Mixed Phase Confirmation of InAsxP1−x Nanowire Array Using Modified Reciprocal Space Mapping

In most cases, despite the bandgap tuning flexibility of ternary semiconducting nanowires, phase mixing during nanowire growth is inevitable because of the surface energy competition between the bulk stable zinc blende (ZB) and the metastable wurtzite (WZ) phase. As the electronic structure of the grown nanowires depends on not only the composition but also the crystal structure of the nanowires, careful characterization of the phase mixing phenomena in the nanowires is significant. However, because most of the phase analysis of grown nanowires relies on transmission electron microscopy (TEM), the phase analysis should be local, requires destructive sample preparation, and has a high time cost. Here, we developed a modified reciprocal space mapping method exploiting laboratory-based high-resolution X-ray diffraction (HR-XRD) for phase analysis in a one-dimensionally grown nanowire array on a (111) Si substrate in one measurement sequence. The main difficulty of phase analysis in a nanowire array using HR-XRD is the overlap of the diffraction peaks resulting from the structural similarity between ZB and WZ. Using the proposed method, we could successfully separate the diffraction overlapping of the WZ and ZB phases and reveal the lattice constants, composition, and effect of the strain of an InAsxP1−x nanowire array corresponding to the growth conditions in one measurement sequence. We also found that the crystallinity of metastable WZ was considerably lower than that of the bulk stable ZB in InAsxP1−x and that a phase fraction of WZ and ZB in InAsxP1−x nanowire arrays could be tuned by adjusting their composition and diameter.