Fast response and broadband self-powered photodetectors based on CZTS/SiNW core-shell heterojunctions for health monitoring

In this work, fast response and broadband self-powered photodetectors based on heterojunctions of vertical smooth silicon nanowires (SiNWs) were proposed, which were achieved through spin-coating p-CZTS on top of n-SiNWs adopting a simple two-step method. First, CZTS was uniformly and tightly attached to the sidewalls of SiNWs in the form of nanoparticles. The prepared CZTS/SiNWs core-shell heterojunctions exhibited typical rectification characteristics in dark and excellent light response characteristics in light illumination. Our device could perform self-driven detection under the UV-VIS-NIR light irradiation without an external energy supply. The responsivity and specific detectivity were estimated to be 14 mAW^-1 and 1.5 × 10¹¹ Jones, which can be improved to 0.35 AW^-1 and 1.2 × 10¹³ Jones at ?1.5 V bias. In addition, the present device also possesses distinct advantages of a large I_light/I_dark ratio exceeding 4.25 × 10⁴, fast response rate with rise/fall times of 1.4/14.2 μs, and outstanding environmental stability. Finally, a heart rate health monitoring application by CZTS/SiNWs detector was proposed. All these results may pave a way for the real application of the self-driven detector in the field of health monitoring in the future.     

In-situ prepared WSe2/Si 2D-3D vertical heterojunction for high performance self-driven photodetector

Two-dimensional (2D) transition metal chalcogenides (TMDs) have shown tremendous feasibility as building blocks for the development of high-performance optoelectronic devices owing to their distinct electrical and optical properties. However, the relatively narrow sensing range as well as the complex fabrication technique impede their technological applications. Here, we demonstrate the mixed-dimensional van der Waals (vdW) WSe₂/Si 2D-3D vertical heterojunction by in-situ fabrication of WSe₂ multilayer on pre-patterned Si, for broadband and fast-speed photodetection. Thanks to the novel high-quality vertical p-n heterojunction, the as-fabricated WSe₂/Si photodetector shows an excellent rectifying characteristic and a prominent photovoltaic effect, making the device capable of light detection in self-driven mode. Additionally, the device reveals remarkable performance in terms of a high specific detectivity of ～8.79 × 10¹³ Jones, a large responsivity of ～294 mA/W, and a fast response time of 4.1 μs. Significantly, the device shows high sensitivity to a wide spectra (200–1550 nm) owing to the production of a type-II band structure of the WSe₂/Si vertical heterojunction. The mechanism of photo-generated carriers separation and transfer in the heterojunction is analyzed by KPFM. Our work offers a potential route to the development of unique 2D-3D heterojunction for optoelectronic devices and system applications.     

Preparation and characteristics study of self-powered and fast response p-NiO/n-Si heterojunction photodetector

The growth of crack-free nanostructured NiO films with good crystalline quality is of high importance for photodetectors to avoid performance failure. In this work, physical properties of spin coated NiO films were controlled by changing diethanolamine (DEA) to nickel acetate (NiAc) molar ratio (0:1–1:1) and post annealing temperature (300–650 °C). NiO film coated at DEA:NiAc molar ratio of 0:1 suffered from severe cracks and poor crystallinity, and by increasing the molar ratio to 1:1 a crack-free NiO with enhanced grain growth was obtained. With the increase of annealing temperature from 300 C to 600 °C, the crystallite size increased from 12.79 to 37.31 nm, and the bandgap decreased from 3.81 to 3.42 eV, indicating an enhancement in NiO film quality. A self-powered photodetector based on p-NiO/n-Si heterojunction showed broadband (UV-NIR) photodetection owing to synergistic photoelectric effect from both NiO film and Si substrate. The responsivity, detectivity, and external quantum efficiency were measured as 13.08, 46.02, 44.49, mA/W, 1.03 × 10¹¹, 3.65 × 10¹¹, 3.53 × 10¹¹, Jones, and 4.43%, 8.62%, 6.47% upon illumination with UV (365 nm), red (660 nm), and NIR (850 nm) lights, respectively. The photodetector showed high on/off current ratio of 1.210 × 10³ and fast response (less than 85 ms). These findings introduce p-NiO/n-Si heterojunction as a promising candidate for next generation optoelectronics.     

