Showing papers on "Responsivity published in 2013"

Chip-integrated ultrafast graphene photodetector with high responsivity

Abstract: A chip-integrated graphene photodetector with a high responsivity of over 0.1 A W−1, high speed and broad spectral bandwidth is realized through enhanced absorption due to near-field coupling. Under zero-bias operation, response rates above 20 GHz and an instrumentation-limited 12 Gbit s−1 optical data link are demonstrated.

High-responsivity graphene/silicon-heterostructure waveguide photodetectors

Abstract: A CMOS-compatible graphene/silicon-heterostructure photodetector formed by integrating graphene onto a silicon optical waveguide on silicon-on-insulator and operating in the near- and mid-infrared regions is demonstrated. A responsivity as high as 0.13 A W−1 is obtained at a bias of 1.5 V for 2.75-μm light at room temperature.

A Comprehensive Review of Semiconductor Ultraviolet Photodetectors: From Thin Film to One-Dimensional Nanostructures

Abstract: Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga2O3, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications.

Narrowband photodetection in the near-infrared with a plasmon-induced hot electron device.

Abstract: In gratings, incident light can couple strongly to plasmons propagating through periodically spaced slits in a metal film, resulting in a strong, resonant absorption whose frequency is determined by the nanostructure periodicity. When a grating is patterned on a silicon substrate, the absorption response can be combined with plasmon-induced hot electron photocurrent generation. This yields a photodetector with a strongly resonant, narrowband photocurrent response in the infrared, limited at low frequencies by the Schottky barrier, not the bandgap of silicon. Here we report a grating-based hot electron device with significantly larger photocurrent responsivity than previously reported antenna-based geometries. The grating geometry also enables more than three times narrower spectral response than observed for nanoantenna-based devices. This approach opens up the possibility of plasmonic sensors with direct electrical readout, such as an on-chip surface plasmon resonance detector driven at a single wavelength.

Few-Layer MoS2 with High Broadband Photogain and Fast Optical Switching for Use in Harsh Environments

Abstract: Few-layered MoS2 as Schottky metal–semiconductor–metal photodetectors (MSM PDs) for use in harsh environments makes its debut as two-dimensional (2D) optoelectronics with high broadband gain (up to 13.3), high detectivity (up to ∼1010 cm Hz1/2/W), fast photoresponse (rise time of ∼70 μs and fall time of ∼110 μs), and high thermal stability (at a working temperature of up to 200 °C). Ultrahigh responsivity (0.57 A/W) of few-layer MoS2 at 532 nm is due to the high optical absorption (∼10% despite being less than 2 nm in thickness) and a high photogain, which sets up a new record that was not achievable in 2D nanomaterials previously. This study opens avenues to develop 2D nanomaterial-based optoelectronics for harsh environments in imaging techniques and light-wave communications as well as in future memory storage and optoelectronic circuits.

Tunable Graphene–Silicon Heterojunctions for Ultrasensitive Photodetection

Abstract: We present the photodetection properties of graphene/Si heterojunctions both in the photocurrent and photovoltage modes. Monolayer graphene/Si junctions were found to be excellent weak-signal detectors with photovoltage responsivity exceeding 107 V/W and with noise-equivalent-power reaching ∼1 pW/Hz1/2, potentially capable of distinguishing materials with transmittance, T = 0.9995 in a 0.5 s integration time. In the photocurrent mode, the response was found to remain linear over at least six decades of incident power (P), with tunable responsivity up to 435 mA/W (corresponding to incident photon conversion efficiency (IPCE) > 65%) obtained by layer thickening and doping. With millisecond-scale responses and ON/OFF ratios exceeding 104, these photodiodes are highly suitable for tunable and scalable broadband (400 < λ < 900 nm) photodetectors, photometers, and millisecond-response switching, spectroscopic and imaging devices, and further, and are architecturally compatible with on-chip low-power optoelectro...

Monolayer graphene/germanium Schottky junction as high-performance self-driven infrared light photodetector.

