Linear Photoresponse Research Articles

Investigation of AlN-based Schottky type photodetector in visible light detection

In this study, we fabricated an AlN-based Schottky photodetector by thermal evaporation technique using commercial AlN/n-Si heterojunction which was fabricated by hydride vapor phase epitaxy. Thus, Au/Ti/AlN/n-Si heterostructure was obtained and tested for photodetector applications for various light power densities from 20 mW/cm2 to 100 mW/cm2 by I–V characteristics. Various parameters of heterostructure were extracted by thermionic emission theory, Norde and Cheung methods to clear the electrical properties of the Au/Ti/AlN/n-Si. Photodetection parameters such as responsivity, photosensitivity, and specific detectivity values were also studied depending on the changing light power density. The Au/Ti/AlN/n-Si photodetector revealed 1.36 A/W responsivity and 7.99 × 109 Jones specific detectivity values. The photoresponse time was investigated by light on-off transient measurements. The Au/Ti/AlN/n-Si photodetector exhibited fast and linear photoresponse to the illumination. The photocapacitance and photoconductance properties of the Au/Ti/AlN/n-Si photodetector were also studied. The results highlighted that Au/Ti/AlN/n-Si photodetector can be a good candidate for fast-response photodetection applications.

Multi‐Factor Modulated Organic Bulk Heterojunction Synaptic Transistor Enabled by Ligand Engineering for Centrosymmetric In‐Sensor Computing

AbstractEfficient in‐sensor computing necessitates linear, bidirectional, and centrosymmetric photoresponse weight updates; however, the realization of these attributes poses a persistent challenge, with most photosensor devices achieving linear analog weight updates while falling short of accomplishing bidirectional and centrosymmetric characteristics. Here, the development of a quantum dot (QD)–based bulk heterojunction synaptic transistor (QBST) with multi‐factor modulation through surface ligand engineering of blend QDs is reported. By controlling the charge transmission between QDs and the semiconductor, the QBST device enables tunable fading memory, which transforms linear weight updates in short‐chain devices into linear, bidirectional, and unprecedented centrosymmetric optical synaptic responses in long‐chain devices. Moreover, through the synergy of chemical and electric factors, the convolutional kernel of QBSTs‐based convolutional neural network realizes enhanced recognition for complex noisy fashion‐costume images, achieving an impressive 90.3% accuracy in the long‐chain device, highlighting the efficiency of centrosymmetric weight updates. The results demonstrate that surface ligand engineering offers a promising approach for customizable synaptic modulation, facilitating energy‐ and time‐efficient in‐sensor computing.

Approaching the Robust Linearity in Dual‐Floating van der Waals Photodiode

AbstractTwo‐dimensional (2D) material photodetectors have gained great attention as potential elements for optoelectronic applications. However, the linearity of the photoresponse is often compromised by the carrier interaction, even in 2D photodiodes. In this study, a new device concept of dual‐floating van der Waals heterostructures (vdWHs) photodiode is presented by employing ambipolar MoTe2 and n‐type MoS2 2D semiconductors. The presence of type II heterojunctions on both sides of channel layers effectively depletes carriers and restricts the photocarrier trapping within the channel layers. As a result, the device exhibits robust linear photoresponse under photovoltaic mode from the visible (405 nm) to near‐infrared (1600 nm) band. With the built‐in electric field of the vdWHs, a linear dynamic range of ≈100 dB, responsivity of ≈1.57 A W−1, detectivity of ≈4.28 × 1011 Jones, and response speed of ≈30 µs are achieved. The results showcase a promising device concept with excellent linearity toward fast and low‐loss detection, high‐resolution imaging, and logic optoelectronics.

Integrated PbS Colloidal Quantum Dot Photodiodes on Silicon Nitride Waveguides.

Colloidal quantum dots (QDs) have become a versatile optoelectronic material for emitting and detecting light that can overcome the limitations of a range of electronic and photonic technology platforms. Photonic integrated circuits (PICs), for example, face the persistent challenge of combining active materials with passive circuitry ideally suited for guiding light. Here, we demonstrate the integration of photodiodes (PDs) based on PbS QDs on silicon nitride waveguides (WG). Analyzing planar QDPDs first, we argue that the main limitation WG-coupled QDPDs face is detector saturation induced by the high optical power density of the guided light. Using the cladding thickness and waveguide width as design parameters, we mitigate this issue, and we demonstrate WG-QDPDs with an external quantum efficiency of 67.5% at 1275 nm that exhibit a linear photoresponse for input powers up to 400 nW. In the next step, we demonstrate a compact infrared spectrometer by integrating these WG-QDPDs on the output channels of an arrayed waveguide grating demultiplexer. This work provides a path toward a low-cost PD solution for PICs, which are attractive for large-scale production.

