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 lambda(ENZ)/100. Perfect absorption in the wavelength range of 600 nm to 2 mu m may be achieved for unpatterned indium tin oxide (ITO) nanolayers with an electron density of 5 x 10(20) to 2 x 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.