Carrier dynamics in small-gap mercury chalcogenide colloidal quantum dots

Devices based on small-gap mercury chalcogenide semiconductor nanocrystal inks have recently demonstrated increasingly high performance photodetection in the short and mid-wave infrared. These new colloidal inks are generating increasing interest because they could provide higher operating temperatures and vastly reduced costs compared to the current epitaxially-grown devices. However, in order to further increase detector operation temperatures and use these materials as infrared light sources, more detailed understandings of the carrier dynamics are required. Described here are picosecond mid-infrared absorption and emission studies of HgTe and HgSe colloidal quantum dots focusing on multicarrier nonradiative relaxation. Comparisons of the interband and intraband transitions in intrinsic and n-type systems reveal phenomena such as suppression of Auger relaxation in nanoparticles vs. bulk materials and slow or absent Auger relaxation in n-type quantum dots. Yet, the measured lifetimes are still limited by other nonradiative pathways that appear unique to small-gap nanomaterials. The deeper understanding of nonradiative relaxation in small-gap nanocrystals afforded by these experiments provides a path towards realizing high performance infrared photodetection near room temperature and robust mid-infrared light emission with colloidal quantum dots.