GeTe/MoTe2 Van der Waals Heterostructures: Enabling Ultralow Voltage Memristors for Nonvolatile Memory and Neuromorphic Computing Applications.

Advanced electronic semiconducting Van der Waals heterostructures (HSs) are promising candidates for exploring next-generation nanoelectronics owing to their exceptional electronic properties, which present the possibility of extending their functionalities to diverse potential applications. In this study, GeTe/MoTe2 HS are explored for nonvolatile memory and neuromorphic-computing applications. Sputter-deposited Ag/GeTe/MoTe2/Pt HS cross-point devices are fabricated, and they demonstrate memristor behavior at ultralow switching voltages (VSET: 0.15 V and VRESET: -0.14 V) with very low energy consumption (≈30 nJ), high memory window, long retention time (104 s), and excellent endurance (105 cycles). Resistive switching is achieved by adjusting the interface between the Ag top electrode and the heterojunction switching layer. Cross-sectional transmission electron microscope images and conductive atomic force microscopy analysis confirm the presence of a conducting filament in the heterojunction switching layer. Further, emulating various synaptic functions of a biological synapse reveals that GeTe/MoTe2 HS can be utilized for energy-efficient neuromorphic-computing applications. A multilayer perceptron is implemented using the synaptic weights of the Ag/GeTe/MoTe2/Pt HS device, revealing high pattern accuracy (81.3%). These results indicate that HS devices can be considered a potential solution for high-density memory and artificial intelligence applications.

Phase Change Heterostructure Memory with Oxygen-Doped Sb2Te3 Layers for Improved Durability and Reliability through Nano crystalline Island Formation.

Phase-change random access memory represents a notable advancement in nonvolatile memory technology; however, it faces challenges in terms of thermal stability and reliability, hindering its broader application. To mitigate these issues, doping and structural modification techniques such as phase-change heterostructures (PCH) are widely studied. Although doping typically enhances thermal stability, it can adversely affect the switching speed. Structural modifications such as PCH have struggled to sustain stable performance under high atmospheric conditions. In this study, these challenges are addressed by synergizing oxygen-doped Sb2Te3 (OST) with PCH technology. This study presents a novel approach in which OST significantly improves the crystallization temperature, power efficiency, and cyclability. Subsequently, the integration of the PCH technology bolsters the switching speed and further amplifies the device's reliability and endurance by refining the grain size (≈7 nm). The resultant OST-PCH devices exhibit exceptional performance metrics, including a drift coefficient of 0.003 in the RESET state, endurance of ≈4 × 108 cycles, an switching speed of 300 ns, and 67.6 pJ of RESET energy. These findings suggest that the OST-PCH devices show promise for integration into embedded systems, such as those found in automotive applications and Internet of Things devices.

Bio-Inspired Photosensory Artificial Synapse Based on Functionalized Tellurium Multiropes for Neuromorphic Computing.

Nanomaterials like graphene and transition metal dichalcogenides are being explored for developing artificial photosensory synapses with low-power optical plasticity and high retention time for practical nervous system implementation. However, few studies are conducted on Tellurium (Te)-based nanomaterials due to their direct and small bandgaps. This paper reports the superior photo-synaptic properties of covalently bonded Tellurium sulfur oxide (TeSOx ) and Tellurium selenium oxide (TeSeOx )nanomaterials, which are fabricated by incorporating S and Se atoms on the surface of Te multiropes using vapor deposition. Unlike pure Te multiropes, the TeSOx and TeSeOx multiropes exhibit controllable temporal dynamics under optical stimulation. For example, the TeSOx multirope-based transistor displays a photosensory synaptic response to UV light (λ = 365 nm). Furthermore, the TeSeOx multirope-based transistor exhibits photosensory synaptic responses to UV-vis light (λ = 365, 565, and 660 nm), reliable electrical performance, and a combination of both photodetector and optical artificial synaptic properties with a maximum responsivity of 1500 AW-1 to 365 nm UV light. This result is among the highest reported for Te-heterostructure-based devices, enabling optical artificial synaptic applications with low voltage spikes (1 V) and low light intensity (21 µW cm-2 ), potentially useful for optical neuromorphic computing.

Unsupervised sequence-to-sequence learning for automatic signal quality assessment in multi-channel electrical impedance-based hemodynamic monitoring.

