High‐Performance Photodetectors of Quasi‐2‐Dimensional Epitaxially‐Connected Quantum Dot Superlattices

ABSTRACT Colloidal semiconductor quantum dots (QDs) are among the promising materials for optoelectronic device applications, including photodetectors. Their size‐tunable bandgap enables wide‐range wavelength photodetection from the visible to the mid‐infrared regime. Most recently, the realization of epitaxially‐connected quantum dot superlattices (QDSLs) addresses one of the critical challenges associated with assemblies of QDs and their electronic transport. These epitaxially‐connected QDSLs demonstrated the possibility of delocalized charge transport, which could improve the electrical transport performance of QD‐based devices. On the other hand, delocalized charge carriers might affect the quantum confinement effect, potentially reducing the merits of QDs for optoelectronic device performance. Here, we demonstrate high‐performance photodetectors based on a monolayer of quasi‐2D epitaxially connected PbS QDSLs, exhibiting higher responsivity and detectivity than those of conventional short‐ligand‐capped QD assemblies. The remarkable photodetection enhancement can be indicated from several aspects: (i) the light intensity‐dependent characteristics reveal evidence of a low trap density within the epitaxially‐connected superlattice, (ii) the time‐resolved measurements show a faster response time and a two‐step charge carrier dynamic, (iii) the wavelength‐dependent analysis further suggests the occurrence of multiple exciton generation under high‐energy photon excitation. These findings establish the epitaxially‐connected QDSL as an optoelectronic metamaterial, an up‐and‐coming candidate for next‐generation, high‐performance photodetectors.