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Showing papers on "Photodiode published in 2018"


Journal ArticleDOI
TL;DR: In this article, a bias-selectable polarization-resolved photodetector that operates without the need for external optics was proposed. But the performance of the two-terminal device was not evaluated.
Abstract: Infrared photodetectors are currently subject to a rapidly expanding application space, with an increasing demand for compact, sensitive and inexpensive detectors. Despite continued advancement, technological factors limit the widespread usage of such detectors, specifically, the need for cooling and the high costs associated with processing of iii–v/ii–vi semiconductors. Here, black phosphorous (bP)/MoS2 heterojunction photodiodes are explored as mid-wave infrared (MWIR) detectors. Although previous studies have demonstrated photodiodes using bP, here we significantly improve the performance, showing that such devices can be competitive with conventional MWIR photodetectors. By optimizing the device structure and light management, we demonstrate a two-terminal device that achieves room-temperature external quantum efficiencies (ηe) of 35% and specific detectivities (D*) as high as 1.1 × 1010 cm Hz1/2 W−1 in the MWIR region. Furthermore, by leveraging the anisotropic optical properties of bP we demonstrate the first bias-selectable polarization-resolved photodetector that operates without the need for external optics.

318 citations


Journal ArticleDOI
TL;DR: The distinctive WSe2 /SnS2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 1013 Jones (Iph /Idark ratio of ≈106 ) and photoresponsivity of 244 A W-1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm-2 ).
Abstract: van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe2 /SnS2 photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe2 /SnS2 vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe2 /SnS2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 1013 Jones (Iph /Idark ratio of ≈106 ) and photoresponsivity of 244 A W-1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm-2 ).

268 citations


Journal ArticleDOI
01 Mar 2018-Small
TL;DR: High-performance photovoltaic photodetectors based on MoTe2 /MoS2 vertical heterojunctions are demonstrated by exfoliating-restacking approach and the fundamental electric properties and band structures of the junction are revealed and analyzed.
Abstract: Van der Waals heterostructures based on 2D layered materials have received wide attention for their multiple applications in optoelectronic devices, such as solar cells, light-emitting devices, and photodiodes. In this work, high-performance photovoltaic photodetectors based on MoTe2 /MoS2 vertical heterojunctions are demonstrated by exfoliating-restacking approach. The fundamental electric properties and band structures of the junction are revealed and analyzed. It is shown that this kind of photodetectors can operate under zero bias with high on/off ratio (>105 ) and ultralow dark current (≈3 pA). Moreover, a fast response time of 60 µs and high photoresponsivity of 46 mA W-1 are also attained at room temperature. The junctions based on 2D materials are expected to constitute the ultimate functional elements of nanoscale electronic and optoelectronic applications.

192 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the physical properties of Cu2O nanowires and their applications in visible light photodiodes and found that they have favorable formation energies, indicative of facile synthesis.

164 citations


Journal ArticleDOI
TL;DR: A comprehensive overview of the recent progress of organic near-infrared (NIR) photodiodes, mainly focusing on diverse device architectures toward superior performance, is provided in this paper, where the authors highlight three primary strategies: (i) the use of truly narrowband absorbers; (ii) the manipulation of internal quantum efficiency via charge collection narrowing; and (iii) the incorporation of a resonant optical microcavity structure to exploit charge transfer absorption.
Abstract: Solution-processable organic photodiodes compensate well for the shortages of the traditional inorganic photodetectors in terms of their unique features, such as rich in varieties, low-cost manufacturing, light weight, high flexibility, and large-area scalability. Owing to the tunable optoelectronic properties of organic materials, both panchromatic and narrowband organic photodiodes have been achieved. In this review, we provide a comprehensive overview of the recent progress of organic near-infrared (NIR) photodiodes, mainly focusing on diverse device architectures toward superior performance. The key to achieving a high specific detectivity is a high responsivity while keeping dark current low. Interfacial engineering plays a critical role in suppressing the dark current, and has been identified as an essential approach for maximizing detectivity of organic photodiodes. Besides, optimization of photoactive layer thickness and morphology is also highly desirable. As to narrowband organic NIR photodiodes, we highlight three primary strategies: (i) the use of truly narrowband absorbers; (ii) the manipulation of internal quantum efficiency via charge collection narrowing; and (iii) the incorporation of a resonant optical microcavity structure to exploit charge-transfer absorption. The latter two creative approaches allow for response tuning by simply adjusting the thickness of photoactive layer and cavity, respectively.

