Nunzio O. Lipari

Unified theory of exciton and impurity states in semiconductors for an arbitrary magnetic field

Abstract We present a theory for exciton and impurity states in semiconductors, which is valid for all values of the magnetic field. The formalism is based on the introduction of tensor operators and includes the effect of the exchange interaction. Accurate solutions forthe ground state are presented and compared with the results of a previous adiabatic method, which is valid only for very large fields. We show that the present analysis is superior to all previously used methods for all values of the magnetic field.

The effective-mass nature of deep-level point-defect states in semiconductors

Abstract The basic premise of Effective-Mass Theory (EMT) is that bound-state wavefunctions are constructible from Bloch functions in a small region or regions of k space. In contrast, deep-level wavefunctions are believed to involve Bloch functions from the entire Brillouin zone and several bands. In this paper we analyse the wavefunction of the deep vacancy level in Si obtained recently by self-consistent Greens-function calculations. We find that this wavefunction has a strong EMT character in that it is composed primarily of Bloch functions from the nearest bands and the corresponding coefficients, i.e. the envelope functions, are peaked about the band extrema. As a further check, we have used a spherical average of the self-consistent vacancy potential in the acceptor EMT equations. The resulting energy level is at E v +0.9 eV, as compared with the Greens-function-theoretic value of E v +0.8 eV. The resulting wavefunction, on the other hand, does not have the correct form. A check of the correction terms left out by the standard EMT equations reveals that their contributions to the energy level are large and tend to cancel one another.

The electronic structure of deep SP-bonded acceptor impurities in semiconductors

Abstract This paper reports self-consistent calculations of the electronic structure of a series of deep impurities in Si. For the first time, these calculations provide a detailed description of gap states as well as the resonances and antiresonances within the band continua with the same accuracy as that of bulk-crystal calculations. The analysis of charge densities and wavefunctions in terms of simple models provides an understanding of the chemical bonding, the degree of localization, and the relevance of ideas based on effective-mass theory.

Hole conductivity through neighboring Si‐H bonds in hydrogenated silicon

The spatially‐resolved electronic states of a model representation of Si‐H bonds on vacancies in hydrogenated amorphous silicon (a‐Si:H) have been calculated using a Greens’s‐funciton technique. We find no gap states in the host Si bandgap. In the vicinity of the defect, states near the valence‐band edge and, to a lesser extent, near the conduction‐band edge are removed. We relate our results to a model of the Si‐H bond as a barrier to band edge carriers. Parameters are derived that pertain to localization due to randomly located hydrogenated defects.

Atomic number dependent non-local pseudopotentials

Abstract A new ab initio method is introduced for constructing accurate pseudopotentials. A new model is obtained with a simple and realistic analytical expression. This contains explicitly both important characteristics of the atomic observables, namely the regular dependence on the atomic number and the non-locality. The application to the Li-like ions of the first row is presented. The whole spectrum of energy eigenvalues is reproduced within 0.3% and HF wavefunctions within 0.5%.