Conventional Photodiodes Research Articles

Ultrahigh-performance heterojunction bipolar phototransistor enabled by bilateral piezoelectric charge modulation effect

Heterojunction photodiodes based on p-n junction with enhanced piezo-phototronic effect have been extensively studied. However, the photoresponsivity of conventional photodiodes is small due to the natural zero current gain. Heterojunction phototransistor usually has greater photoresponsivity due to the non-zero current gain. More importantly, heterojunction phototransistor owns two interfaces, offering the opportunity to introduce the bilateral piezoelectric charge modulation effect for further performance enhancement compared to the conventional single-interface piezo-phototronic effect in photodiode. In this work, a base-floating heterojunction bipolar phototransistor (FHPT) based on n-ZnO/p-Si/n-ZnO structure with a spectral detection range from ultraviolet (UV)–visible is demonstrated. The positive piezoelectric charge generated at the two interfaces of the collector junction and the emitter junction, combined with the optimal base width and low resistance base doping concentration of the FHPT, leads to an excellent photoresponsivity (18046 A/W, 365 nm), high detectivity (5.7×1012 Jones), and a wider modulation (7120 %). The physical mechanism leading to the ultrahigh performance is attributed to the cooperative positive piezoelectric charge at the two interfaces, simultaneously reducing the effective base width and lowering the emitter junction barrier. This work illustrates the regulation of heterojunction phototransistor performance by the bilateral piezoelectric charge modulation effect, providing insightful guidance to high-performance phototransistor design.

108 m Underwater Wireless Optical Communication Using a 490 nm Blue VECSEL and an AOM.

Advanced light sources in the blue-green band are crucial for underwater wireless optical communication (UWOC) systems. Vertical-external-cavity surface-emitting lasers (VECSELs) can produce high output power and good beam quality, making them suitable for UWOC. This paper presents a 108 m distance UWOC based on a 100 mW 490 nm blue VECSEL and an acousto-optic modulator (AOM). The high-quality beam, which is near diffraction-limited, undergoes relatively small optical attenuation when using a conventional avalanche photodiode (APD) as the detector and employing 64-pulse position modulation (PPM). At the time-slot frequency of 50 MHz, the bit error rate (BER) of the UWOC was 2.7 × 10-5. This is the first reported AOM-based UWOC system with a transmission distance over 100 m. The estimated maximum transmission distance may be improved to about 180 m by fully utilizing the detection accuracy of the APD according to the measured attenuation coefficient of the blue VECSEL used. This type of UWOC system, composed of a high-beam-quality light source and a conventional detector, make it more closely suited to practical applications.

Pinning voltage model of vertical pinned photodiode for Dual-Pixel image sensor

This paper presents a simple solution for the pinning voltage of vertical pinned photodiode used in a dual-pixel configuration for phase-detection autofocus applications. Analytic solution of the conventional square deep photodiode has been presented elsewhere. However, this model cannot be adopted to dual pixel where a square pixel contains two rectangular photodiodes. Therefore, we propose a simple analytical model for the rectangular deep photodiode for dual pixels and validate its accuracy by TCAD simulations. The presented model accurately predicts the pinning voltage and potential inside the deep photodiode for dual pixels, thereby confirming its usefulness in the ab-initio design of the pixel as well as in the analysis of the photodiode design.

Ultra‐High Responsivity Black‐Si/Graphene Heterojunction Photodetectors Enabled by Enhanced Light Absorption and Local Electric Fields

AbstractPhotodetectors with high responsivity, fast response, and broad spectral response are of great importance for a wide range of applications in fundamental science and various industries. However, conventional photodiodes operating at low bias voltage do not provide any gain. The graphene (Gr)/Si van der Waals heterostructure, on the other hand, offers a potential gain due to the limited density of states near the Dirac point. In this work, a highly photoresponsive broadband pyramidal black‐Si/Gr heterojunction photodetector is presented. The device, with an active area of 5×5 mm2 and a bias voltage of −5 V, exhibits an ultra‐high responsivity of 4.1 A W−1. The photoresponsivity can be further increased to 1379 A W−1 by reducing the device area. Comparative experiments reveal that the pyramidal black‐Si/Gr photodetectors exhibit the largest responsivity compared with pyramidal‐Si/Gr and flat‐Si/Gr photodetectors. The gain in pyramidal black‐Si/Gr photodetectors is attributed to both the pyramidal nanoporous structures and the shift of the Fermi level of Gr under bias. Furthermore, the high responsivity and stable operation of the photodetectors enable the demonstration of imaging applications. The results provide a new strategy for enhancing the performance of photodetectors based on 2D materials.

