Source Region Research Articles

Inferring long‐distance movements of insects using combined hydrogen isotope and genetic analyses: A case study of the African edible bush‐cricket

Abstract The degree to which individuals within populations vary in whether, how far and what direction they disperse is central in order to understand many foundational questions in ecological entomology, including factors determining population and invasion dynamics, species' ability to respond to climate change or when designing conservation strategies for threatened species. This study combined stable hydrogen isotope analysis of nymphal and adult wing chitin with population genetic analysis of the cytochrome c oxidase subunit I (COI) gene to understand long‐distance movements of African edible bush cricket (Ruspolia differens) in East Africa. Results revealed that at most 77% of non‐swarming adults and 85% swarming adults originated locally, that is, within a range of a few hundred kilometres. In contrast, non‐local adults captured in Uganda likely originated from Ethiopia, Kenya or South Sudan based on the H isotopic evidence. Genetic analysis revealed 150 COI haplotypes with no significant differentiation among geographic source regions and no evidence of genetic isolation by movement distance. The observed frequent long‐distance movements, together with the historical records, which indicate that the swarm movements can be irregular in their direction, suggest that the movements represent nomadism rather than regular long‐distance migration. Our results thus provide a valuable case study of what characterizes nomadic movements in insects, which have been one of the outstanding open questions in movement ecology of animals.

Revegetation Impacts on Moisture Recycling and Precipitation Trends in the Chinese Loess Plateau

AbstractThe Loess Plateau in China has experienced a remarkable greening trend due to vegetation restoration efforts in recent decades. However, the response of precipitation to this greening remains uncertain. In this study, we identified and evaluated the main moisture source regions for precipitation over the Loess Plateau from 1982 to 2019 using a moisture tracking model, the modified WAM‐2layers model, and the conceptual framework of the precipitationshed. By integrating multiple linear regression analysis with a conceptual hydrologically weighting method, we quantified the effective influence of different environmental factors for precipitation, particularly the effect of vegetation. Our analysis revealed that local precipitation has increased on average by 0.16 mm yr−1 and evaporation by 5.17 mm yr−1 over the period 2000–2019 after the initiation of the vegetation restoration project. Regional greening including the Loess Plateau contributed to precipitation for about 0.83 mm yr−1, among which local greening contributed for about 0.07 mm yr−1. Local vegetation contribution is due to both an enhanced local evaporation as well as an increased local moisture recycling (6.9% in 1982–1999; 8.3% in 2000–2019). Thus, our study shows that local revegetation had a positive effect on local precipitation, and the primary cause of the observed increase in precipitation over the Loess Plateau is due to a combination of local greening and circulation change. Our study underscores that increasing vegetation over the Loess Plateau has exerted strong influence on local precipitation and supports the positive effects for current and future vegetation restoration plans toward more resilient water resources managements.

Atmospheric deposition of pollutants at three altitudes on Mount Emei, Sichuan Basin, southwestern China

Comparing the atmospheric deposition chemistry between above and below the planetary boundary layer (PBL) may help understand the impacts from inter-regional air pollutant transport and local emissions to air pollutant deposition. In this study, we monitored ions, soluble and insoluble potentially toxic elements (PTEs), and dissolved organic nitrogen and carbon at the base (M-base: 551 m asl), middle (M-middle: 2400 m asl), and summit (M-summit: 3077 m asl) on Mount Emei. The annual volume-weighted mean (VWM) concentrations of all measured components were substantially higher at M-base than at M-summit, except for Na+, Cl−, and NO2− as Na+ and Cl− at M-summit may be largely from ocean and NO2− to NO3− transformation may be faster at M-base. Not all components had their highest annual deposition fluxes at M-base mainly due to the differences in precipitation. Organic nitrogen and organic carbon accounted for 19 %–26 % and 63 %–71 % of the annual total dissolved nitrogen and carbon at the three sites, respectively. The contributions of soluble and insoluble fractions showed a large variability among the nine PTEs measured (3 %–75 % and 97 %–25 %, respectively) but they were similar among the three sites, as the PETs' solubility largely depended on pH. From low to high elevations, the contributions to the air pollutant deposition fluxes within and outside the SCB decreased and increased, respectively. Even south and southeast Asia were important source regions for some pollutants at M-summit. In sum, this study revealed the basin's large effects on air pollutant accumulation and deposition and the importance of non-SCB emissions above the SCB's PBL; However, either above or within the PBL, the inorganic, organic, soluble, and insoluble portions of air pollutants (particularly nitrogen and PTEs) should be considered together for a better understanding on air pollutants' transport, deposition, and ecological risks.

