Quantum dot engineering in III-V nanowires for applications in photonics

Semiconductor quantum dots (QDs) have emerged over the past decade as a pivotal solid-state platform for on-demand quantum light sources, fundamental for a wide range of quantum technology applications. In particular, QDs emitting within the telecommunication bands (1.3 – 1.55 µm) are of great interest for quantum communication, as this wavelength range coincides with the low-loss window of standard optical fibers, essential for long-distance quantum signal transmission. Among the different material platforms explored so far, InAsₓP1-x QDs embedded in InP nanowires (NW-QDs) stand out as a promising platform, offering precise control over QD size, composition, and density within a scalable growth scheme. Although many milestones have been demonstrated in these NW-QDs, key challenges remain, most notably maintaining crystal phase purity and source brightness when extending QD emission into the telecom range. In conventional wurtzite (WZ) InP NWs grown along the <111> direction, the achievable crystal phase purity is limited by the catalyst diameter, which in turn constrains the QD geometry and emission wavelength flexibility. In this thesis, these challenges are addressed through the investigation of InAsₓP1-x QDs embedded in InP NWs grown along the <100> direction, characterized by a zincblende (ZB) crystal phase. The ZB structure is intrinsically less sensitive to stacking faults formation, allowing greater flexibility in achieving defect-free QDs of larger planar dimensions and tunable emission across the telecom bands. Using Chemical Beam Epitaxy (CBE), the growth parameters are optimized to obtain straight, phase-pure InAsₓP1-x/InP heterostructure NWs and realizing QDs with emission tunable up to the third telecom window. Furthermore, an in-situ grown, monolithic waveguide was developed solely through vapor–liquid–solid (VLS) growth, guided by finite-difference time-domain (FDTD) simulations. The optimized geometry leads to a significant enhancement of the photon extraction efficiency, experimentally confirmed by an order-of-magnitude increase in photoluminescence intensity. Additionally, this work explores the control of crystal phase purity in conventional WZ InP/InAsₓP1-x NWs grown along the <111> direction. It will be demonstrated that the ternary alloy composition plays a key role in stabilizing the crystal phase, with pure-phase WZ structures achieved by tuning the As content. The phenomenon is investigated both experimentally and theoretically. These findings provide a viable route to overcome the well-known diameter-dependent phase purity limitation, extending the design space for WZ NW-QDs emitters. Overall, the results presented in this thesis establish ZB InAsₓP1-x NW-QDs as a flexible and efficient platform for telecom-compatible light sources. The demonstrated control over crystal structure, emission wavelength, and integrated waveguide geometry represents a significant step forward toward scalable, fiber-coupled single-photon emitters for next-generation quantum communication technologies.