Abstract: We report on the simple fabrication of monolayer graphene (MLG)/germanium (Ge) heterojunction for infrared (IR) light sensing. It is found that the as-fabricated Schottky junction detector exhibits obvious photovoltaic characteristics, and is sensitive to IR light with high Ilight/Idark ratio of 2 × 104 at zero bias voltage. The responsivity and detectivity are as high as 51.8 mA W–1 and 1.38 × 1010 cm Hz1/2 W–1, respectively. Further photoresponse study reveals that the photovoltaic IR detector displays excellent spectral selectivity with peak sensitivity at 1400 nm, and a fast light response speed of microsecond rise/fall time with good reproducibility and long-term stability. The generality of the above results suggests that the present MLG/Ge IR photodetector would have great potential for future optoelectronic device applications.

Metal-semiconductor-metal photodetectors based on graphene/p-type silicon Schottky junctions

Abstract: Metal-semiconductor-metal (MSM) photodetectors based on graphene/p-type Si Schottky junctions are fabricated and characterized Thermionic emission dominates the transport across the junctions above 260 K with a zero-bias barrier height of 048 eV The reverse-bias dependence of the barrier height is found to result mostly from the Fermi level shift in graphene MSM photodetectors exhibit a responsivity of 011 A/W and a normalized photocurrent-to-dark current ratio of 455 × 104 mW−1, which are larger than those previously obtained for similar detectors based on carbon nanotubes These results are important for the integration of transparent, conductive graphene electrodes into existing silicon technologies

Increased Responsivity of Suspended Graphene Photodetectors

Abstract: The responsivity of graphene photodetectors depends critically on the elevated temperature of the electronic subsystem upon photoexcitation. We investigate the role of the substrate in providing cooling pathways for photoexcited carriers under ambient conditions by partially suspending few-layer graphene over a trench. Through photocurrent microscopy, we observe p–n junctions near the supported/suspended interfaces that produce photothermoelectric currents. Most importantly, we find the photocurrent in suspended p–n junctions to be an order of magnitude larger than in supported structures. This enhancement is attributed to the elimination of a dominant electronic cooling channel via the surface phonons of the polar substrate. Our work documents this mechanism of energy exchange between graphene and its environment, and it points to the importance of dielectric engineering for future improved graphene photodetectors.

High‐Performance Photoelectrochemical‐Type Self‐Powered UV Photodetector Using Epitaxial TiO2/SnO2 Branched Heterojunction Nanostructure

Abstract: TiO₂/SnO₂ branched heterojunction nanostructure with TiO₂ branches on electrospun SnO2 nanofiber (B-SnO₂ NF) networks serves as a model architecture for efficient self-powered UV photodetector based on a photoelectrochemical cell (PECC). The nanostructure simultaneously offers a low degree of charge recombination and a direct pathway for electron transport. Without correcting 64.5% loss of incident photons through light absorption and scattering by the F-doped tin oxide (FTO) glass, the incident power conversion efficiency reaches 14.7% at 330 nm, more than twice as large as the nanocrystalline TiO₂ (TiO₂ NC, 6.4%)-film based PECC. By connecting a PECC to an ammeter, the intensity of UV light is quantified using the output short-circuit photocurrent density (J(sc)) without a power source. Under UV irradiation, the self-powered UV photodetector exhibits a high responsivity of 0.6 A/W, a high on/off ratio of 4550, a rise time of 0.03 s and a decay time of 0.01 s for J(sc) signal. The excellent performance of the B-SnO₂ NF-based PECC type self-powered photodetector will enable significant advancements for next-generation photodetection and photosensing applications.

Active Terahertz Imaging Using Schottky Diodes in CMOS: Array and 860-GHz Pixel

Abstract: Schottky-barrier diodes (SBD's) fabricated in CMOS without process modification are shown to be suitable for active THz imaging applications Using a compact passive-pixel array architecture, a fully-integrated 280-GHz 4 × 4 imager is demonstrated At 1-MHz input modulation frequency, the measured peak responsivity is 51 kV/W with ±20% variation among the pixels The measured minimum NEP is 29 pW/Hz1/2 Additionally, an 860-GHz SBD detector is implemented by reducing the number of unit cells in the diode, and by exploiting the efficiency improvement of patch antenna with frequency The measured NEP is 42 pW/Hz1/2 at 1-MHz modulation frequency This is competitive to the best reported performance of MOSFET-based pixel measured without attaching an external silicon lens (66 pW/Hz1/2 at 1 THz and 40 pW/Hz1/2 at 650 GHz) Given that incorporating the 280-GHz detector into an array increased the NEP by ~ 20%, the 860-GHz imager array should also have the similar NEP as that for an individual detector The circuits were utilized in a setup that requires neither mirrors nor lenses to form THz images These suggest that an affordable and portable fully-integrated CMOS THz imager is possible

