Short-wave Infrared Photodetectors Research Articles

InSb/InP Core-Shell Colloidal Quantum Dots for Sensitive and Fast Short-Wave Infrared Photodetectors.

Colloidal quantum dot (CQD) technology is considered the main contender toward a low-cost high-performance optoelectronic technology platform for applications in the short-wave infrared (SWIR) to enable 3D imaging, LIDAR night vision, etc. in the consumer electronics and automotive markets. In order to unleash the full potential of this technology, there is a need for a material that is environmentally friendly, thus RoHS compliant, and possesses adequate optoelectronic properties to deliver high-performance devices. InSb CQDs hold great potential in view of their RoHS-compliant nature and─in principle─facile access to the SWIR. However, to date progress in realizing high-performance optoelectronic devices, including photodetectors (PDs), has been limited. Here, we have developed a synthesis method for producing size-tunable InSb CQDs with distinct excitonic peaks spanning a wide range from 900 to 1750 nm. To passivate the surface defects and enhance the photoluminescence (PL) efficiency of InSb CQDs, we further designed an InSb/InP core-shell structure. By employing the InSb/InP core-shell CQDs in a photodiode device stack, we report on robust InSb CQD SWIR photodetectors that exhibit an external quantum efficiency (EQE) of 25% at 1240 nm, a wide linear dynamic range exceeding 128 dB, a photoresponse time of 70 ns, and a specific detectivity of 4.4 × 1011 jones.

Lightly doped In0.53Ga0.47As/InP SWIR photodetectors with diffusion barrier structure

A diffusion barrier structure is proposed to control the accuracies of the Zinc diffusion velocity and depth for lightly doped short-wave infrared (SWIR) InGaAs planar photodetectors. By employing scanning capacitance microscopy and scanning electron microscopy characterizations, the Zinc diffusion profiles were investigated. The introducing of a moderately doped interlayer effectively tailored the diffusion front with reduced depth. In0.53Ga0.47As/InP PIN photodetectors with different structures were fabricated and characterized. Compared with the typical structure, the barrier detector exhibited a significantly lower dark current as well as an approximately three times higher peak detectivity. These results indicated that the diffusion barrier structure is promising for the fabrication of SWIR InGaAs focal plane arrays with both low capacitance and reduced dark current.

Self-formed interfacial oxide layer minimizes reverse bias dark current in PbS colloidal quantum dot photodiodes

PbS colloidal quantum dot (CQD) photodiodes possess high photoresponsivity and broad spectral sensitivity, making them tremendously attractive for low-cost short-wave infrared (SWIR) sensing. A critical challenge in achieving high detectivity in SWIR photodiodes is to minimize their reverse bias dark current density (Jdark) and elucidate the origin of Jdark. We demonstrate in this work how the self-formed AlOx at the ZnO/Al interface dramatically reduced Jdark of the PbS CQD SWIR photodiodes. In such a simple and controlled way, the interfacial states were thoroughly passivated by post-exposure to dry air, which could block the dominant pathways for minority hole injection from Al electrode. The treated photodiode showed low Jdark down to 1.58 × 10−7 A/cm2 at –0.5 V, high photoresponsivity of 0.62 A/W, and high specific detectivity of 2.05 × 1012 Jones at 1413 nm, establishing a readily approach to optimizing detectivity in PbS CQD SWIR photodetectors.

High Performance Shortwave Infrared Organic Photodetectors Adopting Thiadiazole Quinoxaline‐Based Copolymers

AbstractDetection of light in the near‐infrared (NIR) and shortwave infrared (SWIR) spectral range is essential for the wide practical applications of biometrics, surveillance, machine vision, etc., in which organic molecules have gained growing interest as the potential sensing materials. In this study, the newly synthesized donor–acceptor type copolymers consisting of [1,2,5]thiadiazolo[3,4‐g]quinoxaline core unit with phenyl pendant groups as the acceptor and thiophene unit as the donor for achieving high‐efficiency organic SWIR photodetectors are presented. A further variation of the alkoxy chain lengths in the core unit allows the optimized device to exhibit a high external quantum efficiency of 19.5%–21.7% at 1200 nm under the low reverse bias of −1 V, leading to a high detectivity up to 2.96 × 1010 Jones for the spectral range beyond 1 µm. This further suggests the possible origin of the molecular structure‐dependent device performance in terms of the molecular stacking, morphological changes, and charge‐transporting properties in the bulk heterojunction blends.

