Single-photon sources (SPS) are essential for secure quantum communication and quantum
computing. Solid-state systems based on quantum dots (QDs) are particularly attractive for emitting
pure, on-demand single photons, making them ideal candidates for flying qubits in quantum
key distribution protocols. Integrating a SPS into photonic circuits is a key step toward scalable
and "plug-and-play" quantum technologies. However, the SPS with the best performances (III-V
QDs) operate only at cryogenic temperatures, a significant drawback for practical implementation.
Alternatively, CdSe QDs (II-VI) are operational at 300 K and emit in the blue-green range,
thus allowing for free-space long-distance communication in seawater and air. The thesis aims
to develop an on-chip single-photon source that can operate at non-cryogenic temperatures. The
SPS consists of a CdSe QD embedded within a ZnSe nanowire (NW) shell grown by molecular
beam epitaxy on a patterned GaAs (111)B substrate. The nanowire geometry enhances light
extraction by acting as a single-mode waveguide, while the conical ending of the shell improves
emission control. We investigated the optical performance of the as-grown QD-NW emitter at
room temperature, achieving a promising brightness of 0.17 photons per pulse and antibunching
behavior with g(2)(0) < 0.3 within a reduced spectral window. However, the emission spectrum
at 300 K features overlapping broad lines, leading to a trade-off between brightness and
purity. At 6 K, we used a broadband filter to capture entirely the narrow exciton line and measured
directly the photon count rate with an avalanche photodiode. In addition, we observed
strong antibunching with a few percent purity through cathodoluminescence. Phonons impact
the performance of the SPS at high temperatures, where broad lines overlap, and at cryogenic
temperatures, where they reduce the photon indistinguishability. Understanding and controlling
the influence of phonons has increased the need for high-accuracy temperature measurements at
cryogenic temperatures. We present a calibration-free method to extract the local temperature
from the emission spectrum, which we used to investigate the heating effects induced by nonresonant
excitation. Additionally, we analysed the line-broadening mechanisms from cryogenic to
room temperature. An extension of the Huang-Rhys model is developed to analytically describe
the acoustic exciton-phonon interactions, accounting for multi-phonon processes. The model accurately
fits emission spectra from 6 K to 300 K using parameters obtained from low-temperature
data. The tapered nanowire shape is also an advantage for integration into a photonic device,
enabling efficient evanescent coupling when the emitter is positioned next to a waveguide. The
direct transfer using micromanipulators in a scanning electron microscope onto pre-fabricated
waveguides is very challenging due to the tiny size of the waveguide at an emission wavelength
of 550 nm. We developed a new approach, where the emitter is deposited within a large zone
and then embedded within a resist, which serves as a mask during waveguide etching. This
method significantly reduces the need for micro-manipulation and allows for promising prospects.
We used finite-difference time-domain simulations to support the design and fabrication of the
waveguides for optimal coupling.
Supervision :
Kuntheak KHENG & Gilles NOGUES