Photodetectors Research Articles

Improving ZnO ultraviolet Schottky photodetectors by inserting a MoS2 layer

ZnO Schottky junction photodetectors (PDs) has become a research focus due to their wide application, high-performance and low-cost. However, their development has been limited by the low photo-response. Two-dimensional MoS2 exhibit numerous advantages, including a tunable band gap, a strong exciton effect, and broadband absorption. In this work, we incorporate MoS2 into ZnO thin films using a simple spin-coating method to create Schottky ultraviolet (UV) PDs that show a remarkably increased responsivity (by 885%) and a substantially improved photo-current (by one order of magnitude). Furthermore, they exhibit a relatively low noise equivalent power (5.11×10−13 W) and a high normalized detectivity 2.96×1011 Jones. This outstanding performance can be attributed to the enhanced absorption and efficient charge transfer of ZnO film after introduction of MoS2 layer. In this study, an easy method is presented for creating high-performance ZnO Schottky PDs.

PbS/ Si NW Heterojunction on Silicon Chip Based Self-Powered Photo Detector Device for IR Radiations by Chemical Bath Deposition

PbS/ Si NW Heterojunction on Silicon Chip Based Self-Powered Photo Detector Device for IR Radiations by Chemical Bath Deposition

Extended short-wave infrared high-speed all-GeSn PIN photodetectors on silicon

There is an increasing need for silicon-compatible high-bandwidth extended-short wave infrared (e-SWIR) photodetectors (PDs) to implement cost-effective and scalable optoelectronic devices. These systems are quintessential to address several technological bottlenecks in detection and ranging, surveillance, ultrafast spectroscopy, and imaging. In fact, current e-SWIR high-bandwidth PDs are predominantly made of III–V compound semiconductors and thus are costly and suffer a limited integration on silicon besides a low responsivity at wavelengths exceeding 2.3 μm. To circumvent these challenges, Ge1−xSnx semiconductors have been proposed as building blocks for silicon-integrated high-speed e-SWIR devices. Herein, this study demonstrates vertical all-GeSn PIN PDs consisting of p-Ge0.92Sn0.08/i-Ge0.91Sn0.09/n-Ge0.89Sn0.11 and p-Ge0.91Sn0.09/i-Ge0.88Sn0.12/n-Ge0.87Sn0.13 heterostructures grown on silicon following a step-graded temperature-controlled epitaxy protocol. The performance of these PDs was investigated as a function of the device diameter in the 10–30 μm range. The developed PD devices yield a high bandwidth of 12.4 GHz at a bias of 5 V for a device diameter of 10 μm. Moreover, these devices show a high responsivity of 0.24 A/W, a low noise, and a 2.8 μm cutoff wavelength, thus covering the whole e-SWIR range.

Detecting Visible to Near-Infrared II Light via CsPbBr3 Nanocrystals/Y6 Heterojunctions.

In the endeavor to develop advanced photodetectors (PDs) with superior performance, all-inorganic perovskites, recognized for their outstanding photoelectric properties, have emerged as highly promising materials. Due to their unique electronic structure and band characteristics, the majority of all-inorganic perovskite materials are not sensitive to near-infrared (NIR) light. Here, we demonstrate the fabrication of a high-performance broadband PD comprising CsPbBr3 perovskite NCs/Y6 planar heterojunctions. The incorporation of Y6 not only facilitates charge transfer from CsPbBr3 NCs to Y6 for enhancing photodetection performance under visible illumination but also broadens the absorption spectrum range of the whole device toward the NIR regime. As a result, the heterojunction PD exhibits a photo-to-dark-current ratio above 105, a dynamic range of 149.5 dB, and an impressive lowest detection limit of incident power density of 1.6 nW/cm2 under 505 nm illumination. In the NIR regime, where photon energy is below the bandgap of CsPbBr3, electron-hole pairs can still be produced in the Y6 layer even when illuminated at 1120 nm. Consequently, photodetection is uniquely possible in PDs that incorporate heterojunctions when the illumination wavelength is longer than 565 nm. At 850 nm, the heterojunction device is capable of detecting light with power densities as low as 1.3 μW/cm2 corresponding to a LDR of 99.8 dB. The exceptional performance is attributed to the creation of a heterojunction between CsPbBr3 NCs and Y6. These findings propose a novel approach for developing broadband PDs based on perovskite NC materials.

