Photoelectric Detectors Based on Inorganic p-Type Semiconductor Materials

Ultrasensitive, Superhigh Signal-to-Noise Ratio, Self-Powered Solar-Blind Photodetector Based on n-Ga2O3/p-CuSCN Core-Shell Microwire Heterojunction

Solar-blind photodetectors have captured intense attention due to their high significance in ultraviolet astronomy and biological detection. However, most of the solar-blind photodetectors have not shown extraordinary advantages in weak light signal detection because the forewarning of low-dose deep-ultraviolet radiation is so important for the human immune system. In this study, a high-performance solar-blind photodetector is constructed based on the n-Ga₂O₃/p-CuSCN core-shell microwire heterojunction by a simple immersion method. In comparison with the single device of the Ga₂O₃ and CuSCN, the heterojunction photodetector demonstrates an enhanced photoelectric performance with an ultralow dark current of 1.03 pA, high photo-to-dark current ratio of 4.14 × 10⁴, and high rejection ratio (R₂₅₄/R₃₆₅) of 1.15 × 10⁴ under a bias of 5 V. Excitingly, the heterostructure photodetector shows high sensitivity to the weak signal (1.5 μW/cm²) of deep ultraviolet and high-resolution detection to the subtle change of signal intensity (1.0 μW/cm²). Under the illumination with 254 nm light at 5 V, the photodetector shows a large responsivity of 13.3 mA/W, superb detectivity of 9.43 × 10¹¹ Jones, and fast response speed with a rise time of 62 ms and decay time of 35 ms. Additionally, the photodetector can work without an external power supply and has specific solar-blind spectrum selectivity as well as excellent stability even through 1 month of storage. Such prominent photodetection, profited by the novel geometric construction and the built-in electric field originating from the p-n heterojunction, meets greatly well the "5S" requirements of the photodetector for practical application.

Enhanced photocurrent in organic photodetectors by the tunneling effect of a hafnium oxide thin film as an electron blocking layer

To achieve high detectivity of organic photodetectors (OPDs), we investigated hafnium oxide (HfO₂) as an electron blocking layer in an attempt to obtain a low leakage current and high photocurrent by the tunneling effect. The prepared devices consisted of indium tin oxide (ITO)/HfO₂/(poly(3-hexylthiophene-2,5-diyl)[P3HT]:PC₆₀BM)/Yb/Al. To explore the tunneling effect in a hafnium oxide thin film, we fabricated a thin film using successive ionic layer deposition. The results for hafnium oxide were compared with those for aluminum oxide and poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS). We found that hafnium oxide results in a low leakage current and high photocurrent owing to the tunneling effect in the OPDs. The resulting detectivity of 1.76 × 10¹² Jones for a film thickness of 5.5 nm and bandwidth of ∼100 kHz is suitable for commercialization.

Photo-Driven Ion Transport for a Photodetector Based on an Asymmetric Carbon Nitride Nanotube Membrane

Conventional photosensing devices work mainly by electron processing and transport, while visual systems in intelligence work by integrative ion/electron signals. To realize smarter photodetectors, some photoionic device or the combination of ionic and electronic devices are necessary. Now, an ion-transport-based self-powered photodetector is presented based on an asymmetric carbon nitride nanotube membrane, which can realize fast, selective, and stable light detection while being self-powered. Local charges are continuously generated at the irradiated side of the membrane, and none (fewer) at the non-irradiated side. The resulting surface charge gradient in carbon nitride nanotube will drive ion transport in the cavity, thus realizing the function of ionic photodetector. With advantages of low cost and easy fabrication process, the concept of ionic photodetectors based on carbon nitride anticipates wide applications for semiconductor biointerfaces.

High-Performance Self-Powered Ultraviolet Photodetector Based on Nano-Porous GaN and CoPc p-n Vertical Heterojunction