Broadband,high-sensitivity self-powered ferroelectric LuMnO3-based photodetector with large photocurrent output

The broadband spectrum detection from ultraviolet to near-infrared is hankered in the photoelectric applications of imaging, sensing and communication. Here, a new self-powered photodetector based on ferroelectric LuMnO₃ thin film with a narrow bandgap of 1.46 eV exhibits high-sensitivity ultraviolet–visible–near infrared photodetection properties. The responsivity (R) and detectivity (D*) in sunlight are 0.4 A/W and 7.05 × 10¹¹ Jones, which are much higher than that of other ferroelectric photodetectors. Moreover, under the monochromatic light (900 nm), the R and D* can reach 0.39 A/W and 6.89 × 10¹¹ Jones. The outstanding photodetection performances owed to the large photocurrent output, where the short-circuit current density can reach 10.5 mA/cm² under 1 sun illumination. The synergistic effect of ferroelectric photovoltaic effect and interface barrier effect demonstrates that the multi-driving forces can achieve high dissociation efficiency for photon-generated carriers. The excellent photodetection performances open up new application of ferroelectric materials in broadband self-powered photodetectors.     

Depolarization electric field and poling voltage-modulated Pb,La(Zr,Ti)O3-based self-powered ultraviolet photodetectors

Traditional self-powered ultraviolet photodetectors, which are usually designed based on p-n junction interfacial effects, exhibit low responsivity and specific detectivity because the photogenerated electrons and holes cannot be separated effectively. Unlike wide band-gap semiconductor materials, ferroelectrics have large remnant polarization and thus high depolarization electric field throughout the whole bulk region, which can cause effective separation of photogenerated electrons and holes. Based on this, in this study, we prepare Pb_0.93La_0.07(Zr_1-xTi_x)_0.9825O₃ (PLZT) ferroelectric thin films with large remnant polarization and self-powered ultraviolet photodetectors with Au/PLZT/FTO structure. The results indicate that the photoelectric response performances of the detectors improve as the remnant polarization of the PLZT thin film and positive poling voltage increase. By adjusting the Ti content, due to large remnant polarization of 47.4 μC/cm² in the PLZT thin films with 80 mol% Ti, the corresponding photodetector exhibits the best self-powered ultraviolet photoelectric response with the high photo/dark current ratio of 2600, responsivity of 2.05 mA/W, specific detectivity of 5.45 × 10¹⁰ Jones, and fast response speed (rise time of 18 ms). These values are superior to those of recently reported self-powered ultraviolet photodetectors.     

The effects of pulse repetition rate on the structural,surface morphological and UV photodetection properties of pulsed laser deposited Mg-doped ZnO nanorods

The Mg_0.05Zn_0.95O (MZO) nanorod array (NRA) films have been successfully grown onto SiO₂/ n-Si substrates by pulsed laser deposition (PLD) without any template or seed layer and the influence of pulse repetition rate (3 to 15 Hz) of a 248 nm KrF excimer laser on their crystallinity, surface morphology and UV photodetection properties were systematically investigated. All the samples show the hexagonal wurtzite phase with a preferential c-axis orientation and the optimum crystallization of the MZO NRAs occurs at 5 Hz. FE-SEM analysis revealed that the growth of MZO NRAs is strongly influenced by the pulse repetition rate. It was observed that the average film thickness increases almost linearly with the pulse repetition rate and the MZO nanorod arrays grown at 5 Hz exhibits best surface area. Moreover, the room temperature UV photodetection properties of the samples were investigated in metal–semiconductor–metal (MSM) planar configurations and are found to be strongly driven by the pulse repetition rate dependent crystalline and surface morphological features. The device current–voltage (I–V) characteristics were measured under dark and UV light conditions. Then, the photocurrent and responsivity were measured with the variation of optical power density and applied voltage, respectively. Transient photoresponse studies show an exceedingly stable and fast switching UV photoresponse for the photodetector having MZO nanorods grown at 5 Hz, which demonstrates highest responsivity of 17 mA/W upon 2 mW/cm² UV illumination (365 nm), at 5 V bias.     

