Semicondutores magnéticos diluídos ricos em silício

• Ano de defesa: 2008
• Autor(a) principal: Costa, Marcio Jorge Teles da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Programa de Pós-graduação em Física; Física
• Palavras-chave em Português: Semicondutores; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://app.uff.br/riuff/handle/1/19180

We investigated, through ab initio calculations based on density functional theory (DFT) , the possibility of obtaining silicon rich diluted magnetic semiconductors (DMS). A silicon rich DMS would be very interesting technologically. However, when Si is doped with Mn, for instance, the Mn impurities sit preferentially in interstitial sites and consequently they can diffuse easier forming clusters and destroying the ferromagnetism coupling. On the other hand, when Ge is doped with Mn, this impurity prefers to sit in substitutional sites. We performed calculations for tree structures: two nanostrips, with widths of 6.10 Å (nanostrip 12) and 11.75 Å (nanostrip 21) and a infinite plane. The nanostrips are a monolayer of Ge confined by Si in two directions. The infinity plane is a monolayer o Ge confined by Si in one direction. Our calculations showed that it is possible to stabilized a Mn impurity, replacing a Ge atom, in substitutional sites in all three structures. This stability depends on the width of the nanostrip, as the width grows substitutional Mn becomes more stable. We also investigated what kind of magnetic coupling is more stable when we put two Mn impurities, as a second neighbors, in substitutional sites on the Ge monolayer. For all tree the ferromagnetic state is more stable. As the stability, the coupling also depends on the width of the nanostrip. In this case as the width of the nanostrip increase less stable the ferromagnetic coupling becomes. The width of the nanostrip also alters the electronic properties of the materials. For the nanostrip (21) and the infinite plane there are no electronic states crossing the Fermi level. However, for nanostrip (12), there are some majority spin electronic states crossing the Fermi level. The Mn impurity also polarizes the s and p states of the Si and Ge first neighbor host atoms, more distant host atoms are unaltered. The introduced magnetic moment is 3 per atom of Mn and it is concentred around the Mn impurity. Our results indicate that it is possible to obtain a Si-rich DMS.