Crosstalk mitigation and small-pitch consequences in SWIR InGaAs FPAs.

A consistent trend in infrared imaging systems is a drive towards smaller pixel pitches in focal plane arrays. In this work, we present an extensive numerical study on how dark current, quantum efficiency, and modulation transfer function are affected when reducing the pixel pitch in SWIR InGaAs pixel arrays. From the results, we propose the introduction of diffusion control junctions into the pixel sub-architecture to lower dark current and improve modulation transfer function, with a minor decrease in specific detectivity.

Mini fluid chAllenge aNd End-expiratory occlusion test to assess flUid responsiVEness in the opeRating room (MANEUVER study): A multicentre cohort study.

BACKGROUND: The fluid challenge response in surgical patients can be predicted by functional haemodynamic tests. Two tests, the mini-fluid challenge (mini-FC) and end-expiratory occlusion test (EEOT), have been assessed in a few small single-centre studies with conflicting results. In general, functional haemodynamic tests have not performed reliably in predicting fluid responsiveness in patients undergoing laparotomy. OBJECTIVE: This trial is designed to address and compare the reliability of the EEOT and the mini-FC in predicting fluid responsiveness during laparotomy. DESIGN: Prospective, multicentre study. SETTING: Three university hospitals in Italy. PATIENTS: A total of 103 adults patients scheduled for elective laparotomy with invasive arterial monitoring. INTERVENTIONS: The study protocol evaluated the changes in the stroke volume index (SVI) 20 s (EEOT20) and 30 s (EEOT30) after an expiratory hold and after a mini-FC of 100 ml over 1 min. Fluid responsiveness required an increase in SVI at least 10% following 4 ml kg-1 of Ringer's solution fluid challenge infused over 10 min. MAIN OUTCOME MEASUREMENTS: Haemodynamic data, including SVI, were obtained from pulse contour analysis. The area under the receiver operating characteristic curves of the tests were compared with assess fluid responsiveness. RESULTS: Fluid challenge administration induced an increase in SVI at least 10% in 51.5% of patients. The rate of fluid responsiveness was comparable among the three participant centres (P = 0.10). The area under the receiver operating characteristic curves (95% CI) of the changes in SVI after mini-FC was 0.95 (0.88 to 0.98), sensitivity 98.0% (89.5 to 99.6) and specificity 86.8% (75.1 to 93.4) for a cut-off value of 4% of increase in SVI. This was higher than the SVI changes after EEOT20, 0.67 (0.57 to 0.76) and after EEOT30, 0.73 (0.63 to 0.81). CONCLUSION: In patients undergoing laparotomy the mini-FC reliably predicted fluid responsiveness with high-sensitivity and specificity. The EEOT showed poor discriminative value and cannot be recommended for assessment of fluid responsiveness in this surgical setting. TRIAL REGISTRATION: NCT03808753.

Parametric numerical study of the modulation transfer function in small-pitch InGaAs/InP infrared arrays with refractive microlenses.

We report on the modulation transfer function (MTF) in short-wave infrared indium gallium arsenide (InGaAs) on indium phosphide (InP) planar photodetector arrays. Our two-dimensional numerical method consists of optical simulations using the finite-difference time domain method and drift-diffusion simulations using the finite-element method. This parametric study investigates MTF dependence on pitch, the addition of refractive microlenses, the thickness of the InGaAs absorber, and the doping concentration of the InGaAs absorber. A focus is placed on the connection between the lateral diffusion of photogenerated holes in InGaAs and the MTF. It is found that the MTF of small-pitch arrays exhibit sub-ideal behavior due to pixel cross-talk resulting from a long minority carrier diffusion length. By incorporating monolithic microlenses with the InP substrate, the MTF response is improved for all pitches investigated, particularly for spatial frequencies near the respective cutoff frequencies. We also find a strong dependence of the MTF on the thickness and doping concentration in the absorbing region. Trends in dark current and quantum efficiency are reported.

