Probing electron diffusion length in an accumulation layer in a ligand-free lead sulfide colloidal quantum dot monolayer

Abstract

Developing an understanding of the minority carrier diffusion in the effective channel close to the gate dielectric in a field effect transistor (FET) configuration has proven to be challenging because the minority carriers are affected by the gate electric field. We, for the first time, have investigated the minority carrier (electron) diffusion length in ultrathin lead sulfide (PbS) colloidal quantum dots (CQDs) treated with ammonium sulfide ((NH4)2S) using photocurrent microscopy (PCM). With increasing gate voltage, an electron diffusion length is found to be gate-dependent, which can be explained by the increased hole occupancy in the midgap states.Using the FET mobility in the (NH4)2S-treated PbS CQDs, we calculated the electron lifetime. We present the first demonstration of the electric field -modulated electron diffusion length in a PbS CQD film treated with an atomic ligand using PCM.