Nanowire Width Research Articles

(Invited) BEOL-Compatible Oxide Semiconductor Logic and Memory Devices

3D monolithic integration of logic and memory devices has emerged as one of the key enablers for next-generation electronic devices to address the ever-increasing demand for higher integration density, better performance and energy efficiency. BEOL-compatible oxide semiconductors show great potential to revolutionize the field thanks to their unique properties [1].We present our recent advancement related to BEOL-compatible oxide semiconductors for logic and memory applications. The digital-etch-enabled nanowire transistors and α-IGZO-based eDRAM will first be discussed, followed by the ferroelectric (FE) memories with high performance and novel structures utilizing α-IGZO or ALD-deposited ZnO as the channel.Ultra-scaled amorphous IGZO (α-IGZO) nanowire field-effect transistors (NW-FETs) hold great potential for applications demanding high performance and integration density. To realize the fabrication of high-quality and aggressively-scaled nanowire structures, a novel digital etching method for amorphous α-IGZO materials has been proposed and demonstrated [2]. Confirmed by the SEM images of an α-IGZO nanowire before and after digital etching, a notable nanowire width W NW reduction can be observed. We have the thinnest α-IGZO nanowire achieved by the digital etching with a W NW of approximately 20 nm. By further developing the transistor upon the nanowire, the α-IGZO NW-FET attains a good subthreshold swing (SS) of 80 mV/decade and a high peak extrinsic transconductance (G m, ext) of 612 μS/μm at V DS of 2 V (456 μS/μm at V DS = 1 V). Compared to the previous studies, our IGZO NW-FET achieves one of the highest peak G m values among all IGZO-based FETs.Besides the BEOL compatibility and high on-current, ultra-low subthreshold leakage makes α-IGZO FETs extremely promising for eDRAM. We further investigated the potential of α-IGZO eDRAM by developing the charge-domain compute-in-memory (CiM) [3]. Experiments have demonstrated small SS, large on-state current, and long-time charge retention with our dedicated 4T1C memory cell. With differential cell structure, an even higher tolerance for charge loss can be attained. With experiment-calibrated benchmarking in the VGG-8 network for CIFAR-10 image classification tasks, 2092 TOPS/W power efficiency for the CiM core can be expected, outperforming the prior TFT and CMOS-based CiM approaches, exhibiting significant advantages for ultra-low-power applications.The integration of doped-HfO2 FE material and oxide semiconductor, both BEOL-compatible with large-scale and cost-effective deposition, presents a promising avenue for advancing data storage in the future. We have developed the high-performance α-IGZO Fe-FET with a metal-ferroelectric-metal-oxide-semiconductor (MFMIS) structure as well as the Fe TCAM [4]. The α-IGZO Fe-FET achieves a large memory window of ~3 V with high reliability, while the Fe TCAM reduces the transistor number from 16 to 2 compared to the traditional SRAM-based one. Besides α-IGZO, we believe that ALD-based oxide semiconductors featuring high controllability of film thickness and conformal coverage of the 3D structures can create new opportunities for novel device structure and integration. The fin-gate ZnO Fe-FET stands for a great example while not only outstanding device performance but also suppressed device-to-device variation due to the unique structure have been demonstrated, holding tremendous promise for high-density 3D integration [5]. Acknowledgments: This work is supported by Singapore Ministry of Education (Tier 2: MOE2018-T2-2-154, Tier 1: R-263-000-D65-114).

Strain distributions in carbon-doped silicon nanowires along [110] and [100] investigated by X-ray diffraction

Carbon-doped Si films formed on Si substrates have a large tensile strain, and the strain is relaxed by microfabrication into nanowires. We investigated the effects of crystalline orientation, width and carbon concentration on lattice relaxation using reciprocal space mapping (RSM) with X-ray diffraction. RSM profiles of 400–480 periodically aligned C-doped Si nanowires on Si substrates indicate that lattice relaxation of Si0.9917C0.0083 nanowires along the [100] direction was larger than that of [110] nanowires. The effect of crystalline orientation of nanowires is considered to increase as lattice mismatch to the substrate increases, since no difference was observed in residual strains between [100] and [110] Si0.9940C0.0060 nanowires with a smaller lattice mismatch to the Si substrate. It has also been revealed that the strains of C-doped Si nanowires became more relaxed as the nanowire width decreased.

