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The photoconductive gain theory demonstrates that the photoconductive gain is related to the ratio of carrier lifetime to carrier transit time. Theoretically, to achieve higher gain, one can either prolong the carrier lifetime or select materials with high mobility to shorten the transit time. However, the former slows the response speed of the device, while the latter increases the dark current and degrades device sensitivity. To address this challenge, a horizontal p-n-p junction-based photoconductor is proposed in this work. This device utilizes the n-region as the charge transport channel, with the charge transport direction perpendicular to the p-n-p junction. This design offers two advantages: (i) the channel is depleted by the space charge layer generated by the p and n regions, enabling the device to maintain a low dark current. (ii) The photovoltage generated in the p-n junction upon light absorption can compress the space charge layer and expand the conductive path in the n-region, enabling the device to achieve high gain and responsivity without relying on long carrier lifetimes. By adopting this device structure design, a balance between responsivity, dark current, and response speed is achieved, offering a new approach to designing high-performance photodetectors based on both traditional materials and emerging nanomaterials. [ABSTRACT FROM AUTHOR]

Position‐sensitive detectors (PSDs) are widely used in optical inspection applications, such as precise measurement of distance and angle, surface profiling, and motion tracking, etc. The lateral photovoltaic effect is the mechanism employed by most PSDs to determine position, but its gain‐free nature hinders weak‐light detection and applications. Here, a new position recognition mechanism with an intrinsic high gain is proposed and employ it to design a weak‐light and large‐size photoconductor‐type PSD. The position recognition is established by the intrinsic link between the gain and channel length in a photoconductor, and the designed linear correlation between the channel length and position. The photoconductor‐type graphene/Si PSD based on the recognition mechanism shows an active length of over 1 mm, a high spatial position resolution at the sub‐micrometer level, and a low detection limit power of 100 pW. Compared with Si PSDs, the gain of the photoconductor‐type PSD is improved by 3–4 orders of magnitude. In addition, the operational wavelength range of the PSD is expanded to include the near‐infrared region, specifically at 1300 and 1550 nm. The new position recognition mechanism paves the way for the development of ultra‐sensitive light position detection. [ABSTRACT FROM AUTHOR]

Amorphous selenium (a-Se) is a large-area compatible photoconductor that has received significant attention toward the development of UV and X-ray detectors for a wide range of applications in medical imaging, life science, high-energy physics, and nuclear radiation detection. A subset of applications require detection of photons with spectral coverage from UV to infrared wavelengths. In this work, we present a systematic study utilizing density functional theory simulations and experimental studies to investigate optical and electrical properties of a-Se alloyed with tellurium (Te). We report hole and electron mobilities and conversion efficiencies for a-Se1-xTex (x = 0, 0.03, 0.05, 0.08) devices as a function of applied field, along with band gaps and comparisons to previous studies. For the first time, these values are reported at high electric field (>10 V/μm), demonstrating recovery of quantum efficiency in Se-Te alloys. A comparison to the Onsager model for a-Se demonstrates the strong field dependence in the thermalization length and expands on the role of defect states in device performance.

The photoconductive gain theory demonstrates that the photoconductive gain is related to the ratio of carrier lifetime to carrier transit time. Theoretically, to achieve higher gain, one can either prolong the carrier lifetime or select materials with high mobility to shorten the transit time. However, the former slows the response speed of the device, while the latter increases the dark current and degrades device sensitivity. To address this challenge, a horizontal p-n-p junction-based photoconductor is proposed in this work. This device utilizes the n-region as the charge transport channel, with the charge transport direction perpendicular to the p-n-p junction. This design offers two advantages: (i) the channel is depleted by the space charge layer generated by the p and n regions, enabling the device to maintain a low dark current. (ii) The photovoltage generated in the p-n junction upon light absorption can compress the space charge layer and expand the conductive path in the n-region, enabling the device to achieve high gain and responsivity without relying on long carrier lifetimes. By adopting this device structure design, a balance between responsivity, dark current, and response speed is achieved, offering a new approach to designing high-performance photodetectors based on both traditional materials and emerging nanomaterials.

