Magneto-optical probing of weak disorder in a two-dimensional hole gas

In two-beam magneto-photoluminescence spectra of a two-dimensional valence hole gas we identify the three-level energy spectrum of a free positive trion with a field-induced singlet-triplet transition. The recombination spectrum of acceptor-bound trions is also detected, including a cyclotron replica corresponding to the hole shake-up process. The emergence of a shake-up peak at low temperature is shown to be a sensitive probe of the presence of a small number of impurities inside the high-mobility quantum well, and its relative position is directly related to the hole cyclotron mass.Comment: 4 pages, 5 figure

Eight-band k⋅p calculations of the composition contrast effect on the linear polarization properties of columnar quantum dots

We present eight-band k . p calculations of the electronic and polarization properties of columnar InzGa1-zAs quantum dots (CQD) with high aspect ratio embedded in an InxGa1-xAs/GaAs quantum well. Our model accounts for the linear strain effects, linear piezoelectricity, and spin-orbit interaction. We calculate the relative intensities of transverse-magnetic (TM) and transverse-electric (TE) linear polarized light emitted from the edge of the semiconductor wafer as a function of the two main factors affecting the heavy hole-light hole valence band mixing and hence, the polarization dependent selection rules for the optical transitions, namely, (i) the composition contrast z/x between the dot material and the surrounding well and (ii) the dot aspect ratio. The numerical results show that the former is the main driving parameter for tuning the polarization properties. This is explained by analyzing the biaxial strain in the CQD, based on which it is possible to predict the TM to TE intensity ratio. The conclusions are supported by analytical considerations of the strain in the dots. Finally, we present the compositional and geometrical conditions to achieve polarization independent emission from InGaAs/GaAs CQDs. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3346552

Interface intermixing in type II InAs/GaInAsSb quantum wells designed for active regions of mid-infrared-emitting interband cascade lasers

The work has been supported by Project Widelase (no. 318798) of the Seventh Framework Programme of the European Commission.The effect of interface intermixing in W-design GaSb/AlSb/InAs/Ga0.665 In0.335 AsxSb1 − x/InAs/AlSb/GaSb quantum wells (QWs) has been investigated by means of optical spectroscopy supported by structural data and by band structure calculations. The fundamental optical transition has been detected at room temperature through photoluminescence and photoreflectance measurements and appeared to be blueshifted with increasing As content of the GaInAsSb layer, in contrast to the energy-gap-driven shifts calculated for an ideally rectangular QW profile. The arsenic incorporation into the hole-confining layer affects the material and optical structure also altering the InAs/GaInAsSb interfaces and their degree of intermixing. Based on the analysis of cross-sectional transmission electron microscopy images and energy-dispersive X-ray spectroscopy, we could deduce the composition distribution across the QW layers and hence simulate more realistic confinement potential profiles. For such smoothed interfaces that indicate As-enhanced intermixing, the energy level calculations have been able to reproduce the experimentally obtained trend.Publisher PDFPeer reviewe

Electrical tuning of the oscillator strength in type II InAs/GaInSb quantum wells for active region of passively mode-locked interband cascade lasers

This project has received funding from the European Commission's Horizon 2020 Research and Innovation Programme iCspec under grant agreement No. 636930 and has also been supported by the National Science Centre of Poland within Grant No. 2014/15/B/ST7/04663.Two designs of active region for an interband cascade laser, based on double or triple GaInSb/InAs type II quantum wells (QWs), were compared with respect to passive mode-locked operation in the mid-infrared range around 4 µm. The layer structure and electron and hole wavefunctions under external electric field were engineered to allow controlling the optical transition oscillator strength and the resulting lifetimes. As a result, the investigated structures can mimic absorber-like and gain-like sections of a mode-locked device when properly polarized with opposite bias. A significantly larger oscillator strength tuning range for triple QWs was experimentally verified by Fourier-transform photoreflectance.Publisher PDFPeer reviewe

Probing the carrier transfer processes in a self-assembled system with In0.3Ga0.7As/GaAs quantum dots by photoluminescence excitation spectroscopy

We acknowledge financial support from the Polish Ministry of Science and Higher Education within the “Diamond Grant” project No. DI2012 008642 and by the State of Bavaria.In this report we present experimental studies on the energy transfer between the wetting layer and single large elongated In0.3Ga0.7As/GaAs quantum dots. We obtain insight into the electronic and optical properties of In0.3Ga0.7As/GaAs quantum dots by probing their confined electronic states via photoluminescence excitation spectroscopy on the single dot level. We demonstrate that the energy separation between the states of a quantum dot and the wetting layer states affects the carrier transfer efficiency - reduced transfer efficiency is observed for smaller dots with higher indium content. We also discuss the effects of the excited states and the trapping of carriers on confinement potential fluctuations of the wetting layer. Eventually, the transfer of charge carriers from localized wetting layer states to a single quantum dot is evidenced in temperature-dependent photoluminescence excitation spectroscopy.PostprintPeer reviewe

Visualization of melanoma tumor with lectin-conjugated rare-earth doped fluoride nanocrystals

Aim To develop specific fluorescent markers for melanoma tumor visualization, which would provide high selectivity and reversible binding pattern, by the use of carbohydrate- recognizing proteins, lectins, combined with the physical ability for imaging deep in the living tissues by utilizing red and near infrared fluorescent properties of specific rare-earth doped nanocrystals (NC). Methods B10F16 melanoma cells were inoculated to C57BL/6 mice for inducing experimental melanoma tumor. Tumors were removed and analyzed by lectin-histochemistry using LABA, PFA, PNA, HPA, SNA, GNA, and NPL lectins and stained with hematoxylin and eosin. NPL lectin was conjugated to fluorescent NaGdF4:Eu3+-COOH nanoparticles (5 nm) via zero length cross-linking reaction, and the conjugates were purified from unbound substances and then used for further visualization of histological samples. Fluorescent microscopy was used to visualize NPL-NaGdF4:Eu3+ with the fluorescent emission at 600-720 nm range. Results NPL lectin selectively recognized regions of undifferentiated melanoblasts surrounding neoangiogenic foci inside melanoma tumor, PNA lectin recognized differentiated melanoblasts, and LCA and WGA were bound to tumor stroma regions. NPL-NaGdF4:Eu3+ conjugated NC were efficiently detecting newly formed regions of melanoma tumor, confirmed by fluorescent microscopy in visible and near infrared mode. These conjugates possessed high photostability and were compatible with convenient xylenebased mounting systems and preserved intensive fluorescent signal at samples storage for at least 6 months. Conclusion NPL lectin-NaGdF4:Eu3+ conjugated NC permitted distinct identification of contours of the melanoma tissue on histological sections using red excitation at 590- 610 nm and near infrared emission of 700-720 nm. These data are of potential practical significance for development of glycans-conjugated nanoparticles to be used for in vivo visualization of melanoma tumor

Ghost Branch Photoluminescence From a Polariton Fluid Under Nonresonant Excitation

An expanding polariton condensate is investigated under pulsed nonresonant excitation with a small laser pump spot. Far above the condensation threshold we observe a pronounced increase in the dispersion curvature with a subsequent linearization of the spectrum and strong luminescence from a ghost branch orthogonally polarized with respect to the linearly polarized condensate emission. The presence of the ghost branch has been confirmed in time-resolved measurements. The dissipative and nonequilibrium effects in the photoluminescence of polariton condensates and their excitations are discussed.Comment: 13 pages, 4 figure