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arXiv · 1408.1942

Frenkel-like Wannier-Mott Excitons in Few-Layer PbI2

Alexis S. Toulouse·Benjamin P. Isaacoff·Guangsha Shi·Marie Matuchová·Emmanouil Kioupakis·Roberto Merlin
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Abstract

Optical measurements and first-principles calculations of the band structure and exciton states in direct-gap bulk and few-layer PbI2 indicate that the n = 1 exciton is Frenkel-like in nature in that its energy exhibits a weak dependence on thickness down to atomic-length scales. Results reveal large increases of the gap and exciton binding energy with decreasing number of layers, and a transition of the fundamental gap, which becomes indirect for 1-2 monolayers. Calculated values are in reasonable agreement with a particle-in-a-box model relying on the Wannier-Mott theory of exciton formation. General arguments and existing data suggest that the Frenkel-like character of the lowest exciton is a universal feature of wide-gap layered semiconductors whose effective masses and dielectric constants give bulk Bohr radii that are on the order of the layer spacing.

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Alexis S. Toulouse, Benjamin P. Isaacoff, Guangsha Shi, Marie Matuchová, Emmanouil Kioupakis, Roberto Merlin. 2014-08-08. Frenkel-like Wannier-Mott Excitons in Few-Layer PbI2. https://doi.org/10.1103/physrevb.91.165308

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