EXPERIMENTAL STUDIES OF BALLISTIC TRANSPORT IN SEMICONDUCTORS

Les effets rencontrés dans les T.E.C. à grille courte sur AsGa et In0,53Ga0,47As/InP montrent une certaine augmentation de la vitesse moyenne mais les longueurs électriques effectives sont supérieures à celles des grilles. Pour les dipoles courts N+ N N+ avec des longueurs électriques de grille de 0,36 µm, étudiés à la température ambiante, les valeurs de la densité de courant permettent de déduire une vitesse moyenne d'environ 4x107 cm/s pour des polarisations de 0,35 à 0,50 V. A l'aide de résultats expérimentaux sur le seuil de l'effet Gunn à la température ambiante, on montrera que la distance moyenne entre l'émission de phonons optiques polaires est à peine supérieure à 1000 Å pour des valeurs de l'énergie des électrons de l'ordre de 0,1 eV et à 1500 Å pour des valeurs de l'énergie supérieures à 0,3 eV ; de plus l'angle le plus probable après diffusion est faible. Des barrières planaires dopées (PDB) sont présentées comme émetteurs et collecteurs d'électrons balistiques pour des vitesses de l'ordre de 108 cm/s. En utilisant deux structures PDB mises dos à dos une injection balistique et des conditions de dérive peuvent être établies sur les bords opposés d'une base de type N pour des transistors VHF. En réduisant les dimensions du "peigne" aux limites de la photolithographie (0,75 µm), une fréquence maximum supérieure à 200 GHz est attendue pour de tels transistors. L'utilisation de peignes métalliques enterrés inférieurs au micron, une fréquence maximum supérieure à 1000 GHz est attendue.The effects encountered with short-gate FET's in GaAs and In.53Ga.47 As/InP show some enhancement of average velocity, but effective electrical lengths are much longer than the gates. When N+ N N+ short, two-terminal devices, with. 36 µm electrical length, are tested at room temperature, the current density values allow one to infer an average velocity of about 4x107 cm/s for .35-.50 V bias. Using Gunn effect threshold experimental data at room temperature, it will be shown that the average distance between launching polar optical phonons is just over 1000 Å at electron energy values of ~.1 eV, and over 1500 Å at electron energy values of more than .3 eV and the most probable angle after scattering is small. Planar doped barrier (PDB) will be presented as ballistic electron launchers and collectors, for velocity near 1x108 cm/s. Using closely-spaced PDB's back to back, a ballistic injection and drift condition can be set up on opposite sides of an N base region, for very high frequency transistors. By scaling the finger size to the limits of photolithography (.75 µm), over 200 GHz fmax is expected in such transistors in the near future. Using buried metal submicron base fingers, up to 1000 GHz fmax is eventually expected

GROWTH OF PLANAR DOPED BARRIER STRUCTURES IN GALLIUM ARSENIDE BY MOLECULAR BEAM EPITAXY

In the present paper we report results of our experimental study of unipolar gallium arsenide structures with planar doped barriers /1/ grown by molecular beam epitaxy. Rectifying diodes based on planar doped barrier structures have been fabricated by molecular beam epitaxy using modulation doping in GaAs (planar doped n-i-p+-i-n). The barrier height in these structures can be effectively varied from zero to approximately the bandgap, O < qΦBO < Eg through the appropriate choice of the following related parameters : [MATH] the above equation shows that the zero bias barrier height is related to the ionized acceptor charge density (QA) and the distances separating the acceptor plane from the donor planes, (l1, l2)

Multidisciplinary AEC Education Utilising BIM/PLIM Tools and Processes

© IFIP International Federation for Information Processing 2013. The construction industry worldwide is moving towards more collaborative working practices, aided by building information modelling (BIM) tools and processes. BIM could be more accurately described as Project Lifecycle Information Management (PLIM). Many firms are claiming to be ‘doing BIM’, but are just scraping the surface in terms of the benefits that can be leveraged from true integrated, collaborative design and construction. New graduates, trained in collaboration and PLIM techniques will be the best people to drive positive change, but current educational models do not tend to provide these skills. This paper describes current worldwide educational trends in collaborative multidisciplinary education, and a proposed framework to assist academics in implementing changes to AEC curricula