Formation of position-controlled large-grain (10 m) Ge crystals on insulator is realized at low-temperature (300C) by goldinduced-crystallization using a-Ge/Au stacked structures. By introduction of diffusion barriers, i.e., thin-Al2O3 layers (2 nm thickness), having open-windows (3-20 m diameter) into the a-Ge/Au interfaces, Ge crystals are selectively grown from the open windows. For open-windows with diameter of 20 m, the grown areas consist of several Ge (111) grains. This is attributed to that several nuclei acting as seed are generated around the perimeters of the open windows. The number of seeds is linearly decreased by decreasing of the open-window diameter. As a result, (111)-oriented large (10 m) Ge single-crystals, without any grain boundary, are obtained at controlled positions for open-windows with diameter of 3 m. This technique will facilitate realization of flexible electronics and 3-dimensional large-scale integrated circuits, where Ge-based functional high-performance thin-film devices are integrated on flexible plastic substrates and/or amorphous insulating layers.
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