Gallium nitride (GaN) is a superior candidate material for fabricating ultraviolet (UV) photodetectors (PDs) by taking advantage of its attractive wide bandgap (3.4 eV) and stable chemical and physical properties. However, the performance of available GaN-based UV PDs (e.g., in terms of detectivity and sensitivity) still require improvement. Fabricating nanoporous GaN (porous-GaN) structures and constructing organic/inorganic hybrids are two effective ways to improve the performance of PDs. In this study, a novel self-powered UV PD was developed by using p-type cobalt phthalocyanine (CoPc) and n-type porous-GaN (CoPc/porous-GaN) to construct a p–n vertical heterojunction via a thermal vapor deposition method. Under 365 nm 0.009 mWcm⁻² light illumination, our device showed a photoresponsivity of 588 mA/W, a detectivity of 4.8 × 10¹² Jones, and a linear dynamic range of 79.5 dB, which are better than CoPc- and flat-GaN (CoPc/flat-GaN)-based PDs. The high performance was mainly attributed to the built-in electric field (BEF) generated at the interface of the CoPc film and the nanoporous-GaN, as well as the nanoporous structure of GaN, which allows for a higher absorptivity of light. Furthermore, the device showed excellent stability, as its photoelectrical property and on/off switching behavior remained the same, even after 3 months.

All-Perovskite Photodetector with Fast Response

Perovskites have attracted substantial attention on account of their excellent physical properties and simple preparation process. Here we demonstrated an improved photodetector based on solution-processing organic-inorganic hybrid perovskite CH3NH3PbI3-xClx layer decorated with CsPbBr3 perovskite quantum dots. The CH3NH3PbI3-xClx-CsPbBr3 photodetector was operated in a visible light region, which appeared high responsivity (R = 0.39 A/W), detectivity (D* = 5.43 × 109 Jones), carrier mobility (μp = 172 cm2 V-1 s-1 and μn = 216 cm2 V-1 s-1), and fast response (rise time 121 μs and fall time 107 μs). The CH3NH3PbI3-xClx-CsPbBr3 heterostructure is anticipated to find comprehensive applications in future high-performance photoelectronic devices.

Tunability in the Optical and Electronic Properties of ZnSe Microspheres via Ag and Mn Doping

ZnSe microspheres with various Ag and Mn doping levels were prepared by the hydrothermal method using Zn(NO₃)₂·6H₂O and Na₂SeO₃ as precursors and N₂H₄·H₂O as the reducing agent. The effects of Ag and Mn doping on the phase composition, morphology, and optical and electrical properties of the final products were systematically investigated. A remarkable change in morphology from microspheres with a cubic sphalerite structure to rodlike structure was observed by Ag doping, while the pristine structure was nearly unchanged via Mn doping. Moreover, the band gap of ZnSe microspheres could be tunable in a broad range via controlling the Ag and Mn doping concentration, and ZnSe with high electrical properties could be obtained by doping with an appropriate concentration. The first-principle plane-wave method was carried out to explain the above mentioned experimental results.

Cu2O-Au nanowire field-effect phototransistor for hot carrier transfer enhanced photodetection

In metal-semiconductor hybrid nanostructures, metal absorbs incident photons and generates hot carriers. The hot carriers are injected into the adjacent semiconductor and subsequently contribute to photocurrent. This process increases the conversion efficiency of optoelectronic devices and provides a new path of photodetectors. In this work, we report an enhanced photodetector by hot holes transfer, which is based on Au nanoparticles decorated p-type Cu₂O nanowires. The photodetector achieves an enhanced photo-responsivity up to 0.314 A W^-1, a higher detectivity of 3.7 × 10¹⁰ Jones. The response time and external quantum efficiency of the Cu₂O-Au nanowires photodetector are 3.7 times faster and 18.2 times higher than that of the Cu₂O nanowires, respectively. The findings indicate that Cu₂O-Au nanowires would be a promising candidate in developing novel plasmonic hot carrier devices.

Zinc oxide ultraviolet photodetectors: rapid progress from conventional to self-powered photodetectors

Currently, the development of ultraviolet (UV) photodetectors (PDs) has attracted the attention of the research community because of the vast range of applications of photodetectors in modern society. A variety of wide-band gap nanomaterials have been utilized for UV detection to achieve higher photosensitivity. Specifically, zinc oxide (ZnO) nanomaterials have attracted significant attention primarily due to their additional properties such as piezo-phototronic and pyro-phototronic effects, which allow the fabrication of high-performance and low power consumption-based UV PDs. This article primarily focuses on the recent development of ZnO nanostructure-based UV PDs ranging from nanomaterials to architectural device design. A brief overview of the photoresponse characteristics of UV PDs and potential ZnO nanostructures is presented. Moreover, the recent development in self-powered PDs and implementation of the piezo-phototronic effect, plasmonic effect and pyro-phototronic effect for performance enhancement is highlighted. Finally, the research perspectives and future research direction related to ZnO nanostructures for next-generation UV PDs are summarized.

