Mid-wave Infrared Research Articles

A Self‐Powered Photodetector Based on Graphene Enhanced WSe2/PtSe2 Heterodiode with Fast Speed and Broadband Response

AbstractNarrow bandgap 2D layered material platinum selenide (PtSe2) with good environmental stability, high carrier mobility, and high light absorption, has been widely investigated for uncooled midwave‐infrared (MWIR) photodetection. However, the phototransistor based on the PtSe2 operation at room temperature suffered from the high dark current and background noise. Here, a graphene (G)‐enhanced G‐WSe2/PtSe2 hetero‐diode placed on a metal electrode is reported. To enhance the photogain, a graphene layer placed on the WSe2/PtSe2 heterodiode as a local gating layer is designed. The device exhibits an ultra‐high light on/off ratio of up to 108 and ultra‐fast photoresponse speed with raising time τr = 0.9 µs and decay time of τd = 1.5 µs in the visible spectra range. Notably, ultrabroad band photoresponse from 405 to 3366 nm is demonstrated under the self‐power model. Notably, the device presented a competitive photovoltaic effect with a high energy conversion efficiency (PCE) of 3.45%. The results pave the way toward a new approach to tuning the performance of the atomic thin layered materials photodetector.

Polarization‐Sensitive Photodetector Based on Quasi‐1D (TaSe4)2I Nanowire Response to 10.6 µm

AbstractPolarization‐sensitive infrared (IR) photodetection plays an important role in fiber optic communication, environmental monitoring, and remote sensing imaging. Semiconductors with quasi‐1D crystal structures exhibit unique optical and electrical properties due to their 1D carrier transport channels and large surface area‐to‐volume ratio, offering the possibility of high‐performance photodetectors with high photogain (G), polarization sensitivity photodetection. Herein, an ultra‐broadband photodetection (405 nm–10.6 µm) based on a quasi‐1D (TaSe4)2I single‐crystal nanowire is reported. The (TaSe4)2I photodetector exhibits excellent polarization‐sensitive photodetection, with a high dichroic ratio of Imax/Imin = 2.32 under 637 nm illumination. Notably, the (TaSe4)2I nanowire photodetector exhibits a competitive performance in uncooled mid‐wave infrared (MWIR) detection with a high photoresponsivity (R) of 110.5 AW−1 and specific detectivity (D*) of 4.8 × 1010 cmHz1/2W−1. Moreover, in the long‐wave infrared (LWIR) spectral range, an R of 67.6 mAW−1 is demonstrated at room temperature (RT). The (TaSe4)2I nanowire photodetector enables significant advancements for polarization‐sensitive and uncooled MWIR and LWIR photodetection.

Bias-Tunable Quantum Well Infrared Photodetector.

With the rapid advancement of Artificial Intelligence-driven object recognition, the development of cognitive tunable imaging sensors has become a critically important field. In this paper, we demonstrate an infrared (IR) sensor with spectral tunability controlled by the applied bias between the long-wave and mid-wave IR spectral regions. The sensor is a Quantum Well Infrared Photodetector (QWIP) containing asymmetrically doped double QWs where the external electric field alters the electron population in the wells and hence spectral responsivity. The design rules are obtained by calculating the electronic transition energies for symmetric and antisymmetric double-QW states using a Schrödinger-Poisson solver. The sensor is grown and characterized aiming detection in mid-wave (~5 µm) to long-wave IR (~8 µm) spectral ranges. The structure is grown using molecular beam epitaxy (MBE) and contains 25 periods of coupled double GaAs QWs and Al0.38Ga0.62As barriers. One of the QWs in the pair is modulation-doped to provide asymmetry in potential. The QWIPs are tested with blackbody radiation and FTIR down to 77 K. As a result, the ratio of the responsivities of the two bands at about 5.5 and 8 µm is controlled over an order of magnitude demonstrating tunability between MWIR and LWIR spectral regions. Separate experiments using parameterized image transformations of wideband LWIR imagery are performed to lay the framework for utilizing tunable QWIP sensors in object recognition applications.

VO2 wire grid polarizers for MWIR applications

Phase change materials (PCMs) have received a lot of attention recently due to their ability to reversibly switch between phases producing large changes in their optical and electrical properties.VO2 is unique compared to other chalcogenide-based PCMs due to its volatile switching behavior, allowing it to automatically reset when the thermal stimulus is removed. It is able to switch between a metallic rutile phase and a monoclinic semiconducting phase, making it an ideal candidate for polarization control. In this paper, we demonstrate a VO2 wire grid polarizer with an extinction ratio as high as 6 dB in the midwave infrared (MWIR) spectrum that can be thermally turned on and off. We used a novel, to the best of our knowledge, approach to fabricate these devices, using conventional photolithography and lift-off processes on metallic vanadium followed by thermal oxidation in a furnace. This is a significantly simpler and a scalable procedure compared to current processes of patterning and etching VO2.