The Extreme Activity in Comet Hale–Bopp (C/1995 O1): Investigations of Extensive Narrowband Photoelectric Photometry

Conventional narrowband photoelectric photometry of Comet Hale–Bopp (1995 O1) was obtained on 99 nights from mid-1995 to early-2000, yielding gas and dust production rates over an unprecedented range of time and distance. The appearance of Hale–Bopp (H-B) presented a prime opportunity for active comet studies, and its inherent brightness and orbital geometry allowed the characterization of its long-term activity. Throughout the apparition, H-B released, by far, more gas and dust than any other comet ever measured. As a very high dust-to-gas ratio object, dust production was successfully measured throughout the apparition, with the dust consistently slightly red in color. All five gas species including OH and NH were detected just inside of 5 au inbound, while C2 and C3 were detected to just past 5 au outbound, and CN was followed until nearly 7.7 au. Heliocentric distance dependencies ranged between −1.2 and −2.7 in log–log space, with the extremes magnified by the large extrapolations in Haser model parameters at large distances. H-B’s enormous size and associated extremely high outgassing resulted in a much larger collisional zone, which in turn yielded outflow velocities more than 2× higher than ever previously measured at comparable distances. Even so, volatile composition remained within the “typical” classification, consistent with most Oort Cloud comets, and water production follows the expected curve based on a standard water vaporization model. However, seasonal effects provided evidence for inhomogeneities among the major source regions on the surface of the nucleus. Preliminary modeling of the nucleus and coma successfully matches this seasonal behavior.

Short-term anticorrelations between in situ averaged charge states of Fe and O in the solar wind

Context. Observations of the Fe and O charge states in the solar wind and interplanetary coronal mass ejections (ICMEs) generally exhibit a positive correlation between the average charge states of Fe and O (avQFe and avQO). Because Fe and O charge states freeze at different heights in the corona, this positive correlation indicates that conditions at different heights in the corona vary as a whole. Aims. We identify short time periods in the solar wind that exhibit anticorrelations between the average Fe and O charge states and investigate their properties. We aim to distinguish whether these anticorrelations are due to the related solar sources or to transport effects (e.g., differential streaming). We study kinetic properties of the solar wind related to these anticorrelated structures as well as heavy ion differential streaming in order to infer a possible relationship between conditions in coronal source regions and the reported in situ measurements. Methods. We employed a recently developed sliding-window cross-correlation method to locate anticorrelated structures in the solar wind composition measurements between 2001 and 2010 from the Advanced Composition Explorer (ACE). To account for fluctuations and measurement uncertainties, we varied the timescales and temporal lags. We determined the onset and end times of the gradual increases or decreases in the average charge states of O and Fe and analyzed the kinetic and plasma properties of the anticorrelated structures. Results. We identified 103 anticorrelated structures both in the solar wind and in ICMEs. The behavior of avQFe is strongly related to solar wind kinetic properties, including proton speed, proton temperature, and the proton-proton collisional age. We find that the anticorrelation of avQFe and avQO during these time periods cannot be explained by differential streaming nor by unrecorded hot plasma ejections. Thus, the measured anticorrelated variations in avQFe and avQO probably indicate that changes in coronal conditions at different freeze-in heights may follow opposite monotonic trends.