Gate-tunable self-driven photodetector based on asymmetric monolayer WSe2 channel

Two-dimensional (2D) self-driven photodetectors have attracted extensive attention due to the fast photoresponse, low energy consumption and high flexibility. Recently, the metal–semiconductor-metal (MSM) structures with asymmetrical 2D semiconductor channel are exploited for the self-driven photodetection. However, the mechanism is still in dispute and the channel has not yet been forward to monolayer. Here, a self-driven MSM photodetector is fabricated with the directly-grown monolayer WSe2 which is asymmetrically patterned by the controllable scratching lithography. The self-driven behavior mainly originates from the asymmetry of both conduction channel and the Schottky junctions. With the photovoltaic effect driven by asymmetry, the device exhibits linear photoresponse with responsivity of 1.4 mA/W, detectivity of 1010 Jones, dark current level of 0.1 pA and response speed of tens of milliseconds. Moreover, performances show highly gate-tunable characteristics due to the tunable Schottky barriers. This work provides a new route towards self-driven photodetectors based on 2D materials.

A Hemispherical Image Sensor Array Fabricated with Organic Photomemory Transistors.

Hemispherical image sensors simplify lens designs, reduce optical aberrations, and improve image resolution for compact wide-field-of-view cameras. To achieve hemispherical image sensors, organic materials are promising candidates due to the following advantages: tunability of optoelectronic/spectral response and low-temperature low-cost processes. Here, a photolithographic process is developed to prepare a hemispherical image sensor array using organic thin film photomemory transistors with a density of 308 pixels per square centimeter. This design includes only one photomemory transistor as a single active pixel, in contrast to the conventional pixel architecture, consisting of select/readout/reset transistors and a photodiode. The organic photomemory transistor, comprising light-sensitive organic semiconductor and charge-trapping dielectric, is able to achieve a linear photoresponse (light intensity range, from 1 to 50W m-2 ), along with a responsivity as high as 1.6 A W-1 (wavelength = 465nm) for a dark current of 0.24 A m-2 (drain voltage =-1.5V). These observed values represent the best responsivity for similar dark currents among all the reported hemispherical image sensor arrays to date. A transfer method wasfurther developed that does not damage organic materials for hemispherical organic photomemory transistor arrays. These developed techniques are scalable and are amenable for other high-resolution 3D organic semiconductor devices.

Self‐Powered Visible‐Infrared Polarization Photodetection Driven by Ferroelectric Photovoltaic Effect in a Dion–Jacobson Hybrid Perovskite

AbstractFerroelectric materials, particularly the emerging layered hybrid ferroelectrics, have shown great potential for high‐sensitive polarization photodetection owing to their striking bulk photovoltaic effect (BPVE). Despite recent great achievements, the linear photoresponse range based on single‐mode BPVE is still limited in the shortwave region due to the large intrinsic bandgaps. Herein, first, the realization of self‐powered visible–infrared polarization photodetection by exploiting dual‐modal BPVE in a newly developed layered Dion–Jacobson (D‐J) hybrid ferroelectric (BDA)(EA)2Pb3Br10 (1, BDA is 1,4‐butadiammonium, EA is ethylammonium) is reported. Crystallographic investigations indicate that 1 adopts a typical trilayered D‐J perovskite structure with a fascinating ferroelectric feature and a giant two‐photon absorption coefficient as giant as 4.73 cm MW–1. Meanwhile, the bulk single crystal device of 1 exhibits excellent self‐powered direct detection performance under both visible light (405 nm) and near‐infrared light (800 nm), with a current on/off ratio as high as 103. More intriguingly, the device displays high sensitivity to the polarization of illuminated light, showing a considerable anisotropy up to 4.2 (405 nm) and 4.8 (800 nm), which are much larger than the detectors achieved by geometry anisotropy. The realization of self‐powered visible‐infrared dual‐modal polarization photodetection in 1 indicates the tremendous potential of hybrid ferroelectrics in various optoelectronic applications.

Visible to Short-Wave Infrared Photodetectors Based on ZrGeTe4 van der Waals Materials.