152 citations


Journal ArticleDOI
TL;DR: The results of this study indicate that PtSe2 is a promising option for the development of infrared absorbers and detectors for optoelectronics applications with low-temperature processing conditions.
Abstract: Platinum diselenide (PtSe2) is a group-10 transition metal dichalcogenide (TMD) that has unique electronic properties, in particular a semimetal-to-semiconductor transition when going from bulk to monolayer form. We report on vertical hybrid Schottky barrier diodes (SBDs) of two-dimensional (2D) PtSe2 thin films on crystalline n-type silicon. The diodes have been fabricated by transferring large-scale layered PtSe2 films, synthesized by thermally assisted conversion of predeposited Pt films at back-end-of-the-line CMOS compatible temperatures, onto SiO2/Si substrates. The diodes exhibit obvious rectifying behavior with a photoresponse under illumination. Spectral response analysis reveals a maximum responsivity of 490 mA/W at photon energies above the Si bandgap and relatively weak responsivity, in the range of 0.1–1.5 mA/W, at photon energies below the Si bandgap. In particular, the photoresponsivity of PtSe2 in infrared allows PtSe2 to be utilized as an absorber of infrared light with tunable sensitivit...

136 citations


Journal ArticleDOI
TL;DR: A novel 2DM, black phosphorous carbide (b-PC) with a wide absorption spectrum up to 8000 nm is synthesized and a b-PC phototransistor with a tunable responsivity and response time at an excitation wavelength of 2004 nm is demonstrated.
Abstract: Photodetectors with broadband detection capability are desirable for sensing applications in the coming age of the internet-of-things. Although 2D layered materials (2DMs) have been actively pursued due to their unique optical properties, by far only graphene and black arsenic phosphorus have the wide absorption spectrum that covers most molecular vibrational fingerprints. However, their reported responsivity and response time are falling short of the requirements needed for enabling simultaneous weak-signal and high-speed detections. Here, a novel 2DM, black phosphorous carbide (b-PC) with a wide absorption spectrum up to 8000 nm is synthesized and a b-PC phototransistor with a tunable responsivity and response time at an excitation wavelength of 2004 nm is demonstrated. The b-PC phototransistor achieves a peak responsivity of 2163 A W-1 and a shot noise equivalent power of 1.3 fW Hz-1/2 at 2004 nm. In addition, it is shown that a response time of 0.7 ns is tunable by the gating effect, which renders it versatile for high-speed applications. Under the same signal strength (i.e., excitation power), its performance in responsivity and detectivity in room temperature condition is currently ahead of recent top-performing photodetectors based on 2DMs that operate with a small bias voltage of 0.2 V.

97 citations


Journal ArticleDOI
TL;DR: The proposed phototransistor could be potentially used in high-performance visible-blind UV photodetector pixel arrays, and by applying a short positive gate pulse onto the gate, the annoying persistent photoconductivity presented in the wide band gap oxide-based devices could be suppressed conveniently, in hope of improving the response rate.
Abstract: A visible-blind ultraviolet (UV) photodetector was designed based on a three-terminal electronic device of thin-film transistor (TFT) coupled with two-terminal p–n junction optoelectronic device, in hope of combining the beauties of both of the devices together. Upon the uncovered back-channel surface of amorphous indium–gallium–zinc-oxide (IGZO) TFT, we fabricated PEDOT:PSS/SnOx/IGZO heterojunction structure, through which the formation of a p–n junction and directional carrier transfer of photogenerated carriers were experimentally validated. As expected, the photoresponse characteristics of the newly designed photodetector, with a photoresponsivity of 984 A/W at a wavelength of 320 nm, a UV–visible rejection ratio up to 3.5 × 107, and a specific detectivity up to 3.3 × 1014 Jones, are not only competitive compared to the previous reports but also better than those of the pristine IGZO phototransistor. The hybrid photodetector could be operated in the off-current region with low supply voltages (<0.1 V)...

