechanism. Al0.25Ga0.75N/GaN interface related parameters such as well width, deformation potential constant and correlation length were also accurately obtained from the fits of the simple analytical expressions of scattering mechanisms to the 2DEG mobility.