The self-terminated, layered structure of van der Waals materials introduces fundamental advantages for infrared (IR) optoelectronic devices. These are mainly associated with the potential for low noise while maintaining high internal quantum efficiency when reducing IR absorber thicknesses. In this study, we introduce a new van der Waals material candidate, zirconium germanium telluride (ZrGeTe4), to a growing family of promising IR van der Waals materials. We find the bulk form ZrGeTe4 has an indirect band edge around ∼0.5 eV, in close agreement with previous theoretical predictions. This material is found to be stable up to 140 °C and shows minimal compositional variation even after >30 days storage in humid air. We demonstrate simple proof-of-concept broad spectrum photodetectors with responsivities above 0.1 AW-1 across both the visible and short-wave infrared wavelengths. This corresponds to a specific detectivity of ∼109 cm Hz1/2 W-1 at λ = 1.4 μm at room temperature. These devices show a linear photoresponse vs illumination intensity relationship over ∼4 orders of magnitude, and fast rise/fall times of ∼50 ns, also verified by a 3 dB roll-off frequency of 5.9 MHz. As the first demonstration of photodetection using ZrGeTe4, these characteristics measured on a simple proof-of-concept device show the exciting potential of the ZrGeTe4 for room temperature IR optoelectronic applications.

Temperature‐Gradient‐Controlled Method Enabling Shape Control of 2D Perovskite Single Crystals for Photodetection

2D hybrid organic–inorganic lead halide perovskites have been reported as promising photodetection active semiconductor materials due to their excellent photoelectric properties and stability. However, the solution growth of 2D crystal materials is affected adversely by narrow process windows, low process reproducibility, and small crystal sizes. Herein, a temperature‐gradient‐controlled method to grow high‐quality 2D perovskite crystals on the order of centimeters is developed. Using this new method, BA2PbI4 and mixed‐cation BA2FAxMA1−xPb2I7 crystals are produced with shape control and improved quality at the bottom of the precursor solution. Subsequently, their photoelectric responses are investigated comprehensively. Photodetectors based on these single crystals exhibit outstanding performances, affording 10−11 A dark current, > 103 on–off ratio, ≈10 mA W−1 responsivity, excellent stability, and linear photoresponse. Moreover, the annealing of crystals effectively reduces the dark current of the detectors. The mixed‐cation BA2FA0.4MA0.6Pb2I7 crystal demonstrates improved photoelectric response and a significant change in morphology.

Tunable Linearity of High-Performance Vertical Dual-Gate vdW Phototransistors.

Layered 2D semiconductors have been widely exploited in photodetectors due to their excellent electronic and optoelectronic properties. To improve their performance, photogating, photoconductive, photovoltaic, photothermoelectric, and other effects have been used in phototransistors and photodiodes made with 2D semiconductors or hybrid structures. However, it is difficult to achieve the desired high responsivity and linear photoresponse simultaneously in a monopolar conduction channel or a p-n junction. Here, dual-channel conduction with ambipolar multilayer WSe2 is presented by employing the device concept of dual-gate phototransistor, where p-type and n-type channels are produced in the same semiconductor using opposite dual-gating. It is possible to tune the photoconductive gain using a vertical electric field, so that the gain is constant with respect to the light intensity-a linear photoresponse, with a high responsivity of ≈2.5 × 104 A W-1 . Additionally, the 1/f noise of the device is kept at a low level under the opposite dual-gating due to the reduction of current and carrier fluctuation, resulting in a high detectivity of ≈2 × 1013 Jones in the linear photoresponse regime. The linear photoresponse and high performance of the dual-gate WSe2 phototransistor offer the possibility of achieving high-resolution and quantitative light detection with layered 2D semiconductors.

Notice of Removal: Exceptionally Linear and Highly Sensitive Photo-Induced Unipolar Inverter Device

Oxide semiconductors are of particular interest in the field of integrated electronics due to their large-area fabrication, high uniformity, and superior performance. Here, we report an exceptionally sensitive photo-induced inverter device with high linearity based on the unipolar n-type channel material amorphous silicon indium zinc oxide (a-SIZO). The field-effect transistor (FET) based on a-SIZO exhibits maximum mobility of 9.8 cm2/Vs at $\text{V}_{\mathrm{ D}}$ of 5 V, high on/off ratio of $\sim 10^{6}$ , and stable threshold voltage ( $\text{V}_{\mathrm{ Th}}$ ) of −0.35 V. Additionally, the optical properties of the proposed FET include excellent $\text{V}_{\mathrm{ Th}}$ shift and photocurrent ( $\text{I}_{\mathrm{ photo}}$ ) with high linearity under various red-light illumination. The proposed enhancement-load type inverter device shows reliable electrical and optical characteristics with an inverter gain of 0.7 at $\text{V}_{\mathrm{ DD}}$ of 1 V and linear photo-response in terms of inverter gain and voltage shift, demonstrating promising potential in the field of integrated electronics for optoelectronic applications.

