Conventional Photodetectors Research Articles

Bi2O3 Layer‐Integrated, Double‐Sided Responsive, Waveband‐Discriminated Perovskite Photodetector for Encrypted Optical Communication

AbstractEncrypted optical communication is a critical technology in numerous fields, including remote sensing, environmental monitoring, and homeland defense. As a core of wireless interconnect systems, the conventional photodetectors generally receive optical signals from a single direction and fail to distinguish between various wavebands, severely undermining the potential for data transfer and protection. Herein, a Bi2O3 layer‐integrated waveband‐discriminated perovskite photodetector is presented. By rational design of energy band and device architecture, the novel photodetector is self‐powered, double‐sided responsive, and recognizable to the short or long‐wave UV, as well as visible optical signals. Without external bias, the device exhibits a high performance with peak responsivities of 42.1 and 72.3 mA W−1 in frontal and reverse incidence, respectively. Benefiting from these advantages, the photodetector is applicable to optical communication and encryption. In reverse incidence, reversible message delivery is achieved through the conversion and decoding of illumination patterns and binary digits. For a further step, the encrypted processing is fulfilled in frontal incidence. By virtue of the eight irradiation combinations, a secret key containing ten‐bit commands will generate over a billion encryption methods. This work realizes a new mode of communication and encryption that entirely relies on optical signals, offering new insights into wireless communication.

High‐Responsivity Natural‐Electrolyte Undersea Photoelectrochemical Photodetector with Self‐Powered Cu@GaN Nanowires Network

AbstractUndersea optical communication (UOC) has been considered as the most potential next‐generation underwater wireless communication technology for ocean exploration. Photodetector is the essential component in UOC system, however, the harsh undersea environment like light attenuation and seawater corrosivity restricts the applications of conventional photodetectors. Herein, a novel natural‐electrolyte self‐powered photoelectrochemical (PEC) photodetector based on core‐shell structured Cu@GaN nanowires (NWs) network is demonstrated and direct utilization of seawater. High quality GaN shell is encapsulated on the Cu NWs network through Ga‐coating and high temperature nitridation processes. A Schottky junction along radial direction has formed at the Cu/GaN interface due to the outward diffusion of Cu into the GaN layer. Such a structure provides narrowed band detection on blue light as well as efficient carrier separation. A self‐powered undersea PEC photodetector is designed with a mini‐pipes connected device chamber, which allows direct indrawing of seawater and blue channel light communication (458 nm). This photodetector works stably for UOC in both shallow and deep‐sea conditions in Pacific Ocean area. It shows a high responsivity up to 5.04 mA W−1 and rapid response time of 0.68 ms. This photodetector can be easily integrated to marine equipment without waterproof packaging for the future energy‐saving UOC.

Large-Area Black Phosphorus/PtSe2 Schottky Junction for High Operating Temperature Broadband Photodetectors.

High operating temperature (HOT) broadband photodetectors are urgently necessary for extreme condition applications in infrared-guided missiles, infrared night vision, fire safety imaging, and space exploration sensing. However, conventional photodetectors show dramatic carrier mobility decreases and carrier losses with low photoresponsivity at HOT due to the increased carrier scattering in channels at high temperatures. Herein, the HOT broadband photodetectors from room temperature to 470 K are developed for the first time by large-area black phosphorus (BP)/PtSe2 films device arrays via a depletion-enhanced photocarrier dynamics strategy. Attributed to the 2D Schottky junction at BP/PtSe2 interface and resulting in full depleted working channels, the BP/PtSe2 photodetector arrays exhibit high tolerance to carrier mobility decrease during the increasing operating temperature in a wide wavelength range from 532 to 2200nm. Thus, the photodetector shows a state-of-the-art operating temperature at 470 K with the photo-responsivity (R) and specific detectivity (D*) of 25 A W-1 and 6.4 × 1011 Jones under 1850nm illumination, respectively. Moreover, BP/PtSe2 photodetector arrays show high-uniformity photo-response in a large area. This work provides new strategies for high-performance broadband photodetector arrays with HOT by Schottky junction of large-area BP/PtSe2 films.

