Low-threshold nanowire laser based on composition-symmetric semiconductor nanowires.

Low-threshold nanoscale lasers are attractive for their promising applications in highly integrated photonic devices and systems. Here we report the controllable growth of composition-symmetric CdS(x)Se(1-x) nanowires by using a multistep thermal evaporation route with moving sources. Microstructure analyses reveal the obtained wires are high-quality single crystals with the composition gradually changed from the center toward their both ends. Under laser illumination, these wires exhibit symmetrical color distribution along the length direction, with red at the center and green at the both ends. Optically pumped lasing is realized at room temperature using these composition-symmetric nanowires, with the threshold several times lower than that of composition-homogeneous wires. This new nanowire structure will have potential applications as low-threshold nanoscale lasers in integrated nanophotonics.