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Ultrasensitive solution-cast quantum dot photodetectors


Solution-processed electronic1 and optoelectronic2,3,4,5 devices offer low cost, large device area, physical flexibility and convenient materials integration compared to conventional epitaxially grown, lattice-matched, crystalline semiconductor devices. Although the electronic or optoelectronic performance of these solution-processed devices is typically inferior to that of those fabricated by conventional routes, this can be tolerated for some applications in view of the other benefits. Here we report the fabrication of solution-processed infrared photodetectors that are superior in their normalized detectivity (D*, the figure of merit for detector sensitivity) to the best epitaxially grown devices operating at room temperature. We produced the devices in a single solution-processing step, overcoating a prefabricated planar electrode array with an unpatterned layer of PbS colloidal quantum dot nanocrystals. The devices showed large photoconductive gains with responsivities greater than 103 A W-1. The best devices exhibited a normalized detectivity D* of 1.8 × 1013 jones (1 jones = 1 cm Hz1/2 W-1) at 1.3 µm at room temperature: today's highest performance infrared photodetectors are photovoltaic devices made from epitaxially grown InGaAs that exhibit peak D* in the 1012 jones range at room temperature, whereas the previous record for D* from a photoconductive detector lies at 1011 jones. The tailored selection of absorption onset energy through the quantum size effect, combined with deliberate engineering of the sequence of nanoparticle fusing and surface trap functionalization, underlie the superior performance achieved in this readily fabricated family of devices.

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Figure 1: Device structure and electro-optic characteristics for device classes investigated.
Figure 2: Noise characteristics and resultant normalized detectivity of the different device classes investigated.
Figure 3: Photodetector performance characteristics of the highest-sensitivity class of devices.


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We thank D. Grozea and Z. H. Lu for XPS, E. Istrate for discussions, and V. Sukhovatkin for assistance in optical measurements. This research was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Foundation for Innovation, the Province of Ontario, and the Canada Research Chairs programme.

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Correspondence to Edward H. Sargent.

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Konstantatos, G., Howard, I., Fischer, A. et al. Ultrasensitive solution-cast quantum dot photodetectors. Nature 442, 180–183 (2006).

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