Seeding effects of Sn/a-Ge island structures for low-temperature lateral-growth of a-GeSn on insulator

Position control of low-temperature solid-phase crystallization in amorphous-GeSn (a-GeSn) films is investigated using a-GeSn films covering Sn/a-Ge stacked islands on insulator. Two-steps annealing has been performed, i.e., first-step annealing (∼250°C) to crystallize Sn/a-Ge islands for crystalline-seed formation and second-step annealing (≤250°C) to proceed lateral-growth from the crystalline-seed. It is found that Sn thickness exceeding ∼70% of Ge thickness is the essential condition to achieve crystalline GeSn islands (grain size >10 nm) with the diamond structure. This acts as crystalline-seed enabling the lateral-growth of a-GeSn over 80 μm. The present process below the softening-temperature (∼300°C) of plastic substrates facilitates realization of advanced flexible electronics.