Millimeter-Sized Single-Crystal CsPbrB3/CuI Heterojunction for High-Performance Self-Powered Photodetector

Millimeter-sized CsPbBr₃ single crystals were prepared via a facile solvent-evaporation method in ambient environment. The heterojunction between p-type CuI and n-type CsPbBr₃ was formed by a simple immersion process. The as-integrated CsPbBr₃/CuI device exhibits a good rectifying behavior (ratio of 250 at ±2 V). In particular, the photodetector shows excellent self-powered characteristics under 540 nm light illumination, including high photocurrent (near 100 nA); high photosensitivity (on/off ratio of 1.5 × 10³); fast response speed (0.04/2.96 ms); and good wavelength selectivity (565-525 nm), responsivity (1.4 mA W^-1), and detectivity (6.2 × 10¹⁰ Jones). This work provides a simple, low-cost, and effective method for preparing millimeter-level CsPbBr₃ single crystals. The simple device architecture further provides a promising approach for fabricating high-performance self-powered photodetectors.

Nitrogen Boosts Defective Vanadium Oxide from Semiconducting to Metallic Merit

2D metal oxide nanosheets have attracted substantial attention for various applications owing to their appealing advantages. Yet, the exploration of effective methodology for fabrication of metallic 2D metal oxides with a high concentration of N dopants in a scalable manner remains challenging. Herein, a topochemical strategy is demonstrated on vanadium oxide nanosheets by combining 2D nanostructuring, heteroatom-doping, and defect engineering for modulating their intrinsic electronic structure and greatly enhancing their electrochemical property. O vacancies and N dopants (VON and VN bonds) are in situ formed in vanadium oxide via nitridation and lead to semiconductive-to-metallic phase transformation evidenced by experimental results and theoretical calculation. Overall, the N-VO_0.9 nanosheets exhibit a metallic electron transportation behavior and excellent electrochemical performance. These findings shed light on the rational design and electron structure tuning of 2D nanostructures for energy and electronics applications.

Materials and Designs for Wearable Photodetectors

Photodetectors (PDs), as an indispensable component in electronics, are highly desired to be flexible to meet the trend of next-generation wearable electronics. Unfortunately, no in-depth reviews on the design strategies, material exploration, and potential applications of wearable photodetectors are found in literature to date. Thus, this progress report first summarizes the fundamental design principles of turning "hard" photodetectors "soft," including 2D (polymer and paper substrate-based devices) and 1D PDs (fiber shaped devices). In short, the flexibility of PDs is realized through elaborate substrate modification, material selection, and device layout. More importantly, this report presents the current progress and specific requirements for wearable PDs according to the application: monitoring, imaging, and optical communication. Challenges and future research directions in these fields are proposed at the end. The purpose of this progress report is not only to shed light on the basic design principles of wearable PDs, but also serve as the roadmap for future exploration in wearable PDs in various applications, including health monitoring and Internet of Things.

Ultrahigh-Detectivity Photodetectors with Van der Waals Epitaxial CdTe Single-Crystalline Films

Van der Waals epitaxy (vdWE) is crucial for heteroepitaxy of covalence-bonded semiconductors on 2D layered materials because it is not subject to strict substrate requirements and the epitaxial materials can be transferred onto various substrates. However, planar film growth in covalence-bonded semiconductors remains a critical challenge of vdWE because of the extremely low surface energy of 2D materials. In this study, direct growth of wafer-scale single-crystalline cadmium telluride (CdTe) films is achieved on 2D layered transparent mica through molecular beam epitaxy. The vdWE CdTe films exhibit a flat surface resulting from the 2D growth regime, and high crystal quality as evidenced by a low full width at half maximum of 0.05° for 120 nm thick films. A perfect lattice fringe appears at the interfaces, implying a fully relaxed state of the epitaxial CdTe films correlated closely to the unique nature of vdWE. Moreover, the vdWE CdTe photodetectors demonstrate not only ultrasensitive optoelectronic response with optimal responsivity of 834 A W^-1 and ultrahigh detectivity of 2.4 × 10¹⁴ Jones but also excellent mechanical flexibility and durability, indicating great potential in flexible and wearable devices.

Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.