Lead chalcogenide nanoplatelets (NPLs) have emerged as a promising material for devices operating in the near IR and IR spectrum region. Here, we first apply the cation exchange method to PbSe/PbS core/shell NPL synthesis. The shell growth enhances NPL colloidal and environmental stability, and passivates surface trap states, preserving the main core physical properties. To prove the great potential for optoelectrical applications, we fabricate a photoconductor using PbSe/PbS NPLs. The device demonstrates enhanced conductivity and responsivity with fast rise and fall times, resulting in a 13 kHz bandwidth. The carrier transport was investigated with the field effect transistor method, showing p-type conductivity with charge mobility of 1.26 × 10−2 cm2·V−1·s−1. [ABSTRACT FROM AUTHOR]

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]

Achieving large-scale, affordable, and highly dependable production of antimony sulfide is crucial for unlocking its potential in various applications, including photoconductors, solid-state batteries, thermoelectrics, and solar cells. In our study, we introduce a straightforward, economical, and catalyst-free single-step solution process for fabricating one-dimensional Sb _2 S _3 nanostructures on flexible polyimide substrates, and we explore their use as photoconductors in the ultraviolet (UV) and visible light spectrum. The precursor solution for creating the Sb _2 S _3 films is prepared by dissolving specified quantities of elemental Sb and S in a solution mixture of ethylenediamine and 2-mercaptoethanol. This solution is then spin-coated onto a polyimide substrate and subsequently annealed at 300 °C for several minutes. Utilizing field emission scanning electron microscopy, grazing incidence x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we demonstrate that the Sb _2 S _3 films possess high crystallinity, uniform morphology, and a composition that is nearly stoichiometric. Additionally, through Tauc plot analysis, we determine that the films exhibit a direct bandgap of approximately 1.67 eV, which is in close agreement with the bandgap predicted by Heyd–Scuseria–Ernzerhof (HSE06) density-functional theory simulations. The metal-semiconductor–metal photoconductors fabricated with these films display a significant photoresponse to both UV and visible light. These devices achieve a UV on/off ratio of up to 160 at a light intensity of 30 mW cm ^−2 , with brief rise and fall times of 44 ms and 28 ms, respectively.

Lead chalcogenide nanoplatelets (NPLs) have emerged as a promising material for devices operating in the near IR and IR spectrum region. Here, we first apply the cation exchange method to PbSe/PbS core/shell NPL synthesis. The shell growth enhances NPL colloidal and environmental stability, and passivates surface trap states, preserving the main core physical properties. To prove the great potential for optoelectrical applications, we fabricate a photoconductor using PbSe/PbS NPLs. The device demonstrates enhanced conductivity and responsivity with fast rise and fall times, resulting in a 13 kHz bandwidth. The carrier transport was investigated with the field effect transistor method, showing p-type conductivity with charge mobility of 1.26 × 10−2 cm2·V−1·s−1.

Harvesting energetic carriers from plasmonic resonance has been a hot topic in the field of photodetection in the last decade. By interfacing a plasmonic metal with a semiconductor, the photoelectric conversion mechanism, based on hot carrier emission, is capable of overcoming the band gap limitation imposed by the band-to-band transition of the semiconductor. To date, most of the existing studies focus on plasmonic structural engineering in a single metal-semiconductor (MS) junction system and their responsivities are still quite low in comparison to conventional semiconductor, material-based photodetection platforms. Herein, we propose a new architecture of metal-semiconductor-metal (MSM) junctions on a silicon platform to achieve efficient hot hole collection at infrared wavelengths with a photoconductance gain mechanism. The coplanar interdigitated MSM electrode's configuration forms a back-to-back Schottky diode and acts simultaneously as the plasmonic absorber/emitter, relying on the hot-spots enriched on the random Au/Si nanoholes structure. The hot hole-mediated photoelectric response was extended far beyond the cut-off wavelength of the silicon. The proposed MSM device with an interdigitated electrode design yields a very high photoconductive gain, leading to a photocurrent responsivity up to several A/W, which is found to be at least 1000 times higher than that of the existing hot carrier based photodetection strategies. [ABSTRACT FROM AUTHOR]

