Short-wavelength Infrared Region Research Articles

Sensitive Organic Photodetectors With Spectral Response up to 1.3µm Using a Quinoidal Molecular Semiconductor.

Detecting short-wavelength infrared (SWIR) light has underpinned several emerging technologies. However, the development of highly sensitive organic photodetectors (OPDs) operating in the SWIR region is hindered by their poor external quantum efficiencies (EQEs) and high dark currents. Herein, the development of high-sensitivity SWIR-OPDs with an efficient photoelectric response extending up to 1.3µm is reported. These OPDs utilize a new ultralow-bandgap molecular semiconductor featuring a quinoidal tricyclic electron-deficient central unit and multiple non-covalent conformation locks. The SWIR-OPD achieves an unprecedented EQE of 26% under zero bias and an even more impressive EQE of up to 41% under a -4V bias at 1.10µm, effectively pushing the detection limit of silicon photodetectors. Additionally, the low energetic disorder and trap density in the active layer lead to significant suppression of thermal-generation carriers and dark current, resulting in excellent detectivity (Dsh *) exceeding 1013 Jones from 0.50 to 1.21µm and surpassing 1012 Jones even at 1.30µm under zero bias, marking the highest achievements for OPDs beyond the silicon limit to date. Validation with photoplethysmography measurements, a spectrometer prototype in the 0.35-1.25µm range, and image capture under 1.20µm irradiation demonstrate the extensive applications of this SWIR-OPD.

NaGdF4:Yb, Er, Tm Upconversion Nanoparticles for Bioimaging in Shortwave-Infrared Range: Study of Energy Transfer Processes and Composition Optimization

Upconversion nanoparticles are promising for many applications. For triple-doped nanoparticles (NPs), the luminescence intensity shows a non-linear dependence on the rare-earth ion concentration, making it difficult to obtain bright phosphors with high energy output. We investigated the energy transfer processes in β-NaGdF4:Yb-Er-Tm NPs and considered strategies for increasing the thulium luminescence intensity, in particular, the use of core–shell structures. The luminescence spectra were analyzed in the short-wavelength infrared (SWIR) and visible (VIS) regions. The Er3+ and Tm3+ luminescence lifetimes in the VIS region were measured to study the energy transfer processes between the active ions. The quenching of the Tm3+ luminescence in the SWIR region was observed. However, both Er3+ and Tm3+ luminescence bands were observed in the VIS range. We attribute these effects to energy transfer between Tm3+ 3F4 → 3H6 and Er3+ 4I13/2 → 4I9/2, which occurs due to overlap of Er3+ and Tm3+ luminescence bands, and also to competition between Er3+ and Tm3+ for energy transfer from Yb3+. For core–shell NPs, when Tm3+ and Er3+ are separated into adjacent layers, quenching cannot be avoided, likely due to the mutual diffusion of ions during shell synthesis. The most optimal strategy to obtain luminescence in the SWIR range is to use an inert intermediate shell between the layers containing Tm3+ and Er3+.

Control over Charge Carrier Mobility in the Hole Transport Layer Enables Fast Colloidal Quantum Dot Infrared Photodetectors

Solution-processed colloidal quantum dots (CQDs) are promising materials for photodetectors operating in the short-wavelength infrared region (SWIR). Devices typically rely on CQD-based hole transport layers (HTL), such as CQDs treated using 1,2-ethanedithiol. Herein, we find that these HTL materials exhibit low carrier mobility, limiting the photodiode response speed. We develop instead inverted (p-i-n) SWIR photodetectors operating at 1370 nm, employing NiOx as the HTL, ultimately enabling 4× shorter fall times in photodiodes (∼800 ns for EDT and ∼200 ns for NiOx). Optoelectronic simulations reveal that the high carrier mobility of NiOx enhances the electric field in the active layer, decreasing the overall transport time and increasing photodetector response time.

