Ultrafast Charge Carrier Dynamics and Transport Characteristics in HgTe Quantum Dots

Abstract

We investigate the charge carrier dynamics in HgTe quantum dots emitting in the second near-infrared window (1000−2500 nm). To provide a link between fundamental physics and practical application, we made consistent studies of the charge carrier dynamics evolution for quantum dots in different states: colloidal solutions of quantum dots capped with a long-chain ligand; thin films made from them; and finally, exchanged to short-chain ligand films suitable for field effect transistor based devices. Ultrafast transient absorption spectroscopy reveals an ultralow Auger-related nonradiative relaxation threshold at 0.1 exciton per quantum dot, both in colloidal solutions and solid films, with a rate of 30 ns −1 . The exchange from long-to short-chain ligands causing closer packing of the HgTe quantum dots leads to a strong increase of the Auger recombination rate of up to 100 ns −1 . The competition between the Auger process and excitonic recombination significantly affects the performance of HgTe-based thin film photodetectors operating at room temperature, resulting in a 2 orders of magnitude drop in responsivity when the excitation flux was increased from 0.01 to 5 W•cm −2 .

Plasmon‐Assisted Directional Infrared Photoluminescence of HgTe Nanocrystals

“…[ 2 ] Its lack of bulk bandgap enables a unique tunability: from the visible for the strongly confined form of HgTe (i.e., the 2D nanoplatelets [ 3,4 ] ) to the THz range [ 5 ] for the largest particles with sizes above the Bohr radius (40 nm in HgTe [ 6 ] ). Furthermore, this spectral tunability is no longer limited to absorption, and luminescence can be obtained from 0.8 to 5 µm [ 7–11 ] and, more recently, has also been demonstrated in the THz range. [ 12 ]…”

Cation-Exchange-Derived Wurtzite HgTe Nanorods for Sensitive Photodetection in the Short-Wavelength Infrared Range

“…This mobility value is lower than the numbers reported in refs 5, 12, and 47, yet it is several orders of magnitude higher than that of the HgTe quantum dots reported by our group previously. 6,48 The higher activation energies of HgTe NRs capped with S 2− and EDT (Figure S11b) are likely due to uncontrollable and fast liquid-or solid-state exchange procedures, respectively. One should notice that HgTe NRs capped with I − ions are colloidally less stable in solution, which has a significant impact on the film quality and lead to poorer performance of the resulting devices.…”

“…HgTe nanocrystals have attracted a lot of interest among researchers in recent years, showing a great potential as active components in infrared (IR) optoelectronics, such as IR photodetectors − and light-emitting diodes. − In comparison to lead chalcogenides as the most widely studied near-IR emitting semiconductors on the nanoscale, HgTe offers a more convenient band-gap tunability from around 1.5 eV 10 to virtually zero owing to the semimetal nature of HgTe and its large Bohr radius (40 nm) . Additionally, films of HgTe quantum dots were reported to have high carrier mobilities (>1 cm 2 ·V –1 s –1 ) , and free carrier concentrations (>1 per nanocrystal owing to self-doping) .…”

Laser‐Printed Plasmonic Metasurface Supporting Bound States in the Continuum Enhances and Shapes Infrared Spontaneous Emission of Coupled HgTe Quantum Dots

“…This leads to a reduced efficiency of the near‐field enhancement for the upper QD layers, an increasing mismatch between λ R and λ PL (Figure S4, Supporting Information), and a strengthening of the nonradiative decay channels arising from non‐resonant energy transfer between neighboring QDs. [ 13 ] Notably, the highest (up to 13‐fold) PL enhancement was observed for the largest NA of the collecting optics, suggesting a modification of the emission directivity from the QD layer capping the plasmonic metasurface. This inference is also reflected from a comparison of the results of the emission directivity modeling of dipolar emitters capping the plasmonic metasurface (Figure 2d).…”