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In this work, we have investigated the structural and electronic properties of Mg-doped GaAs(111) nanowires synthesized through a vapor–liquid–solid growth mechanism. The crystalline structure of t...

Nanoscale heterostructure engineering is the main target for the development of optoelectronic devices. In this sense, a precise knowledge of local electronic response after materials processing is...

The Stark effect is one of the most efficient mechanisms to manipulate many-body states in nanostructured systems. In mono- and few-layer transition metal dichalcogenides, it has been successfully induced by optical and electric field means. Here, we tune the optical emission energies and dissociate excitonic states in MoSe2 monolayers employing the 220 MHz in-plane piezoelectric field carried by surface acoustic waves. We transfer the monolayers to high dielectric constant piezoelectric substrates, where the neutral exciton binding energy is reduced, allowing us to efficiently quench (above 90%) and red-shift the excitonic optical emissions. A model for the acoustically induced Stark effect yields neutral exciton and trion in-plane polarizabilities of 530 and 630 x 10(-5) meV/(kV/cm)(2), respectively, which are considerably larger than those reported for monolayers encapsulated in hexagonal boron nitride. Large in-plane polarizabilities are an attractive ingredient to manipulate and modulate multiexciton interactions in two-dimensional semiconductor nanostructures for optoelectronic applications.

Monolayer transition metal dichalcogenides with direct bandgaps are emerging candidates for microelectronics, nano-photonics, and optoelectronics. Transferred onto photonic integrated circuits (PICs), these semiconductor materials have enabled new classes of light-emitting diodes, modulators and photodetectors, that could be amenable to wafer-scale manufacturing. For integrated photonic devices, the optical losses of the PICs are critical. In contrast to silicon, silicon nitride (Si3N4) has emerged as a low-loss integrated platform with a wide transparency window from ultraviolet to mid-infrared and absence of two-photon absorption at telecommunication bands. Moreover, it is suitable for nonlinear integrated photonics due to its high Kerr nonlinearity and high-power handing capability. These features of Si3N4 are intrinsically beneficial for nanophotonics and optoelectronics applications. Here we report a low-loss integrated platform incorporating monolayer molybdenum ditelluride (1L-MoTe2) with Si3N4 photonic microresonators. We show that, with the 1L-MoTe2, microresonator quality factors exceeding 3 million in the telecommunication O-band to E-band are maintained. We further investigate the change of microresonator dispersion and resonance shift due to the presence of 1L-MoTe2, and extrapolate the optical loss introduced by 1L-MoTe2 in the telecommunication bands, out of the excitonic transition region. Our work presents a key step for low-loss, hybrid PICs with layered semiconductors without using heterogeneous wafer bonding.

Hybrid organic-inorganic perovskites have emerged as very promising materials for photonic applications, thanks to the great synthetic versatility that allows to tune their optical properties. In the two-dimensional (2D) crystalline form, these materials behave as multiple quantum-well heterostructures with stable excitonic resonances up to room temperature. In this work strong light-matter coupling in 2D perovskite single-crystal flakes is observed, and the polarization-dependent exciton-polariton response is used to disclose new excitonic features. For the first time, an out-of-plane component of the excitons is observed, unexpected for such 2D systems and completely absent in other layered materials, such as transition-metal dichalcogenides. By comparing different hybrid perovskites with the same inorganic layer but different organic interlayers, it is shown how the nature of the organic ligands controllably affects the out-of-plane exciton-photon coupling. Such vertical dipole coupling is particularly sought in those systems, e.g. plasmonic nanocavities, in which the direction of the field is usually orthogonal to the material sheet. Organic interlayers are shown to affect also the strong birefringence associated to the layered structure, which is exploited in this work to completely rotate the linear polarization degree in only few microns of propagation, akin to what happens in metamaterials., Comment: 11 pages, 14 figures (included supporting info)

Semiconductor nanomembranes are promising systems for many applications, since the band structure of a given material can be tailored to achieve specific configurations, which are not feasible by conventional growth procedures on rigid substrates. Here we show that optically active III–V membranes containing InAs quantum dots exhibit a pronounced photoluminescence enhancement with respect to equivalent systems grown on top of flat substrates. The effect is explained by the formation of carrier depletion regions symmetrically located with respect to the optically active layer. This leads to the filling of excited states of the quantum dots and the overall spectra are enhanced at higher energies. Changes on the strain field that are expected to lead to a red-shift of the quantum dot emission play a reduced role in the final emission spectra in comparison with the depletion effects. These effects can be considered as another degree of freedom and a key ingredient for band engineering of extremely thin semico...

In this work we attempt to directly observe anisotropic partial relaxation of epitaxial InAs islands using transmission electron microscopy (TEM) and synchrotron x-ray diffraction on a 15 nm thick InAs:GaAs nanomembrane. We show that under such conditions TEM provides improved real-space statistics, allowing the observation of partial relaxation processes that were not previously detected by other techniques or by usual TEM cross section images. Besides the fully coherent and fully relaxed islands that are known to exist above previously established critical thickness, we prove the existence of partially relaxed islands, where incomplete 60° half-loop misfit dislocations lead to a lattice relaxation along one of the 〈110〉 directions, keeping a strained lattice in the perpendicular direction. Although individual defects cannot be directly observed, their implications to the resulting island registry are identified and discussed within the frame of half-loops propagations.