ZnO UV Photodetectors Research Articles

Hydrothermal Synthesis of ZnO Nanospheres Using Apple Pectin as Biotemplate and Application for UV Sensing

In this study, spherical-like ZnO UV photodetectors based on the facile hydrothermal method, induced different concentrations of apple pectin as the biotemplate. Apple pectin can react with zinc particles and change the pH value, which plays an essential role in modifying surface morphology. Moreover, apple pectin extracted from apple peels as carbon and nitrogen sources can also be used to improve absorption properties and increase depletion region to reduce dark current. The best results were obtained when 150 mg of apple pectin was used, showing a high UV-to-dark current ratio and fast response and recovery times. The UV-to-dark current ratio is as high as 80106.1, which is better than that of pure ZnO (4.47). Fast response and recovery times are also swift. The physical properties were evaluated using various techniques, including scanning electron microscopy, photoluminescence (PL), X-ray diffraction, and energy-dispersive X-ray (EDX), respectively. The results of this study suggest that the use of apple pectin in the hydrothermal synthesis of ZnO may offer a promising approach for modifying ZnO materials.

Ultraviolet Photodetector Based on Poly(3,4-Ethylenedioxyselenophene)/ZnO Core–Shell Nanorods p-n Heterojunction

In this work, we successfully assembled an organic–inorganic core–shell hybrid p-n heterojunction ultraviolet photodetector by the electropolymerization deposition of poly(3,4-ethylenedioxyselenophene) (PEDOS) on the surface of zinc oxide nanoarrays (ZnO NRs). The structures of composite were confirmed by FTIR, UV–Vis, XRD and XPS. Mott–Schottky analysis was used to study the p-n heterojunction structure. The photodetection properties of ZnO NRs/PEDOS heterojunction ultraviolet photodetector were systematically investigated current–voltage (I–V) and current–time (I–t) analysis under different bias voltages. The results showed that PEDOS films uniformly grew on ZnO NRs surface and core–shell structure was formed. The p-n heterojunction structure was formed with strong built-in electric field between ZnO NRs and PEDOS. Under the irradiation of UV light, the device showed a good rectification behavior. The responsivity, detection rate and the external quantum efficiency of the ultraviolet photodetector reached to 247.7 A/W, 3.41 × 1012 Jones and 84,000% at 2 V bias, respectively. The rise time (τr) and fall time (τf) of ZnO NRs/PEDOS UV photodetector were obviously shortened compared to ZnO UV photodetector. The results show that the introduction of PEDOS effectively improves the performance of the UV photodetector.

Comparative evaluation of ZnO nanorod material properties and UV photodetector performance with various transition metal dopings

Comparative evaluation of ZnO nanorod material properties and UV photodetector performance with various transition metal dopings

Research on piezo-phototronic effect in ZnO/AZO heterojunction flexible ultraviolet photodetectors

A novel Al-doped (3 wt%) ZnO (AZO) UV photodetector (PD) and ZnO/AZO heterojunction double-layer UV PD were prepared on a polyethylene terephthalate (PET) substrate by utilizing the radio frequency (RF) sputtering technology and conventional photolithography. Because the ZnO/AZO heterojunction possesses the ability to improve the separation of the photogenerated electron-hole pairs, the responsivity of the ZnO/AZO PD is higher than that of the pure AZO PD under the same bias voltage. Moreover, the responsivity of the obtained ZnO/AZO PD showed a 1.13 fold increase from 5.91 to 6.70 A/W when the tensile variable ɛ was 0.16. These findings also provide a new alternative for the preparation of flexible UV PDs with piezo-phototronic effect, which is low-cost and offers environmental sustainability.

ZnO UV Photodetector Based on Sandwich Structure

ZnO UV Photodetector Based on Sandwich Structure

Self‐Polarized BaTiO3 for Greatly Enhanced Performance of ZnO UV Photodetector by Regulating the Distribution of Electron Concentration

AbstractZnO film ultraviolet photodetectors (UV PDs) have always suffered from slow speed and low photosensitivity that restrict their broader applications. To break through those barriers, high‐performance ZnO UV PD based on self‐polarized BaTiO3 (BTO) is first introduced through a facile one‐step spin‐coating method. Compared with pure ZnO film UV PD with low on/off ratio (65) and slow speed (4.1/7.5 s) at 3 V bias under 350 nm UV light, the BTO‐ZnO bilayer film device exhibits an ultrahigh on/off ratio (14 300) and ultrafast response speed (0.11/5.80 ms), which is much faster than that of the most reported ZnO film‐based UV PDs. The numerical simulation demonstrates that the spatial distribution of electron concentration of ZnO film is regulated by the self‐polarization of BTO film, resulting in low dark current and fast response time of the BTO‐ZnO PD. This work provides a new approach to fabricate high‐performance PDs based on self‐polarized ferroelectric materials.

Effect of thermal annealing on the characteristics of ZnO nanorods UV photodetector

This paper reported a ZnO UV photodetector synthesized by room temperature radio frequency (RF) magnetron sputtering and hydrothermal growth process. In addition, the effect of thermal annealing on the photoresponse properties of the ZnO photodetector was studied. This work may provide a potential approach to enhance the performance of ZnO UV photodetector.

