Biomedical subjects

F Bechstedt

Publications and source records attributed to F Bechstedt.

At least 19 recordsLinked to original sources

PubMed2001

Bulk excitonic effects in surface optical spectra.

We calculate the surface optical properties of the passivated Si(110) surface using a real-space multigrid technique and ab initio pseudopotentials. Rather than from the usual eigenvalue representation, the macroscopic polarizability is obtained from the solution of an initial-value problem, which allows inclusion of excitonic and local-field effects in addition to the electronic self-energy in the surface calculations. It is shown that the electron-hole attraction is largely responsible for the peculiar line shape of the surface reflectance anisotropy.

Journal Article↗

PubMed2001

Origin of the different reconstructions of diamond, Si, and Ge(111) surfaces.

Ab initio calculations of the 2x1, c(2x8), and 7x7 reconstructions of the diamond, Si, and Ge(111) surfaces are reported. The pi-bonded chain, adatom, and dimer-adatom-stacking fault models are studied to understand the driving forces for a certain reconstruction. The resulting energetics, geometries, and band structures are compared for the elemental semiconductors with different atomic sizes, and chemical trends are derived. We show why the lowest-energy reconstructions are different for the group-IV materials considered.

Journal Article↗

PubMed2001

Quantum-kinetic theory of hot luminescence from pulse-excited semiconductors.

A theory of time-resolved luminescence from photoexcited semiconductors is presented. It combines quantum kinetics of hot-carrier relaxation and quantum theory of spontaneous emission. Model calculations show the "transfer" of photoluminescence from the initial signal at the pump frequency via subsequent phonon replicas until the buildup of luminescence at the excitonic resonance. Time-resolved photoluminescence is predicted to be a sensitive measure of electron-LO-phonon quantum kinetics and bottleneck effects.

Journal Article↗

PubMed2001

Field-induced delocalization and Zener breakdown in semiconductor superlattices.

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown.

Journal Article↗

PubMed1996