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Fraunhofer, EV Group work on direct wafer bonding for solar cells

Posted: 06 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:solar cells? direct wafer bonds? semiconductors?

The Fraunhofer Institute for Solar Energy Systems ISE has partnered with EV Group (EVG) to develop equipment and process technology to enable electrically conductive and optically transparent direct wafer bonds at room temperature. According to them, the solutions aim to enable highly mismatched material combinations such as gallium arsenide (GaAs) on silicon, GaAs on indium phosphide (InP), InP on germanium (Ge) and GaAs on gallium antimonide (GaSb).

Direct wafer bonding provides the ability to combine a variety of materials with optimal properties for integration into multi-junction solar cells that can lead to new device architectures with unparalleled performance.

Fraunhofer ISE has developed III-V multi-junction solar cells for more than 20 years and has reached record device efficiencies of up to 41 per cent with its metamorphic triple-junction solar cell technology on Ge. Higher efficiencies require the development of four- and five-junction solar cells with new material combinations to span the full absorption range of the sun's spectrum between 300-2000nm.

III-V multi-junction concentrator solar cells on 4-inch diameter wafer

Figure 1: III-V multi-junction concentrator solar cells on 4-inch diameter wafer.

Integration of III-V solar cells on silicon opens another opportunity to reduce manufacturing cost, especially when combined with modern substrate lift-off technologies. Direct wafer-bonding is expected to play an important role in the development of next-generation III-V solar cell devices with applications in space as well as in terrestrial concentrator photovoltaics (PV).

EVG's ComBond technology has been developed in response to market needs for more sophisticated integration processes for combining materials with different lattice constant and coefficient of thermal expansion (CTE). The process and equipment technology enables the formation of bond interfaces between heterogeneous materials such as silicon to compound semiconductors, compound semiconductors to compound semiconductors, Ge to silicon and Ge to compound semiconductors. This is accomplished at room temperature while achieving excellent bonding strength.

The ComBond technology will be commercially available later this year on a 200mm modular platform currently in development, called EVG580 ComBond, which will include process modules that are designed to perform surface preparation processes on both semiconductor materials and metals.

In addition to PV, other potential application areas for processes developed in cooperation between EVG and Fraunhofer ISE include LEDs and silicon photonics.





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