Theoretical study on the nature of band-tail states in amorphous Si

Citation
Pa. Fedders et al., Theoretical study on the nature of band-tail states in amorphous Si, PHYS REV B, 58(23), 1998, pp. 15624-15631
Citations number
21
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
PHYSICAL REVIEW B-CONDENSED MATTER
ISSN journal
01631829 → ACNP
Volume
58
Issue
23
Year of publication
1998
Pages
15624 - 15631
Database
ISI
SICI code
0163-1829(199812)58:23<15624:TSOTNO>2.0.ZU;2-T
Abstract
Band-tail states are routinely invoked in models of n-Si:H, including defec t pool models and models of light-induced defects. These models describe th e band-tail states as being localized on a single stretched bond. However, to our knowledge, there is no theoretical or experimental work to justify t hese assumptions. In this work we use ab initio calculations to support ear lier tight-binding calculations that show that the band-tail states are ver y delocalized-involving large numbers of atoms as the energy is varied from midgap into the tails. Our work also shows that valence-band-tail states a re statistically associated with short bonds (not long bonds), and conducti on-band states with long bonds. We have slightly modified a 512-atom model of a-Si due to Djordjevic, Thorpe, and Wooten [Phys. Rev. B 52, 5688 (1995) ] to produce a large model of a-Si:H with realistic band tails, radial dist ribution function, and vibrational spectrum. Above all, we created and used a model with no spectral or geometrical defects. [S0163-1829(98)03148-8].