91 citations


Journal ArticleDOI
TL;DR: In this paper, high performance and high reliability photodiodes are demonstrated by using α-CsPbI3 perovskite nanocrystals (NCs) phase-stabilized with a low-temperature solution-treated active layer.
Abstract: High-performance and high-reliability photodiodes are demonstrated by using α-CsPbI3 perovskite nanocrystals (NCs) phase-stabilized with a low-temperature solution-treated active layer. In addition to the high charge mobility, the high absorption coefficient, and IR-blind characteristics of the perovskite material, the defect-tolerant nature of α-CsPbI3 perovskite NCs are combined to realize hysteresis-free and high detectivity photodiodes. To further minimize interface defects originating from multi-layer photodiode construction, a poly(3-hexylthiophene) layer is strategically introduced as a passivation and electron blocking layer, resulting in a low diode ideality factor of 1.5 and a noise equivalent power of 1.6 × 10−13 W Hz−0.5. As a result, high detectivity of 1.8 × 1012 Jones is demonstrated with near-zero hysteresis. Furthermore, the optimized photodiode exhibits excellent stability under high humidity conditions owing to the intrinsic nature of the defect-tolerant α-CsPbI3 perovskite NCs.

89 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a model that accounts for the increasing electric-field dependence of photocurrent in narrow bandgap materials, by decoupling the exciton dissociation efficiency and charge collection efficiency in photocurrent-voltage measurements.
Abstract: While only few organic photodiodes have photoresponse past 1 µm, novel shortwave infrared (SWIR) polymers are emerging, and a better understanding of the limiting factors in narrow bandgap devices is critically needed to predict and advance performance. Based on state-of-the-art SWIR bulk heterojunction photodiodes, this work demonstrates a model that accounts for the increasing electric-field dependence of photocurrent in narrow bandgap materials. This physical model offers an expedient method to pinpoint the origins of efficiency losses, by decoupling the exciton dissociation efficiency and charge collection efficiency in photocurrent–voltage measurements. These results from transient photoconductivity measurements indicate that the main loss is due to poor exciton dissociation, particularly significant in photodiodes with low-energy charge-transfer states. Direct measurements of the noise components are analyzed to caution against using assumptions that could lead to an overestimation of detectivity. The devices show a peak detectivity of 5 × 1010 Jones with a spectral range up to 1.55 µm. The photodiodes are demonstrated to quantify the ethanol–water content in a mixture within 1% accuracy, conveying the potential of organics to enable economical, scalable detectors for SWIR spectroscopy.

83 citations


Journal ArticleDOI
TL;DR: Intensive study has been performed to understand the enhanced absorption of black silicon as well as the response extended to infrared spectrum range, which will provide a meaningful introduction to black silicon and its unique properties.
Abstract: As a widely used semiconductor material, silicon has been extensively used in many areas, such as photodiode, photodetector, and photovoltaic devices. However, the high surface reflectance and large bandgap of traditional bulk silicon restrict the full use of the spectrum. To solve this problem, many methods have been developed. Among them, the surface nanostructured silicon, namely black silicon, is the most efficient and widely used. Due to its high absorption in the wide range from UV-visible to infrared, black silicon is very attractive for using as sensitive layer of photodiodes, photodetector, solar cells, field emission, luminescence, and other photoelectric devices. Intensive study has been performed to understand the enhanced absorption of black silicon as well as the response extended to infrared spectrum range. In this paper, the application of black silicon is systematically reviewed. The limitations and challenges of black silicon material are also discussed. This article will provide a meaningful introduction to black silicon and its unique properties.

Journal ArticleDOI
TL;DR: A dual-gate structure that combines the operation of photodiodes and phototransistors to enable both amplified and linear response without external circuitry is shown, promising for high-performance and scalable photodetector with tunable dynamic range.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, a WSe2/GeSe heterojunction photodiode with type-II band alignment is presented, in which the value of the conduction band and valence band edge in WSe 2 is approximately equal to that of GeSe.

