Publication date: 15th May 2025
HgTe colloidal quantum dots (CQD) are promising for mid-infrared photodetectors, and they can already be background limited at cryogenic temperatures. There is much interest in room temperature photodetectors, and there is still much opportunity to increase performance. Progress should arise from improving the HgTe CQD synthesis and investigating various shapes and surface ligand chemistry.
This work compares films of rather monodispersed spherical, partially spherical, and tetrahedral shapes of HgTe CQDs, with similar mid-infrared cut-off around 2500cm-1, as well and polar and non-polar surface ligands exchange. The absorption spectra, photoluminescence, photoreponsivity, carrier mobility, and detectivity, all show subtle differences. Overall, the best detectivity at 300K is obtained with partially spherical HgTe CQDs. This is rationalized by a compromise, between a relatively sharper band edge, due to a stronger first interband exciton than spherical dots, and a greater colloidal stability, due to smaller facets than tetrahedral dots. It was also found that treating the films with HgCl₂ enhances photoluminescence, increases carrier mobility, and reduces low-frequency 1/f noise. Mechanistic analysis indicates that geminate recombination is the dominant carrier loss pathway, regardless of dot shape or surface treatment, around room temperature. Overall, the polar-exchanged partially-spherical HgTe CQDs give the highest detectivity in the mid-IR so far at room temperature.
The study used simply dried films, but there is a growing interest in exploring the possible benefits of extended superlattices. The self-assembly of spherical HgTe QD in superlattices is demonstrated and their optoelectronic properties are investigated.
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