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Optical antenna resonators enable control of light‐matter interactions on the nano‐scale via electron–photon hybrid states in strong coupling. Specifically, mid‐infrared (MIR) nano‐antennas coupled to saturable intersubband transitions in multi‐quantum‐well (MQW) semiconductor heterostructures allow for the coupling strength to be tuned through antenna resonance and field intensity. Here, tip‐enhanced nano‐scale variation of antenna‐MQW coupling across the antenna is demonstrated, with a spatially‐dependent coupling strength gaq$g_{\rm aq}$ varying from 73 (strong coupling) to 24 cm−1$\rm {cm}^{-1}$ (weak coupling). This behavior is modeled based on the spatially dependent local constructive and destructive interference between tip and antenna fields. Using a quantum‐mechanical density‐matrix model of the MQW system with its designed values of transition dipole moment, doping density, and population decay time, the picosecond IR pulse coupling to intersubband transitions and the associated tip induced strong‐field saturation effects are described. These results present a new regime of nonlinear IR light‐matter control based on the dynamic manipulation of quantum hybrid states on the nanoscale and in the infrared, with a perspective regarding extension to molecular vibrations. [ABSTRACT FROM AUTHOR]

Strong light-matter coupling has recently been demonstrated in subwavelength volumes by coupling engineered optical transitions in semiconductor heterostructures (e.g., quantum wells) to metasurface resonances via near fields. It has also been shown that different resonator shapes may lead to different Rabi splittings, though this has not yet been well explained. In this paper, our aim is to understand the correlation between resonator shape and Rabi splitting, in particular to determine and quantify the physical parameters that affect strong coupling by developing an equivalent circuit network model whose elements describe energy and dissipation. Because of the subwavelength dimension of each metasurface element, we resort to the quasistatic (electrostatic) description of the near field and hence define an equivalent capacitance associated to each dipolar element of a flat metasurface. We show that this is also able to accurately model the phenomenology involved in strong coupling between the metasurface and the intersubband transitions in quantum wells. We show that the spectral properties and stored energy of a metasurface/quantum-well system obtained using our model are in good agreement with both full-wave simulation and experimental results. We then analyze metasurfaces made of three resonator geometries and observe that the magnitude of the Rabi splitting increases with the resonator capacitance in agreement with our theory, providing a phenomenological explanation for the resonator shape dependence of the strong coupling process. © 2014 American Physical Society.

Developing optimized regimens for combination antibiotic therapy is challenging and often performed empirically over many clinical studies. Novel implementation of a hybrid machine‐learning pharmacokinetic/pharmacodynamic/toxicodynamic (ML‐PK/PD/TD) approach optimizes combination therapy using human PK/TD data along with in vitro PD data. This study utilized human population PK (PopPK) of aztreonam, ceftazidime/avibactam, and polymyxin B along with in vitro PDs from the Hollow Fiber Infection Model (HFIM) to derive optimal multi‐drug regimens de novo through implementation of a genetic algorithm (GA). The mechanism‐based PD model was constructed based on 7‐day HFIM experiments across 4 clinical, extensively drug resistant Klebsiella pneumoniae isolates. GA‐led optimization was performed using 13 different fitness functions to compare the effects of different efficacy (60%, 70%, 80%, or 90% of simulated subjects achieving bacterial counts of 102 CFU/mL) and toxicity (66% of simulated subjects having a target polymyxin B area under the concentration‐time curve [AUC] of 100 mg·h/L and aztreonam AUC of 1,332 mg·h/L) on the optimized regimen. All regimens, except those most heavily weighted for toxicity prevention, were able to achieve the target efficacy threshold (102 CFU/mL). Overall, GA‐based regimen optimization using preclinical data from animal‐sparing in vitro studies and human PopPK produced clinically relevant dosage regimens similar to those developed empirically over many years for all three antibiotics. Taken together, these data provide significant insight into new therapeutic approaches incorporating ML to regimen design and treatment of resistant bacterial infections. [ABSTRACT FROM AUTHOR]

