The long free-space wavelengths associated with the mid- to far-infrared spectral range impose significant limitations on the form factor of associated optic and electro-optic components. Specifically, current commercial optical sources, waveguides, optical components (lenses and waveplates), and detector elements are larger than the corresponding diffraction limit, resulting in reduced image resolution and bulky optical systems, with deleterious effects for a number of imaging and sensing applications of interest to commercial, medical, and defense related arenas. The field of nanophotonics, where the ultimate objective is to confine and manipulate light at deeply subwavelength, nanometer length scales, offers significant opportunities to overcome these limitations. The demonstration of nanoscale optics in the infrared can be achieved by leveraging polaritons, quasiparticles comprised of oscillating charges within a material coupled to electromagnetic excitations. However, the predominant polaritonic materials and the characterization techniques and methods implemented for measuring these quasiparticles in the mid- to far-IR require a different approach with respect to similar efforts in the ultraviolet, visible, and near-IR. The purpose of this tutorial is to offer an overview of the basic materials, tools, and techniques for exciting, manipulating, and probing polaritons in the mid- to far-infrared wavelength range, providing a general guide to subwavelength and nanoscale optics for those entering this exciting and burgeoning research field.
We demonstrate strong, narrow-band selective absorption and subsequent selective thermal emission from ultra-thin planar films of polar materials at mid-infrared wavelengths. Our structures consist of AlN layers of varying thicknesses deposited upon molybdenum ground planes. We demonstrate coupling to the Berreman mode at frequencies at, or near, the longitudinal optical phonon energy of AlN. Samples are characterized experimentally by temperature-, angle-, and polarization-dependent Fourier transform infrared reflection and emission spectroscopy and modeled using a transfer matrix method approach. Strong, spectrally selective thermal emission, with near angle-independent spectral position, is demonstrated from an AlN layer with thickness t<λo/100.
Plasmonic materials, and their ability to enable strong concentration of optical fields, have offered a tantalizing foundation for the demonstration of sub-diffraction-limit photonic devices. However, practical and scalable plasmonic optoelectronics for real world applications remain elusive. In this work, we present an infrared photodetector leveraging a device architecture consisting of a “designer” epitaxial plasmonic metal integrated with a quantum-engineered detector structure, all in a mature III-V semiconductor material system. Incident light is coupled into surface plasmon-polariton modes at the detector/designer metal interface, and the strong confinement of these modes allows for a sub-diffractive ( ∼ λ 0 / 33 ) detector absorber layer thickness, effectively decoupling the detector’s absorption efficiency and dark current. We demonstrate high-performance detectors operating at non-cryogenic temperatures ( T = 195 K ), without sacrificing external quantum efficiency, and superior to well-established and commercially available detectors. This work provides a practical and scalable plasmonic optoelectronic device architecture with real world mid-infrared applications.
Epitaxial heterostructures of narrow-gap IV-VI and III-V semiconductors offer a platform for new electronics and mid-infrared photonics. Stark dissimilarities in the bonding and the crystal structure between the rocksalt IV–VIs and the zincblende III–Vs, however, mandate the development of nucleation and growth protocols to reliably prepare high-quality heterostructures. In this work, we demonstrate a route to single crystal (111)-oriented PbSe epitaxial films on nearly lattice-matched InAs (111)A templates. Without this technique, the high-energy heterovalent interface readily produces two populations of PbSe grains that are rotated 180° in-plane with respect to each other, separated by rotational twin boundaries. We find that a high-temperature surface treatment with the PbSe flux extinguishes one of these interfacial stackings, resulting in single-crystalline films with interfaces that are mediated by a monolayer of distorted PbSe. While very thin PbSe-on-InAs films do not emit light, hinting toward a type-III band alignment, we see strong room temperature photoluminescence from a 1.5 μm thick film with a minority carrier lifetime of 20 ns at low-excitation conditions and bimolecular recombination at high excitation conditions, respectively, even with threading dislocation densities exceeding 108 cm−2. We also note near-complete strain relaxation in these films despite large thermal expansion mismatch to the substrate, with dislocations gliding to relieve strain even at cryogenic temperatures. These results bring to light the exceptional properties of IV-VI semiconductors and the new IV-VI/III-V interfaces for a range of applications in optoelectronics.
We report the room temperature photoluminescence and electroluminescence properties of boron incorporated into highly strained InGaAs, forming BGaInAs, grown on GaAs substrates. X-ray diffraction was used to determine the alloy composition and strain of BGaInAs quantum wells on GaAs. As expected, the addition of boron reduced the quantum well compressive strain, preventing strain-relaxation and enabling extension of the peak emission wavelength of InGaAs quantum wells to 1.3 μm on GaAs. We also report both the longest wavelength emission observed from BGaInAs (1.4 μm) and electrically injected photoemission from a dilute-boride active region. We observed a blueshift in electroluminescence, due to unintentional in situ annealing of the active region, which we mitigated to demonstrate a path to realize true 1.3 μm emitters in the presence of in situ annealing.
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