Light–induced transition of charged carrier transport in symmetric metal–semiconductor–metal contacts

Metal–semiconductor (M–S) contact is a basic element in semiconductor integrated circuit. Recent studies on photodetectors extensively focus on M–S contact owing to the easy fabrication and superior performance. Here, we report a light–induced transition of charged carrier transport in planar Cu/Si–doped GaAs single crystal (Si:GaAs) symmetric double Schottky contacts. Different from conventional photodetector, illumination not only gains the carrier concentration but also changes the charged carrier transport mechanism at Cu/Si:GaAs contact. The light-induced transition of charged carrier transport is reflected by the change of shape of current–voltage (I–V) curve caused by illumination. By the construction of theoretical model and its fitting to experimental data, we point out that carrier transport mechanism at Cu/Si:GaAs contact changes from tunneling effect to thermionic emission by illumination. Among that, photovoltaic effect is the crucial driving force. This study presents a novel mechanism for converting optical signal to electrical signal by tailoring Schottky contact in photodetector, which provide a design prototype to new–type optoelectronic device.

Suppression of Nonlinear Optical Effects in DWDM-PON by Frequency Modulation Non-Coherent Detection

We propose a simple and cost-effective method, using a direct frequency modulation (FM) and noncoherent detection (NCD) scheme, to suppress the nonlinear optical effects in dense wavelength division multiplexed (DWDM) optical communication. The FM transmitter comprises a directly modulated distributed feedback laser and a saturable semiconductor optical amplifier. In the NCD receiver, an optical slope filter as the FM to intensity modulation (IM) signal convertor is placed before a conventional photodetector. Because the FM signal has more evenly distributed optical power, bit-pattern-dependent nonlinear effects are consequently suppressed. After analyzing the nonlinear effects in the FM-NCD system and traditional IM direct detection (IM-DD) system, we found that the minimum achievable BER of the proposed FM-NCD scheme is 40 dB smaller. Moreover, a 2 Tbps (10 Gb/s × 200 channels) capacity was achieved by the FM-NCD system in 100 km DWDM passive optical networks (PONs), which is twice the capacity of the IM-DD system (10 Gb/s × 100 channels) under the same condition. These results indicate that WDM-PONs with the cost-effective FM-NCD scheme are strong candidates for future broad access networks and show great potential for the combination of optical access and metro networks for future generations of PONs.

The excellent performance of β-Ga2O3 Schottky photodiode under forward bias and its application in solar-blind ultraviolet communication

In this work, the planar β-Ga2O3 Schottky photodiodes on the sapphire substrates were manufactured by conventional photolithography and lift-off processes. Au and Ti/Au were used as Schottky and Ohmic contacts. After optimizing the geometry layout of β-Ga2O3 Schottky photodiode, R increased by 120%, EQE enhanced by 896.81% and D* gotten a 1540.88% increase. Particularly, β-Ga2O3 Schottky photodiode had exhibited the abnormally excellent performance under forward bias, contrary to most of conventional UV photodetectors. The origin of abnormally excellent performance in β-Ga2O3 Schottky photodiodes under forward bias have been researched systematically. Combined experiments with DFT calculations, we have attributed the ultra high EQE in β-Ga2O3 Schottky photodiode to its unique band structure. While the large photo-to-dark current ratio and D* under forward bias originate from deep-state intrinsic defects of β-Ga2O3. At last, the solar-blind ultraviolet communication system based on β-Ga2O3 Schottky photodiode was achieved and the message, “Hello, HIT!”, was successfully transmitted.

Modulating the Quantum Efficiency of Sb2S3‐Based Photodiodes Based on Conventional and Inverted Structures

AbstractAntimony sulfide (Sb2S3), a binary chalcogenide, has recently emerged as a promising candidate for photovoltaics due to its high absorption coefficient, facile processing, and lower toxicity. However, high‐performance photodiodes based on Sb2S3 have not been achieved and systematically investigated. Herein, Sb2S3‐based photodiodes based on conventional and inverted structures are developed, and their charge transport and spectral dependent quantum efficiency of these two types of devices are carefully modulated. After optimization, the conventional photodetectors achieve broadband responsivity up to 0.3 A W−1, high specific detectivity of 1.25 × 1012 Jones, and fast response speed of 6.4 µs with a small bias voltage of −0.5 V. On the other hand, the inverted devices exhibit imbalanced charge transport and color discrimination, which is promising for narrowband photodetection. These distinct device performances are highly dependent on the device architecture, which is crucial for designing efficient chalcogenide‐based optoelectronic devices.

Responsivity enhancement of a PtSi photodetector with graphene by the photogating effect.

