Mid-IR Colloidal Nanocrystals

Abstract

Colloidal quantum dots presenting optoelectronic properties into the mid-infrared are reviewed with an emphasis on HgTe. Interband transitions with narrow band gap material and intraband transitions with wide band gap semiconductors can both address the infrared range of wavelengths. Semimetals are particularly promising since, by controlling the particle size, a gap can in principle be opened and tuned through the full infrared spectrum. HgTe has been quite successful recently, and colloidal synthesis has allowed the tuning of the absorption edge from 1 and 5 µm at room temperature. The cutoff wavelength and absorption coefficient of these materials have been discussed. Electrochemistry experiments have demonstrated that both n and p nanoparticles are stable. Films of the HgTe colloidal quantum dots have shown room temperature photoconduction when excited in the mid-IR. With novel processing leading to improved detectivity, these materials are becoming of significant interest as an alternative to the much more expensive epitaxial detector technologies.

MoS2–HgTe Quantum Dot Hybrid Photodetectors beyond 2 µm

“…To address these challenges, colloidal quantum dots (CQDs) with small bandgap [6][7][8][9][10] have been extensively studied as an alternative low-cost, CMOS-compatible optoelectronic platform for IR detectors. [11] HgSe and HgTe colloidal quantum dots, in particular, have been considered for IR detection due to their small, tunable bandgap through the full infrared spectrum [12][13][14][15][16] with very favourable optical properties. [13][14][15][16][17][18][19][20][21] Photoconductive detectors based on those QDs have also been reported based on spin-coating, spray-casting or inkjet-printing techniques on integrated electrode structures.…”

“…[11] HgSe and HgTe colloidal quantum dots, in particular, have been considered for IR detection due to their small, tunable bandgap through the full infrared spectrum [12][13][14][15][16] with very favourable optical properties. [13][14][15][16][17][18][19][20][21] Photoconductive detectors based on those QDs have also been reported based on spin-coating, spray-casting or inkjet-printing techniques on integrated electrode structures. [12,[22][23][24][25][26][27][28] The responsivity in those prior reports, however, has been limited to tens of mA/W due to the low carrier mobility, lack of sensitizing centers and the consequent absence of photoconductive gain in contrast to what has been extensively reported in PbS-based CQD photoconductors.…”

Infrared Emitting HgTe Quantum Dots and Their Waveguide and Optoelectronic Devices

“…Hitherto they had experienced difficulty making material with room temperature PL emission much greater than 5000 nm (though with cooling 7000 nm could be achieved [87]). With their standard organic method particles with diameters above 15 nm tended to have poor morphology (branched and irregular shapes) and consequently poor emission and electronic properties.…”

Colloidal and Epitaxial Quantum Dot Infrared Photodetectors: Growth, Performance, and Comparison

“…These QDs can have diameter of about 2 nm to 10 nm. The first routes to successful CQD synthesis were based on aqueous and ionic chemistry (158)(159)(160)(161)(162)(163), where the fundamental principles governing the synthesis of QDs, as well as the understanding of electronic structure, have been explained clearly.…”