We report a novel dual-band barrier infrared detector (DBIRD) design using InAs/GaSb type-II superlattices (T2SLs). The DBIRD structure consists of back-to-back barrier diodes: a “blue channel” (BC) diode which has an nBp architecture, an n-type layer of a larger bandgap for absorbing the blue band infrared/barrier/p-type layer, and a “red channel” (RC) diode which has a pBn architecture, a p-type layer of a smaller bandgap for absorbing the red band infrared/barrier/n-type layer. Each has a unipolar barrier using a T2SL lattice matched to a GaSb substrate to impede the flow of majority carriers from the absorbing layer. Each channel in the DBIRD can be independently accessed with a low bias voltage as is preferable for high-speed thermal imaging. The device modeling of DBIRDs and simulation results of the current–voltage characteristics under dark and illuminated conditions are also presented. They predict that the dual-band operation of the DBIRD will produce low dark currents and 45–56% quantum efficiencies for the in-band photons in the BC with λc = 5.58 μm, and a nearly constant 32% in the RC with λc = 8.05 μm. The spectral quantum efficiency of the BC for 500 K blackbody radiation is approximately 50% over the range of λ = 3–4.7 μm, while that of the RC has a peak of 42% at 5.9 μm. The DBIRD may provide improved high-speed dual-band imaging in comparison with NBn dual-band detectors.

In the search for materials alternate to bulk HgCdTe for high performance infrared imaging applications, colloidal quantum dots (CQDs), particularly HgTe CQDs, have gained traction owing to acceptable detector performance with easy preparation and low cost. In this article, we evaluate alpha-Sn CQDs, an environmentally less reactive and less toxic alternative to HgTe, for infrared sensing applications. Ab initio density functional theory calculations are used to study the shape-dependent stability, electronic bandgap, and absorption coefficient of alpha-Sn CQD nanoparticles (NPs). We consider three possible CQD shape constructions-Wulff, shell-by-shell, and spherical. The CQD of Wulff construction is predicted to be the most stable. However, we find that the size, not the shape, of the NP has a strong effect on the bandgap and absorption coefficient. Consequently, a sharp absorption edge is expected even in an ensemble of CQDs with different shapes. Importantly, the shape determines the position of the band edges with respect to vacuum, and thus offers a possibility of choosing the shape to improve alignment with the energy levels of ligands to enable efficient drift transport, instead of a slower and less efficient hopping transport. (c) 2024 Author(s).

We use an ensemble Monte Carlo transport approach to calculate and compare the impact ionization and avalanche photodiode excess noise characteristics in three materials—a band-engineered InAlAs/InAsSb type-II superlattice, bulk InAs, and HgCdTe—all with an identical bandgap of 370 meV at 250 K. The electronic band structures and energy–momentum conservation conditions are used to calculate the impact ionization rates, carrier histories, multiplication gains, and excess noise characteristics. The calculated impact ionization coefficients and excess noise factors indicate a single carrier species multiplication in all three materials under low applied electric fields. We find the ratio of impact ionization coefficients to be k=7×10−4 for InAs and 3×10−4 for HgCdTe under an applied field of 50 kV/cm, and the superlattice to be k<10−6 at fields up to 400 kV/cm. The bulk materials experience avalanche breakdown as the applied field increases, transitioning to Geiger mode behavior at gains above 103 for InAs and 104 for HgCdTe. However, this breakdown is absent from the superlattice at the highest fields considered in this study due to hole confinement, indicating superior performance compared to the bulk materials. Our results demonstrate the role of superlattice band engineering in designing quality avalanche photodiode materials.

The rising concentration of greenhouse gases, especially methane and carbon dioxide, is driving global temperature increases and exacerbating the climate crisis. Monitoring these gases requires detectors that operate in the extended short-wavelength infrared range (similar to 2.4 mu m), covering methane (1.65 mu m) and carbon dioxide (2.05 mu m) wavelengths. Here, we present a high-performance linear mode avalanche photodetector (APD) with an InGaAs/GaAsSb type-II superlattice absorber and an AlGaAsSb multiplier, matched to InP substrates. This APD achieves a room temperature gain of 178, an external quantum efficiency of 3560% at 2 mu m, low excess noise (less than 2 at gains below 20), and a small temperature coefficient of breakdown (7.58 mV/K center dot mu m). These results indicate that a manufacturable semiconductor material-based APD could significantly advance high-sensitivity receivers for greenhouse gas monitoring, potentially enabling their commercial production and widespread use.

