Now showing items 21-40 of 74

    • Energy relaxation probed by weak antilocalization measurements in GaN heterostructures 

      Cheng H.; Bıyıklı, Necmi; Xie J.; Kurdak Ç.; Morko̧ H. (2009)
      Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85 N/AlN/GaN and Al0.83 In0.17 N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the ...
    • Enhanced hole transport in InGaN/GaN multiple quantum well light-emitting diodes with a p-type doped quantum barrier 

      Ji Y.; Zhang, Z. -H.; Tan S.T.; Ju, Z. G.; Kyaw, Z.; Hasanov N.; Liu W.; Sun X. W.; Demir, Hilmi Volkan (Optical Society of America, 2013)
      We study hole transport behavior of InGaN/GaN light-emitting diodes with the dual wavelength emission method. It is found that at low injection levels, light emission is mainly from quantum wells near p-GaN, indicating ...
    • Enhanced optical characteristics of light emitting diodes by surface plasmon of Ag nanostructures 

      Jang L.-W.; Ju J.-W.; Jeon J.-W.; Jeon, D.-W.; Choi J.-H.; Lee, S.-J.; Jeon, S.-R.; Baek J.-H.; Sarı, Emre; Demir, Hilmi Volkan; Yoon H.-D.; Hwang, S.-M.; Lee I.-H. (SPIE, 2011)
      We investigated the surface plasmon coupling behavior in InGaN/GaN multiple quantum wells at 460 nm by employing Ag nanostructures on the top of a roughened p-type GaN. After the growth of a blue light emitting diode ...
    • Examination of the temperature related structural defects of InGaN/GaN solar cells 

      Durukan, İ. K.; Bayal, Ö.; Kurtuluş, G.; Baş, Y.; Gültekin, A.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Özçelik, S.; Özbay, Ekmel (Academic Press, 2015)
      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 ...
    • Experimental and computational analyses of electroabsorption in polar InGaN/GaN quantum zigzag heterostructures 

      Sarı, Emre; Özel, Tuncay; Koç, Aslı; Ju, J.-W.; Ahn, H.-K.; Lee, I.-H.; Baek, J. H.; Demir, Hilmi Volkan (IEEE, 2008-11)
      Traditional quantum confined Stark effect is well known to lead to strong electroabsorption in multiple quantum well (MQW) structures, yielding only red-shift of the absorption edge with the externally applied electric ...
    • Fabrication of flexible polymer–GaN core–shell nanofibers by the combination of electrospinning and hollow cathode plasma-assisted atomic layer deposition 

      Ozgit Akgun, C.; Kayaci, F.; Vempati S.; Haider A.; Celebioglu A.; Goldenberg, E.; Kizir S.; Uyar, Tamer; Bıyıklı, Necmi (Royal Society of Chemistry, 2015)
      Here we demonstrate the combination of electrospinning and hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) processes by fabricating flexible polymer-GaN organic-inorganic core-shell nanofibers at a ...
    • Fundamentals, progress, and future directions of nitride-based semiconductors and their composites in two-dimensional limit: a first-principles perspective to recent synthesis 

      Kecik D.; Onen, A.; Konuk, M.; Gürbüz, E.; Ersan, F.; Cahangirov, S.; Aktürk, E.; Durgun, Engin; Çıracı, Salim (American Institute of Physics Inc., 2018)
      Potential applications of bulk GaN and AlN crystals have made possible single and multilayer allotropes of these III-V compounds to be a focus of interest recently. As of 2005, the theoretical studies have predicted that ...
    • GaN HEMT based MMIC design and fabrication for Ka-band applications 

      Akoğlu, Büşra Çankaya (Bilkent University, 2020-07)
      Gallium Nitride (GaN) technology has recently dominated the high power applications in the mm-wave frequencies, and its commercial use is emerging with the upcoming 5G technology. High Electron Mobility Transistors (HEMTs) ...
    • GaN-on-SiC LNA for UHF and L-Band 

      Zafar, Salahuddin; Osmanoğlu, Sinan; Çankaya, Büşra; Kashif, A.; Özbay, Ekmel (IEEE, 2019)
      In this paper, we report a broadband GaN HEMT LNA from 100 MHz to 2 GHz, using common source with inductive degeneration and RC feedback topology. Flat gain response of ±1.5 dB variation for 9 V drain voltage with 108 mA ...
    • Gunn oscillations in GaN channels 

