WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 11Citation - Scopus: 11The Effects of Native and Light Induced Defects on Optoelectronic Properties of Hydrogenated Amorphous Silicon-Germanium (a-Sige:h) Alloy Thin Films(Springer Verlag, 2010) Güneş, Mehmet; Yavaş, Mert; Klomfaß, Josef; Finger, FriedhelmEffects of native and light induced defects states in hydrogenated amorphous silicon-germanium alloy thin films with different Ge concentrations have been investigated by using steady-state photoconductivity, dual beam photoconductivity (DBP), transmission spectroscopy and photothermal deflection spectroscopy (PDS) techniques. In the annealed state, sub-bandgap absorption spectra obtained from both PDS and DBP overlap very well at energies above 1.4 eV. However, differences in α (hν) spectrum exist in the lower energy part of absorption spectrum. The α (hν) value measured at 1.0 eV is the lowest for 10% Ge sample and increases gradually as Ge content of the sample increases. In the light soaked state, time dependence of photoconductivity decay obeys to t -x power law, where x changes from 0.30 to 0.60 for samples with low Ge content and 0.05-0.1 for samples with high Ge content. Correspondingly, the increase of the sub-bandgap absorption coefficient at lower energies obeys to t y power law, where y values are lower than the x value of the same sample. It can be inferred that sub-bandgap absorption and photoconductivity measurements are not controlled by the same set of defects created in the bandgap of alloys. © 2009 Springer Science+Business Media, LLC.Article Citation - WoS: 13Citation - Scopus: 14Electronic Transport Properties of Microcrystalline Silicon Thin Films Prepared by Vhf-Pecvd(Springer Verlag, 2004) Okur, Salih; Güneş, Mehmet; Göktaş, Oktay; Finger, Friedhelm; Carius, ReinhardSteady-state photocarrier grating (SSPG) and steady-state photoconductivity, σph, experiments have been carried out to investigate the electronic transport properties of undoped hydrogenated microcrystalline silicon (μc-Si: H) films prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Material with different crystalline volume fractions was obtained by variation of the silane concentration (SC) in the process gas mixture. Pure amorphous silicon material was investigated for comparison. The ambipolar diffusion length, L amb, which is dominated by the minority carrier properties, is obtained both from the best fit to the experimental photocurrents ratio, β, versus grating period (Λ), and from the "Balberg plot" for the generation rates between 1019 and 1021 cm -3 s-1. Lamb increases from 86 nm with increasing SC and peaks around 200 nm for the SC = 5.6% and decreases again for higher SCs. Lamb values obtained from the intercept of the Balberg plot result in a small difference of around 5% for most of the samples. Minority carrier mobility-lifetime (μτ)-products are much lower than those of majority carriers, however, both majority and minority carrier μτ-products in microcrystalline silicon are higher than those of undoped hydrogenated amorphous silicon. The grating quality factor (γ 0) changes from 0.70 to 1.0 indicating almost negligible surface roughness present in the samples.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.