Competition of moir\'e network sites to form electronic quantum dots in reconstructed MoX2{}_2/WX2{}_2 heterostructures

Twisted bilayers of two-dimensional semiconductors offer a versatile platform to engineer quantum states for charge carriers using moir\'e superlattice effects. Among the systems of recent interest are twistronic MoSe${}_{2}$/WSe${}_{2}$ and MoS${}_{2}$/WS${}_{2}$ heterostructures, which undergo reconstruction into preferential stacking domains and highly strained domain wall networks, determining the electron/hole localization across moir\'e superlattices. Here, we present a catalogue of options for the formation of self-organized quantum dots and wires in lattice-reconstructed marginally twisted MoSe${}_{2}$/WSe${}_{2}$ and MoS${}_{2}$/WS${}_{2}$ bilayers, fine tuned by the twist angle between the monolayers from perfect alignment to $\theta \sim 1^{\circ}$, and by choosing parallel or anti-parallel orientation of their unit cells. The proposed scenarios of the quantum dots and wires formation are found using multi-scale modelling that takes into account the features of strain textures caused by twirling of domain wall networks.Comment: 7 pages, 5 figure

Proposal for photoacoustic ultrasonic generator based on Tamm plasmon structures

The scheme of generation of ultrasound waves based on optically excited Tamm plasmon structures is proposed. It is shown that Tamm plasmon structures can provide total absorption of a laser pulse with arbitrary wavelength in a metallic layer providing the possibility of the use of an infrared semiconductor laser for the excitation of ultrasound waves. Laser pulse absorption, heat transfer and dynamical properties of the structure are modeled, and the optimal design of the structure is found. It is demonstrated that the Tamm plasmon-based photoacoustic generator can emit ultrasound waves in the frequency band up to 100 MHz with pre-defined frequency spectrum. Optical power to sound power conversion efficiency grows linearly with frequency of the laser modulation and excitation power

Development of beta-Ga2O3 layers growth on sapphire substrates employing modeling of precursors ratio in halide vapor phase epitaxy reactor

Gallium oxide is a promising semiconductor with great potential for efficient power electronics due to its ultra-wide band gap and high breakdown electric field. Optimization of halide vapor phase epitaxy growth of heteroepitaxial beta-Ga2O3 layers is demonstrated using a simulation model to predict the distribution of the ratio of gallium to oxygen precursors inside the reactor chamber. The best structural quality is obtained for layers grown at 825-850 degrees C and with a III/VI precursor ratio of 0.2. Although the structural and optical properties are similar, the surface morphology is more deteriorated for the beta-Ga2O3 layers grown on 5 degree off-axis sapphire substrates compared to on-axis samples even for optimized process parameters. Cathodoluminescence with a peak at 3.3 eV is typical for unintentionally doped n-type beta-Ga2O3 and shows the appearance of additional emissions in blue and green region at similar to 3.0, similar to 2.8, similar to 2.6 and similar to 2.4 eV, especially when the growth temperatures is lowered to 800-825 degrees C. Estimation of the band gap energy to similar to 4.65 eV from absorption indicates a high density of vacancy defects.Funding Agencies|Linkoping University Library</p

Effect of Plasmonic Ag Nanoparticles on Emission Properties of Planar GaN Nanowires

The combination of plasmonic nanoparticles and semiconductor substrates changes the properties of hybrid structures that can be used for various applications in optoelectronics, photonics, and sensing. Structures formed by colloidal Ag nanoparticles (NPs) with a size of 60 nm and planar GaN nanowires (NWs) have been studied by optical spectroscopy. GaN NWs have been grown using selective-area metalorganic vapor phase epitaxy. A modification of the emission spectra of hybrid structures has been observed. In the vicinity of the Ag NPs, a new emission line appears at 3.36 eV. To explain the experimental results, a model considering the Fröhlich resonance approximation is suggested. The effective medium approach is used to describe the enhancement of emission features near the GaN band gap

Control of the surface plasmon dispersion and Purcell effect at the metamaterial-dielectric interface

The use of metamaterial as a way to mitigate the negative effects of absorption in metals on the Purcell effect in metal-dielectric structures is investigated. A layered metal-dielectric structure is considered as an anisotropic medium in the long-wavelength limit. The dispersion of the surface plasmon appearing at the boundary between such a structure and a different dielectric material, as well as the position of the peak in the local density of states are studied for various combinations of materials and filling factors of the periodic structure. The calculated frequency dependence of the Purcell factor demonstrates an increase in peak value compared to the conventional plasmonic structure. The results obtained using effective media approach are compared to the results of numerical modelling.Peer reviewe

Weak and strong coupling of photons and excitons in planar meso-cavities

The interaction of an exciton and cavity modes is considered in planar meso-cavities, which have lateral sizes corresponding to few wavelengths. In meso-cavities, the frequency interval between the optical modes is comparable or smaller than the value of the Rabi splitting between the exciton and the optical modes. The Hamiltonian of the interaction between the exciton and the cavity modes is constructed, and it is shown that such an interaction between the cavity modes and the exciton can occur both in weak and in strong coupling regimes. The latter case can be accompanied by a pronounced splitting of the emission peaks as shown for modelled meso-cavities of triangular, square and hexagonal shapes, where it is demonstrated that Q-factors for the adjacent cavity modes as well as the strength of interaction with excitons can differ by few orders of magnitude. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing AgreementFunding Agencies|Russian Science FoundationRussian Science Foundation (RSF) [16-12-10503]; VetenskapsradetSwedish Research Council [2019-05154]; Energimyndigheten [46563-1]</p

Quantum analysis of luminescence of an exciton in a meso-cavity

Interaction of cavity modes with an exciton in a meso-cavity (the structure supporting several cavity modes separated by an energy interval comparable to Rabi-splitting of an exciton and cavity modes) has been analyzed using a quantum-mechanical approach. Simultaneous interaction of an exciton and several cavity modes results in few novel effects such as ladder-like increase of the exciton population in the system, quantum beating and non-monotonic dependence of the ground polariton state in the system on the pumping. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.Funding Agencies|Russian Science FoundationRussian Science Foundation (RSF) [21-12-00304]; VetenskapsradetSwedish Research Council [2019-05154]; Energimyndigheten [46563-1]</p

Effect of Plasmonic Ag Nanoparticles on Emission Properties of Planar GaN Nanowires

The combination of plasmonic nanoparticles and semiconductor substrates changes the properties of hybrid structures that can be used for various applications in optoelectronics, photonics, and sensing. Structures formed by colloidal Ag nanoparticles (NPs) with a size of 60 nm and planar GaN nanowires (NWs) have been studied by optical spectroscopy. GaN NWs have been grown using selective-area metalorganic vapor phase epitaxy. A modification of the emission spectra of hybrid structures has been observed. In the vicinity of the Ag NPs, a new emission line appears at 3.36 eV. To explain the experimental results, a model considering the Frohlich resonance approximation is suggested. The effective medium approach is used to describe the enhancement of emission features near the GaN band gap.Funding Agencies|Swedish Research Council [2018-04552, 2019-05154]; Swedish Energy Agency [46563-1]</p