Converting electrical conductivity types in surface atomic-ligand exchanged PbS quantum dots via gate voltage tuning

Here we present the observation of a unique phenomenon of converting electrical conductivity types in surface atomic-ligand exchanged of PbS quantum dots (QDs), while tuning the gate voltage of PbS QD-based thin film field-effect transistors (TFTs). The synthesized PbS-QD thin films showed different conductivity (n- or p-) types depending on the direction of gate voltage sweeping. When increasing gate voltage from negative to positive voltage, the TFT devices produced n-channel characteristics with a typical mobility on the order of mu(n) = 10(-1) cm(2) V-1 s(-1). By contrast, the devices showed p-channel characteristics with similar mobility when sweeping the gate voltage from positive to negative. The studies based on density functional theory (DFT) theoretical calculations and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the band gap of ligand exchanged PbS-QDs changes upon gate voltage sweeping, affecting the surface states of the QDs due to the adhered Br- and therefore altering the conductivity type of the materials. These findings signify the carrier type switching behavior via gate voltage tuning in atomic-ligand exchange QD thin films, suggesting great application potential of QD for advanced new-generation nano-electronic devices. (C) 2017 Elsevier B.V. All rights reserved.