Non-invasive Blood Glucose Monitoring System

The project presents a novel approach to blood glucose monitoring, offering a non-invasive and pain-free method for individuals with diabetes to track their glucose levels. The system utilizes advanced sensor technology coupled with signal processing techniques to detect glucose levels in the body without the need for traditional needle pricking. The key components of the system include a power supply, voltage regulator, ESP32 microcontroller, LCD display, photo sensor, amplifier circuit, and linearization circuit, all seamlessly integrated to provide accurate and real-time glucose readings. This breakthrough technology holds great promise in revolutionizing diabetes management, enhancing the quality of life for millions of affected individuals.By placing the sensor on the individual’s hand, the Glucometer system employs a combination of photonic and electronic principles to non-invasively measure glucose levels. The photo sensor captures specific wavelengths of light that interact with glucose molecules within the tissue, generating a signal proportional to the glucose concentration. This signal is then amplified and processed through the integrated circuits, ensuring accurate linearization and calibration. The ESP32 microcontroller orchestrates these operations, facilitating seamless communication with the LCD display to present the glucose reading in a clear and user-friendly format.The Glucometer’s innovative design eliminates the discomfort associated with traditional blood sampling methods, making it a highly accessible and convenient tool for diabetes management. The system’s efficiency in providing accurate glucose readings without the need for invasive procedures represents a significant advancement in healthcare technology. With further development and refinement, the Glucometer holds the potential to significantly enhance the daily lives of individuals living with diabetes, offering a reliable and painless means of monitoring blood glucose levels.

Photonic-assisted wideband microwave frequency measurement based on optical heterodyne detection

A photonic-assisted microwave frequency measurement (MFM) method based on optical heterodyne detection is proposed and experimentally demonstrated. In the proposed MFM system, a linearly chirped optical waveform (LCOW) from a three-electrode distributed Bragg reflector laser diode (DBR-LD) and a multi-wavelength signal from a Mach-Zehnder modulator (MZM), where the signal under test (SUT) is modulated on an optical carrier from a distributed feedback laser diode (DFB-LD), are heterodyne detected by the photodetector (PD). A bandpass filter then filters the detected signal, and the envelope is detected by an oscilloscope. Then, frequency-to-time mapping is realized, and the signal frequency is measured. Thanks to the fast tuning rate and large tuning range of the DBR-LD, the proposed MFM system has a high measurement speed and a broad instantaneous measurement bandwidth. In the experimental demonstration, a measurement error below 39.1 MHz is achieved at an instantaneous bandwidth of 20 GHz and a measurement speed of 1.12 GHz/µs. The MFM of a frequency-hopping signal is also experimentally demonstrated. The successful demonstration of the MFM system with a simple structure provides a new optical solution for realizing broadband and fast microwave frequency measurements.

Scalable flexible and stretchable high performance UV photodetector based on MoS2-WO3/Ag composite on a PU substrate by utilizing LIG electrodes

The rapid advancements in photodetector device technologies have captivated the optoelectronic industry owing to their strong features, such as wearability, stretchability, energy efficiency, scalability and cost-effectiveness. However, there is still scope for enhancement in device performance, reliability, and scalable fabrication. In this research work, we have proposed a novel strategy for fabricating stretchable ultraviolet (UV) photodetector (PD) on a polyethylene glycol solution-processed synthesis of MoS2-WO3/Ag composite-based nanocrystals onto a polyurethane (PU) substrate. Moreover, laser induced graphene (LIG) interdigitated electrode arrays for swift photogenerated charge extraction due to their high conductivity. The device displays high photoresponsivity, external quantum efficiency, and specific detectivity, measured at 6.84 A/W, 143 %, and 2.87×1011 Jones, respectively. Additionally, the device demonstrates a quick response time of 80 ms when exposed to 360 nm light, indicating its high speed. These essential advantages have a great potential for applications in real life and mass production. The integration of advanced materials and LIG electrodes enhances the device capability for next-generation stretchable, flexible and wearable electronic devices.