We have calculated carrier nonradiative recombination lifetimes limited by Shockley–Read–Hall (SRH) centers in strained layer superlattices (SLSs) for mid-wave and long-wave infrared applications. The capture rate of an electron (hole) in the SLS's conduction (valence) band by the defect level is dominated by a multi-phonon process, which is orders-of-magnitude more efficient than the radiative process. Long-range polar coupling between electrons and optical phonons can account for the observed SRH lifetimes in a variety of SLSs reported in the literature. The capture rate depends on temperature rather weakly, consistent with experimental observations. The efficient capture is caused by the comparable electronic difference and lattice relaxation energy, Ect∼Sℏω, with S and ℏω being the Huang–Rhys factor and optical photon energy in the SLSs. A weaker polar coupling would give rise to a smaller capture cross section, which, for InAs/InAsSb SLSs, can be achieved by increasing Sb in the alloy region.

2D materials for sensing applications offer several advantages-high absorption in thin layers, the lack of surface dangling bonds or major defects, ease of materials synthesis and device fabrication, and relaxed substrate lattice-matching requirements. We theoretically explore two 2D materials, hexagonal boron phosphide and hexagonal boron arsenide, for possible infrared sensing and hyperspectral applications. Using first principles, we calculate the total energy of formation, band structures, and absorption coefficient of monolayer and bilayer materials. We evaluate the bandgap and absorption coefficient of bilayers as a function of layer stacking, number of layers, and applied field across the layers. We find that with a choice of stacking order, number of layers, and applied field, the material can be chosen appropriately for sensing of short-, mid-, or long-wavelength infrared radiation. Furthermore, the absorption is increased in these materials with applied electric fields. With the ability to dynamically change the bandgap with an external electric field, this class of materials is ideally suited for continuous hyperspectral sensing in the infrared. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

High sensitivity avalanche photodiodes (APDs) operating at eye-safe infrared wavelengths (1400–1650 nm) are essential components in many communications and sensing systems. We report the demonstration of a room temperature, ultrahigh gain ( M = 278 , λ = 1550 n m , V = 69.5 V , T = 296 K ) linear mode APD on an InP substrate using a G a A s 0.5 S b 0.5 / A l 0.85 G a 0.15 A s 0.56 S b 0.44 separate absorption, charge, and multiplication (SACM) heterostructure. This represents ∼ 10 × gain improvement ( M = 278 ) over commercial, state-of-the-art InGaAs/InP-based APDs ( M ∼ 30 ) operating at 1550 nm. The excess noise factor is extremely low ( F < 3 ) at M = 70 , which is even lower than Si APDs. This design gives a quantum efficiency of 5935.3% at maximum gain. This SACM APD also shows an extremely low temperature breakdown sensitivity ( C b d ) of ∼ 11.83 m V / K , which is ∼ 10 × lower than equivalent InGaAs/InP commercial APDs. These major improvements in APD performance are likely to lead to their wide adoption in many photon-starved applications.

There is interest in using body temperature changes in sows as an indicator of the onset of estrus. However, the optimum location to measure body temperature has not been established. The objective of this study was to evaluate the relationships between sow body surface temperature (SBST) measured at various locations and rectal temperature. The study involved 98 multiparous sows weaned in 6 groups between September and November. Sows were housed in individual stalls and were checked daily for standing reflex from day 3 to 7 post-weaning. Temperature measurements were taken daily for 10 days post-weaning [at 06:15 (feeding time), 07:00, 07:30 (heat checking time), 09:00, 11:00, 13:00, 15:00, 17:00, 19:00, 21:00, and 23:00]. Surface temperature was measured using a handheld thermal camera at 4 locations: outer ear, back of the head, vulva, and ham. Rectal temperature was measured using a clinical thermometer. The ambient temperature in the room was measured at the same times as the animal measurements were taken. The PROC CORR procedure of SAS was used to determine correlations between SBST, rectal temperature, and average room temperature at the time of each measurement (RMT). All correlations between SBST at the different measurement locations were strong and positive (P < 0.0001; Table 1) with r values ranging from 0.64 (between vulva and the outer ear) to 0.89 (between vulva and ham). However, correlations between SBST and rectal temperature were relatively weak (range r = 0.14 to 0.18; P < 0.0001). Rectal temperature was not correlated with RMT (r = 0.02; P = 0.12); correlations between RMT and SBST measurements were positive, with the strongest correlations being with the outer ear and the back of the head (r = 0.45 and 0.50, respectively; P < 0.0001). In conclusion, this study suggests strong relationships between body surface temperatures at different locations but relatively weak relationships between these measurements and rectal temperature. In addition, these results suggest room temperature has a greater influence on body surface temperature than on rectal temperature.