Numerical study on the optical and carrier recombination processes in GeSn alloy for E-SWIR and MWIR optoelectronic applications.

The Ge1-xSnx alloy is a promising material for optoelectronic applications. It offers a tunable wavelength in the infrared (IR) spectrum and high compatibility with complementary metal-oxide-semiconductor (CMOS) technology. However, difficulties in growing device quality Ge1-xSnx films has left the potentiality of this material unexplored. Recent advances in technological processes have renewed the interest toward this material paving the way to potential applications. In this work, we perform a numerical investigation on absorption coefficient, radiative recombination rate, and Auger recombination properties of intrinsic and doped Ge1-xSnx for application in the extended-short wavelength infrared and medium wavelength infrared spectrum ranges. We apply a Green's function based model to the Ge1-xSnx full electronic band structure determined through an empirical pseudopotential method and determine the dominant recombination mechanism between radiative and Auger processes over a wide range of injection levels.

Temperature characteristics of hot electron electroluminescence in silicon.

Emission spectra of avalanching n(+)p junctions manufactured in a standard CMOS technology with no process modifications were measured over a broad photon energy spectrum ranging from 0.8 eV to 2.8 eV at various temperatures. The temperature coefficients of the emission rates at different photon energies were determined. Below a photon energy of 1.35 eV the temperature coefficient of emission was positive, and above 1.35 eV the temperature coefficient was negative. Two narrowband emissions were also identified from the temperature characterization, namely an enhanced positive temperature coefficient at 1.15 eV photon energy, and an enhanced negative temperature coefficient at 2.0 eV. Device simulations and Monte Carlo simulations were used to interpret the results.

Analysis of InAsSb nBn spectrally filtering photon-trapping structures.

We have numerically analyzed the electromagnetic and electrical characteristics of InAsSb nBn infrared detectors employing a photon-trapping (PT) structure realized with a periodic array of pyramids intended to provide broadband operation. The three-dimensional numerical simulation model was verified by comparing the simulated dark current and quantum efficiency to experimental data. Then, the power and flexibility of the nBn PT design was used to engineer spectrally filtering PT structures. That is, detectors that have a predetermined spectral response to be more sensitive in certain spectral ranges and less sensitive in others.

Numerical simulation of crosstalk in reduced pitch HgCdTe photon-trapping structure pixel arrays.

We have investigated crosstalk in HgCdTe photovoltaic pixel arrays employing a photon trapping (PT) structure realized with a periodic array of pillars intended to provide broadband operation. We have found that, compared to non-PT pixel arrays with similar geometry, the array employing the PT structure has a slightly higher optical crosstalk. However, when the total crosstalk is evaluated, the presence of the PT region drastically reduces the total crosstalk; making the use of the PT structure not only useful to obtain broadband operation, but also desirable for reducing crosstalk in small pitch detector arrays.

Physics-based simulation of the modulation transfer function in HgCdTe infrared detector arrays.

We have developed a numerical technique for performing physics-based simulations of the modulation transfer function (MTF) of infrared detector focal plane arrays. The finite-difference time-domain and finite element methods are employed to determine the electromagnetic and electrical response, respectively. We show how the total MTF can be decomposed to analyze the effect of lateral diffusion of charge carriers and present several methods for mitigation of such effects. We employ our numerical technique to analyze the MTF of a HgCdTe two-color bias-selectable infrared detector array.

Band offsets of Al x Ga1-x N alloys using first-principles calculations.

First-principles calculations are employed for the study of the band offsets of Al x Ga1-x N alloys, taking into account their composition and atomic configuration. Specifically, the band offsets are obtained using PBE, PBEsol, Heyd, Scuseria, and Ernzerhof (HSE), and modified Becke-Johnson calculations, comparing the results and discussing the advantages and disadvantages of each functional. The band alignments are performed using the branch point energies of the materials as their common reference level. HSE calculations predict a valence band offset of 0.9 eV between GaN and AlN. Regarding the alloys, a conduction band edge bowing parameter of 0.55 eV and a practically zero bowing for the valence band edge is predicted on average. The different atomic configurations affect mainly the valence band edges, where deviations from linearity by more than 0.1 eV are observed.

