We demonstrate a novel growth technique, metal-catalyzed, lateral epitaxial growth, to grow Ge films laterally on Si with reduced threading dislocation densities (TDD). In contrast to traditional planar film growth on Si, this technique starts with a small crystal nucleation at a specific position on Si followed by Ge lateral film growth. In plan-view and cross-sectional transmission electron microscopy micrographs, high-density threading dislocations were found to be present in the initial growth areas, while the lateral overgrowth areas demonstrated substantially reduced TDD or even defect-free areas. Furthermore, the X-ray diffraction results showed that the films were fully relaxed and mostly pure Ge. Full relaxation and low TDD Ge films are two surprising results given that the growth occurred at a low temperature (375 °C), which cannot be understood with the current misfit dislocation nucleation and glide model of film relaxation. For these reasons, we suggest the presence of a new relaxation mechanism one in which the strain induced by the lattice mismatch can be relaxed by extending preexisting misfit dislocations and that lateral growth can “build in” dislocations as it grows.

A lateral epitaxial growth technique has been demonstrated to grow high-quality Ge micro-films on Si at low temperatures using the vapor–liquid–solid mechanism. These Ge films were grown within a confined structure to foster horizontal growth in the presence of Au catalyst. In this work the size and geometric shape of the Au catalyst were shown to impact the film size and morphology. In particular, a general trend was observed, as the size of Au catalyst increased the Ge film size initially increased as well until the Ge film size plateaued and eventually decreased. This phenomenon is described by a model, which is a function of Au catalyst size and GeH4 dose and can be used to estimate the final Ge film size. In general, a large-sized Au catalyst absorbs more Ge because of its large vapor–liquid interface but it also requires more Ge to saturate the liquid, and therefore this fact results in a peak in the plot of the Ge film size versus the Au size. In addition, a large GeH4 dose due to more absorption of GeH4 leads to multiple nucleation sites in a small Au catalyst, while a micro-crucible with a larger Au volume or reduced vapor–liquid interface can help to realize single nucleation. These results helped in designing two-opening Au catalysts with asymmetric sides, which preferentially nucleates a large crystal near the wider side.

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.

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