HgTe
colloidal quantum dots (CQDs) are promising absorber systems
for infrared detection due to their widely tunable photoresponse in
all infrared regions. Up to now, the best-performing HgTe CQD photodetectors
have relied on using aggregated CQDs, limiting the device design,
uniformity and performance. Herein, we report a ligand-engineered
approach that produces well-separated HgTe CQDs. The present strategy
first employs strong-binding alkyl thioalcohol ligands to enable the
synthesis of well-dispersed HgTe cores, followed by a second growth
process and a final postligand modification step enhancing their colloidal
stability. We demonstrate highly monodisperse HgTe CQDs in a wide
size range, from 4.2 to 15.0 nm with sharp excitonic absorption fully
covering short- and midwave infrared regions, together with a record
electron mobility of up to 18.4 cm2 V–1 s–1. The photodetectors show a room-temperature
detectivity of 3.9 × 1011 jones at a 1.7 μm
cutoff absorption edge.
Infrared photodetectors (PDs) based on epitaxial semiconductors occupy the majority of the market, but their high cost from material growth and device integration limits their application fields. Colloidal quantum dots (CQDs) provide a high potential candidate for infrared PDs due to their unique infrared sensitivity, tunable physical and chemical properties, and good compatibility with readout integration circuits. In particular, HgTe CQD PDs have demonstrated a wide detection range from shortwave to long-wave infrared. Although significant progress has been achieved in HgTe CQD infrared PDs, they are still in the primary stage of QD synthesis and prototype device fabrication. Here, we develop a new p−i−n photodiode from the traditional p−i device structure. Bismuth sulfide (Bi 2 S 3 ) films were adopted as the electron transport layer, which could favor uniform absorber deposition, superior charge extraction, and suppressed interfacial loss. The Bi 2 S 3 -based photodiodes have achieved a room-temperature dark current density as low as 1.6 × 10 −5 A/cm 2 at −400 mV. Furthermore, their specific detectivity (D*) achieves ∼10 11 Jones at room temperature.
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