Size Dependence of Two-Photon Absorption in Semiconductor Quantum Dots

Journal Article · Tue Jan 01 04:00:00 EST 2013 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4811349· OSTI ID:1192936

Dakovski, Georgi L. ^[1]; Shan, Jie ^[1]

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1. Case Western Reserve Univ., Cleveland, OH (United States)

Quantum confinement plays an important role in the optical properties of semiconductor quantum dots (QDs). In this work, we combine experiment and modeling to systematically investigate the size dependence of the degenerate two-photon absorption (TPA) of below-band-gap radiation in CdSe QDs. The TPA coefficient β at 800 nm of CdSe QDs of varying radii was measured using femtosecond white-light transient absorption spectroscopy by probing the pump-induced bleaching at the first exciton transition energy. β was also calculated using a model based on the multiband effective-mass approximation. Satisfactory agreement between experiment and theory was obtained. Our findings show the evolution of the TPA in the QDs from that of atom-like to bulk-like with increasing the radius R. The TPA coefficient (or the volume normalized TPA cross-section) increases with radius approximately linearly in the strong confinement regime due to the rapid increase of the joint density of states for the two-photon allowed transitions, and saturates for R > 5 nm (the exciton Bohr radius), approaching that of bulk CdSe.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• OSTI ID: 1192936
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 1 Vol. 114; ISSN JAPIAU; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English