Purcell-Enhanced Single Photons at Telecom Wavelengths from a Quantum Dot in a Photonic Crystal Cavity

Quantum dots are promising candidates for telecom single photon sources due to their tunable emission across the different low-loss telecommunications bands, making them compatible with existing fiber networks. Their suitability for integration into photonic structures allows for enhanced brightness through the Purcell effect, supporting efficient quantum communication technologies. Our work focuses on InAs/InP QDs created via droplet epitaxy MOVPE to operate within the telecoms C-band. We observe a short radiative lifetime of 340 ps, arising from a Purcell factor of 5, owing to interaction of the QD within a low-mode-volume photonic crystal cavity. Through in-situ control of the sample temperature, we show both temperature tuning of the QD's emission wavelength and a preserved single photon emission purity at temperatures up to 25K. These findings suggest the viability of QD-based, cryogen-free, C-band single photon sources, supporting applicability in quantum communication technologies

Characterisation and Nanophotonic Device Integration of Droplet Epitaxy Quantum Dots Emitting in the Telecom C-Band

Quantum dots are well established as a source of single photons for applications in quantum cryptography. Having their emission in the telecommunication C-band (1530-1565 nm) is a desirable property as it allows for compatibility with existing low-loss fibre infrastructure. InAs/InP quantum dots grown by droplet epitaxy using metal organic vapour-phase epitaxy are the basis of the work presented in this thesis. Optical characterisation shows the quantum dots to emit in the C-band with narrow linewidths. Further growth development of quantum dots through capping layer engineering, which blue shifts emission wavelengths to the telecommunication O-band, and growth on InGaAs and InGaAsP interlayers, producing high density quantum dots, is presented with the results demonstrating a versatile growth method. Further characterisation of the quantum dots on distributed Bragg reflectors explicitly reveals the presence of undesirable background emission, the origin of which is explored. It is desirable to have high repetition rates for single photon sources which can be achieved with Purcell enhancement of quantum dot emission. A fabrication process for photonic crystal cavities in the InP material system is established which produces high Q factor emission with the aim to achieve enhanced quantum dot emission. Further fabrication development is presented which successfully integrates high density quantum dots on an InGaAsP interlayer in the photonic crystal cavities resulting in candidate quantum dots for Purcell enhancement in the telecommunication C-band