Short spin waves excitation in spin Hall nano-oscillators

This study investigates the excitation of short-wavelength spin waves (SWs) in nanowire-based spin-Hall nano-oscillators (SHNOs). Using micromagnetic simulations, we study the wavelength of propagating SWs as a function of nanowire width, ranging from 10 to 50nm, excited in a 1.7nm-thick CoFeB layer using a pure spin current generated by a 5nm thin platinum layer via the spin Hall effect. Our results showed that SWs with shorter wavelengths are excited in narrow widths at higher magnetic fields and higher currents. In addition, the wavelength of the propagating waves scales linearly with the width of the nanowire. We attribute the emission of short wavelength due to the quantization of SWs in the nanowire. By reducing the nanowire width, SWs with ultrashort wavelengths are excited at high frequencies, with larger propagation speeds and longer attenuation lengths. Our results show that ultrashort SWs with wavelengths as short as 80nm can be generated in metallic-based SHNOs, with a group velocity of vg = 1.6µm/ns and attenuation length of Latt = 0.6µm. These findings have significant implications for the scalability of magnonic devices, which could have potential applications in SW-based logic and neuromorphic computing.

Stabilising transient ferromagnetic states in nanopatterned FeRh with shape-induced anisotropy

It is well-known that FeRh undergoes an antiferromagnetic to ferromagnetic (FM) phase transition where the high temperature phase is a low coercivity FM material. However, little is known about the effect of lateral confinement on the transition dynamics in FeRh thin films. Here, we pattern FeRh thin films into arrays of nanowires with a large aspect ratio (100:1) and, with ultrafast probing of the magnetic state in an applied magnetic field, we determine the influence of demagnetization fields on the stability of laser induced FM domains. In particular, with pump-probe Kerr measurements, we demonstrate that, when a magnetic field is applied along the nanowire length, the nanowire arrays exhibit an FM phase (>3.0ns) that is longer-lived than that observed for continuous thin films (≈2.0 ns). With electrical measurements, we also show that the transition temperature depends on the relative orientation of the magnetic field. Indeed, when the FeRh film is patterned with sub-μm features, the transition temperature decreases by up to 7 K depending on the field direction at applied magnetic fields of 1 T. The effects of sample heating are explored using finite-element simulations to determine the heat dissipation following laser excitation across a range of FeRh nanowire widths. These simulations confirm that the increased lifetimes of the magnetic-field-aligned FM domains in the nanowire arrays are not due to differences in heat dissipation. This suggests that FM domain growth and relaxation through the ultrafast phase transition in FeRh nanowires is strongly dependent on the shape anisotropy. This knowledge is important for the fine control of the phase transition in patterned FeRh thin films for nanoscale devices.

Topological photonic crystal nanowire array laser with edge states.

A topological photonic crystal InGaAsP/InP core-shell nanowire array laser operating in the 1550 nm wavelength band is proposed and simulated. The structure is composed of an inner topological nontrivial photonic crystal and outer topological trivial photonic crystal. For a nanowire with height of 8 µm, high quality factor of 4.7 × 104 and side-mode suppression ratio of 11 dB are obtained, approximately 32.9 and 5.5 times that of the uniform photonic crystal nanowire array, respectively. Under optical pumping, the topological nanowire array laser exhibits a threshold 27.3% lower than that of the uniform nanowire array laser, due to the smaller nanowire slit width and stronger optical confinement. Moreover, the topological NW laser exhibits high tolerence to manufacturing errors. This work may pave the way for the development of low-threshold single-mode high-robustness nanolasers.

Investigating the effects of impurity on electron mobility in quasi-one-dimensional wires

In this research, the electron mobility in GaAs quasi-one-dimensional wires with the presence of ionized impurity at zero temperatures was investigated and the results were compared with the mobility of a two-dimensional electron gas system. GaAs is a non-magnetic semiconductor with a direct band gap. Here for the calculations, the Boltzmann transport equation is used in the relaxation time approximation, taking into account the ionized impurity potential. Focusing on ionized Coulomb scattering and the short-range disorder is our goal. Electron mobility was investigated based on related parameters (Fermi energy and width of nanowires), and its diagram was drawn. In the end, the results of this research were compared with electron mobility in completely two-dimensional electronic systems. As expected, the numerical results showed that the electron mobility in extensive wires converges to the electron gas mobility of a fully two-dimensional plane.

