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19 results on '"Pietag, F."'

4. Gratings for synchrotron and FEL beamlines: a project for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin

Author

Siewert, F., primary, Löchel, B., additional, Buchheim, J., additional, Eggenstein, F., additional, Firsov, A., additional, Gwalt, G., additional, Kutz, O., additional, Lemke, St., additional, Nelles, B., additional, Rudolph, I., additional, Schäfers, F., additional, Seliger, T., additional, Senf, F., additional, Sokolov, A., additional, Waberski, Ch., additional, Wolf, J., additional, Zeschke, T., additional, Zizak, I., additional, Follath, R., additional, Arnold, T., additional, Frost, F., additional, Pietag, F., additional, and Erko, A., additional

Published
2018
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8. Minimum of oscillator strength of excitons in ultra-narrow GaAs/AlGaAs quantum wells: theory and experiment

Author

Andreani, L. C., Iotti, R. C., Schwabe, R., Pietag, F., Gottschalch, V., Bitz, A., and Staehli, J. L.

Subjects
SHALLOW, ENERGY-LEVELS, GaAs/Al0.35Ga0.65As, quantum wells, excitons, Condensed Matter::Other, GAAS, cathodoluminescence, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, oscillator strength, BEHAVIOR
Abstract

A theoretical and experimental study of the exciton in ultra-narrow quantum wells (QWs) is performed. A crossover from strong (separate localization of electron and hole levels) to weak confinement (with localization of excitonic center of mass) is predicted to occur for decreasing thickness, and is characterized by a minimum of the oscillator strength per unit area. Cathodoluminescence measurements performed on a series of GaAs/Al0.35Ga0.65As QWs with thicknesses from one to eight monolayers show a minimum of the oscillator strength, in agreement with theory, and indicate that the crossover from strong to weak confinement occurs at a thickness of about three monolayers for this composition. (C) 1998 Elsevier Science B.V. All rights reserved.

Published
1998

17. Optical properties of ultrathin GaAs layers embedded in AlxGa1-xAs

Author

Bitz, A., Di Ventra, M., Baldereschi, A., Staehli, J. L., Pietag, F., Gottschalch, V., Rhan, H., and Schwabe, R.

Subjects
QUANTUM-WELLS, EXCITONS, BINDING-ENERGIES
Abstract

We present a comparison between the predictions of two theoretical models and experimental results on ultrathin GaAs layers with a thickness in the range from 1 to 8 ML embedded in bulk (AlxGa1-x)As, 0.30 less than or equal to x less than or equal to 0.34. The theoretical predictions, obtained from an empirical tight-binding Green's-function approach and from the usual effective-mass approximation, are compared to photoluminescence and photoluminescence excitation data of a set of multiple quantum-well samples grown by metal-organic vapor-phase epitaxy on substrates with different misorientations. We find that the optical transitions are narrower in samples with slightly misoriented substrates, although their spectral position remains unchanged. This suggests that the substrate misorientation favors a good quality of the ternary alloy. The observed optical transitions of our thin layers compare well with the predictions of both models. However, the lack of a reliable exciton theory for such ultrathin layers becomes apparent.

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