A. Dinger

Wurtzite ZnxCd1 − xS layers grown by combining MBE and hot-wall beam epitaxy

Abstract Zn x Cd 1 − x S alloy layers revealing the wurtzite modification have been successfully grown by molecular beam epitaxy for the first time. The hexagonal crystal structure is achieved by using a wurtzite CdS buffer layer deposited by hot-wall beam epitaxy on a GaAs(111)B substrate. Characterization of the alloy films includes in situ RHEED investigations, X-ray diffraction and optical measurements. TEM diffraction patterns and reflection spectra are used to confirm the Zn x Cd 1 − x S alloys to be of the wurtzite type. Photoluminescence is dominated by localized exciton emission. For layers with high Zn content ( x > 0.4), film quality decreases due to the increased mismatch to the CdS buffer and the fact, that the stable bulk phase for Zn-rich alloys is cubic.

Localization of excitons in ultrathin CdS/ZnS quantum structures

Abstract Monolayer fluctuations in ultrathin, coherently strained CdS/ZnS quantum-well structures result in a very strong localization of excitons. The deepest localized excitons can be considered as individual, decoupled and three-dimensionally confined. Consequently, the optical properties can be well explained by transitions from an ensemble of spatially distributed, quasi-zero-dimensional excitonic states. The efficient photoluminescence (PL) and the optical gain in the deep-blue spectral range exhibit unusually broad and unstructured spectra. In μ-PL measurements of a mesa-etched SQW sample (10 μm × 10 μm mesas down to 100 nm × 100 nm mesas) single, ultranarrow luminescence lines can be resolved when the number of luminescing states is reduced.

Four-wave-mixing spectroscopy of localized excitons in CdS1−xSex

We investigated the dephasing properties of excitons in CdS 1-x Se x in the compositional range 0.07 ? x ? 0.80 by means of transient four-wave-mixing experiments. For 0.35 ? x ? 0.80, the dephasing times of localized excitons are in the order of a few 100 ps up to 1 ns. Thereby, we observe a strong dependence of the dephasing times on the composition x, the localization depth and the spectral excitation width. For very short delay times (a few ps), a beat phenomenon is presented which is interpreted by multiple reflections of propagating exciton-polariton wave packets. In the compositional range 0.07 ? x ? 0.35 the four-wave-mixing signal is strongly suppressed and the slowly dephasing signal is hardly observable or as in the most cases not measureable at all.