Browsing by Author "Islam, M. S."

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An experimental and first-principles study of the effect of B / N doping in TiO2 thin films for visible light photo-catalysis
(Elsevier, 2013) Uddin, M. N.; Shibly, S. U. A.; Ovali, R.; Saiful, I.; Islam, M. S.; Uddin, M. J.; Gulseren, O.; Bengu, E.; Mazumder, M. M. R.
Thin films of TiO2 and boron-nitrogen (B/N) co-doped TiO 2 on glass substrates have been prepared by a simple sol-gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV-vis spectroscopy. The TiO 2 thin films with co-doping of different B/N atomic ratios (0.27-20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO 2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV-vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results. © 2013 Elsevier B.V.
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Fabrication of high-speed resonant cavity enhanced schottky photodiodes
(Institute of Electrical and Electronics Engineers, 1997-05) Özbay, Ekmel; Islam, M. S.; Onat, B.; Gökkavas, M.; Aytür, O.; Tuttle, G.; Towe, E.; Henderson, R. H.; Ünlü, M. S.
We report the fabrication and testing of a GaAs-based high-speed resonant cavity enhanced (RCE) Schottky photodiode. The top-illuminated RCE detector is constructed by integrating a Schottky contact, a thin absorption region (In0.8Ga0.92As) and a distributed AlAs-GaAs Bragg mirror. The Schottky contact metal serves as a high-reflectivity top mirror in the RCE detector structure. The devices were fabricated by using a microwave-compatible fabrication process. The resulting spectral photo response had a resonance around 895 nm, in good agreement with our simulations. The full-width-at-half-maximum (FWHM) was 15 nm, and the enhancement factor was in excess of 6. The photodiode had an experimental setup limited temporal response of 18 ps FWHM, corresponding to a 3-dB bandwidth of 20 GHz.