BACKGROUND AND OBJECTIVE: This study proposes an unsupervised sequence-to-sequence learning approach that automatically assesses the motion-induced reliability degradation of the cardiac volume signal (CVS) in multi-channel electrical impedance-based hemodynamic monitoring. The proposed method attempts to tackle shortcomings in existing learning-based assessment approaches, such as the requirement of manual annotation for motion influence and the lack of explicit mechanisms for realizing motion-induced abnormalities under contextual variations in CVS over time. METHOD: By utilizing long-short term memory and variational auto-encoder structures, an encoder-decoder model is trained not only to self-reproduce an input sequence of the CVS but also to extrapolate the future in a parallel fashion. By doing so, the model can capture contextual knowledge lying in a temporal CVS sequence while being regularized to explore a general relationship over the entire time-series. A motion-influenced CVS of low-quality is detected, based on the residual between the input sequence and its neural representation with a cut-off value determined from the two-sigma rule of thumb over the training set. RESULT: Our experimental observations validated two claims: (i) in the learning environment of label-absence, assessment performance is achievable at a competitive level to the supervised setting, and (ii) the contextual information across a time series of CVS is advantageous for effectively realizing motion-induced unrealistic distortions in signal amplitude and morphology. We also investigated the capability as a pseudo-labeling tool to minimize human-craft annotation by preemptively providing strong candidates for motion-induced anomalies. Empirical evidence has shown that machine-guided annotation can reduce inevitable human-errors during manual assessment while minimizing cumbersome and time-consuming processes. CONCLUSION: The proposed method has a particular significance in the industrial field, where it is unavoidable to gather and utilize a large amount of CVS data to achieve high accuracy and robustness in real-world applications.

Synthesis, Properties, and Application of Ultrathin and Flexible Tellurium Nanorope Films: Beyond Conventional 2D Materials.

Nanomaterials that can be easily processed into thin films are highly desirable for their wide range of applicability in electrical and optical devices. Currently, Te-based 2D materials are of interest because of their superior electrical properties compared to transition metal dichalcogenide materials. However, the large-scale manufacturing of these materials is challenging, impeding their commercialization. This paper reports on ultrathin, large-scale, and highly flexible Te and Te-metal nanorope films grown via low-power radiofrequency sputtering for a short period at 25 °C. Additionally, the feasibility of such films as transistor channels and flexible transparent conductive electrodes is discussed. A 20 nm thick Te-Ni-nanorope-channel-based transistor exhibits a high mobility (≈450 cm2 V-1 s-1 ) and on/off ratio (105 ), while 7 nm thick Te-W nanorope electrodes exhibit an extremely low haze (1.7%) and sheet resistance (30 Ω sq-1 ), and high transmittance (86.4%), work function (≈4.9 eV), and flexibility. Blue organic light-emitting diodes with 7 nm Te-W anodes exhibit significantly higher external quantum efficiencies (15.7%), lower turn-on voltages (3.2 V), and higher and more uniform viewing angles than indium-tin-oxide-based devices. The excellent mechanical flexibility and easy coating capability offered by Te nanoropes demonstrate their superiority over conventional nanomaterials and provide an effective outlet for multifunctional devices.

Self-Powering Sensory Device with Multi-Spectrum Image Realization for Smart Indoor Environments.

The development of organic-based optoelectronic technologies for the indoor Internet of Things market, which relies on ambient energy sources, has increased, with organic photovoltaics (OPVs) and photodetectors (OPDs) considered promising candidates for sustainable indoor electronic devices. However, the manufacturing processes of standalone OPVs and OPDs can be complex and costly, resulting in high production costs and limited scalability, thus limiting their use in a wide range of indoor applications. This study uses a multi-component photoactive structure to develop a self-powering dual-functional sensory device with effective energy harvesting and sensing capabilities. The optimized device demonstrates improved free-charge generation yield by quantifying charge carrier dynamics, with a high output power density of over 81 and 76 µW cm-2 for rigid and flexible OPVs under indoor conditions (LED 1000 lx (5200 K)). Furthermore, a single-pixel image sensor is demonstrated as a feasible prototype for practical indoor operating in commercial settings by leveraging the excellent OPD performance with a linear dynamic range of over 130 dB in photovoltaic mode (no external bias). This apparatus with high-performance OPV-OPD characteristics provides a roadmap for further exploration of the potential, which can lead to synergistic effects for practical multifunctional applications in the real world by their mutual relevance.