Journal ArticleDOI
TL;DR: In this paper, a transparent diodes formed by a heterojunction between p-type CuS-ZnS and n-type ZnO thin films were fabricated by sequential chemical bath deposition and sol-gel spin coating.
Abstract: Transparent diodes formed by a heterojunction between p-type CuS–ZnS and n-type ZnO thin films were fabricated by sequential chemical bath deposition and sol-gel spin coating. The diodes are transparent in the visible (≈70% at 550 nm) and exhibit a good rectifying characteristics, with If/Ir ratios of up to 800 at ±1 V, higher than most of the reported solution-processed diodes measured at a similar bias. More importantly, when operated as a self-powered (zero bias) UV photodetector, they show stable and fast (<1 s) photoresponse with a maximum responsivity of 12 mA W−1 at 300 nm. Both the response time and responsivity of the p-CuZnS/n-ZnO UV photodiode are comparable or superior to similar solution-processed devices reported in the literature.


Journal ArticleDOI
TL;DR: In this article, a fully operational 32 × 32 silicon photonic switch chip having 448 switch cells and 1856 crossings is demonstrated, and the calibration procedure employs an external laser source and follows a reachability-tree sequence to calibrate all switch cells.
Abstract: A packaged and fully operational 32 × 32 silicon photonic switch chip having 448 switch cells and 1856 crossings is demonstrated. The switch chip includes 900 monolithically integrated photodiodes used for calibrating the thermo-optic Mach–Zehnder switch cells. The calibration procedure employs an external laser source and follows a reachability-tree sequence to calibrate all switch cells. The accuracy of the calibration is demonstrated by the measurement of switch cell extinction ratios, for both states of each switch cell. The mean extinction ratio for both states is 35 dB. Arbitrary light path switching is demonstrated. Measurement of the channel-to-channel crosstalk was performed for a large number of aggressor and victim light path combinations. The matrix crosstalk is dominated by contributions from waveguide crossings. The die was wire-bonded to a custom ceramic package, to which a 68-fiber ribbon was permanently attached, which coupled the input and output optical signals to edge couplers on the chip through a waveguide pitch- and mode-concentrating silica chip. The fiber-to-fiber loss of on-chip loopback waveguides was less than 6.5 dB from 1530 to 1565 nm. The entirety of switch cells and monitors was driven by controller boards and A/D chips using a controller field-programmable gate array (FPGA). The calibration procedure was completed in less than 10 min using only the on-chip monitors, without off-chip detectors. The chip was recalibrated after six months storage, and the measured change in drive current was within the calibration uncertainty, indicating that the chip and driver are stable over time.

Journal ArticleDOI
TL;DR: In this paper, a 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described, which is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition robust surveillance.
Abstract: A 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described. The image sensor was fabricated using a wafer process and incorporates back-illumination and an antireflection layer to minimize optical flaring and ghosting problems. In testing, the sensor achieved a polarization transmittance of 63.3% and an extinction ratio of 85 at 550 nm, thereby outperforming conventional polarization sensors. The proposed sensor also exhibited good oblique-incidence characteristics, even with small polarization pixels of $2.5~\mu \text{m}$ . Based on these results, the proposed image sensor is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition-robust surveillance.

Journal ArticleDOI
TL;DR: The spray deposition technique will benefit the fabrication of perovskite QD film optoelectronics on a large scale and is developed to fabricate a CsPbBr3 quantum dot (QD) film photodiode which had a high material utilization ratio and a deposition rate of 9 nm/s.
Abstract: Large-area film deposition and high material utilization ratio are the crucial factors for large-scale application of perovskite optoelectronics. Recently, all-inorganic halide perovskite CsPbBr3 has attracted great attention because of its high phase stability, thermal stability, and photostability. However, most reported perovskite devices were fabricated by spin-coating, suffering from a low material utilization ratio of 1% and a small coverage area. Here, we developed a spray-coating technique to fabricate a CsPbBr3 quantum dot (QD) film photodiode which had a high material utilization ratio of 32% and a deposition rate of 9 nm/s. The film growth process was studied, and substrate temperature and spray time were two key factors for the deposition of uniform and crack-free QD films. The spray-coated photodiode was demonstrated to be more suitable for working in the photodetector mode because a low dark current density of 4 × 10–4 mA cm–2 resulting from an extremely low recombination current contributed...

