Single-photon emitters (SPEs) are quantum systems that can produce individual photons when excited. These photons can be manipulated in their polarization states to encode quantum bits, which are the quantum-mechanical analogs of classical bits. SPEs are critical to the development of quantum information technology applications, including quantum communication, computing, and sensing. Despite their importance, there are currently no solid-state SPEs that meet the requirements for large-scale applications. Researchers have explored various materials hosts, including quantum dots, carbon nanotubes, and bulk semiconductors, but many challenges remain. For example, producing scalable and integrated SPEs with tunable wavelengths, high clocking rates (brightness), and single-photon purity at room temperature is still an ongoing research goal.
In recent years, there has been significant research interest in single-photon emitters (SPEs) in two-dimensional (2D) Van der Waals (VdW) materials. Most research in this area has focused on SPEs in multilayer insulating hexagonal boron nitride (hBN), which can be operated at room temperature, and monolayer tungsten diselenide (WSe2), which is a direct bandgap semiconductor. The SPEs in hBN are derived from defect emission, while those in monolayer WSe2 stem from either defect or strain-bound excitons. Despite this promising research, there are critical challenges that impede the development of these SPEs. For example, hBN is an insulator with a band gap of 6.0 eV, which limits electrical control, and controlling defects is difficult. Additionally, the photo-stability of monolayer WSe2 is vulnerable to environmental fluctuations, such as surface contaminants.
Multilayer gallium selenide (GaSe) is another 2D Van der Waals (VdW) SPE host, and the initial experimental observation of GaSe SPEs was reported by Tonndorf. et al. in 2017.2,3 However, GaSe SPEs have received less attention compared to hBN and WSe2 for several reasons. Firstly, early reports2,3 show that GaSe SPEs arising from defects are less brighter than SPEs in WSe24 and hBN.5 Secondly, increasing the laser power for brighter GaSe SPEs would cause the formation of biexcitons, which degrades the single photon purity.2 Since 2017, to the best of our knowledge, there have been no further experimental studies conducted on overcoming those challenges to improve the performances of GaSe SPEs.
In this dissertation, I present three research projects focused on addressing the challenges of developing single-photon emitters (SPEs) in multilayer gallium selenide (GaSe). First, I achieved localized bright and stable GaSe SPEs in multilayer GaSe through the manipulation of nanoscale strain. Second, I performed below-diffraction limit hyperspectral imaging of strain-localized GaSe SPEs through cathodoluminescence and demonstrated the wide spectral range tunability, significant enhancement of emission intensities controlled by nanoscale strain, as well as the robust spectral stability of GaSe SPEs. In the last project, I demonstrated a 30%-50% improvement in emission intensities of GaSe, converted non-SPEs to SPEs, and increased operating temperatures from 23 K up to 85K above cryogenic temperature through electrostatic doping. The research works in this dissertation lays a crucial foundation for future fundamental studies and the development of GaSe SPEs and their analogues.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49084 |
| Date | 23 July 2024 |
| Creators | Luo, Weijun |
| Contributors | Ling, Xi, Liang, Liangbo |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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