Dual-frequency piezoelectric micromachined ultrasound transducer based on polarization switching in ferroelectric thin films.

Due to its additional frequency response, dual-frequency ultrasound has advantages over conventional ultrasound, which operates at a specific frequency band. Moreover, a tunable frequency from a single transducer enables sonographers to achieve ultrasound images with a large detection area and high resolution. This facilitates the availability of more advanced techniques that simultaneously require low- and high-frequency ultrasounds, such as harmonic imaging and image-guided therapy. In this study, we present a novel method for dual-frequency ultrasound generation from a ferroelectric piezoelectric micromachined ultrasound transducer (PMUT). Uniformly designed transducer arrays can be used for both deep low-resolution imaging and shallow high-resolution imaging. To switch the ultrasound frequency, the only requirement is to tune a DC bias to control the polarization state of the ferroelectric film. Flextensional vibration of the PMUT membrane strongly depends on the polarization state, producing low- and high-frequency ultrasounds from a single excitation frequency. This strategy for dual-frequency ultrasounds meets the requirement for either multielectrode configurations or heterodesigned elements, which are integrated into an array. Consequently, this technique significantly reduces the design complexity of transducer arrays and their associated driving circuits.

Effect of Transition Metal Dichalcogenide Based Confinement Layers on the Performance of Phase-Change Heterostructure Memory.

Phase-change random-access memory is a promising non-volatile memory technology. However repeated phase-change operations can cause durability issues owing to defects formed by long-distance atom diffusion. To mitigate these issues, phase-change heterostructure (PCH) devices with confinement material (CM) layers based on transition metal dichalcogenides (TMDs) such as TiTe2 have been proposed. This study implements PCH devices with additional TMDs, including NiTe2 and MoTe2 , alongside TiTe2 , and analyzes their characteristics by examining the differences in the CM layers. The results show that the NiTe2 -based PCH device demonstrates a RESET current of 1.4 mA, 38% lower than that of the TiTe2 -based device, enabling low-power operation. Furthermore, the MoTe2 -based PCH device exhibits a cycling endurance exceeding 107 cycles, a five-fold improvement in durability compare with the TiTe2 -based device. The performance differences observe in each PCH device can be attributed to the variation in the material properties, such as the cohesive energy and electrical conductivity, of the TMDs used as the CM layer. These results provide critical clues to improve the performance and reliability of conventional PCH memory devices.

Review of Electrochemically Synthesized Resistive Switching Devices: Memory Storage, Neuromorphic Computing, and Sensing Applications.

Resistive-switching-based memory devices meet most of the requirements for use in next-generation information and communication technology applications, including standalone memory devices, neuromorphic hardware, and embedded sensing devices with on-chip storage, due to their low cost, excellent memory retention, compatibility with 3D integration, in-memory computing capabilities, and ease of fabrication. Electrochemical synthesis is the most widespread technique for the fabrication of state-of-the-art memory devices. The present review article summarizes the electrochemical approaches that have been proposed for the fabrication of switching, memristor, and memristive devices for memory storage, neuromorphic computing, and sensing applications, highlighting their various advantages and performance metrics. We also present the challenges and future research directions for this field in the concluding section.

Flexible Memristive Organic Solar Cell Using Multilayer 2D Titanium Carbide MXene Electrodes.

Hybrid systems have attracted significant attention within the scientific community due to their multifunctionality, which has resulted in increasing demands for wearable electronics, green energy, and miniaturization. Furthermore, MXenes are promising two-dimensional materials that have been applied in various areas due to their unique properties. Herein, a flexible, transparent, and conductive electrode (FTCE) based on a multilayer hybrid MXene/Ag/MXene structure that can be applied to realize an inverted organic solar cell (OSC) with memory and learning functionalities is reported. This optimized FTCE exhibits high transmittance (84%), low sheet resistance (9.7 Ω sq-1 ), and reliable operation (even after 2000 bending cycles). Moreover, the OSC using this FTCE achieves a power conversion efficiency of 13.86% and sustained photovoltaic performance, even after hundreds of switching cycles. The fabricated memristive OSC (MemOSC) device also exhibits reliable resistive switching behavior at low operating voltages of 0.60 and -0.33 V (similar to biological synapses), an excellent ON/OFF ratio (103 ), stable endurance performance (4 × 103 ), and memory retention properties (104 s). Moreover, the MemOSC device can mimic synaptic functionalities on a biological time scale. Thus, MXene can potentially be used as an electrode for highly efficient OSCs with memristive functions for future intelligent solar cell modules.