Comparative study of optical characteristics of SQW and DQWs InGaAs/GaAsSb/AlAsSb based compressively strained heterostructures

InP-based InGaAs/GaAsSb/AlAsSb type-II single quantum well (SQW) and double quantum wells (DQWs) heterostructures are compared on the basis of matrix elements, energy dispersion curves, optical gain, and transition energy. The effect on optical gain due to applied external strain and the influence of In-mole fraction and Sb-mole fraction on momentum matrix element and transition wavelength have also been compared between SQW and DQWs heterostructures. The simulation results show that the transition wavelength is located in the short wavelength infrared region (SWIR). SWIR imaging has various applications such as solar cell inspection, surveillance, electronic board inspection, identification and sorting, and more. For the proposed design, a total optical gain of 7450 cm−1 and 13,681 cm−1 is obtained at 0.75 eV and 0.77 eV transition energies for the SQW and DQWs heterostructures. For 1.5 nm QW thickness and 3x1012 cm−2 injected carrier density at 300 K, the transition wavelength increases from 1.67 μm to 1.82 μm and 1.60 μm–1.77 μm for SQW and DQWs heterostructure, respectively on increasing the mole fraction value of In from 0.5 to 0.8 and when the mole fraction value of Sb increases from 0.5 to 0.8, the transition wavelength increases from 1.69 μm to 1.87 μm and 1.62 μm–1.79 μm for SQW and DQWs heterostructure, respectively.

Experimental realization of short-wavelength infrared half wave retarder fabricated from ZnO single crystal plates

With increasing interest in studying fundamental phenomena at near-infrared (NIR) and short-wavelength infrared (SWIR) frequencies, it is essential to find optical devices which can alter polarization state in the NIR and SWIR radiation range. However, simple optical components such as wave plates capable of generating and controlling polarization sates in the NIR and SWIR radiation are rare. Therefore, our use of channelled spectra of polarized white photons is reported to extract the dispersion of the phase birefringence Δnp(λ) of the 112‾0 and 11‾00 plates of ZnO single crystal acting as multiple order wave plates. The phase birefringence Δnp(λ) of the 112‾0 and 11‾00 ZnO plates was extracted using a calculation procedure named the wavenumber difference method. The correctness of the birefringence data obtained was also confirmed by recalculating the plate thickness using the Jones matrix technique. Furthermore, the birefringence group velocity factor of the 112‾0 and 11‾00 ZnO plates was also extracted from the channelled spectra of polarized white photons using simple method. For both 112‾0 and 11‾00 ZnO plates, a broad spectral full width at half maximum (FWHM) is observed in SWIR region (1100–2500 nm), therefore, 112‾0 and 11‾00 ZnO plates can act as if they are functioning as a zero-order wave plate.

Demonstration of SWIR Silicon-Based Photodetection by Using Thin ITO/Au/Au Nanoparticles/n-Si Structure.

Plasmonic photodetection based on the hot-electron generation in nanostructures is a promising strategy for sub-band detection due to the high conversion efficiencies; however, it is plagued with the high dark current. In this paper, we have demonstrated the plasmonic photodetection with dark current suppression to create a Si-based broadband photodetector with enhanced performance in the short-wavelength infrared (SWIR) region. By hybridizing a 3 nm Au layer with the spherical Au nanoparticles (NPs) formed by rapid thermal annealing (RTA) on Si substrate, a well-behaved ITO/Au/Au NPs/n-Si Schottky photodetector with suppressed dark current and enhanced absorption in the SWIR region is obtained. This optimized detector shows a broad detection beyond 1200 nm and a high responsivity of 22.82 mA/W at 1310 nm at −1 V, as well as a low dark current density on the order of 10−5 A/cm2. Such a Si-based plasmon-enhanced detector with desirable performance in dark current will be a promising strategy for realization of the high SNR detector while keeping fabrication costs low.

Extended Short-Wavelength Infrared Photoluminescence and Photocurrent of Nonstoichiometric Silver Telluride Colloidal Nanocrystals.

Demands on nontoxic nanomaterials in the short-wavelength infrared (SWIR) have rapidly grown over the past decade. Here, we present the nonstoichiometric silver chalcogenide nanocrystals of AgxTe (x > 2) and Ag2Te/Ag2S CQDs with a tunable bandgap across the SWIR region. When the atomic percent of the metal and chalcogenide elements are varied, the emission frequency of the excitonic peak is successfully extended to 2.7 μm. Surprisingly, the AgxTe CQD film responds to the SWIR light with a responsivity of 2.1 A/W at 78 K. Also, the Ag2S shell growth over the Ag2Te core enhances not only the emission intensity but also the structural rigidity, preventing crystal morphology deformation under the electron beam. The origin of the enhancement in the emission intensity and air stability of AgxTe and Ag2Te/Ag2S CQDs is carefully investigated by X-ray photoelectron spectroscopy (XPS). The optical properties and infrared photocurrent of AgxTe CQDs will provide new opportunities for solution-based SWIR applications.

