Room-temperature operation is essential for any optoelectronics technology that aims to provide low-cost, compact systems for widespread applications. A recent technological advance in this direction is bolometric detection for thermal imaging, which has achieved relatively high sensitivity and video rates (about 60 hertz) at room temperature. However, owing to thermally induced dark current, room-temperature operation is still a great challenge for semiconductor photodetectors targeting the wavelength band between 8 and 12 micrometres, and all relevant applications, such as imaging, environmental remote sensing and laser-based free-space communication, have been realized at low temperatures. For these devices, high sensitivity and high speed have never been compatible with high-temperature operation. Here we show that a long-wavelength (nine micrometres) infrared quantum-well photodetector fabricated from a metamaterial made of sub-wavelength metallic resonators exhibits strongly enhanced performance with respect to the state of the art up to room temperature. This occurs because the photonic collection area of each resonator is much larger than its electrical area, thus substantially reducing the dark current of the device. Furthermore, we show that our photonic architecture overcomes intrinsic limitations of the material, such as the drop of the electronic drift velocity with temperature, which constrains conventional geometries at cryogenic operation. Finally, the reduced physical area of the device and its increased responsivity allow us to take advantage of the intrinsic high-frequency response of the quantum detector at room temperature. By mixing the frequencies of two quantum-cascade lasers on the detector, which acts as a heterodyne receiver, we have measured a high-frequency signal, above four gigahertz (GHz). Therefore, these wide-band uncooled detectors could benefit technologies such as high-speed (gigabits per second) multichannel coherent data transfer and high-precision molecular spectroscopy.

We report on the implementation of 5 THz quantum well photodetector exploiting a patch antenna cavity array. The benefit of our plasmonic architecture on the detector performance is assessed by comparing it with detectors made using the same quantum well absorbing region, but processed into a standard 45° polished facet mesa. Our results demonstrate a clear improvement in responsivity, polarization insensitivity, and background limited performance. Peak detectivities in excess of 5 × 1012 cmHz1/2/W have been obtained, a value comparable with that of the best cryogenic cooled bolometers.

In this article we have investigated two important properties of metallic nano-resonators which can substantially improve the temperature performances of infrared quantum detectors. The first is the antenna effect that increases the effective surface of photon collection and the second is the subwavelength metallic confinement that compresses radiation into very small volumes of interaction. To quantify our analysis we have defined and discussed two figures of merit, the collection area A coll and the focusing factor F. Both quantities depend solely on the geometrical parameters of the structure and can be applied to improve the performance of any detector active region. In the last part, we describe three-dimensional electronic nano-resonators that provide highly subwavelength confinement of the electromagnetic energy, beyond the microcavity limits and illustrate that these device architectures have a tremendous potential to increase the temperature of operation of infrared quantum detectors.Plasmonic nanostructures constitute an important and attractive research topic in the domain of photonics and nano-electronics [1,2]. They are widely investigated in different ranges of the electromagnetic spectrum, starting from the visible [3,4], through the infrared [5, 6] and down to the terahertz frequencies [7,8]. Plasmonic nanostructure have been already exploited as an efficient mean to compress light in a sub-wavelength region of the space [7,9] in order to improve the performances of optoelectronic devices, both as efficient absorbers [10][11][12][13][14][15][16][17][18][19] or emitters [20][21][22][23]. In particular, a fundamental property of a resonant absorber, such as plasmonic nanoparticle, is its ability to gather photons from a collection area A coll that can be much larger than its geometrical cross section σ [24], as illustrated in figure 1. The ultimate limit of this phenomenon is found in the quantum transition of a single atom at the resonant wavelength λ, where A coll can be identified with an absorption cross section A coll =3λ 2 /4π [25]. While this concept is widely used in antenna-coupled devices in the low-frequency part of the electromagnetic spectrum [26], it is clearly underexploited for infrared and optical quantum detectors of radiation. In particular, we have recently illustrated that in the mid-infrared and THz frequencies ranges, antenna-coupled quantum well infrared photo-detectors (QWIPs) can lead to a substantial reduction of the dark current with respect to the photocurrent signal [15,16]. High temperature, high performance photodetectors in the mid-and far-infrared is an actual issue that would enable the realization of sensitive thermal imaging setups with a broad range of applications [27]. Resonant structures, such as cavities and photonic cristals have already been envisioned for the enhancement for both intrasubband [28] and intersubband photodetectors [20,29], however in these studies the antenna effect was not taken into account.In the current work, we provide a quantitative...

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Quantum cascade detectors (QCD) are unipolar infrared devices where the transport of the photo excited carriers takes place through confined electronic states, without an applied bias. In this photovoltaic mode, the detector's noise is not dominated by a dark shot noise process, therefore, performances are less degraded at high temperature with respect to photoconductive detectors. This work describes a 9 µm QCD embedded into a patchantenna metamaterial which operates with state-of-theart performances. The metamaterial gathers photons on a collection area, Acoll, much bigger than the geometrical area of the detector, improving the signal to noise ratio up to room temperature. The background-limited detectivity at 83 K is 5.5 x 10 10 cm Hz 1/2 W -1 , while at room temperature, the responsivity is 50 mA/W at 0 V bias. Patch antenna QCD is an ideal receiver for a heterodyne detection set-up, where a signal at a frequency 1.4 GHz and T=295 K is reported as first demonstration of uncooled 9µm photovoltaic receivers with GHz electrical bandwidth. These findings guide the research towards uncooled IR quantum limited detection.

High-speed, room-temperature, quantum well infrared photodetectors (QWIPs) at λ ∼ 4.9 μm have been realized in a strain compensated In 0.1 Ga 0.9 As/Al 0.4 Ga 0.6 As heterostructure grown on a GaAs substrate. The high-speed properties at room temperature have been optimized by using a specifically designed air-bridge structure, which greatly reduces the time constant of the effective RC circuit, thus, allowing transmission and detection of high-frequency signals. By modulating a high-speed quantum cascade laser (QCL) centered at λ ∼ 4.7 μm, we were able to record a modulation of the photocurrent up to ∼26 GHz, which is limited by our setup. At 300 K and under a bias voltage of −5 V our device shows high responsivity and detectivity of 100 mA/W and 1 × 10 7 Jones, respectively. The developed high-performance QWIPs at this wavelength are highly promising for optical heterodyne measurement, high-speed free space communications in microwave optical links and frequency comb QCLs characterisations.

A nonlinear intersubband polaritonic metasurface designed for difference‐frequency generation that provides a practical level of nonlinear response under continuous wave illumination is reported. An effective nonlinear susceptibility of up to 340 nm V−1 is measured experimentally. Approximately 0.3% of λ = 5.4 µm photons are downconverted to λ = 12.9 µm photons at the focal spot in the experiment. This work indicates that the ultrathin metasurface devices may provide a versatile nonlinear element for frequency down‐ and upconversion in a relatively broad spectral range and without phase‐matching constrains of traditional bulk nonlinear crystals.