Showing papers on "Photodiode published in 2019"

Dual-band infrared imaging using stacked colloidal quantum dot photodiodes

Abstract: Infrared multispectral imaging is attracting great interest with the increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices. Here, we demonstrate a two-terminal CQD dual-band detector, which provides a bias-switchable spectral response in two distinct bands. A vertical stack of two rectifying junctions in a back-to-back diode configuration is created by engineering a strong and spatially stable doping process. By controlling the bias polarity and magnitude, the detector can be rapidly switched between short-wave infrared and mid-wave infrared at modulation frequencies up to 100 kHz with D* above 1010 jones at cryogenic temperature. The detector performance is illustrated by dual-band infrared imaging and remote temperature monitoring. Colloidal quantum dot detectors, switchable between short-wave infrared and mid-wave infrared, are demonstrated.

High efficiency and fast van der Waals hetero-photodiodes with a unilateral depletion region.

Abstract: Van der Waals (vdW) heterodiodes based on two-dimensional (2D) materials have shown tremendous potential in photovoltaic detectors and solar cells. However, such 2D photovoltaic devices are limited by low quantum efficiencies due to the severe interface recombination and the inefficient contacts. Here, we report an efficient MoS2/AsP vdW hetero-photodiode utilizing a unilateral depletion region band design and a narrow bandgap AsP as an effective carrier selective contact. The unilateral depletion region is verified via both the Fermi level and the infrared response measurements. The device demonstrates a pronounced photovoltaic behavior with a short-circuit current of 1.3 μA and a large open-circuit voltage of 0.61 V under visible light illumination. Especially, a high external quantum efficiency of 71%, a record high power conversion efficiency of 9% and a fast response time of 9 μs are achieved. Our work suggests an effective scheme to design high-performance photovoltaic devices assembled by 2D materials. Photovoltaic devices based on 2D materials still suffer from low quantum efficiencies due to interfacial charge recombination and inefficient contacts. Here, the authors design photovoltaic detectors and photodiodes based on MoS2 and doped AsP heterojunction with unilateral depletion region reporting high external quantum efficiency of 71% under zero applied bias.

Near-field photonic cooling through control of the chemical potential of photons

Abstract: Photonic cooling of matter has enabled both access to unexplored states of matter, such as Bose–Einstein condensates, and novel approaches to solid-state refrigeration1–3. Critical to these photonic cooling approaches is the use of low-entropy coherent radiation from lasers, which makes the cooling process thermodynamically feasible4–6. Recent theoretical work7–9 has suggested that photonic solid-state cooling may be accomplished by tuning the chemical potential of photons without using coherent laser radiation, but such cooling has not been experimentally realized. Here we report an experimental demonstration of photonic cooling without laser light using a custom-fabricated nanocalorimetric device and a photodiode. We show that when they are in each other’s near-field—that is, when the size of the vacuum gap between the planar surfaces of the calorimetric device and a reverse-biased photodiode is reduced to tens of nanometres—solid-state cooling of the calorimetric device can be accomplished via a combination of photon tunnelling, which enhances the transport of photons across nanoscale gaps, and suppression of photon emission from the photodiode due to a change in the chemical potential of the photons under an applied reverse bias. This demonstration of active nanophotonic cooling—without the use of coherent laser radiation—lays the experimental foundation for systematic exploration of nanoscale photonics and optoelectronics for solid-state refrigeration and on-chip device cooling. The ‘negative luminescence’ of a reverse-biased photodiode is harnessed to draw thermal energy from a nearby solid object, thereby realizing photonic cooling without the use of coherent laser radiation.

A high-performance ultraviolet solar-blind photodetector based on a β-Ga2O3 Schottky photodiode

Abstract: UV ray detection near the earth surface has become urgent due to the serious effects of UV rays on human health, the environment and the biological evolution; therefore, the development of energy-saving UV photodetectors with high responsivity, specific detectivity, and sensitivity is urgently desired. Herein, we fabricated a lateral β-Ga2O3 Schottky photodiode on a sapphire substrate via magnetron sputtering using Ti and Ni as ohmic and Schottky contacts, respectively. The photodiode shows rectifying behaviors in the dark and under 254/365 nm UV light illuminations. As a photodetector, it exhibits the high photo-to-dark current ratio of 2.83 × 105 owing to its low dark current (1.32 × 10−11 A) and strong UV absorbance. The responsivity at 250 nm could reach up to 144.46 A W−1 at 10 V. The external quantum efficiency of 64 711% and the ideal specific detectivity of 7.29 × 1014 cm Hz1/2 W−1 (Jones) were also achieved. The rejection ratio (R250 nm/R400 nm) was as high as 4.8 × 103, suggesting high wavelength selectivity. The responsivity of 2301.78 A W−1 at 180 V proves the ability of this photodetector to operate at high voltages. In addition, it can operate with the responsivity of 0.73 mA W−1 and the specific detectivity of 3.35 × 1010 cm Hz1/2 W−1 (Jones) at zero bias. Overall, the lateral Ti/β-Ga2O3/Ni structured Schottky photodiode was verified as an excellent candidate for UV solar-blind detection with high performance and low energy consumption.

