Europhys. Lett, 47 (4), pp. 481-486 (1999)
Floating bonds and gap states in a-Si and a-Si:H from first principles calculations
M. Fornari 1, M. Peressi 1, S. de Gironcoli 2 and A. Baldereschi 1,3
1 Istituto Nazionale di Fisica della Materia (INFM) and
Dipartimento di Fisica Teorica
Università di Trieste - Strada Costiera 11, I-34014 Trieste, Italy
2 Istituto Nazionale di Fisica della Materia (INFM) and Scuola Internazionale
Superiore di Studi Avanzati (SISSA) - via Beirut 2-4, I-34014 Trieste, Italy
3 Institut de Physique Appliquée, Ecole Polytechnique Fédéral de Lausanne
PHB-Ecublens, CH-1015 Lausanne, Switzerland
(received 13 April 1999; accepted in final form 12 June 1999)
PACS. 71.23 - Electronic structure of disordered solids.
PACS. 71.23An - Theories and models; localized states.
PACS. 71.23Cq - Amorphous semiconductors, metallic glasses, glasses.
We study in detail by means of ab initio pseudopotential calculations the electronic structure of five-fold coordinated (T5) defects in a-Si and a-Si:H, also during their formation and their evolution upon hydrogenation. The atom-projected densities of states (DOS) and an accurate analysis of the valence charge distribution clearly indicate the fundamental contribution of T5 defects in originating gap states through their nearest neighbors. The interaction with hydrogen can reduce the DOS in the gap annihilating T5 defects.
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