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ITO thin films prepared by synchronal pulsed RF-DC sputtering

: Heimke, B.; Nyderle, R.; Junghähnel, M.; Hartung, U.; Kopte, T.; Junghähnel, M.


European Commission:
25th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2010. Proceedings : 5th World Conference on Photovoltaic Energy Conversion, 6-10 , September 2010, Valencia, Spain
München: WIP-Renewable Energies, 2010
ISBN: 3-936338-26-4
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <25, 2010, Valencia>
World Conference on Photovoltaic Energy Conversion <5, 2010, Valencia>
Conference Paper
Fraunhofer FEP ()
transparent conductive oxide; TCO; ITO; RF superimposed; DC sputtering

Indium tin oxide (ITO) is used as transparent front contact layer in thin film solar cell systems and other applications. Commonly used (pulsed) DC sputtering of ITO provides high quality transparent conductive layers and is easy to use on large area substrates. The approach of RF superimposed DC sputtering lowers the resistivity of ITO thin films in comparison to DC or pulsed-DC sputtering. Thus the film thickness required and therewith the material costs can be reduced. Furthermore the near infrared transmission of the deposited films can be enhanced. ITO was deposited using a (pulsed) RF and a (pulsed) DC plasma excitation simultaneously. With increasing RF power ratio the resistivity of ITO thin films decreases, even without additional heat exposure to the substrate. However, adding RF power to a (pulsed) DC sputtering process leads to an increase of arc events. A Pulse synchronization module (PSM), which connects the Pulse DC power generator and the RF power generator, was implemented to synchronize both pulsing patterns. The PSM can adjust the pulse-on and -off times (duty cycle) of both generators individually and optimize the sputtering process. This leads to a reduced arcing probability. The ITO films obtained are characterized by a very low resistivity and a high electron mobility. The ITO thin films were analyzed by UV-VIS and IR-spectroscopy as well as Hall-measurements.