High-speed photo detection at two-micron-wavelength: technology enablement by GeSn/Ge multiple-quantum-well photodiode on 300 mm Si substrate.

Abstract: We report high-speed photo detection at two-micron-wavelength achieved by a GeSn/Ge multiple-quantum-well (MQW) p-i-n photodiode, exhibiting a 3-dB bandwidth (f3-dB) above 10 GHz for the first time. The epitaxy of device layer stacks was performed on a standard (001)-oriented 300 mm Si substrate by using reduced pressure chemical vapor deposition (RPCVD). The results showed promise for large-scale manufacturing. To our knowledge, this is also the first photodiodes-on-Si with direct radio-frequency (RF) measurement to quantitatively confirm high-speed functionality with tens of GHz f3-dB at 2 µm, which is considered as a promising candidate for the next data communication window. This work illustrates the potential for using GeSn to extend the utility of Si photonics in 2 µm band integrated optical transceivers for communication applications.

Chiral excitonic organic photodiodes for direct detection of circular polarized light

Abstract: A facile route to soft matter self-powered bulk heterojunction photodiode detectors sensitive to the circular polarization state of light is shown based on the intrinsic excitonic circular dichroism of the photoactive layer blend. As light detecting materials, enantiopure semiconducting small molecular squaraine derivates of opposite handedness are employed. Via Mueller matrix ellipsometry, the circular dichroism is proven to be of H-type excitonic nature and not originating from mesoscopic structural ordering. Within the green spectral range, the photodiodes convert circular polarized light into a handedness-dependent photocurrent with a maximum dissymmetry factor of ±0.1 corresponding to 5% overall efficiency for the polarization discrimination under short circuit conditions. On the basis of transfer matrix optical simulations, it is rationalized that the optical dissymmetry fully translates into a photocurrent dissymmetry for ease of device design. Thereby, the photodiode's ability to efficiently distinguish between left and right circularly polarized light without the use of external optical elements and voltage bias is demonstrated. This allows a straightforward and sustainable future design of flexible, lightweight, and compact integrated platforms for chiroptical imaging and sensing.

Perovskite/Black Phosphorus/MoS2 Photogate Reversed Photodiodes with Ultrahigh Light On/Off Ratio and Fast Response

Abstract: As compared with epitaxial semiconductor devices, two-dimensional (2D) heterostructures offer alternative facile platforms for many optoelectronic devices. Among them, photovoltaic based photodetectors can give fast response, while the photogate devices can lead to high responsivity. Here, we report a 2D photogate photodiode, which combines the benefits of 2D black phosphorus/MoS2 photodiodes with the emerging potential of perovskite, to achieve both fast response and high responsivity. This device architecture is constructed based on the fast photovoltaic operation together with the high-gain photogating effect. Under reverse bias condition, the device exhibits high responsivity (11 A/W), impressive detectivity (1.3 × 1012 Jones), fast response (150/240 μs), and low dark current (3 × 10-11 A). All these results are already much better in nearly all aspects of performance than the previously reported 2D photodiodes operating in reverse bias, achieving the optimal balance between all figure-of-merits. Importantly, with a zero bias, the device can also yield high detectivity (3 × 1011 Jones), ultrahigh light on/off ratio (3 × 107), and extremely high external quantum efficiency (80%). This device architecture thus has a promise for high-efficiency photodetection and photovoltaic energy conversion.

Si-based GeSn photodetectors towards mid-infrared imaging applications

Abstract: This paper reports a comprehensive study of Si-based GeSn mid-infrared photodetectors, which includes: 1) the demonstration of a set of photoconductors with Sn compositions ranging from 10.5% to 22.3%, showing the cut-off wavelength has been extended to 3.65 um. The measured maximum D* of 1.1x10^10 cmHz^(1/2)W(-1) is comparable to that of commercial extended-InGaAs detectors; 2) the development of surface passivation technique on photodiode based on in-depth analysis of dark current mechanism, effectively reducing the dark current. Moreover, mid-infrared images were obtained using GeSn photodetectors, showing the comparable image quality with that acquired by using commercial PbSe detectors.

