Electrical Transport in
Semiconductor Nanocrystal Assemblies
Moon Sung Kang
Department of Chemical Engineering, Soongsil University
23 January, 2013 (Wed), 11AM / #1101, W1-3 Bldg.
Electrical transport in semiconductor nanocrystal (NC) assemblies is discussed in this talk. Firstly, a method to obtain high performance NC transistors, which served as the key device structure in this study, is introduced; a high capacitance gate dielectric based on ionic liquids, named as ion-gel, was employed to accumulate high carrier densities within the NC films at low operation voltages, which resulted in high carrier mobility. Subsequently, the influence of NC size on the charge transport in CdSe NC assemblies based on ion-gel gated transistors is presented; the transport parameters, such as the device turn-on voltage, the electron mobility, and the charge transport activation energy in CdSe NC assemblies varied systematically with NC diameter. To clarify the role of NC diameter on the charge transport, the study on the charge transport mechanism in films of different sized PbSe NCs at varying temperatures is then presented; i) the electron transport between NCs underwent a transition in mechanism from Efros-Shklovskii-variable-range-hopping (ES-VRH) to nearest-neighbor-hopping (NNH), ii) the electron localization length, estimated from the ES-VRH model, was comparable to the NC size and scaled systematically with NC diameter, and iii) the activation energy from the NNH regime was size-dependent which is attributed both to the size-dependent Coulomb effects and the size-distribution of NCs. Finally, preliminary results on charge transport in doped NC assemblies will be briefly introduced, which showed a systematic variance upon doping concentration.