Christine Muccianti, University of Arizona
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Abstract: Two dimensional semiconductor transition metal dichalcogenides (TMDs) are direct band gap semiconductors, allowing for optically induced semiconducting states that can be used as a basis for novel logic operations. For instance, excitons in monolayer TMDs can be optically injected and read out which provides a basis for novel technologies. Additionally, the two distinct valleys and the spin-valley coupling in monolayer TMDs allows for the creation of valley polarized excitons coupled to opposite circular polarizations of light. The valley polarization can be used as a binary index like “1s” or “0s” in potential valley-based logic devices (or “valleytronics”). However, single layer TMD excitons are limited. The excitons are neutral carriers, meaning that transportation of a polarized signal through a system is not possible with easily applied electric fields. Furthermore, the single layer exciton has a short lifetime of 1 ps, which further limits the ability to realize exciton spatial transport. By layering different TMD monolayers with a Type-II band alignment, one can optically achieve interlayer exciton states which have the hole confined to one layer and the electron to the second layer. The geometry for this state increases the lifetime by orders of magnitude, preserves valley polarization as in the monolayer case, and allows for exciton transport through applied fields.
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