For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and multiplication design is widely used. AlInAsSb on an InP substrate is a potential multiplication layer with a lattice match to absorber candidates across the SWIR. Our new measurements demonstrate that AlInAsSb on InP is a promising multiplier candidate with a relatively low dark current density of 10−4 A/cm2 at a gain of 30; a high gain, measured up to 245 in this study; and a large differentiation of electron and hole ionization leading to a low excess noise, measured to be 2.5 at a gain of 30. These characteristics are all improvements over commercially available SWIR detectors incorporating InAlAs or InP as the multiplier. We measured and analyzed gain for multiple wavelengths to extract the ionization coefficients as a function of an electric field over the range 0.33–0.6 MV/cm.

We have demonstrated InGaAs/AlInAsSb separate absorption, charge, and multiplication avalanche photodiodes. The multiplication gain, excess noise, and temperature-dependent dark current have been characterized. InGaAs/AlInAsSb APDs were grown on semi-insulating InP substrates, which is beneficial for bandwidth improvement compared to AlInAsSb APDs grown on GaSb substrates.

An ensemble Monte Carlo framework is used to compare the impact ionization behavior important to avalanche photodiode (APD) performance in a band-engineered InAlAs/InAsSb type-II superlattice with same-energy gap bulk InAs and HgCdTe at 250 K. Impact ionization rates are computed directly from the electronic band structures. The same stochastic transport kernel is used for each material for consistency. A realistic treatment of impact ionization initial and final carrier states is employed in the transport simulations that considers energy and crystal momentum conservation. The major effects of band features on carrier states, transit path lengths between impact ionization events, and impact ionization coefficients support the role of band engineering in materials selection for high-performance APDs.

There is growing interest in the design, development, and demonstration of short wavelength infrared (SWIR) avalanche photodiodes (APDs), notably focusing on spectral coverage over 1.55-2 µm in wavelength. This work investigates GaAsSb/AlGaAsSb APDs on InP substrates for these remote sensing applications. The objective is to develop infrared detectors that will meet or exceed the opto-electronic performance metrics of state-of-the-art technology while operating at high temperatures (>200 K) to reduce SWaP-C and ultimately enable integration of the technology onto small satellite platforms. While our GaAsSb/AlGaAsSb SACM APDs exhibit promising performance, there are several challenges that need to be overcome before their implementation into fieldable remote sensing systems. Chiefly, the detectors exhibit high dark current relative to competing commercial detectors. The dark current must be identified as bulk or surface dominated through careful characterization and analysis. If it is determined that the dominant dark current mechanism is bulk driven, improvements in the APDs will result by improving the material quality through crystal growth optimization. If the APDs are surface dark current limited, then improvements will occur by reassessing the fabrication techniques. Through this, we can further adjust our design, growth, and fabrication processes to achieve high performing SWIR infrared detectors.

High-sensitivity avalanche photodiodes (APDs) are used to amplify weak optical signals in a wide range of applications, including telecommunications, data centers, spectroscopy, imaging, light detection and ranging, medical diagnostics, and quantum applications. This paper reports antimony-based separate absorption, charge, and multiplication structure APDs on InP substrates. Al0.7In0.3As0.79Sb0.21 is used for the multiplier region, and InGaAs is used as the absorber. The excess noise is comparable to that of silicon APDs; the k-value is more than one order of magnitude lower than that of APDs that use InP or InAlAs for the gain region. The external quantum efficiency without an anti-reflection coating at 1550 nm is 57%. The gradient of the temperature coefficient of avalanche breakdown voltage is 6.7 mV/K/μm, which is less than one-sixth that of InP APDs, presenting the potential to reduce the cost and complexity of receiver circuits. Semi-insulating InP substrates make high-speed operation practical for widely reported AlxIn1−xAsySb1−y-based APDs.