Improving the Accuracy of TOF LiDAR Based on Balanced Detection Method.

The ranging accuracy of pulsed time-of-flight (TOF) lidar is affected by walk error and jitter error. To solve the issue, the balanced detection method (BDM) based on fiber delay optic lines (FDOL) is proposed. The experiments are carried out to prove the performance improvement of BDM over the conventional single photodiode method (SPM). The experimental results show that BDM can suppress common mode noise and simultaneously shift the signal to high frequency, which reduces the jitter error by approximately 52.4% and maintains the walk error at less than 300 ps with a non-distorted waveform. The BDM can be further applied to silicon photomultipliers.

Highly Efficient and Stable Self-Powered Perovskite Photodiode by Cathode-Side Interfacial Passivation with Poly(Methyl Methacrylate).

For several years now, organic-inorganic hybrid perovskite materials have shown remarkable progress in the field of opto-electronic devices. Herein, we introduce a cathode-side passivation layer of poly(methyl methacrylate) (PMMA) for a highly efficient and stable self-powered CH3NH3PbI3 perovskite-based photodiode. For effective noise-current suppression, the PMMA passivation layer was employed between a light-absorbing layer of CH3NH3PbI3 (MAPbI3) perovskite and an electron transport layer of [6,6]-phenyl-C61-butyric acid methyl ester. Due to its passivation effect on defects in perovskite film, the PMMA passivation layer can effectively suppress interface recombination and reduce the leakage/noise current. Without external bias, the MAPbI3 photodiode with the PMMA layer demonstrated a significantly high specific detectivity value (~1.07 × 1012 Jones) compared to that of a conventional MAPbI3 photodiode without a PMMA layer. Along with the enhanced specific detectivity, a wide linear dynamic response (~127 dB) with rapid rise (~50 μs) and decay (~17 μs) response times was obtained. Furthermore, highly durable dynamic responses of the PMMA-passivated MAPbI3 photodiode were observed even after a long storage time of 500 h. The results achieved with the cathode-side PMMA-passivated perovskite photodiodes represent a new means by which to realize highly sensitive and stable self-powered photodiodes for use in developing novel opto-electronic devices.

Electronic System of Remote Optical Control of LiNbO3 Mach-Zehnder Modulator Operating Point

A system for integrated optical LiNbO3 Mach–Zehnder modulator operating point remote control and stabilization was developed. It consisted of a conventional telecom photodiode and a passive electronic circuit at the bias input of the modulator. Light from an amplitude-modulated laser was used to remotely set the output voltage of the electronic circuit at the bias input of the Mach–Zehnder modulator. Information regarding the current operating point that had been provided with feedback system implementation was taken from DC values of high frequency photodetector currents. Efficient remote control of the modulator operating point over 1 km of a single-mode optical fiber, which multiplexes an optical carrier at 1550 nm and a low frequency control signal with a peak power of 2 mW at 1310 nm, was demonstrated. The results could be of interest for antenna remoting, radio-over-fiber (RoF) technology, and other applications with broadband optical transmission from remote sources in a distributed network.

