Browsing by Author "Ulker, E."
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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 A hybrid light source with integrated inorganic light-emitting diode and organic polymer distributed feedback grating(Institute of Physics Publishing Ltd., 2008) Butun, B.; Aydin, K.; Ulker, E.; Cheylan, S.; Badenes, G.; Forster, M.; Scherf, U.; Özbay, EkmelWe report a compact light source that incorporates a semiconductor light-emitting diode, nanostructured distributed feedback (DFB) Bragg grating and spin-coated thin conjugated polymer film. With this hybrid structure, we transferred electrically generated 390 nm ultraviolet light to an organic polymer via optical pumping and out-couple green luminescence to air through a second-order DFB grating. We demonstrate the feasibility of electrically driven, hybrid, compact light-emitting devices and lasers in the visible range.Item Open Access MOCVD growth and electrical studies of p-type AlGaN with Al fraction 0.35(Elsevier BV * North-Holland, 2006-04-01) Yu, H.; Ulker, E.; Özbay, EkmelWe present a study on the high performance p-type AlxGa1-xN (x = 0.35) layers grown by low-pressure metalorganic chemical vapor deposition on AIN template/sapphire substrate. The influence of growth conditions on the p-type conductivity of the AlxGa1-xN (x = 0.35) alloy is investigated. From the Hall effect and I-V transmission line model measurements, a p-type resistivity of 3.5 Omega cm for AlxGa1-xN (x = 0.35) epilayers are achieved. To the best of our knowledge, this is the lowest resistivity ever measured for the uniform p-type AlGaN with Al fraction higher than 0.3. The Mg and impurities (O, C and H) of the atom concentration in the epi-layers are analyzed by means of SIMS depth profiles, which reveal the dependence of impurities incorporation on the III elements and growth temperature.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.