Infrared Light Detection Research Articles

Nanosecond laser annealing processed surface-structured hyperdoped silicon for efficient near-infrared detection

Surface-structured engineering of hyperdoped silicon can effectively facilitate the absorption of sub-bandgap photons in pristine single-crystal silicon (sc-Si). Here, we conducted different annealing approaches of ordinary thermal annealing (OTA) and nanosecond laser annealing (NLA) on modification of titanium-hyperdoped silicon (Si:Ti) surface structure, to achieve efficient near-infrared detection. It is presented that both OTA and NLA processes can improve the crystallinity of Si:Ti samples. In detail, atomic-resolved STEM characterization illustrates that NLA treatment will further eliminate the amorphous phase on Si:Ti surface to varying degrees. While one-dimensional periodic stacking fault structure of 9R-Si phase is formed at the surface of sc-Si and embedded in the Si matrix during the OTA process, which reveals the seamless interface of 9R-Si/sc-Si along with [11¯0] direction. Due to the high sub-bandgap light absorption and good crystal structure, the Si:Ti photodetector after NLA treatment with an energy density of 2.6 J cm-2exhibited the highest responsivity, reaching 151 mA W-1at 1550 nm even at a low operating voltage of 1 V. We assume the performance enhancement of NLA processed Si:Ti photodetectors can be attributed to two aspects, the one is NLA can reduce the recombination of photo-generated charge carriers in amorphous surface layer by improving crystallization, and the other is that NLA process can weaken the diffusion of titanium impurities due to the extremely rapid heating and cooling rates. This study presents prospects towards surface-structured silicon in infrared light detection.

Enhanced response over wavelength range of 7–12 µm for quantum wells in asymmetric micro-pillars

Efficient coupling in broad wavelength range is desirable for wide-spectrum infrared light detection, yet this is a challenge for intersubband transition in semiconductor quantum wells (QWs). High-Q cavities mostly intensify the absorption at peak wavelengths but with shrinking bandwidth. Here, we propose a novel approach to expand the operating spectral range of the Quantum Well Infrared Photodetectors (QWIPs). By processing the QWs into asymmetric micro-pillar array structure, the device demonstrates a substantial enhancement in spectral response across the wavelength from 7.1 µm to 12.3 µm with guided mode resonance (GMR) effects. The blackbody responsivity is then increased by 3 times compared to that of the 45° polished edge-coupled counterpart. Meanwhile, the dark current density remains unchanged after the deep etching process, which will benefit the electrical performance of the detector with reduced volume duty ratio. In contrast to the symmetric micro-pillar array that contains simple resonance mode, the detectivity of QWIP in asymmetric pillar structure is found to be improved by 2-4 times within the range of 9.5 µm to 15 µm.

Organic Photodiode Materials for Near-Infrared and Short-Wave Infrared Light Detection

Organic Photodiode Materials for Near-Infrared and Short-Wave Infrared Light Detection

Squaraine Dyes for Single‐Component Shortwave Infrared‐Sensitive Photodiodes and Upconversion Photodetectors

AbstractSensitive detection of shortwave infrared (SWIR) light using organic dyes will be a significant advance toward many applications in industry and research. Furthermore, from a fabrication and optimization view, photogeneration of charges in diodes consisting of a single dye layer will be highly attractive. However, SWIR dyes are scarce and organic photodiodes usually utilize a donor–acceptor materials combination to split excitons into charges. Here, it is demonstrated that single‐component layers of several SWIR squaraine dyes operate as efficient photodetectors, with peak external quantum efficiency > 40% beyond 1000 nm and sensitivity out to 1300 nm. Photocurrents show a superlinear dependence on reverse bias. It is shown that this results from a field‐assisted exciton dissociation mechanism, and not from field‐dependent charge injection or extraction. SWIR photodiodes are combined with organic light‐emitting diodes to fabricate upconversion photodetectors – devices that convert SWIR photons directly into visible light. Upconverters are characterized by a low turn‐on voltage (1.5 V) and a high luminance contrast (on‐off ratio 16 000) and SWIR‐to‐visible (λ = 575 nm) photon conversion efficiency (1.85%). Upconversion photodetectors emerge as a promising alternative to the current inorganic‐based imaging technology.

