Intraband cascade electroluminescence with weakly n-doped HgTe colloidal quantum dots

Room temperature 6 mu m intraband cascade electroluminescence (EL) is demonstrated with lightly n-doped HgTe colloidal quantum dots of similar to 8 nm diameter deposited on interdigitated electrodes in a metal-insulator-metal device. With quantum dot films of similar to 150 nm thickness made by solid-state-ligand-exchange, the devices emit at 1600 cm(-1) (6.25 mu m), with a spectral width of 200 cm(-1), determined by the overlap of the 1S(e)-1P(e) intraband transition of the quantum dots and the substrate photonic resonance. At the maximum current used of 20 mA, the bias was 30 V, the external quantum efficiency was 2.7%, and the power conversion efficiency was 0.025%. Adding gold nano-antennas between the electrodes broadened the emission and increased the quantum efficiency to 4.4% and the power efficiency to 0.036%. For these films, the doping was about 0.1 electron/dot, the electron mobility was 0.02 cm(2) V-1 s(-1), and the maximum current density was 0.04 kA cm(-2). Higher mobility films made by solution ligand exchange show a 20-fold increase in current density and a 10-fold decrease in EL efficiencies. Electroluminescence with weak doping is interesting for eventually achieving electrically driven stimulated emission, and the requirements for population inversion and lasing are discussed.