Doping controlled pyro-phototronic effect in self-powered zinc oxide photodetector for enhancement of photoresponse

The pyro-phototronic effect can be used in pyroelectric semiconductor materials to significantly contribute in enhancing the self-powered photoresponse of photodetectors (PDs) via modulation of the photogenerated charge density. The pyro-phototronic effect in zinc oxide (ZnO) nanorods (NRs) was exploited thoroughly by doping with halogen elements, such as fluorine, chlorine (Cl), bromine and iodine. Cl-doped ZnO NRs (Cl : ZnO NRs) induces a large number of free charge carriers to enhance the self-powered photoresponse behavior (nearly 333% enhancement in response current) due to the pyro-phototronic effect as compared to pristine ZnO NRs. Moreover, 405% enhancement in pyrocurrent was measured for the Cl : ZnO NRs PD under a ultraviolet illumination intensity of 3 mW cm-2, as compared to 0.3 mW cm-2, in the absence of external bias voltage. Furthermore, other photoresponse parameters such as responsivity, external quantum efficiency and specific detectivity are measured to be higher due to the pyro-phototronic effect. Therefore, this study reveals the direct use of the pyro-phototronic effect to enhance the self-powered photoresponse.

Photoresponse Performance Evaluation of ZnO UV Photodetector Based on Noise Analysis

The ZnO film photosensitive chips prepared by sputtering method were post-treated by air-anneal at different temperatures and Ar or air-plasma treatments for different time. Then, photosensitive chips were packaged into UV photodetectors with a standard TO-5 package to meet the sensitivity, selectivity, and stability standards. Noise analysis was used as an efficient tool to evaluate the quality and reliability of ZnO UV photodetectors, and the overall performance evaluation based on 1/f noise physical model is made to build the relationship between photoresponse and surface defect state density. The 1/f noise comes from defect-related carriers’ number fluctuation, which are trap and detrap processes of free electrons from oxygen vacancies at the surface of ZnO. This can be analyzed semi-quantitatively by the surface trap energy density obtained by voltage power spectral density. For the photosensitive chip treated by 300° air-anneal, we can obtain the largest responsivity 6.7 A/W, the smallest noise equivalent power $2.7 \times 10^{-9}$ W, and the largest specific detectivity $9\ast 10^{10}$ Jones at 300 nm under the bias of 5 V. The excellent photoresponse performance is also indicated by large linear dynamic range and fast response and recovery speeds.

Highly Wavelength-Selective Enhancement of Responsivity in Ag Nanoparticle-Modified ZnO UV Photodetector.

We proposed and demonstrated Ag nanoparticles (NPs)-decorated ZnO photodetectors for UV light sensing. After decoration of their surface with random Ag NPs, the dark current density of ZnO UV photodetectors decreases obviously. Moreover, the device exhibits an obvious increase in peak responsivity at around 380 nm, which can be attributed to the narrow-band quadrupole plasmon resonance of Ag NPs in the UV range. Meanwhile, the responsivity at the other wavelengths decreases a lot. As a result, the response peak becomes more significant, and the response of the devices presents an excellent wavelength selectivity after covering with Ag NPs. The detailed mechanism for this phenomenon was explained. We believe that our findings would open a way to harness the high-order plasmon modes in the field of UV optoelectronic devices.

All-inkjet-printed flexible ZnO micro photodetector for a wearable UV monitoring device

Fabrication of small-sized patterns of inorganic semiconductor onto flexible substrates is a major concern when manufacturing wearable devices for measuring either biometric or environmental parameters. In this study, micro-sized flexible ZnO UV photodetectors have been thoroughly prepared by a facile inkjet printing technology and followed with heat treatments. A simple ink recipe of zinc acetate precursor solution was investigated. It is found that the substrate temperature during zinc precursor ink depositing has significant effects on ZnO pattern shape, film morphology, and crystallization. The device fabricated from the additive manufacturing approach has good bendability, Ohmic contact, short response time as low as 0.3 s, and high on/off ratio of 3525. We observed the sensor’s dependence of response/decay time by the illuminating UV light intensity. The whole process is based on additive manufacturing which has many benefits such as rapid prototyping, saving material, being environmentally friendly, and being capable of creating high-resolution patterns. In addition, this method can be applied to flexible substrates, which makes the device more applicable for applications requiring flexibility such as wearable devices. The proposed all-inkjet-printing approach for a micro-sized ZnO UV photodetector would significantly simplify the fabrication process of micro-sized inorganic semiconductor-based devices. A potential application is real-time monitoring of UV light exposure to warn users about unsafe direct sunlight to implement suitable avoidance solutions.

