Browsing by Author "Tut, T."
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Item Open Access Deep-ultraviolet Al0.75Ga0.25N photodiodes with low cutoff wavelength(AIP Publishing LLC, 2006-03-21) Bütün, S.; Tut, T.; Bütün, B.; Gökkavas, M.; Yu, H.; Özbay, EkmelDeep ultraviolet Al0.75Ga0.25N metal-semiconductor-metal photodetectors with high Al concentration have been demonstrated. A metal-organic chemical vapor deposition grown high quality Al0.75Ga0.25N layer was used as a template. Spectral responsivity, current-voltage, optical transmission, and noise measurements were carried out. The photodetectors exhibited a 229 nm cutoff wavelength and a peak responsivity of 0.53 A/W at 222 nm. Some 100x100 mu m(2) devices have shown a dark current density of 5.79x10(-10) A/cm(2) under 50 V bias. An ultraviolet-visible rejection ratio of seven orders of magnitude was obtained from the fabricated devices.Item Open Access Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors(AIP Publishing LLC, 2006) Gökkavas, M.; Bütün, S.; Yu, H.; Tut, T.; Bütün, B.; Özbay, EkmelBackilluminated ultraviolet metal-semiconductor-metal photodetectors with different spectral responsivity bands were demonstrated on a single Alx Ga1-x N heterostructure. This was accomplished by the incorporation of an epitaxial filter layer and the recess etching of the surface. The 11 nm full width at half maximum (FWHM) responsivity peak of the detector that was fabricated on the as-grown surface was 0.12 AW at 310 nm with 10 V bias, whereas the 22 nm FWHM responsivity peak of the detector fabricated on the recess-etched surface was 0.1 AW at 254 nm with 25 V bias. Both detectors exhibited excellent dark current characteristics with less than 10 fA leakage current. © 2006 American Institute of Physics.Item Open Access Experimental evaluation of impact ionization coefficients in Al xGa1-xN based avalanche photodiodes(AIP Publishing LLC, 2006) Tut, T.; Gökkavas, M.; Bütün, B.; Bütün, S.; Ülker, E.; Özbay, EkmelThe authors report on the metal-organic chemical vapor deposition growth, fabrication, and characterization of high performance solar-blind avalanche photodetectors and the experimental evaluation of the impact ionization coefficients that are obtained from the photomultiplication data. A Schottky barrier, suitable for back and front illuminations, is used to determine the impact ionization coefficients of electrons and holes in an AlGaN based avalanche photodiode. © 2006 American Institute of Physics.Item Open Access Fabrication and characterisation of solar-blind Al0.6Ga0.4N MSM photodetectors(The Institution of Engineering and Technology, 2005) Bıyıklı, Necmi; Kimukin, I.; Tut, T.; Aytur, O.; Özbay, EkmelSolar-blind metal-semiconductor-metal (MSM) photodiodes based on MOCVD-grown Al0.6Ga0.4N template have been fabricated and tested. AlGaN detector samples were fabricated using a microwave compatible fabrication process. Optical transmission, current-voltage, spectral responsivity, and temporal pulse response measurements were carried out. The fabricated devices had very low leakage current and displayed true solar-blind response with ∼255 nm cutoff wavelength.Item Open Access High bandwidth-efficiency solar-blind AlGaN Schottky photodiodes with low dark current(Pergamon Press, 2005-01) Tut, T.; Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Aytur, O.; Unlu, M. S.; Özbay, EkmelAl0.38Ga0.62N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solarblind detectors displayed extremely low dark current values: 30 μm diameter devices exhibited leakage current below 3fA under reverse bias up to 12V. True solar-blind operation was ensured with a sharp cut-off around 266nm. Peak responsivity of 147mA/W was measured at 256nm under 20V reverse bias. A visible rejection more than 4 orders of magnitude was achieved. The thermally-limited detectivity of the devices was calculated as 1.8 × 1013cm Hz1/2W-1. Temporal pulse response measurements of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1 GHz bandwidth. A bandwidth-efficiency product of 2.9GHz was achieved with the AlGaN Schottky photodiodes. © 2004 Elsevier Ltd. All rights reserved.Item Open Access High performance AlxGa1-xN-based avalanche photodiodes(Elsevier BV, 2007-10) Tut, T.; Butun, B.; Gokkavas, M.; Özbay, EkmelWe report high performance solar-blind photodetectors with reproducible avalanche gain as high as 820 under ultraviolet illumination. The solar-blind photodetectors have a sharp cut-off around 276 nm. We improved the device performance by designing different epitaxial wafer structure with thinner active multiplication layer. We compare the resulting fabricated devices from these wafers in terms of dark current, photoresponse, avalanche gain performances.Item Open Access High-performance solar-blind photodetectors based on AlxGa 1_xN heterostructures(IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Tut, T.; Aytür, O.Design, fabrication, and characterization of high-performance AI xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky. p-i-n, and metal-semicondnctor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA, leakage currents at 6-V reverse bias were measured on p-i-n samples. