Growth promotion of Al-induced crystallized Ge films on insulators by insertion of a Ge membrane below the Al layer

Al-induced crystallization (AIC) enables low-temperature crystallization of amorphous Ge thin films on insulators. We investigated growth promotion of Ge thin films using Ge membranes (1-10 nm thickness) that are initially inserted below the Al layer. These Ge insertion layers enhanced supersaturation of Al with Ge, which results in low-temperature AIC (275 °C). However, thick (≥ 3 nm) insertion layers result in small grains because of the high nucleation frequency. A 1-nm-thick insertion layer accomplished a growth promotion and yielded large grains of over 100 μm in diameter. Moreover, electron backscatter diffraction measurement revealed that the AIC-Ge layer was highly (111) oriented. This low-temperature crystallization technique opens up the possibility for developing Ge-based electronic devices on inexpensive glass substrates, as well as on flexible polymer substrates.