Epsilon-Near-Zero Modes Enabling Field-Effect-Tunable Perfect Absorption

Light absorption with efficiency above 99% is in demand for light harvesting, high-resolution, and optical coating technologies. Near-IR perfect absorption is achievable in deep subwavelength (λ/100) transparent conducting oxides (TCO) layers through the excitation of plasmon-polariton modes at epsilon-near-zero (ENZ) frequencies. We show the perfect absorption in ultra-thin (< 30 nm) TCO nanolayers due to the excitation of the bound and radiative ENZ modes. TCO nanolayers are deposited by atomic layer deposition and RF sputtering at elevated temperatures to control their ENZ frequency. We also show that single layer ultra-thin films could be layered to create a broadband perfect absorber. We discuss post-fabrication tuning of ENZ perfect absorption by biasing a TCO metal-oxide-semiconductor device. The absorption tuning is enabled by the ENZ modes in TCO nanolayers with the thickness comparable to the electron accumulation Debye length (~1nm). The post-fabrication tuning of about 20% of the full width at half maximum of the absorption peak is predicted for the devices under study.