Charge transport in arrays of PbSe nanocrystals

TL;DR

This study investigates charge transport in PbSe nanocrystal arrays, revealing hole conduction mechanisms, activation energies, and the role of disorder, with implications for nanocrystal-based electronic devices.

Contribution

It provides a detailed model of hopping transport in PbSe nanocrystal arrays, highlighting the role of acceptor states and disorder in charge conduction.

Findings

Holes are the majority carriers, thermally released from acceptor states.

Activation energy depends on source-drain voltage, reflecting different transport regimes.

Fermi energy is near the highest-occupied valence level, consistent with density of states measurements.

Abstract

We report electrical transport measurements of arrays of PbSe nanocrystals forming the channels of field effect transistors. We measure the current in these devices as a function of source-drain voltage, gate voltage and temperature. Annealing is necessary to observe measurable current after which a simple model of hopping between intrinsic localized states describes the transport properties of the nanocrystal solid. We find that the majority carriers are holes, which are thermally released from acceptor states. At low source-drain voltages, the activation energy for the conductivity is given by the energy required to generate holes plus the activation over barriers resulting from site disorder. At high source-drain voltages the activation energy is given by the former only. The thermal activation energy of the zero-bias conductance indicates that the Fermi energy is close to the highest-occupied valence level, the 1Sh state, and this is confirmed by field-effect measurements, which give a density of states of approximately eight per nanocrystal as expected from the degeneracy of the 1Sh state.