Ultra-long distance carrier transportation in bandgap-graded CdS _x Se _1−x nanowire waveguides

Carrier transportation in semiconductor nanowires is essential for their application in integrated opto-electronic devices. Therefore, it is of importance to manipulate and enhance the transportation performance of nanowires through micro-nano scale engineering. In this work, the carrier dynamics of the waveguides in the bandgap-graded CdSxSe1-x nanowires is systematically investigated. By developing a spatially separated time-resolved photoluminescence spectroscopy system, the dependence between the propagation distance/direction and the dynamics of the bandgap gradient driven long-range carrier transportation of the nanowires is characterized. In the meantime, the dynamics of carrier concentration driven spontaneous diffusion is also characterized to be compared to. It is found that the continuous carrier transportation which is driven by the bandgap gradient is the dominant process in the active waveguide, where the maximum transportation distance of 100 μm is detected. Such a transportation distance is up to ∼8-fold larger than the spontaneous carrier diffusion distance in the bandgap-graded CdSxSe1-x nanowires. The ultra-long carrier transportation capability in the bandgap gradient nanowires makes them ideal structures for applications in long-distance photo-energy delivery and micro-nanoscale opto-electronics.