Role of microstructure on optical properties in high-uniformity In _1-xGa_xAs nanowire arrays: Evidence of a wider wurtzite band gap

Accessing fundamental structure-property correlations in ternary semiconductor nanowires is a challenging endeavor often limited by large compositional inhomogeneities. Here, we investigate strongly periodic In _1-xGa_xAs nanowire arrays grown on Si with very high compositional uniformity to identify the role of microstructural features (crystal phase and stacking order) on the phonon and optical properties via transmission electron microscopy, Raman, and photoluminescence spectroscopy. Depending on Ga content and growth kinetics, we show that the nanowire microstructure changes consistently from a wurtzite-dominated stacking to a disordered layer stacking, with broadened Raman modes, upon tuning the composition from In-rich to more Ga-rich In_1-xGa_xAs. Consequently, higher-quality wurtzite stacking leads to enhanced photoluminescence emission intensities and, most strikingly, a blue-shift in the emission energy of ∼30-40 meV with respect to the bulk In _1-xGa_xAs phase. This finding supports the theoretically predicted larger band-gap energy of composition-tuned wurtzite-type In _1-xGa_xAs.