High Responsivity UV Research Articles

A high responsivity UV photodetectors based on ZnO quantum dots/ZnO nanowires homojunction

A high responsivity UV photodetectors based on ZnO quantum dots/ZnO nanowires homojunction

High responsivity UV detector based on TiO2-rGO nanocomposite material

The influence of reduced graphene oxide and the optoelectronic characterictics of a nanocomposites based on rGO and TiO2 were studied. Surface morphology and Raman spectra of nanocomposite materials indicate the presence of initial components. It has been illustrated that during hydrothermal synthesis further reduction of rGO occurs, i.e. the variety of oxygen-containing groups decreases. Studies of current-voltage characteristics have displayed the availability of rGO in the nanocomposite leads to an increase in the photo induced current to more than 40 µA. Next, the photoresponsivity of the samples was determined, which is three orders of value higher than pure titanium dioxide for nano-composite material. And the detectivity also increased 9 times. This parameter allows you to identify the performance of the device. In this regard, the UV detector based on nanocomposite has a higher performance. Studies also show a decrease in reaction time to light irradiation. When irradiated, the nanocomposite material reacts to light three orders of magnitude faster than TiO2.

A high responsivity UV - visible dual band photodetector based on SnO2 microwires with RhB surface sensitization

A SnO2 microwire (MW) based dual band photoconductive photodetector without persistent photoconductivity has been achieved. For expansion of the photo response to visible light, a dual band photodetector with UV and visible light response was fabricated via introducing RhB dye molecules. Due to the surface sensitization, photo responsivity of 43.1 A W−1 was obtained under 520 nm light illumination and 10 V bias for the detector made from a dye modified SnO2 MW, which is a 7-fold increase when compared to a photodetector fabricated from sole SnO2 MW (about 5.3 A W−1). The dual band photodetector also showed about double responsivity at 260 nm (about 351.9 A W−1) when compared to the detector made from sole SnO2 MW (about 183.9 A W−1), indicating improved UV light detection. Furthermore, under light excitations at 260 nm and 550 nm, the detectivity of about 2.38 × 1011 Jones and 3.55 × 1010 Jones can be obtained respectively for RhB molecule surface sensitized SnO2 MW at 10 V bias voltage. Through comparison of the electronic structures, the improved device performance in UV and visible light are attributed to the electron transfer mechanism from RhB to SnO2 surface, which can be verified from the measured I - t curves.

Fabrication of Branched Flower-Like ZnO/Si Hierarchical Heterostructure UV Detector by Aqueous Method.

High performance ZnO/Si hierarchical heterostructure UV detector was fabricated using an aqueous method. The structural, morphological and optical properties of the hierarchical heterostructure were characterized. The heterostructural UV detector was composed of ZnO nanorods grown on Si nanowires to form a flower-like structure. The device results demonstrated that the as-grown ZnO/Si hierarchical heterostructure showed high UV response. The method provides a simple way to fabricate high-response UV photodetectors based on ZnO/Si heterostructure.

Ag nanorods assembled with ZnO nanowalls for near-linear high-response UV photodetectors

We developed a simple method of sonication combined with annealing treatment method to construct ZnO/Ag heterostructures from Ag nanorods assembled in-situ with ZnO nanowalls, which were then characterized by FESEM, EDS, XRD, XPS, PL, UV-vis spectra. A perfect heterojunction was formed by Ag nanorods inserted into the holes of 3D ZnO nanowalls. Compared with pure ZnO nanowalls, the ZnO/Ag heterostructures have more vacancy defects and a red shift in absorption. The effects of the working temperature on sensors fabricated with ZnO/Ag heterojunction were investigated. The photodetector demonstrated higher photo response activity as well as a faster response speed and excellent environmental stability compared to pristine ZnO nanowalls, and the photoresponse exhibited a better linear relationship at 10 °C ∼70 °C. The mechanism of UV photo sensing for the ZnO/Ag heterojunction was discussed. The results indicated that ZnO/Ag heterojunction could act as an interesting material for UV photodetectors with near-linear responses in outdoor temperatures.

Three-dimensional ZnO nanorods growth on ZnO nanorods seed layer for high responsivity UV photodetector

Three-dimensional ZnO nanorods (NRs) were synthesized by hydrothermal method on ZnO seed layer including horizontal ZnO NRs. The ZnO seed layers consist of different values of NRs were synthesized by spin-coating. The different seed layers and ZnO nanorods arrays were characterized using field emission scanning electron microscopy, X-ray diffraction. Horizontally dispersed NRs on the substrate formed an overlapping junction structure into seed layer as ZnO NRs network. NRs grown on the seed layer including horizontal NRs were oriented in different directions to form three-dimensional ZnO NRs in flower shape. The electrical resistance of sensors based NRs array decreased dramatically with increasing NRs added to ZnO seed layer. Results show that ultraviolet photocurrent increased from 1.7 to 23 μA which is suitable for fabrication of practical photodevices.