We demonstrate low noise random alloy (RA) Al0.85Ga0.15AsSb (hereafter AlGaAsSb) avalanche photodiodes (APDs) nearly lattice-matched to InP substrates. In contrast to digital alloy (DA), RAs are manufacturable due to the ease of growth. The 910 nm-thick RA AlGaAsSb was grown at a low temperature around 450 °C to mitigate phase separation by suppressing surface mobility of adatoms. The high quality of the RA AlGaAsSb material was verified by x-ray diffraction, Nomarski, and atomic force microscope images. Capacitance–voltage measurement found that the background doping concentration was 6–7 × 1014 cm−3, indicating very low impurity density in the RA AlGaAsSb material. Current–voltage measurements were carried out under dark condition and 455 nm laser illumination at room temperature. The breakdown occurs at −58 V. The dark current density at a gain of 10 was found to be 70 μA/cm2. This value is three orders of magnitude lower than previously reported DA AlAs0.56Sb0.44 APDs [Yi et al., Nat. Photonics 13, 683 (2019)], one order of magnitude lower than DA AlGaAsSb [Lee et al., Appl. Phys. Lett. 118, 081106 (2021)], and comparable to RA AlInAsSb APDs [Kodati et al., Appl. Phys. Lett. 118, 091101 (2021)]. In addition, the measured excess noise shows a low k (the ratio of impact ionization coefficients) of 0.01. These noise characteristics make the RA AlGaAsSb multiplier suitable for commercial applications, such as optical communication and LiDAR systems.

Digital alloy and random alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 avalanche photodiodes (APDs) exhibit low excess noise, comparable to Si APDs. Consequently, this material is a promising multiplication layer candidate for separate absorption, charge, and multiplication structure APDs with high gain-bandwidth product. Characterization of the impact ionization coefficients of electrons ( α ) and holes ( β ) plays an important role in the simulation of avalanche photodiodes. The multiplication gain curves of eight p + -i-n + and n + -i-p + APDs covering a wide range of avalanche widths have been used to determine the electric field dependence of the impact ionization coefficients of Al 0.85 Ga 0.15 As 0.56 Sb 0.44 . A large impact ionization coefficient ratio between that of electrons to holes was seen across a wide electric field range. Simulations of the avalanche multiplication in these structures using a random path length (RPL) model gave good agreement with experimental results over almost three orders of magnitude, and a mixed injection method was employed to verify the extracted impact ionization coefficients. Interestingly, no difference in the impact ionization coefficients was seen between digital alloy and random alloy Al 0.85 Ga 0.15 As 0.56 Sb 0.44 . This knowledge of impact ionization coefficients is beneficial for the future utilization of the Al x Ga 1-x As y Sb 1-y material system.

We provide an overview of our progress on the development of linear mode avalanche photodiodes (LmAPDs) on InP substrates using antimony (Sb)-based multipliers for short-wavelength infrared (SWIR) spectral region. We identify the key figures of merit of LmAPDs to provide higher sensitivity and speed for applications like light detection and ranging (LiDAR) and remote sensing. We discuss the design of separate absorption, charge, and multiplication (SACM) APDs that are used for narrow gap absorption. We summarize our results on the impact ionization, multiplication gain, dark current, and excess noise of AlGaAsSb and AlInAsSb multipliers lattice-matched to InP substrates. Finally, we identify the key technical challenges associated with the development of SACM APDs on InP substrates.

