Electron Transport in Arrays of Lead Selenide Nanocrystals*

We report on measurements of electron transport in self-assembled arrays of PbSe nanocrystals (NCs). NCs $\sim $8 nm in diameter are colloidally synthesized and drop cast onto an inverted field effect structure. The NCs self assemble into hexagonal close-packed arrays with $\sim $1.5 nm interdot spacing after annealing. The field-effect device enables us to measure the dependence of current on gate voltage (V$_{g})$ as well as source-drain voltage (V$_{ds})$. At high temperature we find that the conductance is exponentially dependent on both V$_{ds}$ and temperature. At low temperature the conductance is still exponentially dependent on V$_{ds}$, but is independent of temperature indicating a tunneling mechanism. While the conductance is independent of V$_{g}$ at high temperatures, it decreases with V$_{g}$ at low temperature suggesting that holes are the dominant carriers.