Estimation of the Depletion Layer Thickness in Silicon Nanowire-Based Biosensors from Attomolar-Level Biomolecular Detection.

Silicon nanowire (SiNW) biosensors have attracted a lot of attention due to their superior sensitivity. Recently, the dependence of biomolecule detection sensitivity on the nanowire (NW) width, number, and doping density has been partially investigated. However, the primary reason for achieving ultrahigh sensitivity has not been elucidated thus far. In this study, we designed and fabricated SiNW biosensors with different widths (10.8-155 nm) by integrating a complementary metal-oxide-semiconductor process and electron beam lithography. We aimed to investigate the detection limit of SiNW biosensors and reveal the critical effect of the 10-nm-scaled SiNW width on the detection sensitivity. The sensing performance was evaluated by detecting antiovalbumin immunoglobulin G (IgG) with various concentrations (from 6 aM to 600 nM). The initial thickness of the depletion region of the SiNW and the changes in the depletion region due to biomolecule binding were calculated. The basis of this calculation are the resistance change ratios as functions of IgG concentrations using SiNWs with different widths. The calculation results reveal that the proportion of the depletion region over the entire SiNW channel is the essential reason for high-sensitivity detection. Therefore, this study is crucial for an indepth understanding on how to maximize the sensitivity of SiNW biosensors.

Laser-Induced Au Catalyst Generation for Tailored ZnO Nanostructure Growth.

ZnO nanostructures, semiconductors with attractive optical properties, are typically grown by thermal chemical vapor deposition for optimal growth control. Their growth is well investigated, but commonly results in the entire substrate being covered with identical ZnO nanostructures. At best a limited, binary growth control is achieved with masks or lithographic processes. We demonstrate nanosecond laser-induced Au catalyst generation on Si(100) wafers, resulting in controlled ZnO nanostructure growth. Scanning electron and atomic force microscopy measurements reveal the laser pulse's influence on the substrate's and catalyst's properties, e.g., nanoparticle size and distribution. The laser-induced formation of a thin SiO2-layer on the catalysts plays a key role in the subsequent ZnO growth mechanism. By tuning the irradiation parameters, the width, density, and morphology of ZnO nanostructures, i.e., nanorods, nanowires, and nanobelts, were controlled. Our method allows for maskless ZnO nanostructure designs locally controlled on Si-wafers.

Brillouin light scattering from quantized spin waves in nanowires with antisymmetric exchange interactions

Antisymmetric exchange interactions lead to non-reciprocal spin-wave propagation. As a result, spin waves confined in a nanostructure are not standing waves; they have a time-dependent phase, because counter-propagating waves of the same frequency have different wavelengths. We report on a Brillouin light scattering (BLS) study of confined spin waves in Co/Pt nanowires with strong Dzyaloshinskii-Moriya interactions (DMI). Spin-wave quantization in narrow ($\lesssim 200$ nm width) wires dramatically reduces the frequency shift between BLS Stokes and anti-Stokes lines associated with the scattering of light incident transverse to the nanowires. In contrast, the BLS frequency shift associated with the scattering of spin waves propagating along the nanowire length is independent of nanowire width. A model that considers the chiral nature of modes captures this physics and predicts a dramatic reduction in frequency shift of light scattered from higher energy spin waves in narrow wires, which is confirmed by our experiments.

Atomic layer etching of nanowires using conventional reactive ion etching tool

Innovative material and processing concepts are needed to further enhance the performance of complementary metal-oxide-semiconductor (CMOS) transistors-based circuits as the scaling limits are being reached. To supplement that, we report on the development of an atomic layer etching (ALE) process to fabricate small and smooth nanowires using a conventional dry etching tool. Firstly, a negative tone resist (hydrogen silsesquioxane) is spin-coated on Silicon Germanium-on-insulator (SiGeOI) samples and electron beam lithography is performed to create nanopatterns. These patterns act as an etch mask and are transferred into the SiGeOI layer using an inductively-coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, an SF6 and Ar+ based ALE process is employed to smoothen the nanowires and reduce their widths. SF6 modifies the surface of the samples, while in the next step Ar+ removes the modified surface. To investigate the effect of this process on the nanowire width, several ALE cycles are performed. The etched features are inspected using scanning electron microscopy. With the increasing number of ALE cycles, a reduction in the width is observed. An etch per cycle of 1.1 Å is obtained.

