Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 4Citation - Scopus: 5Conductance Fluctuations in Undoped Hydrogenated Amorphous Silicon-Germanium Alloy Thin Films(Elsevier Ltd., 2002) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.; Yang, Jeffrey C.; Guha, SubhenduWe report coplanar conductance fluctuations of device quality, undoped hydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) measured from 430 to 490 K. The a-SiGe:H alloys produce noise power spectra similar to coplanar undoped a-Si:H films in the same temperature range. The noise power spectrum S(n) does not fit a single 1/fα power law but rather has two distinct regions, each accurately fitted by a power law, but with different slopes. The low frequency slope α1 is similar to that observed in undoped a-Si:H films varying from 1.30 to 1.46 for different Ge concentrations and shows a slight temperature dependence. At higher frequencies, the slope α2 is less than unity and temperature independent but depends on the Ge content of the film. α2 decreases from 0.60 for no Ge (pure a-Si:H) to 0.15 for 40 at.% Ge. The noise power at lower frequencies increases and at higher frequencies decreases substantially as the temperature increases from 430 to 490 K. We infer that similar noise mechanisms are operating in undoped a-SiGe:H and a-Si:H films but that the Ge content is influencing the noise, particularly the slope at higher frequencies. In addition, the noise has the expected quadratic dependence on bias current and obeys Gaussian statistics.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.Conference Object Citation - WoS: 8Citation - Scopus: 9Diffusion Length Measurements of Microcrystalline Silicon Thin Films Prepared by Hot-wire/Catalytic Chemical Vapor Deposition (hwcvd)(Elsevier Ltd., 2006) Okur, Salih; Güneş, Mehmet; Finger, Friedhelm; Carius, ReinhardHydrogenated microcrystalline silicon (μc-Si:H) films prepared by using the hot-wire/catalytic chemical vapor deposition (HWCVD) technique at low substrate temperatures between 185 °C and 220 °C with different silane concentrations (SC) were investigated using steady-state photocarrier grating (SSPG) and the steady-state photoconductivity methods (SSPC). Crystalline volume fractions (IC RS) obtained from Raman spectroscopy change from 0.22 to 0.77. The diffusion length (LD) is measured at generation rates between G = 1019 and 1021 cm- 3 s- 1. LD changes from 27 nm to 270 nm, with maximum values around SC = 5%. The dependence of LD on SC is similar to that observed for similar quality microcrystalline silicon films prepared using the VHF-PECVD technique. The grating quality factor, γ0, drops from about 0.9 to 0.5 after transition to the microcrystalline regime as indication of scattering from surface patterns.Article Citation - WoS: 10Citation - Scopus: 71/F Noise in Doped and Undoped Amorphous Silicon(Elsevier Ltd., 2000) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.We measured the spectrum of conductance fluctuations in n-type, p-type, and undoped hydrogenated amorphous silicon (a-Si:H) as a function of temperature. In general, the spectra can be fit to a power law, 1/fα, although in the p-type and undoped samples deviations from a strict power law occur. For n-type and p-type samples, the noise magnitude increases with temperature by approximately a factor of 5 from 295 to 450 K. The slope parameter, α, also increases with temperature in the p-type samples from near unity to 1.4 but not in the n-type sample where it remains near 1.05 independent of temperature. The undoped sample could be measured only over a limited range of elevated temperatures, but α does trend larger. The undoped and lightly doped material have similar noise levels but larger p-type doping reduces the noise by two orders of magnitude. Correlation measurements indicate the 1/f noise is Gaussian for all samples. However, intermittent random-telegraph noise is observed in n-type material.Article Citation - WoS: 4Citation - Scopus: 4Conductance Fluctuations in Undoped Intrinsic Hydrogenated Amorphous Silicon Films Prepared Using Several Deposition Techniques(Elsevier Ltd., 2000) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.Coplanar conductance fluctuations in a range of device quality undoped hydrogenated amorphous silicon (a-Si:H) films prepared using different deposition systems were measured in the temperature range of 440-505 K for frequencies from 2 Hz to 3 kHz. The 1/fa type noise spectra had two different power law dependencies, one at lower frequencies with slope α1 close to unity and a second region at higher frequencies with slope α2 around 0.60. The noise power density decreases with increasing temperature in the high frequency region, but only increases much less with temperature at low frequencies. The results indicate that the noise in undoped intrinsic a-Si:H films is due to two independent noise mechanisms operating simultaneously