      Sevik, Cem; Bulutay, Ceyhun (IOP, 2004)
      Gallium nitride with its high negative differential mobility threshold is an appealing material for high power millimetre-wave oscillators as a Gunn diode. By means of extensive ensemble Monte Carlo simulations, the dynamics ...
    • High efficiency 35 GHz MMICs based on 0.2 μm AlGaN/GaN HEMT technology 

      Akoğlu, Büşra Çankaya; Sütbaş, Batuhan; Özbay, Ekmel (Cambridge University Press, 2022-06-16)
      In this paper, two high efficiency monolithic microwave integrated circuits (MMICs) are demonstrated using NANOTAM's in-house Ka-band fabrication technology. AlGaN/GaN HEMTs with 0.2 μm gate lengths are characterized, and ...
    • A high gain and high efficiency 15 W X-Band GaN power amplifier MMIC 

      Gürdal, Armağan; Özipek, Ulaş; Sütbaş, Batuhan; Özbay, Ekmel (IEEE, 2019)
      An X-band microstrip power amplifier MMIC based on our 0.25 μm AlGaN/GaN on SiC process technology is presented in this work. Fabrication steps, HEMT structure and typical device performance are demonstrated. Design procedure ...
    • High power K-band GaN on SiC CPW monolithic power amplifier 

      Cengiz, Ömer; Şen, Özlem; Özbay, Ekmel (IEEE, 2014-10)
      This paper presents a high power amplifier at K-band (20.2-21.2 GHz). The AlGaN/GaN CPW MMIC amplifier is realized with 0.25 μm HEMT process on 2-inch semi-insulating SiC substrate. The amplifier has a small signal gain ...
    • High-efficiency and low-loss gallium nitride dielectric metasurfaces for nanophotonics at visible wavelengths 

      Emani, N. K.; Khaidarov, E.; Paniagua-Domínguez, R.; Fu, Y. H.; Valuckas, V.; Lu S.; Zhang X.; Tan S.T.; Demir, Hilmi Volkan; Kuznetsov, A. I. (American Institute of Physics Inc., 2017)
      The dielectric nanophotonics research community is currently exploring transparent material platforms (e.g., TiO2, Si3N4, and GaP) to realize compact high efficiency optical devices at visible wavelengths. Efficient ...
    • High-performance ALGaN-based visible-blind resonant cavity enhanced Schottky photodiodes 

      Kimukin, İbrahim; Bıyıklı, Necmi; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, Ekmel (Materials Research Society, 2003-04)
      We have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/AlGaN Bragg mirror. The devices were ...
    • High-performance solar-blind AlGaN photodetectors 

      Özbay, Ekmel; Tut, Turgut; Bıyıklı, N. (SPIE, 2005)
      Design, fabrication, and characterization of high-performance Al xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal ...
    • High-performance triangular miniaturized-LEDs for high current and power density applications 

      Lu, S.; Zhang, Y.; Zhang, Zi-H.; Zhu, B.; Zheng, H.; Tan, S. T.; Demir, Hilmi Volkan (American Chemical Society, 2021-08-18)
      This work proposes an effective electrode length model and reveals for the first time the relationship between this model and the mesa shape effect. On the basis of this model, we demonstrate high-performance triangular ...
    • High-speed visible-blind GaN-based ITO-Schottky photodiodes 

      Bıyıklı, Necmi; Kimukin, İbrahim; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, Ekmel (SPIE, 2002)
      In this paper we present our efforts on the design, fabrication and characterization of high-speed, visible-blind, GaN-based ultra-violet (UV) photodiodes using indium-tin-oxide (ITO) Schottky contacts. ITO is known as a ...
    • High-speed visible-blind resonant cavity enhanced AlGaN Schottky photodiodes 

      Bıyıklı, Necmi; Kartaloglu, T.; Aytur, O.; Kimukin, I.; Özbay, Ekmel (Materials Research Society, 2003)
      We have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/Al 0.2Ga 0.8N Bragg mirror. The devices ...
    • A hole modulator for InGaN/GaN light-emitting diodes 

      Zhang, Z-H.; Kyaw, Z.; Liu W.; Ji Y.; Wang, L.; Tan S.T.; Sun, X. W.; Demir, Hilmi Volkan (American Institute of Physics, 2015)
      The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active ...