Challenges in Submarine Fiber‐Optic Earthquake Monitoring

AbstractUtilizing existing telecommunication cables for Distributed Acoustic Sensing (DAS) experiments has eased the collection of seismological data in previously difficult‐to‐access areas such as the ocean bottom. To assess the potential of submarine DAS for monitoring seismic activity, we conducted an experiment from mid‐October to mid‐December 2021 using a 45 km long dark fiber extending from the Greek island of Santorini along the ocean bottom to the neighboring island of Ios. This region is of great geophysical and public interest because of its historical and recent seismic and volcanic activity, especially along the Kolumbo volcanic chain. Besides recording anthropogenic noise and around 1,000 seismic events, we observe the primary and secondary microseisms in the submarine section, the latter inducing Scholte waves in a sediment layer where the cable is well‐coupled. By using the spectral element wave propagation solver Salvus, we compute synthetic strains for earthquakes with varying degrees of model complexity. Despite including topography, a water layer, and a heterogeneous velocity model, we are unable to reproduce the lack of coherence in our observed earthquake waveforms. Backpropagation simulations for four observed earthquakes indicate that clear convergence of the wavefield, and thus the ability to constrain a source region, is only possible when all model complexities are considered. We conclude that, despite the promising emergence of DAS, monitoring capabilities are limited by often unfavorable cable geometries, cable coupling, and the complexity of the medium. Interrogating multiple cables simultaneously or jointly analyzing DAS and seismometer data could help improve future monitoring experiments.

Identification of aerosol and meteorological parameters threshold for visibility conditions over Delhi city

The quantitative assessment of air pollution induced visibility impairment is a prevalent concern across Indian sub-continent. In present study, efforts have been made to identify thresholds of aerosol (PM2.5), meteorological variables (relative humidity, temperature at 2 m, wind speed at 10 m) and boundary layer for shallow (Category (CAT) I: 550–1000 m), moderate (CAT II: 300–550 m), dense (CAT IIIA: 175–300 m & CAT IIIB: 50–175 m) and very dense (CAT IIIC: <50 m) fog categories. A 5-year dataset from 2018 to 2023 for wintertime (December–February) is used to determine thresholds using statistical methods. A unique two-way rolling window correlation analysis is performed for linear, inverse and logarithmic functions considering described visibility classes, PM2.5, RH and temperature. Different sliding windows and subsequent step sizes are taken to ascertain interrelatedness based on significant correlation coefficients. Further, a frequency distribution based averaging method is used for wind speed and boundary layer thresholds. Based on the findings, identified thresholds for PM2.5, RH, temperature, wind speed and boundary layer are >270 μg/m3, >70%, <13 °C, <1.5 m/s, <100 m for CAT I; >250 μg/m3, >70%, <13 °C, <1.2 m/s, <80 m for CAT II; >250 μg/m3, >70%, <11 °C, calm winds, <80 m for CAT IIIA; >220 μg/m3, >80%, <11 °C, calm winds, <70 m for CAT IIIB while 180 μg/m3, >90%, <9 °C, calm winds and <60 m for CAT IIIC. The determined thresholds have been validated using 2023–2024 data based on which shallow, moderate, dense and very dense categories are found to be 65%, 77%, 88%, 90% and 93% compliant with the thresholds of CAT I, CAT II, CAT IIIA, CAT IIIB and CAT IIIC. Trajectory clustering is also included for ascertaining the potential pollution source regions. The study can aid policymakers in predicting fog events. Moreover, appropriate policy interventions can be formulated in wake of the early warning system and information dissemination.

Switchback Patches Evolve into Microstreams via Magnetic Relaxation

Switchbacks, defined as Alfvénic reversals in magnetic field polarity, can dissipate their magnetic energy with heliocentric distance. To further investigate this, two distinct solar wind parcels tracing back to a similar solar source region were examined during a radial alignment between Parker Solar Probe (@25.8RS) and Solar Orbiter (@152RS). The one caveat was that the two probes were located on opposite sides of the heliospheric current sheet during the alignment. The two parcels contained a multitude of switchbacks—the parcel closer to the Sun was characterized as a switchback patch (SBP), where background proton velocity (vp ) is comparable to the pristine solar wind (v sw), while the parcel farther from the Sun showed characteristics attributable to a microstream (MS; v p > v sw). It was found that (1) MS contains, on average, 30% fewer switchbacks than SBP, and (2) dynamic and thermal pressures decreased by up to 20% across switchback boundaries in SBP and relatively unchanged in MS. Magnetic relaxation can explain the lower number of switchbacks in MS compared to SBP. Switchback relaxation inside SBP can, in turn, accelerate plasma inside SBP over time and heliocentric distance, thus resulting in vp > v sw in MS. Therefore, it is hypothesized that magnetic relaxation of switchbacks may cause SBPs to evolve into MSs over time and heliocentric distance.

