Mid-infrared cascade intraband electroluminescence with HgSe–CdSe core–shell colloidal quantum dots

Efficient infrared light sources are needed for machine vision and molecular sensing. In the visible, electroluminescence from colloidal quantum dots is highly efficient, wavelength tunable and cost effective, which motivates using the same approach in the infrared. Despite the promising performances of colloidal quantum dots light-emitting diodes in the near-infrared, mid-infrared devices show quantum efficiencies of about 0.1% due to the much weaker emission. Moreover, these devices relied exclusively on the interband transition, restricting the possible materials. Here we show electroluminescence at 5 µm using the intraband transition between 1Se and 1Pe states within the conduction band of core–shell HgSe–CdSe colloidal quantum dots. The 4.5% quantum efficiency approaches that of commercial epitaxial cascade quantum well light-emitting diodes. The high emission efficiency and the electrical characteristics support a similar cascade process where the electrons, driven by the bias across the device, repeatedly tunnel into 1Pe and relax to 1Se as they hop from quantum dot to quantum dot.