Journal ArticleDOI
TL;DR: In this paper, the characteristics of Ge0.89Sn0.11 photodiodes monolithically grown on a Si substrate were reported for low-cost shortwave infrared detectors.
Abstract: Low-cost shortwave infrared detectors have great potential for emerging civilian night-vision applications. This paper reports the characteristics of Ge0.89Sn0.11 photodiodes monolithically grown on a Si substrate that holds great promise for those applications. At room temperature, the 500 μm diameter active area device demonstrated a longwave cutoff of 2.65 μm and a responsivity of 0.32 A/W at 2 μm, which corresponds to an external quantum efficiency of 20% without any contribution from the Ge buffer layer. The measured peak specific detectivity at 300 K and 77 K is 1.7 × 109 Jones and 4.3 × 109 Jones, respectively. The specific detectivity at 77 K is only one-order-of-magnitude lower than that of the market dominating extended-InGaAs photodiode. The detailed device analysis indicated that the 700-nm thick fully relaxed high-quality GeSn absorbing layer and the modified depletion region lead to the above-mentioned device performance.

Journal ArticleDOI
TL;DR: In this paper, a flexible broadband organic photodiode (OPD) array capable of RGB light separation is presented, which can successfully detect and reconstruct colors in the RGB system, with an average accuracy of 98.5%.

Journal ArticleDOI
TL;DR: In this paper, a 2D WSe2/MoS2 multilayer van der Waals heterojunction PN diode was proposed for visible-near infrared broadband detection.
Abstract: Two dimensional (2D) layered van der Waals (vdW) atomic crystals are an important class of emerging materials due to their unique physical properties. In particular, the nature of dangling–bond–free surfaces in 2D vdW materials enables the formation of heterojunctions without the constraint of atomic lattice match. Here, we report on a 2D WSe2/MoS2 multilayer van der Waals heterojunction PN diode and its application for visible-near infrared broadband detection. The WSe2/MoS2 PN diode shows excellent performance with an ideality factor of 1.5 and a high rectification (ON/OFF) ratio of over 106. This PN diode exhibits spectral photo-responses from the ultraviolet (405 nm) region to the near infrared (808 nm) region with obvious photovoltaic behaviors (very clear open circuit voltage and short circuit current). In addition to the static behavior, photocurrent switching behaviors are clearly observed under periodic illuminations at up to 1 KHz. The device shows a linear response within the optical power density range of 10−5 W cm−2 to 1 W cm−2 and a linear dynamic range is estimated to be 123 dB.

Journal ArticleDOI
TL;DR: This paper develops the key elements to present a simple design tool for the efficient integration of the device with an antenna and presents fabricated device results that show the highest figure of merit to date for photonic THz emitters.
Abstract: High-speed photodiodes are a key element of numerous photonic systems. With the development of potential applications in the THz range such as sensing, spectroscopy, and wireless transmission, devices with integrated antenna covering the frequency range from 0.1 to 3 THz will become essential. In this paper, we discuss the development of uni-traveling carrier photodiodes with integrated antennas to address that need. In particular we develop the key elements to present a simple design tool for the efficient integration of the device with an antenna. We also present fabricated device results that show the highest figure of merit to date for photonic THz emitters. When integrated with well-matched antennas the devices have achieved record level of power up to 1 THz compared to other published photomixers. We also show that these devices can be used as receivers at frequencies up to 560 GHz with conversion losses of the order of 30 dB.

Journal ArticleDOI
TL;DR: In this paper, a unipolar barrier was designed from another layer of colloidal quantum dots (CQDs) with a wider band gap to reduce the dark current injection and enhance the signal-to-noise ratio.
Abstract: Nanocrystals are promising materials for the design of low-cost, infrared (IR) detectors. Here we focus on HgTe colloidal quantum dots (CQDs) as an active material for detection in the extended short-wave infrared (2.5 μm as cutoff wavelength). In this paper, we propose a strategy to enhance the performances of previously reported photodiodes. In particular, we integrate in this diode a unipolar barrier, whose role is to reduce the dark current injection and subsequently enhance the signal-to-noise ratio. We demonstrate that such unipolar barrier can be designed from another layer of HgTe CQDs with a wider band gap. Using a combination of IR spectroscopy and photoemission, we show that the barrier is resonant with the absorbing layer valence band, while presenting a clear offset with the conduction band. The combination of contacts with improved design and use of a unipolar barrier allows us to reach a detectivity as high as 3 × 108 Jones at room temperature with 3 dB cut off frequency above 10 kHz.

