Browsing by Subject "Organic chemicals"

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    ItemOpen Access
    Characterization of AlInN/AlN/GaN heterostructures with different AlN buffer thickness
    (Springer New York LLC, 2016) Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, Ekmel
    Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (101 ¯ 2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (101 ¯ 2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm−2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.
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    ItemOpen Access
    Electric field dependence of radiative recombination lifetimes in polar InGaN/GaN quantum heterostructures
    (IEEE, 2009) Sarı, Emre; Nizamoğlu, Sedat; Lee I.-H.; Baek J.-H.; Demir, Hilmi Volkan
    We report on external electric field dependence of recombination lifetimes in polar InGaN/GaN quantum heterostructures. In our study, we apply external electric fields one order of magnitude less than and in opposite direction to the polarization-induced electrostatic fields inside the well layers. Under the increasing external electric field, we observe a decrease in carrier lifetimes (τ) and radiative recombination lifetimes (τr), latter showing a weaker dependence. Our results on τr show an agreement with our transfer matrix method based simulation results and demonstrate Fermi's golden rule in polar InGaN/GaN quantum heterostructures dependent on electric field. For our study, we grew 5 pairs of 2.5 nm thick In0.15Ga 0.85N quantum well and 7.5 nm thick GaN barrier layers in a p-i-n diode architecture using metal-organic chemical vapor deposition (MOCVD) on a c-plane sapphire substrate. Devices with 300 μm × 300 μm mesa size were fabricated using standard photolithography, reactive ion etching and metallization steps. We used indium-tin oxide (ITO) based semi-transparent contacts in top (p-GaN) layer for uniform application of electric field across the well layers. The fabricated devices were diced and mounted on a TO-can for compact testing. © 2009 IEEE.
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    Examination of the temperature related structural defects of InGaN/GaN solar cells
    (Academic Press, 2015) Durukan, İ. K.; Bayal, Ö.; Kurtuluş, G.; Baş, Y.; Gültekin, A.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Özçelik, S.; Özbay, Ekmel
    In this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 °C. The defect density increased on the GaN layer starting from 350 °C and reaching above 400 °C. A similar trend is observed on the InGaN layer, too.
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    Scattering analysis of two-dimensional electrons in AlGaN/GaN with bulk related parameters extracted by simple parallel conduction extraction method
    (American Institute of Physics, 2010-07-15) Lisesivdin, S. B.; Yildiz, A.; Balkan, N.; Kasap, M.; Ozcelik, S.; Özbay, Ekmel
    We carried out the temperature (22-350 K) and magnetic field (0.05 and 1.4 T) dependent Hall mobility and carrier density measurements on Al 0.22Ga0.78N/GaN heterostructures with AlN interlayer grown by metal-organic chemical-vapor deposition. Hall data is analyzed with a simple parallel conduction extraction method and temperature dependent mobility and carrier densities of the bulk and two-dimensional (2D) electrons are extracted successfully. The results for the bulk carriers are discussed using a theoretical model that includes the most important scattering mechanisms that contribute to the mobility. In order to investigate the mobility of two-dimensional electron gas, we used a theoretical model that takes into account the polar optical phonon scattering, acoustic phonon scattering, background impurity scattering, and interface roughness scattering in 2D. In these calculations, the values are used for the deformation potential and ionized impurity density values were obtained from the bulk scattering analysis. Therefore, the number of fitting parameters was reduced from four to two. © 2010 American Institute of Physics.