A Gate-Controlled Lateral Thyristor-Based Pixel With Low-Light-Level Extension for High Dynamic Range Applications

A pixel configuration based on a gate-controlled lateral thyristor (GC-LT) is proposed to achieve low-light-level extension with a high dynamic range (HDR). Our previous work has demonstrated that the GC-LT has a high sensitivity in low-light-level conditions, and the trigger time is sensitive to the optical power ranging from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{-{9}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5\times 10^{-{6}}$ </tex-math></inline-formula> W/cm2. In this article, a sampling circuit and a slope following method are implemented to obtain the light-sensitive trigger time. A multiple short-period slopes method is proposed to compensate for the leakage current effects in long exposure time. By elaborately designing the operating scheme, the GC-LT can also be shifted as a conventional photodiode. Also, the GC-LT-based pixel can be operated in thyristor, linear, and logarithmic modes to extend the dynamic range. Simulation is performed to validate the newly proposed device and pixel circuit. The results show that by combining the three modes, the dynamic range of the pixel is higher than 160 dB, and the minimum detectable signal is as low as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{-{9}}$ </tex-math></inline-formula> W/cm2.

Using charge collection narrowing to tune from broadband to narrowband all-polymer photodetectors

We report an all-polymer photodiode comprising a new electron-transporting polymer, PNNTH, that contains naphthalene diimide and thiazole moieties. PNNTH has strong absorption at around 670 nm and an electron mobility of ≈10−4 cm2 V−1 s−1. Bulk heterojunction films composed of PNNTH blended with the donor polymer, PBDTT-FTTE, in a weight ratio of 1:2 were found to have electron and hole mobilities of ≈10−5 cm2 V−1 s−1 and ≈10−4 cm2 V−1 s−1, respectively. The photoresponse of conventional and inverted organic photodiodes containing the blend could be tuned from broadband (400–800 nm) to narrowband (50 nm full-width-at-half-maximum) simply by changing the thickness of the all-polymer blend. The narrowband response was achieved using the charge collection narrowing mechanism, which was enhanced by the unbalanced charge mobility. Transfer matrix-based optical modelling confirmed the wavelength dependence of the photoresponse. For both the broadband and narrowband photodiodes, the specific detectivity was greater than 1011 Jones.

Accurate Nonlocal Impact Ionization Models for Conventional and Staircase Avalanche Photodiodes Derived by Full Band Monte Carlo Transport Simulations

We present a procedure to extract the nonlocal impact ionization coefficients in Avalanche Photodiodes (APDs) operating in the linear regime from Full Band Monte Carlo simulations. The Monte Carlo calculations have been calibrated on existing experimental data for GaAs p-i-n APDs with different thickness of the intrinsic region. Inspection of impact ionization generation rate in p-i-n and staircase GaAs APDs led us to identify the limitations of existing nonlocal-history dependent impact ionization models. The introduction of an energy dependent relaxation length for the computation of the effective fields significantly improves the model accuracy in predicting the gain and noise associated to conduction and valence band steps in staircase APDs without additional computational burden. This improved nonlocal-history dependent model is thus a powerful tool to design and optimize APDs with different architectures.

Analytical Model of the Vertical Pinned Photodiode

This article presents a simple analytical model of the vertical pinned photodiode (PPD). In the existing pixels with relatively large sizes, the photodiode is formed byp+-n-p doping in a planar manner, and thus the vertical electric field determines the potential of the photodiode. However, as the pixel size becomes smaller, the size of the photodiode also decreases. Accordingly, the influence of the doping concentration in the periphery becomes larger and the pinning voltage is eventually predominantly determined by the horizontal electric field in the submicrometer region. In this case, the analytical model describing the conventional photodiode structure is no longer applicable. Therefore, in this article, a simple analytical model applicable to a small pixel size is provided and verified through TCAD simulation. It is thought that the proposed simple model helps understand the potential of small pixel size and provides a major starting point for design.

Transient absorption microscopy setup with multi-ten-kilohertz shot-to-shot subtraction and discrete Fourier analysis.

