Infrared multispectral imaging is attracting great interest with the increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information. However, the ...widespread use of such detectors is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices. Here, we demonstrate a two-terminal CQD dual-band detector, which provides a bias-switchable spectral response in two distinct bands. A vertical stack of two rectifying junctions in a back-to-back diode configuration is created by engineering a strong and spatially stable doping process. By controlling the bias polarity and magnitude, the detector can be rapidly switched between short-wave infrared and mid-wave infrared at modulation frequencies up to 100 kHz with D* above 1010 jones at cryogenic temperature. The detector performance is illustrated by dual-band infrared imaging and remote temperature monitoring.Colloidal quantum dot detectors, switchable between short-wave infrared and mid-wave infrared, are demonstrated.
Electronic eye cameras are receiving increasing interest due to their unique advantages such as wide field of view, low aberrations, and simple imaging optics compared to conventional planar focal ...plane arrays. However, the spectral sensing ranges of most electronic eyes are confined to the visible, which is limited by the energy gaps of the sensing materials and by fabrication obstacles. Here, a potential route leading to infrared electronic eyes is demonstrated by exploring flexible colloidal quantum dot (CQD) photovoltaic detectors. Benefitting from their tunable optical response and the ease of fabrication as solution processable materials, mercury telluride (HgTe) CQD detectors with mechanical flexibility, wide spectral sensing range, fast response, and high detectivity are demonstrated. A strategy is provided to further enhance the light absorption in flexible detectors by integrating a Fabry–Perot resonant cavity. Integrated short‐wave IR detectors on flexible substrates have peak D* of 7.5 × 1010 Jones at 2.2 µm at room temperature and promise the development of infrared electronic eyes with high‐resolution imaging capability. Finally, infrared images are captured with the flexible CQD detectors at varying bending conditions, showing a practical approach to sensitive infrared electronic eyes beyond the visible range.
A potential route leading to infrared electronic eyes is demonstrated by exploring flexible colloidal quantum dot (CQD) photovoltaic detectors with mechanical flexibility, wide spectral sensing range, fast response, and high detectivity. Infrared images are captured with the flexible CQDs detectors at varying bending conditions, showing a practical approach to sensitive infrared electronic eyes beyond visible.
Improving charge mobility in quantum dot (QD) films is important for the performance of photodetectors, solar cells and light-emitting diodes. However, these applications also require preservation of ...well defined QD electronic states and optical transitions. Here, we present HgTe QD films that show high mobility for charges transported through discrete QD states. A hybrid surface passivation process efficiently eliminates surface states, provides tunable air-stable n and p doping and enables hysteresis-free filling of QD states evidenced by strong conductance modulation. QD films dried at room temperature without any post-treatments exhibit mobility up to μ ~ 8 cm
V
s
at a low carrier density of less than one electron per QD, band-like behaviour down to 77 K, and similar drift and Hall mobilities at all temperatures. This unprecedented set of electronic properties raises important questions about the delocalization and hopping mechanisms for transport in QD solids, and introduces opportunities for improving QD technologies.
The potential detectivity limits of HgTe nanocrystal quantum dot photodetectors are examined using a microscopic detailed balance model of carrier generation and recombination. We find that even with ...the fast nonradiative recombination typical of present materials, HgTe quantum dot solids can support equilibrium detectivities which are close to those of Auger-limited HgCdTe crystals. It is further shown that if such nonradiative recombination can be reduced so that Auger-limited performance is achieved, the confluence of fast radiative and slow Auger recombination should enable large upper limits on achievable detectivities when compared to HgCdTe. These results are discussed in the context of future advances in infrared photodetection with nanocrystal quantum dots.
Three‐dimensional (3D) subwavelength nanostructures have emerged and triggered tremendous excitement because of their advantages over the two‐dimensional (2D) counterparts in fields of plasmonics, ...photonic crystals, and metamaterials. However, the fabrication and integration of 3D nanophotonic structures with colloidal quantum dots (CQDs) faces several technological obstacles, as conventional lithographic and etching techniques may affect the surface chemistry of colloidal nanomaterials. Here, the direct fabrication of functional quasi‐3D nanophotonic structures into CQD films is demonstrated by one‐step imprinting with well‐controlled precision in both vertical and lateral directions. To showcase the potential of this technique, diffraction gratings, bilayer wire‐grid polarizers, and resonant metal mesh long‐pass filters are imprinted on CQD films without degrading the optical and electrical properties of CQD. Furthermore, a dual‐diode CQD detector into an unprecedented mid‐wave infrared two‐channel polarization detector is functionalized by embedding an imprinted bilayer wire‐grid polarizer within the CQDs. The results show that this approach offers a feasible pathway to combine quasi‐3D nanostructures with colloidal materials‐based optoelectronics and access a new level of light manipulation.
The direct fabrication of functional quasi‐3D nanophotonic structures into colloidal quantum dots (CQDs) films is demonstrated by one‐step imprinting with well‐controlled precision in both vertical and lateral directions. Functional optical structures on CQDs or within CQDs are fabricated without degrading the optical and electrical properties of CQDs.
Slow Electron Cooling in Colloidal Quantum Dots Pandey, Anshu; Guyot-Sionnest, Philippe
Science (American Association for the Advancement of Science),
11/2008, Letnik:
322, Številka:
5903
Journal Article
Recenzirano
Hot electrons in semiconductors lose their energy very quickly (within picoseconds) to lattice vibrations. Slowing this energy loss could prove useful for more efficient photovoltaic or infrared ...devices. With their well-separated electronic states, quantum dots should display slow relaxation, but other mechanisms have made it difficult to observe. We report slow intraband relaxation (>1 nanosecond) in colloidal quantum dots. The small cadmium selenide (CdSe) dots, with an intraband energy separation of ~0.25 electron volts, are capped by an epitaxial zinc selenide (ZnSe) shell. The shell is terminated by a CdSe passivating layer to remove electron traps and is covered by ligands of low infrared absorbance (alkane thiols) at the intraband energy. We found that relaxation is markedly slowed with increasing ZnSe shell thickness.
Colloidal quantum dots (CQDs) with a band gap tunable in the mid-wave infrared (MWIR) region provide a cheap alternative to epitaxial commercial photodetectors such as HgCdTe (MCT) and InSb. ...Photoconductive HgTe CQD devices have demonstrated the potential of CQDs for MWIR photodetection but face limitations in speed and sensitivity. Recently, a proof-of-concept HgTe photovoltaic (PV) detector was realized, achieving background-limited infrared photodetection at cryogenic temperatures. Using a modified PV device architecture, we report up to 2 orders of magnitude improvement in the sensitivity of the HgTe CQD photodetectors. A solid-state cation exchange method was introduced during device fabrication to chemically modify the interface potential, leading to an order of magnitude improvement of external quantum efficiency at room temperature. At 230 K, the HgTe CQD photodetectors reported here achieve a sensitivity of 109 Jones with a cutoff wavelength between 4 and 5 μm, which is comparable to that of commercial photodetectors. In addition to the chemical treatment, a thin-film interference structure was devised using an optical spacer to achieve near unity internal quantum efficiency upon reducing the operating temperature. The enhanced sensitivity of the HgTe CQD photodetectors reported here should motivate interest in a cheap, solution-processed MWIR photodetector for applications extending beyond research and military defense.
HgTe colloidal quantum dots (CQD) in an inorganic As2S3 matrix allow 100‐fold higher mobility with optimized transport properties compared to HgTe‐organic CQD film while remaining intrinsic. The ...material's electronic properties are measured by field effect transistors as a function of temperature and the responsivity and detectivity of the mid‐IR photoconductors are discussed.
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