Room Temperature Operation Research Articles

Multiple Long Wavelength Infrared MOCVD Grown HgCdTe Photodetectors for High Temperature Conditions

This paper presents large area multiple photodetectors of the MOCVD grown HgCdTe heterostructures for operation at temperatures of (200-300)K in the long wavelength infrared range. Conventional long wavelength photovoltaic detectors operating at higher temperatures suffer from low dynamic resistance and multiple photodetectors idea solves this problem. Particular experimental steps are demonstrated starting from MOCVD technology, through etching, angled ion milling, angled contact metal deposition, assembly and electro-optical measurements. MOCVD technique with wide range of composition and donor/acceptor doping and without post growth annealing provides HgCdTe heterostructures for uncooled multiple detectors. CdTe buffer layer deposition allows HgCdTe heterostructure growth on GaAs substrates. Angled ion Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> milling optimal selection parameters is crucial for proper junction formation and conductivity type conversion. Theoretical modelling using APSYS platform supports designing of the detector's structures. Presented technology enable to fabricate large area (4 × 4mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) multiple photodetectors with detectivity D* exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 10.6 μm and room temperature operation useful for many applications.

Electrothermal transport induced material reconfiguration and performance degradation of CVD-grown monolayer MoS2 transistors

Device and material reliability of 2-dimensional materials, especially CVD-grown MoS2, has remained un-addressed since 2011 when the first TMDC transistor was reported. For its potential application in next generation electronics, it is imperative to update our understanding of mechanisms through which MoS2 transistors’ performance degrades under long-term electrical stress. We report, for CVD-grown monolayer MoS2, results on temporal degradation of material and device performance under electrical stress. Both low and high field regimes of operation are explored at different temperatures, gate bias and stress cycles. During low field operation, current is found to saturate after hundreds of seconds of operation with the current decay time constant being a function of temperature and stress cycle. High field operation, especially at low temperature, leads to impact ionization assisted material and device degradation. It is found that high field operation at low temperature results in amorphization of the channel and is verified by device and kelvin probe force microscopy (KPFM) analyses. In general, a prolonged room temperature operation of CVD-grown MoS2 transistors lead to degraded gate control, higher OFF state current and negative shift in threshold voltage (VT). This is further verified, through micro-Raman and photoluminescence spectroscopy, which suggest that a steady state DC electrical stress leads to the formation of localized low resistance regions in the channel and a subsequent loss of transistor characteristics. Our findings unveil unique mechanism by which CVD MoS2 undergoes material degradation under electrical stress and subsequent breakdown of transistor behavior. Such an understanding of material and device reliability helps in determining the safe operating regime from device as well as circuit perspective.

Room temperature operation and low dark current of In0.15Ga0.85As/InAs/In0.15Ga0.85As dot-in-well short-wave infrared photodetector: Experimental and theoretical correlation

Photoluminescence (PL) and Photoluminescence excitation (PLE) measurements have been carried out to investigate the carrier recombination pathways in a GaAs capped InAs quantum dot (QD) and an InAs dot in InGaAs well (DWELL) structure. The presence of an InGaAs quantum well (QW) results in an anomalous behavior in the temperature dependent PL spectra. The carrier trapping in the InGaAs well at low temperature and the redistribution of these carriers as the temperature rises is well explored through the temperature dependent PL spectra. The existence of additional energy states due to the incorporation of an InGaAs QW has been observed through the PLE result and explained schematically. Cross-sectional transmission electron microscopy provides a direct evidence of the formation of hybrid thick QW structure due to the intermixing of InGaAs well and the InAs wetting layer (WL). The strain relaxation in the DWELL structure is substantiated from the simulated strain profile as well as the high-resolution X-ray diffraction (HRXRD) result. Moreover, the DWELL p-i-p quantum dot infrared detector (QDIP) exhibits a room temperature spectral response in the short-wavelength infrared (SWIR) region. A two-order reduced dark current and one order improved detectivity is obtained for the DWELL QDIP compared to the conventional GaAs capped InAs QDIP. • Infrared photodetector with InAs quantum dot in InGaAs well as the active layer. • The carrier recombination process along with temperature is discussed. • PL and PLE results show the dominance of the InGaAs wells at low temperature. • The device showed spectral response in short-wave IR range till room temperature. • The dark current obtained for the QDIP is also very low.