Improved photodetection capabilities of Ag@CeO2 Nanorod composite array using GLAD technique

This work reports the growth of an Ag@CeO₂ nanorod (NR) composite array using the glancing angle deposition (GLAD) technique for UV photodetector application. It showed improvement in performance by decorating plasmonic nanoparticles (NPs) on the semiconductor surface. The interaction between the plasmonic NPs and the semiconductor under the influence of light manifested a localised surface plasmon resonance (LSPR) effect. This allowed for strong absorption, scattering and inducement of an intense electric field, which resulted in the enhancement of photocurrent and, consequently, the device performance. The use of the GLAD technique also allowed the growth of vertically oriented NR composite structures, which assisted in increased absorption. It was found that the fabricated structure exhibited an increase in the responsivity at 370 nm with a value of 18.74 AW^-1 as compared to the previous work of only 4.51 AW^-1. A comparably high detectivity of 3.94 × 10¹² Jones and a low NEP value of 10.67 fW at ?6 V were also exhibited by the device on account of low dark current and enhanced photocurrent. The maximum internal gain obtained for the device was 62.92. The presence of Ag NPs all around the semiconductor NR structure had led to a substantial increase in the photoresponse with a rise time and fall time of 65 ms and 58 ms respectively. These results are believed to offer new ways of harnessing light to boost the functioning of 1D nanostructure-based UV photodetectors.     

Al nanoparticles decorated Er:TiO2 thin film based plasmonic photodetector

Aluminum (Al) nanoparticles (NPs) patterned Erbium-doped Titanium dioxide (Er:TiO₂) thin films (TFs) were synthesized by the combination of sol-gel and glancing angle deposition (GLAD) technique inside the thermal evaporation system. Effects of Al NPs on electrical and optical properties of the Er:TiO₂ TF were experimented and systematically analyzed. Size of NPs was estimated from the field emission scanning electron microscopy (FESEM) image. Diameter of the maximum number of Al NPs was determined to be ～13 nm. The presence of Al was confirmed from the energy dispersive X-ray (EDX) spectra. The optical absorption at around 315 nm revealed the plasmonic resonance of Al NPs. The Au/Er:TiO₂/Al NPs/Er:TiO₂/p-Si Schottky contact-based plasmonic photodetector (PD) was fabricated, which showed excellent photosensitivity under both forward and reverse bias conditions. The responsivity was calculated at an applied voltage of 1 V, which exhibited a high response in the UV region with peak responsivity at 330 nm and 380 nm. The device showed fast switching behaviors under the illumination of 350 nm with a rise time of ～0.55 s and fall time of ～0.13 s. A simple theoretical approach was adopted to evaluate some important parameters of the plasmonic device like photoconductive gain, transit time, and mobility of electrons. Detectivity (1.13 × 10¹² Jones) and noise equivalent power (NEP) (2.46 × 10^?14 W) at 330 nm indicate the suitability of the device as a sensitive UV PD. Hence, the embedded plasmonic Al NPs on Er:TiO₂ TF-based devices can commercially emerge as an efficient and cost-effective UV photodetector.     

