Synthesis and Chracterization of Single-Grain Epitaxially-Fused PbSe Quantum Dot Superlattices

Epitaxially-fused superlattices of colloidal quantum dots (QD epi-SLs) may exhibit electronic minibands and high-mobility charge transport, but electrical measurements of epi-SLs have been limited to large-area, polycrystalline samples in which superlattice grain boundaries and intragrain defects suppress/obscure miniband effects. In this talk, I will first discuss the synthesis of large-grained PbSe QD SLs, including detailed analysis of their chemical and physical structure. Next, I will discuss the mechanism by which a ligand-capped PbSe QD SL is converted into an epi-SL. Finally, I will present systematic measurements of charge transport in individual, highly-ordered PbSe QD epi-SL grains. One technical challenge in making these devices is the inherent mismatch in using traditional microfabrication techniques to make single-grained devices of air-sensitive materials. Here, we demonstrate the air-free fabrication of microscale field-effect transistors (μ-FETs) with channels consisting of single PbSe QD epi-SL grains (~ 1 -10 µm grain sizes) and analyze charge transport phenomena in these samples. The devices exhibit <i>p</i>-channel or ambipolar transport with a hole mobility as high as 3.5 cm² V^–1 s^–1 at 290 K and 6.5 cm² V^–1 s^–1 at 170–220 K, one order of magnitude larger than that of previous QD solids. Device hysteresis at higher temperatures makes the true mobility–temperature curve uncertain and evidence for miniband transport inconclusive.