We report a photoconductor-based terahertz metadevice whose transmission characteristics can be comprehensively controlled by a combination of an optical excitation and electrical bias. A metasurface with interdigitated electrodes is proposed to simultaneously support a terahertz resonance and the photoconductive effect, allowing efficient local and global dual-tuning of the carriers in the semiconductor and thus the terahertz wave, based on the simultaneous external optical and electrical stimuli. Experimental results reveal the opposite tuning trend of optical and electrical excitations, leading to the comprehensive transmission modulation of terahertz wave. Our study demonstrates a proof-of-concept device for sophisticated manipulation of terahertz radiation. [ABSTRACT FROM AUTHOR]

Abstract Ultraviolet‐C (UVC) radiation is employed in various applications, including irreplaceable applications in military and civil fields, such as missile guidance, flame detection, partial discharge detection, disinfection, and wireless communication. Although most modern electronics are based on Si, UVC detection technology remains a unique exception because the short wavelength of UV radiation makes efficient detection with Si difficult. In this review, recent challenges in obtaining ideal UVC photodetectors with various materials and various forms are introduced. An ideal photodetector must satisfy the following requirements: high sensitivity, fast response speed, high on/off photocurrent ratio, good regional selectivity, outstanding reproducibility, and superior thermal and photo stabilities. UVC detection is still in its infancy compared to the detection of UVA as well as other photon spectra, and recent research has focused on different key components, including the configuration, material, and substrate, to acquire battery‐free, super‐sensitive, ultra‐stable, ultra‐small, and portable UVC photodetectors. We introduce and discuss the strategies for fabricating self‐powered UVC photodetectors on flexible substrates in terms of the structure, material, and direction of incoming radiation. We also explain the physical mechanisms of self‐powered devices with various architectures. Finally, we present a brief outlook that discusses the challenges and future strategies for deep‐UVC photodetectors.

Lead oxide (PbO) photoconductors are proposed as X-ray-to-charge transducers for the next generation of direct conversion digital X-ray detectors. Optimized PbO-based detectors have potential for utilization in high-energy and dynamic applications of medical X-ray imaging. Two polymorphs of PbO have been considered so far for imaging applications: polycrystalline lead oxide (poly-PbO) and amorphous lead oxide (a-PbO). Here, we provide the comparative analysis of two PbO-based single-pixel X-ray detector prototypes: one prototype employs only a layer of a-PbO as the photoconductor while the other has a combination of a-PbO and poly-PbO, forming a photoconductive bilayer structure of the same overall thickness as in the first prototype. We characterize the performance of these prototypes in terms of electron–hole creation energy (W±) and signal lag—major properties that define a material's suitability for low-dose real-time imaging. The results demonstrate that both X-ray photoconductive structures have an adequate temporal response suitable for real-time X-ray imaging, combined with high intrinsic sensitivity. These results are discussed in the context of structural and morphological properties of PbO to better understand the preparation–fabrication–property relationships of this material. [ABSTRACT FROM AUTHOR]

