M. Hetterich

Molecular beam epitaxy of phase pure cubic InN

Cubic InN layers were grown by plasma assisted molecular beam epitaxy on 3C-SiC (001) substrates at growth temperatures from 419to490°C. X-ray diffraction investigations show that the layers have zinc blende structure with only a small fraction of wurtzite phase inclusions on the (111) facets of the cubic layer. The full width at half maximum of the c-InN (002) x-ray rocking curve is less than 50arcmin. The lattice constant is 5.01±0.01A. Low temperature photoluminescence measurements yield a c-InN band gap of 0.61eV. At room temperature the band gap is about 0.56eV and the free electron concentration is about n∼1.7×1019cm−3.

Electrical spin injection from ZnMnSe into InGaAs quantum wells and quantum dots

We report on efficient injection of electron spins into InGaAs-based nanostructures. The spin light-emitting diodes incorporate an InGaAs quantum well or quantum dots, respectively, as well as a semimagnetic ZnMnSe spin-aligner layer. We show a circular polarization degree of up to 35% for the electroluminescence from InGaAs quantum wells and up to 21% for InGaAs quantum dots. We can clearly attribute the polarization of the emitted photons to the spin alignment in the semimagnetic layer by comparison to results from reference devices (where the ZnMnSe is replaced by ZnSe) and from all-optical measurements.

Reversible order-disorder related band gap changes in Cu2ZnSn(S,Se)4 via post-annealing of solar cells measured by electroreflectance

We report on order–disorder related band gap changes in Cu2ZnSn(S,Se)4 solar cells which are induced by post-annealing. The band gap changes of the absorber are detected utilizing electroreflectance and analyzed by comparison with predictions of the stochastic Vineyard model. This yields a critical temperature of TC=195 °C above which the Cu2ZnSn(S,Se)4 absorber layer is entirely disordered within the Cu–Zn layers of the kesterite unit cell. The temporal evolution of the band gap during annealing shows that the equilibrium value is reached on a timescale in the order of hours, depending on the annealing temperature. In contrast to other experimental techniques, electroreflectance precisely measures the band gap and is not influenced by defect-mediated radiative recombination.

Systematic investigation into the influence of growth conditions on InAs/GaAs quantum dot properties

The influence of the conditions during growth of InAs/GaAs quantum-dot structures on GaAs(001) by molecular-beam epitaxy was investigated systematically with respect to achieving quantum-dot photoluminescence in the 1 eV range. The growth temperature, As flux, growth rate, InAs deposit, and growth interruption time before cap layer growth were varied. Photoluminescence spectroscopy and transmission electron microscopy were used to study the optical and structural properties. Large InAs quantum dots with photoluminescence in the 1 eV range were obtained at a low growth rate of 0.0056 ML/s. Analyzing in particular the low-growth-rate regime, we found that an InAs deposition of at least 2.4 ML and a growth temperature of 500−510 °C were crucial to obtain large quantum dots with a high size uniformity. Composition analyses by transmission electron microscopy revealed a significantly higher In concentration in the quantum dots grown at low growth rate compared to high-growth-rate samples.

Temperature dependence of the GaAsN conduction band structure

In this contribution the authors investigate the temperature-dependent conduction band structure of GaAs1−xNx for different nitrogen contents. An analysis of their experimental photoreflectance data based on the two-band version of the band anticrossing model shows that with decreasing temperature the energy of the effective nitrogen level EN in GaAsN epilayers shifts significantly to higher energies. Simultaneously, the coupling parameter CNM between the nitrogen states and the host conduction band also rises to higher values.

Optics of semiconductors and their nanostructures

Excitons in Semiconductors.- Hot Excitons in ZnSe Quantum Wells.- Probing Localized Excitons by Speckle Analysis of Resonant Light Scattering.- Donor-Related Exciton Luminescence in Wide-Bandgap Semiconductors: Diamond, Zinc Oxide, and Gallium Nitride.- Spectroscopy of Biexcitons and Trions in II-VI Quantum Dots.- Dynamics of Excitons and Exciton Complexes in Wide-Gap Semiconductors.- Quantum Kinetics and Femtosecond Spectroscopy - The Discovery of Slowness.- Extreme Nonlinear Optics in Semiconductors.- Nonlinear Semiconductor Microcavities.- All-Optical Control of Charge and Spin in GaAs: Densities and Currents.- Semiconductor Quantum Dots for Optoelectronic Applications.- GaInNAs: Fundamentals of a New Material System for Near-Infrared Optoelectronics.- Nitride-Based Light Emitting Diodes and Laser Diodes: Optical Properties and Applications.- Thermodynamics of Solar Cells.

Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation in In x Ga 1 − x As

We have investigated

Influence of indium on the electronic states in GaInNAs/GaAs quantum well structures

{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}

Dependencies of micro-pillar cavity quality factors calculated with finite element methods.

layers grown by molecular-beam epitaxy on

Conduction-band electron effective mass in Zn0.87Mn0.13Se measured by terahertz and far-infrared magnetooptic ellipsometry

\mathrm{GaAs}(001)