Şadan Özcan

Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO2/Si substrate

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 100 V bias, corresponding to 100 pA/cm2 current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100 V 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 de...

Metal–semiconductor–metal photodetector on as-deposited TiO2 thin films on sapphire substrate

TiO2 thin films are prepared on c-plane sapphire substrates by the RF magnetron sputtering method. The performance of the Pt contact metal–semiconductor–metal (MSM) photodetector fabricated on as-deposited films is studied. The dark current density and the responsivity obtained were 1.57 × 10−9 A/cm2 at 5 V bias and 1.73 A/W at 50 V bias, respectively. Breakdown is not observed up to 50 V bias. Rise and fall times for the photocurrent were 7 and 3 s, respectively. Our results show that high quality MSM photodetectors can be fabricated without high temperature and complicated fabrication steps.

Preparation of Nano‐Scale Magnetite Fe3O4 and its Effects on the Bulk Bi‐2223 Superconductors

Nano‐scale magnetite (Fe3O4) powders were prepared from metallic iron and distilled water by wet milling technique. Magnetite powders so obtained were added to Bi1.6Pb0.4Sr2Ca2Oy superconductor by 0.00, 0.05, 0.10 and 0.30 wt % (x), with solid state reaction method. The structural and superconducting properties were studied by x‐ray diffraction, transmission electron microscopy, magnetization and magnetic susceptibility measurements. Single‐phase magnetite samples with average particle size about 25 nm were obtained with the wet milling technique. Nanoscale magnetite additions up to 0.10 wt % enhance the critical current density (Jc) of the superconductor preserving the fraction of the high Tc phase Bi‐2223. Magnetite additions above 0.10 wt % decrease the critical parameters (Tc, Jc) and the fraction of the high Tc phase.