The self-healing and robust photostability of (PEA)2PbI4 perovskite via pressure-induced amorphization and recrystallization

The photostability of hybrid organic-inorganic perovskites (HOIPs) is an important criterion due to unavoidability of light in photoelectric elements of solar cells, light emitting diodes (LEDs) or photo detectors. This research aims to explore the photostability of a compressed two-dimensional (2D) (PEA)2PbI4 crystal. The structural and compositional responses of the sample to laser illumination under pressure were recorded via in-situ photoluminescence (PL) spectroscopy and morphological analysis methods. The enhancement in laser endurance limit from 3 to 11 mW and long-duration photostablity were achieved along with structural self-healing in the recrystallized (PEA)2PbI4 sample. The robust stability of the material was ascribed to pressure-induced suppression of the nonradiative decay and grain boundary minimization in the rebirthed crystal. A similar result was also obtained in compressed (BA)2PbI4 and MAPbI3 crystals. Therefore, high pressure offers an effective and green method to improve the photostability of HOIP crystals and has a profound significance in the widespread application of HOIP-based photoelectric devices.

Recent advancement in the synthesis of zinc sulphide thin films

This research work has given an overview on the preparation of zinc sulphide thin films on different types of substrates (quartz, soda lime glass, silicon, polyethylene terephthalate film, fluorine-doped tin oxide glass, indium tin oxide coated glass, silica, stainless steel, mica, microscopy glass slide and (100) GaAs substrate) using different types of deposition methods. XRD data showed information about the different phases (cubic, wurtzite and hexagonal) presented in the obtained as-deposited films and annealed samples. Based on optical studies, the band gap was observed in the range of 2.6 eV to 3.87 eV with good absorption coefficient value (105 to 106 cm-1). Experimental results indicated these films could be used in solar cell applications, anti-reflection coating, photocatalysts, photo detector devices and laser-oriented coating applications.

A self-powered Ag/β-Ga2O3 photodetector with broadband response from 200 to 980 nm based on the photovoltaic and pyro-phototronic effects

β-Ga2O3, as one of the important 4th generation semiconductors, is widely used in solar-blind ultraviolet (UV) detectors with a short detection range of 200–280 nm benefiting from its ultra-wide bandgap, strong radiation resistance, and excellent chemical and thermal stabilities. Here, a self-powered photodetector (PD) based on an Ag/β-Ga2O3 Schottky heterojunction was designed and fabricated. Through a subtle design of electrodes, the pyro-phototronic effect was discovered, which can be coupled to the common photovoltaic effect and further enhance the performance of the PD. Compared to traditional Ga2O3-based PD, the as-used PD exhibited a self-driving property and a broadband response beyond the bandgap limitations, ranging from 200 nm (deep UV) to 980 nm (infrared). Moreover, the photoresponse time was greatly shrunk owing to the coupling effect. Under laser irradiation, with a wavelength of 450 nm and a power density of 8 mW cm‒2, the photocurrent could be improved by around 41 times compared with the sole photovoltaic effect. Besides, the performances of the Schottky PD were enhanced at both high and low temperatures. The device also possessed long-term working stability. This paper not only reveals basic physics lying in the 4th generation semiconductor Ga2O3 but also sheds light on the multi-encryption transmission of light information using this PD.

