Charge Transport in Semiconductor Nanocrystal Solids

Self-assembly of chemically-synthesized nanocrystals can yield complex long-range ordered structures which can be used as model systems for studying transport phenomena in low-dimensional materials [1]. Treatment of close-packed PbSe nanocrystal arrays with hydrazine enhanced exchange coupling between the nanocrystals and improved conductance by more than ten orders of magnitude compared to native nanocrystal films [2]. The conductivity of PbSe nanocrystal solids can be switched between n- and p-type transports by controlling the saturation of electronic states at nanocrystal surfaces. Nanocrystal arrays form the n- and p-channels of field-effect transistors with electron and hole mobilities of 2.5 cm$^{2}$V$^{-1}$s$^{-1}$ and 0.3 cm$^{2}$V$^{-1}$s$^{-1}$, respectively, and current modulation I$_{on}$/I$_{off} \quad \sim $10$^{3}$-10$^{4}$. The field-effect mobility in PbSe nanocrystal arrays is higher than the mobility of organic transistors while the easy switch between n- and p-transport allows realization of complimentary circuits and p-n junctions for nanocrystal-based solar cells and thermoelectric devices. [1] E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O'Brien, C. B. Murray. \textit{Nature} \textbf{439}, 55 (2006). [2] D. V. Talapin, C. B. Murray. \textit{Science} \textbf{310}, 86 (2005).