Thickness dependent wavelength selective NIR-UV-visible photoresponse in ZnO nanowires and silicon heterojunction

In this paper, we report ZnO nanowires (NWs) and silicon-based type-II PN heterojunction for UV–Visible–Infrared self-powered photodetection. The as-grown ZnO NWs were highly crystalline and aligned along the c-axis in the [002] direction revealed in the HRTEM and XRD measurements. The Hall measurements revealed the n-type behavior for ZnO and p-type for p-Si with carrier concentrations of 4.09 × 10¹⁶ cm^?3 and 1.38 × 10¹⁷ cm^?3, respectively. The depletion widths were estimated to be ～35 nm and ～120 nm, respectively for p-Si and n-ZnO NWs. The Ag/n-ZnO NWs/p-Si/Ag PN heterojunction showed large photoresponse, even at zero bias, under the illumination of commercially available UV–Visible–NIR LEDs, thus acting as a self-powered photodetector. It was interesting to observe that the photoresponse was dependent on the growth time and hence the thickness of ZnO NWs thin film. A maximum zero bias responsivity of ～0.1 A/W at green (515 nm) was observed and was large for the junction with thicker ZnO NWs film (5 h growth), compared with thinner (3 h growth) device under IR (950 nm) LED illumination, however, it was observed otherwise for UV (395 nm) LED. This suggests that tuning the thickness of the ZnO NWs thin film results in the wavelength selective photoresponse, consequently, paving the way towards UV blind IR-visible photodetector based on ZnO NWs. The transient short circuit current (I_sc vs t) and open circuit voltage (V_oc vs t) properties showed fast and large responses under periodic illumination of all LEDs (UV–Vis–NIR). The response was observed to depend on the intensity of light and the maximum V_oc comes out to be ～102 mV and I_sc ～5.58 μA, under the illumination of a red laser diode.     

Improving the fabrication uniformity of ZnO nanowire UV sensor by step-corner growth mode

Uniformity in mass-fabrication of nanostructured device is important for its practical application. In this paper, we developed a step-corner growth mode to on-chip fabricate uniform oblique-bridged ZnO nanowire UV sensor. By strictly controlling the microelectronic processing including photolithography and magnetron sputtering procedures during the seed layer deposition and electrode fabrication, ZnO NW array could nucleate at the upper step-corner of the seed layer due to the high catalytic activities at the surface steps and kinks, and then grow in a distribution of circular sector to form an oblique bridging configuration, which guaranteed the device performance and uniformity at the same time. For the within-chip uniformity, in a 4?×?4 sensor array that randomly chosen under the 365?nm UV light of 2.5?mW/cm² and at the bias voltage of 1?V, the light-to-dark current ratio all kept in the level of 10⁶ with the average value of 1.84?×?10⁶. There were 75% of them in the range of 1.1?×?10⁶ ~ 3?×?10⁶. The detectivity all kept in the level of 10¹⁵Jones with the average value of 3.53?×?10¹⁵Jones. There were 75% of them in the range of 2?×?10¹⁵ ~4?×?10¹⁵Jones. For the chip-to-chip uniformity, in 12 packaged devices that randomly chosen from three fabrication lots, the light-to-dark current ratio all kept in the level of 10⁶ with the average value of 2.70?×?10⁶. There were 75% of them in the range of 1?×?10⁶~ 3?×?10⁶. The detectivity all kept in the level of 10¹⁵Jones with average value of 3.69?×?10¹⁵Jones. There were 75% of them in the range of 1?×?10¹⁵ ~ 4?×?10¹⁵Jones. The uniformity would deteriorate if the step height of seed layer was short, because NW would nucleate at the lower corner of the step and difficult to form the oblique bridge. Fabrication uniformity was also influenced by the step exposure degree, the compactness of the seed layer and the flatness of the substrate.     

A noticeable effect of Pr doping on key optoelectrical properties of CdS thin films prepared using spray pyrolysis technique for high-performance photodetector applications

