J.R. Leite

Multiple scattering-Xα cluster model of GaAs: electronic states of isolated vacancies and substitutional impurities

The multiple scattering-X alpha cluster model was applied to the study of the electronic structure of vacancies and copper and selenium substitutional impurities in GaAs. In order to eliminate the dangling bond effects, a suitable boundary condition at the cluster surface was assumed. Calculations lead to the conclusion that As neutral vacancies are donors, whereas Ga vacancies are acceptors. Cu atoms as substitutional impurities replacing Ga in the GaAs lattice form acceptor levels, quite similar to those generated by Ga neutral vacancies. This explains the experimental difficulties concerning the identification of these centres in GaAs. Se atoms replacing As in the lattice form a donor level near the bottom of the conduction band. The promising agreement with experimental observations leads to the conclusion that the proposed cluster model is an accurate technique for studying the electronic structure of locally perturbed covalent semiconductors.

Hole charge localization and band structures of p-doped GaN/InGaN and GaAs/InGaAs semiconductor heterostructures

Hole band structures of p-doped semiconductor heterostructures are presented. The full six-band Luttinger-Kohn Hamiltonian generalized to treat different materials is solved in conjunction with the Poisson equation in a plane-wave representation. Self-consistent solutions of the multiband effective-mass-Poisson equations are obtained for unstrained and biaxially strained zinc-blende GaN/InxGa1-xN and GaAs/InxGa1-xAs quantum wells and superlattices (SLs), in which the acceptor doping concentration and its profile, the SL period, and the alloy content x are varied. The particular features observed in the valence subband structure of GaN/InGaN systems are stressed in a comparison with other selected In-derived III-V heterostructures, such as GaAs/InGaAs SLs.

A molecular cluster model of the electronic structure of IV and III-V covalent semiconductors: Application to GaAs

A molecular cluster model of the tetrahedrally coordinated semiconductors is discussed within the framework of the self-consistent-field multiple-scattering method. A method to avoid the dangling bond effects is discussed and the model is particularly investigated with respect to gallium arsenide. It is shown that the model leads to a fairly consistent description of the bulk electronic structure.

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 gold substitutional impurity in silicon

The electronic structure of Au+, Au0 and Au-substitutional impurities in silicon are calculated within the framework of the self-consistent-field multiple-scattering molecular cluster model. The results show that centres behave basically as a perturbed silicon vacancy with a filled gold-derived atomic d level localised below the bottom of the crystal valence band.

Parameters of the Kane model from effective masses : Ambiguities and instabilities

The problem of calculating the parameters of the Kane model from experimental effective masses is reinvestigated. Conditions for the applicability of the Kane and Luttinger-Kohn models are derived in terms of experimental effective masses. It is found that different definitions of the Luttinger parameters are used within the Kane model. Some of the parameters of the Kane model are very sensitive to small changes of effective masses. The reason for this unexpected instability is analyzed, and its effects on bulk band structures and energy levels from effective mass theory are discussed.

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.

Electronic structure of ferrocyanide ion calculated by the SCF Xα-scattered wave generalized partitioning method

Abstract A generalized partitioning (GP) version of the Xα scattered-wave (SW) method is used to carry out self-consistent calculations of the electronic states for the ferrocyanide ion. The GP scheme is based on a generalization of the standard muffin-tin partitioning of the molecular space in which the neighboring atomic regions are maintained into local clusters. The calculated energy spectrum leads to interpretation for the X-ray photoelectron emission and optical transitions for the ion in fairly good agreement with the experimental results. It is concluded that the self-consistent GP scheme offers very good possibilities to improve the physical realism of the SW theory for a wide range of open structures.

Molecular cluster model of covalent semiconductors

A multiple-scattering-cluster model of IV and III-V covalent semiconductors is proposed. The feasibility of the model is tested by carrying out calculations on GaAs. The valence band width, the energy band gap and the location of the cationic and anionic d levels obtained are in fairly good agreement with the experimental results for the bulk crystal.

Valence-band structure of undoped and p-doped cubic GaN/InGaN multiple quantum wells

Abstract Valence band structure calculations of cubic GaN/In x Ga 1− x N quantum wells and superlattices are presented, in which coupling between the heavy-, light-, and spin–orbit-split-hole bands, strain effects due to lattice mismatch, and the difference in the parameters due to the materials forming the heterostructures are considered. The calculations are performed within a self-consistent approach to the k · p theory by means of a full six-band Luttinger–Kohn (LK) Hamiltonian. The effects of different materials are taken into account explicitly through the inclusion of different sets of Luttinger parameters and by considering the corresponding additional LK matrix elements, not present in the one-material based heterostructures. Our results show that strain effects and the inclusion of the split-off band play a fundamental role in a realistic description of the valence band structure in these systems. Due to the large difference in hole effective masses, for p-doped systems we find that only heavy-hole bands are occupied in the well.