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Room-temperature optoelectronic devices that operate at short-wavelength and mid-wavelength infrared ranges (one to eight micrometres) can be used for numerous applications1-5. To achieve the range of operating wavelengths needed for a given application, a combination of materials with different bandgaps (for example, superlattices or heterostructures)6,7 or variations in the composition of semiconductor alloys during growth8,9 are used. However, these materials are complex to fabricate, and the operating range is fixed after fabrication. Although wide-range, active and reversible tunability of the operating wavelengths in optoelectronic devices after fabrication is a highly desirable feature, no such platform has been yet developed. Here we demonstrate high-performance room-temperature infrared optoelectronics with actively variable spectra by presenting black phosphorus as an ideal candidate. Enabled by the highly strain-sensitive nature of its bandgap, which varies from 0.22 to 0.53 electronvolts, we show a continuous and reversible tuning of the operating wavelengths in light-emitting diodes and photodetectors composed of black phosphorus. Furthermore, we leverage this platform to demonstrate multiplexed nondispersive infrared gas sensing, whereby multiple gases (for example, carbon dioxide, methane and water vapour) are detected using a single light source. With its active spectral tunability while also retaining high performance, our work bridges a technological gap, presenting a potential way of meeting different requirements for emission and detection spectra in optoelectronic applications.

Black phosphorus (bP), a two-dimensional (2D) layered material, has shown great potential for infrared (IR) optoelectronics owing to the narrow and direct bandgap it exhibits when in multilayer form. However, its thinness and optical anisotropy lead to weak light absorption, which limits the performance of bP-based photodetectors. In this work, we explore plasmonic nanoantennas, optical cavities, and their hybrids that can be integrated with multilayer bP to enhance its light absorption. This is achieved by near-field light intensity enhancement and polarization conversion. In addition, we demonstrate that these nanostructures can boost the spontaneous emission from bP. Light absorption enhancements of up to 185 and 16 times are obtained for linearly polarized and unpolarized IR light, respectively, in comparison with a commonly used device architecture (bP on SiO2/Si). Moreover, IR light emission enhancements of up to 18 times are achieved. The optical nanostructures presented here can be exploited for enhancing the detectivity of photodetectors and electroluminescence efficiency of light-emitting diodes based on bP and other 2D materials.

Thin two-dimensional (2D) material absorbers have the potential to reduce volume-dependent thermal noise in infrared detectors. However, any reduction in noise must be balanced against lower absorption from the thin layer, which necessitates advanced optical architectures. Such architectures can be particularly effective for applications that require detection only within a specific narrow wavelength range. This study presents a Fabry-Perot cavity enhanced bP/MoS2 midwave infrared (MWIR) photodiode. This simple structure enables tunable narrow-band (down to 0.42 μm full width at half-maximum) photodetection in the 2-4 μm range by adjusting the thickness of the Fabry-Perot cavity resonator. This is achieved while maintaining room-temperature performance metrics comparable to previously reported 2D MWIR detectors. Zero bias specific detectivity and responsivity values of up to 1.7 × 109 cm Hz1/2 W-1 and 0.11 A W-1 at λ = 3.0 μm are measured with a response time of less than 3 ns. These results introduce a promising family of 2D detectors with applications in MWIR spectroscopy.

The mid-wave infrared (MWIR) wavelength range plays a central role in a variety of applications, including optical gas sensing, industrial process control, spectroscopy, and infrared (IR) countermeasures. Among the MWIR light sources, light-emitting diodes (LEDs) have the advantages of simple design, room-temperature operation, and low cost. Owing to the low Auger recombination at high carrier densities and direct bandgap of black phosphorus (bP), it can serve as a high quantum efficiency emitting layer in LEDs. In this work, we demonstrate bP-LEDs exhibiting high external quantum efficiencies and wall-plug efficiencies of up to 4.43 and 1.78%, respectively. This is achieved by integrating the device with an Al

Mid-wave and long-wave infrared (MWIR and LWIR) detection play vital roles in applications that include health care, remote sensing, and thermal imaging. However, detectors in this spectral range often require complex fabrication processes and/or cryogenic cooling and are typically expensive, which motivates the development of simple alternatives. Here, we demonstrate broadband (0.43-10 μm) room-temperature photodetection based on copper tetracyanoquinodimethane (CuTCNQ), a metal-organic semiconductor, synthesized via a facile wet-chemical reaction. The CuTCNQ crystals are simply drop-cast onto interdigitated electrode chips to realize photoconductors. The photoresponse is governed by a combination of interband (0.43-3.35 μm) and midgap (3.35-10 μm) transitions. The devices show response times (∼365 μs) that would be sufficient for many infrared applications (e.g., video rate imaging), with a frequency cutoff point of 1 kHz.

The detection of light in the longwave infrared (LWIR) region is crucial for many applications such as environmental monitoring, thermal imaging and surveillance. Many commercial LWIR photodetectors involve complex fabrication processes, require cryogenic temperatures or exhibit slow photoresponse. Hence, there is a continuous pursuit of developing room-temperature, on-chip LWIR photodetectors, using simple fabrication processes [1] . Metal-organic charge transfer complexes typically have a narrow bandgap, which allows them to absorb LWIR wavelengths [2] . Here, we report room temperature LWIR photoresponse in one such charge transfer complex, ie. copper 7,7,8,8-tetracyano-2,3,5,6-tetraflouroquinodimethane (CuTCNQF 4 ), achieved via simple synthesis and fabrication processes.