Two-dimensional CuSe nanosheet array for high-performance photoelectrochemical photodetector using simulated seawater as electrolyte

Photoelectrochemical-type (PEC) photodetectors (PDs) show great promise in underwater optoelectronic devices, but most reports of PEC PDs use acid or basic solutions as electrolytes, hindering their practical application in marine scenarios. In this letter, we reported high-performance 2D CuSe-based PEC PDs with use of the electrolyte of simulated seawater for the first time. The 2D CuSe nanosheet array (NSA) is synthesized by a facile electrodeposition method. The PEC PDs based on 2D CuSe NAS has a superior responsivity of 9.5 mA/W for 455 nm light in the simulated seawater, and exhibits a broadband photoresponse in 365–850 nm, surpassing most TMCs-based PEC PDs. The superior photoresponse originates from the vertical NSA structure, providing more interfacial active sites and higher light absorption. In addition, 2D CuSe NSA-based PEC PDs possess self-powered ability, fast response speed, good stability, and underwater optical communication capability. This work demonstrates the great potential of 2D CuSe NSA in PEC-type optoelectronic devices.

Multistimuli-responsive tetraphenylethene molecular switches displaying acid-sensing, photochromism, and metal ion detection properties

Aggregation-induced emission (AIE) smart materials with multiple stimulus responses have a wide range of applications. Here, a series of tetraphenylethylene (TPE) derivatives, TPEN1S3, TPEN2S2, TPEN3S1 were synthesized. The sensitivity of molecules to pH, UV light, and metal ions could be effectively tuned by modulating the ratio of amino to sulfonic acid groups. These TPE derivatives exhibited yellow emissions in aggregated state due to the AIE characteristics. Acidification conversion of the NH2 groups to NH3+ for three molecules induced the suppression of intramolecular charge transfer (ICT), which resulted in a 72–102 nm blue shift in the fluorescence emission. Solid powders of these compounds exhibited reversible protonation-deprotonation process induced by HCl/NH3·H2O vapor. TPEN1S3, TPEN2S2 and TPEN3S1 in solution could be photoactivated and emit blue fluorescence (ca. 482 nm, 475 nm, and 480 nm). Photocyclo-dehydrogenation reactions of compounds were triggered by the UV irradiation and the maximum cyclization ratios could reach 12%, 66%, and 50%, respectively. Protonation of NH2 group significantly enhanced the rate of the photocyclo-dehydrogenation reaction. Furthermore, the solid powders of protonated compounds displayed pronounced reversible photochromic properties due to the generation of cyclization intermediate. In addition, TPEN1S3, TPEN2S2, and TPEN3S1 exhibited responsiveness to a diverse range of metal ions. Specifically, the TPEN2S2 molecule functioned as a photo sensor for Li + ions with a blue shift in fluorescence emission. The limit of detection (LOD) value was 0.679 μM. These multiple stimuli-responsive AIE molecules hold significant potential for use in advanced photo-controlled patterning, encryption applications, and the detection of metal ions.

Large area MoSe2 and MoSe2/Bi2Se3 films on sapphire (0001) for near-infrared photodetection

The fabrication of heterojunction-based photodetectors (PDs) is well known for the enhancement of PDs performances, tunable nature of photoconductivity, and broadband application. Herein, the PDs based on MoSe2 and MoSe2/Bi2Se3 heterojunction on sapphire (0001) substrates were deposited using a r.f. magnetron sputtering system. The high-resolution x-ray diffraction and Raman spectroscopy characterizations disclosed the growth of the 2-H phase of MoSe2 and the rhombohedral phase of Bi2Se3 thin films on sapphire (0001). The chemical and electronic states of deposited films were studied using x-ray photoelectron spectroscopy and revealed the stoichiometry growth of MoSe2. We have fabricated metal-semiconductor–metal type PD devices on MoSe2 and MoSe2/Bi2Se3 heterojunction and the photo-response measurements were performed at external voltages of 0.1–5 V under near-infrared (1064 nm) light illumination. The bare MoSe2 PD device shows positive photoconductivity behavior whereas MoSe2/Bi2Se3 heterojunction PD exhibits negative photoconductivity. It was found that the responsivity of MoSe2 and MoSe2/Bi2Se3 heterojunction PDs is ~ 1.39 A W−1 and ~ 5.7 A W−1, respectively. The enhancement of photoresponse of MoSe2/Bi2Se3 PD nearly four-fold compared to bare MoSe2 PD shows the importance of heterojunction structures for futuristics optoelectronic applications.