INFRARED DETECTING BEHAVIOURS OF Cu2NiSnS4 PHOTODIODES

A photodetector in Al/p-Si/Cu2NiSnS4/Al form was produced using sol-gel method. Scanning electron microscopy (SEM) was used in the structural assessment of the photodetectors. Microscopic investigations showed that Cu2NiSnS4 structures were formed in nanostructure in granular form. Current–time and current-voltage investigations confirmed that Al/p-Si/Cu2NiSnS4/Al photodiodes have infrared sensing properties. Photodetection properties such as linear dynamic rate, ideality factor, photosensitivity, and photoresponse characteristics were assessed. Results also validate the infrared sensing properties of the diodes. The barrier height of the Al/p-Si/Cu2CoSnS4/Al diodes was calculated as 0.466 eV. Ideality factor of the diodes was found to be 5.16. Results indicate that our Al/p-Si/Cu2CoSnS4/Al diodes are suitable for infrared tracking device applications.

Monolithic Full-Stokes Near-Infrared Polarimetry with Chiral Plasmonic Metasurface Integrated Graphene-Silicon Photodetector.

The ability to detect the full-Stokes polarization of light is vital for a variety of applications that often require complex and bulky optical systems. Here, we report an on-chip polarimeter comprising four metasurface-integrated graphene-silicon photodetectors. The geometric chirality and anisotropy of the metasurfaces result in circular and linear polarization-resolved photoresponses, from which the full-Stokes parameters, including the intensity, orientation, and ellipticity of arbitrarily polarized incident infrared light (1550 nm), can be obtained. The design presents an ultracompact architecture while excluding the standard bulky optical components and structural redundancy. Computational extraction of full-Stokes parameters from mutual information among four detectors eliminates the need for a large absorption contrast between different polarization states. Our monolithic plasmonic metasurface integrated polarimeter is ideal for a variety of polarization-based applications including biological sensing, quantum information processing, and polarization photography.

Investigation of electrical properties of organophosphazene layer based photodiode

New cyclotriphosphazene compound bearing dioxyphenylcoumarin group (DCP-1) was synthesized from the reactions of 7,8-dihydroxy-3-(4-chlorophenyl)coumarin (3) containing chlorine as a side group at para position with cyclotriphosphazene (DCP). The structures of the compounds were determined using 1H, 13C APT, 31P NMR, FT-IR and elemental analysis spectroscopy methods. The organic layer was deposited onto the p-Si substrate to obtain an Al/p-si/phosphazene (DCP-1)/Al diode. The photoresponse and photocapacitance properties of the diode were analyzed under various solar light intensities. The photocurrent and photocapacitance results suggest that the studied device exhibits both photodiode and photocapacitor behavior. The diode indicates a linear photoresponse behavior. The photoswitching behavior of the diode is controlled by solar light intensity. The interface states density of the diode was found to be order of 1012 eV-1cm2. The value of interface states density indicates that the photocapacitor behavior of the diode is significant for photocapacitor applications.

Spin-Polarized Transport and Optoelectronic Properties of a Novel-Designed Architecture with a Porphyrin-Based Wheel and Organometallic Multidecker Sandwich Complex-Based Axle

A novel “wheel-and-axle” architecture (c-P6)m/(FeBz)n, with (c-P6) denoting the wheel formed by six porphyrin-based segments and (FeBz)n the axle formed by the 1D iron benzene multidecker complex, is designed, and its electronic structure, transport property, and linear photoresponse are investigated. (c-P6)m/(FeBz)n shows a spin-polarized transport property. The spin filter efficiency of (c-P6)m/(FeBz)n can be > 90%, suggesting it is a very good candidate for spin filters. Furthermore, a distinct NDR feature is observed for (c-P6)m/(FeBz)n so it is can be used for making electronic switches and oscillators. Under linear light, both the wheel and axle of (c-P6)m/(FeBz)n exhibit a distinct polarized photoresponse character. The magnitude of the photoresponse can be tuned by the photon energy or by the l bias voltage. An off–on–off switch is observed within the considered photon energy range, showing potential application for optical switches. All these fascinating properties of (c-P6)m/(FeBz)n make the new 1D material especially attractive for electronic and optoelectronic devices.