Journal ArticleDOI
TL;DR: In this article, a high-speed surface-illuminated Ge-on-Si pin photodiodes with improved efficiency is demonstrated with photon-trapping microhole features.
Abstract: In this paper, high-speed surface-illuminated Ge-on-Si pin photodiodes with improved efficiency are demonstrated. With photon-trapping microhole features, the external quantum efficiency (EQE) of the Ge-on-Si pin diode is >80% at 1300 nm and 73% at 1550 nm with an intrinsic Ge layer of only 2 μm thickness, showing much improvement compared to one without microholes. More than threefold EQE improvement is also observed at longer wavelengths beyond 1550 nm. These results make the microhole-enabled Ge-on-Si photodiodes promising to cover both the existing C and L bands, as well as a new data transmission window (1620–1700 nm), which can be used to enhance the capacity of conventional standard single-mode fiber cables. These photodiodes have potential for many applications, such as inter-/intra-datacenters, passive optical networks, metro and long-haul dense wavelength division multiplexing systems, eye-safe lidar systems, and quantum communications. The CMOS and BiCMOS monolithic integration compatibility of this work is also attractive for Ge CMOS, near-infrared sensing, and communication integration.

Proceedings ArticleDOI
11 Mar 2018
TL;DR: It is reported a waveguide Ge/Si APD with ultra-high 3dB-bandwidths: 56GHz with a 1310nm responsivity of 1.08A/W and 36GHz with the best performance among all reported APD devices.
Abstract: We report a waveguide Ge/Si APD with ultra-high 3dB-bandwidths: 56GHz with a 1310nm responsivity of 1.08A/W and 36GHz with a 1310nm responsivity of 6A/W, which, to our knowledge, are the best performance among all reported APD devices.

Journal ArticleDOI
TL;DR: In this paper, an atomic layer van der Waals (vdW) heterostructure photodiodes operating in the visible regime were demonstrated, enabled by stacking single to few-layer n-type molybdenum disulfide (MoS2) on top of few layer p-type gallium selenide (GaSe) crystals.
Abstract: We report on the demonstration of atomic layer van der Waals (vdW) heterostructure photodiodes operating in the visible regime, enabled by stacking single- to few-layer n-type molybdenum disulfide (MoS2) on top of few-layer p-type gallium selenide (GaSe) crystals. The atomic layer vdW photodiode exhibits an excellent photoresponsivity of ∼3A/W at the wavelength of 532 nm when symmetric few-layer graphene (FLG) contacts with low contact resistance are used. On the other hand, for a GaSe/MoS2 photodiode with asymmetric GaSe/FLG and MoS2/gold (Au) contacts, a very low noise equivalent power of NEP ∼ 10–14 W/Hz is obtained due to dark current reduction, which demonstrates the feasibility of detecting sub-pW (<10–12 W) level optical illumination. Further, the same photodiode exhibits a large linear dynamic range of DR ≈ 70 dB due to the remarkable photocurrent to dark current ratio. These results show that not only the p–n junction formed at the interface between p-type GaSe and n-type MoS2 but also the metal–...

Journal ArticleDOI
06 Jun 2018-ACS Nano
TL;DR: The results demonstrated in this work show that MacEtch can be a viable technology for advanced light trapping and surface engineering in Ge and other semiconductor based optoelectronic devices.
Abstract: Surface antireflection micro and nanostructures, normally formed by conventional reactive ion etching, offer advantages in photovoltaic and optoelectronic applications, including wider spectral wavelength ranges and acceptance angles. One challenge in incorporating these structures into devices is that optimal optical properties do not always translate into electrical performance due to surface damage, which significantly increases surface recombination. Here, we present a simple approach for fabricating antireflection structures, with self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline Ge (c-Ge) surface using the inverse metal-assisted chemical etching technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated with surface structures involving arrays of pyramids or periodic nano-indentations show clear improvements not only in responsivity, due to enhanced optical absorption, but also in dark current. The dark current reduction is attributed to the Schottky barrier height increase and self-passivation effect of the i-MacEtch induced α-Ge layer formed on top of the c-Ge surface. The results demonstrated in this work show that MacEtch can be a viable technology for advanced light trapping and surface engineering in Ge and other semiconductor based optoelectronic devices.