Recording of transient absorption microscopy images requires fast detection of minute optical density changes, which is typically achieved with high-repetition-rate laser sources and lock-in detection. Here, we present a highly flexible and cost-efficient detection scheme based on a conventional photodiode and an USB oscilloscope with MHz bandwidth, that deviates from the commonly used lock-in setup and achieves benchmark sensitivity. Our scheme combines shot-to-shot evaluation of pump-probe and probe-only measurements, a home-built photodetector circuit optimized for low pulse energies applying low-pass amplification, and a custom evaluation algorithm based on Fourier transformation. Advantages of this approach include abilities to simultaneously monitor multiple pulse modulation frequencies, implement the detection of additional pulse sequences (e.g., pump-only), and expand to multiple parallel detection channels for wavelength-dispersive probing. With a 40 kHz repetition-rate laser system powering two non-collinear optical parametric amplifiers for wide tuneability, we find that laser pulse fluctuations limit the sensitivity of the setup, while the detection scheme has negligible contribution. We demonstrate the 2-D imaging performance of our transient absorption microscope with studies on micro-crystalline molecular thin films.

Performance comparisons between inverted and conventional avalanche photodiodes for larger capacity applications

Performance comparisons between inverted and conventional avalanche photodiodes for larger capacity applications

A Review on Solution-Processed Organic Phototransistors and Their Recent Developments

Today, more disciplines are intercepting each other, giving rise to “cross-disciplinary” research. Technological advancements in material science and device structure and production have paved the way towards development of new classes of multi-purpose sensory devices. Organic phototransistors (OPTs) are photo-activated sensors based on organic field-effect transistors that convert incident light signals into electrical signals. The organic semiconductor (OSC) layer and three-electrode structure of an OPT offer great advantages for light detection compared to conventional photodetectors and photodiodes, due to their signal amplification and noise reduction characteristics. Solution processing of the active layer enables mass production of OPT devices at significantly reduced cost. The chemical structure of OSCs can be modified accordingly to fulfil detection at various wavelengths for different purposes. Organic phototransistors have attracted substantial interest in a variety of fields, namely biomedical, medical diagnostics, healthcare, energy, security, and environmental monitoring. Lightweight and mechanically flexible and wearable OPTs are suitable alternatives not only at clinical levels but also for point-of-care and home-assisted usage. In this review, we aim to explain different types, working mechanism and figures of merit of organic phototransistors and highlight the recent advances from the literature on development and implementation of OPTs for a broad range of research and real-life applications.

Low Excess Noise of Al0.85Ga0.15As0.56Sb0.44 Avalanche Photodiode From Pure Electron Injection

Avalanche photodiodes (APDs) are used in optical receivers of high-speed optical communication systems to improve signal-to-noise ratio over conventional photodiodes. Low excess noise characteristics are crucial for APDs to preserve the benefits associated with high internal gains. In this work, we presented room temperature data of avalanche gain and excess noise factors of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.56</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.44</sub> APDs using pure and mixed carrier injection profiles. Using pure electron injection, the best possible excess noise performance for a given avalanche width was measured with an excess noise factor <; 2 for gains up to 25. This is the lowest excess noise reported for this material system at high gain. Two other injection profiles with increased portion of injected holes worsened the excess noise performance, confirming the need to use pure electron injection for the best possible APD noise performance. The data reported in this article is available from the ORDA digital repository (https://doi.org/10.15131/shef.data.15082455).

Efficient and continuous microwave photoconversion in hybrid cavity-semiconductor nanowire double quantum dot diodes

Converting incoming photons to electrical current is the key operation principle of optical photodetectors and it enables a host of emerging quantum information technologies. The leading approach for continuous and efficient detection in the optical domain builds on semiconductor photodiodes. However, there is a paucity of efficient and continuous photon detectors in the microwave regime, because photon energies are four to five orders of magnitude lower therein and conventional photodiodes do not have that sensitivity. Here we tackle this gap and demonstrate how microwave photons can be efficiently and continuously converted to electrical current in a high-quality, semiconducting nanowire double quantum dot resonantly coupled to a cavity. In particular, in our photodiode device, an absorbed photon gives rise to a single electron tunneling through the double dot, with a conversion efficiency reaching 6%.

