V.M.S. Gomes

Electronic structure calculation of V2+O2 complexes in silicon

Abstract The self-consistent field multiple-scattering Xα molecular cluster model is applied to calculate the electronic states of a divacancy plus two oxygen complex in silicon. The calculations were carried out for the undistorted configuration of the defect. The obtained results, which are in fairly good agreement with EPR measurements, confirm the main features of the accepted microscopic model for the Si - P2 center.

Electronic structure of the Si:O4 complex as related to the thermal donors in silicon

Rigorous self‐consistent electronic structure calculations were carried out for complexes containing four interstitial oxygen atoms in silicon. The isolated tetrahedral site interstitial oxygen impurity was also investigated and the results were correlated to the complexes formation. Our calculations indicate that four oxygen impurities in Td symmetry surrounding a silicon atom at the regular lattice site are deep acceptor centers. It is also found that distortions which drive the complex to one of the observed symmetries, D2d, remove the impurity levels from the gap. Therefore, we conclude that these complexes do not show thermal donor actions in silicon as has been suggested.

Microscopic models of Hg+, Auo and Pt- isoelectronic interstitial impurities in silicon

Abstract Rigourous self-consistent field electronic structure calculations have been carried out, for the first time, for the tetrahedal-site interstitial Hg+, Auo and Pt- isoelectronic impurities in silicon. Compact and fully occupied e(d) and t2(d) levels below the valence band are introduced by mercury and gold impurities, which interact weakly with the host lattice. The presence of a hyperdeep s-like level close to the bottom of the valence band is a relevant feature of the analysed impurities. No shallow donor action was detected for the impurities which are stable in the non paramagnetic Hg2+, Au+ and Pto charge state configurations.

The effect of in-plane magnetic fields on the quantum states of carriers in quantum wells in GaAsAlGaAs heterostructures

Abstract We investigated theoretically the effect of in-plane magnetic fields up to 20 Tesla on the quantum states of electrons and holes confined in quantum wells (QWs) with a non-flat bottom in GaAsA l GaAs heterostructures. Two kinds of QWs were studied: a) QWs bent by the Coulomb interaction in the 2D electron gas in modulation-doped superlattices and b) QWs grown with a triangle-shaped bottom throught controlled grading of the A l concentration in the QW region of undoped heterostructures. In this last kind of QW two special cases were treated: the symmetric QW (SQW) in which the conduction band (CB) edge has a maximum in the middle of the well and the asymmetric QW (AQW) in which the CB edge is at one border of the well. The energy dispersion e(k) for the in-plane direction k perpendicular to the field is considerably affected by the field and for broader QWs the effect becomes dramatic. For the QWs of both kinds the system becomes indirect-gap type at high fields and for AQWs the symmetry e(k) = = e(−k) is broken.

Defect-molecule parameters for the divacancy in silicon

Abstract The hamiltonian eigenvalue problem is solved for a diva cancy in silicon within the framework of the defect-molecule model. A direct connection between the solution of this problem and a self-consistent multiple-scattering cluster calculation is established in order to determine the parameters of the model. The obtained results provide a quantitative confirmation of the currently accepted microscopic picture of the divacancy.

Electronic subbands at GaAsAlGaAs heterojunctions in parallel magnetic fields

We investigated theoretically the effect of in-plane magnetic fields up to 20 T on the quasi-two dimensional (2D) electron gas confined in inversion layers of p-type GaAs at GaAsAlGaAs heterojunctions. The calculations are based on a simultaneous self-consistent solution of the Poisson and Schrodinger equations in the effective mass approximation and including exchange correlation effects. The systems were considered with different values for the 2D electron density (NS) and for the depletion charge density Ndep = 5.0 × 1010 cm−2 in the GaAs channel. The energy dispersion ϵ(k) for the in-plane direction perpendicular to the field is much affected, presenting a diamagnetic shift and a displacement of the single extremum k = 0. The respective charge density is also disturbed. A strong nonparabolicity in ϵ(k) is obtained changing drastically the effective mass of the system at the Fermi level for high magnetic fields.