In this work, metal–semiconductor–metal solar-blind ultraviolet photoconductors were fabricated based on the β-Ga2O3 thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy. Then, the effects of β-Ga2O3 annealing on both its material characteristics and the device photoconductivity were studied. The β-Ga2O3 thin films were annealed at 800, 900, 1000, and 1100 °C, respectively. Moreover, the annealing time was fixed at 2 h, and the annealing ambients were oxygen, nitrogen, and vacuum (4.9 × 10−4 Pa), respectively. The crystalline quality and texture of the β-Ga2O3 thin films before and after annealing were investigated by X-ray diffraction (XRD), showing that higher annealing temperature can result in a weaker intensity of 4 ¯ 02 diffraction peak and a lower device photoresponsivity. Furthermore, the vacuum-annealed sample exhibits the highest photoresponsivity compared with the oxygen- and nitrogen-annealed samples at the same annealing temperature. In addition, the persistent photoconductivity effect is effectively restrained in the oxygen-annealed sample even with the lowest photoresponsivity. [ABSTRACT FROM AUTHOR]

This paper reports a photoconductive type (Ag/Cu2SnS3(CTS) QDs/Ag) Vis-NIR photodetector having small channel spacing ($\sim 63.3 \boldsymbol {\mu }\text{m}$) on glass substrate. The low cost solvothermal processed CTS QDs have been used as carrier transporter as well as broad light absorber. The optical parameters of the proposed structure for small illumination power density have been calculated for broad range light illumination wavelengths (650-1100 nm). The responsivity of device was found to be ~37 (mA/W) for visible (730 nm) and ~67 (mA/W) for NIR (940 nm) illumination wavelengths. The sensitivity of the device was observed to be ~2.28 and ~8.2 for 730 and 940 nm illumination wavelengths, respectively, at 5V. The time response of the device have been measured under Vis-NIR illumination and found to be ~0.96 s (rise time) and ~1.29 s (fall time). [ABSTRACT FROM AUTHOR]

Harvesting energetic carriers from plasmonic resonance has been a hot topic in the field of photodetection in the last decade. By interfacing a plasmonic metal with a semiconductor, the photoelectric conversion mechanism, based on hot carrier emission, is capable of overcoming the band gap limitation imposed by the band-to-band transition of the semiconductor. To date, most of the existing studies focus on plasmonic structural engineering in a single metal-semiconductor (MS) junction system and their responsivities are still quite low in comparison to conventional semiconductor, material-based photodetection platforms. Herein, we propose a new architecture of metal-semiconductor-metal (MSM) junctions on a silicon platform to achieve efficient hot hole collection at infrared wavelengths with a photoconductance gain mechanism. The coplanar interdigitated MSM electrode’s configuration forms a back-to-back Schottky diode and acts simultaneously as the plasmonic absorber/emitter, relying on the hot-spots enriched on the random Au/Si nanoholes structure. The hot hole-mediated photoelectric response was extended far beyond the cut-off wavelength of the silicon. The proposed MSM device with an interdigitated electrode design yields a very high photoconductive gain, leading to a photocurrent responsivity up to several A/W, which is found to be at least 1000 times higher than that of the existing hot carrier based photodetection strategies.

Antimony selenide (Sb 2 Se 3) shows excellent photon absorption in the visible region and hence gaining tremendous attention from the last decade for thin film photovoltaics. Also, it has unique one-dimensional crystal structure and simple binary composition. However, the growth of Sb 2 Se 3 thin films with its predominant orientation along [hk1] to make use of easy electrical charge transport seems challenging due to various governing growth parameters. In this work, we have studied the role of growth temperature (between 200 ℃ and 320 ℃) in the crystalline orientation of Sb 2 Se 3 thin films on glass substrates via close-space thermal evaporation. In addition to growth orientation, we have investigated the effect of growth temperature on the surface morphology, elemental composition, film thickness, and optical properties of Sb 2 Se 3 thin films. Electrical properties and photoresponse were measured on [hkl] and [hk0] oriented films to understand the effect of anisotropy and it is inferred that [hk1] oriented film as a favorable one for the charge transport. Also, the photoresponse results showed fair photoconductance under white light illumination and zero applied bias. [Display omitted] • Growth of Sb 2 Se 3 thin films via close-space evaporation using pre synthesized bulk. • Exhibit orientation dependent electrical properties and photoresponse behaviour. • High absorption coefficient, carrier concentration and Hall mobility values. • Self-powered photoconductivity in Sb 2 Se 3 /Ag junction. [ABSTRACT FROM AUTHOR]