Room-temperature continuous-wave operations of GaN-based vertical-cavity surface-emitting lasers with buried GaInN tunnel junctions

We report GaN-based vertical-cavity surface-emitting lasers (VCSELs) with buried GaInN tunnel junctions (TJs). Under room-temperature continuous-wave operation, the VCSEL with an 8 μm aperture exhibited a low operating voltage of 5.3 V at 10 kA cm−2 and a differential resistance of 110 Ω. In addition, the VCSEL with a 10 μm aperture showed a threshold current of 14.4 mA and a peak output power of 2.0 mW. An influence of an absorption loss at the GaInN TJ on laser performance was estimated using an analysis of a one-dimensional optical intensity profile based on a cross-sectional STEM image.

Detection of single human hairs with a terahertz nonlinear quantum cascade laser.

We report the demonstration of imaging of a single human hair with a terahertz quantum cascade laser (THz-QCL) source based on intracavity difference-frequency generation. A single human hair whose diameter was about 100 µm was detected using the THz-QCL source operating at 240 K, of which the THz beam had a linear polarization. The results show that the THz image of a human hair clearly depends on the polarization direction of the THz beam. The THz QCL sources that are capable of room temperature operation will be useful for detection of small foreign objects like human hairs.

All-optical transistor using deep-level defects in nitride semiconductors for room temperature optical computing

The essential device for optical computing is an all-optical transistor in which a weak “gate” light controls the strong “source” light. Particularly promising for application in logic operations are all-optical transistors using quasiparticles in a semiconductor because they can be easily integrated into circuits in a way similar to that of conventional electronic ones. However, the practical development of such devices has so far been limited due to extreme difficulties in achieving room temperature operation. In this work, we proposed and numerically verified a scheme of the high-temperature stable all-optical transistor, where light controls light by using deep-level defects in non-polar InGaN/GaN heterostructure and photo-exited holes as an intermediate medium. The developed optical switching concept fulfills all criteria for the useful all-optical transistor listed in Miller, Nat. Photonics 4, 3 (2010), in particular fan-out and cascadability, which are the most difficult to meet. For the design of our transistor, we applied an entirely new approach to III-nitride device physics: we turned usually undesirable deep-level defects into a key, active element of the transistor in which they realize on and off operations. Due to this, the developed device was able to obtain excellent operation stability in a wide temperature range up to 500 K as well as an extremely high on/off ratio (106) and gain (100). Finally, in order to show that the proposed transistor concept is feasible, we performed the gated-photoluminescence experiment for metal–oxide–semiconductor GaN structures.

Hydrogen Sulfide Detection by Sensors Based on Conductive Polymers: A Review

Coming from natural and anthropogenic sources, hydrogen sulfide gas (H2S) is a smelly hazardous substance at sub-ppm level, which can lead to poisoning deaths at higher concentration. Researchers have been working for decades to design sensors with sufficient/good/robust metrological properties and good stability in order to monitor and control in real-time the risk associated to this gas. Among the devices proposed, chemiresistive sensors based on conductive polymer appear as a good alternative to the most common solutions such as electrochemical and optical sensors. They present various advantages in term of design (easy fabrication, easy tuning of physical and chemical properties, low cost, etc.) and performances (good sensitivity, good reproducibility, room temperature operation, short response time, etc.). In this review, we summarize the progresses made on conductive polymers sensors dedicated to H2S detection, including the performance of the different materials and sensing mechanisms. Finally, we identify the limitations of these sensors and highlight the most promising approaches to enable the use of these technologies in real-world applications.