High-speed uni-traveling carrier photodiode for 2 μm wavelength application

Abstract: Current optical communication systems operating at the 1.55 μm wavelength band may not be able to continually satisfy the growing demand on data capacity within the next few years. Opening a new spectral window around the 2 μm wavelength with recently developed hollow-core photonic bandgap fiber and a thulium-doped fiber amplifier is a promising solution to increase transmission capacity due to the low-loss and wide-bandwidth properties of these components at this wavelength band. However, as a key component, the performance of current high-speed photodetectors at the 2 μm wavelength is still not comparable with those at the 1.55 μm wavelength band, which chokes the feasibility of the new spectral window. In this work, we demonstrate, for the first time to our knowledge, a high-speed uni-traveling carrier photodiode for 2 μm applications with InGaAs/GaAsSb type-II multiple quantum wells as the absorption region, which is lattice-matched to InP. The devices have the responsivity of 0.07 A/W at 2 μm wavelength, and the device with a 10 μm diameter shows a 3 dB bandwidth of 25 GHz at −3 V bias voltage. To the best of our knowledge, this device is the fastest photodiode among all group III-V and group IV photodetectors working in the 2 μm wavelength range.

High Responsivity and Quantum Efficiency of Graphene/Silicon Photodiodes Achieved by Interdigitating Schottky and Gated Regions

Abstract: Graphene/silicon (G/Si) heterostructures have been studied extensively in the past years for applications such as photodiodes, photodetectors, and solar cells, with a growing focus on efficiency and performance. Here, a specific contact pattern scheme with interdigitated Schottky and graphene/insulator/silicon (GIS) structures is explored to experimentally demonstrate highly sensitive G/Si photodiodes. With the proposed design, an external quantum efficiency (EQE) of >80% is achieved for wavelengths ranging from 380 to 930 nm. A maximum EQE of 98% is observed at 850 nm, where the responsivity peaks to 635 mA/W, surpassing that of conventional Si p-n photodiodes. This efficiency is attributed to the highly effective collection of charge carriers photogenerated in Si under the GIS parts of the diodes. The experimental data is supported by numerical simulations of the diodes. On the basis of these results, a definition for the “true” active area in G/Si photodiodes is proposed, which may serve toward standar...

Solar blind Schottky photodiode based on an MOCVD-grown homoepitaxial β-Ga2O3 thin film

Abstract: We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-ti...

2D Perovskites with Giant Excitonic Optical Nonlinearities for High-Performance Sub-Bandgap Photodetection

Abstract: Two-dimensional (2D) perovskites have proved to be promising semiconductors for photovoltaics, photonics, and optoelectronics. Here, a strategy is presented toward the realization of highly efficient, sub-bandgap photodetection by employing excitonic effects in 2D Ruddlesden-Popper-type halide perovskites (RPPs). On near resonance with 2D excitons, layered RPPs exhibit degenerate two-photon absorption (D-2PA) coefficients as giant as 0.2-0.64 cm MW-1 . 2D RPP-based sub-bandgap photodetectors show excellent detection performance in the near-infrared (NIR): a two-photon-generated current responsivity up to 1.2 × 104 cm2 W-2 s-1 , two orders of magnitude greater than InAsSbP-pin photodiodes; and a dark current as low as 2 pA at room temperature. More intriguingly, layered-RPP detectors are highly sensitive to the light polarization of incoming photons, showing a considerable anisotropy in their D-2PA coefficients (β[001] /β[011] = 2.4, 70% larger than the ratios reported for zinc-blende semiconductors). By controlling the thickness of the inorganic quantum well, it is found that layered RPPs of (C4 H9 NH3 )2 (CH3 NH3 )Pb2 I7 can be utilized for three-photon photodetection in the NIR region.

