Microcrystal-Induced Crystallization Effect for High-Quality Germanium/Silicon Heteroepitaxial Nanofilms

Material crystallinity is paramount in determining the photoelectric performances and device applications. Moreover, a high-quality crystalline layer, especially a multilayer film or a heteroepitaxial film, is continuously explored to cater for low defect density and ultrahigh structure integrity as well as low cost, yet is challenging. In this study, the crystallization effect of Ge/Si heteroepitaxial nanofilms (<100 nm) is investigated in detail to pursue low crystallization temperature and the underlying mechanism. It is demonstrated that the crystallinity and the crystallographic orientation of the underlying layer can tune the crystallization behavior of the upper-layer film. This interfacial inducing effect on crystallization originating from the buffer layer is verified on inversed architecture of the Si/Ge film and is proposed to be the microcrystal-induced crystallization (MIC) effect. Based on a point-defect model describing an order/disorder microcrystal structure, the MIC effect is flexibly supported by the results of binding energy and charge transfer via first-principles calculations for the first time. This work also provides a facile strategy and theoretical support to prepare high-crystalline multilayer films or intact crystals for urgent microelectronics and optoelectronics applications.