Double-Layered Ge Thin Films on Insulators Formed by an Al-Induced Layer-Exchange Process

Abstract

A large-grained (111)-oriented Ge thin film is achieved on a SiO2 glass substrate using an Al-induced crystallization (AIC) technique. Low-temperature (350 °C) AIC of an amorphous Ge thin film (50 nm thickness) resulted in a self-organized double-layered structure of polycrystalline Ge layers. The top Ge layer consisted of randomly oriented small grains (1 μm diameter) with a high defect density; in contrast, the bottom Ge layer was of high quality. Based on the growth model, we annihilated the top Ge layer using preferential etching. The bared bottom Ge layer provided a (111)-oriented area fraction of 99% and an average grain size of 90 μm. This Ge layer appears promising for use in Ge-based thin-film devices, as well as a heteroepitaxial seed layer for group III–V compound semiconductors, aligned nanowires, and other advanced materials.