| 1. |
- Wang, Guilei, et al.
(författare)
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Growth of SiGe layers in source and drain regions for 10 nm node complementary metal-oxide semiconductor (CMOS)
- 2020
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 31, s. 26-33
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the integration of Si 1−x Ge x (50% ≤ x ≤ 60%) selective epitaxy on source/drain regions in 10 nm node FinFET has been presented. One of the major process issues was the sensitivity of Si-fins’ shape to ex- and in-situ cleaning prior to epitaxy. For example, the sharpness of Si-fins could easily be damaged during the wafer washing. The results showed that a DHF dip before the normal cleaning, was essential to clean the Si-fins while in-situ annealing in range of 780–800 °C was needed to remove the native oxide for high epitaxial quality. Because of smallness of fins, the induced strain by SiGe could not be directly measured by X-ray beam in a typical XRD tool in the lab or even in a Synchrotron facility. Further analysis using nano-beam diffraction technique in high-resolution transmission electron microscope also failed to provide information about strain in the FinFET structure. Therefore, the induced strain by SiGe was simulated by technology computer-aided design program and the Ge content was measured by using energy dispersive spectroscopy. Simulation results showed 0.8, 1 and 1.3 GPa for Ge content of 40%, 50% and 60%, respectively. A kinetic gas model was also introduced to predict the SiGe profile on Si-fins with sharp triangular shape. The input parameters in the model includes growth temperature, partial pressure of the reactant gases and the exposed Si coverage in the chip area.
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| 2. |
- Xiong, Wenjuan, et al.
(författare)
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SiNx films and membranes for photonic and MEMS applications
- 2020
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 31, s. 90-97
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a novel process to form SiN x films and process for membranes with excellent mechanical properties for micro-electro-mechanical systems application as well as integration as IR waveguide for photonic application. The SiN x films were fabricated in SiNgen apparatus which is a single wafer chamber equipment compared to conventional low pressure chemical vapor deposition furnace process. The films showed low stress, good mechanical properties, but the synthesis also eradicates the issues of particle contamination. Through optimizing of the growth parameters and post annealing profile, low stress (40 Mpa) SiN x film could be finally deposited when annealing temperature rose up to 1150 °C. The stress relaxation is a result of more Si nano-crystalline which was formed during annealing, according to the FTIR results. The mechanical properties, Young’s modulus and hardness, were 210 Gpa and 20 Gpa respectively. For the waveguide application, a stack of three layers, SiO 2 /SiN x /SiO 2 was formed where the optimized layer thicknesses were used for minimum optical loss according to simulation feedback. After deposition of the first two layers in the stack, the samples were annealed in range of 900–1150 °C in order to release the stress. Chemical mechanical polish technique was applied to planarize the nitride layer prior to the oxide cladding layer. Such wafers can be used to bond to Si or Ge to manufacture advanced substrates.
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| 3. |
- Zhao, Xuewei, et al.
(författare)
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Design impact on the performance of Ge PIN photodetectors
- 2020
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Ingår i: Journal of materials science. Materials in electronics. - : Springer. - 0957-4522 .- 1573-482X. ; 31:1, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- This article presents the impact of epitaxial quality, contact resistance and profile of Ge PIN photodetectors (PDs) on dark current and responsivity. The PD structures were processed with either selectively grown Ge with integrated waveguides on SOI wafer or globally grown Ge on the entire wafer. The contact resistance was lowered by introducing NiGe layer prior to the metallization. The n-type doped Ge PIN structure was formed by ion implantation and the contact resistivity was estimated to 2.6x10(-4) ohm cm(2). This value is rather high and it is believed to be due to fomation of defects during implantation. The results show a minor difference in dark currents for selectively and globally grown PDs but in both types, it depends on detector area and the epitaxial quality of Ge. For example, the threading dislocation density (TDD) in non-selectively grown PDs with thickness of 1 mu m was estimated to be 10(6) cm(-2) yielding relatively low dark currents while it dramatically changes for PDs with thinner Ge layers where TDD increases to 10(8) cm(-2) and the dark current levels increase almost by 1.5 magnitude. Surprisingly, for selectively grown PDs with Ge thickness of 500 nm, TDD was still low resulting in low dark currents. The dark current densities at -1 V bias of non-selectively and selectively grown PDs with optimized profile were measured to be 5 mA/cm(2) and 47 mA/cm(2), respectively, while the responsivity of these detectors were 0.17 A/W and 0.46 A/W at lambda similar to 1.55 mu m, respectively. Excellent performance for selectively grown PD shows an appropriate choice for detection of 1.55 mu m wavelength.