Arresting Ion Migration from the ETL Increases Stability in Infrared Light Detectors Based on III-V Colloidal Quantum Dots.

III-V colloidal quantum dots (CQDs) are of interest in infrared photodetection, and recent developments in CQDs synthesis and surface engineering have improved performance. Here this work investigates photodetector stability, finding that the diffusion of zinc ions from charge transport layers (CTLs) into the CQDs active layer increases trap density therein, leading to rapid and irreversible performance loss during operation. In an effort to prevent this, this work introduces organic blocking layers between the CQDs and ZnO layers; but these negatively impact device performance. The device is then, allowing to use a C60:BCP as top electron-transport layer (ETL) for good morphology and process compatibility, and selecting NiOX as the bottom hole-transport layer (HTL). The first round of NiOX -based devices show efficient light response but suffer from high leakage current and a low open-circuit voltage (Voc) due to pinholes. This work introduces poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) with NiOX NC to form a hybrid HTL, an addition that reduces pinhole formation, interfacial trap density, and bimolecular recombination, enhancing carrier harvesting. The photodetectors achieve 53% external quantum efficiency (EQE) at 970nm at 1V applied bias, and they maintain 95% of initial performance after 19 h of continuous illuminated operation. The photodetectors retain over 80% of performance after 80 days of shelf storage.

Improvement on the topological localized interface enabled by chiral symmetry

Zero-energy topological states, which are protected by chiral symmetry against certain perturbations topologically, localize at interfaces between trivial and non-trivial phases in the Su–Schrieffer–Heeger (SSH) chain model. Here, we propose and demonstrate a method to manipulate chiral symmetry itself to improve the localized interfaces and enlarge the mode volume of topological states in the SSH model, thus optimizing the lasing performance of localized interfaces. As multiple defects corresponding to off-diagonal perturbations in an eigenmatrix are introduced, the topological state expands and extends to extra defects at the topological interface without breaking chiral symmetry. We apply the proposed method in electrical pumping semiconductor laser arrays to verify our theoretical prediction and optimize the output characteristics of the devices. The measured results of the proposed multi-defect SSH laser array show that the output power has been increased by 27%, and the series resistance and far-field divergence have been reduced by half compared to the traditional SSH laser array, establishing a high-performance light source for integrated silicon photonics, infrared light detection and ranging, and so on. Our work demonstrates that the proposed method is capable of improving topological localized interfaces and redistributing zero-energy topological states. Furthermore, our method can be applied to other platforms and inspire optimizations of more devices in broader areas.

MoSe2/WS2 heterojunction photodiode integrated with a silicon nitride waveguide for near infrared light detection with high responsivity

We demonstrate experimentally the realization and the characterization of a chip-scale integrated photodetector for the near-infrared spectral regime based on the integration of a MoSe2/WS2 heterojunction on top of a silicon nitride waveguide. This configuration achieves high responsivity of ~1 A W−1 at the wavelength of 780 nm (indicating an internal gain mechanism) while suppressing the dark current to the level of ~50 pA, much lower as compared to a reference sample of just MoSe2 without WS2. We have measured the power spectral density of the dark current to be as low as ~1 × 10−12 A Hz−0.5, from which we extract the noise equivalent power (NEP) to be ~1 × 10−12 W Hz−0.5. To demonstrate the usefulness of the device, we use it for the characterization of the transfer function of a microring resonator that is integrated on the same chip as the photodetector. The ability to integrate local photodetectors on a chip and to operate such devices with high performance at the near-infrared regime is expected to play a critical role in future integrated devices in the field of optical communications, quantum photonics, biochemical sensing, and more.

