Colloidal quantum dots (QDs) based on lead sulfide (PbS) have acquired scientific interest for infrared optoelectronic devices with potential bandgap tunability and ease of fabrication on arbitrary substrates. In this work, we show how device analysis data feed back into process optimization, towards the realization of high performance QD NIR photodetectors. Using the combination of transient PL, carrier transport and CV measurements we obtain the carrier density, lifetime and diffusion length in the layers. From the measured short diffusion length of the minority carriers, we deduce the need to achieve a wide depletion region to minimize recombination and thus enhance the carrier harvesting. Process optimization lead to a depletion region of more than 150 nm, resulting in high photon to carrier conversion. Furthermore, the complex index of refraction of all layers is characterized using ellipsometry and reflection/transmission, and these values are used as input for a transfer matrix method. Using the first interference peak, we show that a maximum EQE of 25% can be expected from optical modeling, a value that we almost reach experimentally (20%). Combining all of the above, we demonstrate 1450-nm photodetectors with dark current in the range of μA and specific detectivity (D*) of 10^11 Jones.
Epimitheas Georgitzikis, Pawel E. Malinowski, Mehedi Mamun, Oscar Enzing, Jorick Maes, Zeger Hens, Paul Heremans, and David Cheyns, "Determining charge carrier extraction in lead sulfide quantum dot near infrared photodetectors (Conference Presentation)," Proc. SPIE 10348, Physical Chemistry of Semiconductor Materials and Interfaces XVI, 103480B (Presented at SPIE Nanoscience + Engineering: August 07, 2017; Published: 29 September 2017); https://doi.org/10.1117/12.2273935.5593109723001.
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