Browsing by Author "Merdan, Z"

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    Dielectrical parameters and relaxation of Al/NFT/p-Si schottky diode with frequency dependence
    Karagöz, E; Varol, SF; Sayin, S; Merdan, Z
    The fabricated Al/ Naphthalimide /p-Si Schottky diode's dielectrical parameters and series resistance effect have been investigated by using the DC and AC measurements. We have developed a facile interface structure that consisted of double-layer films in order to investigate the capacitance volume and series resistance effect through the device. The organic interlayer with little nanometer thickness between electrode and inorganic semiconductor drastically reduce the series resistance at the interface. The dielectric parameters have increased with decreasing frequency. Interestingly, the value of epsilon ' (approximate to 3) even at 1 kHz shows that the prepared naphthalimide (with Thiophene property) nano-interlayer can provide more charges or energy storage ability and so it can be used instead of traditional interfacial layers.
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    Comparative Studies of Undoped/Al-Doped/In-Doped ZnO Transparent Conducting Oxide Thin Films in Optoelectronic Applications
    Koralli, P; Varol, SF; Mousdis, G; Mouzakis, DE; Merdan, Z; Kompitsas, M
    In this paper, undoped, Al-, and In-doped zinc oxide thin films were deposited. Film growth was performed using the sol-gel technique. The method included (a) preparing homogeneous and stable solutions of zinc acetate 2-hydrate, (b) mixing them with aluminum nitrate and indium acetate in 2-methoxyethanol and 2-aminoethanol solutions with various concentrations, and (c) spin coating them onto transparent glass substrates. After thermal annealing, the films showed a high transparency (80-90%) and good stability. Using typical diagnostic tools, the structural, morphological, optical, and electrical film properties were investigated and linked to the dopant type, and concentrations in view of optoelectronics were investigated.
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    Improved performance of near UV-blue n-ZnO/p-GaN heterostructure LED with an AlN electron blocking layer
    Unal, D; Varol, SF; Brault, J; Chenot, S; Al Khalfioui, M; Merdan, Z
    High quality single crystalline n-type ZnO films, with a thickness of 200 nm, were grown on top of AlN/GaN layers under 25 W, 50 W and 100 W sputtering powers. The AlN and p-type GaN layers were deposited by metalorganic chemical vapor deposition (MOCVD). From X-ray diffraction measurements, the samples exhibited the (000l) peaks corresponding to both ZnO, GaN and AlN monocrystalline layers. As the sputtering power was increased, the ZnO grain size increased and the dislocation density decreased. This result is supported by a reduction of the rms values obtained on the ZnO layers from Atomic Force Microscopy (AFM) results. In addition, photoluminescence peaks of ZnO at 372 nm, 375 nm and 380 nm were seen as dependent on the sputtering power. We have used an AlN electron blocking layer between ZnO and GaN films to improve the electroluminescence from the n-ZnO side. Room temperature electroluminescence (EL) of the LEDs demonstrated near UVblue emission consisting of predominating peaks centred at 405 nm, 390 nm and 380 nm for the device with ZnO deposited at 25 W, 50 W and 100 W sputtering powers, respectively. Moreover, the I-V curves of the LEDs showed a rectifying behavior with 6.8 V, 6.4 V, 5.2 V threshold voltages for 25 W, 50 W and 100 W values.
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    Optimization of HIL-HTL-free naphthalimide: Isoquinoline TEOLEDs with BZO top electrode
    Varol, SF; Sayin, S; Merdan, Z
    The present work focuses mainly on HIL/HTL-free TEOLEDs with furan-appended naphthalimide: isoquinoline (furan IQ) and morpholine-appended naphthalimide: isoquinoline (morpholine IQ), which were synthesized from the reaction between naphthalic anhydride and a substituent such as 2-furoic hydrazide or 4-aminomorpholine. Both of the emitters displayed aggregation-induced emission enhancement (AIEE) behavior. This new structure was constructed between modified indium tin oxide (ITO) with caesium fluoride (CsF) (5.18 eV) and boron-doped zinc oxide (BZO) (3.20 eV) with ideal work functions. The current densities were 400 mA.cm(-2) and 387 mA.cm(-2) and luminances were in the range of 9500 cd.m(-2) 9000 cd.m(-2) for the furan IQ and morpholine IQ emitters, respectively. We have introduced a new CsF-ITO/EML/LiF/BZO design with external quantum efficiencies (EQEs) of 9.50 % and 7.57%. We have achieved a standard deep violet/blue CIE coordinates of (0.15, 0.06) and (0.16, 0.05) for furan IQ and morpholine IQ emitters with a high color stability.