Sub-ns intrinsic response time of PbS nanocrystal IR-photodetectors

TL;DR

This study reveals that PbS nanocrystal photodetectors have an intrinsic response time of about 1 nanosecond, setting a fundamental speed limit for their use in high-frequency optical communication.

Contribution

The paper identifies the intrinsic response time of PbS nanocrystal photodetectors using a novel two-pulse technique, providing insights into their fundamental speed limits.

Findings

Intrinsic response time of ~1 ns measured

Bandwidth limit of ~0.55 GHz established

Surface defects and ligand coverage influence response time

Abstract

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 fs-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.