arXiv subjects

K. A. Mader

Publications and source records attributed to K. A. Mader.

3 recordsLinked to original sources

arXiv1995

Localization and band-gap pinning in semiconductor superlattices with layer-thickness fluctuations

We consider (AlAs)_n/(GaAs)_n superlattices with random thickness fluctuations Delta-n around the nominal period n. Using three-dimensional pseudopotential plane-wave band theory, we show that (i) any amount Delta-n/n of thickness fluctuations leads to band-edge wavefunction localization, (ii) for small Delta-n/n the SL band gap is pinned at the gap level produced by a single layer with ``wrong'' thickness n + Delta-n, (iii) the bound states due to monolayer thickness fluctuations lead to significant band-gap reductions, (iv) <001> AlAs/GaAs SL's with monolayer thickness fluctuations have a direct band gap, while the ideal <001> SL's are indirect for n<4.

mtrl-th↗

arXiv1995

Electronic structure of intentionally disordered AlAs/GaAs superlattices

We use realistic pseudopotentials and a plane-wave basis to study the electronic structure of non-periodic, three-dimensional, 2000-atom (AlAs)_n/(GaAs)_m (001) superlattices, where the individual layer thicknesses n,m = {1,2,3} are randomly selected. We find that while the band gap of the equivalent (n = m = 2) ordered superlattice is indirect, random fluctuations in layer thicknesses lead to a direct gap in the planar Brillouin zone, strong wavefunction localization along the growth direction, short radiative lifetimes, and a significant band-gap reduction, in agreement with experiments on such intentionally grown disordered superlattices.

mtrl-th↗

arXiv1993

Electronic Structure and Bonding in Epitaxially Stabilized Cubic Iron Silicides

We present an ab initio full-potential linearized augmented plane-wave (FLAPW) study of the structural and electronic properties of the two bulk unstable compounds FeSi (CsCl structure) and FeSi$_2$ (CaF$_2$ structure) which have recently been grown by molecular beam epitaxy on Si(111). We obtain equilibrium bulk lattice constants of 2.72 Å and 5.32 Å for FeSi and FeSi$_2$, respectively. The density of states (DOS) of FeSi agrees well with experiment, and shows metallic behavior. In agreement with a previous calculation the DOS of FeSi$_2$ shows a large density of $d$-states at the Fermi level, explaining the instability of the bulk phase. The electron charge distributions reveal a small charge transfer from Si to Fe atomic spheres in both compounds. While in FeSi the Fe-Si bond is indeed partially ionic, we show that in FeSi$_2$ the electron distribution corresponds to a covalent charge accumulation in the Fe-Si bond region. The reversed order of $d$-bands in FeSi with respect to FeSi$_2$ is understood in terms of crystal field splitting and Fe-Fe nearest neighbor $dd$-interactions in the CsCl structure, and a strong Si $p$/Fe $d$ bonding in the fluorite structure, respectively.

cond-mat↗