Lead oxide (PbO) photoconductors are proposed as X-ray-to-charge transducers for the next generation of direct conversion digital X-ray detectors. Optimized PbO-based detectors have potential for utilization in high-energy and dynamic applications of medical X-ray imaging. Two polymorphs of PbO have been considered so far for imaging applications: polycrystalline lead oxide (poly-PbO) and amorphous lead oxide (a-PbO). Here, we provide the comparative analysis of two PbO-based single-pixel X-ray detector prototypes: one prototype employs only a layer of a-PbO as the photoconductor while the other has a combination of a-PbO and poly-PbO, forming a photoconductive bilayer structure of the same overall thickness as in the first prototype. We characterize the performance of these prototypes in terms of electron–hole creation energy (W±) and signal lag—major properties that define a material’s suitability for low-dose real-time imaging. The results demonstrate that both X-ray photoconductive structures have an adequate temporal response suitable for real-time X-ray imaging, combined with high intrinsic sensitivity. These results are discussed in the context of structural and morphological properties of PbO to better understand the preparation–fabrication–property relationships of this material.

Using a metal/insulator/metal (MIM) structure with a gold nanoantenna array made by electron beam lithography, the responsivity of a HgTe colloidal quantum dot film is enhanced in the mid-infrared. Simulations indicate that the spatially averaged peak spectral absorption of an 80 nm film is 60%, enhanced 23-fold compared to that of the same film on a bare sapphire substrate. The field intensity enhancement is focused near the antenna tips, being 20-fold 100 nm away, which represents only 1% of the total area and up to 1000-fold at the tips. The simulated polarized absorption spectra are in good agreement with the experiments, with a strong resonance around 4 μm. A responsivity of 0.6 A/W is obtained at a 1 V bias. Noise measurements separate the 1/f noise from the generation-recombination white noise and give a spatially averaged photoconductive gain of 0.3 at 1 V bias. The spatially averaged peak detectivity is improved 15-fold compared to the same film on a sapphire substrate without an MIM structure. The experimental peak detectivity reaches 9 × 10 9 Jones at 2650 cm -1 and 80 kHz, decreasing at lower frequencies. The MIM structure also enhances the spatially averaged peak photoluminescence of the CQD film by 16-fold, which is a potential Purcell enhancement. The good agreement between simulations and measurements confirms the viability of lithographically designed nanoantenna structures for vastly improving the performance of mid-IR colloidal quantum dot photoconductors. Further improvements will be possible by matching the optically enhanced and current collection areas.

Efficient charge transport of plasmon-induced hot electrons to the semiconductor junction is the key factor to develop hot electron-based electronics devices. In this work, a plasmon induced hot electrons photodetector has been fabricated from an in situ-grown silver (Ag)/titanium oxide (TiO 2) nano-heterojunction thin film via a solution-processed technique. This nano-heterojunction thin film has been grown from a sol-gel derived Na 2 Ti 3 O 7 (NTO) thin film that contains mobile Na ion (Na+) via ion exchange (Na+→ Ag+) and reduction method. This device has been fabricated in photoconductor geometry on a glass substrate. For this device fabrication, a solution-processed SnO 2 has been deposited on top of a glass substrate which works as a charge transport layer. Afterward, a nano-heterojunction thin film of Ag–TiO 2 has been grown on top of this SnO 2 , which transfers plasmon-induced hot electrons from Ag nanoparticles to the SnO 2 layer via TiO 2. This SnO 2 layer efficiently transports electrons to the respective electrode due to its high electron mobility. The contribution of Plasmon induced hot carrier to photocurrent generation has been realized through external quantum efficiency (EQE) measurement which shows intense photocurrent generation in the plasmonic absorption region of the nano-heterojunction thin film. As a consequence, the photodetector shows a narrowband photodetection with a peak position at 443 nm and FWHM of 50 nm. The maximum EQE of 1.54 % has been detected at that wavelength under 10 V external bias whereas the responsivity and detectivity under this measurement condition reach to 0.52 A/W and 1.25 × 1010 Jones respectively. • Solution processed Na 2 Ti 3 O 7 (NTO) thin film fabrication. • In-situ grown Ag–TiO 2 in NTO film by solution processed technique. • Application of Ag–TiO 2 thin film as hot-electron driven photodetector. • Fabrication of narrowband photodetector. [ABSTRACT FROM AUTHOR]

