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

Intraband electroluminescence (EL) from n-doped core-shell HgSe-CdSe colloidal quantum dots is observed around the wavelength of 5 & mu;m. The measured EL quantum efficiency is 4.5% at the injection current of 2 A cm(-2), benefiting from the cascade effect. The power efficiency is 0.05%. 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 & mu;m using the intraband transition between 1S(e) and 1P(e) 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 1P(e) and relax to 1S(e) as they hop from quantum dot to quantum dot.

Automated summary

Intraband electroluminescence from n-doped core-shell HgSe-CdSe colloidal quantum dots is observed around the wavelength of 5μm. The measured EL quantum efficiency is 4.5% at the injection current of 2 A cm(-2), benefiting from the cascade effect. Efficient infrared light sources are needed for machine vision and molecular sensing, and the application of colloidal quantum dots in the infrared region is promising. However, mid-infrared devices currently have low quantum efficiencies and rely exclusively on interband transitions. In this study, we demonstrate efficient intraband electroluminescence at 5μm using core-shell HgSe-CdSe colloidal quantum dots, achieving a quantum efficiency comparable to commercial epitaxial cascade quantum well light-emitting diodes.