High Sensitivity Shortwave Infrared Photodetector Based on PbS QDs Using P3HT.

Shortwave infrared (SWIR) photodetectors are being actively researched for their application in autonomous vehicles, biometric sensors, and night vision. However, most of the SWIR photodetectors that have been studied so far are produced by complex semiconductor fabrication processes and have low sensitivity at room temperature because of thermal noise. In addition, the low wavelength band of the SWIR photodetectors currently used has a detrimental effect on the human eye. To overcome these disadvantages, we propose a solution-processed PbS SWIR photodetector that can minimize harmful effects on the human eye. In this study, we synthesized PbS quantum dots (QDs) that have high absorbance peaked at 1410 nm and fabricated SWIR photodetectors with a conductive polymer, poly(3-hexylthiophene) (P3HT), using the synthesized PbS QDs. The characteristics of the synthesized PbS QDs and the current-voltage (I-V) characteristics of the fabricated PbS SWIR photodetectors were measured. It was found that the maximum responsivity of the optimized PbS SWIR photodetector with P3HT was 2.26 times that of the PbS SWIR photodetector without P3HT. Moreover, due to the high hole mobility and an appropriate highest occupied molecular orbital level of P3HT, the former showed a lower operating voltage.

Air-stable and ultrasensitive solution-cast SWIR photodetectors utilizing modified core/shell colloidal quantum dots

InGaAs-based photodetectors have been generally used for detection in the short-wave infrared (SWIR) region. However, the epitaxial process used to grow these materials is expensive; therefore, InGaAs-based photodetectors are limited to space exploration and military applications. Many researchers have expended considerable efforts to address the problem of SWIR photodetector development using lead sulfide (PbS) quantum dots (QDs). Along with their cost-efficient solution processability and flexible substrate compatibility, PbS QDs are highly interesting for the quantum-size-effect tunability of their bandgaps, spectral sensitivities, and wide absorption ranges. However, the performance of PbS QD-based SWIR photodetectors is limited owing to inefficient carrier transfer and low photo and thermal stabilities. In this study, a simple method is proposed to overcome these problems by incorporating CdS in PbS QD shells to provide efficient carrier transfer and enhance the long-term stability of SWIR photodetectors against oxidation. The SWIR photodetectors fabricated using thick-shell PbS/CdS QDs exhibited a high on/off (light/dark) ratio of 11.25 and a high detectivity of 4.0 × 1012 Jones, which represents a greater than 10 times improvement in these properties relative to those of PbS QDs. Moreover, the lifetimes of thick-shell PbS/CdS QD-based SWIR photodetectors were significantly improved owing to the self-passivation of QD surfaces.

Evaporated Sex Te1- x Thin Films with Tunable Bandgaps for Short-Wave Infrared Photodetectors.

Semiconducting absorbers in high-performance short-wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single-crystalline germanium and III-V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Sex Te1- x alloy thin films with tunable bandgaps for the fabrication of high-performance SWIR photodetectors are reported. From absorption measurements, it is shown that the bandgaps of Sex Te1- x films can be tuned continuously from 0.31 eV (Te) to 1.87 eV (Se). Owing to their tunable bandgaps, the peak responsivity position and photoresponse edge of Sex Te1- x film-based photoconductors can be tuned in the SWIR regime. By using an optical cavity substrate consisting of Au/Al2 O3 to enhance its absorption near the bandgap edge, the Se0.32 Te0.68 film (an optical bandgap of ≈0.8 eV)-based photoconductor exhibits a cut-off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW-1 and implied detectivity of 6.5 × 1010 cm Hz1/2 W-1 at 1.55 μm at room temperature. Importantly, the nature of the thermal evaporation process enables the fabrication of Se0.32 Te0.68 -based 42 × 42 focal plane arrays with good pixel uniformity, demonstrating the potential of this unique material system used for infrared imaging sensor systems.

Ultralow-Transition-Energy Organic Complex on Graphene for High-Performance Shortwave Infrared Photodetection.

