Abstract
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.
Highlights
Thin-film light absorbers have recently received considerable attention due to their straightforward fabrication, low cost, and wide range of potential applications, they have been restricted to the near infrared range or they are not tunable, or they are not perfect absorbers
If the absorption could be controlled in real time, multiple new applications can be envisioned such as high speed, high resolution, high grey scale displays, smart windows, and a variety of telecommunication devices to compete with those currently available
Metals have a plasma frequency in the UV-visible range. This significant change in the optical properties of n-InSb paves the way for many potential applications in optoelectronic devices such as electrically tunable color filters and high resolution real-time displays
Summary
The optimum ENZ material should have a real permittivity near zero in the visible or infrared region. Ε∞ = 1 and γ ≪ ωp, and the ENZ wavelength ωENZ, where the real part of the permittivity vanishes, coincides with the plasma frequency ωp according to the Drude model. At a fixed plasma frequency, an ENZ material with a smaller effective mass has a smaller carrier density according to the Drude model. This is favorable for carrier density modulation because the carrier density of ENZ materials can be increased with an applied negative voltage. Metals have a plasma frequency in the UV-visible range This significant change in the optical properties of n-InSb paves the way for many potential applications in optoelectronic devices such as electrically tunable color filters and high resolution real-time displays
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