In this paper, by adding graphene to the platinum silicide (PtSi) photodetector and using the photogating effect, the responsivity is significantly improved in the PtSi photodetector. In this photodetector, the PtSi layer detects the light, and the graphene increases the responsivity with the photogating effect. The responsivity of the PtSi photodetector with graphene is 1.5A/W in the optical power of 13.6µW. The responsivity in the PtSi photodetector with graphene and without graphene is compared. By adding graphene to the PtSi photodetector, the responsivity is much improved compared to the conventional PtSi photodetector.

High-Speed and High-Power Ge-on-Si Photodetector with Bilateral Mode-Evolution-Based Coupler

We propose a germanium-on-silicon photodetector with a bilateral mode-evolution-based coupler. Based on the double-sided mode-evolution, the light illuminates the whole Ge absorption region uniformly, which alleviates the space-charge effects and decreases the saturation effects. The simulated results show 53% more photocurrent generation and more than 19 times the opto-electrical bandwidth than conventional butt-coupled photodetectors under high-power illumination. In addition, an equivalent circuit model is presented to investigate the limiting factors of bandwidth. A genetic algorithm is used to extract the parameter values of components in an equivalent circuit by fitting the simulated two-port S22 parameter. The results show significant improvement in high-power and high-speed performance compared with conventional butt-coupled detectors.

Gold Nanorod-Activated Graphene/MoS2 Nanosheet-Based Photodetectors for Bidirectional Photoconductance

Graphene and its nanohybrid photodetectors (PDs) offer unique interfacial and synergistic properties in contrast to conventional semiconductor-based PDs. In this work, we compare the performance of identically fabricated PDs based on pure chemical vapor deposition-grown monolayer graphene, demonstrating a positive photoresponse, that exhibits a gain in photoresponsivity (R) with the addition of two-dimensional MoS2 (chemically exfoliated). However, further addition of plasmonic gold nanorods (AuNRs), on the MoS2/graphene PD, results in the flipping of the photoconductivity to negative. The negative photoresponse is explained by an increased dark current via the complex conductive network model and a lower photocurrent due to the photogenerated electron capture by the AuNRs in the AuNRs/MoS2/graphene PD. The contrasting shape and nature of the dynamic photoresponses are modeled using theoretical fitting and explained based on carrier transport in individual components. The highest R in the moderately fast graphene PD device is ∼2 × 104 A W–1 under 808 nm which could be slightly improved to ∼3 × 104 A W–1 by introducing MoS2 nanoflakes, albeit at the cost of the response time which slows down from ∼90 ms (in the former) to 558 ms in the latter. The introduction of AuNRs did speed up the response time in the AuNRs/MoS2/graphene PD to 20.5 ms but produced a strikingly different negative photoresponse attributed to a higher dark current in the material. We proposed a single mechanism to explain the positive and negative photoresponses reported so far for the hybrid PDs.

High-Performance Diamond Phototransistor with Gate Controllable Gain and Speed.

This paper presents a fabricated solar-blind phototransistor based on hydrogen-terminated diamond. The phototransistor shows a large photocurrent and enhancement of responsivity over conventional two-terminal diamond-based photodetector. These enhancement effects are owing to the internal gain of the phototransistor. The fabricated phototransistor exhibits a high photoresponsivity (R) of 2.16 × 104 A/W and a detectivity (D*) of 9.63 × 1011 jones, with gate voltage (VG) and drain voltage of approximately -1.5 V and -5 V, respectively, under 213 nm light illumination. Even at ultralow operating voltage of -0.01 V, the device records satisfactory performance with R and D* of 146.7 A/W and 6.19 × 1010 jones, respectively. By adjusting the VG, photocurrent generation in the device can be continuously tuned from the fast photoconductive effect to the optical gating effect with high optical gain. When VG increases from 1.4 to 2.4 V, the decay time decreases from 1512.0 to 25.5 ms. Therefore, responsivity, dark current, Iphoto/Idark, and decay time of the device can be well tuned by VG.

Engineering graphitic carbon nitride for next-generation photodetectors: a mini review.

Semiconductor photodetectors, as photoelectric devices using optical-electrical signal conversion for detection, are widely used in various fields such as optical communication, medical imaging, environmental monitoring, military tracking, remote sensing, etc. Compared to the conventional photodetector materials including silicon, III-V semiconductors and metal sulfides, graphitic carbon nitride (g-C3N4) as a metal-free polymeric semiconductor, has many advantages such as low-price, easy preparation, efficient visible light response, and relatively good thermal stability. In the meantime, the polymer characteristics also endow the g-C3N4 with good mechanical properties. Apart from being used for photo(electro)catalysts during the past decades, the potential use of g-C3N4 in photodetectors has attracted great research interests very recently. In this review, we first briefly introduce the structure and properties of g-C3N4 and the key performance parameters of photodetectors. Then, combining the very recent progress, the review focuses on the active materials, fabrication methods and performance enhancement strategies for g-C3N4 based photodetectors. The existing challenges are discussed and the future development of g-C3N4 based photodetectors is also forecasted.