Effects of the thermal treatments on the optical properties of SiO2 anti-reflective coatings on sapphire windows

The SiO2 films were deposited on sapphire substrates using radio frequency (RF) magnetron sputtering to enhance the mid-wave infrared (IR) transmittance. The effects of thermal treatments by annealing and in-situ heating on the SiO2 films were investigated. After annealing at 600 °C, the surface morphology, microstructure, chemical states, and optical constants were investigated. No obvious microcracks or delamination were observed on the film surfaces, indicating excellent adhesion to the sapphire substrates. With an increase in the annealing time, gradual oxidation of Si atoms within the SiO2 thin films occurred, resulting in the release of OH groups and evaporation of moisture. The refractive index exhibited slight changes, while the extinction coefficient showed a significant reduction, thus the transmittance was improved. According to the in-situ heating tests from the annealed samples, it revealed a slight increase in average transmittance with prolonged annealing time. Finally, we assessed the performance of the annealed samples by rapid heat shock to 600 °C at a very short time, which demonstrated outstanding optical performance and heat-resistant properties. The present work supports the feasibility of applying the SiO2 films under harsh high-temperature environments.

Laser doping of n-type 4H-SiC with boron using solution precursor for mid-wave infrared optical properties

Laser doping of n-type 4H-silicon carbide (SiC) semiconductor substrates with boron (B) using a pulsed Nd:YAG laser (λ = 1064 nm) is reported. An aqueous boric acid solution was used as a boron precursor. A simple theoretical heat transfer model was employed to select the laser processing parameters, i.e., laser power and laser-substrate interaction time, and determine the appropriate temperature to dope 4H-SiC substrates. The selected processing parameters ensured that the temperature at the laser-substrate interaction zone was below the SiC peritectic temperature to prevent any crystalline phase transformations in SiC. Fourier-transform infrared spectrometry was conducted to determine the optical properties of both undoped and boron-doped 4H-SiC substrates within the mid-wave infrared (MWIR) wavelength range (3–5 μm). Boron atoms create an acceptor energy level at 0.29 eV above the valence band in the 4H-SiC bandgap, which corresponds to λ = 4.3 μm. Boron-doped 4H-SiC substrate exhibited reduced reflectance and increased absorptance for the MWIR range. An absorption peak at λ = 4.3 μm was detected for the doped substrate. This confirmed the creation of the acceptor energy level in the 4H-SiC bandgap and, thus, doping of 4H-SiC with boron. A notable decrease in the refractive index, i.e., from 2.87 to 2.52, after laser doping of n-type 4H-SiC with boron was achieved.

Room-temperature nanostructured PbSe/CdSe mid-infrared photodetector: Annealing effects

Room-temperature (RT) photoconductor using mid-wave infrared (MWIR) nanostructured lead selenide (PbSe)/cadmium selenide (CdSe) is presented on a commercially available silicon dioxide on silicon (100) (SiO2/Si) wafer. This device is fabricated through vapor phase deposition (VPD) and subsequently annealed in oxygen to create interconnected nanostructures, which establish efficient pathways for photogenerated carriers and passivate defects within the material. RT specific detectivity (D*) of 8.57 × 108 Jones and a peak D* of 2.49 × 109 Jones are achieved with interband cut-off wavelength of 4 μm. Additionally, the utilization of nanostructured thin film deposition on cost-effective SiO2/Si(100) substrates via the affordable VPD method significantly reduces production costs and facilitates the potential of monolithic integration with Si-based readout integrated circuitry enabling low-cost large-scale production.

RISIR: Rapid Infrared Spectral Imaging Restoration Model for Industrial Material Detection in Intelligent Video Systems

Material detection by industrial infrared imaging spectrometer (IRIS) is a key technique in multiple industrial applications, including garbage collection, material analysis, and robot vision. However, IRIS often suffers from overlapped bands and random noises, which limit the precision of subsequent processing. In this article, we propose a novel Gabor transform-based mid-wave infrared (MWIR) spectrum restoration model by successfully exploring the intrinsic structure of the clean MWIR spectrum from the degraded one. First, a total variation-regularized Gabor coefficient adjustment descriptor is designed and incorporated into the spectrum restoration model. In addition to adjusting the Gabor coefficient distribution by total variation-norm, the L2-norm of gradient is leveraged to regulate the smoothness of the instrument degradation function. Then, the proposed model is inferred using an efficient optimization approach based on split Bregman iteration method and alternating minimization algorithm. Quantitative and qualitative experimental results demonstrate that the proposed model favorably outperforms the state-of-the-art approaches. The restored high-resolution MWIR spectrum can be used to rapidly detect different materials in intelligent video systems.