High-quality thin film-based photodetectors containing praseodymium doped cadmium sulfide (Pr:CdS) were fabricated through spray pyrolysis and studied for various opto-electrical applications. Field emission electron microscopy (FE-SEM) revealed that the prepared films were highly compacted with an extremely fine nanostructure without any pinhole or crack. X-ray diffraction and FT-Raman spectroscopy studies confirmed the single hexagonal phase of all the films. The crystallite size was found to lie between 19 and 32 nm. Optical spectroscopy revealed that the fabricated films have low absorbance and high transmittance (in range of 70–80%). The energy gap was found to lie in the range of 2.40–2.44 eV. The PL spectra contained an intense green emission band at ~531 ± 5 nm (2.33 eV), and its intensity was enhanced by increasing the Pr doping content in CdS. The dark and photo currents of CdS increased by approximately 950 and 42 times, respectively with the addition of 5.0 wt% Pr. The responsivity (R) and specific detectivity (D*) were remarkably enhanced to 2.71 AW^-1 and 6.9 × 10¹¹ Jones, respectively, for the 5.0 wt% Pr:CdS film. The external quantum efficiency (EQE) of 5 wt% Pr:CdS films was 43 times that of pure CdS films, and the on/off ratio was 3.95 × 10² for 5.0 wt% Pr:CdS film. Its high R, D*, and EQE values, and photo-switching behavior make Pr:CdS a good contender for high quality photodetector applications.     

An experimental and theoretical understanding of a UV photodetector based on Ag nanoparticles decorated Er-doped TiO2 thin film

Glancing angle deposition (GLAD) was employed to synthesise plasmonic Silver (Ag) nanoparticles (NPs) on the chemically prepared Erbium-doped Titanium dioxide (Er:TiO₂) thin films (TFs). The impact of using Ag NPs on the morphological, optical, and electrical aspects of Er:TiO₂ TFs were sequentially analysed. From the field emission scanning electron microscopy (FESEM) image, the Ag NPs appeared spherical and uniformly distributed on the Er:TiO₂ TFs. The size (diameter) of the maximum number of Ag NPs was ~15 nm (calculated from FESEM image). Energy dispersive X-ray (EDX) spectra assured the presence of Ag NPs on the TFs. X-ray diffraction (XRD) pattern for Ag NPs decorated Er:TiO₂ TFs closely resembled the face centred cubic crystal structure of Ag NPs and body centred tetragonal Ag–O compound. The optical spectroscopy (UV–visible diffuse reflectance and photoluminescence) elucidated that the absorption of light was significantly enhanced in the UV–visible spectral range for the TFs in which Ag NPs were sandwiched between Er:TiO₂ TF layers (Er:TiO₂/Ag NPs/Er:TiO₂). The Schottky contact-based Au/Er:TiO₂/Si photodetector (PD) and Au/Er:TiO₂/Ag NPs/Er:TiO₂/Si (plasmonic) PD were constructed. The plasmonic PD offered a better photo-responsivity of ~4.5 fold higher as compared to Er:TiO₂ TF-based PD upon 380 nm illumination under ?6 V bias. An increase in detectivity and a decrease in noise equivalent power was observed for the plasmonic device compared to Er:TiO₂ device in the UV region. A theoretical approach had been adopted to calculate the wavelength-dependent responsivity for both devices. Further, the important parameters like photoconductive gain, electron transit time and electron mobility were calculated by simulating the experimental responsivity curves of the devices. These parameters exhibited improvement in the UV regime for the plasmonic PD. The fast temporal response with short rise and decay time proves the excellent efficiency of the plasmonic UV PD.     

Low noise ultraviolet photodetector with over 100% enhanced lifetime based on polyfluorene copolymer and ZnO nanoparticles

Stability and noise current of a hybrid UV photodetector with inverted planar heterojunction (PHJ) structure indium‐tin‐oxide/ZnO nanoparticles (NPs)/poly[9,9′‐dioctyl‐fluorene‐2,7‐diyl]‐copoly[diphenyl‐p‐tolyl‐amine‐4,4′‐diyl] (BFE)/Ag are investigated. ZnO NPs as the acceptor and BFE as the donor were deposited as the active layer. Under UV light illumination, light to dark current ratio of about 10² is observed at a very low bias voltage of ?1.5 V. The spectral response of the device is located near UV region with a maximum responsivity of ～57 mA/W at wavelength of 350 nm. In particular, the prepared device exhibits remarkably higher photoresponse (～350%) and stability (～115%) enhancement under ambient condition compared to the reference device. In addition, the presented results show that the noise current of our device with PHJ structure is about an order of magnitude lower than that of commonly used bulk heterojunction system. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46533.     

