Electron Microscopy characterization of the Interface between a (111)-Si Substrate and GaAs Nanowires grown by Self-Catalysis by MBE

Abstract

The interface between zincblende (ZB) GaAs nanowires (NWs) grown by selfcatalysisin MBE, and a 111-Si substrate was studied. This was done with thepurpose of determining if any defects, stacking fault, twins, different phases,or other irregularities were present at the interface. Three sample preparationtechniques were adapted to be able to characterize the interface (micro-cleavage,microtomy, and focused ion beam), and these are compared and analyzed. Bycomparing the results from the different techniques, artifacts could be identifiedor ruled out. The NWs were found to grow epitaxially on the surface, with {1-10}side facets and a hexagonal shape. At the NW-substrate interface, a transitionzone of 5 15 nm, where most of the mismatch strain is thought to be relaxed,was seen for several wires. In parts of other interfaces, an amorphous layer wasobserved. Parasitic crystal growth on the substrate was also studied. The crystalgrowth was ZB with twinning in the {111} direction. Planar defects in the {1-1-1} is also common, and these are linked to differences in strain at the interface. Thesame effect may apply for NWs.