Colloidal nanocrystals (NCs), especially lead sulfide NCs, are promising candidates for solution-processed next-generation photodetectors with high-speed operation frequencies. However, the intrinsic response time of PbS-NC photodetectors, which is the material-specific physical limit, is still elusive, as the reported response times are typically limited by the device geometry. Here, we use the two-pulse coincidence photoresponse technique to identify the intrinsic response time of 1,2-ethanedithiol-functionalized PbS-NC photodetectors after femtosecond-pulsed 1560 nm excitation. We obtain an intrinsic response time of ∼1 ns, indicating an intrinsic bandwidth of ∼0.55 GHz as the material-specific limit. Examination of the dependence on laser power, gating, bias, temperature, channel length, and environmental conditions suggest that Auger recombination, assisted by NC-surface defects, is the dominant mechanism. Accordingly, the intrinsic response time might further be tuned by specifically controlling the ligand coverage and trap states. Thus, PbS-NC photodetectors are feasible for gigahertz optical communication in the third telecommunication window.

We investigate the time-resolved photoelectric response of WSe2 crystals on glass and flexible polyimide substrates to determine the effect of a changed dielectric environment on the speed of the photodetectors....

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