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Ultra-broad spectral detection is critical for several technological applications in imaging, sensing, spectroscopy, and communication. Carbon nanotube (CNT) films are a promising material for ultra-broadband photodetectors because their absorption spectra cover the entire ultraviolet to the terahertz range. However, because of the high binding energy of excitons, photodetectors based on CNT films always require a strong electric field, asymmetric electrical contacts, or hybrid structures with other materials. Here, we report an ultra-broadband bolometric photodetector based on a suspended CNT film. With an abundant distribution of tube diameters and an appropriate morphology (spider web-like), the CNT films display a strong absorption spectrum from the ultraviolet up to the terahertz region. Under illumination, heat generated from the electron–photon interaction dominates the photoresponse of our devices. For small changes in temperature, the photocurrent shows a convincing linear dependence with the absorbed light’s power across 3 orders of magnitude. When the channel length is reduced to 100 μm, the device demonstrates a high performance with an ultraviolet responsivity of up to 0.58 A/W with a bias voltage of 0.2 V and a short response time of ∼150 μs in vacuum, which is better than that of many other photodetectors based on CNTs. Moreover, this performance could be further enhanced by optimization.

Photothermoelectric materials have important applications in many fields. Here, we joined a silver nanostructure film and a carbon nanotube film by van der Waals force to form a heterojunction, which shows excellent photothermal and photoelectric conversion properties. The local temperature difference and the output photovoltage increase rapidly when the heterojunction is irradiated by lasers with wavelengths ranging from ultraviolet to terahertz. The maximum temperature difference reaches 215.9 K, which is significantly higher than that of other photothermoelectric materials reported in the literature. The photothermal and photoelectric responsivity depend on the wavelength of lasers, which are 175~601 K W-1 and 9.35~40.4 mV W-1, respectively. We demonstrate that light absorption of the carbon nanotube is enhanced by local surface plasmons, and the output photovoltage is dominated by Seebeck effect. The proposed heterostructure can be used as high-efficiency sensitive photothermal materials or as ultra-wideband fast-response photoelectric materials.

We investigate the photon emission in coupled quantum dots based on symmetry considerations. With the help of a new theorem we proved, we reveal the origin of the various emission patterns, which is the combinative symmetry in the time domain and spectrum domain. We are able to tailor the emission patterns and obtain emission spectra with odd harmonics only, even harmonics only, both odd and even harmonic components, or even the quenching of all components. These interesting emission patterns can be obtained in experiments by careful design of the nanostructures, which are of many applications in optical-electric nanodevices.

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An ultra-broadband upconversion device is demonstrated by direct tandem integration of a p-type GaAs/AlxGa1-xAs ratchet photodetector (RP) with a GaAs double heterojunction light emitting diode (DH-LED) using the molecular beam epitaxy. An ultra-broadband photoresponse from the terahertz (THz) to near-infrared (NIR) region (4–200 THz) was realized, which covered a much wider frequency range compared with existing upconversion devices. Broadband IR/THz radiation from a 1000 K blackbody was upconverted into NIR light that could be detected via a commercial Si-based device. The normal incidence absorption of the RP simplified the structure of the RP-LED device and made it more compact than the intersubband transition-based upconverters. In addition to upconversion, the proposed upconverter was investigated as a photovoltaic detector in the infrared region (detection range from 18 to 150 THz) based on the ratchet effect without an applied bias voltage.