Nanolaser arrays: toward application-driven dense integration

AbstractThe past two decades have seen widespread efforts being directed toward the development of nanoscale lasers. A plethora of studies on single such emitters have helped demonstrate their advantageous characteristics such as ultrasmall footprints, low power consumption, and room-temperature operation. Leveraging knowledge about single nanolasers, the next phase of nanolaser technology will be geared toward scaling up design to form arrays for important applications. In this review, we discuss recent progress on the development of such array architectures of nanolasers. We focus on valuable attributes and phenomena realized due to unique array designs that may help enable real-world, practical applications. Arrays consisting of exactly two nanolasers are first introduced since they can serve as a building block toward comprehending the behavior of larger lattices. These larger-sized lattices can be distinguished depending on whether or not their constituent elements are coupled to one another in some form. While uncoupled arrays are suitable for applications such as imaging, biosensing, and even cryptography, coupling in arrays allows control over many aspects of the emission behavior such as beam directionality, mode switching, and orbital angular momentum. We conclude by discussing some important future directions involving nanolaser arrays.

Liquid-Metal Synthesized Ultrathin SnS Layers for High-Performance Broadband Photodetectors.

Atomically thin materials face an ongoing challenge of scalability, hampering practical deployment despite their fascinating properties. Tin monosulfide (SnS), a low-cost, naturally abundant layered material with a tunable bandgap, displays properties of superior carrier mobility and large absorption coefficient at atomic thicknesses, making it attractive for electronics and optoelectronics. However, the lack of successful synthesis techniques to prepare large-area and stoichiometric atomically thin SnS layers (mainly due to the strong interlayer interactions) has prevented exploration of these properties for versatile applications. Here, SnS layers are printed with thicknesses varying from a single unit cell (0.8 nm) to multiple stacked unit cells (≈1.8 nm) synthesized from metallic liquid tin, with lateral dimensions on the millimeter scale. It is reveal that these large-area SnS layers exhibit a broadband spectral response ranging from deep-ultraviolet (UV) to near-infrared (NIR) wavelengths (i.e., 280-850 nm) with fast photodetection capabilities. For single-unit-cell-thick layered SnS, the photodetectors show upto three orders of magnitude higher responsivity (927 A W-1 ) than commercial photodetectors at a room-temperature operating wavelength of 660 nm. This study opens a new pathway to synthesize reproduceable nanosheets of large lateral sizes for broadband, high-performance photodetectors. It also provides important technological implications for scalable applications in integrated optoelectronic circuits, sensing, and biomedical imaging.

Recent advances in energy-saving chemiresistive gas sensors: A review.

With the tremendous advances in technology, gas-sensing devices are being popularly used in many distinct areas, including indoor environments, industries, aviation, and detectors for various toxic domestic gases and vapors. Even though the most popular type of gas sensor, namely, resistive-based gas sensors, have many advantages over other types of gas sensors, their high working temperatures lead to high energy consumption, thereby limiting their practical applications, especially in mobile and portable devices. As possible ways to deal with the high-power consumption of resistance-based sensors, different strategies such as self-heating, MEMS technology, and room-temperature operation using especial morphologies, have been introduced in recent years. In this review, we discuss different types of energy-saving chemisresitive gas sensors including self-heated gas sensors, MEMS based gas sensors, room temperature operated flexible/wearable sensor and their application in the fields of environmental monitoring. At the end, the review will be concluded by providing a summary, challenges, recent trends, and future perspectives.

