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(a) <110> projection HRTEM image of a CdSe/ZnSe submonolayer (SML) superlattice structure. (b) Color-coded maps of the local lattice parameter in the vertical <001> direction and (c) the total atom displacements with respect to the underlying ZnSe layer plane for the same area
Anticorrelated arrangement of SML QDs was first clearly revealed
for CdSe QDs in a ZnSe matrix, as it is shown in Fig. 7 .
Significant extension of the strain fields of SML islands can be
seen in Fig. 7 b in the total lattice displacement map, which
evidences the 2D-like shifted flat pedestal regions on top of the
By comparison of the experimental image in Fig. 7 with the
modeling data in Fig. 8 and assuming significant averaging
due to the small lateral island size as compared to the HRTEM foil
(∼15 nm), one may conclude that the actual CdSe composition of
SML islands is at or higher than 40% and the adatom-induced
“wetting layer” composition is 15–20% or lower. .
Ledentsov, N. N.; Bimberg, D.; Hopfer, F.; Mutig, A.; Shchukin, V. A.; Savel’ev, A. V.; Fiol, G.; Stock, E.; Eisele, H.; Dähne, M.; Gerthsen, D.; Fischer, U.; Litvinov, D.; Rosenauer, A.; Mikhrin, S. S.; Kovsh, A. R.; Zakharov, N. D.; Werner, P.Journal: Nanoscale Research Letters
Issue 9DOI: 10.1007/s11671-007-9078-0Published: 2007-09-17Institution(s):
VI System GmbH, The Institut für Festkörperphysik, Technische Universität Berlin, Universität Karlsruhe, NL-Nanosemiconductor (Innolume) GmbH, Max-Planck-Institut für Mikrostrukturphysik
We report on progress in growth and applications of submonolayer (SML) quantum dots (QDs) in high-speed vertical-cavity surface-emitting lasers (VCSELs). SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 μm range vertical-cavity surface-emitting lasers (VCSELs) is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10−12 has been achieved in a temperature range 25–85 °C without current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission.
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