Combined In-Pixel Linear and Single-Photon Avalanche Diode Operation With Integrated Biasing for Wide-Dynamic-Range Optical Sensing

This article presents a fully integrated, wide linear dynamic range (DR) optical sensor array combining linear and single-photon avalanche diode (SPAD) operation within each pixel. A pulse-counting readout scheme provides in-pixel digitization in an area-efficient manner for both the operation modes, enabling fully parallel measurement across the array. The proposed dual-mode optical sensor array alternately requires high-voltage (10–20 V) and low-voltage supply (2–5 V) for reverse bias of the photodiodes, which is provided by a reconfigurable, closed-loop high-voltage charge pump in the same substrate. An $8\times 8$ array architecture along with the dual-mode bias generator is fabricated in a general purpose 180-nm CMOS process and demonstrates 129-dB DR while maintaining linear photoresponse operating with a dual-mode frame rate of 20 Hz. We present a pixel design methodology for implementing a dual-mode optical sensor scalable to an array format, as well as high-voltage dc–dc conversion in a low-voltage CMOS process.

Bi2Te3 photoconductive detector under weak light

Bi2Te3 − xSex photoconductive detectors are attractive due to their linear photo-response (LPR), potential in ultrabroadband photo-detection, and compatibility with CMOS technology. However, as a fundamental issue for photo-detectors, the weak-light photo-response of Bi2Te3 − xSex detectors was covered by the bolometric response, the photo-thermoelectric effect, and the 300 K background black-body radiation from the optical window. Here, using a window-less system, we systematically measure the weak-light photo-response of a Bi2Te3 photoconductive detector. The bolometric response and photo-thermoelectric effect are carefully excluded. It shows that LPR can persist to a small light power density of P < 10−8 W/cm2. Meanwhile, the response is maximized at ∼80 K temperature. We suggest that the LPR is rooted in the unique carrier recombination configuration of Bi2Te3, which can result in a constant lifetime for light-generated carriers. The concerned trap level is manifested by a negative photo-response under reduced light intensity. The signature of surface state related signal is presented as a photo-response with the maximum at ∼10 K temperature, which is fragile under increased light intensity. Although the window-less photo-response measurement is at its early stage, it provides a perspective which is different from that of the traditional optical-window based measurement.

Tapered InP nanowire arrays for efficient broadband high-speed single-photon detection.

Superconducting nanowire single-photon detectors with peak efficiencies above 90% and unrivalled timing jitter (<30 ps) have emerged as a potent technology for quantum information and sensing applications. However, their high cost and cryogenic operation limit their widespread applicability. Here, we present an approach using tapered InP nanowire p-n junction arrays for high-efficiency, broadband and high-speed photodetection without the need for cryogenic cooling. The truncated conical nanowire shape enables a broadband, linear photoresponse in the ultraviolet to near-infrared range (~500 nm bandwidth) with external quantum efficiencies exceeding 85%. The devices exhibit a high gain beyond 105, such that a single photon per pulse can be distinguished from the dark noise, while simultaneously showing a fast pulse rise time (<1 ns) and excellent timing jitter (<20 ps). Such detectors open up new possibilities for applications in remote sensing, dose monitoring for cancer treatment, three-dimensional imaging and quantum communication.

Effect of Photo-response Nonlinearity on the Diffraction Efficiency of Holograms

The effect of the photo-response nonlinearity of a holographic material on the achievable diffraction efficiency of holograms has been studied. It has been shown that the interaction between the hologram form factor and the photo-response nonlinearity leads to an increase in diffraction efficiency compared to a linear photo-response. Numerical calculations for the photo-response nonlinearity corresponding to Reoxan phase holographic material are presented.

Dual-gate organic phototransistor with high-gain and linear photoresponse

The conversion of light into electrical signal in a photodetector is a crucial process for a wide range of technological applications. Here we report a new device concept of dual-gate phototransistor that combines the operation of photodiodes and phototransistors to simultaneously enable high-gain and linear photoresponse without requiring external circuitry. In an oppositely biased, dual-gate transistor based on a solution-processed organic heterojunction layer, we find that the presence of both n- and p-type channels enables both photogenerated electrons and holes to efficiently separate and transport in the same semiconducting layer. This operation enables effective control of trap carrier density that leads to linear photoresponse with high photoconductive gain and a significant reduction of electrical noise. As we demonstrate using a large-area, 8 × 8 imaging array of dual-gate phototransistors, this device concept is promising for high-performance and scalable photodetectors with tunable dynamic range.