Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Conference Object Citation - WoS: 6Citation - Scopus: 9Sub-Bandgap Optical Absorption Spectroscopy of Hydrogenated Microcrystalline Silicon Thin Films Prepared Using Hot-Wire Cvd (cat-Cvd) Process(Elsevier Ltd., 2006) Göktaş, Oktay; Işık, Nebile; Okur, Salih; Güneş, Mehmet; Carius, Reinhard; Klomfaß, Josef; Finger, FriedhelmHydrogenated microcrystalline silicon (μc-Si:H) thin films with different silane concentration (SC) have been prepared using the HW-CVD technique. Dual beam photoconductivity (DBP), photothermal deflection spectroscopy (PDS), and transmission measurements have been used to investigate the optical properties of the μc-Si:H films. Two different sub-bandgap absorption, α(hν), methods have been applied and analyzed to obtain a better insight into the electronic states involved. A good agreement has been obtained in the absorption spectrum obtained from the PDS and DBP measurements at energies above the bandgap. Differences between PDS and DBP spectra exist below the bandgap energy where DBP spectra always give lower α(hν) values and show a dependence on the SC. For some films, differences exist in the α(hν) spectra when the DBP measurements are carried out through the film and substrate side. In addition, for some films, there remains fringe pattern left on the spectrum after the calculation of the fringe-free absorption spectrum, which indicates structural inhomogeneities present throughout the film.Article Developing a Trilayer Processing Technique for Superconducting Yba 2cu3o7-? Thin Films by Using Ge Ion Implantation(IOP Publishing Ltd., 2005) Avcı, İlbeyi; Tepe, Mustafa; Öktem, Bülent; Serincan, Uğur; Turan, Raşit; Abukay, DoğanFor making trilayer superconducting devices based on YBa2Cu 3O7-δ (YBCO) thin film processing, we developed a new technique by employing Ge ion implantation. A YBCO thin film of 150 nm thickness having high c-axis orientation and a transition temperature, T c, of 90 K was implanted with 80 keV, 1 × 1016 Ge ions cm-2 at room temperature. By the result of TRIM calculation, Ge ions were found to penetrate into the YBCO thin film approximately 60 nm below the surface of the film, thus leaving the lower part of the film as a superconductor. Upon implantation with Ge ions, the implanted upper part of the sample lost its electrical conductivity and diamagnetism while its original crystalline structure was preserved. The implanted ions we found did not alter the overall crystal structure of the YBCO thin film; this allowed us to grow an epitaxial superconducting upper layer of YBCO on top of the implanted area, leaving no need to use any buffer layer. The superconducting properties of the upper layer were similar to those of the pure YBCO base layer with an increased room temperature resistivity and a lowered Tc (88 K). This process provides an effective method for fabrication of a trilayer HTS device structure.Conference Object Citation - WoS: 1Citation - Scopus: 1Conductance Fluctuations in Vhf-Pecvd Grown Hydrogenated Microcrystalline Silicon Thin Films(Springer Verlag, 2003) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.; Finger, Friedhelm; Lambertz, AndreasCoplanar conductance fluctuations or excess noise of undoped hydrogenated microcrystal-line silicon (μc-Si : H) thin films grown by VHF-PECVD from silane-hydrogen mixtures with silane concentrations from 2% to 6% have been studied between room temperature and 470 K. We report that undoped μc-Si : H thin films show similar noise-power spectra to those of undoped a-Si : H films in a coplanar sample geometry. At lower temperatures, the noise with the slope α = 0.60 ± 0.07 and at higher temperatures, the noise with the slope α close to unity dominate the spectrum. The noise magnitude decreases with decreasing silane concentration and becomes strongly temperature dependent with increased crystal unity.Conference Object Citation - WoS: 5Citation - Scopus: 5Photoconductivity Spectroscopy in Hydrogenated Microcrystalline Silicon Thin Films(Springer Verlag, 2003) Güneş, Mehmet; Akdaş, Deniz; Göktaş, Oktay; Carius, Reinhard; Klomfaß, Josef; Finger, FriedhelmSteady-state photoconductivity and sub-bandgap absorption measurements by the dual-beam photoconductivity (DBF) method were carried out on undoped hydrogenated microcrystalline silicon thin films prepared by VHF-PECVD and hot-wire chemical vapor deposition. The results are compared with those of the constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS). It is found that DBP, CPM, and PDS provide complementary data on the optoelectronic processes in microcrystalline silicon.