Infrared Light Detection Technology Based on Organics

This decade has seen rapid developments in infrared light sensing and imaging, utilizing innovative materials and deliberate structural designs. Organic semiconducting materials are promising in the next-generation infrared sensing applications due to their unique properties including solution processability, tunable optoelectronic property, and biocompatibility. This Spotlight aims to provide a snapshot of the recent advances in organic infrared light detection technology, specifically for wavelengths beyond 1000 nm, focusing on performance enhancements and new function realizations. Several innovative proof-of-concept demonstrations illustrate the benefits of the rapidly developing organic infrared technology. Finally, we discuss the challenges and perspectives of organic infrared technology.

Optimization of capacitively coupled Low Gain Avalanche Diode (AC-LGAD) sensors for precise time and spatial resolution

Capacitively-coupled Low-Gain Avalanche Diode (AC-LGAD) sensors are being developed for high-energy particle physics experiments as a detector which provides fast time information with fine spatial resolution. This paper describes optimizations of AC-LGAD sensor fabrication parameters, such as doping concentrations of the gain and electrode layers as well as the AC insulator capacitance, to realize O(10) μm spatial resolution, small charge cross talk to the neighboring electrodes, detection efficiency higher than 99% at a 10−4 noise rate and time resolution of about 30 ps. The radiation tolerance of the sensor is presented. In addition, further application to a device capable of visible and infra-red light detection is discussed.

Tailoring the electronic and optical properties of ZrS2/ZrSe2 vdW heterostructure by strain engineering

Under framework of first-principles calculation, we construct ZrS2/ZrSe2 heterostructure and explore the effects of the uniaxial and biaxial strains on its electronic and optical properties. Band structure shows the unstrained ZrS2/ZrSe2 heterostructure has a type-II band alignment. The large binding energy and small interface distance indicate there is a chemical combination between ZrS2 and ZrSe2 layers beyond the van der Waals interaction. Due to the redistribution of charge, a built-in electric field from ZrSe2 to ZrS2 is formed on the interface of the ZrS2/ZrSe2 heterostructure. In addition, constructing the ZrS2/ZrSe2 heterostructure can enhance light absorption intensity. Then we investigate the effects of uniaxial and biaxial strains in the range of −8%∼8% on the electronic and optical properties of the ZrS2/ZrSe2 heterostructure. The band gap of the ZrS2/ZrSe2 heterostructure increases (decreases) with the increase of tensile (compressive) strain, this tunable band gap shows its potential applications in electronic devices. The band type is very sensitive to strain, because the type-II alignment can be converted to type-I alignment. In addition, under uniaxial (−4% and −2%) and biaxial (−2%) compressive strains, a red-shift phenomenon is occurred compared to the unstrained ZrS2/ZrSe2 heterostructure, indicating the better optical gas sensitivity and can be used in infrared light detectors. These findings make possible the application of two-dimensional ZrS2/ZrSe2 heterostructure in multifunctional electronic and optoelectronic devices.

Mid-Infrared Response from Cr/n-Si Schottky Junction with an Ultra-Thin Cr Metal.

Infrared detection technology has been widely applied in many areas. Unlike internal photoemission and the photoelectric mechanism, which are limited by the interface barrier height and material bandgap, the research of the hot carrier effect from nanometer thickness of metal could surpass the capability of silicon-based Schottky devices to detect mid-infrared and even far-infrared. In this work, we investigate the effects of physical characteristics of Cr nanometal surfaces and metal/silicon interfaces on hot carrier optical detection. Based on the results of scanning electron microscopy, atomic force microscopy, and X-ray diffraction analysis, the hot carrier effect and the variation of optical response intensity are found to depend highly on the physical properties of metal surfaces, such as surface coverage, metal thickness, and internal stress. Since the contact layer formed by Cr and Si is the main role of infrared light detection in the experiment, the higher the metal coverage, the higher the optical response. Additionally, a thicker metal surface makes the hot carriers take a longer time to convert into current signals after generation, leading to signal degradation due to the short lifetime of the hot carriers. Furthermore, the film with the best hot carrier effect induced in the Cr/Si structure is able to detect an infrared signal up to 4.2 μm. Additionally, it has a 229 times improvement in the signal-to-noise ratio (SNR) for a single band compared with ones with less favorable conditions.