Organic Multi-Channel Optoelectronic Sensors for Wearable Health Monitoring

Abstract: Recent progress in printed optoelectronics and their integration in wearable sensors have created new avenues for research in reflectance photoplethysmography (PPG) and oximetry. The reflection-mode sensor, which consists of light emitters and detectors, is a vital component of reflectance oximeters. Here, we report a systematic study of the reflectance oximeter sensor design in terms of component geometry, light emitter and detector spacing, and the use of an optical barrier between the emitter and the detector to maximize sensor performance. Printed red and near-infrared (NIR) organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) are used to design three sensor geometries: (1) Rectangular geometry, where square OLEDs are placed at each side of the OPD; (2) Bracket geometry, where the OLEDs are shaped as brackets and placed around the square OPD; (3) Circular geometry, where the OLEDs are shaped as block arcs and placed around the circular OPD. Utilizing the bracket geometry, we observe 39.7% and 18.2% improvement in PPG signal magnitude in the red and NIR channels compared to the rectangular geometry, respectively. Using the circular geometry, we observe 48.6% and 9.2% improvements in the red and NIR channels compared to the rectangular geometry. Furthermore, a wearable two-channel PPG sensor is utilized to add redundancy to the measurement. Finally, inverse-variance weighting and template matching algorithms are implemented to improve the detection of heart rate from the multi-channel PPG signals.

Direct Synthesis of a Self-Assembled WSe2 /MoS2 Heterostructure Array and its Optoelectrical Properties.

Abstract: Functional van der Waals heterojunctions of transition metal dichalcogenides are emerging as a potential candidate for the basis of next-generation logic devices and optoelectronics. However, the complexity of synthesis processes so far has delayed the successful integration of the heterostructure device array within a large scale, which is necessary for practical applications. Here, a direct synthesis method is introduced to fabricate an array of self-assembled WSe2 /MoS2 heterostructures through facile solution-based directional precipitation. By manipulating the internal convection flow (i.e., Marangoni flow) of the solution, the WSe2 wires are selectively stacked over the MoS2 wires at a specific angle, which enables the formation of parallel- and cross-aligned heterostructures. The realized WSe2 /MoS2 -based p-n heterojunction shows not only high rectification (ideality factor: 1.18) but also promising optoelectrical properties with a high responsivity of 5.39 A W-1 and response speed of 16 µs. As a feasible application, a WSe2 /MoS2 -based photodiode array (10 × 10) is demonstrated, which proves that the photosensing system can detect the position and intensity of an external light source. The solution-based growth of hierarchical structures with various alignments could offer a method for the further development of large-area electronic and optoelectronic applications.

Green Synthesis and Electrical Properties of p-CuO/n-ZnO Heterojunction Diodes

Abstract: Green production of nanomaterials and their materials properties studies are majorly important for the futuristic development of nanodevices. We had green synthesized the ZnO and CuO nanoparticles using the extract of “Eucalyptus globulus” leaves. The obtained ZnO and CuO nanoparticles were studied for their structural, morphological and optical properties. The green synthesized CuO and ZnO nanoparticles have showed the crystalline size of about 12.29 and 10.16 nm. The transmission electron microscopic images of green synthesized ZnO and CuO nanoparticles revealed the morphological information and their respective average sizes of 46 and 32 nm. Optical absorbance spectrum revealed the existence of morphology based quantum confinement in the green ZnO and CuO nanoparticles. Further we have fabricated the p-CuO/n-ZnO heterojunction device using the green synthesized nanoparticles and also evaluated the electrical properties of the p–n junction diode. Under the light illumination the photodiode characteristic were studied for the obtained p–n junction diode. Finally, the energy band diagram of the photodiode responsible for the electronic transport had also discussed.

Multimechanism Synergistic Photodetectors with Ultrabroad Spectrum Response from 375 nm to 10 µm.

Abstract: Broadening the spectral range of photodetectors is an essential topic in photonics. Traditional photodetectors are widely used; however, the realization of ultrabroad spectrum photodetectors remains a challenge. Here, a photodetector constructed by a hybrid quasi-freestanding structure of organic ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with molybdenum disulfide (MoS2) is demonstrated. The 2D MoS2 with the ultrathin structure brings a great benefit of heat dissipation for the pyroelectric infrared detector. By coupling the mechanisms of pyroelectrics, photoconductor, and phototransistor effect, an ultrabroad spectrum response ranging from ultraviolet (375 nm) to long-wavelength infrared (10 µm) is achieved. In the 2.76-10 µm spectral range, the 2D MoS2 is used to read and amplify the photocurrent induced by the pyroelectric effect of P(VDF-TrFE). The sensitivity of the device in this spectral range is greatly enhanced. A high responsivity of 140 mA W-1, an on/off photocurrent switching ratio up to 103, and a quick response of 5.5 ms are achieved. Moreover, the ferroelectric polarization field dramatically enhances the photoconductive properties of MoS2 and restrains dark current and noise. This approach constitutes a reliable route toward realizing high-performance photodetectors with a remarkable ultrabroad spectrum response, high responsivity, low power consumption, and room-temperature operation.

