High-Mobility Hole Transport in Single-Grain PbSe Quantum Dot Superlattice Transistors

Abstract

Epitaxially-fused superlattices of colloidal quantum dots (QD epi-SLs) may exhibit electronic minibands and highmobility 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. Systematic measurements of charge transport in individual, highly-ordered epi-SL grains would facilitate the study of minibands in QD films. Here, we demonstrate the air-free fabrication of microscale field-effect transistors (μ-FETs) with channels consisting of single PbSe QD epi-SL grains (2−7 μm channel dimensions) and analyze charge transport in these single-grain devices. The eight devices studied show p-channel or ambipolar transport with a hole mobility as high as 3.5 cm 2 V −1 s −1 at 290 K and 6.5 cm 2 V −1 s −1 at 170−220 K, one order of magnitude larger than that of previous QD solids. The mobility peaks at 150−220 K, but device hysteresis at higher temperatures makes the true mobility−temperature curve uncertain and evidence for miniband transport inconclusive.

PbI2 Passivation of Three Dimensional PbS Quantum Dot Superlattices Toward Optoelectronic Metamaterials

“…After the in-depth structural characterization, we studied the transport properties of the fabricated SLs employing ion gel-gated field-effect transistors (IGFET). This technique relies on the use of the electrical double layer (EDL) to accumulate a high charge carrier density in the film (above 10 14 cm –2 in optimal conditions). ,− In this way, allowing to fill a considerable amount of trap states in the CQD solid, it is possible to measure the close-to intrinsic transport properties of the SLs. , The problem of trap density is highly relevant especially for lead chalcogenide CQD SLs as evidenced by the moderate mobilities that can be achieved in solid-state gated transistors. ,, In recent years, the use of EDL to gate SL transistors has enabled the understanding of the full potential of both PbS , and PbSe assemblies. ,, As mentioned earlier, in a recent work, we demonstrated electron mobilities up to 270 cm 2 V –1 s –1 in three-dimensional PbSe CQD superlattices, owing to the much-improved ordering of these structures with respect to the 2D ones . Encouraged by this result, we set out to study the transport properties of PbS superlattices, which show high coherence lengths in both IP and OP directions.…”

“… 8 , 55 The problem of trap density is highly relevant especially for lead chalcogenide CQD SLs as evidenced by the moderate mobilities that can be achieved in solid-state gated transistors. 20 , 29 , 50 In recent years, the use of EDL to gate SL transistors has enabled the understanding of the full potential of both PbS 39 , 41 and PbSe assemblies. 22 , 43 , 46 As mentioned earlier, in a recent work, we demonstrated electron mobilities up to 270 cm 2 V –1 s –1 in three-dimensional PbSe CQD superlattices, owing to the much-improved ordering of these structures with respect to the 2D ones.…”

“…Superlattices with various geometries, structural features, and degree of ordering have been fabricated both with PbSe and PbS CQDs. − While PbSe has been historically preferred because of showcasing higher mobilities in the bulk and easiness of synthesis with higher monodispersity, in the CQDs counterpart, its chemistry makes it particularly susceptible to oxidation. Lead sulfide instead shows better stability and is ubiquitously employed for most SWIR optoelectronic applications nowadays.…”

Thermal‐Assisted Multiscale Patterning of Nonplanar Colloidal Nanostructures for Multi‐Modal Anti‐Counterfeiting

“…[ 57 ] Quantum dots (QDs) superlattice and patterning present a promising avenue for exploring novel physics, such as miniband effects, [ 58 ] and for the realization of a variety of devices, including high‐resolution displays [ 59 ] and photodetectors. [ 60 ] However, the color of quantum dots originates from the light absorption determined by their bandgap characteristics. QDs of multiple materials and structures are typically required for a full‐color device.…”