Poole-Frenkel (PF)-MOS: A Proposal for the Ultimate Scale of an MOS Transistor.

This work reports, for the first time, the phenomenon of lateral Poole-Frenkel current conduction along the dielectric/Si interface of a silicon nanowire metal-oxide semiconductor (MOS) transistor. This discovery has a great impact on the study of device characteristic modeling and device reliability, leading to a new kind of electronic device with a distinct operation mechanism for replacing the existing MOS transistor structure. By measuring the current-voltage characteristics of silicon nanowire MOS transistors with different nanowire widths and at elevated temperatures up to 450 K, we found that the current level in the conventional ohmic region of MOS transistors, especially for the transistors with a nanowire width of 10 nm, was significantly enhanced and the characteristics are no longer linear or in an ohmic relationship. The enhancement strongly depended on the applied drain voltage and strictly followed the Poole-Frenkel emission characteristics. Based on this discovery, we proposed a new type of MOS device: a Poole-Frenkel emission MOS transistor, or PF-MOS. The PF-MOS uses the high defect state Si/dielectric interface layer as the conduction channel and is expected to possess several unique features that have never been reported. PF-MOS could be considered as the ultimate MOS structure from a technological point of view. In particular, it eliminates the requirement of a subnanometer gate dielectric equivalent oxide thickness (EOT) and eradicates the server mobility degradation issue in the sub-decananometer nanowires.

8-band k ⋅ p modeling of strained InxGa(1−x)As/InP heterostructure nanowires

An 8-band k⋅p theory is implemented for studying the electronic properties of near-surface lateral InxGa(1−x)As/InP heterostructure nanowires in the (100) direction. The change in bandgap and effective mass due to inhomogeneous strain are compared to unstrained scenario nanowires, and the lattice mismatch is varied from −3.2% to 1%. The nanowires' height is H = 5, 13 nm, and the width varies from the smallest possible width for a given height to 100 nm. The change in the bandgap exhibited a nonlinear trait with strain for all sizes of the nanowire. The tensile strain reduces the bandgap irrespective of the width of the nanowire for a given height, while the effect of compressive strain on change in the bandgap becomes width dependent. Minima and maxima in the change in effective mass with respect to the nanowire width are observed in compressively and tensile strained nanowires, respectively, due to the interplay of quantum confinement and strain. The electrical performance of a single nanowire In0.85Ga0.15As/InP MOSFET in quantum capacitance limit is discussed for various nanowire sizes. The implemented 8-band k⋅p method is verified with the available experimental work and demonstrated that the developed model can be extended to study electronic parameters of arbitrarily shaped core–shell structures over a wide range of strain.

Design and fabrication of the superconducting single-photon detector operating at the 5 - 10 micrometer wavelength band