Identification of Internal Defects in Potato Using Spectroscopy and Computational Intelligence Based on Majority Voting Techniques.

Potatoes are one of the most demanded products due to their richness in nutrients. However, the lack of attention to external and, especially, internal defects greatly reduces its marketability and makes it prone to a variety of diseases. The present study aims to identify healthy-looking potatoes but with internal defects. A visible (Vis), near-infrared (NIR), and short-wavelength infrared (SWIR) spectrometer was used to capture spectral data from the samples. Using a hybrid of artificial neural networks (ANN) and the cultural algorithm (CA), the wavelengths of 861, 883, and 998 nm in Vis/NIR region, and 1539, 1858, and 1896 nm in the SWIR region were selected as optimal. Then, the samples were classified into either healthy or defective class using an ensemble method consisting of four classifiers, namely hybrid ANN and imperialist competitive algorithm (ANN-ICA), hybrid ANN and harmony search algorithm (ANN-HS), linear discriminant analysis (LDA), and k-nearest neighbors (KNN), combined with the majority voting (MV) rule. The performance of the classifier was assessed using only the selected wavelengths and using all the spectral data. The total correct classification rates using all the spectral data were 96.3% and 86.1% in SWIR and Vis/NIR ranges, respectively, and using the optimal wavelengths 94.1% and 83.4% in SWIR and Vis/NIR, respectively. The statistical tests revealed that there are no significant differences between these datasets. Interestingly, the best results were obtained using only LDA, achieving 97.7% accuracy for the selected wavelengths in the SWIR spectral range.

Short-wavelength optoacoustic spectroscopy based on water muting

Infrared (IR) optoacoustic spectroscopy can separate a multitude of molecules based on their absorption spectra. However, the technique is limited when measuring target molecules in aqueous solution by strong water absorption at IR wavelengths, which reduces detection sensitivity. Based on the dependence of optoacoustic signal on the temperature of the probed medium, we introduce cooled IR optoacoustic spectroscopy (CIROAS) to mute water contributions in optoacoustic spectroscopy. We showcase that spectral measurements of proteins, lipids, and glucose in the short-wavelength IR region, performed at 4 °C, lead to marked sensitivity improvements over conventional optoacoustic or IR spectroscopy. We elaborate on the dependence of optoacoustic signals on water temperature and demonstrate polarity changes in the recorded signal at temperatures below 4 °C. We further elucidate the dependence of the optoacoustic signal and the muting temperature on sample concentration and demonstrate that changes in these dependences enable quantification of the solute concentration. We discuss how CIROAS may enhance abilities for molecular sensing in the IR.

Spatial Optimization of Modulation Doping in P-I-P QDIPs: Towards Achieving Higher Operating Temperature

We report short wavelength infrared (SWIR) photodetectors using multi-stacked modulation doped Indium-Arsenide (InAs) self-assembled quantum dots (QDs). The detriments of direct doping on the energy levels of InAs QDs have been eliminated by choosing modulation doping. We have considered three P-I-P Indium Arsenide/Gallium Arsenide (InAs/GaAs) quantum dot infrared photodetector (QDIP) heterostructures in which a thin (3 nm) P-doped GaAs layer is introduced at a distance of 7, 12 and 17 nm away from each InAs dot layer respectively. The structures have been analyzed for their morphological and optical characteristics and an optimum separation between the active layer and modulation doped layer has been achieved. The fabricated single pixel detectors exhibit a broad spectral response from 1 to 3.5 μm in the SWIR region for all the samples. The infrared photocurrent survives up to a maximum temperature of 200K for the optimized device with a peak responsivity of 1.439 A/W at wavelength λ = 1.77 μm and temperature T = 200 K.

(Invited) Emerging Designs for Polymer-Based Energy Storage Devices and Sensors

Conducting polymers are an important class of Faradaic materials for energy storage, as they present opportunities to create energy dense supercapacitors. The vast majority of conducting polymers are p-type cathodes and already operating at or close to the upper voltage limit of non-aqueous electrolytes. On the other hand, it is generally safe for electrolytes to operate down to -2 V vs Standard Hydrogen Electrode. Therefore, extending the operational voltage in the negative range is an attractive route to increase energy density. Here we present promising n-type polymers that retained 90% of initial capacitance after 1000 charge-discharge cycles. We measure in operando the electronic and ionic transport in conducting polymers by current-voltage and spectroscopic measurements, where spatial variations of film absorption would be mapped to discern electronic versus ionic degradation. We infer the mechanisms that lead to capacitance fade and suggests structural and electrochemical strategies to realize high-endurance energy storage devices for wearable systems. In addition, organic polymers responsive to the short wavelength infrared (SWIR) spectra are used to realize photodetectors that is relevant to a variety of applications including environmental monitoring and medical diagnosis. Here we show novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the polymers are processed into bulk heterojunction photodiodes with photoresponse up to wavelength of 1.7 micron. The performances of devices with different polymer structures were compared through metrics including detectivity, quantum efficiency, response time and rectification ratio. Example applications including hemodynamics and tissue composition measurements will be demonstrated.

