Cd_xPb_{1- x}S alloy nanowires and heterostructures with simultaneous emission in mid-infrared and visible wavelengths

Alloying of CdS and PbS could potentially provide an important semiconductor with a wide range of bandgaps, with bandedge emission from mid-infrared to visible green, for various optoelectronic applications. We investigate the possibility of CdPbS alloy formation in nanowire and nanobelt forms, especially the dependence of alloy composition on two different cooling routes. Our results show that rapid cooling immediately after the growth phase can lead to a high-quality uniform alloy with Cd composition larger than possible at thermal equilibrium and by natural cooling. On the contrary, unassisted natural cooling leads to the formation of axial or core-shell heterostructures, containing segments with pure CdS and CdPbS alloys with lower Cd content than through rapid cooling. Such heterostructures with green and mid-infrared emission provide simultaneous access to two widely separated wavelengths from a single monolithic structure and can be important for many applications. Our results can help identify strategies for growing nanostructures with uniform alloy of high Cd incorporation, core-shell structures with shell serving as a passivating or protecting layer, or interesting longitudinal heterostructures. Both various heterostructures and uniform alloys of these materials could be important for high-efficiency solar cells, novel detectors, and nanolasing in wide spectral ranges.