Gallium is incorporated into the strain-balanced In(Ga)As/InAsSb superlattice system to achieve the same mid-wave infrared cutoff tunability as conventional Ga-free InAs/InAsSb type-II superlattices, but with an additional degree of design freedom to enable optimization of absorption and transport properties. Time-resolved photoluminescence measurements of InGaAs/InAsSb superlattice characterization- and doped device structures are reported from 77 to 300 K and compared to InAs/InAsSb. The low-injection photoluminescence decay yields the minority carrier lifetime, which is analyzed with a recombination rate model, enabling the determination of the temperature-dependent Shockley–Read–Hall, radiative, and Auger recombination lifetimes and extraction of defect energy levels and capture cross section defect concentration products. The Shockley–Read–Hall-limited lifetime of undoped InGaAs/InAsSb is marginally reduced from 2.3 to 1.4 μs due to the inclusion of Ga; however, given that Ga improves the vertical hole mobility by a factor of >10×, a diffusion-limited InGaAs/InAsSb superlattice nBn could expect a lower bound of 2.5× improvement in diffusion length with significant impact on photodetector quantum efficiency and radiation hardness. At temperatures below 120 K, the doped device structures are Shockley–Read–Hall limited at 0.5 μs, which shows promise for detector applications. [ABSTRACT FROM AUTHOR]

We show that Sb substitution for As in a MBE grown InAs/InAsSb strained layer superlattice (SLS) is accompanied by significant strain fluctuations. The SLS was observed using scanning transmission electron microscopy along the [100] zone axis where the cation and anion atomic columns are separately resolved. Strain analysis based on atomic column positions reveals asymmetrical transitions in the strain profile across the SLS interfaces. The averaged strain profile is quantitatively fitted to the segregation model, which yields a distribution of Sb in agreement with the scanning tunneling microscopy result. The subtraction of the calculated strain reveals an increase in strain fluctuations with the Sb concentration, as well as isolated regions with large strain deviations extending spatially over ∼1 nm, which suggest the presence of point defects. [ABSTRACT FROM AUTHOR]

The electrically pumped stripe length method measures the optical gain and spontaneous emission in type-II GaAsSb-InGaAs emitting at 1.3 [mu]m. The functions of current injection and temperatures are determined.

An examination is presented of the large blue shift in the emission with excitation in a GaAsSb-based type-II quantum well. The topic is approached both experimentally and theoretically.

High temperature operation (250-340K) of short-wavelength interband cascade infrared photodetectors (ICIPs) with InAs/GaSb/Al0.2In0.8Sb/GaSb superlattice absorbers has been demonstrated with a 50% cutoff wavelength of 2.9 lm at 300 K. Two ICIP structures, one with two and the other with three stages, were designed and grown to explore this multiple-stage architecture. At λ = 2.1 μm, the two- and three-stage ICIPs had Johnson-noise-limited detectivities of 5.1 × 109 and 5.8 × 109 cm Hz1/2/W, respectively, at 300 K. The better device performance of the three-stage ICIP over the two-stage ICIP confirmed the advantage of more stages for this cascade architecture. An Arrhenius activation energy of 450 meV is extracted for the bulk resistance-area product, which indicates the dominance of the diffusion current at these high temperatures. [ABSTRACT FROM AUTHOR]

Type-2 multiple quantum-wells (MQWs) are analyzed in terms of their optical nonmlinearities. Indirect transition energies are diverted by the space-charge potential resulting from the separation of electrons from holes in the MQWs while direct transitions remain unaffected by the space-charge field. A Coulomb-enhancement peak occurs at the hole quasi-chemical with the blue shift developing fully as low lattice temperatures are reached in hole distribution.