Luminescent nanothermometry using short-wavelength infrared light

We analyzed the potentiality of the short-wavelength infrared (SWIR) emissions of different lanthanide ions (Er3+, Tm3+ and Ho3+) embedded in different hosts for luminescence thermometry. The 1.55 μm emission band generated by Er3+ has different Stark sub-levels that can be used in temperature sensing purposes. However, the thermal sensitivity that can be achieved with this emission is relatively low, ranging from 0.06 to 0.15% K−1. In the case of Tm3+, the emissions arising from the 3F4 and 3H4 electronically coupled energy levels are useful for luminescence thermometry, with a linear evolution for the intensity ratio in the biological range as the temperature increases, which simplifies the calibration procedure for luminescent thermometers based on this parameter. When co-doped with Ho3+, an efficient energy transfer between the Tm3+ and Ho3+ ions is generated, that results in a new emission line centered at 1.96 μm that can be also used for luminescence thermometry purposes, with an enhanced thermal sensitivity when pumped at 808 nm. The thermal sensitivities achieved with these doping ions are higher than those obtained with Er3+ and are comparable to those reported previously for some lanthanide-doped materials operating in the visible, and in the I- and II-BWs. We demonstrated the potentiality of these emissions in the SWIR region for luminescence thermometry and imaging in ex-vivo experiments by monitoring the increase of temperature induced in chicken breast meat, with an experimental thermal resolution of ∼0.5 K, below the theoretical value of 0.8 K predicted for particles operating in this spectral region, and a penetration depth of at least 0.5 cm.

Multispectral absorptance from large-diameter InAsSb nanowire arrays in a single epitaxial growth on silicon

Vertical III-V nanowires are capable of resonant absorption at specific wavelengths by tuning the nanowire diameter, thereby exceeding the absorption of equivalent thin films. These properties may be exploited to fabricate multispectral infrared (IR) photodetectors, directly integrated with Si, without the need for spectral filters or vertical stacking of heterostructures as required in thin film devices. In this study, multiple InAsSb nanowire arrays were grown simultaneously on Si by molecular beam epitaxy with nanowire diameter controlled by the nanowire period (spacing between nanowires). This is the first such study of patterned InAsSb nanowires where control of nanowire diameter and multispectral absorption are demonstrated. The antimony flux was used to control axial and radial growth rates using a selective-area catalyst-free growth method, achieving large diameters, spanning 440–520 nm, which are necessary for optimum IR absorption. Fourier transform IR spectroscopy revealed IR absorptance peaks due to the HE11 resonance of the nanowire arrays in agreement with optical simulations. Due to the dependence of the HE11 resonance absorption on nanowire diameter, multispectral absorption was demonstrated in a single material system and a single epitaxial growth step without the need for bandgap tuning. This work demonstrates the potential of InAsSb nanowires for multispectral photodetectors and sensor arrays in the short-wavelength IR region.

Impact of damages in monocrystalline n‐Si on material photosensitivity

The optical and electrical characteristics of p–n photodiodes based on monocrystalline n‐Si (wafers with ρ = 70 and 10 Ohm · cm and SOI) implanted with B+ in the dose range of 1 × 1014–1 × 1015 сm−2 and annealed at 900 °C (20 min) are studied. The p–n structures exhibit photosensitivity in the short‐wavelength infrared region (SWIR) with different maximum intensities depending on dose and n‐Si resistivity. Leakage currents are also dose‐dependent. The character of the SOI spectra is somewhat different. The optical and electrical properties of p–n photodiodes are described in terms of formation of extended defects with deep levels in the bandgap appearing after B implantation and annealing of n‐Si. The importance of the damaged surface layer in the starting material for the observed effects is confirmed experimentally. The relation of the SWIR photoresponse intensity to the content of C and O gettered to the p–n structure surface is revealed. The innovative aspects of technology application are discussed.