Unraveling the Effect of the Water Content in the Electrolyte on the Resistive Switching Properties of Self-Assembled One-Dimensional Anodized TiO2 Nanotubes.

The applied potential, time, and water content are crucial factors in the electrochemical anodization process because the growth of one-dimensional nanotubes can be accelerated by enhancing the corrosive effect. We investigated the effect of the water content on the resistive switching (RS) properties of Ti foils by anodizing the foils and varying the water content in an electrolyte (1-10 vol %). By increasing the water content, we facilitated a slow transition from nanopores to nanotubes and realized an increase in the tube wall diameter and tube length. All of the fabricated memristive devices exhibited a reliable and reproducible bipolar resistive switching effect. The optimized device exhibited bipolar RS properties with good dc endurance (104 cycles) and data retention capability (105 s). Our results suggest that as the water content increases to 5 vol %, the RS process improves; further increases in the water content impair the RS process.

Amorphous Boron Nitride Memristive Device for High-Density Memory and Neuromorphic Computing Applications.

Although two-dimensional (2D) nanomaterials are promising candidates for use in memory and synaptic devices owing to their unique physical, chemical, and electrical properties, the process compatibility, synthetic reliability, and cost-effectiveness of 2D materials must be enhanced. In this context, amorphous boron nitride (a-BN) has emerged as a potential material for future 2D nanoelectronics. Therefore, we explored the use of a-BN for multilevel resistive switching (MRS) and synaptic learning applications by fabricating a complementary metal-oxide-semiconductor (CMOS)-compatible Ag/a-BN/Pt memory device. The redox-active Ag and boron vacancies enhance the mixed electrochemical metallization and valence change conduction mechanism. The synthesized a-BN switching layer was characterized using several analyses. The fabricated memory devices exhibited bipolar resistive switching with low set and reset voltages (+0.8 and -2 V, respectively) and a small operating voltage distribution. In addition, the switching voltages of the device were modeled using a time-series analysis, for which the Holt's exponential smoothing technique provided good modeling and prediction results. According to the analytical calculations, the fabricated Ag/a-BN/Pt device was found to be memristive, and its MRS ability was investigated by varying the compliance current. The multilevel states demonstrated a uniform resistance distribution with a high endurance of up to 104 direct current (DC) cycles and memory retention characteristics of over 106 s. Conductive atomic force microscopy was performed to clarify the resistive switching mechanism of the device, and the likely mixed electrochemical metallization and valence change mechanisms involved therein were discussed based on experimental results. The Ag/a-BN/Pt memristive devices mimicked potentiation/depression and spike-timing-dependent plasticity-based Hebbian-learning rules with a high pattern accuracy (90.8%) when implemented in neural network simulations.

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter: A Universal Approach Toward High-Performance Blue TADF Top Emission OLED.

A novel device structure for thermally activated delayed fluorescence (TADF) top emission organic light-emitting diodes (TEOLEDs) that improves the viewing angle characteristics and reduces the efficiency roll-off is presented. Furthermore, we describe the design and fabrication of a cavity-suppressing electrode (CSE), Ag (12 nm)/WO3 (65 nm)/Ag (12 nm) that can be used as a transparent cathode. While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency (EQE) and improved angular dependency than the device fabricated using the microcavity-based Ag electrode, it suffers from low color purity and severe efficiency roll-off. These drawbacks can be reduced by using an optimized multi-quantum well emissive layer (MQW EML). The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE (18.05%), high color purity (full width at half maximum ~ 59 nm), reduced efficiency roll-off (~ 46% at 1000 cd m-2), and low angular dependence. These improvements can be attributed to the synergistic effect of the CSE and MQW EML. An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence, and the MQW EML effectively confines charges and excitons, thereby improving the color purity and EQE significantly. The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

Dopant-Tunable Ultrathin Transparent Conductive Oxides for Efficient Energy Conversion Devices.

