Epitaxial Deposition of Germanium Thin Films on Low-Cost, Large-Area, Flexible, Single-Crystal-Like Substrates

Germanium (Ge) films were heteroepitaxially grown on flexible, large-area, single-crystal-like metallic substrates. Multiple, heteroepitaxial, buffer layers of nanoscale dimensions were deposited on the triaxially textured, single-crystal-like Ni-W alloy substrate. Ge films were deposited on the CeO₂-terminated buffer stack on the metallic substrate using electron beam evaporation. The X-ray diffraction θ-2θ scan showed (400) Ge peak and the RHEED image indicates that the Ge surface is smooth and the film is essentially single-crystal-like and heteroepitaxial. The full-width-half-maximum (FWHM) of the Ge film rocking curve is 0.93°. The X-ray phi-scan of the (111) Ge showed FWHM value of within 4°. According to the X-ray omega-scan, phi-scan and pole-figures, the Ge film was grown on CeO₂terminated buffer stack of metal substrate with in-plane and out-of-plane aligned in the cube-on-cube heteroepitaxial relationship. The cross-section TEM reveals the sharp interface between the Ge film and the CeO₂buffer layer with a very low defect density. The Ge film grown on flexible metal substrate exhibit high electron mobilities, similar to single-crystal Ge films grown on standard single-crystal substrates. Such single-crystal-like semiconductor films on low-cost, flexible, large-area, single-crystal-like metallic substrates could potentially enable high-performance electronic devices for a range of applications.