Physician Deserts: Navigating the Texas Terrain of Provider Supply and Demand with GIS Mapping.

Background: Rural health disparities in Texas impact population health due to limited healthcare access, insurance, and transportation challenges, especially in medically underserved areas. A shortage of specialists in rural regions worsens these issues, leading to increased morbidity and mortality rates. Objective: Our research aimed to address a knowledge gap by investigating the availability of three medical specialists-cardiologists, pulmonologists, and endocrinologists-in rural counties of Texas and identifying areas where access to healthcare is limited. Methods: Utilizing data from regional, state, and federal sources, the analysis geocoded specialist locations and created GIS maps to visualize the distribution of specialists across Texas's 254 counties. Physician demand was calculated by considering disease incidence and population size, resulting in a county-level physician availability index to highlight areas with shortages. Results: Our findings demonstrate a significant deficiency of cardiologists in 196 counties when considering a maximum reasonable travel distance of 50 miles. Comparable deficiencies were observed for pulmonologists and endocrinologists, with western rural counties predominantly comprising the deficiency areas for each specialty. These results emphasize a significant rural-urban disparity concerning access to the three investigated health specialists. Conclusions: Addressing geographic disparities can reduce health inequities, improve rural healthcare access, and promote a more equitable healthcare system across Texas. Solutions may include incentives for specialists to work in underserved areas, expanded telemedicine services, and transportation assistance.

Mapping and reconstruct suspended sediment dynamics (1986–2021) in the source region of the Yangtze River, Qinghai-Tibet Plateau using Google Earth Engine

Using remote sensing to measure suspended sediment concentration (SSC) in mountainous rivers can compensate for the scarcity of in situ sediment observations, providing valuable direct supplementation to observational records. However, for inland rivers, remote sensing SSC assessments face challenges such as data quality, long-term water body changes, environmental noise, flood events, and the transferability of local calibrations. Here, we introduce and apply remote sensing big data techniques using 12,445 cloud-free Landsat 5, 7, and 8 satellite images to calibrate SSC in the source region of the Yangtze River (SRYR). Utilizing Google Earth Engine, we implemented a series of image preprocessing techniques and water fraction methods to extract precise inland river water masks. Then we used unsupervised K-Means clustering and machine learning algorithms to model the relationship between water optical properties and SSC. By integrating these methodologies, we achieved an average relative calibration error of 0.26 for each optical cluster, and an average relative station deviation of 0.24 based on in situ measurements, minimizing SSC calibration to acceptable levels. Additionally, our results reveal that geomorphic patterns significantly influence sediment yield and transport by regulating sediment sources and sinks, fluvial morphology, and water-sediment connectivity. Over the past two decades, approximately 35.73 % of the sediment relative to the basin outlet discharge in the SRYR has been temporarily stored or confined within sediment sinks. These methods and findings hold significant implications for assessing and projecting fluvial sediment dynamics and the associated ecological and environmental issues in ungauged cold headwater regions.

Brexit consequences on supply chains: towards a risk management framework

ABSTRACT This article investigates Brexit-induced consequences on supply chains and logistics – as well as potential solutions and strategies by carrying out a content analysis through a literature review, the first to our knowledge. Our findings reveal that Brexit-induced consequences for supply chains include increased customs duty rate, labour supply issues, increased costs related to expected delays, tariff and nontariff barriers, added complexity to guarantee food safety, authenticity or security, increased food prices, as well as low-skilled households carrying the major load. Our findings regarding typical supply chain strategies or solutions for abovementioned Brexit-induced consequences include supply chain redesign, relocation of operations and markets, changing sourcing countries or regions, new information and communication technologies solutions such as traceability and blockchains, vertical and horizontal collaboration, resilience, better risk-recovery strategies, as well as the switch to ‘other’ metrics. Another result refers to the fact that we observe only a low level of theoretical grounding in (supply chain) risk management literature among the considered articles.

