Electrically tunable perfect light absorbers as color filters and modulators

Methods for spectrally controlling light absorption in optoelectronic devices have attracted considerable attention in recent years. It is now well known that a Fabry-Perot nanocavity comprising thin semiconductor and metal films can be used to absorb light at selected wavelengths. The absorption wavelength is controlled by tailoring the thickness of the nanocavity and also by nanostructure patterning. However, the realization of dynamically tuning the absorption wavelength without changing the structural geometry remains a great challenge in optoelectronic device development. Here it is shown how an ultrathin n-type doped indium antimonide integrated into a subwavelength-thick optical nanocavity can result in an electrically tunable perfect light absorber in the visible and near infrared range. These absorbers require simple thin-film fabrication processes and are cost effective for large-area devices without resorting to sophisticated nanopatterning techniques. In the visible range, a 40 nm spectral shift can be attained by applying a reasonable bias voltage to effect the color change. It is also shown that these electrically tunable absorbers may be used as optical modulators in the infrared. The predicted (up to) 95.3% change in reflectance, transforming the device from perfectly absorbing to highly reflective, should make this technology attractive to the telecommunication (switching) industry.