Browsing by Subject "Indium tin oxide"

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    45-GHz bandwidth-efficiency resonant-cavity-enhanced ITO-Schottky photodiodes
    (IEEE, 2001) Bıyıklı, Necmi; Kimukin, I.; Aytür, O.; Gökkavas, M.; Ünlü, M. S.; Özbay, Ekmel
    High-speed Schottky photodiodes suffer from low efficiency mainly due to the thin absorption layers and the semitransparent Schottky-contact metals. We have designed, fabricated and characterized high-speed and high-efficiency AlGaAs-GaAs-based Schottky photodiodes using transparent indium-tin-oxide Schottky contact material and resonant cavity enhanced detector structure. The measured devices displayed resonance peaks around 820 nm with 75% maximum peak efficiency and an experimental setup limited temporal response of 11 ps pulsewidth. The resulting 45-GHz bandwidth-efficiency product obtained from these devices corresponds to the best performance reported to date for vertically illuminated Schottky photodiodes.
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    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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    High-speed transparent indium-tin-oxide based resonant cavity Schottky photodiode with Si/sub 3/N/sub 4//SiO/sub 2/ top Bragg mirror
    (IEEE, Piscataway, NJ, United States, 2000) Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel; Gokkavas, M.; Unlu, S.
    Photodetectors demonstrating high bandwidth-efficiency (BWE) products are required for high-performance optical communication and measurement systems. For conventional photodiodes the BWE product is limited due to the bandwidth-efficiency trade-off. A resonant cavity enhanced (RCE) photodetection scheme offers the possibility to overcome this limitation. Very high BWE products are achieved using Schottky and p-i-n type RCE photodiodes, which could not be reached with conventional detector structures. Even better performances should be possible for RCE Schottky photodiodes if one can get rid of the optical losses and scattering caused by the Schottky metal, Au, which also serves as the top mirror of the resonant cavity. The transparent, low resistivity material indium-tin-oxide (ITO) is a potential alternative to thin semi-transparent Au as a Schottky-barrier contact material. We report our work on high-performance ITO-based RCE Schottky photodiodes.
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    Planar indium tin oxide heater for improved thermal distribution for metal oxide micromachined gas sensors
    (MDPI AG, 2016) Çakır, M. C.; Çalışkan, D.; Bütün, B.; Özbay, Ekmel
    Metal oxide gas sensors with integrated micro-hotplate structures are widely used in the industry and they are still being investigated and developed. Metal oxide gas sensors have the advantage of being sensitive to a wide range of organic and inorganic volatile compounds, although they lack selectivity. To introduce selectivity, the operating temperature of a single sensor is swept, and the measurements are fed to a discriminating algorithm. The efficiency of those data processing methods strongly depends on temperature uniformity across the active area of the sensor. To achieve this, hot plate structures with complex resistor geometries have been designed and additional heat-spreading structures have been introduced. In this work we designed and fabricated a metal oxide gas sensor integrated with a simple square planar indium tin oxide (ITO) heating element, by using conventional micromachining and thin-film deposition techniques. Power consumption-dependent surface temperature measurements were performed. A 420 °C working temperature was achieved at 120 mW power consumption. Temperature distribution uniformity was measured and a 17 °C difference between the hottest and the coldest points of the sensor at an operating temperature of 290 °C was achieved. Transient heat-up and cool-down cycle durations are measured as 40 ms and 20 ms, respectively. © 2016 by the authors; licensee MDPI, Basel, Switzerland.
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    The role of ITO resistivity on current spreading and leakage in InGaN/GaN light emitting diodes
    (Academic Press, 2017) Sheremet, Volodymyr; Genç, M.; Elçi, M.; Sheremet, Nina; Aydınlı, Atilla; Altuntaş, İsmail; Ding, Kai; Avrutin, Vitaliy; Özgür, Ümit; Morkoç, Hadis
    The effect of a transparent ITO current spreading layer on electrical and light output properties of blue InGaN/GaN light emitting diodes (LEDs) is discussed. When finite conductivity of ITO is taken into account, unlike in previous models, the topology of LED die and contacts are shown to significantly affect current spreading and light output characteristics in top emitting devices. We propose an approach for calculating the current transfer length describing current spreading. We show that an inter-digitated electrode configuration with distance between the contact pad and the edge of p-n junction equal to transfer length in the current spreading ITO layer allows one to increase the optical area of LED chip, as compared to the physical area of the die, light output power, and therefore, the LED efficiency for a given current density. A detailed study of unpassivated LEDs also shows that current transfer lengths longer than the distance between the contact pad and the edge of p-n junction leads to increasing surface leakage that can only be remedied with proper passivation.