Migration as a Catalyst of Change: The Impact of Indian Labour Migration to the GCC

The idea of emigration as a method of subsistence has long gained traction in India. Emigration and remittances have been praised as financial sources for the transformation of communities and households. Due to its historical links to international migration and its position as one of India's top labor exporting states, Kerala is an especially intriguing state that has been one of the most significant source regions for Indian temporary workers, primarily to the GCC (Gulf Cooperative Council) countries. Kerala is home to almost 2.1 million migrants, and 36% of the state's net state product comes from their contributions. This study looks at empirical data from the socioeconomic discourses surrounding Gulf migration with respect to the emigrants, their households, and the place from where they migrated in order to comprehend how migrant houses differ from non-migrant households. The study covers empirical research on the reasons behind migration, mobility trends, and the issue of using migration as a strategy to lower state unemployment. The paper goes on to discuss the significance of emigration in the socioeconomic transformations of the state.

Ag-decorated hollow copper microtubes as a photocathode for the hydrogen evolution reaction

This paper presents the results of a photoelectrocatalytic study for a copper-silver system obtained in the form of microtubes using electrochemical template synthesis. CuOx/Cu hollow microtubes (HT) decorated with nanoscale silver particles by electrodeposition demonstrate the cathode photocurrent in 7.6 uAcm–2 when using LED light sources in the UVA-Vis spectral region and low polarization values. It was shown that the highest intensity of the photoresponse is achieved in the visible region at a wavelength of 450 nm. The stability test suggests that the retention of Ag/CuOx-HT is 95% after 12 hours of functioning.

Velocity structure of crust and mid-strong earthquake preparation characteristics in the Huoshan region, East China

The Huoshan region, located on the northern margin of the Dabie Orogenic Belt at the junction of the North China Plate and the Yangtze Plate, is one of the most seismically active and concentrated areas in the Dabie Orogenic Belt and adjacent regions. Utilizing the travel time data from 4,427 seismic events observed by 202 stations, we investigated the deep medium structure of the Huoshan region using the double-difference tomography method. The results reveal the medium structure and characteristics of mid-strong earthquake preparation in the region. The crustal medium in the study area exhibits significant lateral heterogeneity. The Dabie Orogenic Belt shows notably high velocity, whereas the North China Plate and the Yangtze Plate display relatively lower velocities. The Tan-Lu Fault Zone exhibits segmentation characteristics; with the crustal medium velocity south of Lujiang being relatively high, north of Jiashan being relatively low, and between Lujiang and Jiashan being intermediate. The epicenters of mid-strong earthquakes are located on the gradient zones of velocity and Poisson’s ratio. The source regions of these earthquakes show significant anomalies of high Poisson’s ratio and low S-wave velocity, which may indicate the presence of fluids. These anomalies possibly reflect the intrusion of deep materials along the fault zone, which could be the driving force for the preparation of mid-strong earthquakes.

Genetic evidence points to distinct paternal settlers of the Faroe Islands and Iceland.

The Faroe Islands are a small archipelago located in the North Atlantic likely colonized by a small group of founders sometime between 50 and 300 CE. Post colonization, the Faroese people have been largely isolated from admixture with mainland and other island populations in the region. As such, the initial founder effect and subsequent genetic drift are likely major contributors to the modern genetic diversity found among the Faroese. In this study, we assess the utility of Y-chromosomal microsatellites to detect founder effect in the Faroe Islands through the construction of haplotype networks and a novel empirical method, mutational distance from modal haplotype histograms (MDM), for the visualization and evaluation of population bottlenecks. We compared samples from the Faroe Islands and Iceland to possible regional source populations and documented a loss of diversity associated with founder events. Additionally, within-haplogroup diversity statistics reveal lower haplotype diversity and richness within both the Faroe Islands and Iceland, consistent with a small founder population colonizing both regions. However, in the within haplogroup networks, the Faroe Islands are found within the larger set of potential source populations while Iceland is consistently found on isolated branches. Moreover, comparisons of within-haplogroup MDM histograms document a clear founder signal in the Faroes and Iceland, but the strength of this signal is haplogroup-dependent which may be indicative of more recent admixture or other demographic processes. The results of the current study and lack of conformity between Icelandic and Faroese haplotypes implies that the two populations were founded by different paternal gene pools and there is no detectable post-founder admixture between the two groups.

