NanoExcitonics: Implementing Basic Circuit Elements on 2-D Carbon System
Objectives: We explore exciton-based information transmission and manipulation by demonstrating two types of basic functionalities, waveguide and gate-controlled switch, using highly adaptive 2-D single-crystalline biased bilayer graphene (BBG) system that exhibits unique tunable band-gap and exciton binding energy under perpendicular electric field. The goal is to understand fundamental excitonic characteristics such as field-dependent effects, relaxation lifetime manipulation & engineering, and drift mobility which are vital to the implementation of ?excitonic circuits?.
Intellectual Merits: The research is based on innovations at several levels: (1) new concepts of excitonic waveguide and switch, (2) 2-D bilayer graphene as the material platform, (3) excitonic lifetime manipulation via a coupled quantum well structure to create indirect excitons, (4) a strategy to drive excitons with energy gradient made by local band-gap modulation, (5) acquisition and exploration of undiscovered excitonic features of band-gap opened BBG system, and (6) a method to in-situ measure the exciton mobility.
Broader Impact: This work aims at developing fast, highly-scalable, and energy-efficient information transmission using non-charge-based carrier. The research may also find broader applications such as highly efficient, adaptive solar photovoltaics and nanophotonics. The research opens opportunities for graduate and undergraduate students to gain multi-disciplinary experience in physics, optics, nano-devices, integrated circuits, and nanofabrication. An outreach program comprises on-site demonstration of nanoscale scientific and engineering techniques for K-12 students. The dissemination of research results by journal and conference publications and its inclusion in new curriculum developed will ensure broad scientific and educational impacts to general public community.
We explore graphene-based quantum structures which potentially offer the possibility of tunable band structures and formation of indirect excitons. The goal is to prepare specific testing structures and study key properties such as field-dependent effect, carrier relaxation, and transport characteristics. We developed the CVD growth process for direct assembly of few-to-monolayer graphene on hexagonal boron nitride (hBN). The critical processes would be used to construct graphene/hBN heterostructure which serves as the hosting quantum structure for excitons. We conducted material characterization on the synthesized 2D material samples and their respective heterostructures using various metrology tools (SEM, Raman, AFM, XPS, TEM, etc.) to acquire key information such as chemical composition, surface morphology, domain size, domain density, layer configuration, defectivity, etc. We constructed a graphene-hBN-graphene quantum heterostructure. Research has been conducted to understand the carrier transport dynamics. Reduction in inter-layer carrier scattering was observed in the non-AB-stacked graphene layers. Higher carrier mobility is observed, indicating the preservation of Fermi velocity. The results would serve as the foundation for studying exciton dynamics in graphene quantum wells. Training in material growth and nanofabrication has provided the participating graduate student with hands-on experience. The research has generated scientific understanding in material processing and physical properties of carbon nanostructures. While the research contributed to the advancement of knowledge in nanoscale science and engineering, the results could be potentially valuable in developing a new material for information processing in the "post-silicon" era, replacing silicon-based technology which is rapidly approaching its scaling limits. Graphene-based quantum structures could potentially impact applications in information processing and communication. The research may contribute to the implementation of future-generation electronics and cost-effective manufacturing.
