F. Grosse

Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II

The optical exciton Aharonov-Bohm effect—i.e., an oscillatory component in the energy of optically active bright states—is investigated in nanorings. It is shown that a small effective electron mass, strong confinement of the electron, and high barrier for the hole, achieved, e.g., by an InAs nanoring embedded in an AlGaSb quantum well, are favorable for observing the optical exciton Aharonov-Bohm effect. The second derivative of the exciton energy with respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations even for the lowest bright state unambiguously. A connection between the theories for infinitesimal narrow and finite width rings is established. Furthermore, the magnetization is compared to the persistent current, which oscillates periodically with the magnetic field and confirms thus the nontrivial connected topology of the wave function in the nanoring.

Time-Resolved In Situ Spectroscopy During Formation of the GaP/Si(100) Heterointerface.

Though III-V/Si(100) heterointerfaces are essential for future epitaxial high-performance devices, their atomic structure is an open historical question. Benchmarking of transient optical in situ spectroscopy during chemical vapor deposition to chemical analysis by X-ray photoelectron spectroscopy enables us to distinguish between formation of surfaces and of the heterointerface. A terrace-related optical anisotropy signal evolves during pulsed GaP nucleation on single-domain Si(100) surfaces. This dielectric anisotropy agrees well with the one calculated for buried GaP/Si(100) interfaces from differently thick GaP epilayers. X-ray photoelectron spectroscopy reveals a chemically shifted contribution of the P and Si emission lines, which quantitatively corresponds to one monolayer and establishes simultaneously with the nucleation-related optical in situ signal. We attribute that contribution to the existence of Si-P bonds at the buried heterointerface. During further pulsing and annealing in phosphorus ambient, dielectric anisotropies known from atomically well-ordered GaP(100) surfaces superimpose the nucleation-related optical in situ spectra.

Monte Carlo growth simulation for AlxGa1−xAs heteroepitaxy

Abstract A kinetic Monte Carlo model describing the growth of Al x Ga 1− x As heterostructures is presented. It is successfully applied to vicinal surfaces, quantum wells and V-grooved substrates by taking into account the real cation lattice and the differences between Al and Ga atoms. The effective parameters are determined by comparing with RHEED intensity oscillations on vicinal surfaces. The differences between the normal and inverted interface of AlGaAs/GaAs quantum wells are explained by the lower diffusivity of Al compared with Ga adatoms. Simulating heteroepitaxy on V-grooved substrates, the formation of self-organized crescent-shaped quantum wires and a vertical quantum well are found, in agreement with experiment. This can be traced to the dependence of cation mobility on species and surface orientation.

Electron-phonon interaction in embedded semiconductor nanostructures

The modification of acoustic phonons in semiconductor nanostructures embedded in a host crystal is investigated including corrections due to strain within continuum elasticity theory. Effective elastic constants are calculated employing {\em ab initio} density functional theory. For a spherical InAs quantum dot embedded in GaAs barrier material, the electron-phonon coupling is calculated. Its strength is shown to be suppressed compared to the assumption of bulk phonons.

Impurity-induced step interactions: a kinetic Monte Carlo study

A one-dimensional (1D) continuum description of growth on vicinal surfaces in the presence of immobile impurities predicts that the impurities can induce attractive step interactions when they suppress the diffusion of adatoms on the surface, thus destabilizing the equidistant step train. In the present communication, we verify this prediction by kinetic Monte Carlo simulations of a 2D solid-on-solid model. We identify the conditions where quasi-1D step flow is stable against island formation or step meandering, and analyse in detail the statistics of the impurity concentration profile. The sign and strength of the impurity-induced step interactions is determined by monitoring the motion of pairs of steps. Assemblies containing up to 20 steps turn out to be unstable towards the emission of single steps. This behaviour is traced back to the small value of the effective, impurity-induced attachment asymmetry for adatoms. An analytic estimate for the critical number of steps needed to stabilize a large step bunch is derived and confirmed by simulations of a 1D model.

Electron‐Acoustic Phonon Interaction in Semiconductor Nanostructures

Acoustic phonon modes are investigated in semiconductor nanostructures within continuum elasticity theory. At the example of spherically symmetric quantum dots the influence of the structural confinement and intrinsic strain onto the electron‐acoustic phonon interaction compared to bulk phonon modes is discussed. The calculation of effective elastic constants, closely related to the acoustic phonons, is based on first principles calculations and compared to recent analytic theories.

An experimental-theoretical atomic-scale study - in situ analysis of III–V on Si(100) growth for hybrid solar cells

We consider GaP/Si(100) as quasi-substrate for III-V-on-silicon growth targeting solar energy exploration in dual junction devices for both photovoltaics as well as photoelectrochemical tandem diodes with optimum bandgaps. We prepare Si(100) surfaces with majority domains of either type, grow thin GaP layers free of anti-phase disorder, find that abrupt Si-P interfaces are favored over abrupt Si-Ga interfaces and, finally, observe an RAS signal attributed to N incorporation in GaPN/Si(100). Combining in situ reflection anisotropy spectroscopy during metalorganic vapor phase epitaxy with UHV-based surface techniques and ab initio DFT calculations, we aim to understand the interface formation at the atomic scale.

Exciton Aharonov‐Bohm Effect in Embedded Nanostructures

Exciton properties in an embedded semiconductor nanoring under perpendicular magnetic field are investigated. Due to the unique nonsimply connected topology of the exciton wave function, oscillations of the transition energies with magnetic field (exciton Aharonov‐Bohm effect) and a persistent current appear. The amplitudes of these effects depend on the effective strength of the Coulomb interaction.