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

Silicon has long been established as the material of choice for the microelectronics industry. This is not yet true in photonics, where the limited degrees of freedom in material design combined with the indirect bandgap are a major constraint. Recent developments, especially those enabled by nanoscale engineering of the electronic and photonic properties, are starting to change the picture, and some silicon nanostructures now approach or even exceed the performance of equivalent direct-bandgap materials. Focusing on two application areas, namely communications and photovoltaics, we review recent progress in silicon nanocrystals, nanowires and photonic crystals as key examples of functional nanostructures. We assess the state of the art in each field and highlight the challenges that need to be overcome to make silicon a truly high-performing photonic material.

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Silicon nanostructures for photonics and photovoltaics

The structural and electronic properties of Cu2ZnSnS4 and Cu2ZnSnSe4 are studied using first-principles calculations. We find that the low energy crystal structure obeys the octet rule and is the kesterite (KS) structure. However, the stannite or partially disordered KS structures can also exist in synthesized samples due to the small energy cost. We find that the dependence of the band structure on the (Cu,Zn) cation ordering is weak and predict that the band gap of Cu2ZnSnSe4 should be on the order of 1.0 eV and not 1.5 eV as was reported in previous absorption measurements.

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Crystal and electronic band structure of Cu2ZnSnX4 (X=S and Se) photovoltaic absorbers: First-principles insights

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field

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Semiconductor Spintronics

Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level, and post synthetically via chemical oxidation and reduction, photochemical control, and electrochemical control In this review, we will discuss the fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs Here, we will illustrate how free carrier dielectric properties are induced in various semiconductor materials including metal oxides, metal chalcogenides, metal nitrides, silicon, and other materials We will highlight the applicability and limitations of the Drude model as applied to semiconductors considering the complex band structures 

Localized Surface Plasmon Resonance in Semiconductor Nanocrystals

Light-emitting silicon nanocrystals embedded in ${\mathrm{SiO}}_{2}$ have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding ${\mathrm{SiO}}_{2}$ is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric ${\mathrm{SiO}}_{2}.$ This region plays an active role in the light-emission process.

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Role of the interface region on the optoelectronic properties of silicon nanocrystals embedded in SiO 2

We report on an ab initio study of the structural and electronic properties of B- and P-doped Si nanoclusters. The neutral impurities formation energies are calculated. We show that they are higher in smaller nanoclusters and that this is not related to the structural relaxation around the impurity. Their dependence on the impurity position within the nanocluster is also discussed. Finally, we have calculated the B and P activation energies showing the existence of a nearly linear scaling with the nanocluster inverse radius. Interestingly, no significant variation of the activation energy on the impurity species is found and the cluster relaxation gives a minor contribution to it.

First-principles study of n- and p-doped silicon nanoclusters

Electronic and structural properties of small hydrogenated silicon nanoclusters as a function of dimension are calculated from ab initio technique. The effects induced by the creation of an electron-hole pair are discussed in detail, showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure after an electronic excitation of the cluster is analyzed together with the role of the symmetry constraint during the relaxation. We point out how the overall effect is that of significantly changing the electronic spectrum if no symmetry constraint is imposed to the system. Such distortion can account for the Stokes shift and provides a possible structural model to be linked to the four-level scheme invoked in the literature to explain recent results for the optical gain in silicon nanoclusters. Finally, formation energies for clusters with increasing dimension are calculated and their relative stability discussed.

Ab initio structural and electronic properties of hydrogenated silicon nanoclusters in the ground and excited state

Abrupt InAs/GaSb superlattices have In-Sb and Ga-As interfacial chemical bonds that are not present in the constituent materials InAs and GaSb. We study the effect of interfacial atomic mixing on the electronic structure of such superlattices, including electron and hole energies and wave function localization, interband transition energies, and dipole matrix elements. We combine an empirical pseudopotential method for describing the electronic structure with two different structural models of interfacial disorder. First, we use the ``single-layer disorder'' model and change in a continous way the composition of the interfacial bonds. Second, we study interfacial atomic segregation using a layer-by-layer kinetic model of molecular beam epitaxy growth, fit to the observed scanning tunneling microscopy segregation profiles. The growth model provides a detailed structural model of segregated InAs/GaSb superlattices with atomic resolution. The application of the empirical pseudopotential method to such structures reveals remarkable electronic consequences of segregation, among them a large blueshift of the band gap. This result explains the surprising gap increase with growth temperature observed for similar structures. In particular we find that (i) superlattices with only In-Sb interfacial bonds have lower band gaps (by 50 meV) than superlattices with only Ga-As interfacial bonds. (ii) Heavy-hole--to--electron transition energies increase with the number of Ga-As interfacial bonds more than light-hole--to--electron transition energies. (iii) The heavy-hole $\mathrm{hh}1$ wave functions show a strong localization on the In-Sb interfacial bonds. The heavy-hole wave functions have very different amplitudes on the Ga-As interface and on the In-Sb interface. (iv) Sb segregates at InAs-on-GaSb growth, whereas As and In segregate at GaSb-on-InAs growth, but Ga does not segregate. (v) The segregation of Sb and In induces a blueshift in the band gap. (vi) There is an in-plane polarization anisotropy due to the low symmetry of the no-common-atom InAs/GaSb superlattice. This anisotropy is reduced by interfacial segregation.

Effects of interfacial atomic segregation and intermixing on the electronic properties of InAs/GaSb superlattices

We consider the classic Madelung problem of a lattice with N sites labeled i, each occupied by either an A or a B atom, and bearing a point charge ${\mathit{Q}}_{\mathit{i}}$ that depends on the environment of i. We find that, out of the ${2}^{\mathit{N}}$ possible lattice configurations of this binary ${\mathit{A}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathit{B}}_{\mathit{x}}$ fcc alloy, the lowest-energy ``ground-state structures'' are the ${\mathit{A}}_{3}$B-, ${\mathit{A}}_{2}$${\mathit{B}}_{2}$- and ${\mathit{AB}}_{3}$-ordered superlattices with ordering vector (1,0,1/2). On the other hand, for the pseudobinary ${\mathit{A}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathit{B}}_{\mathit{x}}$C zinc-blende alloy, the ground state corresponds to phase separation into AC+BC. Contrary to the accepted view, the Madelung energy of the random binary alloy is found to be nonvanishing.

Rita Magri

Papers

Role of the interface region on the optoelectronic properties of silicon nanocrystals embedded in SiO 2

First-principles study of n- and p-doped silicon nanoclusters

Ab initio structural and electronic properties of hydrogenated silicon nanoclusters in the ground and excited state

Effects of interfacial atomic segregation and intermixing on the electronic properties of InAs/GaSb superlattices

Ground-state structures and the random-state energy of the Madelung lattice.