Fast response hydrogen gas sensor based on Pd/Cr nanogaps fabricated by a single-step bending deformation

The development of low-cost and high performing hydrogen gas sensors is important across many sectors, including mining, energy and defense using hydrogen (H2) gas. Herein, we demonstrate a new concept of H2 sensors based on Pd/Cr nanogaps created by using a simple mechanical bending deformation technique. These nanogap sensors can selectively detect the H2 gas based on transduction of the volume expansion after H2 uptake into an electrical signal by palladium-based metal-hydrides that allows closure of nanogaps for electrons flowing or tunneling. While this break-junction architecture, according to literature, can provide several advantages with research gaps in terms of fabricating nanogap sensors with ultra-fast response (≤4 s), the size of nanogap (≤20 nm) and their relationship with time response and recovery as addressed in this paper. Based on the computational modelling outcome, the size of the nanogaps can be investigated in order to optimize the fabrication conditions. Indeed, a single nanogap with optimum width (15 nm) acts as an on-off switch for best performing hydrogen detection. Moreover, with the unique design of Pd/Cr nanogap, the developed sensing device meets major requirement of advanced H2 gas sensor including room temperature (25 °C) operation, detection of trace amounts (10–40,000 ppm), good linearity, ultra-fast response-recovery time (3/4.5 s) and high selectivity. The presented economical lithography-free fabrication method has simple circuitry, low power consumption, recyclability, and favorable aging properties that promises great potential to be used for many practical applications of H2 detection.

Single-electron transistor: review in perspective of theory, modelling, design and fabrication

Integrated circuit (IC) technology has grown tremendously over the last few decades. The prime goal has been to achieve low-power and high-performance in logic and memory devices with minimal footprint. This has lead to continuous scaling of devices and interconnects over silicon chips. Scaling of technology plays an important role for improvement of IC performance in terms of delay, signal-integrity and power-dissipation. Novel devices like FinFET, nano-electromechanical systems, graphene-FETs and single-electron transistor (SET) offer several advantages over various shortcomings of scaling. The future of IC industry is proposed to be heterogeneous 3D integration of different technologies. A SET is a potential nano device that works on quantum mechanical principle and can be co-integrated with the widely adopted complementary metal-oxide semiconductor technology to enhance its performance at scaled technology nodes. To explore the feasibility of SET, an extensive literature review has been carried out in this paper. The literature review comprises comprehensively research work related to SET theory, design and fabrication. Also, the SET based computing system design is presented for room temperature operation. The extensive literature review and thereafter execution of varying analyses reveal that the SET is a potential nano-device for futuristic applications.

Excitonic Lasers in Atomically Thin 2D Semiconductors

Two-dimensional (2D) atomically thin transition-metal dichalcogenides (TMD) and their van der Waals (vdW) heterostructures offer a platform with tightly bound intralayer/interlayer excitons for the on-chip fabrication of ultracompact nanolasers. Excitons in 2D TMD materials present a considerable binding energy of up to hundreds of meV, which permits a high Mott transition density of 1014 cm–2 and stable excitonic lasing under room-temperature operation and high pump fluences. Here, we review the recent progress on the lasing emission from intralayer excitons in TMD monolayers and interlayer excitons in vdW heterostructures incorporated with various high-quality optical cavities, including photonic-crystal, whispering-gallery-mode, distributed-feedback, distributed-Bragg-reflector cavities. Lasing emissions in TMD monolayers and heterostructures have been demonstrated by narrow emission peaks, a clear threshold for nonlinear amplification, time- and spatial coherence under either continuous-wave or pulsed light pumping. Finally, prospective and frontier research topics, including large-scale on-chip integration of TMD nanolasers, electrically pumped lasers, spin-polarized nanolasers, and exciton–polariton Bose–Einstein condensation (BEC) are highlighted.

Real-time dynamic wavelength tuning and intensity modulation of metal-clad nanolasers.

