R. Rettig

Experimental investigation of structures of interior interfaces in GaAs

A method for the structural investigation of interior inverted GaAs/AlAs interfaces is presented which combines highly selective etching and subsequent atomic force microscopy. It provides three-dimensional mappings of interior GaAs interfaces on a lateral scale on the order of micrometers with angstrom z resolution. The perfection of this method is demonstrated, which allows the observation of the real interface monolayer island and terrace structure. Potential aluminum residues on the uncovered interfaces are below the detection limit of Auger electron spectroscopy, which is estimated to 16% of aluminum in a single monolayer on a GaAs crystal. The structure of an interior interface can differ significantly from that of a corresponding surface layer after cooling down from the growth temperature. The substantial restructuring of the interface morphology caused by growth interruptions is investigated in detail for metalorganic vapor phase epitaxy.

Relaxation Dynamics of Electron–Hole Pairs Studied by Spatiotemporal Pump and Probe Experiments

The temporal evolution of the ambipolar diffusivity of optically excited electron–hole pairs is investigated for a strained quantum well structure by temporally and spatially resolved pump and probe experiments. Dependent on the excitation conditions the diffusivity transients reflect the cooling and heating processes of excitons as well as the formation dynamics of excitons out of free electron–hole pairs within less than 10 ps. Diffusivity transients obtained by Monte Carlo simulations of a simplified excitonic Boltzmann equation display all features of the experimental curves and support our interpretation of the lateral propagation dynamics in terms of formation, cooling and heating of excitons.

GaAs-based VCSEL-structures with strain-compensated (GaIn)As/Ga(PAs)-MQWH active regions grown by using TBAs and TBP

Abstract GaAs-based vertical cavity surface emitting laser structures (VCSEL) with strain-compensated (GaIn)As/Ga(PAs) multiple quantum well heterostructures (MQWH) active regions have been deposited using the less hazardous, liquid group-V-sources tertiarybutyl arsine (TBAs) and tertiary butyl phosphine (TBP) in metal organic vapour phase epitaxy (MOVPE). We report on growth optimization, characterization of the VCSEL structures, and ultrafast emission dynamics after femtosecond optical excitation. The improved decomposition characteristics of the alternative compounds yield a small variation in the cavity thickness of only ±0.35% across the 2″ wafer. The high quality of the VCSEL structures having a 2 λ cavity with 4 stacks of 3 (GaIn)As/Ga(PAs)-MQWH and AlAs/GaAs-Bragg mirrors is revealed by the large normal mode splitting of 10.6xa0meV. Excellent pulse response with a pulse width of 3.2xa0ps and a peak delay of 4.8xa0ps at 30xa0K is obtained after femtosecond optical excitation. The high crystalline perfection with respect to layer homogeneity, optical properties as well as ultrafast emission dynamics demonstrate the advantages of the strain-compensated material system for VCSEL structures grown by MOVPE using TBAs and TBP.

Excitonic Quantum Beating in Space- and Time- Resolved Pump and Probe Experiments

In spatially and temporally resolved pump and probe experiments we observe a spatial beating which reflects the coherent dynamics of an excitonic wave packet.

X-ray diffraction study of intentionally disordered (GaIn)As/Ga(PAs) heterostructures

The influence of layer thickness fluctuations and deviation from perfect periodicity on high resolution x-ray diffraction (HR XRD) profiles are investigated experimentally and theoretically for (GaIn)As/Ga(PAs) symmetrically strained multiple quantum well heterostructures. Structural properties are deduced from the experimental HR XRD profiles by comparison with full dynamical XRD simulations. Samples with periodic thickness modulations are systematically studied with respect to periodicity, amplitude of modulation and layer mismatch. The high sensitivity of XRD in the strained (GaIn)As/Ga(PAs) material system allows a quantitative description of the nature (type), amplitude, and period of modulation. The results are experimentally compared to the lattice matched AlAs/GaAs material system. The influence of the modulation function of periodic modulations is studied. We investigate two types of graded structures with layer thickness grading either for one ternary layer (one side grading) or for both ternary...

Confinement Dependence of Biexcitonic Binding Energies in Semiconductor Quantum Wells

We study the dependence of the biexciton binding energy on confinement in semiconductor quantum wells. A set of symmetrically strained (GaIn)As/Ga(PAs) quantum wells with different well depths and equal well widths is investigated by quantum beat spectroscopy based on transient degenerate four-wave mixing. The ratio of biexcitonic to excitonic binding energy increases with stronger confinement. This new experimental result is discussed in the framework of recent theoretical predictions and experimental results.

Growth and structural properties of (GaIn)AsGa(PAs) intentionally disordered superlattice structures grown by metalorganic vapor phase epitaxy

Abstract We present an X-ray diffraction (XRD) study of symmetrically strained superlattice structures with intentionally fluctuating individual layer thicknesses. Samples with periodic, aperiodic (random) and graded fluctuations have been realized by metalorganic vapor phase epitaxy (MOVPE). The precise structural properties of the disordered multilayer structures have been determined by high resolution XRD in combination with both kinematical as well as dynamical XRD theory. Periodic modulation of the compressive-strained (GaIn)As layers leads to peak splitting on the “tensile-strained” part of the XRD spectrum, while periodic variation of the tensile-strained Ga(PAs) layers results in splitting on the “compressive-strained” part. Aperiodic variation causes a broadening of the respective peaks. The study demonstrates the power of XRD to quantify fluctuations of layer thicknesses in the growth direction down to the monolayer level.

Normal-Mode Linewidths in a Semiconductor Microcavity with Various Cavity Qualities

We measure the normal-mode linewidths in a semiconductor microcavity with various exciton–photon interaction strengths. Variation of the normal mode coupling and thus of the exciton–photon interaction is obtained reducing the cavity quality by stepwise removing of top mirror pairs. Excellent agreement of the measured linewidths with results of a linear dispersion theory is obtained.