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In recent years, the construction of lateral heterostructures of two-dimensional (2D) monolayers of transition metal dichalcogenides (TMDC) has been attracting considerable interest due to its numerous applications in electronic and optoelectronic devices. In this work, the optical absorption coefficient of the Lateral Single Quantum Well (LSQW) based on MoS 2 / WSe 2 is analyzed theoretically. For this purpose, we rederive the absorption coefficient equation for LSQW and investigate the parameters affecting the absorption coefficient of LSQW such as the type of polarization and incident angle as well as spin–orbit coupling (SOC). Our results show the significant effect of the spin–orbit effect on the maximum value of the absorption coefficient so that by including the SOC, the values ​​of absorption coefficient increases. We surprisingly found that increasing the well width enhances the optical absorption in LSQW. Our findings and predictions might be implemented in new emerged optovalleytronic devices. (a) Absorption coefficient as a function of the photon energy with various incident angle. (b) Absorption coefficient as a function of the incident angle. [ABSTRACT FROM AUTHOR]

In this paper the excitons of armchair graphene nanoribbons with layers of different width and thickness have been investigated. In this investigation, the band structure and energy gap of armchair graphene nanoribbons have been calculated using a tight-binding model including edge deformation effects (all edge atoms have been passivated with hydrogen atoms). Also, by calculating the conductance in armchair graphene nanoribbons (A-GNRs) optical absorption of armchair graphene nanoribbon in the single-electron approximation has been obtained. Finally, the binding energy of excitons in armchair graphene nanoribbons has been calculated using the Wannier model, Hartree-Fock approximation and the Bethe-Salpeter equation. [ABSTRACT FROM AUTHOR]

The present work investigates the nonlinear optical properties of a GaN quantum dot in the disk limit via the exciton and biexciton states using the compact density matrix formalism. Based on this model, we calculate the ground state energy of the exciton and biexciton states by the variation method, within envelope function and effective mass approximations. Linear and nonlinear optical absorption ( α, α) and oscillator strengths attributed to the optical transitions are obtained. The details of the behaviour of α and α around the resonance frequencies and for different quantum dot geometries are presented. It is found that the size of quantum dot and the optical intensity have a remarkable effect on the optical absorption, and the biexcitonic two-photon absorption coefficient( K) has also been calculated in this system. The results show that this parameter is strongly affected by the size of the quantum dot. [ABSTRACT FROM AUTHOR]

We present a detailed study of localized defect modes in finite two-dimensional magnetic photonic crystal consisting of cylindrical ferrite material in air background by using the scattering matrix method. It is shown that due to having positive and negative value of the effective magnetic permeability in interested photonic band gap, the defect modes present different behavior. Our results show that the modes appeared in positive permeability region have features similar to the modes supported by the dielectric photonic crystal while those created in the negative permeability region are strongly localized at the interface of defect ferrite rod with air background. Moreover, results indicate that defect modes occurred in the negative region are sharper than those appeared in the positive one which means the quality factor of former case is extremely high. [ABSTRACT FROM AUTHOR]

The ground state energy of an exciton and biexciton states, in a GaN/AlxGa1-xN quantum disk are investigated by the variation method, within envelope function and effective mass approximations. Exciton and biexciton binding energy, and the dipole moments related to the transition between ground, exciton and biexciton states, are calculated as a function of quantum disk geometry. The optical nonlinearity via the exciton and biexciton states is studied on the basis of a three level model through the density matrix formalism. The behavior of different terms of third order susceptibility χ(3), are studied around resonance frequencies and for different geometries of disk. The effect of values of the decay rates on χ(3) are studied. It is found that these values have remarkable effect on the second term of, χ(3). [ABSTRACT FROM AUTHOR]

Due to their wurzite structure, GaN quantum wells and dots arecharacterized by large built-in piezoelectric fields.These induce a spatial separation between the confined electron andholes, thus favouring the formation of electric dipoles.Here, we theoretically investigate the effects of the long-range,dipole-dipole interaction between two excitons in a GaN/AlxGa1-xNmicrodisk.These Coulomb interactions are shown to strongly affect the biexcitonground state. In particular, they induce strong spatial correlationsbetween the two excitons and result in biexciton binding energiesof the order of 1 meV. [ABSTRACT FROM AUTHOR]