The Lorentz-like effective medium resonance (LEMR) exhibited by the longitudinal effective permittivity of semiconductor hyperbolic metamaterials (SHMs) has been known for some time. However, direct observation of this resonance proved to be difficult. Herein, we experimentally demonstrate its existence by strongly coupling SHMs to plasmonic metasurfaces. We consider four strong coupling implementations of SHMs that exhibit different LEMR absorption profiles (both in frequency and in strength) to validate our approach. [ABSTRACT FROM AUTHOR]

Flip-chip heterogeneously integrated n-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with integrated thermal management on wide-bandgap AlN substrates followed by GaAs substrate removal are demonstrated. Without thermal management, substrate removal after integration significantly aggravates self-heating effects, causing poor $I$ – $V$ characteristics due to excessive device self-heating. An electrothermal codesign scheme is demonstrated that involves simulation (design), thermal characterization, fabrication, and evaluation. Thermoreflectance thermal imaging, electrical-temperature sensitive parameter-based thermometry, and infrared thermography were utilized to assess the junction temperature rise in HBTs under diverse configurations. In order to reduce the thermal resistance of integrated devices, passive cooling schemes assisted by structural modification, i.e., positioning indium bump heat sinks between the devices and the carrier, were employed. By implementing thermal heat sinks in close proximity to the active region of flip-chip integrated HBTs, the junction-to-baseplate thermal resistance was reduced over a factor of two, as revealed by junction temperature measurements and improvement of electrical performance. The suggested heterogeneous integration method accounts for not only electrical but also thermal requirements providing insight into realization of advanced and robust III-V/Si heterogeneously integrated electronics. [ABSTRACT FROM AUTHOR]

We present our recent electronic transport results in top-gated InAs/GaSb quantum well hybrid structures with superconducting Ta electrodes. We show that the transport across the InAs--Ta junction depends largely on the interfacial transparency, exhibiting distinct zero-bias behavior. For a relatively resistive interface, a broad conductance peak is observed at zero bias. When a transparent InAs--Ta interface is achieved, a zero-bias conductance dip appears with two coherent-peak-like features forming at bias voltages corresponding to the superconducting gap of Ta. The conductance spectra of the transparent InAs--Ta junction at different gate voltages can be fit well using the standard Blonder-Tinkham-Klapwijk theory. [ABSTRACT FROM AUTHOR]

We utilize the unique dispersion properties of leaky plasmon polaritons in epsilon-near-zero (ENZ) thin films to demonstrate thermal radiation control. Owing to its highly flat dispersion above the light line, a thermally excited leaky wave at the ENZ frequency out-couples into free space without any scattering structures, resulting in a narrowband, wide-angle, p-polarized thermal emission spectrum. We demonstrate this idea by measuring angle- and polarization-resolved thermal emission spectra from a single layer of unpatterned, doped semiconductors with deep-subwavelength film thickness (d/k0 ~ 6 x 10-3, where d is the film thickness and k0 is the free space wavelength). We show that this semiconductor ENZ film effectively works as a leaky wave thermal radiation antenna, which generates far-field radiation from a thermally excited mode. The use of semiconductors makes the radiation frequency highly tunable by controlling doping densities and also facilitates device integration with other components. Therefore, this leaky plasmon polariton emission from semiconductor ENZ films provides an avenue for on-chip control of thermal radiation. [ABSTRACT FROM AUTHOR]

A nonlinear intersubband polaritonic metasurface designed for difference‐frequency generation that provides a practical level of nonlinear response under continuous wave illumination is reported. An effective nonlinear susceptibility of up to 340 nm V−1 is measured experimentally. Approximately 0.3% of λ = 5.4 µm photons are downconverted to λ = 12.9 µm photons at the focal spot in the experiment. This work indicates that the ultrathin metasurface devices may provide a versatile nonlinear element for frequency down‐ and upconversion in a relatively broad spectral range and without phase‐matching constrains of traditional bulk nonlinear crystals. An optically thin nonlinear metasurface for difference‐frequency generation that provides efficient frequency conversion under continuous wave illumination is reported. Approximately 0.3% of λ1 ≈ 5.4 µm photons are down‐converted to λ ≈ 12.9 µm photons at the focal spot using continuous‐wave CO2 laser pumping at λ2 ≈ 9.3 µm. The metasurface nonlinear susceptibility of up to 3.4 × 105 pm V−1 is measured experimentally. [ABSTRACT FROM AUTHOR]