Broadband photodetector based on MoS2/Ge heterojunction for optoelectronic applications

In this work, we demonstrate high quality MoS2/i-Ge heterojunction photodetector (PD) and its optoelectrical properties are analyzed over a broad spectral range which is compared with the conventional Ge Schottky PD. The MoS2/i-Ge heterojunction PD was highly sensitive in the broadband range from 300 nm to 1700 nm, having a responsivity of 0.7 A/W, the quantum efficiency of 56.1% against 0.55 A/W and 44.4% for the conventional Ge Schottky PD at the incident wavelength of 1550 nm. For the visible light range, heterojunction PD exhibited a much higher responsivity and quantum efficiency of >0.3 A/W and ∼60%, respectively than conventional Ge Schottky PD. The improvement of Schottky PD and heterojunction PD is analyzed using the photocurrent mapping method. Finally, heterojunction PDs exhibited excellent photo-responsive switching properties. The photocurrent of MoS2/i-Ge heterojunction PDs shows superior performance than Ge Schottky PDs for increased wavelength and optical powers. These results imply that MoS2/Ge heterojunction PD may have great potential for broadband light detection applications as high-performance devices.

Computational spectropolarimetry with a tunable liquid crystal metasurface

While conventional photodetectors can only measure light intensity, the vectorial light field contains much richer information, including polarization and spectrum, that are essential for numerous applications ranging from imaging to telecommunication. However, the simultaneous measurement of multi-dimensional light field information typically requires the multiplexing of dispersive or polarization-selective elements, leading to excessive system complexity. Here, we demonstrate a near-infrared spectropolarimeter based on an electrically-tunable liquid crystal metasurface. The tunable metasurface, which acts as an encoder of the vectorial light field, is tailored to support high-quality-factor guided-mode resonances with diverse and anisotropic spectral features, thus allowing the full Stokes parameters and the spectrum of the incident light to be computationally reconstructed with high fidelity. The concept of using a tunable metasurface for multi-dimensional light field encoding may open up new horizons for developing vectorial light field sensors with minimized size, weight, cost, and complexity.

Advances in Flexible Organic Photodetectors: Materials and Applications.

Future electronics will need to be mechanically flexible and stretchable in order to enable the development of lightweight and conformal applications. In contrast, photodetectors, an integral component of electronic devices, remain rigid, which prevents their integration into everyday life applications. In recent years, significant efforts have been made to overcome the limitations of conventional rigid photodetectors, particularly their low mechanical deformability. One of the most promising routes toward facilitating the fabrication of flexible photodetectors is to replace conventional optoelectronic materials with nanomaterials or organic materials that are intrinsically flexible. Compared with other functional materials, organic polymers and molecules have attracted more attention for photodetection applications due to their excellent photodetection performance, cost-effective solution-fabrication capability, flexible design, and adaptable manufacturing processes. This article comprehensively discusses recent advances in flexible organic photodetectors in terms of optoelectronic, mechanical properties, and hybridization with other material classes. Furthermore, flexible organic photodetector applications in health-monitoring sensors, X-ray detection, and imager devices have been surveyed.

Addressing gain-bandwidth trade-off by a monolithically integrated photovoltaic transistor

The gain-bandwidth trade-off limits the development of high-performance photodetectors; i.e., the mutual restraint between the response speed and gain has intrinsically limited performance optimization of photomultiplication phototransistors and photodiodes. Here, we show that a monolithically integrated photovoltaic transistor can solve this dilemma. In this structure, the photovoltage generated by the superimposed perovskite solar cell, acting as a float gate, is amplified by the underlying metal oxide field-effect transistor. By eliminating deep-trap defects through processing optimization, we achieved devices with a maximum responsivity close to 6 × 104 A/W, a specific detectivity (D*) of 1.06 × 1013 Jones, and an f3dB of 1.2 MHz at a low driving voltage of 3 V. As a result, a record gain-bandwidth product is achieved. The device further exhibits the advantage in photoplethysmography detection with weak illuminations, where our device accurately detects the detailed features that are out of the capability of conventional photodetectors.

Light-Trapping-Enhanced Photodetection in Ge/Si Quantum Dot Photodiodes Containing Microhole Arrays with Different Hole Depths.

