Polarization-Independent, Tunable, Broadband Perfect Absorber Based on Semi-Sphere Patterned Epsilon-Near-Zero Films

• ENZ and LSPR modes in corrugated ITO films are designed for broadband perfect absorption. • Nanoparticle size and plasmonic frequency can tune the absorption bandwidth and location. • Polarization-independent broadband light absorption (A > 98%) can be obtained below 20°incident angle. • The device is compatible with self-assembly technology, enabling low-cost, large-area fabrication. Epsilon-near-zero (ENZ) optical materials, whose real part of the dielectric constant crosses zero, have been demonstrated to enhance linear and nonlinear optical responses in the ENZ region. Here, a new broadband light absorption design concept based on the coupling of ENZ and localized surface plasmon resonance (LSPR) modes is proposed. It is verified by a single-layer semi-sphere patterned indium tin oxide (ITO) film based on large-area and low-cost self-assembly technology. Simulation and experimental results show that the 91 nm thick ITO film on the two-dimensional microsphere array can simultaneously excite the ENZ and LSPR modes without complex coupling structures, which enable >98% light absorption in the range of 1435–1680 nm. The perfect absorber based on a corrugated ITO film has typical polarization-independent, large-angular-spectrum, adjustable-absorption-bandwidth, and field-enhanced resonance absorption characteristics. These findings provide a new design solution for low-cost broadband perfect absorbers based on ENZ materials, which have wide prospects for application in near-infrared sensors, photoelectric detection, and ENZ photonics.