Elektrik- Elektronik Mühendisliği

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Browsing Elektrik- Elektronik Mühendisliği by Subject "Amorphous semiconductors."

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    High vacuum evaporation, deposition monitoring, and rate control
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1982., 1982.) Karyot, Turgut Berat.; Balkan, Naci.
    In order to determine the physical properties of amorphous semiconductor materials it is required to obtain thin film layers by high vacuum evaporation technique. Physical properties of such films are known to be strongly influenced by the rate of deposition. This project therefore involves the construction of a thickness monitor and rate controller which monitors the thicness of thin film layers continuously during the evaporation process and keeps the evaporation rate constant at any desired value. The change of thickness of the thin film layer is observed by monitoring the change in the oscillation frequency of a quartz crystal situated by the side of the thin film deposit. All required functions are generated digitally.
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    Study of law-frequency noise in amorphous silicon
    (Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1987., 1987.) Pekcan, İ. Hakan.; Ülgen, Yekta.
    In this thesis, amorphous silicon films are fabricated and their low-frequency noise properties are investigated over the range of 10 Hz to 4.4 kHz. The ohmic contacted films are produced in two different geometries using the electron gun vacuum-evaporation technique. The noise measurements carried out at low-frequencies show that, 1/f noise is dominant in this frequency region. Effects of d.c. biasing and increasing ambient temperature are also investigated; increasing temperature (> 300 °K ) decreases the low-frequency noise power level. The relationship between the hopping rate and the 1/f noise is verified. It is also shown that, the density of states near the Fermi level can be calculated from 1/f noise measurements. Amorphous silicon films are found to be noisier than the crystalline structure.
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    Study of teh D.C conductance mechanism of evaporated amorphous silicon films
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1984., 1984.) Atağ, Yılmaz.; Ülgen, Yekta.; Aktaş, Gülen, 1951- .
    In this thesis the d.c bulk characteristis of amorphous silicon films are investigated. The films are prepared by electron gun evaporation in a conventional vacuum system. Ohmic contacts are established between the silicon films and the aluminum electrodes. I-V and I-T measurements are performed in the temperaturege range, 110°K to 430°K. Room temperature measurements show that the preparation conditions such as evaporation rate, aging and subsequent annealing all affect the d.c conductivities of the films. In the low temperature range, the data analyzed with the existing models of amorphous semiconductors and the density of states near the Fermi level is calculated. The high temperature data are used to calculate the mobility gap of the amorphous silicon film. The results are then compared with the previously published work.
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    Study of the AC conductance mechanism of evaporated amorphous silicon films
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) Gülsoy, Ayhan O.; Aktaş, Gülen, 1951- .