Low-Timing-Jitter GHz-Gated InGaAs/InP Single-Photon Avalanche Photodiode for LIDAR

InGaAs/InP single-photon avalanche diodes (SPADs) attract increasing attention for the infrared light detection and ranging (LIDAR) due to the low-cost and compact-size construction. Although constant endeavor has been dedicated to improve the dead time and timing jitter, it remains challenging to implement high-speed and high-resolution LIDAR. Here, we develop a high-performance GHz-gated InGaAs/InP APD operated in the quasi-free-running mode, while its gating signal is unlocked from the light source. The used low-pass filtering technique enables us to continuously adjust the repetition frequency of the gate for carefully optimizing photon detection efficiency (PDE) and timing jitter. Increasing the gates’ repetition frequency from 1 GHz to 2.75 GHz, the PDE improves dramatically from 2.02% to 3.30%, while the timing jitter drops from 156 ps to 114 ps. Furthermore, we verify that changes in the PDE have little effect on the timing characteristics, making the SPAD more suitable for LIDAR with large dynamic range. Meanwhile, the dead time is about 4 ns, which is much shorter than that of the SPAD working in the free-running mode, guaranteeing rapid mapping of targets. Finally, as a proof-of-principle demonstration, the InGaAs/InP SPAD is used in a time-of-flight LIDAR system, which demonstrates a sub-centimeter depth resolution directly.

Electrical and Optical Doping of Silicon by Pulsed-Laser Melting

Over four decades ago, pulsed-laser melting, or pulsed-laser annealing as it was termed at that time, was the subject of intense study as a potential advance in silicon device processing. In particular, it was found that nanosecond laser melting of the near-surface of silicon and subsequent liquid phase epitaxy could not only very effectively remove lattice disorder following ion implantation, but could achieve dopant electrical activities exceeding equilibrium solubility limits. However, when it was realised that solid phase annealing at longer time scales could achieve similar results, interest in pulsed-laser melting waned for over two decades as a processing method for silicon devices. With the emergence of flat panel displays in the 1990s, pulsed-laser melting was found to offer an attractive solution for large area crystallisation of amorphous silicon and dopant activation. This method gave improved thin film transistors used in the panel backplane to define the pixelation of displays. For this application, ultra-rapid pulsed laser melting remains the crystallisation method of choice since the heating is confined to the silicon thin film and the underlying glass or plastic substrates are protected from thermal degradation. This article will be organised chronologically, but treatment naturally divides into the two main topics: (1) an electrical doping research focus up until around 2000, and (2) optical doping as the research focus after that time. In the first part of this article, the early pulsed-laser annealing studies for electrical doping of silicon are reviewed, followed by the more recent use of pulsed-lasers for flat panel display fabrication. In terms of the second topic of this review, optical doping of silicon for efficient infrared light detection, this process requires deep level impurities to be introduced into the silicon lattice at high concentrations to form an intermediate band within the silicon bandgap. The chalcogen elements and then transition metals were investigated from the early 2000s since they can provide the required deep levels in silicon. However, their low solid solubilities necessitated ultra-rapid pulsed-laser melting to achieve supersaturation in silicon many orders of magnitude beyond the equilibrium solid solubility. Although infrared light absorption has been demonstrated using this approach, significant challenges were encountered in attempting to achieve efficient optical doping in such cases, or hyperdoping as it has been termed. Issues that limit this approach include: lateral and surface impurity segregation during solidification from the melt, leading to defective filaments throughout the doped layer; and poor efficiency of collection of photo-induced carriers necessary for the fabrication of photodetectors. The history and current status of optical hyperdoping of silicon with deep level impurities is reviewed in the second part of this article.