High-performance mid-wave and long-wave infrared single-photon detectors not only have significant research value in the fields of infrared astronomy and defense technology, but are also challenging to be realized in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performance in the near-infrared band. However, how to further improve the cutoff wavelength <i>λ</i><sub>c</sub> is a topic of widespread concern. In this paper, the method for improving <i>λ</i><sub>c</sub> by applying the regulation of the superconducting disorder is discussed, and a detector with an operating wavelength band of 5 - 10 μm is designed and fabricated. <br>Studies have shown that the multiplication and diffusion behaviors of the quasiparticles always occur during the photon detection events, although the microscopic photodetection mechanism of SNSPD still lacks a perfect theoretical explanation. Therefore, the theoretical analysis mainly considers the influence of the quasiparticles in this paper, and the mathematical formula of the detection cutoff wavelength <i>λ</i><sub>c</sub> can be obtained based on the phenomenological quasiparticle diffusion model. Furthermore, the disorder-dependent superconducting phase transition temperature <i>T</i><sub>c</sub>, superconducting energy gap <i><teshuzifu>D</i>, and electron thermalization time <i>τ</i><sub>th</sub> are also considered, in order to get more precise results.<br>Theoretical analysis suggests that the increase in the sheet resistance <i>R</i><sub>s</sub>, which evaluates the disorder strength, will help to increase <i>λ</i><sub>c</sub>. For example, when the nanowire width is kept at 30 nm and <i>R</i><sub>s</sub> > 380 Ω/□, it can be deduced that <i>λ</i><sub>c</sub> is larger than 10 μm.<br>Experimentally, the active area of the device consists of a straight superconducting nanowire with a length of 10 μm and a width of 30 nm, so that it can effectively reduce the probability of the defects on the nanowire and avoid the current crowding effect. We have fabricated a 30 nm-wide Mo<sub>0.8</sub>Si<sub>0.2</sub> mid infrared SNSPD, which has a cutoff wavelength <i>λ</i><sub>c</sub> no more than 5 μm, the effective strength of the disorder - the film sheet resistance <i>R</i><sub>s</sub> = 248.6 Ω/□. As a comparison, the sheet resistance, which is controlled by the film thickness, is increased to about 320 Ω/□ in this experiment.<br>It is demonstrated that the Mo<sub>0.8</sub>Si<sub>0.2</sub> detector with <i>R</i><sub>s</sub> ~320 Ω/□ can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at the wavelength of 10.2 μm can be obtained when the detector works at a bias current of 0.9 <i>I</i><sub>SW</sub> (<i>I</i><sub>SW</sub> is the superconducting transition current), and it can theoretically reach a maximum value of 92% if the compression of switching current is excluded. Therefore, it can be predicted that the disorder regulation may become another efficient approach for designing high-performance mid-wave and long-wave infrared SNSPDs, in addition to the optimization of the superconducting energy gap and the cross section of superconducting nanowire.<br>However, the continuous increase in the disorder will cause a decrease in both the superconducting phase transition temperature <i>T</i><sub>c</sub> and <i>I</i><sub>SW</sub> of the detector from the point of detector fabrication and application. This downward trend is especially pronounced when the nanowire width is ultranarrow, which is not conducive to the signal readout of the detector. Thus, exploring the optimal disorder regulation technology and balancing the relationship between the operating temperature, the signal-to-noise ratio, and the cutoff wavelength will have key scientific and application value for the development of high-performance mid-wave and long-wave infrared SNSPDs.

Beol-Compatible Ingazno-Based Devices for 3D Integrated Circuits

Due to its attractive materials and electrical properties, indium-gallium-zinc-oxide (IGZO) has been extensively researched in many emerging technologies, especially for three-dimensional (3D) monolithic integration and back-end-of-line (BEOL) compatible applications [1]. On the pathway toward the realization of high-performance 3D monolithic integrated chips (ICs), a wide range of building blocks with different functionalities are required. 3D monolithic ICs also demand optimization in device performance and circuit architecture design.In this paper, we discuss our recent research development in IGZO-based techniques at both device and circuit levels. This includes nanowire structure for IGZO-based transistors, as well as the BEOL-compatible ferroelectric ternary content-addressable memory (TCAM) and embedded dynamic random-access-memory (eDRAM) for compute-in-memory (CiM) using IGZO-based transistors.A novel digital etch technique for amorphous IGZO (α-IGZO) material as well as the formation of α-IGZO nanowires were realized, enabling high performance α-IGZO nanowire field-effect transistors (NWFETs) with ultra-scaled nanowire width (W NW) [2]. The scanning electron microscopy (SEM) images of α-IGZO nanowire before and after the digital etch show that the nanowire structure as well as W NW reduction after digital etch can be clearly observed. The smallest α-IGZO nanowire after digital etch has a W NW of ~20 nm. By leveraging the ultra-scaled nanowire structure, the NWFET with the smallest W NW achieves decent subthreshold swing of 80 mV/decade as well as high peak extrinsic transconductance (G m,ext) of 612 μS/μm at a drain to source voltage (V DS) = 2 V (456 μS/μm at V DS = 1 V). As compared with previous works in literature, our IGZO NWFET achieves one of the highest peak G m among all IGZO-based FETs. α-IGZO ferroelectric FETs (Fe-FETs) with a metal-ferroelectric-metal-oxide-semiconductor (MFMIS) structure were further realized based on the α-IGZO transistor process modules. The smallest L CH is as small as 40 nm. The cross-sectional transmission electron microscopy (TEM) image of the device shows sharp interface. The α-IGZO Fe-FETs achieve a large memory window of 2.9 V, high endurance of 108 cycles, high conductance ratio, and small cycle-to-cycle variation. By leveraging the low temperature processed α-IGZO Fe-FETs with good electrical characteristics, a BEOL-compatible ferroelectric TCAM circuit with 2 Fe-FETs connected in parallel was realized [3], showing an extremely large sensing margin. In addition, such α-IGZO Fe-FET TCAM reduces the transistor number from 16 to 2 as compared to traditional SRAM-based TCAM. Smaller cell size and higher energy efficiency can also be obtained.IGZO transistors can play an important role in in-memory computing as well. SEM image of the eDRAM CiM cell shows utilization of IGZO transistors. The smallest device has L CH of 45 nm [4]. The IGZO transistor-based eDRAM CiM with differential cell structure achieves low leakage current, low variation, low charge loss sensitivity, and the control-friendly charge-domain computing without DC power. By evaluating the key figure-of-merits, including precision, power efficiency, computing density, retention time, and robustness, it can be concluded that our IGZO transistor-based eDRAM CiM is promising for low-power and scalable compute-in-eDRAM design. Acknowledgments: This work is supported by Singapore Ministry of Education (Tier 2: MOE2018-T2-2-154, Tier 1: R-263-000-D65-114).

