Abstract
Transparent conducting oxides have recently gained great attention as CMOS-compatible materials for applications in nanophotonics due to their low optical loss, metal-like behavior, versatile/tailorable optical properties, and established fabrication procedures. In particular, aluminum doped zinc oxide (AZO) is very attractive because its dielectric permittivity can be engineered over a broad range in the near infrared and infrared. However, despite all these beneficial features, the slow (> 100 ps) electron-hole recombination time typical of these compounds still represents a fundamental limitation impeding ultrafast optical modulation. Here we report the first epsilon-near-zero AZO thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation and recombination time below 1 ps) and an outstanding reflectance modulation up to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the result of a low temperature fabrication procedure promoting oxygen vacancies and an ultra-high carrier concentration. As a proof-of-concept, an all-optical AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and operating at THz frequencies is numerically demonstrated. Our results overcome the traditional "modulation depth vs. speed" trade-off by at least an order of magnitude, placing AZO among the most promising compounds for tunable/switchable nanophotonics.
Highlights
Introduction iTransparent conducting oxides (TCOs) Based Tunable Nanophotonics With the advent of plasmonics and metamaterials, it has become of paramount importance to develop new CMOScompatible platforms possessing metal-like behavior and great optical transparency
We develop a CMOS-compatible, oxygen-deprived aluminum doped zinc oxide (AZO) film which achieves both of the desired properties simultaneously
In order to further investigate the applicability of our oxygen-deprived AZO, we propose a scheme for an all‐optical plasmonic modulator using CMOS-compatible materials which achieves 3 dB modulation in 7.5 μm with less than 0.1 dB/μm insertion loss
Summary
Introduction iTCO Based Tunable Nanophotonics With the advent of plasmonics and metamaterials, it has become of paramount importance to develop new CMOScompatible platforms possessing metal-like behavior and great optical transparency. The optical properties of these materials can be tailored in many ways such as by altering the deposition conditions, through post‐processing steps (e.g. annealing) and/or by varying the material stoichiometry [8, 10, 12,13,14,15,16]. This enables one material to serve several roles. A lowly doped TCO can be used as a dielectric material in the near infrared (NIR) range with an index near that of glass, while a highly-doped TCO can serve as a metal to support surface plasmon oscillations [17, 18]
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