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Characterization of GaN:ZnO p-n junctions
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]
In this master thesis, thin lms of ZnO doped with various cobalt concentra- tions have been grown using Pulsed Laser Deposition (PLD). This growth technique is preferred because it is able to grow thin lms from a target material without changing the elemental ratios from the target. The targets using during deposition are sintered pellets of ZnO doped with cobalt, with doping concentrations of 10, 20 and 30 %. The material was chosen because of its potential for Intermediate Band Solar Cells (IBSC). IBSC is a new concept which aims to create solar cells which have higher eciencies than the solar cells available today. From de- tailed balance theory, the concept of intermediate band solar cells shows a potential of a 86 % eciency limit under perfect conditions, which is remark- able compared to the conventional silicon solar cell devices on the market today with a eciency limit of 41 %. A series of ZnO thin lms of 10, 20 and 30 % cobalt concentration were deposited by PLD on a sapphire substrate. These lms were, together with a similar series containing 1,2 and 5 % cobalt concentration deposited on both silicon and sapphire substrates, characterized using Scanning Electron Mi- croscopy (SEM), Energy Dispersive X-ray (EDX) Microanalysis, X-ray Pho- toelectron Spectroscopy (XPS), Hall measurements, X-ray diraction (XRD) and optical transmission spectroscopy. In addition, an attempt to make Schottky diodes of the cobalt doped ZnO thin lms and a p-IB-n junction using GaN:Mg and ZnO:Al as the p- and n- emitter was done. These intermediate band solar cell devices were going to be studied by recording dark and illuminated current-voltage (I-V) characteristics. The focus in the study has been to determine which cobalt doping con- centration gives the desired properties for use of ZnO:Co in an intermediate band solar cell device, and to study how a solar cell device with an inter- mediate band material can be realized. The experiments were carried out at NTNU NanoLab, NTNU Department of Physics, NTNU Department of Electronics and Telecommunications and SINTEF Oslo. Optical transmission spectroscopy and XPS showed that the cobalt in the ZnO:Co lms were Co2+. This indicates that cobalt is substituting for zink in the ZnO lattice. XRD showed the crystal structure to be c-oriented with reasonable order. The carrier concentration in the ZnO:Co lms were in the order of 1018- 1019, decreasing with increasing cobalt concentration. The resistivity in the samples increased with increasing doping concentration. Investigation of the GaN:Mg wafer showed that it did not have the desired properties for device fabrication as it showed n-type conductivity instead of p-type. The Schottky diodes made of Au-ZnO:Co and Pt-ZnO:Co did not show diode behavior because of surface states in ZnO:Co making ohmic contacts.
Place, publisher, year, edition, pages
Institutt for fysikk , 2011. , 100 p.
Keyword [no]
ntnudaim:6632, MTFYMA fysikk og matematikk, Teknisk fysikk
URN: urn:nbn:no:ntnu:diva-13262Local ID: ntnudaim:6632OAI: diva2:436564
Available from: 2011-08-24 Created: 2011-08-24

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