(Invited, Digital Presentation) Photoactivated In2O3/GaN NW Sensors for Monitoring NO2 with High Sensitivity and Low Power

We report and discuss our results on the performance of our photoactivated In3O2/GaN NW sensors, for monitoring NO2 at various levels of relative humidity and operating power. A 1ppm sensitivity as high as 29% was demonstrated at operating power of 5 mW and relative humidity 40%.Nanostructure-based semiconductor gas sensors such as nanowires, nanotubes or nanorods have seen significant progress in recent years, owning to their large surface-to-volume ratio proprieties, which lead to considerably increased sensitivity and improve the time response to analyte gases. In particular, Gallium Nitride (GaN) nanostructure-based gas sensors have generated a lot of interest due to its unique combination of sensor “friendly” properties such as, direct bandgap, excellent carrier mobility, high heat capacity and high breakdown voltage. These properties combined with suitable surface engineering make GaN and GaN-based nanostructures an excellent candidate for portable gas sensors.In this work, Gallium Nitride (GaN) nanowire (NW)-based NO2 sensors, functionalized with either pure In2O3 or In2O3 covered with an evaporated Au nanolayer, were developed for low operating power and high sensitivity. An AlGaN buffer layer was first deposited on a Si substrate to minimize lattice mismatch and improve adhesion between the Si substrate and the GaN NWs. Then the GaN NWs were patterned by stepper lithography-assisted dry-etching, followed by Induced Coupled Plasma etching using a metal hard mask to protect the GaN NW. The nanowire width target ranged between 200-600nm. Subsequently, electrodes composed of Ti/Al/Ti/Au metal stacks were deposited on top of the GaN to form Ohmic contacts. A thin In2O3 layer metal oxide receptor was deposited on all devices, using RF magnetron sputtering on top of the exposed GaN NW and this was followed for a subgroup of devices by coating the In2O3 with an evaporated Au nanolayer. Finally, rapid thermal annealing (RTA) at 700 0C was performed to crystalize the receptor layers and improve the ohmic contact. The surface quality of the resulting sensors was inspected with the help of Scanning Electron Microscope (SEM) micrographs.Several devices of each group (In2O3 and In2O3/Au ) were wire bonded and mounted onto an array board chamber. The devices were biased under 5V DC. Photoconductivity measurements, humidity testing and NO2 gas testing (1ppm and 10ppm concentration) were conducted. The sensors were illuminated under constant UV LED illumination throughout the duration of the testing at two wavelengths, 265 nm and 365 nm and three irradiance levels, 5mW, 30mW and 60mW. In general, the In3O2 GaN NW sensors where characterized by low sensitivity levels, whereas the In3O2/Au GaN NW sensors achieved excellent sensitivity levels. Fig.1 shows typical dynamic responses to 1ppm NO2 of the In3O2/Au GaN NW sensors under illumination at 265 nm and 365 nm, respectively, and Fig.2 the response at various relative humidity (RH) levels. An increase in resistance upon exposure to NO2 is observed, confirming the oxidizing nature of the NO2 gas. At this NO2 concentration level, the highest response value (29%) was obtained under (5mW, 265 nm) illumination, whereas the sensitivity under (5mW, 365nm) illumination was lower. For (30mW, 265nm) illumination, the sensitivity was 23% and for (30mW, 365nm) illumination it dropped to 15%. This phenomenon has been observed in the past by other authors also, and although its origins are not yet understood unambiguously, it may be caused by a higher rate of phonon energy relaxation at the surface at higher wavelengths, thereby reducing the effectiveness of chemisorption at the surface. In conclusion, room-temperature low-power photoactivated In3O2/Au GaN NW sensors with excellent levels of sensitivity at elevated relative humidity were designed, fabricated and tested. Figure 1

