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We present our recent progress in the monolithic integration and epitaxial gain control of GaAs-based nanowire (NW) lasers on Si photonic platform. First, we describe the challenges in realizing vertical-cavity NW lasers on Si and SOI-based waveguides based on the stringent requirements for high gain, low-loss wave-guiding and coupling efficiency as illustrated by detailed numerical simulations. Consequently, we discuss bottom-up, epitaxial schemes for site-selective integration of individual GaAs NW lasers on planar Si and non-planar Si ridge waveguides under different geometries, demonstrating vertical-cavity NW lasers with remarkably low lasing threshold (< 20 µJ/cm2) and high spontaneous emission coupling factor (B > 0.2) under pulsed optical excitation. First experiments of individual NW-lasers with direct coupling of lasing emission into the underlying Si-ridge waveguides are also shown.
To further improve the threshold gain and lasing characteristics and achieve wavelength tunability, we further tailor the active gain media using low-dimensional systems embedded in the NW resonator cavity. Here, we particularly emphasize the challenges in the growth of GaAs-based cavities that incorporate coaxial GaAs-AlGaAs and InGaAs-AlGaAs multiple quantum well (MQW) heterostructures and illustrate even routes towards quantum-wire or quantum-dot based gain media. Finally, we provide a direct comparison of the lasing characteristics of 3D-bulk like GaAs NW lasers with coaxial NW-MQW heterostructure lasers, and show how the control of composition and structure of the MQW shifts the lasing emission to longer wavelengths.
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