Trap-state whispering-gallery mode lasing from high-quality tin-doped CdS whiskers

High-quality surface tin-doped hexagonal CdS whiskers were synthesized by a well-controlled in situ source exchange chemical vapor deposition route. Under local light excitation, the detected microphotoluminescence from any positions along the length of these whiskers exhibits strong and multi-mode trap-state whispering-gallery (WG) mode emission. With elevating the pumping power, some of these WG modes start lasing at an ultra-low threshold, with lasing wavelength covering a broad range from ∼540 to ∼750 nm. Calculations using a plane-wave model of WG modes show that all these trap-state lasing modes are transverse magnetic polarized, which was well explained by a two-dimensional finite element simulation. The surface doped semiconductor structures have potential applications as low-threshold tunable micro/nanoscale lasers in optical storage, lighting, and optical communications.