Characterization of Ge Films on Si(001) Substrates Grown by Nanocontact Epitaxy

Epitaxial growth of Ge films on Si substrates has been studied intensively because the properties of these films are promising for various kinds of applications, such as light emission in optoelectronic integrated circuits, a channel material in field-effect transistors, a material in high-speed optoelectronic devices (transistor or photodetector), and virtual substrates for GaAs films. In general, heteroepitaxial growth is difficult in systems with large lattice mismatch. In the case of Ge/Si, a lattice mismatch of ~4% can be a cause for introducing dislocations resulting in the degradation of film crystallinity. Recently, nanocontact epitaxy method was developed where elastically strain-relaxed nanodots (NDs) formed by ultrathin SiO₂ film technique were used as nucleation sites for the epitaxial growth. The nanocotact epitaxy brought the epitaxial growth of high quality and flat thin Ge films on Si substrates. In this study, we qualitatively analyze the crystallinity and strain of the Ge films formed by nanocontact epitaxy.