In Situ Control Over The Sublattice Orientation Of Gap/Si(100): As Virtual Substrates For Tandem Absorbers

III-V integration on Si processed in MOCVD ambient which contains As opens up new opportunities for high-efficiency multi-junction solar cells. Here, we study the interaction of As with vicinal Si(100) surfaces, the formation of atomically well-ordered, As-modified Si(100) surfaces and its impact on subsequently grown GaP epilayers. We combine optical in situ spectroscopy with surface science techniques in ultra-high vacuum to understand the As-modified Si(100) surface and the III-V/Si interface at atomic scale. We demonstrate that depending on dimer orientation on the Si(100) surface, we are able to control the sublattice orientation of subsequently grown GaP.