Mid-infrared Intraband Transitions in InAs Colloidal Quantum Dots

III-V Colloidal quantum dots (CQDs) have been widely studied for their applications as detectors and emitters from visible to short-wave infrared. They might also be used in the mid-infrared if they can be stably <i>n</i>-doped to access their intraband transitions. Mid-infrared intraband transitions are therefore studied for InAs, InAs/InP, and InAs/ZnSe CQDs with an energy gap of 1.4 μm. Using electrochemistry, the quantum dot films show state-resolved mobility, state-resolved electron filling, and intraband absorption in the 3-8 μm range. The InAs/ZnSe films need a more reducing potential than the InAs, but the InAs/InP films need a lower reduction potential. As a result, we found that dry films of InAs/InP dots show stable <i>n</i>-doping of the 1S_e state, with a steady-state intraband absorption in the 3-5 μm range and intraband luminescence at 5 μm. With low toxicity, high thermal stability, and stable <i>n</i>-doping, InAs quantum dots become an interesting material for mid-infrared applications.