Maria Steślicka

A possible role of surface states in field-ion microscopy of semiconductors

Abstract Kronig-Penney model is employed to study the behaviour of surface states under the conditions typical for field ion microscopy. The dependence of the energy of surface states on the distance of an image gas atom from the crystal surface is found numerically and used to calculate the critical distance for field-ionization. The obtained results are in a good agreement with those calculated by Ernst and Block on the basis of the measurements for germanium.

Internal surface effects in superlattices in contact with substrate

Using the direct matching procedure and the interface response theory, the effects of the internal surface of a superlattice (i.e., the substrate/superlattice interface) are studied as a function of superlattice parameters while the substrate parameters are kept constant. Surface states are found inside mini-gaps and their localization properties are investigated. The crossings of these states with mini-bands are observed and examined by means of the variational density of states.

A new property of electronic states in a doubly δ-defected superlattice

Abstract Electronic properties of an infinite superlattice (SL) containing two δ-type defects within neighbouring barriers are discussed with emphasis on some unusual local density-of-states (LDOS) characteristics. Explanation of the origin and properties of the pronounced LDOS resonance peak, appearing within SL miniband, is based on a comparison with the energy spectrum and spatial distributions of eigenstates of a doubly δ-defected triple-quantum-well system.

Superlattice with two δ-type defects: electronic structure and density of states

Abstract The electronic-level structure and local density-of-states (LDOS) distributions are investigated for an infinite GaAs/Al x Ga 1− x As superlattice (SL) with two strongly spatially confined defect layers (the so-called δ -defects). The energy spectrum is determined by using a multi-matching procedure within the envelope-function approximation, while the LDOS is computed via combined factorization and direct methods in the framework of the Greens function formalism. In general, insertion of two δ -defects leads to the appearance of two localized states inside the minigaps, whose energy positions and space-charge distributions can be tuned by adjusting the defect parameters. A substantial change in the LDOS distribution is also observed. In particular, the region consisting of n periods between the defected SL layers exhibits—for large enough δ -defect strengths—an energy spectrum of n quasi-discrete resonances within the miniband range, whereas outside this region the LDOS takes the form characteristic of semi-infinite SLs terminated at the defect sites.

Shockley states in a semi-infinite Kronig-Penney model

Abstract A semi-infinite Kronig-Penney model with a symmetric surface potential is analyzed and it is shown that Shockley states can appear when a strong positive electric field is applied.

Surface electronic structure of zinc-blende-type GaN(111)

The electronic structure (layer resolved density of states) has been calculated for the gallium nitride (111) oriented slab, using the linear combination of atomic orbitals procedure. The existence of surface states on both Ga- and N-terminated surfaces has been shown. The origin and localization properties of these states have also been analysed.

Density of states of a terminated superlattice with periodically arrangedδ-defects

Surface electronic structure and the local density of states (LDOS) of a periodicallyδ-doped GaAs/AlxGa1−xAs superlattice (SL), terminated by an AlyGa1−yAs substrate, are investigated using the wave-function multi-matching procedure within an effectivemass approximation and a Green-function formalism based on factorization and direct techniques. The considered system is described in terms of a semi-infinite Kronig-Penneytype of model interleaved with a periodic array ofδ-function-like potentials, representing deep-center defect sheets. It is shown that the spectrum of surface-localized states and the corresponding space-charge distributions within particular SL minibands can be tailored by varying the terminating conditions (i.e., the substrate parameters) as well as the properties of inserted defects (i.e., the weight and position ofδ-potentials). In this respect, importance of a symmetric/nonsymmetric arrangement ofδ-dopants inside SL barriers and the related effect of miniband crossing/anticrossing are emphasized.

Electronic surface states in superlattice with complex basis

The electronic structure of a semi-infinite superlattice (SL) with a complex basis consisting of two identical wells coupled via two different barriers is investigated. The possibility of the surface state existence for a periodic termination of the SL potential (i.e., without perturbing the SL potential at the surface) is shown for such a two-barrier basis, in contrast to the conventional one of single well and barrier. This main conclusion is based on analytical considerations, however, some numerical results for the GaAs/AlAs SL are also presented.

Image and surface states in the field emission microscopy (text of a lecture)

Abstract Basic properties of surface (crystal-potential-induced) and image (image-potential-induced) states are presented. A behaviour of these states in an external field is considered and a possible experimental application is also discussed.

The influence of the crystal potential on the field- induced electronic states—II. Localized states

Abstract A positive electric field applied to a metal surface leads to the appearance of the high-energy empty electronic states which occur between the field-induced potential barrier and the metal surface. For the (111) surface of some fcc metals these states exist usually as resonances, with energies corresponding to the energy band of the metal band structure. This type of electronic resonance plays an important role in such experiemental technique as STM and FIM. In this paper, the influence of the crystal potential on the energy spectrum of the field-induced resonances has been studied for the (111) surfaces of Al, Au, Cu and Pt. Using the Green function approach the density-of-states distributions were calculated in the region of the field-induced potential barrier. It has been shown that the inclusion of the crystal potential causes significant changes in the energy spectra of the field- induced resonances at the metal surfaces.