Bandgap engineering of 2D semiconductors for quantum and optoelectronic technologies

Abstract

Two-dimensional semiconductors such as transition metal dichalcogenides and thin films of gallium nitride are promising platforms for applications in quantum and optoelectronic technologies. These materials can host quantum emitters, which are key components of many quantum devices that rely on light in some form. Quantum emitters are atom-like states embedded in solid materials that emit single photons in narrow energy bands. In two-dimensional semiconductors, quantum emitters have been realized by inducing localized strain or by dilute doping, both of which create in-gap defect states and locally modulate the band gap. Understanding how these processes alter the band structure of two-dimensional semiconductors can provide insight into the formation mechanisms of quantum emitters, ultimately enabling greater control of their properties for technological applications. This dissertation presents work that (i) investigates the optical properties at the interface of a transition metal dichalcogenide lateral heterostructure that may host quantum emitters, (ii) induces quantum emitters in nanoindented transition metal dichalcogenides, and (iii) reports narrow, sub-bandgap emission from thin films of uranium-doped gallium nitride, evidencing a new set of potential actinide-based quantum emitter states. Room and low-temperature spectroscopies, sub-diffraction-limited spectroscopy, and atomic force microscopy were utilized to perform this work. To grow the novel uranium-doped gallium nitride molecular beam epitaxy was used. Together, these studies advance understanding of how strain-induced techniques, such as nanoindentation, can be used to control quantum emitter formation. Furthermore, this work introduces two novel material systems--the lateral heterostructure interface and uranium-doped gallium thin films--as new platforms to explore for new solid-state quantum emitters.