Si-MoS2 Vertical Heterojunction for a Photodetector with High Responsivity and Low Noise Equivalent Power.

Abstract: In this study, we propose the fabrication of a photodetector based on the heterostructure of p-type Si and n-type MoS2. Mechanically exfoliated MoS2 flakes are transferred onto a Si layer; the resulting Si–MoS2 p–n photodiode shows excellent performance with a responsivity (R) and detectivity (D*) of 76.1 A/W and 1012 Jones, respectively. In addition, the effect of the thickness of the depletion layer of the Si–MoS2 heterojunction on performance is investigated using the depletion layer model; based on the obtained results, we optimize the photoresponse of the device by varying the MoS2 thickness. Furthermore, low-frequency noise measurement is performed for the fabricated devices. The optimized device shows a low noise equivalent power (NEP) of 7.82 × 10–15 W Hz–1/2. Therefore, our proposed device could be utilized for various optoelectronic devices for low-light detection.

Solution-Processed Phototransistors Combining Organic Absorber and Charge Transporting Oxide for Visible to Infrared Light Detection

Abstract: This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 1012 Jones under a low power illumination of 20 nW/cm2, outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions.

Avalanche Gain in Metal–Semiconductor–Metal Ga2O3 Solar-Blind Photodiodes

Abstract: Metal–semiconductor–metal structured photodetectors based on β-Ga2O3 thin films were fabricated. Because of the high dark-resistance and considerable photoconduction, extremely uneven distribution ...

Memory phototransistors based on exponential-association photoelectric conversion law.

Abstract: Ultraweak light detectors have wide-ranging important applications such as astronomical observation, remote sensing, laser ranging, and night vision. Current commercial ultraweak light detectors are commonly based on a photomultiplier tube or an avalanche photodiode, and they are incompatible with microelectronic devices for digital imaging applications, because of their high operating voltage and bulky size. Herein, we develop a memory phototransistor for ultraweak light detection, by exploiting the charge-storage accumulative effect in CdS nanoribbon. The memory phototransistors break the power law of traditional photodetectors and follow a time-dependent exponential-association photoelectric conversion law. Significantly, the memory phototransistors exhibit ultrahigh responsivity of 3.8 × 109 A W−1 and detectivity of 7.7 × 1022 Jones. As a result, the memory phototransistors are able to detect ultraweak light of 6 nW cm−2 with an extremely high sensitivity of 4 × 107. The proposed memory phototransistors offer a design concept for ultraweak light sensing devices. CdS nanostructures can enable memory based photodetection by charge-storage accumulative effect. Here, the authors report CdS nanoribbons-based memory phototransistors with high responsivity of 3.8 × 109 A/W and detectivity of 7.7 × 1022 Jones that can detect weak light of 6 nW/cm2.

Effect of gate dielectric thicknesses on MOS photodiode performance and electrical properties

Abstract: Different film thickness was used to investigate the effect of the Al2O3 as a dielectric material for the fabrication of Al/AL2O3/Si/Al MOS diode. Chemical spray pyrolysis method was employed in this work. A high rectification behavior was observed from current-voltage (I-V) measurements in forward and reverse in dark. Optimum ideality factor of (2.36) at 5 sprayed layers was observed, the breakdown voltage found to be 5 MV cm−1 while the barrier height was (0.65 eV) at the same layer thickness. Capacitance-voltage (C–V) measurements was carried out which ensure the formation of abrupt junction; the incorporating built-in potential (Vbi) was estimated and found to be (0.8 eV). In addition, the photodiode shows a good Responsivity of about (1.4, 1.8) Amp/watt at Uv and IR region respectively.

High-Speed Photodetectors for Microwave Photonics

Abstract: This paper reviews high-power photodiodes, waveguide photodetectors, and integrated photodiode-antenna emitters with bandwidths up to 150 GHz. Results from heterogeneous III-V photodiodes on silicon and Ge-on-Si photodiode arrays for analog applications are presented.