Deep ultraviolet photodiodes based on β-Ga2O3/SiC heterojunction

Abstract: A deep Ultraviolet (UV) photodiode was fabricated using a heterojunction between β-Ga2O3 with a band gap of 4.9 eV, and 6H-SiC with a band gap of 3.02 eV, and investigated its UV sensitivity. A thin β-Ga2O3 layer (200 nm) was prepared on a p-type 6H-SiC substrate through gallium evaporation in oxygen plasma. The device showed good rectifying properties. Under reverse bias, the current increased linearly with increasing deep-UV light intensity. The responsivity of the photodiode was highest to deep-UV light below a wavelength of 260 nm. The photodiode's response time to deep-UV light was in the order of milliseconds.

High responsivity, fast ultraviolet photodetector fabricated from ZnO nanoparticle–graphene core–shell structures

Abstract: We report a simple, efficient and versatile method for assembling metal oxide nanomaterial–graphene core–shell structures. An ultraviolet photodetector fabricated from the ZnO nanoparticle–graphene core–shell structures showed high responsivity and fast transient response, which are attributed to the improved carrier transport efficiency arising from graphene encapsulation.

High-Sensitivity and Fast-Response Graphene/Crystalline Silicon Schottky Junction-Based Near-IR Photodetectors

Abstract: Schottky junction near-infrared photodetectors were constructed by combing monolayer graphene (MLG) film and bulk silicon. Notably, the device could operate at zero external voltage bias because of the strong photovoltaic behavior of the MLG/Si Schottky junction, giving rise to high responsivity and detectivity of 29 mAW-1 and 3.9×1011 cmHz1/2W-1, respectively, at room temperature. Time response measurement revealed a high response speed of 100 μs, which allowed the device following a fast varied light with frequency up to 2100 Hz. In addition, the device showed great potential for low light detection with intensity at 10 K.

GaN nanowire ultraviolet photodetector with a graphene transparent contact

Abstract: We report on the fabrication of graphene contact to GaN nanowire ensemble and on the demonstration of photodetectors using chemical vapor deposition-grown few-layered graphene as a transparent electrode. The optimization of the transfer method allowed to form a continuous contact to the nanowires over a large area. The adhesion energy of the graphene sheet to the nanowire ensemble is estimated to be 0.3–0.7 J/m2. Ultraviolet photodetectors with a room-temperature responsivity of ∼25 A/W at 357 nm were fabricated. The photocurrent spectrum shows that the device has a strong response up to 4.15 eV confirming a good transparency of the top graphene contact.

Graphene-Si Schottky IR Detector

Abstract: This paper reports on photodetection properties of the graphene-Si schottky junction by measuring current–voltage characteristics under 1.55- $\mu{\rm m}$ excitation laser. The measurements have been done on a junction fabricated by depositing mechanically exfoliated natural graphite on top of the pre-patterned silicon substrate. The electrical Schottky barrier height is estimated to be (0.44–0.47) eV with a minimum responsivity of 2.8 mA/W corresponding to an internal quantum efficiency of 10%, which is almost an order of magnitude larger than regular Schottky junctions. A possible explanation for the large quantum efficiency related to the 2-D nature of graphene is discussed. Large quantum efficiency, room temperature IR detection, ease of fabrication along with compatibility with Si devices can open a doorway for novel graphene-based photodetectors.

Fullerene Photodetectors with a Linear Dynamic Range of 90 dB Enabled by a Cross-Linkable Buffer Layer

