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SUMMARY:Electronic transport and the origin of Urbach tails in amorphous s
 ilicon - David Drabold (University of Ohio)
DTSTART:20090126T160000Z
DTEND:20090126T170000Z
UID:TALK15560@talks.cam.ac.uk
CONTACT:Ian Farnan
DESCRIPTION:Electronic transport and the origin of Urbach tails in amorpho
 us silicon\nD. A. Drabold\, Ohio University\nRecently\, we have studied th
 e structure of the electron states in large and realistic models\nof a-Si.
  We have explored the nature of the electronic localized-delocalized (Ande
 rson)\ntransition by direct calculation\, and have found that important as
 pects of this transition\nare universal1 (similar in different materials\,
  and even different physical quantities\, such\nas classical vibrations). 
 The valence (conduction) band tail states are shown to derive\nfrom short 
 (long) bonds. What is more\, we find that one-dimensional filamentary\nstr
 uctures (connected short bonds and connected long bonds) exist in good qua
 lity\nrelaxed network models\, and these filaments are responsible for the
  observed exponential\n(Urbach) edges observed in the material2. We also b
 riefly report on transport calculations\nusing the Kubo formula and a simp
 le thermal averaging procedure\, and show that the\ntemperature dependence
  of the electrical conductivity and the Meyer-Neldel relation can\nbe obta
 ined from ab initio simulations on suitable structural models of the mater
 ial3.\n\n\n1 J. J. Ludlam\, S. N. Taraskin\, S. R. Elliott and D. A. Drabo
 ld\, Universal features of\neigenstates in disordered systems \, J. Phys. 
 Cond. Matter 17 L321 (2005).\n\n2 Y. Pan\, F. Inam\, M. Zhang and D. A. Dr
 abold\, Atomistic origin of Urbach tails in\namorphous silicon\, Phys. Rev
 . Lett. 100 206403 (2008).\n\n3 T. A. Abtew\, M. Zhang and D. A. Drabold\,
  Ab initio estimate of the temperature\ndependence of electrical conductiv
 ity in a model disordered material: a-Si:H Phys. Rev.\nB 76 045212 (2007).
LOCATION:Harker 2 lecture room\, Department of Earth Sciences\, Downing Si
 te
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