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Revista mexicana de física

Print version ISSN 0035-001X

Rev. mex. fis. vol.48 n.6 México Dec. 2002




The atomic and electronic structure of amorphous silicon nitride


F. Álvarez and A. A. Valladares*


Instituto de Investigaciones en Materiales, UNAM, Apartado Postal 70-360, 04510, México D.F., * e-mail:


Recibido el 20 de marzo de 2002.
Aceptado el 2 de julio de 2002.



Using a novel approach to the ab initio generation of random networks we constructed two nearly stoichiometric samples of amorphous silicon nitride with the same content x=1.29. The two 64-atom periodically-continued cubic diamond-like cells contain 28 silicons and 36 nitrogens randomly substituted, and were amorphized with a 6 fs time step by heating them to just below their melting temperature with a Harris-functional based, molecular dynamics code in the LDA approximation. The averaged total radial distribution function (RDF) obtained is compared with some existing Tersoff-like potential simulations and with experiment; ours agree with experiment. All the partial radial features are calculated and the composition of the second peak also agrees with experiment. The electronic structure is calculated and the optical gaps obtained using both a HOMO-LUMO approach and the Tauc-like procedure developed recently that gives reasonable gaps.

Keywords: Amorphous semiconductors; radial distribution functions; amorphous silicon nitride.



Utilizando un enfoque innovador ab initio para la generación de redes estocásticas, hemos construido dos muestras casi estequiométricas de nitruro de silico amorfo con el mismo contenido x=1.29. Las dos celdas de 64 átomos, cúbicas tipo diamante, con condiciones periódicas, contienen 28 silicios y 36 nitrógenos substituidos al azar y fueron amortizadas con un time step de 6 fs calentándolas hasta una temperatura justo abajo de la de fusión, con un código de dinámica molecular, en la aproximación LDA, basado en la funcional de Harris. La función de distribución radial (RDF) total obtenida se compara con simulaciones clásicas que utilizan potenciales tipo Tersoff y con el experimento; las nuestras concuerdan con el experimento. Se calculan todas las características radiales parciales; la composición del segundo pico concuerda también con el experimento. La estructura electrónica también se calcula y las brechas (ópticas obtenidas, utilizando tanto un enfoque HOMO-LUMO, como el procedimiento tipo Tauc que desarrollaremos recientemente, dan brechas razonables.

Descriptores: Semiconductores amorfos; funciones de distribución radial; nitruro de silicio amorfo.


PACS: 71.23.Cq; 71.15.Pd; 71.55.Jv





A.A.V. thanks DGAPA-UNAM for financing Project IN101798 and IN100500. FA thanks CONACyT for supporting his PhD studies. This work was carried out on an Origin 2000 computer provided by DGSCA, UNAM.



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