Transmission electron microscopy dislocation study of Ge-on-Si films supporting a new lattice-mismatch relaxation mechanism

Abstract

We present an in-depth study of Ge(Si), Ge with a potential for some Si, films grown laterally on Si using plan-view transmission electron microscopy (TEM). Earlier, we reported that high-quality Ge films can be grown on Si by using a metal-catalyzed, lateral epitaxial growth technique. In particular, the lateral overgrowth areas of the films demonstrated a much lower dislocation density compared to the first-to-nucleate areas in cross-sectional TEM. Here, we further studied both the film and dislocation morphologies in plan-view TEM to understand more about the growth process and relaxation mechanism. For a film closely studied in plan-view TEM, the center of the film was thicker and contained much more dislocations and there were some thickness variations near the edges. For the central thicker region, the composition was analyzed and three areas within the film were found to be relatively Si-rich and are, therefore, likely to be one of the first-to-nucleate parts of the film. We investigated the dislocation morphology in depth in this film, counting dislocation numbers in both the Si-rich/first-to-nucleate and lateral overgrowth areas of the film. This study indicates that the Si-rich areas contained high dislocation densities (108 or 109 #/cm2), at least one or two magnitudes higher than that of the lateral overgrowth areas, and many dislocations were found to originate from them and extend toward the edge of the film. The observations in this study provide more evidence to support the idea that a new relaxation is present to enable high-quality, lateral Ge growth on Si.