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| 4. |
- An, Yiming, et al.
(författare)
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Temporal changes on soil conservation services in large basins across the world
- 2022
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Ingår i: Catena (Cremlingen. Print). - : Elsevier BV. - 0341-8162 .- 1872-6887. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- Soil erosion is one of the main drivers of land degradation across the world, thus soil conservation service has received increasing attention. Limited studies have focused on it, hence this study investigates spatial and temporal patterns on soil conservation service in four large representative basins globally (i.e., Amazon, Mississippi, Yangtze, and Yellow River Basins), between 2001 and 2018. Annual soil conservation service and soil erosion rate are estimated under RUSLE framework, and temporal trends are analyzed using Mann-Kendall test. Additionally, impacts of soil erosion factors on spatial distribution of soil conservation service are assessed through fitting stepwise regressions annually and calculating the factors' contributions. Furthermore, driving factors of temporal changes are identified as climate or land cover dominated, and combined effect of both, according to Z scores from Mann-Kendall test for soil conservation service, R and C factors. Results show the Yangtze River Basin produces the highest average annual erosion rate (mean values of 133.28 Mg ha(-1) yr(-1) in 2001 and 143.21 Mg ha(-1) yr(-1) in 2018) and average soil conservation service (mean values of 2663.57 Mg ha(-1) yr(-1) in 2001 and 3126.43 Mg ha(-1) yr(-1) in 2018). Amazon River Basin yields the lowest average annual soil erosion rate (15.96 Mg ha(-1) yr(-1) in 2001 and 21.30 Mg ha(-1) yr(-1) in 2018), whereas the Mississippi River Basin produces the lowest average soil conservation service (388.48 Mg ha(-1) yr(-1) in 2001 and 730.70 Mg ha(-1) yr(-1) in 2018). Over the study period, soil conservation service shows an increasing trend in the Yangtze and Yellow River Basins, with average changing rates of 27.23 Mg ha(-1) yr(-1) and 16.60 Mg ha(-1) yr(-1), respectively. Increasing soil conservation service is mainly driven by climate change (i.e., rainfall) and the combined effect of climate and land cover changes, but terrain conditions are the main spatial drivers.
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| 5. |
- Bai, Xiaohang, et al.
(författare)
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Precipitation drives the floristic composition and diversity of temperate grasslands in China
- 2021
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Ingår i: Global Ecology and Conservation. - : Elsevier BV. - 2351-9894. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Effects of environmental factors on plant diversity in temperate grasslands are of interest since experiments have found plant diversity is related to ecosystem function. Although previous studies have focused on the effects of environmental factors on plant diversity, the dominant environmental factors driving diversity differences among plant community types in temperate grasslands at regional scale remains unclear. We established 38 sampling sites (45 m x 45 m) in the main distribution areas of temperate grasslands to analyze the responses of plant community along different environmental gradients and identifies the dominant environmental factors driving the floristic composition and diversity in Inner Mongolia, China. In addition, environmental variables (annual mean temperature, annual precipitation, altitude, disturbance intensity, soil pH, soil density, soil water content, soil organic carbon, soil total nitrogen, soil total phosphorus, soil calcium carbonate), species diversity indices (richness, heterogeneity, evenness), functional diversity indices (abundance, evenness, divergence, dispersion) and plant biomass were analyzed. A total of 179 vascular plant species belonging to 43 families and 113 genera were recorded and classified into six plant community types (Stipa grandis community, Leymus chinensis community, Stipa capillata community, Artemisia frigida community, Cleistogenes squarrosa community, Artemisia halodendron community) based on Ward's agglomerative hierarchical clustering. According to canonical correspondence analysis and Monte Carlo permutation test, mean annual precipitation was the dominant environmental factor driving temperate grasslands, promoting species richness, heterogeneity, evenness, functional divergence and biomass. Soil organic carbon, water content and total nitrogen played positive effects on species diversity, meanwhile, mean annual temperature, altitude, grazing intensity and soil pH inhibited species diversity, functional abundance, dispersion and biomass. Furthermore, the presence of these plant communities dominated by Cleistogenes squarrosa and Artemisia halodendron indicate that grassland degradation is imminent or has already begun. In summary, our results provide evidence on the responses of composition, functional traits and biomass among different plant community types to environmental factors and demonstrate that precipitation is the dominant factors driving the floristic composition and diversity in temperate grasslands.