Room-temperature, high-sensitivity, and broadband photodetection up to the shortwave infrared (SWIR) region is extremely significant for a wide variety of optoelectronic applications, including contamination identification, thermal imaging, night vision, agricultural inspection, and atmospheric remote sensing. Small-bandgap semiconductor-based SWIR photodetectors generally require deep cooling to suppress thermally generated charge carriers to achieve increased sensitivity. Meanwhile, the photogating effect can provide an alternative way to achieve superior photosensitivity without the need for cooling. The optical photogating effect originates from charge trapping of photoinduced carriers at defects or interfaces, resulting in an extremely high photogain (106 or higher). Here, a highly sensitive SWIR hybrid photodetector, fabricated by integrating an organic charge transfer complex on a graphene transistor, is reported. The organic charge transfer complex (tetrathiafulvalene-chloranil) has an exceptional low-energy intermolecular electronic transition down to 0.5 eV, with the aim of achieving efficient SWIR absorption for wavelengths greater than 2 µm. The photogating effect at the organic complex and graphene interface enables an extremely high photogain and a high detectivity of ≈1013 Jones, along with a response time of 8 ms, at room temperature for a wavelength of 2 µm.

Heavy-Metal-Free Flexible Hybrid Polymer-Nanocrystal Photodetectors Sensitive to 1.5 μm Wavelength.

Photodetection in the short-wave infrared (SWIR) wavelength window represents one of the core technologies allowing for many applications. Most current photodetectors suffer from high cost due to the epitaxial growth requirements and the ecological issue due to the use of highly toxic heavy-metal elements. Toward alternative SWIR photodetection strategies, in this work, high-performance heavy-metal-free flexible photodetectors sensitive to λ = 1.5 μm photons are presented based on the formation of a solution-processed hybrid composed of a conjugated diketopyrrolopyrrole-base polymer/PC70BM bulk heterojunction organic host together with inorganic guest NaYF4:15%Er3+ upconversion nanoparticles (UCNPs). Under the illumination of λ = 1.5 μm SWIR photons, optimized hybrid bulk-heterojunction (BHJ)/UCNP photodetectors exhibit a photoresponsivity of 0.73 and 0.44 mA/W, respectively, for devices built on rigid indium tin oxide (ITO)/glass and flexible ITO/polyethylene terephthalate substrates. These hybrid photodetectors are capable of performing SWIR photodetection with a fast operation speed, characterized by a short photocurrent rise time down to 80 μs, together with an excellent mechanical robustness for flexible applications. Exhibiting simultaneously multiple advantages including solution-processability, flexibility, and the absence of toxic heavy metal elements together with a fast operation speed and good photoresponsivity, these hybrid BHJ(DPPTT-T/PC70BM)/UCNP photodetectors are promising candidates for next-generation low-cost and high-performance SWIR photodetectors.

High-Performance and Flexible Shortwave Infrared Photodetectors Using Composites of Rare Earth-Doped Nanoparticles.

The growing demand of infrared sensors for emerging applications such as autonomous vehicles and remote control and sensing systems has driven the development of flexible, low-power, and sensitive infrared detectors for seamless product integration. Although semiconducting polymer (SCP)-based photodetectors are promising solutions, challenges in synthesis chemistry and high thermal dark currents associated with narrowing of band gaps have limited their progress. To address these challenges, we have designed a new class of composites comprising SCPs with moderate band gap and rare earth doped-nanoparticles (RENPs) that enable photon-to-electron conversion beyond the SCP's response range. Using this RENP-SCP (RE-SCP) composite, we demonstrated detection at multiple wavelengths (808, 975, and 1532 nm) for planar-type photodetectors. Notably, the RE-SCP composite-based device detected an eye-safe, shortwave infrared (SWIR) source at 1532 nm with high SWIR responsivity of 0.02 A/W and an SWIR external quantum efficiency of 2%. The key attribute governing the excellent SWIR responsivity and sensitivity was the distinctive SWIR upconversion characteristic of RENPs that extended and improved the SCP's detection range and performance, respectively. Additionally, the absence of significant performance degradation of the SWIR photodetector for bending curvatures from 0-0.67 cm-1 highlights the promise of our RE-SCP composite-based flexible SWIR photodetectors.

Emerging Design and Characterization Guidelines for Polymer-Based Infrared Photodetectors.

