Low-Loss Infrared ultrawide Type I hyperbolic metamaterial based on III-V semiconductors

In the infrared spectrum, polar dielectrics have been used to overcome the high losses associated with large free carrier absorption inherent to traditional metals. However, polar dielectrics, which rely on the excitation of phonon coupled charge oscillations, are limited to narrow operational bandwidths (<100cm^-1/10meV) due to the Reststrahlen effect. In this work, we demonstrate an ultrawide, low-loss, Type I hyperbolic metamaterial covering a bandwidth of 2000 cm^-1 for wavelengths larger than 5.3 µm. We achieve this by using molecular beam expitaxy to grow hyperbolic metamaterials that consist of intercalated heavily doped InAs and undoped InAs epilayers. The InAs epilayer was heavily doped with tellurium to obtain electron concentrations on the order of 10¹⁹ cm^-3 and the optical properties of this stack were measured by infrared ellipsometry. This structure was then dry etched to form one-dimensional (1D) gratings (with periods from 2 to 10 µm) and the structure was modeled using finite element electromagnetic field simulations in COMSOL. The simulations show agreement with experimental measurements and show the formation of hyperbolic plasmon polaritons at the same frequencies where experimental features were observed. Additionally, we have identified an epsilon-near-zero (ENZ) mode associated with long range surface plasmon polaritons confined to the dielectric layers of undoped InAs. We also show experimental limits to a commonly used effective medium approximation (EMA) used on similar structures. This work demonstrates that low loss high subdiffractional light confinement can be achieved with a III-V metamaterial that can be monolithically integrated into traditional III-V semiconductor infrared devices such as photodetectors and emitters at a large scale.