Journal ArticleDOI
TL;DR: A method to perform color imaging with a single photodiode by using light structured illumination generated with a low-cost color LED array to perform 3D imaging by using a non-calibrated photometric stereo technique.
Abstract: We propose a method to perform color imaging with a single photodiode by using light structured illumination generated with a low-cost color LED array. The LED array is used to generate a sequence of color Hadamard patterns which are projected onto the object by a simple optical system while the photodiode records the light intensity. A field programmable gate array (FPGA) controls the LED panel allowing us to obtain high refresh rates up to 10 kHz. The system is extended to 3D imaging by simply adding a low number of photodiodes at different locations. The 3D shape of the object is obtained by using a non-calibrated photometric stereo technique. Experimental results are provided for an LED array with 32 × 32 elements.

Journal ArticleDOI
TL;DR: In this article, a linear-mode optical sensor for the feasible applications of unmanned vehicle LiDAR systems, in which a pulsed-erbium fiber laser is exploited as a light source and a 16-channel transimpedance amplifier (TIA) array is utilized in an optical Rx module with low-cost InGaAs PIN photodiodes.
Abstract: This paper presents a linear-mode optical sensor for the feasible applications of unmanned vehicle LiDAR systems, in which a pulsed-erbium fiber laser is exploited as a light source and a 16-channel transimpedance amplifier (TIA) array is utilized in an optical Rx module with low-cost InGaAs PIN photodiodes. In particular, a voltage-mode CMOS feedforward (VCF-TIA) is newly proposed to achieve twice higher transimpedance gain with lower noise and similar bandwidth characteristics than a conventional inverter TIA, thereby enabling longer detection. Test chips of the 16-channel VCF-TIA array realized in a standard 0.18- $\mu \text{m}$ CMOS process demonstrate 76.3-dB $\Omega $ transimpedance gain, 6.3-pA/sqrt(Hz) average noise current spectral density, less than −33-dB crosstalk between channels, and 29.8-mW power dissipation per channel from a single 1.8-V supply. Automatic gain control is also equipped to extend input dynamic range for near-range detection. Hence, the proposed linear-mode optical sensor clearly detects the reflected optical pulses from the target of 5% reflection rate within the range of 0.5–25 m.

Journal ArticleDOI
13 Jun 2018
TL;DR: In this article, a flexible photodiode based on monolayer MoS2 lateral p-n homojunction with significant enhancement in photoresponsivity and detectivity was developed.
Abstract: Transition-metal dichalcogenides (TMDCs) have recently open a new perspective in electronics and optoelectronics due to their unique planar crystal structures and incredible physical characteristics. Strong in-plane piezoelectricity is their unique property owing to non-centrosymmetric structure, differing from other two dimension (2D) materials, such as graphene and black phosphorus. In this work, we develop a flexible photodiode based on monolayer MoS2 lateral p-n homojunction with significant enhancement in photoresponsivity and detectivity. Piezo-phototronic effect is used to achieve this enhancement by adjusting the barrier height and broadening depletion zone at p-n junction interface under external strain. The wider depletion zone benefits the separation and transport of photogenerated carriers, thus enhancing the photocurrent. When a 0.51% external static tensile strain was applied, the photoresponsivity and detectivity are improved up to 1162 A W−1 and 1.72 × 1012 Jones, with about 619% and 319% enhancement compared with strain-free state, respectively. Consequently, this work provides an effective strategy to utilize unavoidable external strain to improve TMDCs-based optoelectronic devices performance. At the same time, it has reference meaning to achieve flexible, low-consumption and high-performance 2D devices without electric gate-control.