Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
In the quest for faster and more efficient electronic and opto-electronic devices, phosphorene has recently attracted attention1. Phosphorene consists of a monolayer or a few layers of black phosphorous and has properties that depend on the number of layers and are significantly different from bulk. This is similar to the difference between graphene and carbon. It is a very promising semiconductor because of its direct electronic band gap that depending on the number of layers covers an energy range from 1.5 eV to 0.35 eV. Furthermore, its high charge carrier mobilities render it an interesting material for electronic applications. However, before phosphorene can be treated as a viable alternative to existing technologies, a lot of its fundamental properties remain to be understood.
We produce phosphorene by liquid exfoliation2 using different solvents such as hexane, N-Methyl-2-pyrrolidone, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate. We characterize the phosphorene using atomic force microscopy, scanning electron microscopy, and Raman spectroscopy to determine the distribution of the number of layers (thickness) of the phosphorene. Using electrodeless time-resolved microwave3 (frequency of oscillating electric field near 30 GHz) or terahertz4 (THz = 1012 Hz) conductivity experiments, we provide answers to the following questions: How does the mobility of electrons, holes, and excitons depend on the thickness of the phosphorene? Is quantum confinement resulting in a different mobility as theoretically predicted and which thickness is the optimum for optoelectronic applications?
1. Li, L. et al. Black phosphorus field-effect transistors. Nat. Nanotechnol. 9, 372–7 (2014).
2. Brent, J. R. et al. Production of few-layer phosphorene by liquid exfoliation of black phosphorus. Chem. Commun. (Camb). 50, 13338–41 (2014).
3. Grozema, F. C. & Siebbeles, L. D. A. Charge mobilities in conjugated polymers measured by pulse radiolysis time-resolved microwave conductivity: From single chains to solids. J. Phys. Chem. Lett. 2, 2951–2958 (2011).
4. Ulbricht, R., Hendry, E., Shan, J., Heinz, T. F. & Bonn, M. Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy. Rev. Mod. Phys. 83, 543–586 (2011).
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