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Title:	Electronic structure and optical characteristics of diluted magnetic semiconductor (DMS) ZnS doped with Co and Fe
Authors:	Selmani Sofiane. (P49194)
Supervisor:	Huda Abdullah, Dr.
Keywords:	Magnetic semiconductors.
Issue Date:	20-Jun-2011
Description:	Dilute magnetic semiconductors (DMS) are materials with the substitution of magnetic or ferromagnetic ions. These semiconductor materials may enable a new generation devices based on the spin and charge of electron. The aim of this study was to investigate the electronic structure, optical and structural properties of II-VI ZnS semiconductors doped with Co and Fe. Zn1-xCoxS and Zn1-xFexS with x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30 nanocrystals have been successfully prepared by chemical bath deposition method at room temperature. The surface morphology and the film thickness had been examined using a scanning electron microscope (SEM). It has been observed that the surface was totally different when ZnS was doped by Co or Fe. The Zn1-xCoxS films showed an increase in grain size with Co concentration. However, for Zn1-xFexS the particles size were clearly observed and the particles get smaller with the increase of Fe concentrations. To determine the crystalline characteristics of these materials, X-ray diffractometer had been used. All the films revealed a zinc blend crystal structure. The peaks appeared at 2θ = 25.55°, 47.50° and 65.85° correspond to the (111), (220) and (311) planes respectively. However, when Zn1-xFexS was prepared by co-precipitation method, the crystallinity were totally different and a wurtzite crystal structure was observed. To clarify the luminescence origin and the energy-level structure of the doped ZnS, optical measurements had been made. The optical bandgap of the samples were calculated using UV-Visible spectroscopy. The bandgap decreased with further increase in Co and Fe concentration. The bandgap results of Zn1-xCoxS were Eg = 3.90, 3.85, 3.73, 3.69, 3.65 and 3.50 eV for x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30 respectively. On the other hand, for Zn1-xFexS the results were Eg = 3.50, 3.30, 3.05, 2.65, 2.40 and 2.20 eV for x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30 respectively. The photoluminescence spectra of the films showed two emission peaks. The first in the low wavelength due to the band to band transitions and the second in the high wavelength due to the transition probabilities and the concentration of the substituted ions on ZnS. For Zn1-xFexS the quenching effect was clearly observed. The electrical properties were measured using the four point probe. For ZnS doped Co, the temperature dependence of resistivity showed a semiconducting behaviour for T ≥ Tp.,Master
Pages:	91
Call Number:	QC611.8.M25 S445 2011 3
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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