We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

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Core/Shell semiconductor nanocrystals.

The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch–the metamaterial perfect absorber (MPA)–has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201200674

Metamaterial Electromagnetic Wave Absorbers

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Organic Optoelectronic Materials: Mechanisms and Applications

We report on the temperature dependence of the photoluminescence (PL) spectrum and of the PL relaxation dynamics for colloidal $\mathrm{Cd}\mathrm{Se}∕\mathrm{Zn}\mathrm{S}$ core/shell quantum dots (QDs) embedded in an inert polystyrene matrix. We demonstrate that the confinement energy in the QDs is independent of the temperature. The coupling with both acoustic and optical phonons is also studied. Quantum confinement results in a strong increase of the exciton\char21{}acoustic-phonon coupling constant, up to $71\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{eV}∕\mathrm{K}$, and in a reduced exciton\char21{}longitudinal-optical (LO)-phonon coupling constant, down to $21\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, with respect to bulk CdSe. In addition, we demonstrate that the main nonradiative process that limits the quantum efficiency of the QD at room temperature is the thermal escape from the dot assisted by scattering with four LO phonons. Thermally activated trapping in surface states is also observed at low temperature, with an activation energy of about $15\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$.

Temperature dependence of the photoluminescence properties of colloidal Cd Se ∕ Zn S core/shell quantum dots embedded in a polystyrene matrix

We report a novel, non-hydrolytic route to ZnO nanocrystals by means of thermal decomposition of zinc acetate (ZnAc2) in alkylamines, in the presence of tert-butylphosphonic acid (TBPA). The slow heating of an alkylamine/TBPA/ZnAc2 mixture is a simple, safe, and scalable approach to synthesize ZnO nanocrystals from handy chemicals. The obtained ZnO nanocrystals were characterized by UV-vis absorption, photoluminescence (PL) and infrared (FT-IR) spectroscopies, and by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The growth of ZnO particles in the nanoscopic regime and their final size were governed by the TBPA/ZnAc2 molar ratio in the reaction mixtures. The various roles played by TBPA in the conditions of the synthesis are discussed on the basis of the experimental evidence. The presented synthetic approach provides a unique tool for designing the synthesis of ZnO crystals of a desired size in the nanoscale regime and can be potentially extended to other nanoscale materials.

ZnO Nanocrystals by a Non-hydrolytic Route: Synthesis and Characterization

An analytical overview of experimental results about the heat transfer capabilities of nanofluids is presented, using widely scattered available information from diverse literature sources. It is shown that, despite the large number of publications available about this issue, only few studies provide quantitative estimates on a complete set of experimental conditions so far and many studies are not coherent. Bearing in mind this problem, in this study a selection of the most valuable papers has been done, taking into account different points of view and hypotheses. Even if this work cannot be considered exhaustive of the complete literature in the field of nanofluids, it can be taken into account as a quick reference guide to have an overview of the different heat transfer phenomena in nanofluids and how the most important parameters (size, shape, concentration, materials etc.) influence the expected thermal performance of nanofluids.

Review of heat transfer in nanofluids: Conductive, convective and radiative experimental results

We have investigated the effects of the built-in electric field in ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{N}$ quantum wells by photoluminescence spectroscopy. The fundamental electron heavy-hole transition redshifts well below the GaN bulk gap for well widths larger than 3 nm for the specific quantum wells investigated and exhibits a concomitant reduction of the intensity with increasing well thickness. The experimental data are quantitatively explained by means of a self-consistent tight-binding model that includes screening (either dielectric or by free-carriers), piezoelectric field and spontaneous polarization field. The impact of the built-in field on the exciton stability is discussed in detail. We demonstrate that the exciton binding energy is substantially reduced by the built-in field, well below the values expected from the quantum size effect in the flat band condition.

Spontaneous polarization and piezoelectric field in G a N / A l 0.15 Ga 0.85 N quantum wells: Impact on the optical spectra

We have studied the interactions in the solid phase between a blue-light-emitting organic conjugated polymer {poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(9,ethyl-3,6-carbazole)]} and colloidal CdSe∕ZnS core shell quantum dots. We demonstrate by time resolved photoluminescence measurements that efficient Forster energy transfer takes place from the polymer acting as the donor and the CdSe∕ZnS dots, acting as the acceptors. A Forster radius of about 80±15A is extracted from the analysis of the relaxation dynamics based on the solution of the donor-acceptor coupled rate equations. This value is in good agreement with the value extracted from the steady state spectra and indicates that efficient energy tranfer from a polymeric host to a nanocrystal guest can occur. Our results are relevant to the application of hybrid organic/inorganic systems to light-emitting devices.

Mauro Lomascolo

Papers

Temperature dependence of the photoluminescence properties of colloidal Cd Se ∕ Zn S core/shell quantum dots embedded in a polystyrene matrix

ZnO Nanocrystals by a Non-hydrolytic Route: Synthesis and Characterization

Review of heat transfer in nanofluids: Conductive, convective and radiative experimental results

Spontaneous polarization and piezoelectric field in G a N / A l 0.15 Ga 0.85 N quantum wells: Impact on the optical spectra

Förster energy transfer from blue-emitting polymers to colloidal CdSe∕ZnS core shell quantum dots