Shape-Controlled HgTe Quantum Dots for Room-Temperature Mid-Infrared Photoconductors

HgTe quantum dots are synthesized as relatively monodispersed nanoparticles with spherical, partially spherical, and tetrahedral shapes. The colloidal stability is in the order spherical ≈ partially spherical > tetrahedral, and the first exciton strength is in the order tetrahedral ≈ partially spherical > spherical. Intrinsic films are made using nonpolar and polar ligand exchange and treated with a mild etching solution of HgCl2. They are tested as mid-IR photoconductors with a 4 μm cutoff. For all films, the carrier lifetime is geminate recombination-limited between 250 and 330 K. Partially spherical dots emerge with the longer carrier lifetime and higher signal-to-noise ratio. 200 nm thick films deposited on an optical resonant grating architecture with a 1.5 μm channel gap achieve a saturated external quantum efficiency of 65% at 2 V bias, for light polarized across the gap, with a room temperature detectivity of 0.8 × 1010 Jones at 2450 cm–1, 10 kHz and 0.27 V bias, and response time of about 200 ns. This is the highest room temperature detectivity achieved for HgTe dots at 2450 cm–1 and below.