Self-Powered, Broad Band, and Ultrafast InGaN-Based Photodetector

A self-powered, broad band and ultrafast photodetector based on n⁺-InGaN/AlN/n-Si(111) heterostructure is demonstrated. Si-doped (n⁺ type) InGaN epilayer was grown by plasma-assisted molecular beam epitaxy on a 100 nm thick AlN template on an n-type Si(111) substrate. The n⁺-InGaN/AlN/n-Si(111) devices exhibit excellent self-powered photoresponse under UV-visible (300-800 nm) light illumination. The maximum response of this self-powered photodetector is observed at 580 nm for low-intensity irradiance (0.1 mW/cm²), owing to the deep donor states present near the InGaN/AlN interface. It shows a responsivity of 9.64 A/W with rise and fall times of 19.9 and 21.4 μs, respectively. A relation between the open circuit voltage and the responsivity has been realized.

Low-cost writing method for self-powered paper-based UV photodetectors utilizing Te/TiO2 and Te/ZnO heterojunctions

It has always been a challenge to prepare self-powered ultraviolet photodetectors (UV PDs) utilizing a green, facile and low-cost method. Here, we provide such an approach for fabricating self-powered photodetectors based on Te nanowire/TiO₂ nanoparticle (NP) and Te nanowire/ZnO nanoparticle (NP) heterojunctions. It is noteworthy that such devices were prepared via simply brushing non-toxic solution-processed Te nanowires and commercial TiO₂ and ZnO nanoparticles onto paper. The as-obtained UV PDs can work under zero bias due to photovoltaic effects from the Te/TiO₂ and Te/ZnO heterojunctions. This study not only presents high-performance UV PDs, but also provides a general and effective method for developing environmentally-friendly and energy-efficient optoelectronic devices for practical applications. The concept of employing daily-use brushes and recyclable paper provides a facile way to fabricate green low-cost PDs.

Cathodic "signal-on" photoelectrochemical aptasensor for chloramphenicol detection using hierarchical porous flower-like Bi-BiOI@C composite

A novel p-type semiconductor-based cathodic "signal-on" photoelectrochemical (PEC) aptasensor was proposed for highly sensitive and selective detection of chloramphenicol (CAP). The photocathode was fabricated with hierarchical porous flower-like Bi-BiOI@C composite synthesized via a one-pot solvothermal method using glucose as both green reductant and carbon precursor. Due to the surface plasmon resonance (SPR) effect of Bi and high-conductivity of carbon, the composite exhibited an enhanced cathodic photocurrent as compared with pure BiOI or Bi-BiOI. When CAP-binding aptamer was immobilized as recognition element on Bi-BiOI@C modified electrode, a cathodic PEC aptasensor showing specific "signal-on" response to CAP was constructed. Some influencing factors such as coating amount of Bi-BiOI@C suspension, applied bias potential, and aptamer concentration were studied. Under the optimum conditions, the cathodic photocurrent of the constructed PEC aptasensor increased linearly with CAP concentration from 2 to 250 nM, with a detection limit (3S/N) of 0.79 nΜ. The proposed sensor was successfully applied to the determination of CAP in pharmaceutical tablet, eye drop and lake water samples.

High-performance solar-blind SnO2 nanowire photodetectors assembled using optical tweezers

One-dimensional semiconducting SnO2 nanowires with wide bandgaps are promising candidates to build many important optoelectronic devices. Because building these devices involves the assembly of nanowires into complex structures, manipulation of the active materials needs to be done with high spatial precision. In this paper, an optical tweezer system, comprising a spatial light-modulator, a microscope, and optical elements, is used to individually trap, transfer, and assemble SnO2 nanowires into two-terminal photodetectors in a liquid environment. After the assembly using optical trapping, the two ends of the SnO2 nanowire photodetectors, which are connected with the electrodes, were further stabilized using a focused laser. During exposure to 275 nm deep-ultraviolet light, the as-assembled photodetectors show a high Iph/Idark ratio of 2.99 × 105, a large responsivity of 4.3 × 104 A W-1, an excellent external quantum efficiency of 1.94 × 105, and a high detectivity of 2.32 × 1013 Jones. The photoresponse-speed of the devices could be improved further using passivation with a polymer. The rise and decay times are about 60 ms and 100 ms, respectively. As a result of this study, we can confirm that non-contact optical trapping can enable the construction of nanowire architectures for optoelectronic, bioelectronic, and other devices.