Multispectral photodetection using low-cost sputtered NiO/Ag/ITO heterostructure: From design concept to elaboration

High-performance multispectral photodetectors (PDs) are highly attractive for the emerging optoelectronic applications. In this work, a new broadband PD based on p-NiO/Ag/n-ITO heterostructure was fabricated by RF magnetron sputtering technique at room temperature. The tri-layered structure offering multispectral detection property was first identified using theoretical calculations based on combined FDTD and Particle Swarm Optimization (PSO) techniques. The crystal structure of the elaborated sensor was analyzed using X-ray diffraction (XRD) method. The device optical properties were investigated by UV–Vis–NIR spectroscopy. The NiO/Ag/ITO heterostructured PD shows a high average absorbance of 63% over a wide spectrum range of [200 nm–1100nm]. Compared with NiO and ITO thin-films, the performances of the heterostructured device are considerably enhanced. It was found that the prepared PD with NiO/Ag/ITO heterostructure merges the benefits of multispectral photodetection with reduced optical losses and efficient transfer of photo-induced carrier. The device demonstrated a high I_ON/I_OFF ratio of 78 dB and an enhanced responsivity under UV, visible and NIR lights (171 mA/W at 365 nm, 67 mA/W at 550 nm and 93 mA/W at 850 nm). The broadband photodetection property enabled by the optimized NiO/Ag/ITO heterostructure opens a new route for the elaboration of low-cost devices that can offer multiple sensing purposes, which are highly suitable for optoelectronic applications.     

Realization of a self-powered ZnSnO MSM UV photodetector that uses surface state controlled photovoltaic effect

Self-powered ultraviolet (UV) photodetectors (PDs) that use a vertical p-n junction generally involve a complex fabrication process if they are to be integrated with optoelectronic integrated circuits (OEICs). This study demonstrates the fabrication of a self-powered metal-semiconductor-metal (MSM) UV PD with simple planar structure using nontoxic and earth abundant ZnSnO (ZTO). The self-powering characteristic is realized using a localized UV-assisted thermal annealing (LUV-TA) process that selectively modifies the surface states underneath different contacts and creates asymmetric Schottky barrier heights (SBHs) for the MSM PD. The a-ZTO MSM PD with assymmetric SBHs operates at a zero bias and has a responsivity of 18.2 mA/W at 350 nm. The open-circuit voltage is 0.40 V under UV illumination at a wavelength of 365 nm (50 mW/cm²). The device exhibits a fast response speed, with a rise time of 38 ms and a decay time of 180 ms. This study demonstrates that this strategy can be extended to other MSM PDs, particularly those that use an amorphous oxide semiconductor as the active layer.     

Electrospun ZnO Nanofibers‐Based Ultraviolet Detector with High Responsivity

In this report, a metal–semiconductor–metal (MSM) ultraviolet photodetector based on ZnO nanofiber film with Au electrodes was demonstrated. The ZnO nanofibers were synthesized via effective electrospinning process and characterized by means of XRD, SEM, XPS, and UV–visible absorption spectra. At 5 V bias, the dark current of the device was 17.8 nA. Under the irradiation of 260 nm ultraviolet light, the photocurrent could reach 11.5 μA and a high responsivity of 790 A/W was achieved due to the large internal gain. The mechanism of the high internal photoconductive gain was discussed in the article. The experiment presented a general and simple approach to integrate electrospun nanomaterials into photodevices directly.     

