A comparison is made between the conventional non-selective vapour-liquid-solid growth of InP nanowires and a novel selective-area growth process where the Au-seeded InP nanowires grow exclusively in the openings of a SiO(2) mask on an InP substrate. This new process allows the precise positioning and diameter control of the nanowires required for future advanced device fabrication. The growth temperature range is found to be extended for the selective-area growth technique due to removal of the competition between material incorporation at the Au/nanowire interface and the substrate. A model describing the growth mechanism is presented which successfully accounts for the nanoparticle size-dependent and time-dependent growth rate. The dominant indium collection process is found to be the scattering of the group III source material from the SiO(2) mask and subsequent capture by the nanowire, a process that had previously been ignored for selective-area growth by chemical beam epitaxy.

A method to integrate nanowire‐based quantum dot single photon sources on‐chip using evanescent coupling is demonstrated. By deterministically placing an appropriately tapered III‐V nanowire, containing a single quantum dot, on top of a silicon‐based ridge waveguide, the quantum dot emission directed toward the taper can be transferred to the ridge waveguide with calculated efficiencies close to 100%. As the evanescent coupling is bidirectional, the source can be optically pumped in both free‐space and through the ridge waveguide. The latter configuration paves the way toward a self‐contained, all‐fiber, plug‐and‐play solution for applications requiring a bright on‐demand single photon source. Using InAsP quantum dots embedded in InP nanowire waveguides, coupling efficiencies to a SiN ridge waveguide of 74% with a single photon purity of 97% are demonstrated. The technique to demonstrate deterministic placement of single quantum emitters onto pre‐fabricated waveguides is used, an important step toward the fabrication of complex quantum photonic circuits.

Sources of quantum light that utilize photonic nanowire designs have emerged as potential candidates for high efficiency non-classical light generation in quantum information processing. In this review we cover the different platforms used to produce nanowire-based sources, highlighting the importance of waveguide design and material properties in achieving optimal performance. The limitations of the sources are identified and routes to optimization are proposed. State-of-the-art nanowire sources are compared to other solid-state quantum emitter platforms with regard to the key metrics of single photon purity, indistinguishability and entangled-pair fidelity to maximally entangled Bell states. We also discuss the unique ability of the nanowire platform to incorporate multiple emitters in the same optical mode and consider potential applications. Finally, routes to on-chip integration are discussed and the challenges facing the development of a nanowire-based scalable architecture are presented.

Site-selective epitaxy is used to deterministically control the nucleation site of a single quantum dot. A photonic crystal cavity is fabricated at the dot site for a true single quantum dot-cavity system which, by design, contains no background emitters. Cavity tuning at fixed temperature is used to measure the dot-cavity coupling over a large (>15$\hskip0.3em${}meV) detuning range using nonresonant excitation. The low-excitation spectra are modeled using a master equation model based on incoherent excitation. We find that pure phonon dephasing alone does not account for the observed nonresonant cavity emission and an additional cavity feeding mechanism, consistent with phonon-assisted dot-cavity coupling, must be included to reproduce the experimental spectra.

The far-field second-order radiation pattern from a wavelength-scale, InP-based photonic crystal microcavity that confines light in three dimensions is measured when excited on resonance by $300\mu \mathrm{W}$ of continuous-wave power from a laser diode. The measurements are accurately simulated using the finite-difference time-domain method, showing that both absorption and scattering play significant roles in determining the pattern of the radiation. The results show that the bulk second-order nonlinear susceptibility mediates the nonlinear process. In a separate set of experiments, a short-pulse laser is used to simultaneously populate two distinct modes of a similar microcavity. The detected second-order spectra show features due to the second harmonic generated by each mode, as well as the sum-frequency generation due to nonlinear intermode mixing. The key phenomena that determine the second-order response of these fundamentally small optical cavities are identified.