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| 6. |
- Bai, Xiaohang, et al.
(författare)
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Reducing plant community variability and improving resilience for sustainable restoration of temperate grassland
- 2022
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Ingår i: Environmental Research. - : Elsevier BV. - 0013-9351 .- 1096-0953. ; 207
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Tidskriftsartikel (refereegranskat)abstract
- Grassland ecosystem is important for the realization of the global sustainable development goals (e.g. Goal 15) since it provides irreplaceable services for human beings, supporting human health and sustainable development. Most studies have focused on improving grassland restoration techniques, but less attention has been paid to grassland ecosystem stability in succession. Plant community stability of temperate grassland in arid and semi-arid regions is analyzed through 38 sampling sites in Inner Mongolia, China. The degradation succession sequence of grassland is established by principal component analysis, and the species diversity and functional diversity along degradation gradient analyzed by multivariate statistical analysis. The results show that (1) functional diversity has higher explanatory power for community stability than species diversity due to the functional dispersion of plant traits; (2) climate factors rather than grazing or soil control plant community diversity and stability at regional scale; (3) the resistance of plant community does not change in degradation succession, but the trade-off effect of stability components in different plant communities differ, such as the order of trade-off effects (e.g. community resilience (ET)＞community resistance (RT)＞structural variability (St)＞functional variability (Fu) in the community dominated by Stipa grandis, RT＞ET＞St＞Fu in Leymus chinensis community, St＞ET＞Fu＞RT in Stipa capillata community, RT＞St＞Fu＞ET in Artemisia frigida community, St＞Fu＞ET＞RT in Cleistogenes squarrosa community, and Fu＞St＞RT＞ET in Artemisia halodendron community); (4) grassland ecosystem with higher diversity shows greater resilience and lower variability than those with single species, which supports the established diversity hypothesis. Furthermore, sustainable grassland restoration should reduce community variability and improve resilience. These findings highlight the response of diversity to stability in temperate grassland and provide scientific support for grassland ecosystem protection and restoration.
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| 7. |
- Duan, Ningyuan, et al.
(författare)
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Reduction of NiGe/n- and p-Ge Specific Contact Resistivity by Enhanced Dopant Segregation in the Presence of Carbon During Nickel Germanidation
- 2016
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Ingår i: IEEE Transactions on Electron Devices. - : IEEE. - 0018-9383 .- 1557-9646. ; 63:11, s. 4546-4549
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Tidskriftsartikel (refereegranskat)abstract
- This brief explores the specific contact resistivity (rho(c)) of NiGe/n- and p-Ge contacts with and without carbon pregermanidation implantation. It is found that in the presence of carbon, not only the thermal stability of NiGe films is improved, but also the rho(c) of the NiGe/n- and p-Ge contacts is reduced remarkably due to enhanced phosphorus (P) and boron (B) dopant segregation (DS) at the NiGe/Ge interface after nickel germanidation. At 500 degrees C germanidation temperature, the.c values are reduced from 1.1 x 10(-4) Omega-cm(2) and 2.9 x 10(-5) Omega-cm(2) for NiGe/n- and p-Ge contacts without carbon to 7.3 x 10(-5) Omega-cm(2) and 1.4 x 10(-5) Omega-cm(2) for their counterparts with carbon, respectively.
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| 8. |
- Ferreira, Carla S. S., et al.