Conformal MoS2/Silicon Nanowire Array Heterojunction with Enhanced Light Trapping and Effective Interface Passivation for Ultraweak Infrared Light Detection

Abstract2D layered materials have attracted considerable attention for fabricating IR photodetectors. However, performance, especially for weak signal detection, of these IR photodetectors is often limited by the low absorbance of the very thin active materials as well as unsuppressed dark currents. Herein, a photodetector with high sensitivity for ultraweak IR signals based on a conformal MoS2/silicon nanowire array heterojunction with an ultrathin Al2O3 interfacial passivation layer is reported. The conformal light‐trapping nanoarray structure can greatly enhance broadband IR absorption, while the Al2O3 layer can suppress interface carrier recombination effectively and thus lower reverse dark current. The photodetectors exhibit broadband photoresponse ranging from 300 to 1600 nm, low noise current of 0.11 pA Hz−1/2, large responsivity up to 0.61 A W−1 at zero bias voltage, and high specific detectivity of 1011–1012 Jones. Significantly, the devices are capable of detecting ultraweak IR signals (e.g., 100 pW at 808 nm and 3 nW at 1310/1550 nm) with high on–off ratios without applying any external bias. This work proposes a new strategy to enhance light absorption of 2D materials and construct high‐quality junction based on them, which is promising for low‐cost and high‐performance optoelectronic devices.

Self‐Powered Organic Photodetectors with High Detectivity for Near Infrared Light Detection Enabled by Dark Current Reduction

AbstractOrganic photodetectors (OPDs) for near infrared (NIR) light detection represents cutting‐edge technology for optical communication, environmental monitoring, biomedical imaging, and sensing. Herein, a series of self‐powered OPDs with high detectivity are constructed by the sequential deposition (SD) method. The dark currents (Jd) of SD devices are effectively reduced in comparison to blend casting (BC) ones due to the vertical phase segregation structure. Impressively, the Jd values of SD devices based on D18 and Y6 system is reduced to be 2.1 × 10−11 A cm−2 at 0 V, which is two orders of magnitude lower than those of the BC devices. The D* value of the SD device is superior to that of BC device under different bias voltages (0, −0.5, −1.0, and −2.0 V) due to the reduction of dark current, which originates from the fine vertical phase separation structure of the SD device. The mechanism studies shows that the vertical phase segregation structure can effectively suppress the unfavorable charge injection, thus reducing the dark current. Also, the surface energy is proven to play a key role in the photocurrent stability. In addition, the flexible OPDs demonstrate excellent performance in photoplethysmography test.

Monolithically integrated InGaAs/AlGaAs multiple quantum well photodetectors on 300 mm Si wafers

Near infrared light detection is fundamental for sensing in various application fields. In this paper, we detail the properties of InGaAs/AlGaAs multiple quantum well (MQW) photodetectors (PDs) monolithically integrated by direct epitaxy on 300 mm Si(001) substrates. A MQW high crystalline quality is achieved using 300 mm Ge/Si pseudo-substrates with a low threading dislocation density of 4 × 107 cm−2 from electron channeling contrast imaging measurements. The localized states in the MQW stack are investigated using temperature-dependent photoluminescence. Two non-radiative recombination channels are identified. The first one is due to delocalized excitons generated by potential’s fluctuations because of the InGaAs/AlGaAs interfacial roughness (with an activation energy below 4 meV). The second one is due to exciton quenching because of the presence of numerous threading dislocations. A low dark current density of 2.5 × 10−5 A/cm2 is measured for PDs on Ge/Si substrates, i.e., a value very close to that of the same PDs grown directly on GaAs(001) substrates. A responsivity of 36 mA/W is otherwise measured for the photodiode on Ge/Si at room temperature and at −2 V.