Abstract: Organic photodetectors have attracted signifi cant attention for their immediate application to the replacement of conventional devices based on expensive inorganic semiconductors. Potential new uses in both civil and defense applications take advantage of organic photodetectors’ light weight, fl exibility, and excellent form factors. [ 1 ] An example of a unique application for an organic photodetector is the capability to form organic thin fi lm devices on curved surfaces for things such as an artifi cial eye and a hemispherical array detector for imaging (HARDI), which allows a very wide fi eld of view without the aberrations encountered in a fl at focal plane. [ 2 ] In addition to the low cost of materials and the fabrication process, which is the typical advantage of organic electronic devices, organic photodetectors have the potential to outperform their inorganic counterparts; because their low conductivity enables them to dramatically reduce noise. A recent study shows that polymer-based organic photodetectors can have higher sensitivity than traditional photo detectors, such as silicon and InGaAs photodetectors in some wavelength range. [ 3 ] The response characteristics, such as linearity, to very weak light are of ultimate importance when detectivity of organic photodetectors reaches the parity with traditional photodetectors. Recent studies on organic photodetectors have focused on improving detectivity, but little attention was paid to the linearity of the organic photodetector’s responsivity, especially in a low light intensity region. The reported detectivities were mostly calculated according to the organic photodetector’s reponsivity at relatively strong light levels: orders of magnitude larger than the calculated noise equivalent power (NEP). It has not been shown yet whether the organic photodetectors can still maintain the high responsivity at low incident light intensity close to the NEP. However, there is concern that the organic photodetector would loss its high responsivity at such a low light level as there is generally a much higher density of charge traps in organic rather than inorganic semiconductor materials due to the amorphous or polycrystalline organic semiconductors used. When the charge density generated by the incident light is comparable to the charge trap density, the photogenerated charges might be trapped rather than contribute to the device photocurrent. In this paper, we report on a highly sensitive, fullerene-based organic photodetector device which shows linear response from the indoor light intensity all the way down to 12 pW m 2 . This type of organic photodetector presents a linear dynamic range of 90 dB. Our fi rst step is to fabricate a photodetector with very small noise current so that the weak light generated small photocurrent can be distinguishable from the noise current. The lightabsorbing material used in this study is fullerene (C 60 ) which is one of the most broadly studied materials for devices, including organic solar cells and organic fi eld effect transistors, because of its excellent optoelectronic properties, such as a large light absorption coeffi cient, of 1.21 ◊ 10 5 cm 1 at 442 nm, [ 4 ] and high electron mobility, of up to 6~11 cm 2 V 1 s 1 . [ 5 ] In our organic photodetector devices, the thickness of C 60 is around 80 nm which allows more than 60% of the light above its optical bandgap to be absorbed. In our previous study, it was found that C 60 is a good photoconductor material with much longer hole trapping time than electron transit time. A photoconductive gain above 50 under reverse bias below −5 V has been observed in the device with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

A high-sensitivity near-infrared phototransistor based on an organic bulk heterojunction

Abstract: High-gain photodetectors with near-infrared (NIR) sensitivity are critical for biomedical applications such as photoplethysmography and optical coherence tomography where detected optical signals are relatively weak. Current photodetection technologies rely on avalanche photodiodes and photomultipliers to achieve high sensitivity. These devices, however, require a high operation voltage and are not compatible with CMOS based read-out circuits (ROCs). In this work we demonstrate a solution-proceeded NIR phototransistor structure based on a bulk heterojunction (BHJ) of a narrow bandgap polymer, poly(N-alkyl diketopyrrolo-pyrrole dithienylthieno[3,2-b]thiophene) (DPP-DTT), and [6,6]-phenyl-C61-butyric acid methylester (PCBM). The device exhibits ultrahigh responsivity (∼5 × 105 A W−1) as well as wide tunability (>1 × 104) of photoconductive gain. Using the current–voltage and transient photocurrent measurements we show that the high responsivity is due to the combined effects of fast transport of holes in the polymer matrix and slow detrapping of electrons from the isolated PCBM domains. The wide gain tunability and the efficient suppression of noise current are achieved through the use of the optically tunable gate terminal. We demonstrate that our phototransistor can be used as the detection unit in a photoplethysmography sensor for non-invasive, continuous finger pulse wave monitoring. The high-sensitivity of the phototransistor allows the use of a low-power light source, thus reducing the overall power consumption of the sensor. This, together with the solution processibility and the simple device configuration (which is compatible with conventional ROCs), make the phototransistor a very promising component for the next generation low-cost, mobile biomedical devices for health monitoring and remote diagnostics.