To realize ubiquitously used photonic integrated circuits, on-chip nanoscale sources are essential components. Subwavelength nanolasers, especially those based on a metal-clad design, already possess many desirable attributes for an on-chip source such as low thresholds, room-temperature operation and ultra-small footprints accompanied by electromagnetic isolation at pitch sizes down to ∼50 nm. Another valuable characteristic for a source would be control over its emission wavelength and intensity in real-time. Most efforts on tuning/modulation thus far report static changes based on irreversible techniques not suited for high-speed operation. In this study, we demonstrate in-situ dynamical tuning of the emission wavelength of a metallo-dielectric nanolaser at room temperature by applying an external DC electric field. Using an AC electric field, we show that it is also possible to modulate the output intensity of the nanolaser at high speeds. The nanolaser's emission wavelength in the telecom band can be altered by as much as 8.35 nm with a tuning sensitivity of ∼1.01 nm/V. Additionally, the output intensity can be attenuated by up to 89%, a contrast sufficient for digital data communication purposes. Finally, we achieve an intensity modulation speed up to 400 MHz, limited only by the photodetector bandwidth used in this study, which underlines the capability of high-speed operation via this method. This is the first demonstration of a telecom band nanolaser source with dynamic spectral tuning and intensity modulation based on an external E-field to the best of our knowledge.

SnO2 nanowires decorated by insulating amorphous carbon layers for improved room-temperature NO2 sensing

We fabricated gas sensors by decorating amorphous carbon layers on the surfaces of SnO2 nanowires. Pretreatment and functionalization were not required for the synthesis of the SnO2-based nanocomposite, requiring only short few-second processing times. A sensing mechanism is proposed to explain the room-temperature (24 °C) operation of the gas sensor. The amorphous carbon not only increased the surface area, but also provided electronic effects improving the NO2 gas sensing likely by supplying electrons to the SnO2 and/or changing the conducting channel width inside the SnO2 by carrier transfer. The optimized gas sensor, having high response and high selectivity, can be utilized for room-temperature NO2 gas sensing applications.

Terahertz Nonreciprocal Isolator Based on Magneto-Plasmon and Destructive Interference at Room Temperature

A terahertz isolator is demonstrated for the THz nonreciprocal reflections in the magneto-optical microstructure composed of InSb and metasurface with a dielectric interlayer. In the Voigt magnetic field configuration, the reflectance of the p-polarization waves obliquely impinging on the InSb wafer exhibits high nonreciprocity, while the reflectance of the s-polarized wave is reciprocal. Based on the unique magneto-plasmonic modes on the InSb surface, the nonreciprocal reflection in this device can be enhanced by using the destructive interference between the direct reflection and the multiple reflections in the resonance cavity between the InSb and metasurface. After the optimization, the isolation power of the device exceeds 55 dB with the insertion loss of only −3.92 dB under a very weak magnetic field of 0.2 T at room temperature. More importantly, the introduction of the metasurface can reduce the operating frequency of the isolator from 2.434 THz to 2.136 THz. This low-loss, weak magnetic field, room temperature operating, and high isolation THz isolator shows its broad potential in THz application systems.

Photovoltaic Self-Powered Gas Sensing: A Review

The self-powered sensing system could harness ambient energy to power the sensor without the need for external electrical energy. Recently, the concept of photovoltaic (PV) self-powered gas sensing has aroused wider attentions due to room-temperature operation, low power consumption, small size and potential applications. The PV self-powered gas sensors integrate the photovoltaic effects and the gas sensing function into a single chip, which could truly achieve the goal of zero power consumption for an independent gas sensing device. As an emerging concept, the PV self-powered gas sensing has been achieved by using different strategies, including integrated gas sensor and solar cell, integrated light filter and solar cell, gas-sensitive heterojunction photovoltaics, and gas-sensitive lateral photovoltaics, respectively. The purpose of this review is to summarize recent advances of PV self-powered gas sensing and also remark on the directions for future research in this topic.

Comparison of thermionic filament and carbon nanotube field emitter-based electron ionization sources in cycloidal coded aperture mass analyzers

This work compares the coded aperture imaging performance of thermionic filament and carbon nanotube (CNT) field emitter-based electron sources in cycloidal-coded aperture mass spectrometers. The use of spatially coded apertures in mass spectrometry enables miniaturization by improving throughput without sacrificing resolution. CNT-based electron ionization sources for mass spectrometers provide several potential benefits over conventional thermionic emitters, including low voltage and low power consumption, room temperature operation, long lifetime, and ability to emit electrons in a pulsed mode. However, spatiotemporal variation in electron emission from CNTs is a major disadvantage. In this study, electron emission stability and spatiotemporal stability of the coded aperture image were compared for coded aperture cycloidal mass analyzers with either a CNT-based ion source or a thermionic filament-based ion source. We found that the thermionic filament-based ion source produced a significantly more stable coded aperture image than the CNT based ion source. The aperture image fluctuations in the CNT-based source are likely a result of adsorption and desorption of molecules on the CNT surface that cause local work function changes and induce spatiotemporal variation in electron emission and subsequent ion generation.