Achieving High-Quality Sn–Pb Perovskite Films on Complementary Metal-Oxide-Semiconductor-Compatible Metal/Silicon Substrates for Efficient Imaging Array

Abstract: Although Sn-Pb perovskites sensing near-ultraviolet-visible-near-infrared light could be an attractive alternative to silicon in photodiodes and imaging, there have been no clear studies on such devices constructed on metal/silicon substrates, hindering their direct integration with complementary metal-oxide semiconductor (CMOS) and silicon electronics. Typically, high surface roughness and severe pinholes of Sn-rich binary perovskites make it difficult for them to fulfill the requirements of efficient photodiodes and imaging. These issues cause inherently high dark current and poor (dark and photo-) current uniformity. Herein, we propose and demonstrate the room-temperature crystallization in the Sn-rich binary perovskite system to effectively control film crystallization kinetics. With experimental and theoretical studies of the crystallization mechanism, we successfully tune the density and location of nanocrystals in precursor films to achieve compact nanocrystals, which coalesce into high-quality (smooth, dense, and pinhole-free) perovskites with intensified preferred orientation and decreased trap density. The high-quality perovskites reduce dark current and improve (dark and photo-) current uniformity of perovskite photodiodes on CMOS-compatible metal/silicon substrates. Meanwhile, self-powered devices achieve a high responsivity of 0.2 A/W at 940 nm, a large dynamic range of 100 dB, and a fast fall time of 2.27 μs, exceeding those of most silicon-based imaging sensors. Finally, a 6 × 6 pixel integrated photodiode array is successfully demonstrated to realize the imaging application. The work contributes to understanding the fundamentals of the crystallization of Sn-rich binary perovskites and advancing perovskite integration with Si-based electronics.

InGaAs-GaAs Nanowire Avalanche Photodiodes Toward Single-Photon Detection in Free-Running Mode.

Abstract: Single-photon detection at near-infrared (NIR) wavelengths is critical for light detection and ranging (LiDAR) systems used in imaging technologies such as autonomous vehicle trackers and atmospheric remote sensing. Portable, high-performance LiDAR relies on silicon-based single-photon avalanche diodes (SPADs) because of their extremely low dark count rate (DCR) and afterpulsing probability, but their operation wavelengths are typically limited up to 905 nm. Although InGaAs-InP SPADs offer an alternative platform to extend the operation wavelengths to eye-safe ranges, their high DCR and afterpulsing severely limit their commercial applications. Here we propose a new separate absorption and multiplication avalanche photodiode (SAM-APD) platform composed of vertical InGaAs–GaAs nanowire arrays for single-photon detection. Among a total of 4400 nanowires constituting one photodiode, each avalanche event is confined in a single nanowire, which means that the avalanche volume and the number of filled traps can be drastically reduced in our approach. This leads to an extremely small afterpulsing probability compared with conventional InGaAs-based SPADs and enables operation in free-running mode. We show a DCR below 10 Hz, due to reduced fill factor, with photon count rates of 7.8 MHz and timing jitter less than 113 ps, which suggest that nanowire-based NIR focal plane arrays for single-photon detection can be designed without active quenching circuitry that severely restricts pixel density and portability in NIR commercial SPADs. Therefore, the proposed work based on vertical nanowires provides a new degree of freedom in designing avalanche photodetectors and could be a stepping stone for high-performance InGaAs SPADs.

90-Gb/s NRZ Optical Receiver in Silicon Using a Fully Differential Transimpedance Amplifier

Abstract: We present the design and implementation of a 90 -Gb/s non-return-to-zero (NRZ) direct detection optical receiver that consists of a low-noise transimpedance amplifier (TIA), fabricated in a 55-nm SiGe BiCMOS technology, and a Ge photodiode integrated into a Silicon Photonic integrated circuit. Low-noise broadband operation is achieved using a fully differential TIA that provides the photodiode reverse bias. 50-, 56-, and 64-Gb/s NRZ operation is demonstrated at bit-error ratios (BERs) below $10^{-12}$ at sensitivities of $-$ 12.3-, $-$ 11.2-, and $-$ 11.1-dBm optical modulation amplitude (OMA) while consuming 128, 141, and 157 mW, respectively. Furthermore, a BER below $10^{-12}$ is achieved at 80 Gb/s with a sensitivity of $-$ 6.1 dBm (OMA) at 165 mW, and operation below KP4-FEC $({2.4 \times {10}^{-4}})$ is demonstrated up to 90 Gb/s with a sensitivity of $-$ 7.1 dBm (OMA) while consuming 222 mW. All BERs were measured in real time and without DSP or equalization to compensate the receiver. The presented receiver achieves the best reported sensitivities up to 90 Gb/s, at the second-lowest power consumption, and is the first reported integrated optical RX up to 90 Gb/s that is tested in real time without any equalization or DSP to compensate the receiver. The presented optical receiver is ideally suited for upcoming short-reach applications.