Electrical Transport in Semiconductor Nanocrystal Assemblies
The size-tunable electronic properties and the solution processability of colloidal semiconductor nanocrystals (NCs) have made these materials promising candidates for thin-film optoelectronics including solar cells, light emitting diodes, and photodetectors. However, successful incorporation of NCs into practical devices is still challenging since assemblies of NCs are, in general, not highly conductive and the electrical transport in NC assemblies has been less explored. Considering that most of these devices typically involve electrical conduction between NCs, their charge transport properties should also be well-understood and methods to obtain highly conductive NC assemblies should be developed.
In this talk, the electrical transport in NC assemblies is discussed. To begin with, 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 in turns 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 [2]; 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. The study on the charge transport mechanism in films of different sized PbSe NCs is then presented, to clarify the role of NC diameter on the charge transport at varying temperatures [3]; 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. These will lead to improved device performance that takes full advantage of the characteristic properties of NCs in optoelectronic applications.
* 일시 : 2012년 5월 10일 목요일 오후 4시 30분
* 장소 : 베어드홀 103호
* 연사 : 강 문 성 교수 (숭실대 화공과)