Biogas production by co-digestion of municipal wastewater and food waste: Performance in semi-continuous and continuous operation.

Municipal wastewater has recently attracted interest in relation to anaerobic wastewater treatments. Biogas production with co-digestion of mixed substrates has been proposed and has many potential benefits for municipal wastewater. The aim of this research was to assess the performance of biogas production during co-digestion of municipal wastewater and food waste under semi-continuous and continuous operation with various hydraulic retention times (HRTs). A laboratory-scale continuous stirred tank reactor (CSTR) at room temperature operation (27-32°C) was employed in this research. The highest methane yields of 167.41±66.52, 194.35±85.44, and 214.81±85.44ml/g-Vs were found in semi-continuous mode, respectively, at 30, 10, and 10days of HRTs with a 10:90 ratio of municipal wastewater to food waste (based on TS). Result finding of optimum condition (10days of HRTs) presented a methane yield of 485.58±82.35ml/g with continuous operation. Hence, food waste has practical implications for use as a co-substrate with the optimization condition of HRT and operation mode for biogas production from municipal wastewater. PRACTITIONER POINTS: Food waste has good potential for use as a co-substrate for biogas production from municipal wastewater. HRT reduction from 30 to 10days in semi-continuous, biogas production from municipal wastewater and food waste increased by 59%. Co-digestion of municipal wastewater and food waste with continuous mode and 10days of HRT was the effective biogas production.

Enhancement of Low-Temperature Gas-Sensing Performance Using Substoichiometric WO3-x Modified with CuO.

To verify the effect of oxygen vacancy on gas sensitivity, we have systematically investigated the gas-sensing performance of copper oxide/substoichiometric tungsten oxide (CuO/WO3-x) nanocomposite sensors. Oxygen deficiency in WO3-x facilitates the reaction of hydrogen sulfide (H2S) gas with chemisorbed oxygen species (i.e., O2-, O-, and O2-) at low temperature. The oxygen/sulphur exchange reaction between CuO and H2S in the sensing process can achieve room temperature operation of gas sensors. After the WO3-x nanorods were modified by a low content of CuO nanoparticles (Cu:W = 1:20), the sensors present an n-type sensing behavior. Their best working temperatures drop from 289 °C (or 386 °C) to 99 °C (or 70 °C) at which the responses are improved by 14 to 163 times for different x values. Among them, CuO(L)/W5O14 shows the highest sensitivity of 1575.7 to 10 ppm H2S at 99 °C and 171.5 to 10 ppm H2S at room temperature. Once WO3-x were loaded with a high concentration of CuO nanoparticles (Cu:W = 1:2), they exhibit a p-type behavior, and the optimal working temperatures reduce suddenly to room temperature at which CuO(H)/W18O49 displays the most sensitive response of 7.2 even toward trace amounts of H2S as low as 100 ppb. In addition, p-type CuO weakens the metal-like characteristics of W18O49 and such weakening effect enhances with an increase in the CuO content. Therefore, the sensing performance of the CuO/W18O49 composite is the best among the four CuO/WO3-x sensors. The two designs for low and high Cu/W molar ratios all achieve enhanced room-temperature H2S gas response, with a fast recovery time of ∼60 s under heating pulse, as well as an excellent selectivity, which makes the sensors a promising candidate for practical applications. Moreover, the micro-Raman spectra confirmed CuS formation and the thermal effect on the decomposition of CuS in the sensing process was studied.