Quantum dots could expand live imaging

When it comes to imaging live tissue, short-wavelength infrared (SWIR) radiation penetrates farther and scatters less than more-traditional near-IR and visible light. But a lack of agents that fluoresce brightly in the SWIR region (about 1,000 to 2,000 nm) has impeded the development of this type of imaging in the body. Moungi G. Bawendi, Oliver T. Bruns, and Thomas S. Bischof of MIT and coworkers have now created quantum dots that could expand SWIR live imaging (Nat. Biomed. Eng. 2017, DOI: 10.1038/s41551-017-0056). They coated InAs cores with CdSe, CdS, CdSe-ZnSe, or CdS-ZnSe single or double layers and derivatized the resulting quantum dots with organic functional groups to customize them—for instance, to have long blood circulation times. The quantum dots emit SWIR radiation about an order of magnitude more strongly, are more stable, and have narrower and more tunable emission spectra than previous SWIR probes. In live imaging, the quantum dots

Infrared to visible image up-conversion using optically addressed spatial light modulator utilizing liquid crystal and InGaAs photodiodes

Combination of InGaAs/InP heterojunction photodetector with nematic liquid crystal (LC) as the electro-optic modulating material for optically addressed spatial light modulator for short wavelength infra-red (SWIR) to visible light image conversion was designed, fabricated, and tested. The photodetector layer is composed of 640 × 512 photodiodes array based on heterojunction InP/InGaAs having 15 μm pitch on InP substrate and with backside illumination architecture. The photodiodes exhibit extremely low, dark current at room temperature, with optimum photo-response in the SWIR region. The photocurrent generated in the heterojunction, due to the SWIR photons absorption, is drifted to the surface of the InP, thus modulating the electric field distribution which modifies the orientation of the LC molecules. This device can be attractive for SWIR to visible image upconversion, such as for uncooled night vision goggles under low ambient light conditions.

Genetic analysis of the Fourier-transform infrared spectra of bovine milk with emphasis on individual wavelengths related to specific chemical bonds

Fourier-transform infrared (FTIR) spectra are used to predict the fat, protein, casein, and lactose contents of milk. These estimates are currently used to predict the individual estimated breeding values of animals. The objective of the present study was to estimate the genetic variation and heritabilities of the milk transmittance spectrum at each individual FTIR wave. Milk was sampled once per cow from a total of 1,064 Italian Brown Swiss cows from 30 herds, sired by 50 artificial insemination sires. The FTIR spectra of all samples were collected within 3h of sampling from 25mL of milk. The obtained spectral range comprised wavenumbers 5,000 to 930×cm−1, corresponding to wavelengths 2.00 to 10.76μm and frequencies from 149.9 to 27.9THz, for a total of 1,056 waves. These were acquired using a MilkoScan FT120 FTIR interferometer (Foss Electric A/S, Hillerød, Denmark). Each spectral data point was treated as a single trait and analyzed using an animal model REML method. The results indicated that the transmittance of the bovine milk FTIR spectrum was heritable for most individual waves in the wavenumber interval from 5,000 to 930×cm−1. Moreover, the transmittance of contiguous FTIR waves was much more highly correlated in terms of the average value and phenotypic variation, compared with genetic variation. In the present study, we characterized 5 regions of the FTIR spectrum that were relevant to the analysis of milk; 2 regions, one in the transition area between the short-wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) divisions of the electromagnetic spectrum (SWIR-MWIR region) and another very short region in the MWIR division (MWIR-2 region), were characterized by very high phenotypic variability in the transmittance of individual milk samples within each wave. This was caused by the absorption peaks of water, which can mask the effects of other important milk components. These regions also showed high genetic variability in transmittance, and the heritability estimates of individual waves were generally very low (with some exceptions). The 3 other identified regions contained many transmittance peaks that represented important chemical bonds; these showed much lower phenotypic and genetic variability in terms of individual waves, but relatively higher and less variable heritability estimates. Among them, the SWIR region (near-infrared) showed a peculiar cyclic pattern of the heritability coefficients of transmittance, the MWIR-1 region was particularly important for the estimation of fat, and the MWIR-LWIR region (also known also as the “fingerprint region”) had 3 areas of relatively high heritability. In summary, we found that the transmittance data from the FTIR spectra of milk have genetic variability that may prove useful for the direct genetic improvement of dairy species, rather than only through indirect phenotypic predictions of individual milk quality and technological traits.