Electrical Characterization of Type II Superlattice Midwave Infrared Photodetectors Irradiated by Protons

Electrical Characterization of Type II Superlattice Midwave Infrared Photodetectors Irradiated by Protons

(Invited) Transistor-Injected Quantum-Cascade Devices: Novel Sources for Mid-Wave Infrared Emission

Quantum Cascade Lasers (QCLs) [1] are important sources for coherent mid-wave infrared (MWIR) light that find widespread use in applications such as molecular spectroscopy, free-space optical communications, and defense countermeasures. These applications demand tunability of emission wavelength and high output powers. The conventional QCL is a two-terminal n-i-n device in which an externally applied bias establishes the necessary electric field in the cascade region for proper alignment of the quantum states, defines the emission wavelength, and also determines the current through the cascade structure. Because QCLs are 2-terminal devices, changing bias directly changes both wavefunction overlap and energy separation. The spectral location and magnitude of the gain peak thus has a strong dependence on applied voltage, impacting the capability to modulate. To overcome these limitations, the transistor-injected quantum-cascade laser (TI-QCL) has been proposed [2]. The TI-QCL is a three-terminal device in which the cascade region is placed within a heterojunction bipolar transistor. In forward-active mode the current injection is controlled by a forward-biased emitter-base junction, and the reverse bias on the base-collector junction is used to control the electric field for alignment of the quantum states. This novel structure enables the decoupling of emission wavelength and output power. This extra control positions the TI-QCL to impact a wide range of applications such as spectroscopy with its wide tunability, and free-space communication with its capability to separately modulate power and frequency.Previously, transistor characteristics and near-infrared (NIR) band-to-band base emission was demonstrated in a GaAs design [3, 4] before moving to an InP-based design [5]. We will review the progress made to push the TI-QCL concept towards full functionality, focusing on InP-based epitaxial designs. A self-consistent Schrodinger-Poisson solver and non-equilibrium Green’s function method is used to aid in the active-region design of the structure, which is optimized for a peak emission wavelength of 8.27 μm as shown in Figure 1 [6]. A wide wavelength tunability from approximately 7.8 μm to 8.8 μm is projected based on computational analysis. The InP-based structure is grown using molecular beam epitaxy by IntelliEpi; a cross-section of the material is depicted in Figure 2. It contains an active-region composed of 30 repeated periods of In0.41Ga0.59As/In0.36Al0.64As strain-balanced superlattice. The devices are fabricated using standard III-V processing. An image of a fabricated TI-QCL bar consisting of a sloped, 20 μm wide emitter mesa and evaporated SiO2 as the passivation layer is depicted in Figure 3. The fabricated devices are diced and cleaved into 2 to 4 mm x 500 μm die and mounted onto In-plated copper mounts followed by wire bonding. The devices are electrically characterized at room temperature, 77 K, and 18 K. Under cryogenic temperatures, the common-base characteristics exhibit negative differential resistance (NDR) in collector current at all emitter injection currents as shown in Figure 4, which signifies tunneling transport through the quantum cascade superlattice region. The base current also exhibits corresponding NDR behavior and switching in the band-to-band NIR light (1.57 m) output from the In0.53Ga0.47As base is experimentally observed when biased in a region where transport through the cascade region is rejected due to quantum state misalignment.

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers.

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability. Here we propose, demonstrate, and analyze a mid-infrared absorber architecture leveraging monolayer films of nanoplasmonic colloidal tin-doped indium oxide nanocrystals (ITO NCs). We fabricate a series of ITO NC monolayer films using the liquid-air interface method; by synthetically varying the Sn dopant concentration in the NCs, we achieve spectrally selective perfect absorption tunable between wavelengths of two and five micrometers. We achieve monolayer thickness-controlled coupling strength tuning by varying NC size, allowing access to different coupling regimes. Furthermore, we synthesize a bilayer film that enables broadband absorption covering the entire midwave IR region (λ = 3-5 μm). We demonstrate a scalable platform, with perfect absorption in monolayer films only hundredths of a wavelength in thickness, enabling strong light-matter interaction, with potential applications for molecular detection and ultrafast nonlinear optical applications.