Long-wave infrared (LWIR) photodetection is of high technological importance, having a wide range of applications that include thermal imaging and spectroscopy. Two-dimensional (2D) noble-transition-metal dichalcogenides, platinum diselenide (PtSe2) in particular, have recently shown great promise for infrared detection. However, previous studies have mainly focused on wavelengths up to the short-wave infrared region. In this work, we demonstrate LWIR photodetectors based on multilayer PtSe2. In addition, we present an optical cavity substrate that enhances the light-matter interaction in 2D materials and thus their photodetection performance in the LWIR spectral region. The PtSe2 photoconductors fabricated on the TiO2/Au optical cavity substrate exhibit responsivities up to 54 mA/W to LWIR illumination at a wavelength of 8.35 μm. Moreover, these devices show a fast photoresponse with a time constant of 54 ns to white light illumination. The findings of this study reveal the potential of multilayer PtSe2 for fast and broadband photodetection from visible to LWIR wavelengths.

Room-temperature optoelectronic devices that operate at short-wavelength and mid-wavelength infrared ranges (one to eight micrometres) can be used for numerous applications

We demonstrate long wave infrared photodetectors based on the transition metal dichalcogenide platinum diselenide (PtSe2) in its bulk form for the first time to our knowledge. Fabricated devices show sub-millisecond response times.

The long-wave infrared photodetector device we study in this work is shown in Fig. 1 (a) and (b). A bull's eye grating collects the incident light from a large area (101 μm diam.), and couples it into surface plasmon polaritons (SPPs) [1] that converge at its center, at which there is an opening in the Au plate on which the grating sits. Within this opening (or aperture), Au nanobar antennas separated by small gaps are arranged in a radial fashion. These enhance the electromagnetic field in the near-field zone, particularly in the gaps, through localized surface plasmon resonances (LSPRs) [2]. This enhances the absorption in the underlying material, here a small circle (6.32 μm diam.) of graphene. The absorption is boosted further by forming an optical cavity under the graphene. We optimized the geometrical parameters to maximise absorption in the graphene at λ = 9.4 μm via finite-difference time-domain electromagnetic simulations. These geometric parameters are listed in Fig. 1 (c)-(f).

Owing to their high propensity for bundling and aggregation, effective and stable dispersion of nanocarbons in polar solvents is of key significance in the preparation of carbon nanotube (CNT) and graphene nanosheet (GNS)-based devices and nanocomposites. Previous studies have shown that oxidation of CNT side walls and GNS surfaces ameliorates their stability in polar solvents. In this study, large-scale all-atom molecular dynamics simulations were employed to shed light on the stability mechanisms of nanocarbons in polar solvents and explicate the role of surface modification in their dispersibility enhancement. The concepts of potential of mean force (PMF) and translational kinetic energy (TKE) were utilized for this purpose. Our studies disclosed the physical facts lying behind the remarkably higher stability of modified nanocarbons in polar solvents compared to the pristine ones. First, the oxidized nanocarbons are intrinsically much less motivated to form aggregates, and second, the solvent-induced r...

A comprehensive study is conducted on the electron transport in conductive polymer matrix composites (CPMCs), employing the nonequilibrium Green’s function formalism. This paper provides a microscopic insight into the electron tunneling through the potential barriers existing between conducting sites. It is shown that Wentzel–Kramers–Brillouin approximation as well as other models with simple barrier shapes, which are widely used in literature, can lead to inaccurate results in comparison with the quantum mechanical approach using a hyperbolic barrier. In this paper, unlike most previous ones, percolation-related effects are disregarded for further focus on electron transport through the polymer potential barriers. It is assumed that a tunneling-conductive channel exists between the electrodes. This can be created either by applying electric field alignment or using a filler volume fraction higher than the percolation threshold. A two electrode resistive device is studied and the results indicate that a conductor–insulator transition occurs at a barrier thickness of $\sim 1.7$ nm and the barrier thickness should be larger than several angstroms. Next, a novel tunneling field-effect structure based on CPMCs is introduced and its characteristics are comprehensively investigated. This device features a remarkably simple structure, an extremely high channel to gate coupling, a large transconductance, and a high current level. Besides, it has the advantage of being based on polymers. This ensures favorable physical properties, ease of fabrication, and low-cost processing techniques.

Two-dimensional (2D) materials have exhibited potential for infrared detection at room temperature, yet their low light absorption impedes their widespread application. In addition, micromechanical cleavage, which is the main method by which high-quality 2D layers are achieved, typically leads to small-area flakes, hampering their application as photodetectors. In this work, we designed a hybrid plasmonic structure, comprising a metallic bull's eye grating and optical nanoantennas, to collect and concentrate light into a piece of single-layer graphene with sub-wavelength lateral extent. This boosts the interaction between the graphene and light, thereby improving its photodetection performance in the technologically important long-wave infrared (LWIR) region. Finite-difference time-domain electromagnetic simulations were performed to this end. The plasmonic structure we present is predicted to enhance the absorption of light by the graphene by ∼558 times, which in turn is predicted to enhance the detectivity of the LWIR photodetector by ∼32 times.