We demonstrate subpicosecond photocarrier lifetimes at 1.55 mum in GaSb/ErSb nanoparticle superlattices grown by molecular beam epitaxy. Pump-probe measurements were made with a 1.55 mum mode-locked laser in transmission geometry to determine the photocarrier lifetime. The lifetime is found to be dependent on the size of the ErSb particles, amount of ErSb, and the distance between layers of particles. Through manipulation of these three parameters the photocarrier lifetime can be tuned down to less than 300 fs, the temporal limit of our experiment. (C) 2004 American Institute of Physics.

This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.

Abstract The influence of small molecule (SM) α, ω-di-hexyl-sexithiophene (DH6T) concentration, in the blends of conjugated polymer (CP) poly (3-hexylthiophene) (P3HT) and DH6T, was investigated in terms of barrier potential reduction and improved photoresponse of the fabricated photoconductor using these blends. Barrier potential in Au/P3HT:DH6T/Au device structure, occurring at the interface of Au (top)/P3HT:DH6Twas estimated by Fowler Nordheim (FN) tunneling model-based analysis of I-V characteristics. The barrier potential of the fabricated device was observed to decrease upon addition of a small quantity of DH6T in comparison to the pristine polymer-based device. This reduction in barrier was attributed to the improved ordering and morphology of the polymer chains upon blending it with an SM. The variation in the ordering of the polymer chains was further confirmed with Photoluminescence spectroscopy, Absorption spectroscopy, and XRD data. Subsequently, it was also observed that only up to a definite SM concentration (25% in this study) ordering of polymer chains improved causing a reduction in barrier potential and subsequent improvement in the photoresponse of the fabricated devices. Finally, it was observed that the optimized blending of CP and SM could to be useful in reducing the effect of penetration of Au inside the CP matrix in the top contact configuration thereby resulting in the reduction of a barrier for carrier injection which is generally lower in the bottom contact configurations. These studies are critical from the point of view of the development of photoconductors and photosensitive top contact organic field effect transistors (OFETs). Graphical abstract Image 1 Highlights • Blending of DH6T with P3HT was performed. • Polymer-metal interface morphology is critical to decide charge injection and collection; hence device performance. • Blending helps to restrict the Au penetration during electrode deposition in top electrode geometry devices. • Interpenetrating network of P3HT and DH6T helps in exciton dissociation; hence improved photoresponse. [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]

Highlights • HOT LWIR T2SLs InAs/InAsSb photodetectors grown on GaAs substrate. • The immersion lens was formed from GaAs substrate. • Single pixel detector detectivity (D∗) of ∼2.0 × 1010 cm Hz1/2/W at 210 K. Abstract We report on of high operating temperature (HOT) long-wavelength infrared radiation (LWIR) type-II superlattices (T2SLs) InAs/InAsSb photoconductor grown on buffered semi-insulating GaAs substrate. The absorber of the device consists of a 300 periods of T2SLs InAs/InAsSb. The high resolution X-ray diffraction (HRXRD), photoluminescence (PL), Hall, Optical Parametric Oscillator (OPO) measurements are presented and analyzed. The detector reached a 50% cut-off wavelength of 9.8 μm and 10.4 μm at 210 K and 230 K, respectively. The time constant of 24 ns is observed at 210 K under 0.5 V bias. The detectivity (D∗) of ∼ 2.0 × 1010 cm Hz1/2/W at 210 K is reached. [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]

