Nano-Photonic Engineering of Low-Dimensional Materials for Optoelectronics

Low-dimensional layered semiconductors have emerged as promising platforms for next-generation optoelectronic, nanophotonic, sensing, and other technological applications, owing to their strong optical transitions, tunable band structures, and compatibility with nanoscale integration. However, weak room-temperature light-matter interactions, particularly radiative emission, coupled with poor light extraction efficiency and performance degradation in multilayer or bulk-like forms, severely limit device scalability and performance. Strategies that enhance optical coupling while preserving intrinsic electronic and vibrational properties are therefore essential to unlock their full potential. To address these challenges in multilayer semiconductors, this thesis develops nanophotonic engineering as a versatile, material-agnostic approach to boost emission and photodetection. It explores two complementary strategies: (1) dielectric nanophotonic gratings that enable resonance-assisted enhancement via tailored electromagnetic environments, and (2) "Nanolaminate" substrates, nanoscale electrostatic superlattices formed by periodic gating at the few-nanometer scale, to induce substrate-driven band-structure modification in overlying 2D materials. Three representative systems spanning bulk-like to few-layer regimes are unified under a one-dimensional dielectric grating platform: • Bulk-like gallium telluride (GaTe) • Thin multilayer indium selenide (InSe) • Few-layer tungsten disulfide (WS2) Frequency-domain finite-element simulations (COMSOL Multiphysics) guide the design of guided-mode and quasi-guided resonances, optimizing polarization dependence and moderate-Q conditions that balance near-field intensification with radiative out-coupling, critical for room-temperature broadband emitters. Fabrication employs atomic layer deposition, electron-beam lithography, and plasma processing, verified by atomic force and scanning electron microscopy. GaTe Results: Grating integration yields clear photoluminescence (PL) and Raman enhancements without peak shifts or linewidth broadening, confirming photonic rather than strain viii or defect origins. GaTe photodetectors exhibit enhanced photocurrent, stable I-V characteristics, and repeatable time-resolved photoresponse, matching simulated field localization. WS2 and InSe Progress: Nanofabrication successfully reproduces target geometries, with structural validation complete. Optical characterization (PL, Raman) is quantifying resonance effects. Nanolaminate Development: Sub-10 nm periodic oxide substrates (~8 nm lateral periodicity) have been fabricated and planarized, transferred to collaborators for 2D material integration, gating, and optoelectronic validation of quantum confinement and band modification. This thesis demonstrates that nanoscale electrostatic superlattices and resonant dielectric nanophotonics provide a robust, general framework to engineer optoelectronic responses in layered semiconductors, paving the way for high-performance devices across diverse material classes.