Browsing by Author "Adegboyega, G.A"

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    The effects of oxygen precipitates on the electrical properties of silver impurities in p-type silicon
    (1996-07) Adegboyega, G.A; Passari, L; Butturri, M.A; Susi, E
    Some characteristics of the silver impurity in silicon with and without oxygen precipitates are studied by means of the four-point probe, minority carrier lifetime, and infra-red absorption spectroscopy measurements. The relative effect of varying contents of oxygen precipitate on the impurity is also investigated. Silver proved to be a donor-type impurity in p-type silicon and its presence led to a reduction, by up to a factor of 21, in the lifetime of the minority carriers by the formation of deep level traps. While the presence of oxygen precipitate in the substrate has little or no effect on the donor-type behaviour, it improved slightly the value of the minority carrier lifetime by gettering some of the Ag impurities and there appears to be a linear dependence of the improved lifetime on the quantity of precipitated oxygen.
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    Electrical Properties of Silver Impurities and their Annealing Behaviour in p-Type Fz Silicon
    (Journal de Physique III, 1691-12) Adegboyega, G.A; Passari, L; Butturri, Maria Angela; Poggi, Antonella
    The electrical activity of silver as well as its annealing properties in 10 Omega cm p-type Fz silicon substrate are studied by means of the four-point probe and minority carrier lifetime measurements. Silver atom concentration in the range 10^{14} to 10^{15} cm^{-3} consistently showed a donor type behaviour in the material and its presence led to a reduction of up to two orders of magnitude in the lifetime of minority carriers by the formation of deep-level traps. Isochronal annealing of silver contaminated specimens showed some gettering of the Ag impurities with resulting temperature dependent changes in the resistivity as well as the minority carrier lifetime values. Analysis of our results shows that a large fraction of the silver impurity atoms present forms the deep level defects and both the deep- and donor-levels appear to originate from the same source
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    Intrinsic gettering of Cr impurities in p-type Cz silicon
    ( physica status solidi (a, 1990-09) Adegboyega, G.A; Poggi, Antonella
    The gettering of chromium impurities by means of high temperature oxygen precipitates is studied by means of resistivity, lifetime, and infrared absorption spectroscopy measurements. The results show that the density of interstitial oxygen, following an oxygen precipitation step, is rather low, and the presence of this interstitial oxygen is closely connected with the formation of the so-called new donor defect. Most of the high temperature (T = 1000°C) oxygen precipitates seem to appear in the form of SiO2 and there is a strong evidence of a redissolution of the oxygen precipitates due to Cr diffusion. The presence of this high temperature oxygen precipitate shows a high efficiency in the gettering of Cr impurities.Das Gettern von Chromverunreinigungen mittels Hochtemperatur-Sauerstoffpräzipitaten wird mittels Widerstands-, Lebensdauer- und Infrarotspektroskopiemessungen untersucht. Die Ergebnisse zeigen, daß die Dichte des Zwischengittersauerstoffs nach dem Sauerstoffpräzipitationsschritt ziemlich niedrig ist, und die Anwesenheit dieses Zwischengittersauerstoffs eng verbunden ist mit der Bildung von sogenannten „new-Donor”-Defekten. Die meisten der Hochtemperatursauerstoffpräzipitate (T = 1000°C) scheinen in Form von SiO2 vorzuliegen, und es existiert ein starker Hinweis auf die Wiederauflösung der Sauerstoffpräzipitate infolge der Cr-Diffusion. Die Anwesenheit dieser Hochtemperatursauerstoffpräzipitate zeigen einen hohen Wirkungsgrad für die Getterung der Cr-Verun-reinigungen
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    Oxidation-induced changes in the electro-optical properties of thin copper films
    (Il Nuovo Cimento D, 1989-07) Adegboyega, G.A
    The room temperature oxidation of vapour deposited copper films has been investigated as a function of film thickness and time by the sheet resistance and optical transmittance measurements. An increase of both sheet resistance and transmittance with a tendency to saturation has been observed. Time variation of the sheet resistance shows that the kinetics of oxidation could be described by a model whereby an initial logarithmic oxide growth changes to an inverse logarithmic one as time progresses; the thicker the film, the longer the change-over time. Absorption coefficients of oxidized films show that the resulting oxide is most probably Cu2O. Evaluation of the oxidized films for possible use as transparent electrode material shows the existence of an optimum thickness value
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    Preparation and characterization of MOCVD thin films of indium tin oxide
    (Optical Materials, 1999-11) Akinwunmi, O.O; Eleruja, Marcus Adebola; Olowolafe, J.O; Adegboyega, G.A
    Indium Tin Oxide (ITO) was deposited by pyrolysis of mixed metal acetylacetonate (a single solid-source precursor). This study demonstrates that the properties of the as-deposited film depend on the deposition temperature. Films with a resistivity of , a visible transmission of over 80%, and a direct optical energy gap of 3.76 eV were deposited.