Effect of the buffer layer on the metal-semiconductor-metal UV photodetector based on Al-doped and undoped ZnO thin films with different device structures

ZnO and Al-doped ZnO (AZO) thin films were grown on the ZnO buffer layer by a chemical spray pyrolysis method. The metal–semiconductor–metal (MSM) UV photodetector based on ZnO thin films with two device configuration Ag/AZO/ZnO/Ag and Ag/ZnO/ZnO/Ag have been studied. AZO and ZnO thin films were grown on the ZnO buffer layer by a chemical spray pyrolysis technique. The effect of the buffer layer on the physicochemical and UV-sensing properties of the AZO and ZnO thin-film-based UV photodetectors were analyzed. The XRD results suggested that the buffer layer improves the crystalline quality of the ZnO thin films. The device with configuration Ag/AZO/ZnO/Ag exhibits a maximum photocurrent of about 876 µA at 5 V bias at 365 nm peak wavelength. The linear I–V characteristic of the photodetector reveals the good ohmic contacts between metal–semiconductor junctions. The AZO-based UV photodetector with ZnO buffer layer shows a maximum photoresponsivity of about 340 A/W, which is much higher than that of the ZnO-based UV photodetector with ZnO buffer layer. The photoresponse and photoswitching characteristics of the device demonstrate that a ZnO UV photodetector with a buffer layer offers a new way to fabricate devices on a buffer-layer-coated substrate.

An ultrafast response grating structural ZnO photodetector with back-to-back Schottky barriers produced by hydrothermal growth

Nanostructured ZnO UV photodetector produced by UV-NIL with hydrothermal growth achieved ultrafast response time.

Copper Doped ZnO Thin Film for Ultraviolet Photodetector with Enhanced Photosensitivity

ABSTRACTUltraviolet photoconductivity in Copper doped ZnO (Cu:ZnO) thin films synthesized by sol-gel technique is investigated. Response characteristics of Pure ZnO thin film and Cu:ZnO thin film UV photodetector with 1.3 at. wt % Cu doping biased at 5 V for UV radiation of λ = 365 nm and intensity = 24 µwatt/cm2 has been studied. Cu:ZnO UV photodetector is found to exhibit a high photocoductive gain (K = 1.5×104) with fast recovery (T90% = 23s) in comparison to pure ZnO thin film based photodetector (K = 4.9×101 and T90% = 41s). Cu2+ ions have been substituted in ZnO lattice which has been confirmed by X-ray diffraction (XRD) and Raman spectroscopy leading to lowering of dark current (Ioff ∼ 1.44 nA). Upon UV illumination, more electron hole pairs are generated in the photodetector due to the high porosity and roughness of the surface of the film which favours adsorption of more oxygen on the surface of the photodetector. The photogenerated holes recombined with the trapped electrons, increasing the concentration of photogenerated electrons in the conduction band enhancing the photocurrent (Ion ∼ 0.02 mA) of the Cu:ZnO photodetector.

Optical Applications of ZnO Nanowires

This paper discusses different aspects of optical applications of ZnO nanowires NWs. After a description of the relevant synthesis and fabrication techniques, light-emitting diodes based on ZnO NW and NW arrays are introduced and different experimental realizations from the literature are discussed. The working principle of ZnO UV photodetectors is presented, and improvements and limitations of ZnO- NW-based dye-sensitized solar cells are discussed. Different aspects of ZnO-NW waveguides and their potential application for biological sensing are described. Finally, the current status of ZnO-NW-based UV lasers is presented.

Effect of a buffer layer on the properties of UV photodetectors based on a ZnO/diamond film structure

In this paper, ZnO films were grown on the nucleation sides of freestanding diamond substrates with and without a ZnO homobuffer layer by the radio-frequency (RF) magnetron sputtering method. The effects of buffer layers on the properties of the ZnO film and UV photodetectors based on a ZnO/freestanding diamond film structure were studied. The experimental results suggested that the buffer layer was helpful in improving the crystalline quality of ZnO/diamond heteroepitaxial films and the electrical property of the ZnO photodetectors was relative to the crystalline quality of ZnO films. For the photodetector based on the ZnO film with a buffer layer, a higher value of photo-responsivity under a 10 V bias voltage and a better time-dependent photocurrent characteristic were obtained.

Fabrication OF ZnO and ZnMgO Thin Films and UV Photodetectors by Mist Chemical Vapor Deposition Method

ABSTRACTDeposition of Zn1-xMgxO thin films on glass substrates has been investigated by the simple and cost-effective mist CVD technique. A water solution of zinc acetate and magnesium acetate was used as the source of Zn and Mg. The solution was ultrasonically atomized, and the aerosols hence formed were supplied by the N2 carrier gas to the substrates. The band gap energy of ZnMgO was successfully controlled from 3.25 eV (ZnO) to 3.75 eV with the concentration ratio [Mg]/([Zn]+[Mg]) in the solution. The transparency in the visible region was higher than 90% and the surface RMS roughness was 7.5 nm (an example for ZnO) despite the polycrystalline structure; they are satisfactory for the optical applications. A UV photodetctor with interdigital electrode structure on the ZnMgO surface was fabricated, where the photoresponsivity of 2.6 A/W at 350 nm and the lowest detectable power of about 1 μW were obtained. Although these values are satisfactory for the simple UV detection but the existence of deep defects is deteriorating the dynamic response of the detector device.