Engineering quantum emitters in WSe2 films on metal films

Abstract

The discovery of single photon emitters (SPEs) in van der Waals materials, in particular, from point defects in Tungsten Diselenide (WSe2) and hexagonal Boron Nitride (hBN), has sparked tremendous research interest in the utilization of these materials as quantum light sources. The sparse distribution of these emitters was an initial roadblock towards practical device applications. This has been circumvented by transferring the host material on specially patterned substrates, which facilitates a spatially deterministic creation of quantum emitters. The integration of WSe2 with various plasmonic resonators provides the dual advantage of deterministic fabrication of SPEs, along with a large enhancement in the emission intensity. In this thesis, we discuss the possibility of transferring monolayer TMDs directly on metal films towards enhancing the brightness and purity of single photon emission from WSe2 monolayers. Enhanced purity manifests as a significant quenching of the free exciton peak on the metal and a surprising enhancement of narrow defect peaks. Based on simulation and experimental data, we conclude that the roughness of the metal film plays a crucial role in the enhancement of the sharp defect peaks. The enhanced defect peaks on the metal film also show a noticeable narrowing of the Gaussian linewidth - which we conclude to be a manifestation of reduced spectral diffusion in the presence of the metal film. Also, sandwiching a thin dielectric between the metal and TMD serves to obscure the sharp features, as the entire PL spectrum enhances. From the perspective of applications in quantum photonic technologies, electrical excitation of SPEs is a more attractive option. In the final part of the thesis, I discuss ways in which the project can be taken forward with regard to achieving electrically triggered quantum light emission. I also propose some methods in which the single photon emission can be tuned with respect to energy and brightness.