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Hohenstein-Ernstthal, Germany

Gerhard C.,HAWK University of Applied Sciences and Arts | Gerhard C.,Fraunhofer Institute for Surface Engineering and Thin Films | Weihs T.,HAWK University of Applied Sciences and Arts | Luca A.,Roth and Rau AG | And 3 more authors.
Journal of the European Optical Society | Year: 2013

In this paper, surface smoothing of optical glasses, glass ceramic and sapphire using a low-power dielectric barrier discharge inert gas plasma at atmospheric pressure is presented. For this low temperature treatment method, no vacuum devices or chemicals are required. It is shown that by such plasma treatment the micro roughness and waviness of the investigated polished surfaces were significantly decreased, resulting in a decrease in surface scattering. Further, plasma polishing of lapped fused silica is introduced. Based on simulation results, a plasma physical process is suggested to be the underlying mechanism for initialising the observed smoothing effect. Source


Tofflinger J.A.,Helmholtz Center Berlin | Laades A.,CiS Forschungsinstitut FurMikrosensorik Und Photovoltaik GmbH | Leendertz C.,Helmholtz Center Berlin | Montanez L.M.,Helmholtz Center Berlin | And 4 more authors.
Energy Procedia | Year: 2014

The charge dynamics and the interface defect state density of AlOx/SiNx passivation stacks deposited by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) wafers are investigated. High frequency (1 MHz) capacitance voltage (C-V) measurements were performed on stacks in the as deposited state and after an annealing step. C-V sweeps reveal an initially high negative charge density for the as deposited sample, activated by the thermal budget during SiNx deposition. However, this charge state is unstable and reduced owning to electron detrapping and emission into the c-Si upon applying moderate voltages. In the annealed sample, the AlOx/SiNx stack has a stable negative fixed charge. Both for as deposited and for annealed samples, applying a positive or negative constant gate voltage stress (Vstress) enhances or reduces the negative effective charge density (Qox,eff), respectively. Injection of charges from the c-Si into traps in the AlOx/SiNx stack is identified as the mechanism responsible for this behavior. We conclude that in addition to fixed negative charges trapping of negative charges near the interface is a crucial mechanism contributing to the total effective negative charge of the stack. Their contribution depends on the temperature and duration of the thermal treatment. Additionally, a large Vstress leads to generation of additional Si dangling bond defects over the entire c-Si bang gap at the c-Si/AlOx interface. © 2014 The Authors. Published by Elsevier Ltd. Source


Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Sperlich H.-P.,Roth and Rau AG | Bahr M.,CiS Research Institute for Micro Sensors and Photovoltaics | Sturzebecher U.,CiS Research Institute for Micro Sensors and Photovoltaics | And 5 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2012

The interface passivation of a -AlO x/a -SiN x:H stacks deposited on p-type silicon by plasma enhanced chemical vapor deposition is investigated by means of charge carrier lifetime and surface photovoltage measurements. To control the quality of the interface, we performed different surface preparation steps prior to a -AlO x/a -SiN x:H stack deposition. Our investigation is focussing on the interface passivation upon post-deposition thermal treatments such as annealing at 425 °C and firing as applied in the silicon solar cell industry. We demonstrate that the interface recombination is mainly controlled by the interface state density as demonstrated by lifetime and SPV measurements. The increase of the negative charge density after thermal steps as revealed by FTIR spectroscopy evidences that the field effect has at least an enhancing effect in improving the passivation level. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Sturzebecher U.,CiS Research Institute for Micro Sensors and Photovoltaics | Sperlich H.-P.,Roth and Rau AG | Moller C.,CiS Research Institute for Micro Sensors and Photovoltaics | And 2 more authors.
Solid State Phenomena | Year: 2014

We are investigating the effect of different wet chemical surface preconditioning sequences for silicon wafers prior to the deposition of aluminum oxide based passivation layers produced by plasma enhanced chemical vapor deposition. We are focusing on the development of a simple and industrially feasible preconditioning process to achieve a high level of interface passivation after the firing process applied to industrial solar cells. Our process optimization is monitored by characterizing the passivation quality before and after a firing process. We are also investigating the effectiveness of the removal of residual surface iron concentrations by the wet chemical process. © (2014) Trans Tech Publications, Switzerland. Source


To fflinger J.A.,Helmholtz Center Berlin | Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Korte L.,Helmholtz Center Berlin | Leendertz C.,Helmholtz Center Berlin | And 4 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

The negative charge formation, the charge-trapping mechanisms and the interface defect passivation of aluminum oxide/silicon nitride (AlOx/SiNx) stacks deposited by plasma-enhanced chemical vapor deposition on p-type crystalline silicon (c-Si) are investigated. Constant voltage stress (CVS) investigations combined with capacitance-voltage (C-V) hysteresis analysis indicate the influence of different thermal treatments on the negative charge formation and allow discerning between fixed and trapped charges in the AlOx/SiNx system. The thermal budget during SiNx deposition activates negatively charged traps. An annealing step leads to the formation of a stable, fixed negative charge and reduces the defect state density (D it) at the c-Si/AlOx interface. A wet-chemical silicon oxidation (SiOx) of the c-Si surface reduces D it even further, but introduces additional traps at the wet-chemical SiOx/AlOx interface. These traps lead to instabilities of the negative charge density and have a detrimental effect on the passivation quality. However, a firing step leads to the formation of a higher negative charge density due to charged traps. Combined with the enhanced chemical passivation, this results in a higher passivation quality than upon annealing. The trap-related negative charge upon firing is unstable due to electron detrapping. However, a positive CVS can recharge traps in the wet-chemical SiOx/AlOx/SiNx system negatively through electron injection from the c-Si. © 2014 Elsevier B.V. Source

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