Anomalous heat flow in 8-Pmmn borophene with tilted Dirac cones.

We analytically establish an anomalous transverse flow of heat in 8- Pmmn borophene, one of the several two-dimensional allotropes of Boron. The dispersion of this allotrope contains a pair of anisotropic and tilted Dirac cones which are gapped by placing the 2D B sheet under an intense circularly-polarized illumination. A gap in the Dirac dispersion leads to a finite Berry curvature and connected anomalous Hall effects. In the case of thermoelectrics, this manifests as a heat current perpendicular to the temperature gradient-the thermal Hall effect. A quantitative calculation of the attendant thermal Hall conductivity reveals dependence on the intrinsic anisotropy and tilt of the Dirac cone. Further, by estimating the longitudinal thermal conductivity using the Wiedemann-Franz law, we also outline steps to compute the thermal Hall angle that gauges the generation efficiency of such transverse heat processes. Finally, we touch upon the idea of thermal rectification wherein the direction of flow of the anomalous heat reverses through a simple switch of the polarization of incident light and is of interest in thermal logic circuits.

Scattering times and surface conductivity of Dirac fermions in a 3D topological insulator film with localised impurities.

The zero gap surface states of a 3D-topological insulator host highly mobile Dirac fermions with spin locked to the momentum. The high mobility attributed to the absence of back scattering is reduced in the presence of impurities on the surface. In particular, we discuss and compare scattering times for localised impurities on the surface, scattering between states of opposite helicity located on different surfaces coupled through a hybridisation potential and the role of magnetic impurities. Magnetic impurities give rise to an additional spin suppression factor. The role of warped bands and their influence on topological factors that can enhance the overall surface mobility is examined. Finally, employing a linearised Boltzmann equation approach, surface conductivity calculations for Dirac fermions in a 3D TI is outlined.

The evaluation of non-topological components in Berry phase and momentum relaxation time in a gapped 3D topological insulator.

The zero gap surface states of a 3D-topological insulator host Dirac fermions with spin locked to the momentum. The gap-less Dirac fermions exhibit electronic behaviour different from those predicted in conventional materials. While calculations based on a simple linear dispersion can account for observed experimental patterns, a more accurate description of the physics of these systems and a better agreement between experimental data theoretical results can be obtained by including higher order k terms in the Hamiltonian. In this work, in presence of a time reversal symmetry breaking external magnetic field and higher order warping term, alteration to the topologically ordained Berry phase of (2n + 1)π, momentum relaxation time, and the magneto-conductivity tensors is established. The relation between scattering times and the deviations to topological Berry phase of π is also emphasized.

Inhalational anesthetics in acute severe asthma.

Acute severe asthma is characterized by a state of airway inflammation and increased bronchiolar smooth-muscle tone that leads to increased resistance to expiration and lung hyperinflation. Despite the better knowledge of its pathophysiology, the incidence and severity of asthma in the last twenty years is increased worldwide, although with significant age and geographic variation. As a result, the number of patients requiring more intensive medical therapy has also increased. In the most severe cases, often referred to as near-fatal asthma, the institution of mechanical ventilation may be required. Volatile anesthetics have bronchodilator effects on the bronchial smooth muscle. The use of inhalational anesthetic agents for treatment of severe status asthmaticus has been documented in case reports, case series and small uncontrolled studies. Their use may be considered in any mechanically ventilated patients whose severe bronchospasm failed to respond to maximal medical treatment. In the present review article, we aim to provide a brief description of the physio-pathological and clinical features of acute severe asthma, and of the principles of treatment, focusing our attention on the use of the inhalational anesthetics in severe patients requiring mechanical ventilation and not responding to conventional therapy.