Self-powered ultraviolet photodiode based on lateral polarity structure GaN films

In this work, we report on a self-powered ultraviolet photodiode realized using lateral polarity structure (LPS) GaN films. The opposite nature of the polarization charge yields different barrier heights at the standard Ni/Au Schottky contact interface of N-polar and III-polar GaN films. As a result, a natural nonzero built-in potential is obtained in the LPS GaN photodiode, which showed photoresponsivity even at 0 V applied bias. The self-powered mechanism inside such an LPS GaN photodiode is discussed in detail by a combination of simulation prediction and experimental validation. Furthermore, a variation in the doping concentration of the adjacent III- and N-polar GaN domain is shown to improve the photoresponsivity compared to the conventional III-polar photodiode. Thus, this work validates that the LPS GaN photodiode is a promising candidate to realize self-powered operation and a general design rule for the photodiode with in-plane built-in potential.

Pulsed‐Laser Detectors Based on Metal Halide Perovskites

AbstractConventionally, the detection of pulsed‐lasers is mainly based on thermal effects, such as thermoelectric detectors and pyroelectric detectors, which possess a photothermal conversion process, resulting in slow response and significant energy loss. Fast photodiodes are also introduced to calibrate pulsed‐lasers. However, they require advanced oscilloscopes with high bandwidth and amplification systems, limiting their practical application to some extent. To address the issues of these two types of pulsed‐laser detectors, an interfacial modification strategy is introduced to the conventional perovskite photodiodes. The incorporation of the polyvinylidene fluoride layer can effectively slow down the photovoltage decay of the perovskite devices via electric‐field induced polarization, which enables the detection of both modulated light emitting diodes and ultra‐fast pulsed‐lasers in a facile way. With such effect, the polyvinylidene fluoride (PVDF) based photodetectors can effectively convert the pulsed light input to a quasi‐DC output, which can be easily recorded with a multimeter or source meter. These devices also exhibit low noise voltage of &lt;10−5 V Hz−1/2, high responsivity of &gt;2 × 104 V W−1 @ 1 µW cm−2, indicating great potential for real applications.

Niobium nitride plasmonic perfect absorbers for tunable infrared superconducting nanowire photodetection.

Quantum technologies such as quantum computing and quantum cryptography exhibit rapid progress. This requires the provision of high-quality photodetectors and the ability to efficiently detect single photons. Hence, conventional avalanche photodiodes for single photon detection are not the first choice anymore. A better alternative are superconducting nanowire single photon detectors, which use the superconducting to normal conductance phase transition. One big challenge is to reduce the product between recovery time and detection efficiency. To address this problem, we enhance the absorption using resonant plasmonic perfect absorber effects, to reach near-100% absorption over small areas. This is aided by the high resonant absorption cross section and the angle insensitivity of plasmonic resonances. In this work we present a superconducting niobium nitride plasmonic perfect absorber structure and use its tunable plasmonic resonance to create a polarization dependent photodetector with near-100% absorption efficiency in the infrared spectral range. Further we fabricated a detector and investigated its response to an external light source. We also demonstrate the resonant plasmonic behavior which manifests itself through a polarization dependence detector response.

A Wheeled Robot Chain Control System for Underground Facilities Inspection Using Visible Light Communication and Solar Panel Receivers

The underground facilities require to be inspected regularly for long term and safe-use. Several mobile inspection systems are widely used, but some crucial problems with the limited inspection distance still exist due to the unstable wireless communication and cable restrictions in complex facilities. To solve these problems, we propose a wheeled robot chain control system (RCCS) for underground facilities inspection based on visible light communication (VLC) and solar panel receivers. The RCCS consists of a leader and follower robot and can extend the inspection range with special “optical signal relay” technology. VLC can provide not only illumination for inspection but also less attenuation, higher information security, and stronger antielectromagnetic interference capability, compared with conventional radio communication in complex underground facilities. Using solar panels can increase the receiving area of optical signals, environmental adaptability, and system robustness, compared with conventional photodiode (PD) receivers. Moreover, to ensure longer and more stable communication, we develop an optical signal relay mechanism along-side an attenuation control module. We performed several experiments to evaluate the signal waveform, communication quality, effective communication region, and cooperative movement. The results indicated that the proposed system could extend the inspection range with higher communication quality and environmental adaptability than VLC-based system with PD receivers.