Polarization dependence of electroluminescence from closely-stacked and columnar quantum dots

Quantum dots (QDs) have a potential for application in semiconductor optical amplifiers (SOAs), due to their high saturation power related to the low differential gain, fast gain recovery and wide gain spectrum compared to quantum wells. Besides all advantages, QDs realized by Stranski-Krastanov growth mode have a flat shape which leads to a gain anisotropy and a related transverse magnetic (TM) and -electric (TE) polarization dependence as compared to bulk material. This has so far prevented their applications in SOAs. It has been suggested that control of optical polarization anisotropy of the QD can be obtained through QD shape engineering, in closely stacked or columnar QDs (CQDs). To this aim, we have fabricated and tested SOA structures based on closely-stacked and columnar QDs. Closely-stacked InAs QDs with 4, 6 and 10 nm GaAs spacer showed a minor improvement in the ratio of TM and TE integrated electroluminescence (EL) over standard QDs along with a strong reduction in efficiency. In contrast, a large improvement was obtained in CQDs, depending on the number of stacked submonolayers which can be attributed to the more symmetric shape of columnar QDs. A relatively small spectral separation (ΔE ~ 21 meV) between TE- and TM-EL peaks has been observed showing that heavy- and light hole-like states, respectively are energetically close in these QDs. These results indicate that columnar QDs have a significant potential for polarization-independent QD SOA.     

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Untersuchungen zur Wasseraufnahme und zum Löseverhalten von Cyanäthylcellulosen

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Optical model and DWBA analysis of the α-particle scattering for the nuclei26Mg and28,30Si including Hauser-Feshbach contributions

The elastic and inelastic α-scattering cross section has been measured for the nuclei²⁶Mg,^28,30Si at 15 bombarding energies between 15.0 and 16.4 MeV. The energy averaged scattering cross sections can be described by an incoherent sum of contributions from direct and compound reactions. The direct reaction part has been calculated by the optical model or DWBA, the compound reaction part by a simple Hauser-Feshbach formula. From the analyses deformation parameters and spin cut-off parameters are obtained.     

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Über die Beeinflussung der Löslichkeit von Elektrolyten durch Nichtelektrolyte

Zusammenfassung Die Wirkung von Zusätzen von Alkohol, Aceton, Isopropylalkohol, Harnstoff und Glykokoll auf die Löslichkeit von binären Elektrolyten, hauptsächlich bestehend aus Komplexionen von der Wertigkeit 1 bis 3, wurde untersucht. Die einfache elektrostatische Theorie reicht, auch bei mehrwertigen Ionen, zur quantitativen Beschreibung der Effekte nicht aus. Nichtelektrostatische Kräfte sind in vielen Fällen nicht vernachlässigbar und in manchen ausschlaggebend.Herrn Prof. Dr.E. Abel zum 80. Geburtstag gewidmet.