Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.111
Publication date: 6th July 2018
Solution-processed two-dimensional (2D) semiconductors with tunable band gaps represent highly promising materials for next generation ultrathin electronics. Their dimensionality-dependent optoelectronic properties differ significantly from their zero-, one- and three-dimensional counterparts and can be tuned by colloidal chemistry methods for controlling the structures’ thickness.
We use optical pump-terahertz probe (OPTHzP) spectroscopy as a non-contact method to determine the thickness-dependent transient charge carrier mobility in 2D PbS nanosheets of different thickness (4 – 16 nm) and find high values ranging from 231 cm2/Vs in the thinnest, 4 nm thick sheets, up to 472 cm2/Vs and 427 cm2/Vs in 6 nm and 16 nm thick PbS nanosheets, respectively. Furthermore, we model the frequency dependent charge carrier mobility of 2D PbS nanosheets with a Drude-Smith behavior and reveal a growing contribution of photoexcited excitons in thinner PbS nanosheets due to their increased exciton binding energy.[1]
We find that by carefully controlling the reaction kinetics, the thickness of colloidal 2D PbS layers can be reduced to < 2 nm to the formation of ultrathin PbS nanoplatelets. Ultrathin 2D PbS layers are particularly interesting due to their increasing carrier multiplication (CM) efficiency with decreasing nanosheet/nanoplatelet thickness.[2,3] We show that in thicker PbS nanosheets, free and mobile charges are generated under photoexcitation, whereas in ultrathin PbS nanoplatelets bound excitons are formed. A photoluminescence quantum yield of up to 20 % is obtained by surface passivation of the significantly blue-shifted PbS nanoplatelets (Abs: 683 nm, 1.8 eV, PL: 705 nm, 1.75 eV) and underpins their potential for NIR light-emitting applications.[4] Our work emphasizes the excellent usability of colloidal chemistry and spectroscopy methods for producing 2D tailor-made band gap materials for high mobility AND light emitting optoelectronics.
[1] Lauth, J., Failla, M, Klein, E., Klinke, C., Kinge, S., Siebbeles, L. D. A., submitted 2018.
[2] Bielewicz, T.; Dogan, S.; Klinke, C., Small 2015,11, 826-833.
[3] Aerts, M.; Bielewicz, T.; Klinke, C.; Grozema, F. C.; Houtepen, A. J.; Schins, J. M.; Siebbeles, L. D. A., Nat. Commun. 2014,5, 3789.
[4] Manteiga Vazquéz, F., Yu, Q., Crisp, R., Kinge, S., Houtepen, A. J., Siebbeles, L. D. A., Lauth, J., in preparation.
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