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We have studied the influence of InP buffer-layer morphology in the formation of InAs nanostructures grown on InP͑001͒ substrates by solid-source molecular-beam epitaxy. Our results demonstrate that when InP buffer layers are grown by atomic-layer molecular-beam epitaxy, InAs quantum dot-like structures are formed, whereas InP buffer layers grown by MBE produce quantum-wire-like structures. The optical properties of these corrugated structures make them potential candidates for their use in light-emitting devices at 1.55 m. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00309-0͔InAs nanostructures grown on InP͑001͒ are promising candidates for light emitting devices in the wavelength range 1.3-1.55 m. 1-3 A widely investigated technological approach is to use self-organized nanostructures that appear spontaneously as an efficient way to relax elastic strain in lattice-mismatched heteroepitaxy. In order to obtain a welldefined emission wavelength, nanostructures should have a good uniformity in size and shape. Ordering in the growth plane and a precise control of the nanostructure morphology is a key issue for self-organized systems. Due to a 3.2% lattice mismatch of InAs on InP͑001͒, elastic strain relaxation takes place above a certain critical thickness via a change of morphology from two-dimensional ͑2D͒ to threedimensional ͑3D͒. Much of the research developed on selforganized growth of InAs on InP substrates is devoted to quantum-dot ͑QD͒ formation. 1-4 However, very recent results 5 have shown that the chemical composition of the buffer layer ͑InP, InGaAs, or InAlAs͒ is determinant in configuring the final shape of the InAs self-organized nanostructures.In this letter, we demonstrate that the growth conditions of the InP buffer layer also controls the surface rearrangement of the strained InAs layer grown on top. Therefore, it is possible to obtain either QD or quantum-wire ͑QWr͒ structures for identical InAs coverage and growth conditions.There are two sets of samples grown for this work. In the first one, InAs was deposited on a 200-nm-thick InP buffer layer grown either by molecular-beam epitaxy ͑MBE͒ or by atomic-layer molecular-beam epitaxy ͑ALMBE͒ ͑Ref. 6͒ using solid sources. MBE buffer layers were grown in the 2ϫ4 surface reconstruction at T s ϭ460°C and at a beamequivalent pressure ͑BEP͒ (P 2 )ϭ5ϫ10 Ϫ6 Torr. For the ALMBE InP buffer layers, a substrate temperature T s ϭ400°C is used. The P 2 pulsed flux reaching the surface sample is controlled by means of the reflectivity difference ͑RD͒ technique in order to optimize surface stoichiometry for growing InP planar surfaces. 6 The InAs layers, 2.5 ͑ML͒ thick, were deposited at a BEP (As 4 )ϭ1.5-2ϫ10 Ϫ6 Torr, a growth rate of 0.5 ML/s, and T s ϭ400°C, which is chosen to minimize the P/As exchange. After InAs growth, an annealing at 480°C under arsenic pressure during 10-20 s was performed. We observe, in agreement with other authors, 3,4 that InAs growth takes place in a 2D mode. The 2D-3D transition occurs during the annealing process at T s ϭ48...

A perovskite–quantum dot exciplex has been detected, opening a broad range of possibilities for advanced optoelectronic devices.

InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.

The efficiency of perovskite optoelectronic devices is increased by a novel method; its suitability for perovskite solar cells, light-emitting diodes, and optical amplifiers is demonstrated. The method is based on the introduction of organic additives during the anti-solvent step in the perovskite thin-film deposition process. Additives passivate grain boundaries reducing non-radiative recombination. The method can be easily extended to other additives.

Leuthold, J.; Hoessbacher, C.; Muehlbrandt, S.; Melikyan, A.; Kohl, M.; Koos, C.; Freude, W.; Dolores Calzadilla, V.M.; Smit, M.K.; Suarez, I.; Martin, A.; Martinez Pastor, J.; Fitrakis, E.P.; Tomkos, I. Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. J u e r g L e u t h o ld a n d c o ll e a g u e s J u e r g L e u t h o ld a n d c o ll e a g u e sSe e en d of ar tic le fo r fu ll au th or lis t.Illustations by Phil Saunders/spacechannel.org

Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150fs pulses with 5ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100mA. The obtained results open the way for ultrafast (>200GHz) operation in p-doped QD based SOAs at 1.3μm telecommunications wavelengths.