Ultrathin film-based transparent conductive oxides (TCOs) with a broad work function (WF) tunability are highly demanded for efficient energy conversion devices. However, reducing the film thickness below 50 nm is limited due to rapidly increasing resistance; furthermore, introducing dopants into TCOs such as indium tin oxide (ITO) to reduce the resistance decreases the transparency due to a trade-off between the two quantities. Herein, we demonstrate dopant-tunable ultrathin (≤ 50 nm) TCOs fabricated via electric field-driven metal implantation (m-TCOs; m = Ni, Ag, and Cu) without compromising their innate electrical and optical properties. The m-TCOs exhibit a broad WF variation (0.97 eV), high transmittance in the UV to visible range (89-93% at 365 nm), and low sheet resistance (30-60 Ω cm-2). Experimental and theoretical analyses show that interstitial metal atoms mainly affect the change in the WF without substantial losses in optical transparency. The m-ITOs are employed as anode or cathode electrodes for organic light-emitting diodes (LEDs), inorganic UV LEDs, and organic photovoltaics for their universal use, leading to outstanding performances, even without hole injection layer for OLED through the WF-tailored Ni-ITO. These results verify the proposed m-TCOs enable effective carrier transport and light extraction beyond the limits of traditional TCOs.

Giant Thermoelectric Seebeck Coefficients in Tellurium Quantum Wires Formed Vertically in an Aluminum Oxide Layer by Electrical Breakdown.

High efficiency thermoelectric (TE) materials still require high thermopower for energy harvesting applications. A simple elemental metallic semiconductor, tellurium (Te), has been considered critical to realize highly efficient TE conversion due to having a large effective band valley degeneracy. This paper demonstrates a novel approach to directly probe the out-of-plane Seebeck coefficient for one-dimensional Te quantum wires (QWs) formed locally in the aluminum oxide layer by well-controlled electrical breakdown at 300 K. Surprisingly, the out-of-plane Seebeck coefficient for these Te QWs ≈ 0.8 mV/K at 300 K. This thermopower enhancement for Te QWs is due to Te intrinsic nested band structure and enhanced energy filtering at Te/AO interfaces. Theoretical calculations support the enhanced high Seebeck coefficient for elemental Te QWs in the oxide layer. The local-probed observation and detecting methodology used here offers a novel route to designing enhanced thermoelectric materials and devices in the future.

Work Function-Tunable Amorphous Carbon-Silver Nanocomposite Hybrid Electrode for Optoelectronic Applications.

Parameters such as electrode work function (WF), optical reflectance, electrode morphology, and interface roughness play a crucial role in optoelectronic device design; therefore, fine-tuning these parameters is essential for efficient end-user applications. In this study, amorphous carbon-silver (C-Ag) nanocomposite hybrid electrodes are proposed and fully characterized for solar photovoltaic applications. Basically, the WF, sheet resistance, and optical reflectance of the C-Ag nanocomposite electrode are fine-tuned by varying the composition in a wide range. Experimental results suggest that irrespective of the variation in the graphite-silver composition, smaller and consistent grain size distributions offer uniform WF across the electrode surface. In addition, the strong C-Ag interaction in the nanocomposite enhances the nanomechanical properties of the hybrid electrode, such as hardness, reduced modulus, and elastic recovery parameters. Furthermore, the C-Ag nanocomposite hybrid electrode exhibits relatively lower surface roughness than the commercially available carbon paste electrode. These results suggest that the C-Ag nanocomposite electrode can be used for highly efficient photovoltaics in place of the conventional carbon-based electrodes.

Ti3C2-Based MXene Oxide Nanosheets for Resistive Memory and Synaptic Learning Applications.

MXene, a new state-of-the-art two-dimensional (2D) nanomaterial, has attracted considerable interest from both industry and academia because of its excellent electrical, mechanical, and chemical properties. However, MXene-based device engineering has rarely been reported. In this study, we explored Ti3C2 MXene for digital and analog computing applications by engineering the top electrode. For this purpose, Ti3C2 MXene was synthesized by a simple chemical process, and its structural, compositional, and morphological properties were studied using various analytical tools. Finally, we explored its potential application in bipolar resistive switching (RS) and synaptic learning devices. In particular, the effect of the top electrode (Ag, Pt, and Al) on the RS properties of the Ti3C2 MXene-based memory devices was thoroughly investigated. Compared with the Ag and Pt top electrode-based devices, the Al/Ti3C2/Pt device exhibited better RS and operated more reliably, as determined by the evaluation of the charge-magnetic property and memory endurance and retention. Thus, we selected the Al/Ti3C2/Pt memristive device to mimic the potentiation and depression synaptic properties and spike-timing-dependent plasticity-based Hebbian learning rules. Furthermore, the electron transport in this device was found to occur by a filamentary RS mechanism (based on oxidized Ti3C2 MXene), as determined by analyzing the electrical fitting curves. The results suggest that the 2D Ti3C2 MXene is an excellent nanomaterial for non-volatile memory and synaptic learning applications.

