Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Colloidal nanocrystals made from semiconducting II-IV and IV-VI compounds have attracted enormous interest in the last decades [1]. The oriented attachment of the nanocrystals is currently emerging as a route to form 2D single-crystalline semiconductors which are of interest in optoelectronics [2].
In my research, , I use electrolyte-gated transistors to study the electronic properties and transport characteristics such as the carrier type and mobility of 2-D PbX and CdX superstructures [3]. The potential of the gate electrode determines the carrier density and thus the Fermi level with respect to the 2-D conduction band (CB) or valance band (VB). By the differential capacitance measurement the number of injected charge per nanocrystal can be calculated for a slight change of the Fermi level. The source-drain conductivity is measured as a function of the Fermi level position. Finally, the mobility of the system is calculated from conductivity and charge density. The actual position of the Fermi level can also be obtained by measuring the inter-band light absorption quenching which monitors the occupation of the bands, not the defect levels. I will present the results obtained on 2-D PbSe semiconductors with a square or honeycomb geometry.
In addition, the optical properties of our 2D superstructures are of strong interest. Our theoretical results show that square and graphene-type honeycomb systems have a different absorption spectrum. The absorptivity per allowed transition is close to π times the fine structure constant, in agreement with results obtained on graphene [4] and InAs quantum membrane [5].
[1] A.P. Alivisatos et al., J. Phys. Chem. 100, (1996)
[2] W.H. Evers et al., Nonao Lett. 13, 1312-1316 (2013)
[3] D. Vanmaekelbergh et al., Electrochemica Acta, 53, 1140-1149 (2007)
[4] A.K. Geim et al., Science 320, 1308 (2008)
[5] H. Fang et al., PNAS 110, 11688-11691 (2013)
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