Thermophoretic convection in porous atmosphere due to boosting temperature of plume: Climate change effects

A computational analysis of the impacts of thermophoretic convective heat transfer on climate change within a saturated porous atmosphere is predicted. A mathematical model is developed for the proposed problem, employing a Cartesian coordinate system for the source region, a cylindrical coordinate system for the plume region, and a spherical coordinate system for the atmospheric region. The temperature along the central axis of the plume is assumed to be variable, as is the surface temperature of the source region. In the source region, fossil fuel combustion releases thermophoretic particles that travel through the plume into the atmosphere. The climate impact of these particles is calculated via temperature difference across each region. Numerical simulations are performed to gain insights into the physical implications of the model, using the finite difference method to discretise and solve the governing partial differential equations. The effect of various parameters in the flow model, such as mixed convection parameter λT, modified mixed convection parameter λC, Schmidt number Sc, variable viscosity parameter γ, variable thermal conductivity parameter ε, porosity parameter ΩA thermophoretic parameter Nt and indexes of variable surface temperature, are analysed and presented graphically and in tabular form. The primary findings show that an increase in the porosity parameter ΩA results in increase in velocity and temperature profile, while the thermophoretic concentration decreases, potentially moderating climate impact. Further, the thermophoretic rate of heat transfer is maximum at α=1.5rad and minimum at α=πrad in the saturated porous atmosphere. The fundamental innovation of the current work is that three models from three regions are linked via trans-boundaries in terms of temperature differences. The accuracy of the obtained results is ensured by the prescribed boundary conditions and is highlighted graphically as well as in tabular form.

“Ensembled transfer learning approach for error reduction in landslide susceptibility mapping of the data scare region”

Landslide susceptibility map (LSM) plays an important role in providing the knowledge of slopes prone to future landslides. However, the applicability of LSM is often hindered due to high cost of data collection especially in mountainous region such as Himalayas. Therefore, this study proposes transfer learning approach (TL) to improve the performance of LSM by transferring the information from the data rich region (source) to data scare region (target). Two machine learning based model are trained in source area which is then transferred for prediction in target area and a source trained model combined with the knowledge of target is used for the prediction in the target area. The applicability of the proposed approach is tested considering Mandi district as source area and Kullu and Rudraprayag districts as target areas. Independent variables which included 11 landslide conducive factors from the source and target area, the independence was critically analysed using multi-collinearity test, while the geomorphic similarity was assessed using KL divergence method. Efficient machine learning method such as random forest (RF) and multi-layer perceptron (MLP) was used to train the models in both areas, statistical measure such as AUC-ROC, precision, recall, F-score, and accuracy were used to evaluate the performance of the LSMs. The results demonstrated the proposed approach for target area 1, the AUC value increased from 0.908 (Target trained on itself), to 0.942 (Target-Transfer Learned (TL)) and 0.959 (Target Combined) for RF and 0.896, 0.907 and 0.946 for MLP. Additionally, an increase in the precision was observed in RF while all other statistical measures increased to 0.023 for precision, 0.022 for recall, 0.023 for F-score and 0.066 for accuracy in the case of MLP. While on the other hand, in the case of target area 2, the AUC value for RF, ranged from 0.95 (Target area trained on itself), 0.80 (target TL) and 0.98 (target combined) and for MLP the AUC ranged from 0.82 for the source trained model while 0.84 for LSM obtained when both target and source data was used. Thus, the results revealed that proposed TL approach can be effective in improving the performance of LSM in data scare region in Himalayan region, thereby providing a promising approach in overcoming the issue of data limitation.