Self-powered flexible artificial synapse for near-infrared light detection

In the era of artificial intelligence, photonic artificial synapses that are capable of light detection and information storage are attracting much attention, although complex device configuration and high energy consumption are two remaining challenges. Here, a flexible polymer-based optical synapse for infrared light detection in the absence of applied voltage is fabricated to emulate human synaptic photoplasticity. Investigation into the mechanism of the self-powered properties demonstrates that both the localized electric field of the polyethylene terephthalate (PET) substrate and the high dielectric constant of narrow-band conjugated polymer contribute to spontaneous exciton dissociation. Moreover, array imaging and data encryption are achieved by modulating light for the flexible devices, which exhibit excellent mechanical flexibility and long-term air stability. Thus, this work may provide a strategy to develop self-powered artificial synapses for infrared light detection. Short-wavelength infrared light-responsive organic synapse Self-powered flexible photonic synapse with two-terminal device structure Polymer with dielectric constant as high as 5.8 Visual memory array imaging and encryption model application for near-infrared light To mimic the human visual system, Chen et al. adopt organic materials to sense and memorize light, including infrared light. The simple device can operate without voltage, and the strategy may provide sustainable energy solutions for artificial intelligence applications.

Self-Powered Flexible Artificial Synapse for Near-Infrared Light Detection

In the era of artificial intelligence, the photonic artificial synapses that are capable of light detecting and information storage are attracting much attention. The complex device configuration and high energy consumption are two main challenges. Here, a flexible polymer-based optical synapse for infrared light detection is fabricated to emulate human synaptic photo-plasticity in the absence of applied voltage. The mechanism investigation of self-powered property demonstrated that both localized electric field of the PET substrate and high dielectric constant of PBTT contribute to the spontaneous exciton dissociation. Moreover, array imaging and data encryption were achieved by modulating light for the flexible devices, which exhibited excellent mechanical flexibility and long-term air stability. Thus, this work provides an idea to develop self-powered artificial synapses for infrared light detection.

Two-Dimensional Bi2Sr2CaCu2O8+δ Nanosheets for Ultrafast Photonics and Optoelectronics.

Two-dimensional (2D) Bi2Sr2CaCu2O8+δ (BSCCO) is a emerming class of 2D materials with high-temperature superconductivity for which their electronic transport properties have been intensively studied. However, the optical properties, especially nonlinear optical response and the photonic and optoelectronic applications of normal state 2D Bi2Sr2CaCu2O8+δ (Bi-2212), have been largely unexplored. Here, the linear and nonlinear optical properties of mechanically exfoliated Bi-2212 thin flakes are systematically investigated. 2D Bi-2212 shows a profound plasmon absorption in near-infrared wavelength range with ultrafast carrier dynamics as well as tunable nonlinear absorption depending on the thickness. We demonstrated that 2D Bi-2212 can be applied not only as an effective mode-locker for ultrashort pulse generation but also as an active medium for infrared light detection due to its plasmon absorption. Our results may trigger follow up studies on the optical properties of 2D BSCCO and demonstrate potential opportunities for photonic and optoelectronic applications.

Organic Upconversion Imager with Dual Electronic and Optical Readouts for Shortwave Infrared Light Detection

AbstractThere remains a critical need for large‐area imaging technologies that operate in the shortwave infrared spectral region. Upconversion imagers that combine photo‐sensing and display in a compact structure are attractive since they avoid the costly and complex process of pixilation. However, upconversion device research is primarily focused on the optical output, while electronic signals from the imager remain underutilized. Here, an organic upconversion imager that is efficient in both optical and electronic readouts, extending the capability of human and machine vision to 1400 nm, is designed and demonstrated. The imager structure incorporates interfacial layers to suppress non‐radiative recombination and provide enhanced optical upconversion efficiency and electronic detectivity. The photoresponse is comparable to state‐of‐the‐art organic infrared photodiodes exhibiting a high external quantum efficiency of ≤35% at a low bias of ≤3 V and 3 dB bandwidth of 10 kHz. The large active area of 2 cm2 enables demonstrations such as object inspection, imaging through smog, and concurrent recording of blood vessel location and blood flow pulses. These examples showcase the potential of the authors’ dual‐readout imager to directly upconvert infrared light for human visual perception and simultaneously yield electronic signals for automated monitoring applications.