NCAT PHYSICS COLLOQUIUM SIRIES
2007/2008
Contact: Dr. Abebe Kebede
336-285 2113 or email abkebede@gmail.com






  Dr.Tesfaye Abtew







Tesfaye Abtew (PhD)

North Carolina State University
Center for High Performance Simulation
851 Main Campus Drive, PIII 137
Raleigh, NC 27695-7518
E-mail :  abtew@chips.ncsu.edu
Web: www.chips.ncsu.edu/~abtew
Phone  :  (919) 515 9123
April 28, 2008

Marteena Hall, Room 310  Time- 4:00 PM

Title: Abinitio simulation of light-induced effect and DC-conductivity in hydrogenated amorphous silicon

Abstract

We employ ab initio molecular dynamics to study light induced effect (the Staebler-Wronski effect) and DC-conductivity of a-Si and a-Si:H. In addition to studies of atomic dynamics in the electronic ground state, we also adopt a simple procedure to track the H dynamics in light-excited states. Consistent with recent experiments and computer simulations, we find that dihydride structures are formed for dynamics in the light-excited states, and we give explicit examples of pathways to these states. The Kubo-Greenwood formula is used to obtain the DC-conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with EMNR =0.06 eV and a temperature coe±cient of resistance close to experiment for a-Si: H. In general, experimental trends are reproduced by these calculations, and this suggests the possible utility of the approach for modeling carrier transport in othe disordered systems.

References

1. Abtew et al, J. Phys. Cond. Matt.(18) L1 (2006).
2. Abtew et al, Phys. Rev. B (74) 085201 (2006).
3. Abtew et al, Phys. Rev. B (76) 045212 (2007).
4. Abtew et al, J. Non-Cryst. Sol. (In Press).