ErAs:In(Al)GaAs superlattice photoconductors are grown using molecular beam epitaxy (MBE) with excellent material characteristics for terahertz timedomain spectroscopy (TDS) systems operating at 1550 nm. The transmitter material (Tx) features a record resistivity of 3.85 kΩcm and record breakdown field strength of 170±40 kV/cm (dark) and 130±20 kV/cm (illuminated with 45mWlaser power). Receivers (Rx) with different superlattice structures were fabricated showing very high mobility (775 cm2/Vs). The TDS system using these photoconductors features a bandwidth larger than 6.5 THz with a laser power of 45 mW at Tx and 16 mW at Rx. [ABSTRACT FROM AUTHOR]

In the field of artificial intelligence, neuromorphic computing offers the allure of human brain simulation. The capacity of optoelectronic synapses to intelligently handle optoelectronic input signals makes them a key component of neuromorphic computing. In this work, we fabricated ZnO-based optoelectronic synapses and investigated their electronic and photonic synaptic plasticity. The device fabrication process flow is as follows: photolithography is performed on ITO glass, followed by hydrochloric acid etching and degumming to obtain interdigital electrodes on the glass substrate, and a ZnO film is grown on the interdigitated electrodes by magnetron sputtering. A good Ohmic contact is formed between the ZnO and ITO electrodes, and the device exhibits a linear relationship between current and voltage under dark field conditions, and exhibits excellent synaptic properties and sensitivity in UV switching response experiments. Additional processes were subsequently introduced through growing ZnO nanowires and annealing, and the synaptic properties of ZnO device were improved. The shift from short-term to long-term memory, short-term plasticity, long-term plasticity, paired-pulse facilitation, and learning to experience behavior are only a few of the synaptic activities of the nervous system that have been successfully described. The manufactured array device also includes a special memory recall feature that may retrieve previous optoelectronic data. This work will advance the field of artificial intelligence and stimulate additional study on optoelectronic synapses. [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]

Purpose: Some recent studies on bendable sensors have reported the reduction of distortion in X-ray shots caused by the patient's physical structure. In the field of diagnostic radiology, images are nowadays captured using flat panel detectors, but it is difficult to take the geometrical body type and physical characteristics of patients into consideration with flat panels; this may distort images. This study evaluates the bending and electrical properties of bottom electrode-based sensors with bending capability. Methods: This study evaluates the bending and electrical properties of bottom electrode-based sensors with aluminium, copper, and indium tin oxide films. These sensors are fabricated, and their performance concerning bending resistance, sensitivity, and signal-to-noise ratio are evaluated and compared with a reference sensor. Results: These sensors are shown to provide similar results to the reference sensor in what concerns the cubic functionality (of approx. 99%) of their response to tube voltage variations. The Al film-based sensor shows he lowest SNR value; the Cu film shows excellent sensitivity, but with a slightly high dark current, resulting in a low SNR value. Conclusions: Bendable detectors are possible solutions to mitigate the distortion in X-rays obtained with flat panel detector. The results of this study can potentially be used as basic research to support the next-generation bendable detectors, and thus improve these distortions, caused by the X-ray patient's physical structure. [ABSTRACT FROM AUTHOR]

We describe energy-dependent incomplete signal generation in semiconductor detectors with a simple planar geometry using deep charge trapping and depth-of-interaction models. Based on this formalism, we have characterized mercuric iodide (HgI_2) photoconductors by extracting performance parameters from x-ray-induced signals under mammographic imaging conditions. The HgI_2 sample photoconductors were prepared using a simple screen-printing method. For an x-ray tube output from tungsten target and 30-kV setting, the quantum absorption efficiency of samples with a thickness of approximately 0.1 mm was measured to be \sim 70\%. X-ray sensitivity was measured to be 0.4~\nC cm^ - 2 mR^ - 1. Mobility-lifetime products for electrons and holes were measured as \sim 2 \times 10^ - 6~\cm^2~\V^ - 1 and \sim 0.9 \times 10^ - 6~\cm^2~\V^ - 1, respectively. Considering incomplete charge collection, the W-value (or w) was estimated to be \sim 27 ~\eV. Since the characterization method described in this study is simple and does not require sophisticated equipment, it can be useful for the characterization of photoconductor materials. [ABSTRACT FROM AUTHOR]

