Browsing by Author "Demir, İ."
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Item Open Access Distributed contact flip chip InGaN/GaN blue LED; comparison with conventional LEDs(Elsevier, 2019) Genç, M.; Sheremet, Volodymyr; Elçi, M.; Kasapoğlu, A.; Altuntaş, İ.; Demir, İ.; Eğin, G.; İslamoğlu, Serkan; Gür, E.; Muzafferoğlu, N.; Elagöz, S.; Gülseren, Oğuz; Aydınlı, A.This paper presents high performance, GaN/InGaN-based light emitting diodes (LEDs) in three different device configurations, namely Top Emitting (TE) LED, conventional Flip Chip (FC) and Distributed Contact (DC) FC. Series resistances as low as 1.1 Ω have been obtained from FC device configurations with a back reflecting ohmic contact of Ni/Au/RTA/Ni/Ag metal stack. A small shift has been observed between electroluminescence (EL) emissions of TE LED and the FC LEDs. In addition, FWHM value of the EL emission of DCFC LED has shown the minimum value of 160 meV (26.9 nm). Furthermore, DCFC LED configuration has shown the highest quantum efficiency and power output, with 330 mW at 500 mA current injection, compared to that of traditional wire bonded TE LEDs and the conventional FC LEDs.Item Open Access Monetary policy responses to the exchange rate: Empirical evidence from the ECB(Elsevier, 2014) Demir, İ.The exchange rate is an important part of the transmission mechanism in the determination of monetary policy because movements in the exchange rate have significant effect on the macroeconomy. It can be difficult to measure the reaction of monetary policy to the movements of the exchange rate, due to the simultaneous response of monetary policy to the exchange rate and the possibility that both variables respond to several other variables. This study addresses these problems by using an identification method based on the heteroscedasticity in the high-frequency data. The results in this paper suggest that the ECB systematically responds to exchange rate movements but that quantitative effects are small. Such a significant but small reaction coefficient seems consistent with the hypothesis that the central banks do not target the fluctuations in the exchange rate but consider them only to the extent they impact on the expected inflation and output path. © 2014 Elsevier B.V.Item Open Access PECVD grown SiN photonic crystal micro-domes for the light extraction enhancement of GaN LEDs(SPIE, 2020) Genç, M.; Sheremet, Volodymyr; Altuntaş, İ.; Demir, İ.; Gür, E.; Elagöz, S.; Gülseren, Oğuz; Özgür, Ü.; Avrutin, V.; Morkoç, H.; Aydınlı, A.; Fujioka, H.; Morkoç, H.; Schwarz, U. T.In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the sapphire substrate is reflected upwards to the top surface and the amount of light extracted from the LED is expected to increase. In an alternative approach, SiN micro-domes forming a two dimensional photonic crystal, 2 μm in diameter and 80 nm in height in average, are deposited on the light emitting surface of the device with a period of 2 μm. Coating the backside with Ag has increased the efficiency of a top emitting LED by 11%. By introducing the SiN photonic crystal onto the Ag backside coated sample, total internal reflection is reduced via scattering and the amount of light emitted has been increased by 30% at 5·104 mA/cm2. Integration of SiN micro-domes with Ag coating has significantly impacted light extraction which has been shown to increase the efficiency of GaN based LEDs. Fabrication process and the results are discussed in detail.