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Organic materials are suitable for light sensing devices showing unique features such as low cost, large area, and flexibility. Moreover, transparent photodetectors are interesting for smart interfaces, windows, and display-integrated electronics. The ease of depositing ultrathin organic films with simple techniques enables low light absorbing active layers, resulting in the realization of transparent devices. Here, we demonstrate a strategy to obtain high efficiency organic photodetectors and phototransistors based on transparent active layers with a visible transmittance higher than 90%. The photoactive layer is composed of two phases, each a few nanometers thick. First, an acceptor polymer, which is a good electron-transporting material, on top of which a small molecule donor material is deposited, forming noncontinuous domains. The small molecule phase acts as a trap for holes, thus inducing a high photoconductive gain, resulting in a high photoresponsivity. The organic transparent detectors proposed here can reach very high external quantum efficiency and responsivity values, which in the case of the phototransistors can be as high as ∼74000% and 340 A W-1at 570 nm respectively, despite an absorber total thickness below 10 nm. Moreover, frequency dependent 2D photocurrent mapping allows discrimination between the contribution of a fast but inefficient and highly spatially localized photoinduced injection mechanism at the electrodes, and the onset of a slower and spatially extended photoconductive process, leading to high responsivity

Deformable mirrors are key optical elements in modern astronomical telescopes and instrumentation both for active and adaptive optical systems. Different technological approaches have been exploited for the realization of the deformable mirrors, especially for adaptive optics devices. A new approach is here presented, namely the photo-controlled deformable mirrors, where the size and density of actuators is set by an illumination pattern projected on the back side of a photoconductor. The working principle and an electric model are presented highlighting the features of the material that affect the performances of the mirror in terms of dynamic range and response time. Based on these results, a prototype exploiting ZnSe as photoconductor is reported together with its characterization.

International audience; Recently we have improved the efficiency and the output power of our optically pumped continuous-wave THz sources. These sources are based on the beating of two laser lines in a wide bandwidth photodetector. Its intrinsic nonlinear behaviour is used to produce a beatnote at the frequency difference between the two laser lines (photomixing). These photomixers are continuously tunable THz sources working at room temperature. We have developed two kinds of photomixers: GaAs-based for 0.8 mu m pumping and InP-based for 1.5 mu m pumping. On GaAs the best results has been obtained thanks to low-temperature-grown GaAs (LTG-GaAs) photoconductors (PC). Efficiency and power were optimized by designing a new type of thin PC placed in a Fabry-Perot resonator. The high impedance of the PC is a well-known limitation of this device but with our approach it was possible to reduce its impedance by a factor 100. Moreover by designing an impedance matching network it was possible to obtain 1.8 mW at 252 GHz with a total efficiency of 0.5 %. On InP the best results are obtained with uni-travelling-carrier photodiodes (UTC-PD). The device was improved by designing a new heterostructure and new semi-transparent contacts with sub-wavelength apertures. The active layer was also bonded to a silicon substrate thanks to metal thermocompression. It is demonstrated that with this approach it is possible to obtain a power of 0.7 mW at 300 GHz with a total efficiency of 0.7 %. More generally the efficiency of optically pumped terahertz sources will be discussed.

This work reports on the development and characterization of bi-dimensional deep-UV sensor arrays based on synthetic diamond to address the requirements of space-born astrophysical experiments. The material was synthesized at the University of Rome “Tor Vergata” where both heteroepitaxial polycrystalline diamond films and homoepitaxial single-crystal diamonds are grown using a tubular MWCVD reactor. The quality of chemical vapour deposited diamond was characterized by cathodoluminescence, photoluminescence, Raman spectroscopy and thermally stimulated currents. Then, suitable samples were selected and used to fabricate photoconductive single-pixel and 2D array devices by evaporating metal contacts on the growth surface. The electro-optical characterization of the devices was carried out in a wide spectral region, ranging from 120 to 2400 nm. A deuterium lamp and a 0.5 m vacuum monochromator were used to measure the detector responsivity under continuous monochromatic irradiation in the 120–250 nm spectral range, while an optical parametric oscillator tunable laser producing 5 ns pulses was used as light source from 210 up to 2400 nm. Time response, signal-to-noise ratio, responsivity and visible rejection factor were evaluated and the results are hereafter summarized.

New pin-photodiode and metal–semiconductor–metal (MSM) photoconductor devices based on diamond material have been produced showing high responsivity around 200 nm. LYRA, the Large Yield RAdiometer, will use such detectors for the first time for a solar physics space instrument. A set of measurement campaigns was carried out to obtain their XUV-to-VIS characterization (responsivity, linearity, stability and homogeneity). The diamond pin and MSM photodetectors exhibit a high responsivity of 27 mA/W around 200 nm and demonstrate a visible rejection ratio (200 nm versus 500 nm) of six and four orders of magnitude, respectively. We show that these diamond photodetectors are sensitive sensors for the wavelength range of interest (1 nm to 220 nm), stable within a few percent, with a good linearity and moderate homogeneity.

