We report the formation of self-assembling CdSe quantum dots during molecular beam epitaxial growth on ZnSe and ZnMnSe. Atomic force microscopy measurements on specimens with uncapped dots show relatively narrow dot size distributions, with typical dot diameters of 40±5 nm, and with a diameter-to-height ratio consistently very close to 4:1. Uncapped CdSe dots are unstable with time: their density was observed to drop by an order of magnitude in 10 days, with clear evidence of ripening observed for some dots. Photoluminescence from capped dots indicates exciton localization much stronger than in ZnCdSe/ZnSe quantum wells, due to the additional lateral confinement.

A minimally invasive laser-induced injury model is described to study thrombus development in mice in vivo. The protocol involves focusing the beam of an argon-ion laser through a compound microscope on the vasculature of a mouse ear that is sufficiently thin such that blood flow can be visualized by intravital microscopy. Two distinct injury models have been established. The first involves direct laser illumination with a short, high-intensity pulse. In this case, thrombus formation is inhibited by the GPIIb/IIIa antagonist, G4120. However, the anticoagulants, hirulog, PPACK, and NapC2 have minimal effect. This indicates that thrombus development induced by this model mainly involves platelet interactions. The second model involves low-intensity laser illumination of mice injected with Rose Bengal dye to induce photochemical injury in the region of laser illumination. Thrombi generated by this latter procedure have a slower development and are inhibited by both anticoagulant and anti-platelet compounds.

The energy levels of nanometer size InGaAs quantum dots epitaxially grown on GaAs by the coherent islanding effect are probed using selectively excited photoluminescence (PL), and PL excitation. A lateral-confinement-induced interlevel spacing of ∼30 meV between the first two states can be deduced from the spectra.

The localization of excitons on quantum-dot-like compositional fluctuations has been observed in temperature-dependent near-field magnetophotoluminescence spectra of InGaAsN. Localization is driven by the giant bowing parameter of these alloys and manifests itself by the appearance of ultranarrow lines (half-width <1 meV) at temperatures below 70 K. We show how near-field optical scanning microscopy can be used for the estimation of the size, density, and nitrogen excess of individual compositional fluctuations (clusters), thus revealing random versus phase-separation effects in the distribution of nitrogen.

We report on the optical characterization of the strained InGaAs/GaAs quantum dots (QDs). The temperature dependence of the photoluminescence (PL) indicates that the onset energy of the thermal quenching in ∼20-nm-diam QDs is enhanced by a factor of ∼2 as compared to a quantum well (QW), due to the additional confinement. At low temperature, an increased carrier lifetime is observed for the QDs as compared to a reference QW (880 vs 330 ps). The carrier lifetime in the QDs was found to be independent of the temperature for T&lt;30 K. In addition to this different dynamics of the localized excitons, we find that in the steady state PL and PL excitation, there is virtually no overlap between the emission and the absorption energies.

The InAs/Ga1−xInxSb strained-layer superlattice (SLS) holds promise as an alternative III–V semiconductor system for long wavelength infrared detectors. In this article, we present the first investigation, to the best of our knowledge, of heterojunction photodiodes using this new material. The devices were grown by molecular beam epitaxy on GaSb substrates, and are comprised of a 38 Å InAs/16 Å Ga0.64In0.36Sb SLS used in double heterojunctions with GaSb contact layers. The structures were designed to optimize the quantum efficiency while minimizing transport barriers at the heterointerfaces. The photodiodes are assessed through the correlation of their performance with the SLS material quality and the detector design. X-ray diffraction, absorption, and Hall measurements are used to determine the SLS material properties. The electrical and optical properties of the photodiodes are determined using current–voltage and spectral responsivity measurements. At 78 K, these devices exhibit rectifying electrical behavior and photoresponse out to a wavelength of 10.6 μm corresponding to the SLS energy gap. The responsivity and resistance in these thin-layered (0.75 μm), unpassivated photodiodes result in a detectivity of 1×1010 cm √Hz/W at 8.8 μm and 78 K. Based upon the performance of these devices, we conclude that high-sensitivity operation of long-wavelength photovoltaic detectors at temperatures well in excess of conventional III–V band gap-engineered systems, and potentially in excess of HgCdTe, is feasible using this material system.

Raman spectra of coherently strained layers of GaAs 1Ϫx N x grown on ͑001͒ GaAs with xϭ0 -0.05 by metalorganic molecular-beam epitaxy are reported. The optical phonons of the GaAs and GaN types, as well as disorder-activated acoustical phonons, are observed. A strongly confined GaAs optical mode at ϳ255 cm Ϫ1 , indicating the ordering of As and N atoms, is also detected. The GaAs-and GaN-type optical phonons exhibit strong diagonal components, forbidden for the zinc-blende structure. A bond polarizability analysis of the Raman selection rules shows that these components are activated by the trigonal distortion of the alloy lattice. The trigonal distortion arises from the formation of ordered ͕111͖-(GaN) m (GaAs) n clusters with nϭmϭ1.

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