UV-curable thiol-ene system for broadband infrared transparent objects

Conventional infrared transparent materials, including inorganic ceramic, glass, and sulfur-rich organic materials, are usually processed through thermal or mechanical progress. Here, we report a photo-curable liquid material based on a specially designed thiol-ene strategy, where the multithiols and divinyl oligomers were designed to contain only C, H, and S atoms. This approach ensures transparency in a wide range spectrum from visible light to mid-wave infrared (MWIR), and to long-wave infrared (LWIR). The refractive index, thermal properties, and mechanical properties of samples prepared by this thiol-ene resin were characterized. Objects transparent to LWIR and MWIR were fabricated by molding and two-photon 3D printing techniques. We demonstrated the potential of our material in a range of applications, including the fabrication of IR optics with high imaging resolution and the construction of micro-reactors for temperature monitoring. This UV-curable thiol-ene system provides a fast and convenient alternative for the fabrication of thin IR transparent objects.

Trap levels analysis in MWIR InAs/InAsSb T2SL photodiode

Mid-wave infrared (MWIR) photodiode with an InAs/InAsSb superlattice active layer was characterized by the photoluminescence (PL), spectral response (SR) and deep level transient spectroscopy (DLTS) measurements. Three independent methods, in combination with the theoretical calculations, were used to determine the transitions between superlattice minibands, as well as to and from the trap states. The determined effective band gap of the investigated superlattice is 251 meV at 70 K. Most of the detected trap states lie within the energy gap, around 60 and 80 meV below the first electron miniband, and near the mid-gap. Moreover, trap states located above the first electron miniband and below the first light hole miniband were also observed. It is worth emphasizing that the PL and DLTS measurements give consistent results. Additionally, the activation energy of 16 meV for the Be acceptor dopant was determined using the PL measurement.

Large-scale efficient mid-wave infrared optoelectronics based on black phosphorus ink

The mid-wave infrared (MWIR), ranging from 2 to 5 micrometers, is of substantial interest for chemical sensing, imaging, and spectroscopy. Black phosphorus (bP)–based MWIR light emitters and detectors have been shown to outperform the state-of-the-art for commercial devices due to the low Auger recombination coefficient of bP. However, the scalability of these devices remains a challenge. Here, we report a bP ink formula that preserves the exceptional MWIR optoelectronic properties of bP to deposit centimeter-scale, uniform, and pinhole free films with a photoluminescence quantum yield higher than competing III-V and II-VI semiconductors with similar bandgaps at high excitation regime. As a proof of concept, we use bP ink as a “phosphor” on a red commercial light-emitting diode to demonstrate bright MWIR light emission. We also show that these films can be integrated into heterostructure device architectures with electron and hole selective contacts for direct-injected light emission and detection in MWIR.

Ultrabroadband High Photoresponsivity at Room Temperature Based on Quasi-1D Pseudogap System (TaSe4 )2 I.

Narrow bandgap materials have garnered significant attention within the field of broadband photodetection. However, the performance is impeded by diminished absorption near the bandgap, resulting in a rapid decline in photoresponsivity within the mid-wave infrared (MWIR) and long-wave infrared (LWIR) regions. Furthermore, they mostly worked in cryogenic temperature. Here, without the assistance of any complex structure and special environment, it is realized high responsivity covering ultra-broadband wavelength range (Ultraviolet (UV) to LWIR) in a single quasi-1D pseudogap (PG) system (TaSe4 )2 I nanoribbon, especially high responsivity (From 23.9 to 8.31AW-1 ) within MWIR and LWIR region at room temperature (RT). Through direct probing the carrier relaxation process with broadband time-resolved transient absorption spectrum measurement, the underlying mechanism of majorly photoconductive effect is revealed, which causes an increased spectral weight extended to PG region. This work paves the way for realizing high-performance uncooled MWIR and LWIR detection by using quasi-1D PG materials.

Synthesis of Deuterated and Sulfurated Polymers by Inverse Vulcanization: Engineering Infrared Transparency via Deuteration.

The synthesis of deuterated, sulfurated, proton-free, glassy polymers offers a route to optical polymers for infrared (IR) optics, specifically for midwave IR (MWIR) photonic devices. Deuterated polymers have been utilized to enhance neutron cross-sectional contrast with proteo polymers for morphological neutron scattering measurements but have found limited utility for other applications. We report the synthesis of perdeuterated d14-(1,3-diisopropenylbenzene) with over 99% levels of deuteration and the preparation of proton-free, perdeuterated poly(sulfur-random-d14-(1,3-diisopropenylbenzene)) (poly(S-r-d14-DIB)) via inverse vulcanization with elemental sulfur. Detailed structural analysis and quantum computational calculations of these reactions demonstrate significant kinetic isotope effects, which alter mechanistic pathways to form different copolymer microstructures for deutero vs proteo poly(S-r-DIB). This design also allows for molecular engineering of MWIR transparency by shifting C-H bond vibrations around 3.3 μm/3000 cm-1 observed in proteo poly(S-r-DIB) to 4.2 μm/2200 cm-1. Furthermore, the fabrication of thin-film MWIR optical gratings made from molding of deuterated-sulfurated, proton-free poly(S-r-d14-DIB) is demonstrated; operation of these gratings at 3.39 μm is achieved successfully, while the proteo poly(S-r-DIB) gratings are opaque at these wavelengths, highlighting the promise of MWIR sensors and compact spectrometers from these materials.

