Colloidal quantum dots for mid-infrared detection (Presentation Recording)

Colloidal quantum dots present an opportunity as infrared and liquid processed materials. Initial results in 2011 showed mid-infrared detection with HgTe colloidal quantum dots in the mi-IR range, 3-5 microns. This has been now extended to the long-wave IR, 8-12 microns. The infrared response from the HgTe colloidal quantum dots arises from the absorption of light across the gap created by the confinement. The large dots absorbing the LWIR are about 20 nm in size and the size dispersion will need improvements. While Interband absorption requires the material to be zero or small-gap semiconductors, intraband transitions have no such limitations. However, this requires doped colloidal quantum dots. Two colloidal quantum dot materials, the small gap (0.6 eV) b-HgS and the zero-gap HgSe turn out to be stably doped with electrons. This has led to the observation of Mid-IR intraband photoconduction in both systems and alternative materials for IR detection. There are several basic challenges, besides fabrication and reliability. The proximity of the surface from the excitation leads to very short excited lifetimes due to nonradiative processes. Controlling the surface will be the avenue to lengthen the lifetime, while plasmonic coupling may lead to shorter radiative lifetime. Since the surface is easily chemically modified, it also leads to strong changes in the Fermi level and this will need to be controlled. In this talk, I will describe my understanding of the potential and limitations of this material approach to infrared detection, while discussing aspects of transport, photoluminescence, doping and photovoltaic responses.