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The interest in nanowire photodetectors stems from their unique properties, such as high sensitivity, fast response times, and compatibility with integrated circuit technology, making them well suited for diverse application domains, including solar cells, cameras, biomedical sensors, and communication systems. Implementing devices based on nanowire ensembles requires a planarization process, which must be conceived to preserve the advantages of the nanowire geometry. This is particularly challenging in the ultraviolet (UV) range, where spin coating with hydrogen silsesquioxane (HSQ) appears as an interesting approach in terms of transmittance and refractive index. Here, we report a comprehensive study on UV photodetectors based on GaN or AlGaN/AlN nanowire ensembles encapsulated in HSQ. We show that this material is efficient for passivating the nanowire surface, and it introduces a compressive strain in the nanowires and preserves their radiative efficiency. We discuss the final performance of planarized UV photodetectors based on three kinds of nanowire ensembles: (i) non-intentionally doped (nid) GaN nanowires, (ii) Ge-doped GaN nanowires, and (iii) nid GaN nanowires terminated with an AlGaN/AlN superlattice. The incorporation of the superlattice allows tuning the spectral response with bias, which can enhance the carrier collection from the AlGaN/AlN superlattice or from the GaN stem. In all the cases, the performance of the planarized devices remains determined by the nanowire nature since their characteristics in terms of linearity and spectral selectivity are closer to those demonstrated in single nanowires than those of planar devices. Thus, the visible rejection is several orders of magnitude, and there is no indication of persistent photocurrent, which makes all the samples suitable for UV-selective photodetection applications. [ABSTRACT FROM AUTHOR]

Abstract The organic photodetectors (OPDs) can be proposed in two different ways: a photodiode system or a photoconductor type, where the external quantum efficiency (EQE) cannot exceed 100% in the former one but it can in the latter one. Whether the electrode-active layer contacts can inject at least one kind of carriers is the critical factor to determine the specific photodetector type. Therefore, the role of electrode/semiconductor contacts in the OPDs needs to be fully understood. In this work, we demonstrate the high performance OPDs based on PTB7:PC 71 BM bulk heterojunction with the different top metal electrodes (Ag, Au, Al) by incorporating the PFN modified ITO electrode. Ultraviolet photoelectron spectroscopy shows that the work function of ITO is effectively reduced from 4.7 eV to 4.1 eV due to the PFN dipole layer. Combined with current density-voltage characteristics and the EQE, the results indicate the devices show different working modes: a photodiode or photoconductor type OPDs. For the Ag or Au electrode device, the photogenerated charges can rapidly transport to the corresponding electrodes and then to be collected under reverse bias, which meets the photodiode type. However, the Al electrode device with more than 100% EQE presents the photoconductor mode, which is contributed to that the photogenerated charges accumulate around the interface between the PFN layer and the active layer, and then create a tunneling charge injection under reverse bias. Although both the proposed photodiode and photoconductor devices exhibit large signal-to-noise ratio (104∼105), fast response (∼μs), and low working voltage (−0.5 V), these two type devices show their unique strengths due to the different working modes. The photodiode devices have higher detectivity (more than 1013 Jones) and broader linear dynamic range (over 120 dB), while the photoconductor ones possess more than 100% EQE and the better responsivity (0.56 A/W). This work may pave a way to obtain the desirable working mode of the photodetectors by simply tuning the electrode work function. Graphical abstract We demonstrate the work-function-controlled operation mode transition between photodiode and photoconductor modes in organic photodetectors. Image 1 Highlights • High performance organic photodetectors with PFN modified ITO electrode. • The Ag (Au) electrode device meets the photodiode type. • The Al electrode device presents the photoconductor mode. • The above two type devices show their unique strengths. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) allow for wavelength-tunable, economic, and elegant access to the infrared (IR) spectrum by utilizing inter- and intraband excitonic transitions in narrow bandgap semiconductors. With the emergence of new applications for IR detection, developing competitive non-toxic and environmentally benign alternatives to heavy metal-containing semiconductors is of increasing importance. Over the last decade, silver selenide (Ag 2 Se) has emerged as an alternative to lead- and mercury-based QDs, especially with large, intraband Ag 2 Se CQDs showing promising performance in the mid-wave IR. Herein we explored the critical nucleation and growth mechanisms of ultrasmall (2.5–3.5 nm) interband absorbing Ag 2 Se CQDs operating in the near to short-wave IR. Classical nucleation and growth was observed at most reaction conditions, with a growth temperature of 140 °C and a Ag:Se precursor molar ratio of 1:2 providing the most robust control over the IR absorption spectrum. We proceeded to perform an in-depth study of the impact of surface ligand chemistry of CQD thin-films on resulting optoelectronic properties. By tuning the functional groups and optimizing ligand exchange parameters, we obtained IR responsivity values of ∼25 mA/W in photoconductor devices and ∼1.8 mA/W in photodiode devices in the range 800 – 1250 nm. [Display omitted] [ABSTRACT FROM AUTHOR]

