Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 13Noise in Hydrogenated Amorphous Silicon(Institute of Electrical and Electronics Engineers, 2002) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.Published work on conductance fluctuations in hydrogenated amorphous silicon is surveyed. There are many reports of 1/f noise. some describing unusual features Such as non-Gaussian statistics. The relative insensitivity to doping and temperature is highlighted. In addition to the 1/f noise. random-telegraph-like noise is often reported. The successes and failures of generation-recombination models for 1 f noise and current filament models for the telegraph noise are summarised.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: 3Citation - Scopus: 31/F Noise in Amorphous Silicon and Silicon-Germanium Alloys(SPIE, 2003) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.We report measurements of conductance noise of a-Si1-XGeX:H in two different geometries; one where the current flow is transverse to the surface and the other longitudinal to it. Because of the large increase in sample resistance in going from transverse to longitudinal conduction, it was not possible to measure both geometries at the same temperature. However, the temperature trends are compatible with a common noise source. For both geometries, alloying with up to 40% Ge reduces the noise magnitude by a factor of 50 over that found in a-Si:HConference Object Citation - WoS: 6Citation - Scopus: 101/F Noise in Hydrogenated Amorphous Silicon-Germanium Alloys(Institute of Electrical and Electronics Engineers, 2003) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.Measurements were made of conductance noise of a-Si:H and a-Si 1-xGex:H in two different geometries: one where the current flow is transverse to the surface and the other where it is longitudinal to the surface. Because of the large change in sample resistance between the two geometries, it was not possible to measure both geometries at the same temperature. For both geometries, alloyinzg with up to 40% Ge reduces the noise magnitude by several orders of magnitude over that found in a-Si:H. The decrease is incompatible with several popular noise models. Extrapolating the temperature trends for each geometry shows that it is possible that the noise observed in the transverse samples has the same origin as the higher frequency part of the double power law spectra observed in the longitudinal 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: 1Citation - Scopus: 2Conductance Fluctuations in A-Si:h: Effects of Alloying and Device Structure(Springer Verlag, 2003) Kasap, Safa O.; Güneş, Mehmet; Johanson, Robert E.; Wang, Q.; Yang, Jeffrey; Guha, SubhenduWe present measurements of conductance noise in undoped a-Si:H and a-SiGe: H thin films in both a transverse and coplanar electrode geometry. For a-Si:H with coplanar electrodes, the noise spectrum is not a pure f-α power law but consists of two linear regions with different slope parameters α. The spectral shape and its temperature dependence are similar for all samples, regardless of the growth technique. Adding Ge results in qualitatively similar spectra; however, α at high frequencies and the temperature dependence are altered. For both a-Si:H and a-SiGe:H with transverse electrodes, the noise spectra are pure f-α power laws, and α decreases with the Ge content.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 simultaneouslyArticle Citation - WoS: 15Citation - Scopus: 141/F-noise Study of Undoped Intrinsic Hydrogenated Amorphous Silicon Thin Films(American Physical Society, 1999) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.Conductance fluctuations in four samples of undoped intrinsic hydrogenated amorphous silicon (a-Si:H) were measured in the temperature range of 450 K to 500 K and for frequencies from 2 Hz to 3 kHz. The noise spectra divide into two regions that each fit a 1/fα power law but with different slope parameters α and different temperature dependences. At low frequencies, α is greater than unity and increases with temperature. At high frequencies, α is near 0.6 and temperature independent, but the noise magnitude decreases rapidly with temperature. We infer from the different dependences on temperature that the noise is generated by two independent mechanisms operating simultaneously in a-Si:H. We also observe that the 1/f noise exhibits a quadratic dependence on bias current and Gaussian statistics.