Browsing by Subject "Absorption characteristics"

Now showing 1 - 4 of 4

Open Access
Hybrid functional calculated optical and electronic structures of thin anatase TiO2 nanowires with organic dye adsorbates
(Elsevier, 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtioğlu, Ş.; Mete, E.
The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics.
Open Access
Plasmonic gratings for enhanced near infrared sensitivity of Silicon based Schottky photodetectors
(IEEE, 2011) Polat, Kazım Gürkan; Aygun, Levent Erdal; Okyay, Ali Kemal
Schottky photodetectors have been intensively investigated due to their high speeds, low device capacitances, and sensitivity in telecommunication standard bands, in the 0.8μm to 1.5μm wavelength range. Due to extreme cost advantage of Silicon over compound semiconductors, and seamless integration with VLSI circuits, metal-Silicon Schottky photodetectors are attractive low cost alternatives to InGaAs technology. However, efficiencies of Schottky type photodetectors are limited due to thin absorption region. Previous efforts such as resonant cavities increase the sensitivity using optical techniques, however their integration with VLSI circuits is difficult. Therefore, there is a need for increasing Schottky detector sensitivity, in a VLSI compatible fashion. To address this problem, we design plasmonic grating structures to increase light absorption at the metal-Silicon Schottky interface. There are earlier reports of plasmonic structures to increase Schottky photodetector sensitivity, with a renowned interest in the utilization of plasmonic effects to improve the absorption characteristics of metal-semiconductor interfaces. In this work, we report the design, fabrication and characterization of Gold-Silicon Schottky photodetectors with enhanced absorption in the near infrared region. © 2011 IEEE.
Open Access
Thin film MoS2 nanocrystal based ultraviolet photodetector
(Optical Society of American (OSA), 2012) Alkis, S.; Öztaş, T.; Aygün L.E.; Bozkurt F.; Okyay, Ali Kemal; Ortaç, B.
We report on the development of UV range photodetector based on molybdenum disulfide nanocrystals (MoS2-NCs). The inorganic MoS2- NCs are produced by pulsed laser ablation technique in deionized water and the colloidal MoS2-NCs are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and UV/VIS absorption measurements. The photoresponse studies indicate that the fabricated MoS 2- NCs photodetector (MoS2-NCs PD) operates well within 300-400 nm UV range, with diminishing response at visible wavelengths, due to the MoS2- NCs absorption characteristics. The structural and the optical properties of laser generated MoS2-NCs suggest promising applications in the field of photonics and optoelectronics. © 2012 Optical Society of America.
Open Access
ZnO based optical modulator in the visible wavelengths
(SPIE, 2013) Okyay, Ali Kemal; Aygun, Levent E.; Oruç, Feyza B.
In order to demonstrate tunable absorption characteristics of ZnO, photodetection properties of ZnO based thin-film transistors are investigated. By controlling the occupancy of the trap states, the optical absorption coefficient of ZnO in the visible light spectrum is actively tuned with gate bias. An order of magnitude change of absorption coefficient is achieved. An optical modulator is proposed exploiting such tunable absorption mechanism. © 2013 SPIE.