Thin-film optical transducers integrated in lab-on-a-chip (LoC) devices have the potential to facilitate miniaturization, multiplexing capabilities, portability, and sensitivity. However, there are few systematic studies that provide detailed characterization of these photosensors to particular miniaturized bioassays at reduced light intensities. A more detailed representation of the photosensors performance at low light levels is thus needed in order to improve the engineering of integrated detectors for the next generation of portable biosensors. Here, an assessment of the performance of hydrogenated amorphous silicon (a-Si:H) photosensors, at ultra-low light intensity, based on two different device configurations for integration in a microfluidic platform for biomolecular detection is presented. Both p-i-n photodiodes and parallel contact photoconductors show low dark current density (~10−10 A.cm−2) and photosensitivity comparable with high performing crystalline silicon photosensors. The a-Si:H photosensors were integrated in microfluidic devices for the detection of antibody-horseradish peroxidase conjugates (Ab-HRP) in a chemiluminescence-based assay. Surface concentrations of Ab-HRP as low as ~26 amol.cm−2 and ~9 fmol.cm−2 (corresponding to ~103 and ~106 HRP molecules) were detected with detectors in photodiode and photoconductor configurations, respectively, with the sensitivity of the former being comparable with that of bulky and ultra-sensitive photomultiplier tubes. The excellent sensitivity and dynamic range obtained, together with the miniaturization and arraying potential, highlight the potential of a-Si:H photosensors as an effective means of integrating the multiplexed acquisition of optical data in real time in point-of-need LoC systems. [ABSTRACT FROM PUBLISHER]

Abstract: 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. [Copyright &y& Elsevier]

We constructed ultraviolet (UV) photodetectors using thin films of silicon nanoparticles as active media. The Si nanoparticle films are electrodeposited at room temperature on Si p-type substrates. Uniform silicon nanoparticles of 1-nm diameter are dispersed from Si wafers using electrochemical etching. The nanoparticles are ultrabright under UV excitation, with nanosecond luminescence time characteristics. Current-voltage (I--V) characteristics indicate a photoconductor in series with a diode-like junction with a large enhancement in the forward current under UV illumination. Our results point to a sensitive UV detector with good visible blindness where the particle films effectively constitutes a wide-bandgap material. [ABSTRACT FROM PUBLISHER]

A planar metal/semiconductor/metal structure with Schottky barriers at both ends has attracted much attention as a competitive photodetector in an optical signal processing system. We report the influence of operating conditions on the low frequency (100 Hz–2 MHz) optical response of molybdenum/n-type silicon/molybdenum structure having a long undepleted neutral region. It was found that the spectra of the photoresponse of this structure displayed an appreciable change due to biasing conditions. An explanation for these results was given. Further, numerical simulations were performed using its equivalent circuit model. A good agreement between the simulated and observed results was obtained. [Copyright &y& Elsevier]

In this work, we report novel heterojunctions perovskite photodetector architecture utilizing metal-free contact electrodes. The metal-free contact electrodes were exploited to fabricate photoconductor – type perovskite photodetector. The attempt to investigate the effect of passivating the active layers of the as – proposed architecture with electrolytic MAI gave rise to a photodiode – type perovskite photodetector. These two photodetector types are sensitive and responsive to light sources through their dual transparent electrodes faces (N-face and T-face). We also showed that passivating the surfaces of the sandwiched perovskite layers with MAI solution improves the performance of the fabricated photodetectors, where the detectivity is enhanced by a factor of hundred compared to non-passivated devices. The proposed photodetectors architectures demonstrate champion dual-detectivity (1.77 × 1014 Jones for N-face and 4.64 × 1014 Jones for T-face), dual-responsivity (1.94 × 103 A/W for N-face and 1.61 × 103 A/W for T-face) and high dual – sensitivity (3.3 × 102 for N-face and 1.1 × 102 for T-face). All these properties were obtained from the two faces of the MAI passivated photodetectors under 0.02 mW/cm2 red LED illumination and at −2.0 bias voltage. This novel architecture may scale up towards building energy and cost efficient classes of optoelectronic and photovoltaic devices which are responsive to light in two directions. Image 1 • Sandwiched architecture heterojunction bifacial perovskite photodetectors was designed for direct illumination. • Effects of passivating the layers of sandwiched perovskite layer with MAI solution was investigated. • The photodetectors were electrically, optically and electrochemically characterized as bifacial devices. • Excellent performance with detectivity and responsivity ~5.96 × 1013 Jones & 1110 A/W was achieved. • Quantum efficiency of 3000% was recorded for the MAI passivated photodetector at 450 nm. [ABSTRACT FROM AUTHOR]