Michael Haugk

• Paderborn University

A density-functional theory based nonorthogonal tight-binding scheme is used to investigate the nonpolar surfaces of GaN in the wurtzite and zinc-blende phases. In III-V semiconductors the nonpolar surfaces mainly reconstruct by a bond-length conserving rotation of the surface atoms. In contrast to that for all nonpolar GaN surfaces this bond-lengt...

The present contribution is based on the assumption that the probabilistic character of quantum mechanics does not originate from uncertainties caused by the process of measurement or observation, but rather reflects the presence of objectively existing vacuum fluctuations whose action on massive particles is calibrated by Planck's constant and eff...

The purpose of this article is to show that the introduction of hidden variables to describe individual events is fully consistent with the statistical predictions of quantum theory. We illustrate the validity of this assertion by discussing two fundamental experiments on correlated photons which are believed to behave ``violently non-classical''....

SummaryA parallel implementation of the selfconsistent-charge density-functional based tight-binding (SCC-DFTB) method is used to examine large scale structures in III-V semiconductors. We firstly describe the parallel implementation of the method and its efficiency. We then turn to applications of the parallel code to complex GaAs systems. The geo...

We present a modified version of Nelson's seminal paper on the derivation of the time-dependent Schrödinger equation which draws on the equation of motion of a particle that moves under the influence of a classical force field and additional stochastic forces. The emphasis of our elaboration is focused on the implication of allowing stochastic forc...

We present a modified version of Nelson's seminal paper on the derivation of the time‐dependent Schrödinger equation which draws on the equation of motion of a particle that moves under the influence of a classical force field and additional stochastic forces. The emphasis of our elaboration is focused on the implication of allowing stochastic forc...

Using a density-functional-based tight-binding method we investigate the stability of various vacancy clusters up to a size of 17 vacancies. Additionally, we compute the positron lifetimes for the most stable structures to compare them to experimental data. A simple bond-counting model is extended to take into account the formation of new bonds. Th...

To investigate the lattice distortion caused by point defects in As-rich GaAs, we make use of a self-consistent-charge density-functional based tight-binding method. Both relevant defects, the As antisite and the As interstitial, cause significant lattice distortion. In contrast to As interstitials, isolated As antisites lead to lattice strain as w...

While reliable experimental positron lifetimes exist for mono- and divacancies in silicon, up to now no agreement has been reached on the sizes of vacancy clusters detected in irradiated and partly annealed silicon. Hence, using a density-functional based Tight-Binding method, we investigate the stability of different vacancy clusters (up to 17 vac...

Experimental investigations of plastically deformed elemental and III-V semiconductors prove that a high number of vacancies and vacancy clusters are formed. The formation of point defects by the motion of jogged dislocations is analysed. Vacancies formed behind the jog are not stable as a simple chain of vacancies. Instead, they are transformed im...

A parallel implementation of the selfconsistent-charge density-functional based tight-binding (SCC-DFTB) method is used to examine large scale structures in III-V semiconductors. We firstly describe the parallel implementation of the method and its efficiency. We then turn to applications of the parallel code to complex GaAs systems. The geometries...

There is a need to understand the degradation mechanism which results in the loss of substitutional CAs shallow acceptors in AlAs and GaAs containing high concentrations (≳1020 cm−1) of carbon. The activation energy for the migration of interstitial carbon atoms, Ci, in AlAs and GaAs is calculated using a local-density functional-based method, AIMP...

Self-consistent-charge density-functional tight-binding (SCC-DFTB) calculations have been performed to survey the potential-energy surface for a single interstitial carbon atom introduced into GaAs. The results provided a possible model for the diffusion of carbon through GaAs with an activation energy of less than 1 eV. The carbon atom moves via s...

To investigate the stability of various atomic arrangements of vacancy aggregates in GaAs, we make use of a self-consistent-charge density-functional-based tight-binding method. In contrast to silicon, where the corresponding number is 6, we find the first such stable aggregate to be made up of 12 vacancies. This is explained by the added possibili...

Using a self-consistent-charge density-functional based tight-binding approach the structural properties and relative stabilities of Si-terminated reconstructions of the (100) surface in β-SiC are discussed. All low-energy surfaces are found to be semiconducting. Over a wide range of growth conditions a model with 2×3 periodicity has a low formatio...

