Abstract
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.
Highlights
The dispersion equation and envelope wave functions of electrons confined by the nanoplatelets were derived analytically
By considering symmetric core/shell nanoplatelets made of alternating ZnSe and CdTe layers as an example, we showed that their subbands can be degenerate due to the strong localization of electrons inside the shell
This degeneracy was found to occur near the Brillouin zone center for the low-energy subbands if the affinity of electron in the core is less than that in the shell and at sufficiently large electron wave vectors for all subbands in the opposite case
Summary
The confinement of charge carriers in semiconductor nanostructures endows them with physical properties that are not observed in the macroworld [1,2,3,4,5,6] and which can be controlled at the fabrication stage or by exposing fabricated nanostructures to external stimuli, such as electric [7,8,9,10,11,12] or magnetic [13,14,15,16] fields. The use of different semiconductors and the construction of heterojunctions significantly expand the scope of nanostructure design, allowing one, for example, to localize electrons and holes in certain parts of nanostructure to enhance the quantum yield of photoluminescence [26,27] or to increase the spatial separation of charge carriers for photovoltaic applications [28,29]. Core/shell nanostructures, where one material (core) is isolated while another (shell) is exposed to the environment, are of particular practical importance [33,34,35]
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