Detection of phosphorus species in water: technology and strategies

This review highlights recent advances in methods of detection of total phosphorus in water, including photoelectric strategies, spectroscopy techniques, and modeling algorithms.

Isovalent bismuth ion-induced growth of highly-disperse Sb2S3 nanorods and their composite with p-CuSCN for self-powered photodetectors

Trace amounts of Bi ions are able to cause the growth of highly-disperse, thin Sb₂S₃ nanorods, which exhibit potential in UV-visible self-powered photodetectors when coupled with p-CuSCN crystal clusters.

Self-Powered Ultraviolet Photodetector with Superhigh Photoresponsivity (3.05 A/W) Based on the GaN/Sn:Ga2O3 pn Junction

Ultraviolet (UV) radiation has a variety of impacts including the health of humans, the production of crops, and the lifetime of buildings. Based on the photovoltaic effect, self-powered UV photodetectors can measure and monitor UV radiation without any power consumption. However, the current low photoelectric performance of these detectors has hindered their practical use. In our study, a super-high-performance self-powered UV photodetector based on a GaN/Sn:Ga₂O₃ pn junction was generated by depositing a Sn-doped n-type Ga₂O₃ thin film onto a p-type GaN thick film. The responsivity at 254 nm reached up to 3.05 A/W without a power supply and had a high UV/visible rejection ratio of R_254 nm/ R_400 nm = 5.9 × 10³ and an ideal detectivity at 1.69 × 10¹³ cm·Hz^1/2·W^-1, which is well beyond the level of previous self-powered UV photodetectors. Moreover, our device also has a low dark current (1.8 × 10^-11A), a high I_photo/ I_dark ratio (∼10⁴), and a fast photoresponse time of 18 ms without bias. These outstanding performance results are attributed to the rapid separation of photogenerated electron-hole pairs driven by a high built-in electric field in the interface depletion region of the GaN/Sn:Ga₂O₃ pn junction. Our results provide an improved and easy route to constructing high-performance self-powered UV photodetectors that can potentially replace traditional high-energy-consuming UV detection systems.

p-GaN/n-ZnO nanorods: the use of graphene nanosheets composites to increase charge separation in self-powered visible-blind UV photodetectors

ZnO-based heterojunctions have found applications as self-powered ultraviolet photodetectors (PDs). However, high doping levels are not compatible with high mobility for metallic doped ZnO-based PDs so further development has been inhibited. This study demonstrates a method to increase the open-circuit voltage (V _oc) that allows keeping a sufficiently high level of mobility of ZnO, using a ZnO nanorod/GaN heterojunction that incorporates graphene nanosheets as the active layer. These hybrid PDs have triple the value for V _oc of PDs that have only pure ZnO and better exhibit photo-response characteristics. The results of surface Kelvin probe microscopy and x-ray photoelectron spectrometer show that the complex defects that occur because Zn interstitials form a shallow donor in ZnO are mainly responsible for the increase in the value of V _oc. Using this functional nanostructure as an active layer represents a new method for the manufacture of high-performance self-powered PDs.

UV Photodetectors Based on BiOCl Nanosheet Arrays: The Effects of Morphologies and Electrode Configurations

A facile chemical bath method is adopted to grow bismuth oxychloride (BiOCl) nanosheet arrays on a piece of Cu foil (denoted as BiOCl-Cu) and isolated BiOCl nanosheets are collected by ultrasonication. A self-supporting BiOCl film is obtained by the removal of Cu foil. Photodetectors (PDs) based on these BiOCl materials are assembled and the effects of morphologies and electrode configurations on the photoelectric performance of these PDs are examined. The BiOCl nanosheet PD achieves high responsivities in the spectral range from 250 to 350 nm, while it presents quite a small photocurrent and slow response speed. The BiOCl film PD yields low photocurrents and near-unity on-off ratios, demonstrating poor photoelectric performance. The photocurrent of the BiOCl-Cu PD with both electrodes on the BiOCl film is much higher than those of these above-mentioned PDs, and the response times are fast. Meanwhile, the BiOCl-Cu PD with separate electrodes on the BiOCl film and Cu foil achieves even higher photocurrents and presents a self-powering characteristic, depicting the improved photodetecting performances induced by the specific morphology and distinct electrode configuration. These results would promote the applications of BiOCl nanostructures in the photoelectric devices.