The diffusion properties of fluorine ions in GaN are investigated by means of Time-of-Flight secondary ion mass spectroscopy. Instead of incorporating fluorine ions close to the sample surface by plasma, fluorine ion implantation with an energy of 180 keV is utilized to implant fluorine ions deep into the GaN bulk, preventing the surface effects from affecting the data analysis. It is found that the diffusion of fluorine-ions in GaN is a dynamic process, featuring a two-step process. A defect-assisted diffusion model is proposed to account for the experimental observations. Fluorine ions tend to occupy Ga vacancies induced by fluorine ion implantation and diffuse to vacancy rich regions. The fluorine ions become stable after continuous vacancy chains are significantly reduced or removed by thermal annealing. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
A hybrid molecular dynamics (MD)/kinetic Monte Carlo (KMC) model is developed for atomistic modeling of fluorine ion implantation and diffusion in AlGaN/GaN heterostructures. The MD simulation reveals the F distribution profiles and the corresponding defect profiles, and most importantly, the potential energies of fluorine ions in the III-nitride material system. Using the results from the MD simulation, the diffusion process is simulated with KMC method, and the modeling results are validated by the secondary-ion-mass-spectrum (SIMS) measurement. The surface effect on the fluorine's stability and its improvement by passivation are also successfully modeled.
The PrAIRie2005 campaign took place in the summer of 2005 in the city of Edmonton, Alberta. The measurement campaign was designed and led by air-quality modellers with the scientific objective of determining the extent to which air pollution events in the city are the result of locally emissions versus long-range transport. A nested version of the AURAMS model was constructed for post-campaign simulations and evaluation against the measurement data. The nested model runs at different resolutions, the highest of which is a 3 km horizontal resolution centered on the urban area. The high resolution model results show good agreement with observations, with side-by-side sampling through the real and model atmosphere. The comparison shows the same features for particle composition (Aerodyne AMS measurements compared to speciated PM1), for airborne gases (continuous NO, NO2, O-3) and ground-based measurements of gases, particle composition and particle layering structure. The simulations reveal that air-quality in the Edmonton area is complex, largely due to multiple local sources, with occasional long-range-transport events.
Zhang E, Zhao D, Zhang Y, Liu H, Ma S, Wang R. A JND Guided Foveation Video Coding, in Advances in Multimedia Information Processing - PCM 2008, 9th Pacific Rim Conference on Multimedia, Tainan, Taiwan, December 9-13, 2008. Proceedings.; 2008:31–39. 访问链接
Yuan L, Wang M, Chen KJ. Molecular Dynamics Simulation Study on Fluorine Plasma Ion Implantation in AlGaN/GaN Heterostructures, in 2008 9TH INTERNATIONAL CONFERENCE ON SOLID-STATE AND INTEGRATED-CIRCUIT TECHNOLOGY, VOLS 1-4. IEEE Beijing Sect; Chinese Inst Elect; IEEE Electron Devices Soc; IEEE EDS Beijing Chapter; IEEE Solid State Circuits Soc; IEEE Circuits & Syst Soc; IEEE Hong Kong EDS, SSCS Chapter; IEEE SSCS Beijing Chapter; Japan Soc Appl Phys; Elect Div IEEE; URSI Com; 2008:1090-1093.Abstract
Fluorine plasma ion implantation is a robust technique that enables shallow implantation of fluorine ions into group III-nitride epitaxial structures. This technique has been used to achieve robust threshold control of the AlGaN/GaN high electron mobility transistors (HEMTs) and. led to the realization of self-aligned enhancement-mode devices. To reveal the atomic scale interactions and provide a modeling tool for process design and optimization, a molecular dynamics (MD) simulation is conducted for carbon tetrafluoride (CF(4)) plasma implantation. Specific potential functions are applied to calculate the interactions among atoms and simulate the dynamics process of fluorine ions' penetration and stopping in III-nitride materials. The MD simulation provides accurate information on dopant profiles that are verified by secondary ion mass spectrum (SIMS) measurements. Defect formation and distributions, that are critical in process development, are also investigated. The MD simulation tool is capable of providing 2-dimensional fluorine dopant profiles.