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The success of III-V concentrator photovoltaic devices is closely linked to the productivity of manufacturing technology for large wafer areas as well as the quality of the electrical and structural properties of the device structures grown. As of today most of the multiple junction solar cells are produced on 4" diameter Germanium substrates. Following industry guidelines for cost reduction a migration to 6" diameter substrates for next generation cells is envisaged. This 225% increase of usable wafer area, however, has to be weighted against a more complex process control due to the peculiar mechanical properties of the Germanium substrates which give rise to extensive thermo-mechanically induced bowing. This, in turn, leads to the requirement of mitigating the resultant inconsistent thermal contact to the wafer carrier, especially for thermally sensitive material properties such as composition and doping controlling the tunnel junctions.