For the first time, we report a complete control of crystal structure in InAs(1-x)Sb(x) NWs by tuning the antimony (Sb) composition. This claim is substantiated by high-resolution transmission electron microscopy combined with photoluminescence spectroscopy. The pure InAs nanowires generally show a mixture of wurtzite (WZ) and zinc-blende (ZB) phases, where addition of a small amount of Sb (∼2-4%) led to quasi-pure WZ InAsSb NWs, while further increase of Sb (∼10%) resulted in quasi-pure ZB InAsSb NWs. This phase transition is further evidenced by photoluminescence (PL) studies, where a dominant emission associated with the coexistence of WZ and ZB phases is present in the pure InAs NWs but absent in the PL spectrum of InAs0.96Sb0.04 NWs that instead shows a band-to-band emission. We also demonstrate that the Sb addition significantly reduces the stacking fault density in the NWs. This study provides new insights on the role of Sb addition for effective control of nanowire crystal structure.

No abstract

We report the observation of room-temperature optically pumped lasing modes from a single GaN pyramid microcavity on a metallic mirror. The mode at 367.2 nm exhibits a low threshold (0.4-0.5  MW/cm) and a narrow linewidth (0.054 nm), by which the quality factor can be estimated to be >6000. These lasing behaviors can be attributed to the specific wet-etching approach by selectively etching away defects and pyramid geometry with bottom Ag reflectors for better light confinement. Optical resonances in these pyramids are further investigated in combination with three-dimensional finite-difference time-domain simulations.

No abstract