Automatic Signature and Photo Detection from the Uploaded Document using AI and OCR

In our modern era, it is important for organizations in different industries to have efficient document processing capabilities. One key aspect is the identification of signatures and images in documents, which typically requires manual review. Fortunately, advancements in Artificial Intelligence (AI) and Optical Character Recognition (OCR) technologies present viable options for automating this task. This paper presents a novel method that utilizes AI and OCR techniques to automatically identify signatures and images in uploaded documents.The process starts with preparing documents and utilizing AI technology for recognizing signatures and photos. Optical Character Recognition (OCR) is also used for a thorough examination. This method enhances efficiency, precision, and adaptability in handling documents. It is applicable in various fields like finance, legal, and administration. The solution aims to transform document processing by providing a smooth and dependable way to detect signatures and photos in the modern age.

Deep-ultraviolet n-ZnGa2O4/p-GaN heterojunction photodetector fabricated by pulsed laser deposition.

Zinc gallium oxide (ZnGa2O4) has attracted considerable interest in deep-ultraviolet photodetectors, due to the ultrawide bandgap, high transmittance in the ultraviolet (UV) region, and excellent environmental stability. In this study, ZnGa2O4 thin films were deposited on p-GaN epi-layers using pulsed laser deposition, resulting in improved crystalline quality. The ZnGa2O4 film exhibited a bandgap of 4.93 eV, calculated through absorption spectra. A heterojunction photodetector (PD) was constructed, demonstrating a rectification effect, an on/off ratio of 12,697 at -5.87 V, a peak responsivity of 14.5 mA/W, and a peak detectivity of 1.14 × 1012 Jones (262 nm, -6 V). The PD exhibited a fast response time (39 ms) and recovery time (30 ms) under 262 nm illumination. The band diagram based on the Anderson model elucidates the photoresponse and carrier transport mechanism. This work paves the way for advancing next-generation optoelectronics.

Realization of Self‐Powered High‐Performance Photodetection via Electrostatic Field Enhancement and Dark Current Suppression

Self‐powered photodetectors (PDs) are particularly attractive in the construction of environmentally friendly and sustainable Internet of Things. Utilizing dual functions of PTFE of electrostatic field enhancement and dark current suppression, a high‐performance self‐powered ITO/PTFE/TiO2/GaN UV PD is developed herein. The introduction of PTFE not only significantly reduces the dark current, but also facilitates the separation of photogenerated carriers by coupling the internal electrostatic field at the PTFE/TiO2 interface with the built‐in electric field of the TiO2/GaN heterojunction. With 0 V bias, the light‐to‐dark current (Ilight/Idark) ratio of the PD with PTFE is improved by 2297 times and the response time is faster by 1.69/2.96 times compared to the ITO/TiO2/GaN PD. In addition, a microstructured M‐ITO/PTFE/TiO2/GaN PD with micrometer‐sized cylindrical TiO2 arrays exhibits a high Ilight/Idark ratio of 3.65 × 105, a responsivity of 280.1 mA W−1, a high detectivity of 1.97 × 1013 Jones, and a response time of 4.3/3.0 ms under 360 nm illumination. Our strategy provides a promising way to develop high‐performance self‐powered PD.

Optimizing the depletion width to enhance the performance of CH3NH3PbI3 flexible photodetector based on the piezo-phototronic effect

The research on organic-inorganic hybrid halide perovskites in the field of optoelectronics has greatly advanced the field of photodetection. However, the reported heterojunction structure of perovskite results in complex preparation processes. A simple method was designed to enhance the performance of CH3NH3PbI3 flexible photodetector (PD) by optimizing the depletion width based on the piezo-phototronic effect. Under 5 V bias conditions, when the electrode width of PD is 3, 5, and 8 μm, where the response peaks at 760 nm are 0.06, 0.02, and 0.01 A/W, respectively. This depends on the decrease of electrode width and the increase of depletion width. As the strain increases, the PD response of the interdigital electrode at 3 μm increases from 0.020 to 0.0482 A/W. When the strain is 0.3, the responsiveness increases by 240 %. As the strain increases, the PD response of the interdigital electrode at 5 μm increases from 0.010 to 0.0255 A/W and the PD response of the interdigital electrode at 8 μm increases from 0.006 to 0.0137 A/W. Therefore, devices with a wide depletion width have significant performance advantages. This work improves the responsivity of perovskite flexible PD based on the piezo-phototronic effect by optimizing the depletion width, providing a simple and effective method for manufacturing perovskite thin film devices on high-performance flexible substrates.

