Nitrides have been a mature class of material to the light emitting diode (LED) industry for years with high quantum efficiency at room temperature, and have many outstanding properties including doping characteristic, robustness, and wide optical emission range. GaN nanowire is an emerging structure for the next-generation LED due to its outstanding crystal and optical properties. Nitride quantum dots embedded in nanowires (dot-in-a-wire) have recently become a focus due to the advantage of dislocation-free crystal structure and the suppression of quantum confined Stark effect (QCSE) by taking advantage of the free-surface relaxation of lattices. However, challenges remain such as wire alignment, phase segregation, the formation of basal plane stacking faults due to the growth-temperature variation in the hetero-structure, and the density and diameter control of the nanowires.  In this talk, fabrication of single dot-in-a-nanorod with small rod diameter (9~35 nm) and low rod-density (< 10⁸ cm^-2) fabricated without extensive processing steps will be reported. Excitation power-dependent PL spectrum of single QD reveals multi-excitonic peak with 0.75 meV (exciton) and 0.33 meV (trion) blue-shift across 3 orders of magnitude increasing power, indicating the present system is spectrally stable and nearly free of QCSE, due to the strain relaxation induced by free surface of small rod diameters. The emission of single quantum dot is fully polarized with degree of polarization around 90% and with a high working temperature. Optical property is further investigated by multiple methods including scanning near-field optical microscopy for the single dot-in-a-wire emissions. Diffusion length of photo-excited excitons in the nanowire is estimated and related to the surface effect of the nanowire which is crucial for the application of naon-devices.  For the growth of nanowire, the nucleation mechanism crucial for the device fabrication remains unclear. We present direct evidences which show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands and the Si(111) substrate surface. Accordingly, the growth and density control of low density, uniform, and narrow GaN nanorods is exploited by a ‘narrow-pass’ approach that only narrow nanorod can be grown, and wide rods merge to the surroundings automatically. A nucleation scenario based on statistical results will be reported as a tentative blueprint for the fabrication of uniform single nanorods. 

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