Positive Temperature Coefficient of Resistance and Bistable Conduction in Lead Selenide Quantum Dot Thin Films

We report the observation of a positive temperature coefficient of resistance in strongly coupled quantum dot (QD) arrays. Conductivities of lead selenide (PbSe) QD thin films treated with 1,2-ethanedithiol increase when cooled from room temperature to 78 K, consistent with bulk PbSe crystals and indicating bandlike transport. Small angle X-ray scattering and infrared absorption spectroscopy results confirm a very strong electronic coupling among QDs. These QD thin films also exhibit bistable conduction above 160 K. As the electric field reaches a threshold, on the order of 0.1 V/mu m, the film conductance increases abruptly by up to 10 orders of magnitude and remains high until the bias voltage is reduced to about zero volts. This bistability is likely induced either by filament formation or by a trap-related electronic switching.