Nanoscale 3D Stackable Ag-Doped HfOx-Based Selector Devices Fabricated through Low-Temperature Hydrogen Annealing.

Electrochemical metallization-based threshold switching devices with active metal electrodes have been studied as a selector for high-density resistive random access memory (RRAM) technology in crossbar array architectures. However, these devices are not suitable for integration with three-dimensional (3D) crossbar RRAM arrays due to the difficulty in vertical stacking and/or scaling into the nanometer regime as well as the asymmetric threshold switching behavior and large variation in the operating voltage. Here, we demonstrate bidirectional symmetric threshold switching behaviors from a simple Pt/Ag-doped HfOx/Pt structure. While fabricating the Pt/Ag-doped HfOx/Pt film using a 250 nm hole structure, filaments composed of Ag nanoclusters were constructed through a low-temperature (∼200 °C) hydrogen annealing process where the shape of the film in a nanoscale via a hole structure was maintained for integration with 3D stackable crossbar RRAM arrays. Finite Ag filament paths in the HfOx layer led to uniform device-to-device performances. Moreover, we observed that the hydrogen annealing process reduced the delay time through the reduction of the oxygen vacancies in the HfOx layer. Consequently, the proposed Pt/Ag-doped HfOx/Pt-based nanoscale selector devices exhibited excellent performance of high selectivity (∼105), ultralow OFF current (∼10 pA), steep turn-on slope (∼2 mV/decade), and short delay time (3 µs).

Controllable Seebeck Coefficients of a Metal-Diffused Aluminum Oxide Layer via Conducting Filament Density and Energy Filtering.

We investigate the intrinsic thermoelectric (TE) properties of the metal-diffused aluminum oxide (AO) layer in metal/AO/metal structures, where the metallic conducting filaments (CFs) were locally formed in the structures via an electrical breakdown (EBD) process as shown by resistive switching memory devices, by directly measuring cross-plane Seebeck coefficients on the CF-containing insulating AO layers. The results showed that the Seebeck coefficients of the CF-containing AO layer in metal/AO/metal structures were influenced by the generation of the metallic CFs, which is due to the diffusion of the metal into the insulating AO layers when exposed to a temperature gradient in the direction of the cross plane of the sample. In addition, the increase in the Seebeck coefficients of the CF-containing AO layer when the number of EBD-processed patterns was increased is satisfactorily explained by the low-energy carrier (i.e., minority carriers) filtering through the metal-oxide interfacial barriers in the metal/AO/metal structures.

A novel low-temperature resistive NO gas sensor based on InGaN/GaN multi-quantum well-embedded p-i-n GaN nanorods.

In gas sensors, metal oxide semiconductors have been considered as favorable resistive-type toxic gas sensing materials. However, the higher temperature operation of metal oxides becomes a barrier for their wide range of applications in explosive and flammable gas environments. In this regard, great efforts have been devoted to reducing the operating temperature of the sensor. We demonstrated a chemical resistor-type NO gas sensor based on p-i-n GaN nanorods (NRs) consisting of InGaN/GaN multi-quantum wells (MQW). The sensor exhibited superior NO gas sensing performance to p-type GaN NRs. Furthermore, it also showed a remarkably improved response and fast recovery under UV irradiation (λ = 367 nm) of different UV intensities (7 to 20 mw cm-2) under reverse bias. The sensing performance of MQW-embedded p-i-n GaN NRs was enhanced with the boosted response by 4-fold at 35 °C under UV irradiation. The significant decrease in the resistance of the sensor under UV irradiation was mainly due to the extraction of photo-generated carriers under reverse bias, which can enhance the ionization of oxygen molecules. In addition, the effect of relative humidity (30%-60%) on the gas sensing performance was also manifested in this study. The selectivity of the sensor was determined by using other gases (NO, NO2, O2, NH3, H2S, CO, and H2), which exhibited a low response towards all tested gases other than NO. The experimental results demonstrated that p-i-n GaN NRs with InGaN/GaN MQW is a promising material for the detection of NO gas. Specific emphasis was laid on the enhanced response of p-i-n GaN NRs in reverse bias under UV irradiation.