Study of Optical Coupling of Excitons & Trions in Colloidal Quantum Wells with Photonic Metasurface Resonators & Microcavities

Abstract

Quantum photonics held immense potential for applications such as quantum metrology and cryptography. In this thesis, we investigated the optical properties of colloidal quantum wells (CQWs) integrated with photonic metasurface resonators (MSRs) and microcavities to harness the unique properties of excitons (X⁰) and trions (X⁻). The research is organized into three chapters, each addressing critical advancements in this field. In the first part, a unique photonic platform that significantly enhanced the brightness and narrowed the emission linewidth of nanoscale quantum emitters was developed. Here, we combined CQWs composed of Cadmium Selenide (CdSe) with a guided mode MSR, consisting of a periodic arrangement of holes in a square-lattice geometry, fabricated on a SiN slab-waveguide platform. As a result, we observed an enhancement in emission intensity, accompanied by an astounding 95% reduction in linewidth of the out-of-plane emission. Similarly, the in-plane guided emission captured at sample’s edge was found to exhibit a significantly reduced linewidth of 5.67 meV as compared to the natural linewidth of 81.4 meV. We demonstrated long-range exciton-mediated photon transport via in-plane slab waveguide modes. Theoretical frameworks explained experimental observations, including MSR-modified Lamb shifts and Purcell decays, highlighting the platform's promise for on-chip photonic quantum information processing. Next, we selectively enhanced X⁻ and X⁰ emission characteristics in CdSe CQWs integrated with a MSR using temperature as a tuning parameter. Such wavelength selective emission enhancements were realized based on the spectral overlap between the narrow-band MSR response and broader X⁻ and X⁰ emissions from CQWs Time-resolved photoluminescence measurements confirmed Purcell enhancement at resonant temperatures, underscoring the role of MSR coupling in boosting emission efficiency. The asymmetric MSR design induced linear polarization in coupled emissions, offering novel control for nanophotonic devices. Lastly, we attempted to enhance light hole (LH) and heavy hole (HH) absorption in CQWs by adjusting layer thickness integrated with a distributed Bragg reflector (DBR) structure. Results showed significant LH and HH absorption enhancements when CQW layer thickness aligns to satisfy the interference condition, utilizing resonant cavity effects. Despite enhanced absorption, photoluminescence revealed a forbidden conduction band (CB) to LH transition due to selection rules. A close cavity system with core/shell CQWs achieved amplified spontaneous emission (ASE) and LH emission at higher thresholds, underscoring DBR integration's potential for fine-tuning optical properties.