(Invited) High Mobility GeSn Nanowire CMOS

As transistor scaling advances, the necessity to replace silicon with materials possessing superior carrier mobilities intensifies. Group-IV semiconductors, with a particular emphasis on GeSn alloys, are distinguished by their exceptional electron and hole mobilities, rendering them prime candidates for advanced electronic applications. The vertical gate-all-around (GAA) nanowire transistor emerges as the pivotal device architecture, offering enhanced electrostatic control and a minimized physical footprint. This paper provides a comprehensive overview of vertical GAA GeSn nanowire CMOS devices. We construct vertical GAA nanowire transistors with epitaxial GeSn heterostructures, capitalizing on advancements in material growth, precise in-situ doping, and strategic band engineering across the source, channel, and drain regions. By harnessing GeSn's superior mobilities for both electrons and holes, we have developed and fabricated both p-FETs and n-FETs. The p-FET benefits from the high hole mobility of the Ge channel and the elevated injection velocity from the GeSn source, yielding significantly enhanced performance compared to devices solely made of Ge. For n-FETs, our findings reveal that incrementally increasing the Sn content in GeSn alloys leads to continuous performance enhancements, with an 11% Sn composition achieving a fivefold increase in on-current compared to traditional Ge-based devices. These outcomes underscore the immense potential of GeSn alloys in elevating the performance and energy efficiency of next-generation nanoelectronic devices.

The Effect of Doping Conditions on Amorphous IGZO Electrical Conductivity

In recent years, there has been a noticeable increase in interest in thin-film transistors (TFTs) employing oxide semiconductors in the display industry. Among various oxide semiconductors, amorphous indium gallium zinc oxide (a-IGZO) has emerged as a particularly promising material and being used for the backplane of the OLED (organic light emitting diode) TV. It offers several advantages over conventional materials such as amorphous silicon (a-Si) and organic semiconductors, including higher electron mobility, lower leakage current, and wide area process applicability.For the top-gate self-aligned structure offers distinct advantages over the bottom-gate structure, reducing parasitic capacitance between source/drain and gate electrodes. For low contact resistance between the source/drain electrodes and a-IGZO, the doping process on the IGZO layer is necessary to enhance conductivity at the source and drain region. Various doping techniques are employed for a-IGZO, including ultraviolet (UV) irradiation [1], ion implantation, and plasma treatment [2]. Ion implantation is a widely used method in semiconductor manufacturing, where ions are injected into the semiconductor using high-energy ion beams. UV irradiation, on the other hand, utilizes ultraviolet light to shift the Fermi level below the conduction band, thereby making the semiconductor conductive. Plasma doping, the focus of this study, typically involves using equipment such as PECVD (Plasma Enhanced Chemical Vapor Deposition) or RIE (Reactive Ion Etching) to dope a-IGZO within a low-pressure chamber using plasma generated. Reactive gases are introduced, and plasma ions with high energy disrupt the metal-oxygen bonds within a-IGZO, enhancing conductivity and reducing sheet resistance.In this study, plasma doping was employed and the changes in sheet resistance was investigated under different plasma conditions, particularly focusing on various reaction gases. Doping experiments were conducted for various gases, while the effects of plasma treatment were evaluated through the sheet resistance measurements and comprehensive composition analysis. The results of this study provide insights into the relationship between plasma doping through controlled reaction gases and changes in sheet resistance in a-IGZO.Our experimental results reveal that plasma treatment leads to a decrease in the electrical conductivity of the IGZO layer. Moreover, we explore how varying plasma treatment time and power levels influence this conductivity reduction. Furthermore, we examine the effect of post-annealing on the electrical conductivity of plasma treated IGZO layers. Our findings demonstrate that post-annealing conditions play a crucial role in determining the final electrical conductivity of IGZO layers after plasma treatment.[1] H. Seo, et al. "Permanent optical doping of amorphous metal oxide semiconductors by deep ultraviolet irradiation at room temperature," Appl. Phys. Lett. 96, 222101 (2010).[2] W. -S. Liu, C. -H. Hsu, Y. Jiang, Y. -C. Lai, and H. _C. Kuo, “Improving device characteristics of dual-gate IGZO thin-film transistors with Ar-O2 mixed plasma treatment and rapid thermal annealing,” Membranes 12, 49 (2022).

