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Characterization of ZnS:Cr films for Intermediate Band Solar Cells
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]
In this thesis samples of ZnS:Cr thin films have been made through physical vapor deposition (PVD) with resistive heating and characterized by several methods. The thin films are of various thicknesses and contain different concentration of Cr. ZnS:Cr is a candidate to a bulk material for intermediate band solar cell, IBSC, and was therefore selected for this thesis. IBSC is a concept for solar cells with a much higher effiency than todays common solar cell. The goal for the project was to put together the deposition system, make the samples, measure the thicknesses and concentrations and characterize them. Methods like X-Ray Diffraction (XRD), Auger electron spectroscopy (AES), profilometer, four point measurement, Hall-measurement and optical transmission measurements have been used to determine structure, concentrations, thicknesses, resistivity, number of carriers and transmission respectively. The samples and the characterization performed with XRD, AES, profilometer, Hall-measurement and four point measurement were done at NTNU. The spectrum measurements were done at NTNU and the University in Vienna. Samples with thicknesses in the range of 200 Å to 3340 Å have been investigated. Some were deposited in room temperature, some were annealed afterwards for 2 hours at 4500C and some were deposited on substrates with a temperature of 3000C. The thicknesses were measured with a contact profilometer. The theoretical concentration of the samples were in the range of 4% to 31%. There was impossible to measure samples with a lower concentration than 7%, even though these were made. Transmission spectra were made in five overlapping specrophotometerss. Two were used in the visible region (UV-VIS), two in the near infra-red (NIR) region, and one Fourier Transform Infra-Red spectroscopy (FTIR) for the long wavelength region. The range was from 250 nm up to 25000 nm. No Cr2+ absorption lines were found. This can indicate a cluster form of the Cr and not a substitution of Cr2+ with Zn2+ ions. The band gap found from the transmission spectra were in the range of >4.5 eV to 2.95 eV. The high band gap imply insulating samples and inactive Cr states in cluster form. No peaks from lattice configuration were found in the XRD spectrum. This indicates an amorphous structure for both the samples deposited in room temperature, the annealed samples and the sample deposited on hot substrate. The lattice configuration of the sapphire substrate was found for 3 samples. This was the [300] reflection for sapphire at 68.2 degrees. Four samples were investigated in AES. A 3340 Å 7% sample, a 800 Å <5% sample, a 370 Å 31% sample and a 830 Å >4% deposited on hot substrate. Less Cr than expected was found for the sample of 800 Å and 830 Å. However, all samples contained O and C. The sample deposited on hot substrate should contain 80 Å Cr theoretically, but no traces were found. The same applies for the 800 Å sample with less than 5%. Both charged badly which imply non-conductive samples. The 31% and the 7% sample did not show the same charging which implies conductivity. The samples showed a great amount of Cr, but did also contain O and C. However, from the Hall-measurement and four probe measurement none of the samples showed conductive properties. This emphasize the suspicion of incorporation of Cr clusters in inactive states making the samples insulating.
Place, publisher, year, edition, pages
Institutt for fysikk , 2011. , 114 p.
Keyword [no]
ntnudaim:5778, MLREAL Lektorutdanning med master i realfag, Fysikk og matematikk
URN: urn:nbn:no:ntnu:diva-12828Local ID: ntnudaim:5778OAI: diva2:426661
Available from: 2011-06-24 Created: 2011-06-24

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