We developed an x-ray diffraction (XRD) method that uses relative satellite peak intensities to assess the width of the alloy interfaces in InAs/InAsSb Type 2 superlattices (T2SLs). Specifically, our method simulates XRD patterns for T2SLs based on a model of alloy cross-incorporation and fits the simulated pattern to experimental data through a small set of model parameters. We model the Sb distribution function with two forms (i) a Gaussian function, or (ii) two error functions. We compared the model with experimental data extracted from the literature. The first example is a T2SL with 50 periods of 7.0 nm thick InAs and 2.3 nm thick InAs 1-x Sb x with the targeted alloy composition of x = 0.23. The second example is a T2SL with 100 periods of 4.6 nm thick InAs and 1.7 nm thick InAs 1-x Sb x with the targeted composition of x = 33.3%. The width of the alloy interface is about 2.54 nm for the first example with the Gaussian model, and with the error function model is 2.8 nm. In the second example, we observed a lower width of the alloy interface of about 0.48 nm with the Gaussian model, and 0.5 nm with the error function model.

Background doping polarity is a critical design parameter for the performance of many optoelectronic devices, including avalanche photodiodes. We have applied a technique by using capacitance–voltage (CV) measurements on double mesa structures with a p-i-n or n-i-p homojunction to determine the background polarity type of the unintentionally doped intrinsic region. Because CV measurements scale with the size of the mesa, they support design flexibility in producing variable-sized top and bottom mesa diameters. In this work, we grew, fabricated, and tested AlGaAsSb and AlInAsSb random alloy double mesa p-i-n structures and undertook CV measurements at 295, 150, and 77 K. It was found that the capacitance varied with the top mesa diameter for both material systems, and not the bottom mesa diameter, indicating that the unintentionally doped intrinsic region is n-type in nature.

Avalanche photodiodes (APDs) are critical components for a variety of remote sensing applications, particularly for 3D imaging using light detection and ranging (LiDAR). APDs can provide higher sensitivity and faster response times than traditional PIN diodes due to their internal gain. To apply LiDAR to gas monitoring applications, including greenhouse gases, APDs need to be sensitive further into the infrared than Si APDs can detect. This work investigates an absorber that is sensitive to 2 μm and compatible with an APD. A separate absorption, charge, and multiplication (SACM) heterostructure is often used to reduce the dark current of an infrared APD. In a SACM design, the absorber is placed in a low field region to minimize tunneling and the multiplier is placed in a high field region to maximize impact ionization. We have previously explored high performance multipliers that are lattice matched to InP substrates. In this work, we explore a candidate lattice-matched absorber, an In0.53Ga0.47As/GaAs0.51Sb0.49 Type II superlattice (T2SL). We have demonstrated photoluminescence at 2 μm using a 5 nm InGaAs/5 nm GaAsSb T2SL structure. We have grown and fabricated 1-micron thick PIN diodes with this absorber material and obtained an n-type background carrier concentration of 5×1015 cm-3 . We are currently undertaking the radiometric characterization of these devices to support their integration into a SACM APD.

There is limited data available on variation in sow temperature following weaning. The objective of this study was to determine variation (diurnal and with day post-weaning) in rectal (RT) and vulva surface (VT) temperature following weaning. A cross-sectional survey was carried out using 114 multi-parous sows weaned in 7 groups between September and December. Sows were housed in individual stalls and were checked daily for standing reflex from d 4 to 8 post-weaning. Sow RT (measured with a standard thermometer) and VT (measured with an infrared thermal camera) were measured daily [at 06:15 (feeding time), 07:00, 07:30 (heat checking time), 09:00, 11:00, 13:00, 15:00, 17:00, 19:00, 21:00, and 23:00]. A repeated-measures analysis was carried out using PROC MIXED of SAS; models included the fixed effect of either study day or measurement time, and random effect of group. The number of sows exhibiting standing reflex on d 4, 5, 6, 7, and 8 post-weaning was 1, 45, 45, 19, 1, respectively; 3 sows did not exhibit standing reflex. Average VT and RT over the study period were 30.8 ± 3.23 and 38.2 ± 0.60°C, respectively; the correlation between these measurements was 0.08 (P < 0.05). There was considerable day-to-day variation in average VT (range between day: 29.5 to 32.6°C) and to a lesser extent RT (range: 37.7 to 38.5°C). The VT was higher (P < 0.05) on d 3 to 5 post-weaning compared with other days. Also, VT was higher (P < 0.05) between 06:15 and 07:30 than at the other measurement times. There was no clear pattern for either day-to-day or diurnal variation in RT. In conclusion, this study described between-sow variation in RT and VT following weaning. Further research is needed to determine if any of this variation in temperature is associated with the onset of estrus.