Design of uncooled mid-wave infrared detectors based on lead selenide barrier structure

Mid- and long-wavelength IR photodetectors incorporating narrow-bandgap semiconductors often face the challenge of large RT dark current, limiting their applications in military and civilian use. Herein, a novel pBn+ barrier detector architecture based on a lead selenide/indium selenide barrier structure is proposed to significantly suppress the dark current, so that uncooled mid-wave IR (MWIR) photodetectors with high performance can be achieved. The finite element analysis of the detector demonstrates reduced RT dark current down to 55 mA cm−2 under −0.1 V bias, which is a two-fold decrease compared to the InAs/InAsAb type-II superlattice detector. In addition, at RT, the optimized pBn+ barrier detector exhibits excellent responsivity and detectivity of 1.23 A W−1 and 9.47 × 109 cm Hz1/2·W−1 at 3.8 μm, respectively. The PbSe-based barrier architecture provides a promising industrialization solution for high-performance uncooled MWIR photodetectors.

Black Phosphorus Molybdenum Disulfide Midwave Infrared Photodiodes with Broadband Absorption-Increasing Metasurfaces.

Black phosphorus (BP) has been established as a promising material for room temperature midwave infrared (MWIR) photodetectors. However, many of its attractive optoelectronic properties are often observable only at smaller film thicknesses, which inhibits photodetector absorption and performance. In this work, we show that metasurface gratings increase the absorption of BP-MoS2 heterojunction photodiodes over a broad range of wavelengths in the MWIR. We designed, fabricated, and characterized metasurface gratings that increase absorption at selected wavelengths or broad spectral ranges. We evaluated the broadband metasurfaces by measuring the room temperature responsivity and specific detectivity of BP-MoS2 photodiodes at multiple MWIR wavelengths. Our results show that broadband metasurface gratings are a scalable approach for boosting the performance of BP photodiodes over large spectral ranges.

An All‐Silicon Metalens Integrated with a Mid‐Wave Infrared Black Phosphorus Photodiode

AbstractBlack phosphorus (BP) is a promising material for mid‐wave infrared (MWIR) photodetection because of its direct tunable bandgap and compatibility with a wide range of substrates, particularly silicon. However, optical signal collection in BP devices can be limited by its absorber thickness or active area. Dielectric metasurface lenses, which can be directly integrated into a device's substrate, are a scalable approach to increase the signal collected by BP photodetectors. This work presents the design, fabrication, and characterization of an all‐silicon metasurface lens for focusing MWIR light through its substrate. Then, a BP‐MoS2 heterojunction photodetector is integrated with the metalens, and MWIR photodetection increases at room temperature. These results demonstrate that integrated metasurface lenses are an excellent approach for boosting the performance of MWIR BP photodetectors.

Whole-infrared-band camouflage with dual-band radiative heat dissipation

Advanced multispectral detection technologies have emerged as a significant threat to objects, necessitating the use of multiband camouflage. However, achieving effective camouflage and thermal management across the entire infrared spectrum, especially the short-wave infrared (SWIR) band, remains challenging. This paper proposes a multilayer wavelength-selective emitter that achieves effective camouflage across the entire infrared spectrum, including the near-infrared (NIR), SWIR, mid-wave infrared (MWIR), and long-wave infrared (LWIR) bands, as well as the visible (VIS) band. Furthermore, the emitter enables radiative heat dissipation in two non-atmospheric windows (2.5–3 μm and 5–8 μm). The emitter’s properties are characterized by low emittance of 0.270/0.042/0.218 in the SWIR/MWIR/LWIR bands, and low reflectance of 0.129/0.281 in the VIS/NIR bands. Moreover, the high emittance of 0.742/0.473 in the two non-atmospheric windows ensures efficient radiative heat dissipation, which results in a temperature decrement of 14.4 °C compared to the Cr reference at 2000 W m−2 input power density. This work highlights the role of solar radiance in camouflage, and provides a comprehensive guideline for developing multiband camouflage compatible with radiative heat dissipation, from the visible to LWIR.