Browsing by Author "Bütün, B."

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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, Ekmel
Deep 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.
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, Ekmel
Backilluminated 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.
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, Ekmel
The 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.
Open Access
Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO2/Si substrate
(AIP Publishing, 2014) Caliskan, D.; Bütün, B.; Çakır, M. C.; Özcan, S.; Özbay, Ekmel
ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO2 on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100V bias, corresponding to 100 pA/cm(2) current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio and dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation. (C) 2014 AIP Publishing LLC.
Open Access
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.