A self-powered and flexible deep ultraviolet photodetector based on NiO/Ga2O3 heterojunction and employing stable MXene electrodes

Wearable photodetectors (PDs) have gained significant attention for their importance in smart monitoring applications. The future of wearable electronics emphasizes the development of self-powered devices, necessitating precise material selection and fabrication techniques to achieve optimal electrical and mechanical performance. Traditionally, p-n photodetector junctions have been fabricated using non-oxide materials such as GaN and SiC, but these materials are prone to conductivity degradation due to oxidation of the p-type component. In this investigation, we have successfully engineered a NiO/Ga2O3 heterojunction deep ultraviolet photodetector on both rigid and flexible substrates. The flexible version incorporates Ti3C2TX MXene electrodes, which offer exceptional mechanical stability even in harsh mechanical circumstances. Our photodetector showcases a responsivity of 47 μA/W, a photoresponse time of 0.24 s, a specific detectivity (D*) of 3.84 ×109 jones, and an Ilight/Idark ratio of 121. It also demonstrates excellent repeatability under 254 nm light exposure. The NiO/Ga2O3 heterojunction photodetector exhibits outstanding optoelectronic performance even under harsh mechanical conditions, specifically withstanding 40% stretchability and various bending angles while maintaining self-powered capabilities. This makes it ideal for wearable devices, meeting requirements for both durability and functionality.

Monolithic integrated chip of AWG and PD for an FBG interrogation system

To advance the development of a compact and highly integrated fiber Bragg grating (FBG) interrogation system, to the best of our knowledge, this paper is the first to present the design and fabrication of a monolithic integration chip based on silicon-on-insulator (SOI), which is specifically intended for application in fiber grating sensing interrogation systems. By considering the impact of coupling structure dimensions on coupling efficiency as well as the effect of the photodetector (PD) parameters on the optical absorption efficiency of the device, we refine the structure of the monolithic integrated chip for arrayed waveguide grating (AWG) and PD. The test results reveal that the coupling loss between AWG and PD is -2.4 dB. The monolithic integrated interrogation chip achieves an interrogation accuracy of approximately 6.79 pm within a dynamic range of 1.56 nm, accompanied by a wavelength resolution of 1 pm. This exceptional performance highlights the potential of the monolithic integrated chip to enhance the integration of AWG-based fiber grating interrogation systems.

Wet Chemical Synthesis of Ultrathin γ-Ga2O3 Quantum Wires Enabling Far-UVC Photodetection with Ultrahigh Selectivity and Sensitivity.

As compared to solar-blind ultraviolet (UV) photodetectors (PDs), far-UVC PDs not only show some irreplaceable advantages but also are more challenging to be developed. To solve this challenge, we report herein a soft template-assisted solvothermal route to synthesize ultrathin γ-Ga2O3 quantum wires (UQWs) with diameters down to 1-2 nm. These UQWs all exhibit a cluster-like absorption feature with a strong peak located between 190 and 230 nm and an edge below 250 nm, allowing highly selective absorption to far-UVC light. Notably, their normalized absorption coefficients were experimentally and theoretically confirmed to increase obviously with decreasing their diameters. Self-powered photoelectrochemical-type PDs based on Ga2O3 QWs of 1.7 nm diameter were therefore fabricated, exhibiting an excellent far-UVC detection performance with an unprecedented ultrahigh spectral selectivity (R210 nm/R250 nm = 452). As a proof of concept, this paper offers a new idea for developing ultrawide bandgap semiconductor materials and devices by leveraging a strong quantum confinement effect.