AlxGa1-xN-based back-illuminated solar-blind photodetectors with external quantum efficiency of 89%

Abstract: We report on high performance AlxGa1−xN-based solar-blind ultraviolet photodetector (PD) array grown on sapphire substrate. First, high quality, crack-free AlN template layer is grown via metalorganic chemical vapor deposition. Then, we systematically optimized the device design and material doping through the growth and processing of multiple devices. After optimization, uniform and solar-blind operation is observed throughout the array; at the peak detection wavelength of 275 nm, 729 μm2 area PD showed unbiased peak external quantum efficiency and responsivity of ∼80% and ∼176 mA/W, respectively, increasing to 89% under 5 V of reverse bias. Taking the reflection loses into consideration, the internal quantum efficiency of these optimized PD can be estimated to be as high as ∼98%. The visible rejection ratio measured to be more than six orders of magnitude. Electrical measurements yielded a low-dark current density: <2 × 10−9 A/cm2, at 10 V of reverse bias.

High-detectivity InAs nanowire photodetectors with spectral response from ultraviolet to near-infrared

Abstract: InAs is a direct, narrow band gap (0.354 eV) material with ultrahigh electron mobility, and is potentially a good optoelectronic device candidate in the wide UV-visible-near-infrared region. In this work we report the fabrication of InAs nanowire-based photodetectors, which showed a very high photoresponse over a broad spectral range from 300 to 1,100 nm. The responsivity, external quantum efficiency and detectivity of the device were respectively measured to be 4.4 × 103 AW−1, 1.03 × 106%, and 2.6 × 1011 Jones to visible incident light. Time dependent measurements at different wavelengths and under different light intensities also demonstrated the fast, reversible, and stable photoresponse of our device. Theoretical calculations of the optical absorption and the electric field component distribution were also performed to elucidate the mechanism of the enhanced photoresponse. Our results demonstrate that the single-crystalline InAs NWs are very promising candidates for the design of high sensitivity and high stability nanoscale photodetectors with a broad band photoresponse. Open image in new window

High efficiency NiO/ZnO heterojunction UV photodiode by sol–gel processing

Abstract: We studied the thin film heterojunction photodiode made of nickel oxide (NiO) and zinc oxide (ZnO) deposited by low cost energy-efficient sol–gel spin coating. The highly visible-transparent heterojunction photodiode with a smooth interface gives rise to a good photoresponse and quantum efficiency under ultra-violet (UV) light illumination. With an applied reverse bias of 5 V, a very impressive peak photo responsivity of 21.8 A W−1 and an external quantum efficiency (EQE) of 88% at an incident light wavelength of 310 nm were accomplished.

Characterization and modeling of a ZnO nanowire ultraviolet photodetector with graphene transparent contact

Abstract: We report the demonstration of a ZnO nanowire ultraviolet photodetector with a top transparent electrode made of a few-layered graphene sheet. The nanowires have been synthesized using a low-cost electrodeposition method. The detector is shown to be visible-blind and to present a responsivity larger than 104 A/W in the near ultraviolet range thanks to a high photoconductive gain in ZnO nanowires. The device exhibits a peak responsivity at 370 nm wavelength and shows a sub bandgap response down to 415 nm explained by an Urbach tail with a characteristic energy of 83 meV. The temporal response of the detector and the power dependence are discussed. A model of the photoconductive mechanism is proposed showing that the main process responsible for the photoconductive gain is the modulation of the conducting surface due to the variation of the surface depletion layer and not the reduction of recombination efficiency stemming from the electron-hole spatial separation. The gain is predicted to decrease at high incident power due to the flattening of the lateral band bending in agreement with experimental data.

Bi-material terahertz sensors using metamaterial structures.

Abstract: In this paper we report on the design, fabrication and characterization of terahertz (THz) bi-material sensors with metamaterial absorbers. MEMS fabrication-friendly SiOx and Al are used to maximize the bimetallic effect and metamaterial absorption at 3.8 THz, the frequency of a quantum cascade laser illumination source. Sensors with different configurations were fabricated and the measured absorption is near 100% and responsivity is around 1.2 deg/μW, which agree well with finite element simulations. The results indicate the potential of using these detectors to fabricate focal plane arrays for real time THz imaging.

Mid‐Infrared HgTe/As2S3 Field Effect Transistors and Photodetectors

Abstract: HgTe colloidal quantum dots (CQD) in an inorganic As(2)S(3) matrix allow 100-fold higher mobility with optimized transport properties compared to HgTe-organic CQD film while remaining intrinsic. The material's electronic properties are measured by field effect transistors as a function of temperature and the responsivity and detectivity of the mid-IR photoconductors are discussed.