Infrared photodetectors are essential to many applications, including surveillance, communications, process monitoring, and biological imaging. The short-wave infrared (SWIR) spectral region (λ = 1-3 μm) is particularly powerful for health monitoring and medical diagnostics because biological tissues show low absorbance and minimal SWIR autofluorescence, enabling greater penetration depth and improved resolution in comparison with visible light. However, current SWIR photodetection technologies are largely based on epitaxially grown inorganic semiconductors, which are costly, require complex processing, and impose cooling requirements incompatible with wearable electronics. Solution-processable semiconductors are being developed for infrared detectors to enable low-cost direct deposition and facilitate monolithic integration and resolution not achievable using current technologies. In particular, organic semiconductors offer numerous advantages, including large-area and conformal coverage, temperature insensitivity, and biocompatibility, for enabling ubiquitous SWIR optoelectronics. This Account introduces recent efforts to advance the spectral response of organic photodetectors into the SWIR. High-performance visible to near-infrared (NIR) organic photodetectors have been demonstrated by leveraging the wealth of knowledge from organic solar cell research in the past decade. On the other hand, organic semiconductors that absorb in the SWIR are just emerging, and only a few organic materials have been reported that exhibit photocurrent past 1 μm. In this Account, we survey novel SWIR molecules and polymers and discuss the main bottlenecks associated with charge recombination and trapping, which are more challenging to address in narrow-band-gap photodetectors in comparison with devices operating in the visible to NIR. As we call attention to discrepancies in the literature regarding performance metrics, we share our perspective on potential pitfalls that may lead to overestimated values, with particular attention to the detectivity (signal-to-noise ratio) and temporal characteristics, in order to ensure a fair comparison of device performance. As progress is made toward overcoming challenges associated with losses due to recombination and increasing noise at progressively narrower band gaps, the performance of organic SWIR photodetectors is steadily rising, with detectivity exceeding 1011 Jones, comparable to that of commercial germanium photodiodes. Organic SWIR photodetectors can be incorporated into wearable physiological monitors and SWIR spectroscopic imagers that enable compositional analysis. A wide range of potential applications include food and water quality monitoring, medical and biological studies, industrial process inspection, and environmental surveillance. There are exciting opportunities for low-cost organic SWIR technologies to be as widely deployable and affordable as today's ubiquitous cell phone cameras operating in the visible, which will serve as an empowering tool for users to discover information in the SWIR and inspire new use cases and applications.

Solution-Synthesized High-Mobility Tellurium Nanoflakes for Short-Wave Infrared Photodetectors.

Two-dimensional (2D) materials, particularly black phosphorus (bP), have demonstrated themselves to be excellent candidates for high-performance infrared photodetectors and transistors. However, high-quality bP can be obtained only via mechanical exfoliation from high-temperature- and high-pressure-grown bulk crystals and degrades rapidly when exposed to ambient conditions. Here, we report solution-synthesized and air-stable quasi-2D tellurium (Te) nanoflakes for short-wave infrared (SWIR) photodetectors. We perform comprehensive optical characterization via polarization-resolved transmission and reflection measurements and report the absorbance and complex refractive index of Te crystals. It is found that this material is an indirect semiconductor with a band gap of 0.31 eV. From temperature-dependent electrical measurements, we confirm this band-gap value and find that 12 nm thick Te nanoflakes show high hole mobilities of 450 and 1430 cm2 V-1 s-1 at 300 and 77 K, respectively. Finally, we demonstrate that despite its indirect band gap, Te can be utilized for high-performance SWIR photodetectors by employing optical cavity substrates consisting of Au/Al2O3 to dramatically increase the absorption in the semiconductor. By changing the thickness of the Al2O3 cavity, the peak responsivity of Te photoconductors can be tuned from 1.4 μm (13 A/W) to 2.4 μm (8 A/W) with a cutoff wavelength of 3.4 μm, fully capturing the SWIR band. An optimized room-temperature specific detectivity ( D*) of 2 × 109 cm Hz1/2 W-1 is obtained at a wavelength of 1.7 μm.

Synergistic Effects of Plasmonics and Electron Trapping in Graphene Short-Wave Infrared Photodetectors with Ultrahigh Responsivity.

Graphene's unique electronic and optical properties have made it an attractive material for developing ultrafast short-wave infrared (SWIR) photodetectors. However, the performance of graphene SWIR photodetectors has been limited by the low optical absorption of graphene as well as the ultrashort lifetime of photoinduced carriers. Here, we present two mechanisms to overcome these two shortages and demonstrate a graphene-based SWIR photodetector with high responsivity and fast photoresponse. In particular, a vertical built-in field is employed in the graphene channel for trapping the photoinduced electrons and leaving holes in graphene, which results in prolonged photoinduced carrier lifetime. On the other hand, plasmonic effects were employed to realize photon trapping and enhance the light absorption of graphene. Thanks to the above two mechanisms, the responsivity of this proposed SWIR photodetector is up to a record of 83 A/W at a wavelength of 1.55 μm with a fast rising time of less than 600 ns. This device design concept addresses key challenges for high-performance graphene SWIR photodetectors and is promising for the development of mid/far-infrared optoelectronic applications.