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W -1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2×104 was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.Item Open Access High-performance visible-blind GaN-based p-i-n photodetectors(AIP Publishing LLC, 2008) Butun, B.; Tut, T.; Ulker, E.; Yelboga, T.; Özbay, EkmelWe report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c -plane sapphire substrates. The dark current of the 200 μm diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was ∼0.23 AW at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7× 103 for wavelengths longer than 400 nm.Item Open Access High-speed characterization of solar-blind AlxGa 1-xN p-i-n photodiodes(Institute of Physics, 2004) Bıyıklı, Necmi; Kimukin, I.; Tut, T.; Kartaloglu, T.; Aytur, O.; Özbay, EkmelWe report on the temporal pulse response measurements of solar-blind AlxGa1-xN-based heterojunction p-i-n photodiodes. High-speed characterization of the fabricated photodiodes was carried out at 267 nm. The bandwidth performance was enhanced by an order of magnitude with the removal of the absorbing p+ GaN cap layer. 30 μm diameter devices exhibited pulse responses with ∼70 ps pulse width and a corresponding 3 dB bandwidth of 1.65 GHz.Item Open Access Photonic band gaps, defect characteristics, and waveguiding in two-dimensional disordered dielectric and metallic photonic crystals(American Physical Society, 2001) Bayındır, Mehmet; Cubukcu, E.; Bulu, I.; Tut, T.; Özbay, Ekmel; Soukoulis, C. M.We experimentally investigated the influence of positional disorder on the photonic band gap, defect characteristics, and waveguiding in two-dimensional dielectric and metallic photonic crystals. Transmission measurements performed on the dielectric photonic crystals have shown a stop band even if a large amount of disorder was introduced to these structures. On the other hand, the photonic band gap of the metallic crystals was found to be very sensitive to disorder, while the metallicity gap was not affected significantly. We addressed how the transmission characteristics of a cavity were affected in the presence of weak disorder. Since the translational symmetry was broken by disorders, we measured different cavity frequencies when we generated defects at various locations. We also demonstrated the propagation of photons by hopping through coupled-cavity structures in both dielectric and metallic two-dimensional photonic crystals. Effects of weak disorder on guiding and bending of electromagnetic waves through the coupled-cavity waveguides were also investigated.Item Open Access Solar-blind AlGaN-based p-i-n photodetectors with high breakdown voltage and detectivity(AIP Publishing LLC, 2008) Tut, T.; Yelboga, T.; Ulker, E.; Özbay, EkmelWe report on the high performance solar-blind AlGaN-based p-i-n photodetectors that are grown by metal-organic chemical vapor deposition on c -plane sapphire substrates. The dark current of the 200 μm diameter devices was measured to be on the order of 5 fA for bias voltages up to 10 V. The breakdown voltages were higher than 200 V. The responsivities of the photodetectors were 0.052 and 0.093 AW at 280 nm under 0 and 40 V reverse biases, respectively. We achieved a detectivity of 7.5× 1014 cm Hz12 W for 200 μm diameter AlGaN p-i-n detectors.Item Open Access Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity(American Institute of Physics, 2002) Bıyıklı, Necmi; Aytur, O.; Kimukin, I.; Tut, T.; Özbay, EkmelWe report on the design, fabrication, and characterization of solar-blind Schottky photodiodes with low noise and high detectivity. The devices were fabricated on n-/n+ AlGaN/GaN heterostructures using a microwave compatible fabrication process. True solar-blind operation with a cutoff wavelength of ∼274nm was achieved with AlxGa1-xN (x=0.38) absorption layer. The solar-blind detectors exhibited <1.8nA/cm2 dark current density in the 0-25 V reverse bias regime, and a maximum quantum efficiency of 42% around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6×1012cmHz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3×10-29A2/Hz at 10 kHz. © 2002 American Institute of Physics.Item Open Access Solar-blind AlxGa1-xN-based avalanche photodiodes(American Institute of Physics, 2005) Tut, T.; Butun, S.; Butun, B.; Gokkavas, M.; Yu, H. B.; Özbay, EkmelWe report the Metalorganic Chemical Vapor Deposition (MOCVD) growth, fabrication, and characterization of solar blind AlxGa1-xN/GaN-based avalanche photodiodes. The photocurrent voltage characteristics indicate a reproducible avalanche gain higher than 25 at a 72 V applied reverse bias. Under a 25 V reverse bias voltage, the 100 mu m diameter devices had a maximum quantum efficiency of 55% and a peak responsivity of 0.11 A/W at 254 nm, and a NEP of 1.89x10(-16) W/Hz(1/2).