A 0.32 THz SiGe 4x4 Imaging Array Using High-Efficiency On-Chip Antennas

Abstract: This paper presents a 0.32 THz 4x4 imaging array based on an advanced SiGe technology. Each pixel is composed of a high efficiency on-chip antenna meeting all metal-density rules, which is coupled to a SiGe detector and a low noise CMOS operational amplifier. A quartz superstrate is used on top of the imaging chip to improve the radiation efficiency. The array results in an average NEP of 34 pW/Hz 1/2 at an IF of 10-100 kHz for a detector bias current of 50-150 μA, a responsivity of 18 kV/W and a 3-dB bandwidth of 25 GHz. The power consumption is 2.4 mW/pixel. Extensive measurements are presented which show the challenges encountered in obtaining accurate measurements at THz frequencies using a quasi-optical set-up, and the decisions taken to quote the average NEP values.

Photothermoelectric p–n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films

Abstract: Light polarization is used in the animal kingdom for communication, navigation, and enhanced scene interpretation and also plays an important role in astronomy, remote sensing, and military applications. To date, there have been few photodetector materials demonstrated to have direct polarization sensitivity, as is usually the case in nature. Here, we report the realization of a carbon-based broadband photodetector, where the polarimetry is intrinsic to the active photodetector material. The detector is based on p–n junctions formed between two macroscopic films of single-wall carbon nanotubes. A responsivity up to ∼1 V/W was observed in these devices, with a broadband spectral response spanning the visible to the mid-infrared. This responsivity is about 35 times larger than previous devices without p–n junctions. A combination of experiment and theory is used to demonstrate the photothermoelectric origin of the responsivity and to discuss the performance attributes of such devices.

High-responsivity GeSn short-wave infrared p-i-n photodetectors

Abstract: Surface-illuminated GeSn p-i-n photodetectors (PDs) with Ge0.964Sn0.036 active layer on Ge substrate were fabricated. Photodetection up to 1.95 μm is achieved with a responsivity of 0.13 A/W. High responsivities of 0.56 and 0.71 A/W were achieved under a reverse bias voltage of 3 V at 1640 and 1790 nm, respectively. A low dark current of 1.08 μA was obtained at a reverse bias of 1 V with a diameter of 150 μm, which corresponds to a current density of 6.1 mA/cm2. This value is among the lowest dark current densities reported among GeSn PDs.

High sensitivity of middle-wavelength infrared photodetectors based on an individual InSb nanowire.

Abstract: Single-crystal indium antimony (InSb) nanowire was fabricated into middle-infrared photodetectors based on a metal–semiconductor-metal (M-S-M) structure. The InSb nanowires were synthesized using an electrochemical method at room temperature. The characteristics of the FET reveal an electron concentration of 3.6 × 1017 cm−3 and an electron mobility of 215.25 cm2 V−1 s−1. The photodetectors exhibit good photoconductive performance, excellent stability, reproducibility, superior responsivity (8.4 × 104 A W−1), and quantum efficiency (1.96 × 106%). These superior properties are attributed to the high surface-to-volume ratio and single-crystal 1D nanostructure of photodetectors that significantly reduce the scattering, trapping, and the transit time between the electrodes during the transport process. Furthermore, the M-S-M structure can effectively enhance space charge effect by the formation of the Schottky contacts, which significantly assists with the electron injection and photocurrent gain.

Self-powered flexible and transparent photovoltaic detectors based on CdSe nanobelt/graphene Schottky junctions.

Abstract: Flexible and transparent electronic and optoelectronic devices have attracted more and more research interest due to their potential applications in developing portable, wearable, low-cost, and implantable devices. We have fabricated and studied high-performance flexible and transparent CdSe nanobelt (NB)/graphene Schottky junction self-powered photovoltaic detectors for the first time. Under 633 nm light illumination, typical photosensitivity and responsivity of the devices are about 1.2 × 105 and 8.7 A W−1, respectively. Under 3500 Hz switching frequency, the response and recovery times of them are about 70 and 137 μs, respectively, which, to the best of our knowledge, are the best reported values for nanomaterial based Schottky junction photodetectors up to date. The detailed properties of the photodetectors, such as the influences of incident light wavelength and light intensity on the external quantum efficiency and speed, are also investigated. Detailed discussions are made in order to understand the observed phenomena. Our work demonstrates that the self-powered flexible and transparent CdSe NB/graphene Schottky junction photovoltaic detectors have a bright application prospect.