Nucleation-controlled gold-induced-crystallization for selective formation of Ge(100) and (111) on insulator at low-temperature (∼250 °c)

Selective formation of Ge(100) and (111) on amorphous-insulator at low-temperatures (∼250 °C) is realized through gold-induced- crystallization using a-Ge/Au/SiO₂ stacked-structures by combining interface-energy-modulation of substrates. Introduction of thin-Al ₂O₃ layers (∼7 nm thickness) at a-Ge/Au interfaces enables large-grain (≥20 μm) Ge(111) formation, which is speculated to be due to suppression of random bulk-nucleation and domination of (111)-oriented interface-nucleation on SiO₂. To examine this speculation, Al ₂O₃-covered substrates are employed. This results in formation of Ge(100), due to energetically favorable (100)-oriented interface-nucleation on Al₂O₃. Consequently, large-grain (≥20 μm) Ge(100) and (111) are achieved on amorphous-insulators at 250 °C. This technique is very useful to realize flexible-electronics.