An asymmetric small molecule composed of anthracene and alkylated thienothiophene (2-(anthracen-2-yl)-5-hexylthieno[3,2-b]thiophene) was synthesized via the Suzuki coupling reaction. The thermal stability, photochemical properties, and morphological characteristics were investigated using thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, UV–visible spectroscopy, and X-ray diffraction techniques. The compound demonstrated a good thermal stability of 5% at a decomposition temperature of 336 °C. The solution-processed single-crystal transistor, devised with 2-(anthracen-2-yl)-5-hexylthieno[3,2-b]thiophene, exhibited high performance with a hole mobility of 0.1 cm 2 /Vs. Furthermore, by utilizing the high mobility of 2-(anthracen-2-yl)-5-hexylthieno[3,2-b]thiophene, we demonstrated its unprecedented high photoresponsivity of 3370 A/W, a finding that can be attributed to the very efficient photoconductive behavior of a single crystal of 2-(anthracen-2-yl)-5-hexylthieno[3,2-b]thiophene. [ABSTRACT FROM AUTHOR]

We present an optocoupler device based on a blue organic light-emitting diode (OLED) as input unit, and a pentacene photoconductor as output unit. The optocoupler was realized on a transparent glass substrate. The luminance was found larger than 10 3 cd/m 2 with a blue peak emission at 450 nm for the optimized ZnO (120 nm)/ITO (150 nm)/α-NPB (40 nm)/BCP (15 nm)/Alq3 (20 nm)/Al structure. The I ds-Illum / I ds-Dark current ratio, the sensitivity and the current density transfer ratio of the optocoupler are of about 7, 10 −1 A/W, and 10 −1 , respectively. The rise as well as full times were found faster for high bias voltages. The equilibrium regime with less persistent current was reached more quickly, as evidenced by the fast current response for higher bias voltage, indicating a more favorable recombination processes of the charge carriers. The organic optocoupler with a blue OLED reveals promising results; thus, it can be investigated as a good candidates for practical uses in organic optoelectronic circuits with high bias voltages. [ABSTRACT FROM AUTHOR]

In this report, we demonstrate a photoconductive device based on difluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT). The light intensity dependences of the transient photocurrent combined with theoretical analyses clearly show that a simple device architecture consisting of diF-TES-ADT and two Au electrodes patterned in parallel forms an efficient, trap-limited, gain-generating photoconductive device, resulting in high responsivity up to approximately 500 A/W. Moreover, the efficient gain-generating nature of diF-TES-ADT enables efficient tuning of the charge carrier density in the channel region, resulting in unprecedentedly sensitive phototransistor performance with high current modulation exceeding 10 6 as well as hysteresis-free threshold voltage shifts. [ABSTRACT FROM AUTHOR]

We investigate properties of MBE grown photoconductive terahertz (THz) antennas based on the InGaAs/InAlAs/InP material system aimed for an excitation wavelength of approx. 1060 nm. Therefore, we analyze several different approaches concerning growth parameters, layer and material compositions as well as doping. The carrier dynamics are probed via transient white-light pump-probe spectroscopy as well as THz Time Domain Spectroscopy (TDS) measurements. We find that the electron capture probability is reduced for higher electron energies. By adjusting the material band gap this can be resolved and lifetimes of 1.3 ps are obtained. These short lifetimes enable the detection of THz TDS spectra with a bandwidth exceeding 4 THz. [ABSTRACT FROM AUTHOR]