We present the design, fabrication, and realization of an electrically tunable metamaterial operating in the mid-infrared spectral range. Our devices combine intersubband transitions in semiconductor quantum-wells with planar metamaterials and operate in the strong light-matter coupling regime. The resonance frequency of the intersubband transition can be controlled by an external bias relative to the fixed metamaterial resonance. This allows us to switch dynamically from an uncoupled to a strongly coupled system and thereby to shift the eigenfrequency of the upper polariton branch by 2.5 THz (corresponding to 8% of the center frequency or one full linewidth) with a bias of 5 V. [ABSTRACT FROM AUTHOR]

Narrow-bandgap (<0.25 eV) photovoltaic (PV) devices are demonstrated at room temperature and above. These PV devices are based on interband cascade (IC) structures and can achieve a high open-circuit voltage (∼0.65 V at 300 K) that significantly exceeds the single bandgap limited value. This work demonstrates the capabilities and advantages of ICPV devices designed to effectively convert long wavelength (>5 μm) infrared photons from relatively low-temperature radiation sources (<1000 K) into electricity. Detailed characteristics of these PV devices are presented and discussed. [ABSTRACT FROM AUTHOR]

InPSb and InAsPSb have been investigated for use as absorber materials in GaSb-based n-type/barrier/n-type (nBn) detectors with cutoff wavelengths shorter than 4.2 μm. The growth temperature window for high-quality InPSb lattice-matched to GaSb by molecular beam epitaxy is approximately 440-460 °C. InPSb films with thicknesses greater than approximately 1 μm or films grown outside this temperature window have high densities of large defects, with films grown at lower temperatures exhibiting evidence of significant phase separation. In contrast, InAsPSb films can be grown with excellent surface morphologies and no apparent phase separation over a wide temperature range. InAsPSb samples with low-temperature photoluminescence between 3.0 and 3.4 μm and lattice mismatch of less than 1 × 10-3 have been grown, although both photoluminescence and x-ray diffraction data exhibit peak splitting indicative of compositional nonuniformity. AlAsSb-barrier nBn detectors with InPSb and InAsPSb absorbers have been fabricated. At 160 K, InPSb-absorber devices have a photocurrent responsivity edge at approximately 2.8 μm and a dark current of approximately 1.4 × 10-7 A/cm2, and InAsPSb devices with responsivity edges of 3.1-3.2 μm have a dark current of 2.3 × 10-8 A/cm2. Both InPSb and InAsPSb devices require significant reverse bias for full photocurrent collection at low temperature, suggesting the existence of an undesirable valence band energy discontinuity. The temperature dependence of dark current indicates that it is dominated by a mechanism other than generation in the undepleted absorber region. [ABSTRACT FROM AUTHOR]

Charge transport physics in InAs/GaSb bi-layer systems has recently attracted attention for the experimental search for two-dimensional topological superconducting states in solids. Here we report measurement of charge transport spectra of nano devices consisting of an InAs/GaSb quantum well sandwiched by tantalum superconductors. We explore the current-voltage relation as a function of the charge-carrier density in the quantum well controlled by a gate voltage and an external magnetic field. We observe three types of differential resistance peaks, all of which can be effectively tuned by the external magnetic field, and, however, two of which appear at electric currents independent of the gate voltage, indicating a dominant mechanism from the superconductor and the system geometry. By analyzing the spectroscopic features, we find that the three types of peaks identify Andreev reflections, quasi-particle interference, and superconducting transitions in the device, respectively. Our results provide a basis for further exploration of possible topological superconducting state in the InAs/GaSb system., (© 2021 IOP Publishing Ltd.)