Field-Effect Tunable and Broadband Epsilon-Near-Zero Perfect Absorbers with Deep Subwavelength Thickness

We report perfect light absorption due to the excitation of bound and radiative p -polarized optical modes in epsilon-near-zero (ENZ) conducting oxide nanolayers with thicknesses as thin as λ ENZ /100. Perfect absorption in the wavelength range of 600 nm to 2 μm may be achieved for unpatterned indium tin oxide (ITO) nanolayers with an electron density of 5 × 10 20 to 2 × 10 21 cm –3 . Multilayer stacks of ITO nanolayers with a gradient of electron densities and optimized thicknesses enable broadband perfect absorption. The postfabrication tuning, of the perfect absorption wavelength, of 32 nm is achieved in a metal-oxide-semiconductor (MOS) geometry with applied voltage of 5 V. Such ultrathin and tunable broadband perfect absorbers have many potential applications in nonlinear flat ENZ optics, thermophotovoltaics, hot-electron generation in the ENZ regime, and other fields.