Graphene, owing to its ability to support plasmon polariton waves in the terahertz frequency range, enables the miniaturization and electrical tunability of antennas to allow wireless communications among nanosystems. One of the main challenges in the characterization and demonstration of graphene antennas is finding suitable terahertz sources to feed the antenna. This paper characterizes the performance of a graphene RF plasmonic antenna fed with a photoconductive source. The terahertz source is modeled and, by means of a full-wave EM solver, the radiated power as well as the tunable resonant frequency of the device is estimated with respect to material, laser illumination, and antenna geometry parameters. The results show that with this setup the antenna radiates terahertz pulses with an average power up to 1 μW and shows promising electrical frequency tunability., United States. Office of Naval Research. Presidential Early Career Awards for Scientists and Engineers, Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies, Spain. Ministerio de Educacion y Ciencia (FPU Grant), Catalonia (Spain) (Grant 2014SGR-1427)

In this work a novel concept based on low power semiconducting, mid infrared components and new, low cost measurement cells for use in harsh environmental conditions, such as permafrost areas, is presented. Due to the small changes of the environmen tal carbon dioxide (CO 2 ) concentration in this area a high resolution of 5 ppm CO 2 is required. The current sensor design achieves a resolution of up to 6 ppm CO 2 and offers further optimization potential at overall low costs.

In this paper, two kinds of colloidal quantum dots, PbS and HgTe, are explored for SWIR photodetectors application. The colloidal dots are prepared by hot injection chemical synthesis, with organic ligands around the dots keeping them stable in solution. For the purpose of achieving efficient carrier transport between the dots in a film, these long organic ligands are replaced by shorter, inorganic ligands. We report uniform, ultra-smooth colloidal QD films without cracks realized by dip-coating and corresponding ligand exchange on a silicon substrate. Metal-free inorganic ligands, such as OH- and S2-, are investigated to facilitate the charge carrier transport in the film. Both PbS and HgTe-based quantum dot photoconductors were fabricated on interdigitated gold electrodes. For PbS-based detectors a responsivity of 200A/W is measured at 1.5μm, due to the large internal photoconductive gain. A 2.2μm cut-off wavelength for PbS photodetectors and 2.8μm for HgTe quantum dot photodetectors are obtained.

The optical analyzers used in on-line and off-line process measurements set a large variety of special demands for optical detectors, i.e. customized detectors are needed. Both the detector (array) and its read-out circuit are affected. The typical volume for process analyzers is so low that fully customized ASICs easily become too expensive for signal recovery solutions in optical detectors. This is due to high fixed costs in ASIC development. Low Temperature Co-fired Ceramics (LTCC) substrates allow high integration grade and the smart packaging solutions needed in optical detectors. The ceramic substrate is suitable for hermetic packaging. The high integration grade is possible thanks to multilayer capability, with narrow metal strips as well as blind and buried vias which can be placed directly underneath the solder pads. Standard connection methods can be used, i.e. soldering, gluing and wire bonding for components and detector chip assembly. By using small passive components and bare chip or chip scale packaged active components, one is able to integrate the read-out functions in a small enough space. This paper briefly presents three different cases where infrared photoconductive detector arrays are attached to read-out circuitry which is made on LTCC substrate. The detector read-out hybrids are packaged in hermetic metal packages. The packages have been either non-cooled or thermoelectrically cooled. 24 element PbS, 4 by 4 element PbS and 128 element MCT cases are handled. Also an example of an integrated infrared light emitting diode array for an LEDspectrometer is presented. General feasibility analysis, including some electrical test results and the management of substrate dimensional tolerances, is given. (7 refs.)

Photoconductivity spectra of unstressed and stressed Ge:Ga detectors were measured. The experiments were performed with a polarizing step scan Fourier transform spectrometer using the synchrotron facility BESSY, which was operated in a dedicated mode with a low momentum compaction factor. By this way powerful and coherent synchrotron radiation below 50 cm -1 was generated. We observed a significant response of unstressed and stressed Ge:Ga detectors below 50 cm -1 and 25 cm -1 , respectively. This response can be attributed to transitions between bound excited states or from bound excited states to the valence band. The results indicate that in germanium detectors a fraction of the recombining holes is captured into bound excited states.

The photoresponse of different photoconductive diamond sensors to excimer laser pulses is investigated as a function of the pulse energy E over three order of magnitude. The integrated photoresponse pulse intensity changes according to the power law I ∝ E β . Initially, the pulse intensity increases linearly with the pulse energy up to a turning point, which depends on the electronic quality of the diamond film, where a sublinear behavior ( β =0.5) is found. The photoresponse pulse shape also changes accordingly, largely broadening at high pulse energies. Such behavior has been interpreted in terms of monomolecular and bimolecular recombination mechanisms acting in different pulse intensity ranges. A further reduction of β is also observed at very high intensity in less defected samples, where the induced carrier density is high enough to cause carrier–carrier scattering and mobility reduction.

A detailed investigation of diamond-based UV planar photoconductors with interdigitated contacts is presented, analyzing in particular the influence of film morphology and texturing on device performance. Photoluminescence and photocurrent spectroscopies reveal a strong correlation between structural defects and detector selectivity, whereas impurities affect photocurrent yield mainly in highly oriented materials. Responsivity measurements show that diamond-based devices give the highest UV-visible discrimination in comparison to UV-enhanced Si- and GaN-based sensors. For λ ≤225 nm, an almost linear photocurrent-light intensity relationship is observed, although, in a few cases, a superlinear dependence on illumination intensity is found. A theoretical model, capable of describing the observed field dependendence of photocurrent gain is presented, giving minority carriers lifetime and mobility in the range 0.1–1 ns and 10–300 cm2V−1s−1, respectively.

We report on colloidal PbS quantum dot near infrared photoconductors operating at low voltage. In order to maximize the device sensitivity, we exploited the advantages of different measurement techniques and methods for dark current cancellation and noise reduction including the DC volt-amperometric measurement with offset cancellation, a Wheatstone-bridge configuration and impedance measurements. We demonstrate that even photodetectors with moderate detectivity (10 9 -10 10 cmHz 1/2 /W), exhibit very large SNR.