A fundamental strategy is developed in this dissertation to enhance the light-matter interaction of ultra-thin films based on a strong interference effect in planar nanocavities, and overcome the limitation between the optical absorption and film thickness of energy harvesting/conversion materials. This principle is quite general and is particularly useful for the development of atomically-thin energy harvesting/conversion devices.

This dissertation systematically investigated the enhancement introduced by nanocavities, including the theoretical design of the nanocavities, experimental validation of the enhanced light-matter interactions, and application development based on this strategy.

In Chapter 2, the nanocavities are theoretically designed for different ultra-thin material systems. Phasor diagrams and the concept of topological darkness are introduced to better understand the design.

In Chapter 3, the enhanced light-matter interaction is validated experimentally. Stronger absorption is achieved and confirmed by the stronger photoluminescence signal.

In Chapter 4, an optoelectronic application of single-crystalline germanium nanomembrane photodetectors on foreign nanocavities was developed with field effect and spectral selectivity.

This dissertation aims to analyze the both the strength and the limit of this strategy based on nanocavities and paves the way towards miniaturization of optoelectronic devices.