Performance of SOI Ω-Gate Nanowires from Cryogenic to High Temperatures

This review paper presents the electrical characteristics of Silicon-On-Insulator Ω-Gate nanowires in a wide range of temperatures. The operation in cryogenic and high-temperature environments will be experimentally explored. The influence of nanowire width and channel length will be discussed. Nanowires with and without strain will be investigated from room temperature down to cryogenic ones, showing that strained nanowires improve carrier mobility in the whole temperature range. At high temperatures, it is demonstrated that nanowires can operate successfully up to 580 K, maintaining the ideal body factor. The effect of high temperatures on Gate-Induced Drain Leakage will also be studied. The experimental results in the whole temperature range confirm that SOI nanowires are an excellent alternative for FinFET replacement in future technological nodes.

Electrical Characteristics of In0.53Ga0.47As Gate-All-Around MOSFETs With Different Nanowire Shapes

In this article, we investigate the electrical properties of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As gate-all-around (GAA) MOSFETs with different nanowire shapes. InGaAs GAA MOSFETs with trapezoid and triangle nanowire shapes have been fabricated and characterized. Improved output performance was observed as the nanowire top width reduces from 20 to 11 nm. It was found that the electrical characteristics degraded as the nanowire top width was decreased to nearly 0 nm. To explain the carrier transport mechanism in ultralow-scale devices, TCAD simulation has been performed to study the electron density distribution for different nanowire widths and explain the transport mechanism in these ultralow-scale transistor devices.

Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires.

Optoelectronic micro- and nanostructures have a vast parameter space to explore for modification and optimization of their functional performance. This paper reports on a data-led approach using high-throughput single nanostructure spectroscopy to probe >8000 structures, allowing for holistic analysis of multiple material and optoelectronic parameters with statistical confidence. The methodology is applied to surface-guided CsPbBr3 nanowires, which have complex and interrelated geometric, structural, and electronic properties. Photoluminescence-based measurements, studying both the surface and embedded interfaces, exploits the natural inter nanowire geometric variation to show that increasing the nanowire width reduces the optical bandgap, increases the recombination rate in the nanowire bulk, and reduces the rate at the surface interface. A model of carrier recombination and diffusion ascribes these trends to carrier density and strain effects at the interfaces and self-consistently retrieves values for carrier mobility, trap densities, bandgap, diffusion length, and internal quantum efficiency. The model predicts parameter trends, such as the variation of internal quantum efficiency with width, which is confirmed by experimental verification. As this approach requires minimal a priori information, it is widely applicable to nano- and microscale materials.

Lasing action in a strongly coupled silicon nanowire pair.

High-index dielectric nanostructures are of particular interest for nanoscale lasing due to their low absorption losses. However, the relatively weak near-field restricts the isolated dielectric cavities as low-threshold integrated on-chip laser sources. Here, we demonstrate lasing action in a silicon nanowire pair with 32 nm gap coated with dye-doped shell on the silicon-on-insulator platform. It is found that the quality factor Q is dominated by the coupling of the silicon nanowire pair, which depends on the gap size, the nanowire width, and the dye thickness. A lasing peak at the wavelength of 529 nm with FWHM of 0.6 nm is experimentally realized by the Si nanowire pair width, and the corresponding pumping power threshold is ∼34 µW/cm2. The proposed strategy, based on the well-established Si planar process, lays the groundwork for practical integrated nanolasers that have potential applications in photonic circuits.

Study of Cryogenic Unmasked Etching of "Black Silicon" with Ar Gas Additives.

The influence of Ar gas additives on ≪black silicon≫ formation is shown in this work. The way to achieve the conical shape of Si texture using low Ar dilution is demonstrated. Also, a possibility of silicon nanowire width reduction keeping a high density of array is shown. No damage to the Si structure caused by Ar plasma was detected. The introduction of Ar into the plasma also does not affect electrical properties. The lifetime value after cryogenic etching with 5 sccm Ar flow remains at the same level of 0.7 ms. The resulting black silicon has a low total reflectance of 1 ± 0.5% in the range of 450–1000 nm in the overall 100 mm Si wafer surface.