Photodetection based on assemblies of quantum dots (QDs) is able to tie the advantages of both the conventional photodetector and unique electronic properties of zero-dimensional structures in an unprecedented way. However, the biggest drawback of QDs is the small absorbance of infrared radiation due to the low density of the states coupled to the dots. In this paper, we report on the Ge/Si QD pin photodiodes integrated with photon-trapping hole array structures of various thicknesses. The aim of this study was to search for the hole array thickness that provided the maximum optical response of the light-trapping Ge/Si QD detectors. With this purpose, the embedded hole arrays were etched to different depths ranging from 100 to 550 nm. By micropatterning Ge/Si QD photodiodes, we were able to redirect normal incident light laterally along the plane of the dots, therefore facilitating the optical conversion of the near-infrared photodetectors due to elongation of the effective absorption length. Compared with the conventional flat photodetector, the responsivity of all microstructured devices had a polarization-independent improvement in the 1.0–1.8-μm wavelength range. The maximum photocurrent enhancement factor (≈50× at 1.7 μm) was achieved when the thickness of the photon-trapping structure reached the depth of the buried QD layers.

Optically Programmable Circularly Polarized Photodetector.

The detection of circularly polarized light (CPL) has aroused wide attention from both the scientific and industrial communities. However, from the optical activity of the chiral layer in the conventional CPL photodetectors, the sign inversion property is difficult to be achieved. As a result, great challenges arise during the preparation of miniaturized and integrated devices for tunable CPL detection applications. Along these lines, in this work, by taking advantage of the CPL-induced chirality characteristics of the achiral poly(9,9-di-n-hexylfluorene-alt-benzothiadiazole) (F6BT) and the good crystalline and electrical properties of the poly(3-hexylthiophene) (P3HT) film, an optically programmable CPL photodetector was fabricated. Interestingly, the device exhibited excellent discrimination between left- and right-handed CPL, while the maximum anisotropy factor of responsivity was 0.425. On top of that, the rigorously controlled chirality of the F6BT and the capability to be switched by the handedness of CPL was leveraged to realize the switchable detection of both L-CPL and R-CPL. Furthermore, a CPL photodetector array was fabricated, and the image processing and cryptographic characteristics were demonstrated. The proposed device configuration can find application in various scientific fields, including photonics, emission, conversion, or sensing with CPL but also is anticipated to play a key role for imaging and anticounterfeiting applications.

Shot and Johnson noises in interband cascade infrared photodetectors

Shot and Johnson noises are often incorrectly thought of as two independent noise sources. This incorrect picture has affected the evaluation of detectivities in interband cascade infrared photodetectors (ICIPs). In this work, a unified picture of shot and Johnson noises is developed for ICIPs based on a fundamental framework to understand the origin of Johnson noise and clarify the possible confusion between Johnson and shot noises. General, yet concise expressions are derived to evaluate the current noise power spectral density and detectivity for ICIPs even with complicated structures. Also, simple expressions for the signal current due to absorption of photons and the corresponding photon noise are derived, consistent with the previous results derived from alternative methods. Furthermore, a formula is derived to correctly evaluate the detectivity for conventional photodetectors under a reverse bias. The derived formulas with discussion are expected to improve the understanding of noises in ICIPs and other types of photodetectors and help us to appropriately evaluate their detectivities.

Five-layer planar hot-electron photodetectors at telecommunication wavelength of 1550 nm.

Cost-effective and high-responsivity photodetectors at a telecommunication wavelength of 1550 nm are highly desired in optical communication systems. Differing from conventional semiconductor-based photodetectors, several planar hot-electron photodetectors (HE PDs) that operate at 1550 nm have been reported. However, these devices were often comprised of many planar layers and exhibited relatively low responsivities. Herein, we propose a design of high-performance planar HE PDs consisting of five layers. Utilizing Fabry-Pérot (FP) resonance, the nearly perfect absorption of the proposed device can be achieved at the targeted wavelength of 1550 nm. Simulation results show that FP resonance orders are crucial for the optical absorption efficiencies, and then electrical responses. Analytical electrical calculations reveal that, benefiting from the strong absorption (>0.6) in the ultrathin Au layer with a thickness of 5 nm and the low Schottky barrier (0.5 eV) of Au-MoS2 contact, predicted responsivity of proposed HE PD at zero-order FP resonance is up to ∼10 mA/W. Our design provides a new approach to realize low-cost and efficient photodetection for optical communication technology.