Low-Loss Infrared Ultrawide Type I Hyperbolic Metamaterial Based on III-V Semiconductors

While ionic crystals provide natural low-loss infrared hyperbolic resonances through the excitation of phonon polaritons (PhPs), the operational bandwidth of these materials is limited to a few hundred wavenumbers (cm^-1) or tens of millielectronvolts. Additionally, the integration of these materials with large-scale infrared optoelectronic devices presents its own challenges. In this work, we implement an ultrawide low-loss Type I hyperbolic metamaterial covering a spectral bandwidth of 2000 cm^-1 for wavelengths above 5.3 μm. We produced the hyperbolic metamaterial with a stack of intercalated heavily-doped InAs and undoped InAs epilayers grown by molecular beam epitaxy (MBE). The InAs epilayer was heavily doped with Tellurium to obtain electron concentrations of 10¹⁹ cm^-3 and the optical properties of this stack were measured by infrared ellipsometry. These materials were then dry etched to form one-dimensional (1D) square gratings (with periods from 2 to 10 μm) and modeled by finite element electromagnetic calculations (COMSOL). The models agree with measurements, showing 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 contained in the dielectric layers. This work demonstrates that highly subdiffractional light confinement can be achieved with a III-V metamaterial that can be integrated with III-V semiconductor infrared devices such as photodetectors and emitters at a large scale.