Band Structure and Intersubband Transitions of Three-Layer Semiconductor Nanoplatelets

This paper presents the first general theory of electronic band structure and intersubband transitions in three-layer semiconductor nanoplatelets. We find a dispersion relation and wave functions of the confined electrons and use them to analyze the band structure of core/shell nanoplatelets with equal thicknesses of the shell layers. It is shown that the energies of electrons localized inside the shell layers can be degenerate for certain electron wave vectors and certain core and shell thicknesses. We also show that the energies of intersubband transitions can be nonmonotonic functions of the core and shell thicknesses, exhibiting pronounced local minima and maxima which can be observed in the infrared absorption spectra. Our results will prove useful for the design of photonic devices based on multilayered semiconductor nanoplatelets operating at infrared frequencies.

Effects of a magnetic field on the optoelectronic properties of mono- and bi-layer transition metal dichalcogenides

We report a theoretical study on the effects of an external magnetic field on the electronic and optical properties of mono- and bi-layer MoS₂, and bilayer MoS₂/WS₂ heterostructures. The direction of an applied magnetic field determines (i) the strength of the coupling between the atomic orbital moments of the structure and the field, and (ii) Zeeman contribution to the splitting of the VB and CB levels with the amplitude of the applied field. Whereas for a magnetic field applied perpendicular to the structure, calculated real part of optical conductivity reveals optical transitions red-shifted compared to zero magnetic field case, conductivity is unaffected by the the amplitude of an in-plane applied magnetic field. We show that through modifying atomic d-orbitals conduction and valence band states by an applied electric field, we can determine and control the impact of a magnetic field on the optical response of these materials. We employ our parametrized tight-binding model with non-orthogonal sp³d⁵ orbitals and spin-orbit coupling, which was advanced to include the effects of an external magnetic field through Peierls substitution in the wave vector and the Zeeman energy term.

Electronic and optical properties of nanostructured MoS2 materials: influence of reduced spatial dimensions and edge effects

Theoretical prediction of how the electronic and optical properties of nanostructured MoS₂ materials are influenced by reducing spatial dimensions and edge effects is presented. We open pathways for further experimental studies and potential optoelectronic applications.

Engineered nanomaterials for solar energy conversion

Understanding how to engineer nanomaterials for targeted solar-cell applications is the key to improving their efficiency and could lead to breakthroughs in their design. Proposed mechanisms for the conversion of solar energy to electricity are those exploiting the particle nature of light in conventional photovoltaic cells, and those using the collective electromagnetic nature, where light is captured by antennas and rectified. In both cases, engineered nanomaterials form the crucial components. Examples include arrays of semiconductor nanostructures as an intermediate band (so called intermediate band solar cells), semiconductor nanocrystals for multiple exciton generation, or, in antenna-rectifier cells, nanomaterials for effective optical frequency rectification. Here, we discuss the state of the art in p-n junction, intermediate band, multiple exciton generation, and antenna-rectifier solar cells. We provide a summary of how engineered nanomaterials have been used in these systems and a discussion of the open questions.