Demonstration of VGAA-TFETs using InAs/Si Heterojunction on SOI substrate

Introduction Miniaturization of field-effect transistors (FETs) have serious issues in enhanced leakage current, short-channel effect, and power consumption. In this regard, the vertical gate all-around (VGAA) structure using the III-V compound semiconductor nanowires (NWs) is expected as alternative transistor to solve the problems in leakage current and short channel effect. There is still challenge in decreasing power consumption of the FET because the reduction in subthreshold slope (SS) has physical limitation in thermionic carrier transport (SS = 60 mV/dec). Tunnel FETs (TFETs) can lower the SS less than the physical limitation in MOSFETs and are expected to be used as next-generation low-voltage switching devices. We have demonstrated vertical gate-all-around (VGAA) TFET using III-V/Si tunnel junction which was formed by the selective-area growth of III-V NWs on Si and achieved a steep SS characteristics and complementary operation [1]. These demonstrations should be expanded on silicon-on-insulator (SOI)(111) platforms toward circuit applications using the III-V/Si VGAA-TFETs. Here, selective-area growth of the InAs NWs on thin SOI(111) substrates and demonstrated InAs/Si VGAA-TFETs on SOI platforms.Experimental procedureFirst, a 35-nm-thick SiO2 film was formed on p-type SOI(111) by thermal oxidation. The SOI thickness was 600 nm. Periodical circular openings were formed using electron beam lithography and dry/wet etchings. Next, InAs NWs were grown by selective-area growth. Here, we used a pulse growth technique to orient NWs in the vertical <111>B direction on a nonpolar SOI substrate, making the substrate surface polar (111)B, and aligning vertical NWs [2]. Next, we fabricated VGAA-TFETs by using three-dimensional device process in previous reports [1]. First, Hf0.8Al0.2O were formed as gate oxides by atomic layer deposition (ALD). Next, 200 nm-thick tungsten (W) was deposited around the NW sidewalls as gate metal. After that source metal (Ti/Au) was evaporated 20 nm/50 nm on the substrate by EB vapor deposition. Next, benzocyclobutene (BCB) was used as isolation layer between gate and drain metals. Then drain metal (Ti/Pd/Au) was evaporated 20 nm/20 nm/50nm on the top of the NWs. Finally, the VGAA-TFETs were annealed at 350 - 400°C in order in N2 for ohmic contacts in the source and drain regions. VGAA-TFETs were measured after annealing for each temperature.ResultsThe growth results showed vertical InAs NWs were successfully integrated on the p-SOI(111) substrates. The grown InAs NWs have hexagonal pillar structures surrounded with {-110} vertical facets and (111) B planes. Each NWs were composed of axial Zn-pulse doped intrinsic/Si-doped n-type/Sn-pulse doped n+-type NW segments. The average height is inversely proportional to the square of the diameter. Therefore, as similar to the conventional selective growth of InAs NWs on Si(111), the surface diffusion process of In atoms was dominant for the NW growth on SOI(111) surface.Transfer characteristics of the fabricated VGAA-TFET after annealed at 350°C indicated the tunnel current in the InAs/Si tunnel junction was electrically modulated by gate bias. The minimum SS was 37 mV/dec at VDS = 0.50 V, which was less than the theoretical limitation of conventional MOSFETs.The on-state current was 21 nA/μm at drain and source (VDS) of 1.00 V. The off current was 6.5 fA/μm when VDS was 1.00 V. Also, the threshold voltage (VTH) was 0.55 V. Transconductance was 31 nS/μm at VDS = 0.50 V. The measured current and transconductance were normalized by the number of NWs and the gate outer perimeter.We also investigated anneal temperature dependence of the device performance. The increasing in anneal temperature slightly lowered the minimum SS from 37 mV/dec to 23 mV/dec. And the on-state current was increased with increasing the anneal temperature. However, nonlinearity in the output IDS – VDS curve was enhanced with increasing the anneal temperature. This was assumed to be formed Schottky contact on the source metal. At the higher anneal temperature above 380°C, Ti/Au source metal possibly formed silicide (TiSi2) layer at the Ti/p-SOI interface. Thus, the contact resistance was decreased by the silicidation, and the on-state current was increased. However, Schottky contact of Au/Si was partially formed through the silicidation layer due to the very thin Ti interlayer. One of the possible approaches was to increase the Ti thickness or to use Al or Cu as single layer film. Further improvement of the device performance will be discussed.[1] K.Tomioka et al., IEEE IEDM. Tech. Dig. (2020) 429-432[2] K.Tomioka et al., Nano Lett. 8(2008) 3475-3480