Tapering and crystal structure of indium phosphide nanowires grown by selective area vapor liquid solid epitaxy

We present a study of indium phosphide nanowires grown by the selective area vapor liquid solid technique using metalorganic molecular beam epitaxy. Transmission electron microscopy revealed that nanowires grown at a temperature of up to 450 °C had a pure wurtzite structure, but at 480 °C a mixed wurtzite-zincblend structure was obtained. We also accurately measured the migration length of growth precursors along the side facets of the nanowires by monitoring the length of the non-tapered section of the nanowire adjacent to the gold catalyst. The migration length was found to be of the order of 0.3-0.7 µm and to depend on the diameter of the nanowire. Up to the growth temperature of 450 °C the migration length was temperature independent, but it increased dramatically to more than 2 µm when the nanowires were grown at 480 °C. Possible explanations for the observed effects are suggested.