Klaus Maschke

Band structure of semiconductor alloys beyond the virtual crystal approximation. effect of compositional disorder on the energy gaps in GaPxAs1−x

Abstract A general method to study the band structure of compositionally disordered semiconductors is proposed. The effects of chemical disorder are added to the virtual-crystal band structure using the pseudopotential method and second order perturbation theory. In GaPxAs1−x, chemical disorder is shown to give a significant contribution to the experimentally observed non-linear behaviour of the lowest energy gaps as function of composition.

Electron charge density of alkali halides beyond the rigid-ion approximation

Abstract The dependence of the electron charge distribution in alkali halides on the lattice constant is examined. It is found that in the case of NaCl the non-rigid behavior of the electron charge density calculated from first principles can be well understood if one starts from the free-ion functions and takes into account the mutual overlap between them. The relevance of our results for the structural properties of alkali halides is pointed out in connection with recent ab-initio calculations.

Thermalization of photoexcited carriers in a-Si:H

Abstract The transient photoluminescence properties of a-Si:H are explained within the framework of an extended multiple trapping model. The model gives a satisfactory description of our experimental results for the time decay of the photoluminescence after a pulsed photoexcitation, as well as of the dependence on the temperature and on the intensity of an external bias. The same model can be used for the description of the transient phototransport properties of a-Si:H.

An extended multiple-trapping model for the photoluminescence in a-Si:H

Abstract We present an extended multiple-trapping model for the description of the photoluminescence in amorphous systems. Time- and energy-resolved photoluminescence spectra are interpreted in terms of this model. We show that the experimentally observed features indicate a strong energy dependence of the localization length near the mobility edges.

AB-Initio calculation of chemical bonding in the low temperature phases of silver halides

Abstract The nature of the chemical bonding in AgCl, AgBr and AgI is investigated through abinitio self-consistent pseudopotential calculations. The electron charge density is calculated for both the rocksalt structure and the zincblende structure. Our results show that the ionic picture is not appropriate for the description of these materials. In particular, both the directional character of the chemical bonding and the delocalization of the charge density become more significant on passing from AgCl to AgI.

Magnetoelectric effect in a hydrogen molecule

The symmetry breaking due to a magnetic field applied on a hydrogen molecule H2 generates an electric polarization. This magnetoelectric effect occurs for electrons in a triplet state provided the magnetic induction field is not aligned with the symmetry axis of the molecule.

Relevance of non-linear screening in covalent semiconductors

Abstract The electronic response of a Si crystal to both long- and short-range external periodic perturbatations is calculated by the SCF pseudopotential method. The decomposition of the total response into linear and higher order contributions shows that non-linear terms are quite important and that their relevance increases with the localization of the perturbation.

Quantum Coherence Effects in One-Dimensional Chains with Inelastic Scattering

To describe the ballistic transport in a 1 D chain Landauer [1] has calculated the resistance R of a series of elastic scatterers from their transmission coefficient T

Influence of stacking disorder on the electronic properties of layered semiconductors

R = \frac{h}{{{e^2}}}\frac{{1 - T}}{T}