Interface-controlled integration of functional oxides with Ge

Integration of oxides with semiconductor substrates merges functional properties of the two material systems. Significant progress has been made in controlled synthesis of crystalline oxides on silicon. Other semiconductors, such as germanium, are however lagging behind but would benefit from the range of functionalities provided by oxides. Here, we develop a synthetic route to epitaxial oxide/Ge heterostructures. Comparative analysis, employing diffraction and microscopy techniques, demonstrates distinct advantage of synthesis on the reconstructed Ge surface over traditional growth on metal reconstructions. In particular, a direct single-crystal-to-single-crystal contact between the ferromagnetic semiconductor EuO and Ge(001) has been designed and manufactured, a welcome development for semiconductor spintronics. The results mimicking those for silicon establish a general platform for integration of functional oxides with mature semiconductor technologies. 2D phases at the interface are shown to control synthesis of functional oxide/germanium heterostructures. The long-standing problem of EuO integration with the Ge platform is solved.