Local density-functional methods are used to examine the behaviour of O and O-related defect complexes at {1010}-type surfaces in GaN. We find that O has a tendency to segregate to the (1010) surface and we identify the gallium vacancy surrounded by three oxygen impurities (VGa-(ON)3) to be a particularly stable and electrically inert complex. We s...

We present a parallel version of a selfconsistent-charge density-functional based tight-binding (SCC-DFTB) method for total energy calculations and geometry optimizations of clusters and periodic structures. On single processor machines the SCC-DFTB method has been successfully applied to systems up to several hundred atoms with an accuracy compara...

A density-functional-based non-orthogonal tight-binding (DF-TB) scheme is used to investigate models for the reconstructions of GaAs(110), (100) and (111) surfaces. The relative stabilities of the competing reconstructions are then determined as a function of the chemical potential, thus simulating a wide range of possible MBE growth conditions. We...

We present a theoretical study of the relative formation energies for possible models of the reconstruction found under Ga-rich growth conditions at the surface. The energetically most favourable model has fourfold-coordinated Ga atoms on the surface, exhibiting metallic bonding character. This structure differs as regards the electron-counting rul...

A review is given of the results of first principles calculations used to investigate the structures and electronic properties of screw and edge dislocations in GaN. The atoms at the core of the full core screw dislocation possess heavily strained bonds leading to deep gap states. Removing the first shell of Ga and N atoms gives a screw dislocation...

Available from http://www3.interscience.wiley.com/cgi- bin/abstract/40001180/START

We present density–functional theory studies for a variety of surfaces and extended defects in GaN. According to previous theoretical studies ¹ {10 0} type surfaces are electrically inactive. They play an important role in GaN since similar configurations occur at open–core screw dislocations and nanopipes as well as at the core of threading edge d...

Local-density-functional methods are used to examine the atomic geometries, energetics, and electrical properties of different models for domain boundaries on {112¯0} planes in wurtzite GaN. In agreement with recent experiments, we find that the energetically most favorable model is characterized by a displacement of 1/2〈101¯1〉 and has no inversion...

Local density–functional methods are used to examine the behavior of O and O-related defect complexes on the walls of nanopipes in GaN. We find that O has a tendency to segregate to the (100) surface and identify the gallium vacancy surrounded by three oxygen impurities [VGa–(ON)3] to be a particularly stable and electrically inert complex. We sugg...

Local-density-functional methods are used to examine the behavior of the oxygen defect, gallium vacancy, and related defect complexes trapped at threading-edge dislocations in GaN. These defects are found to be particularly stable at the core of the dislocation where oxygen sits twofold coordinated in a bridge position. VGa-ON is found to be a deep...

We present a theoretical study of atomic structures and formation energies for a variety of possible oxygen induced reconstructions at the GaN (0001) and (0001̄) surfaces. We find that at the nominally Ga terminated (0001) surface a coverage of ΘO=0.375ML on top of the ideal surface is stable. Only in a very oxygen rich environment a full monolayer...

We outline details about an extension of the tight-binding (TB) approach to improve total energies, forces, and transferability. The method is based on a second-order expansion of the Kohn-Sham total energy in density-functional theory (DFT) with respect to charge density fluctuations. The zeroth order approach is equivalent to a common standard no...

We present a theoretical study of atomic structures, electrical properties and formation energies for a variety of possible reconstructions with 1 × 1 and 2 × 2 periodicity of the GaN (0 0 0 1) and (0 0 0 1) surfaces. We find that during MBE growth in the (0 0 0 1) direction 2 × 2 structures become stable under N rich growth conditions while Ga ric...

We present density-functional theory studies for a variety of surfaces and extended defects in GaN. According to previous theoretical studies {1010} type surfaces are electrically inactive. They play an important role in GaN since similar configurations occur at open-core screw dislocations and nanopipes as well as at the core of threading edge dis...

We describe the ab initio construction of two-center tight-binding (TB) hamiltonians, which at a properly chosen input density upon non-selfconsistent solution of the related Kohn-Sham equations transform the energy within density-functional theory (DFT) into a tight-bindinglike expression. In cases, where the electron density of the interacting ma...

We determine here the Hamiltonian and overlap matrix elements necessary in a non-orthogonal two-centre tight-binding (TB) scheme for gallium, aluminium, arsenic, gallium arsenide and aluminium arsenide using a local density-functional method. The repulsive energy required by such methods is described by radial short-range repulsive pair contributio...

Paderborn, Universiẗat, Diss., 1999. Computerdatei im Fernzugriff.

Paderborn, Gesamthochsch., Diss., 1999.