Person:

Spaepen, Frans

We demonstrate liquid‐metal‐mediatedhomoepitaxialcrystal growth of Ge on Ge(111) at temperatures in the range of 400–450 °C. Crystal growth proceeds by diffusion of Ge through a liquid layer, followed by precipitation onto the substrate by the vapor‐liquid‐solid mechanism. The liquid‐metal phase at the interface is a Au‐Ge alloy formed by initial deposition of a thin Au layer above the eutectic temperature. Ge vapor is provided by a molecular‐beam evaporator. The resulting films revealed high‐crystalline quality by in situ high‐energy ion scattering and channeling analysis and ex situ by cross‐sectional transmission electron microscopy.

In molecular-beam epitaxy a monolayer of Pb on the Si(111) surface induces single-crystal growth at temperatures well below those required for similar growth on a bare surface. We demonstrate that the suppression of dopant segregation at the lower temperatures attainable by Pb-mediated growth allows the incorporation of As donors at concentrations reaching a few atomic percent. When Pb and Si are deposited on an As-terminated Si(111) substrate at 350 °C, the Pb segregates to the surface without doping the Si film while the As is buried within nanometers of the substrate–film interface. The resulting concentration of electrically active As, 1.8×10²¹cm^–3, represents the highest concentration of As donors achieved by any delta-doping or thin-film deposition method.

High quality homoepitaxialgrowth of Si on Si(111) through an overlayer of Au is shown to occur at 450–500 °C, far below the temperature required for growth of Si of similar quality on bare Si(111). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry ion channeling measurements (χmin=2.2%). A distinct range of Au coverage (0.4–1.0 monolayer) results in the best quality epitaxy, with no measurable amount of Au trapped at either the interface or within the grownfilms. Cross‐sectional transmission electron microscopy reveals that in filmsgrown with Au coverages below and above the optimum range, the predominant defects are twins on (111) planes and Auinclusions, respectively.