Amorphous-AlZnN/graphene heterostructure for solar-blind ultraviolet photovoltaic detectors

Based on the characteristics of ultra-wide bandgap, radiation resistance, high thermal and chemical stability, AlN has been regarded as an ideal material with great potential for ultraviolet detectors. However, its application in solar-blind ultraviolet (SBUV) detection (between 200 nm and 280 nm) is limited by the absorption cutoff edge that is generally less than 200 nm. Here, a photovoltaic SBUV detector with p-Gr/i-AlZnN/n-Si heterojunction structure is first fabricated based on amorphous AlZnN film with an absorption cutoff edge of 258 nm, which is obtained by doping Zn atoms into AlN and controlling the proportion of Zn atoms. The device exhibits outstanding SBUV detection performance, such as the open-circuit voltage (V_oc) reaching 0.87 V at 255 nm, a responsivity of 20.81 mA/W, an EQE of 10.13%, a detection rate of 3.98 × 10¹² Jones, a rise time of 33.2 ms and a fall time of 155 ms under 0 V bias. The results of this study indicate that amorphous AlZnN films applicable to SBUV detectors can be well prepared by energy band engineering, which also work as a reference for the preparation of AlZnN SBUV detectors with excellent performance.     

High-Responsivity Heterojunction Photodetector Based on Bi2O3-Decorated MWCNTs Nanostructure Grown on Silicon via Laser Ablation in Liquid

We prepared a high-responsivity bismuth oxide Bi₂O₃ nanoparticles-decorated multiwalled carbon nanotubes MWCNTs/Si heterojunction photodetector by two-step laser ablation in liquid. The structural properties of the hybrid Bi₂O₃NPs-decorated MWCNTs were investigated by X-ray diffraction, which revealed the formation of α-Bi₂O₃ NPs with a monoclinic phase and graphite at the C(002) plane. Scanning electron microscopy results show the formation of spherical Bi₂O₃NPs attached to well-dispersed MWCNTs. The nanotubes' diameters ranged from 30 to 50 nm, their lengths from 1 to 3 m, and the average particle size of Bi₂O₃ NPs is 25 nm. The I–V characteristics for the Bi₂O₃NPs-decorated MWCNTs/Si photodetector were investigated in the dark and under illumination. The Bi₂O₃NPs-decorated MWCNTs/n-Si photodetectors show a responsivity of 1.37 A/W at a wavelength of 560 nm, with a corresponding external quantum efficiency of 3?×?10²%. At equilibrium, band alignment for Bi₂O₃-MWCNTs /Si heterojunction was realized.

     

Hybrid structures of organic dye and graphene for ultrahigh gain photodetectors

A hybrid structure comprising organic dye molecules (e.g., rhodamine 6G) and graphene was developed for the realization of high-performance optoelectronic devices. The fabricated photodetector offered a broad spectral photo-response across wavelengths in the infrared, visible, and ultraviolet regions, as well as a high responsivity (∼460 A/W at illumination power of 1 μW). The photocurrent generated in the hybrid photodetector (∼mA) was much higher than that generated in a pristine graphene photodetector (<μA). The performance of the dye-sensitized photodetector relied on enhanced photoabsorption and the implementation of a photocurrent gain arising from the photo-excited charges.     

The suppression of dark current for achieving high-performance Ga2O3 nanorod array ultraviolet photodetector

Gallium oxide (Ga₂O₃) is a promising candidate for next-generation solar-blind photodetectors (PDs) because of its large bandgap of 4.9 eV. Its single-crystal nanorod structure improves its photoelectric performance, which promotes carrier transformation and separation. However, Ga₂O₃ nanorods fabricated by the hydrothermal method have many oxygen vacancies, which largely enhance the dark current and reduce the on/off ratio of PDs, restricting application of such devices. Therefore, in this paper, dual strategies are applied to reduce the dark current of a metal–semiconductor–metal-structured Ga₂O₃ nanorod PD fabricated by the hydrothermal method. Through these dual strategies, which include annealing treatment and the application of a polymethyl methacrylate (PMMA) coating, the dark current of the PD is reduced from 1.34 × 10^?7 to 2.04 × 10^?9 A at 1 V, resulting in the on/off ratio of the PD reaching as high as 3.24 × 10⁴. Besides, the responsivity and detectivity of the device reach 1.73 A/W and 2.53 × 10¹² Jones respectively, which represents better performance than those of other reported Ga₂O₃ nanorod array PDs. Results have shown that the new strategy adopted can greatly improve the performance of Ga₂O₃-based ultraviolet photodetectors.