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We have employed a multiband envelope function method to study wurtzite [0001] InN nanowires of cylindrical cross section. The electronic subband structure and optical absorption spectrum are calculated as a function of the nanowire radius. The energies of the Γ -point conduction band states show a monotonous increase with decreasing radius. On the other hand, the size dispersion of the valence band states is more involved, showing various crossing and anticrossing effects due to the interplay between the confinement and band mixing effects. Thus, for small ( R < 2 nm ) nanowires the highest valence band state has dominant p z -symmetry, but for R > 2 nm the highest state has dominant p ⊥ -symmetry, although it is optically inactive. The optical absorption spectra polarized along or perpendicular to the nanowire axis are different on account of the different transitions involved. The spectra of the smaller nanowires display a distinguishable sequence of peaks reflecting the one-dimensional density-of-states. The absorption peaks become denser for larger nanowires, and for radii larger than 10 nm the spectrum starts to ressemble that of bulk InN. [ABSTRACT FROM AUTHOR]

Highlights: [•] We model H-passivated and oxidized SOI structures using ab initio and k·p methods. [•] The thickness (TSi) of the UTSOI structures ranges from 0.6 to 6.3nm. [•] Bandgap values for oxidized SOI with TSi 3nm show oscillating behavior with TSi. [•] Effective masses m∗ extracted from ab initio and k·p are compared. [•] Bulk Si parametrizations for k·p and m∗ are only adequate for TSi >3nm. [Copyright &y& Elsevier]

Abstract: We present results of room temperature photoreflectance (PR) and photoluminescence (PL) measurements of molecular-beam epitaxy (MBE)-grown GaAsSb/GaAs quantum dot structures: one with an In0.14Ga0.86As capping quantum well and one without it. PL was used to determine the structures’ ground-state transition energies. This result was employed in an 8-band k·p Hamiltonian to achieve a band structure of the structures, which have different electron confinement. The dot emission energies suggest a large amount of As incorporation into the dots, which is due to enhanced adatom mixing at a higher than normal growth temperature of 510°C. Our calculations indicate a dot composition of 25–50% Sb gives the best fit to experiment. This uncertainty in composition arises due to the fact that different bowing parameters of the ternary alloy could be applied in the calculations. The theoretical analysis accounts well for the main feature in the PR spectra of both samples. [Copyright &y& Elsevier]

The effect of thickness of cesium lead halide perovskite CsPbBr 3 nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k·p model with the consideration of exciton binding energy. We first reported the CsPbBr 3 nanoplatelets' band structure and optical gain with exciton effect. As the thickness of NPLs decreases, their bandgap increases and the band mixing is more obvious which influences the transition matrix element (TME). The optical gain of CsPbBr 3 nanoplatelets is calculated by taking into account of TME, Fermi factor, injected carrier density and thickness. A blue shift of peak position in optical gain can be observed as the thickness of NPLs decreases. As the injected carrier density arises, the maximum optical gain of thicker NPLs reach saturation much faster than the thinner ones. To obtain high differential gain, NPLs with less thickness are better choices. Experimental work is carried out and the results agree with our theoretical results very well. • We first reported the CsPbBr3 nanoplatelets' band structure and optical gain with exciton effect. • The effect of thickness on energy band and optical properties of perovskite CsPbBr 3 NPLs is revealed with the help of the 8-band k.p model. • The maximum optical gain of thinner NPLs need higher carrier density to reach saturation, which means a higher differential gain can be obtained. • The exciton enhanced optical gain spectrum are obtained. [ABSTRACT FROM AUTHOR]

Layered halide hybrid organic-inorganic perovskites (HOP) have been the subject of intense investigation before the rise of three-dimensional (3D) HOP and their impressive performance in solar cells. Recently, layered HOP have also been proposed as attractive alternatives for photostable solar cells and revisited for light-emitting devices. In this review, we combine classical solid-state physics concepts with simulation tools based on density functional theory to overview the main features of the optoelectronic properties of layered HOP. A detailed comparison between layered and 3D HOP is performed to highlight differences and similarities. In the same way as the cubic phase was established for 3D HOP, here we introduce the tetragonal phase with D 4h symmetry as the reference phase for 2D monolayered HOP. It allows for detailed analysis of the spin-orbit coupling effects and structural transitions with corresponding electronic band folding. We further investigate the effects of octahedral tilting on the band gap, loss of inversion symmetry and possible Rashba effect, quantum confinement, and dielectric confinement related to the organic barrier, up to excitonic properties. Altogether, this paper aims to provide an interpretive and predictive framework for 3D and 2D layered HOP optoelectronic properties.