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.
A novel notion of turbulent structure-the local cascade structure-is introduced to study the convection phenomenon in a turbulent channel flow. A space-time cross-correlation method is used to calculate the convection velocity. It is found that there are two characteristic convection speeds near the wall, one associated with small-scale streaks of a lower speed and another with streamwise vortices and hairpin vortices of a higher speed. The new concept of turbulent structure is powerful to illustrate the dominant role of coherent structures in the near-wall convection, and to reveal also the nature of the convection-the propagation of patterns of velocity fluctuations-which is scale-dependent.
The low-lying structures of the self-conjugate ( N = Z ) nuclei 8241Nb41 and 8643Tc43 have been investigated using isomeric-decay spectroscopy following the projectile fragmentation of a 107Ag beam. These represent the heaviest odd®Codd N = Z nuclei in which internal decays have been identified to date. The resulting level schemes shed light on the shape evolution along the N = Z line between the doubly-magic systems 5628Ni and 10050Sn and support a preference for T = 1 states in T z = 0 odd®Codd nuclei at low excitation energies associated with a T = 1 neutron®Cproton pairing gap. Comparison with Projected Shell Model calculations suggests that the decay in 82Nb may be interpreted as an isospin-changing K isomer.