(författare)
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Wetlands as nature-based solutions for water management in different environments
- 2023
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Ingår i: Current Opinion in Environmental Science & Health. - : Elsevier BV. - 2468-5844. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Wetlands are multifunctional systems performing as nature-based solutions (NBS) for water management. This paper provides an overview of natural and constructed wetlands and their potential to support the regulation of hydrological fluxes and water quality. Wetlands can modulate peak flows by storing runoff and slowly releasing it over time, with positive impacts on soil moisture. They can also change the overall water balance by influencing evapotranspiration, infiltration, and groundwater recharge. They can enhance resilience of a catchment to floods and torrents, especially with relative low return periods (<50 years), and safeguard water availability during droughts. Wetlands may remove or reduce a number of organic and inorganic pollutants (e.g., nutrients, heavy metals, hydrocarbons, pesticides) by different physical, chemical, and biological processes developed between vegetation, microorganisms, soil/growth substrate, and water. They have proven to be efficient and effective in improving the quality of water from different sources, such as runoff from agriculture and urban areas, and domestic and industrial wastewater. The overall performance of wetlands is determined by their characteristics (e.g., size, design, type of vegetation), within-catchment position, type and amount of water and pollutants, and local conditions (e.g., climate). A focus on wetlandscape, rather than individual wetlands, is required for optimal water management and maximization of other ecosystem services.
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| 9. |
- Han, Yi, et al.
(författare)
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Soil erodibility for water and wind erosion and its relationship to vegetation and soil properties in China's drylands
- 2023
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 903
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Tidskriftsartikel (refereegranskat)abstract
- Drylands with fragile socio-ecological systems are vulnerable to soil erosion. China's drylands face the dual threat of water (WAE) and wind erosion (WIE). To mitigate soil erosion in drylands, China has implemented numerous ecological restoration measures. However, whether vegetation and soil have different effects on soil erodibility for water erosion (soil erodibility, K) and wind erosion (soil erodible fraction, EF) in drylands is unclear, hindering decision makers to develop suitable ecological restoration strategies. Here, we conducted a large-scale belt transect survey to explore the spatial variation of K and EF in China's drylands, and examined the linear and nolinear effects of aridity (aridity index), vegetation (fractional vegetation cover and below-ground biomass), and soil properties (bulk density, total nitrogen, and total phosphorus) on K and EF. The results showed in China's drylands that the K ranges from 0.02 to 0.07, with high values recorded in the northern Loess Plateau and the eastern Inner Mongolia Plateau. The EF ranges from 0.26 to 0.98, and shows longitudinal zonation with higher values in the east and lower values in the west. Aridity has a negative linear effect on K and an inverse U-shaped nonlinear effect on EF. Aridity can affect K and EF by suppressing vegetation growth and disrupting soil properties. However, K and EF had different responses to some vegetation and soil variables. K and EF had opposite relationships with soil bulk density, and EF was significantly affected by fractional vegetation cover, while K was not. Overall, the effects of aridity and soil properties on soil erodibility were more pronounced than those from vegetation, whose effect on soil erodibility was limited. This study provides relevant information to support reducing soil water and wind erosion by highlighting the hotspot areas of soil erodibility, relevant for implementing vegetation restoration and soil conservation measures in drylands.
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| 10. |
- Lixing, Zhou, et al.
(författare)
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Understanding dipole formation at dielectric/dielectric hetero-interface
- 2018
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 113:18
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Tidskriftsartikel (refereegranskat)abstract
- Band alignment and dipole formation at the hetero-interface still remain fascinating and, hence, are being intensively investigated. In this study, we experimentally investigate the dipole formation by employing a dielectric/dielectric (Al2O3/GeO2) interface. We investigate the dipole dependence on various post-deposition annealing (PDA) ambiences from the viewpoints of electrical extraction and the X-ray photoelectron spectroscopy measurement. The core level shift at the Al2O3/GeO2 interface is consistent with the dipole changes in various PDA ambiences. We discover that the dipole formation can be well explained by the interface gap state and charge neutrality level theory. These results further confirm the feasibility of gap state theory in explaining the band alignment at hetero-junctions. This study can be a booster to enhance the comprehension of dipole origin at hetero-junction interfaces.
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