Electron Depleted ZnO Nanowalls-Based Broadband Photodetector

Pristine ZnO has been extensively reported for high responsivity UV photodetectors based applications. However, in general, its photo-response in visible and NIR region is very poor. In this article, a simple and cost-effective technique of synthesizing pristine ZnO honeycomb nanostructure based high responsivity broadband (200 nm - 950 nm) photodetector is demonstrated. The dark current of the device was found to be as low as 5.6 pA at 10 V applied bias. The maximum photo-current to dark current ratio was $\sim 3.2 \times 10^{7}$ at 300 nm wavelength (measured at −10 V applied bias). The calculated linear dynamic range of the device is as high as 128.9 dB. The maximum specific photodetectivity, photoresponsivity and external quantum efficiency (@ 300 nm) calculated at −10 V bias was $2.07 \times 10^{15}$ cm $\cdot $ Hz $^{1/2} \cdot \text{W}^{-1}$ , 115 $\text{A}\cdot \text{W}^{-1}$ and 47,583% respectively, which is comparable to some of the existing commercial broadband photodetectors.

Low Dark Current and High Responsivity UV Detector Based on TiO2 Nanowire/RGO Thin Film Heterostructure

A UV detector was fabricated using glancing angle deposition (GLAD)-synthesized TiO2 nanowires (NWs) over spin-coated reduced graphene oxide (RGO) thin films (TFs) on a Si substrate. The field-emission scanning electron microscopy (FE-SEM) images showed that TiO2 NWs were grown with a length of ~140 nm. The fabricated TiO2 NWs were amorphous in nature, as depicted by the selected area electron diffraction (SAED) pattern which was also verified by X-ray diffraction (XRD) analysis. On average, ninefold enhanced optical absorption was observed for the TiO2 NW/RGO TF/Si sample compared to the bare TiO2 NW/Si sample. A significantly low dark current of 2.9 nA (at +1 V) was obtained after the incorporation of the RGO TF beneath the TiO2 NWs. The fabricated Au/TiO2 NW/RGO TF/Si device showed high responsivity and detectivity of 75.7 A/W and ${6.86} \times {10}^{{13}}$ Jones, respectively, under 380-nm light illumination having a power density of as low as $0.8~\mu \text{W}$ /cm2. A low noise-equivalent power (NEP) of 49 fW was also obtained from the resulting detector. The rise and fall times of the Au/TiO2 NW/RGO TF/Si detector were 0.8 and 1.09 s, respectively.

Enhanced performance of ultraviolet photodetector based on sputtered ZnO/Au/ZnO multilayer structure

Abstract This work presents the optimization, elaboration and characterization of a new MSM UV photodetector (PD) design based on an amended active region with ZnO/Au/ZnO (ZAZ) heterostructure. An experimental investigation assisted by Genetic Algorithm (GA) global optimization was conducted for engineering the proposed ZAZ multilayer in order to achieve high-responsivity UV sensor. The RF magnetron sputtering technique was then used to elaborate the optimized tri-layered structure yielding the highest photoresponse. The structural and optical properties of the sputtered multilayer design were also investigated via X-ray diffraction (XRD) and UV–Vis absorbance measurements. Interestingly, electrical characterizations show that the optimized design is beneficial in two ways, firstly an ultrahigh responsivity of 1.3A/W was successfully demonstrated and secondly, the dark current was greatly reduced in comparison with that of the conventional design. This is attributed to the global optimization approach, enabling exciting opportunities for promoting strong light-matter interactions by improving the light trapping capability and photocurrent generation. Moreover, the inserted Au layer induces the band bending gradient benefit, leading to an efficient transfer of the photogenerated carrier and hinders the recombination effects, which paves a new path toward fabricating high-responsivity UV PDs based on low-cost ZnO earth abundant material.

Correlation of donor-acceptor pair emission on the performance of GaN-based UV photodetector

High responsivity UV photodetector has been realized by fabricating single crystalline epitaxial GaN-based devices grown on silicon substrate by using molecular beam epitaxy system. The influence of trap states existing within the forbidden gap on GaN-based optoelectronic devices has been investigated. The quality and performance of the fabricated GaN based UV photodetector with distinct AlN buffer layer grown at low and high substrate temperature are substantiated. A detailed analysis reveals that high temperature buffer can yield improved crystalline quality of GaN with similar morphological properties as compared to buffer layer grown at low temperature. However, the distinct buffer layer influence the optical properties as the photoluminescence analysis explains that both the films possess superior band-to-band edge emission where GaN grown with high temperature AlN buffer consists of dominant acceptor defect states in comparison to GaN with low temperature AlN buffer layer. The existence of acceptor states has been accredited by the presence of Ga vacancy related states in the band gap. The fabricated devices yield high photoresponsivity of 2.1 and 1.5 A/W at 1 V from GaN films bearing low and high accepter defect states which explain a clear correlation of device performance with trap states within the band-gap region.

Single CdS Nanorod for High Responsivity UV–Visible Photodetector

1D nanoscale photodetectors have been extensively investigated for the unique geometry structure and novel physical and chemical properties. The 1D CdS materials have received much attention in the field due to its high photosensitivity and fast response, while how to achieve high responsivity is still in development, despite it is the crucial target to the excellent photodetector. Single crystal CdS nanorods (NRs) are synthesized on SiO2/Si substrate over large scale via the chemical vapor deposition method. The individual single CdS nanorod photodetector have been fabricated by using photolithography process and the responsivity of the photodetector is investigated systematically. At a very low percentage of illumination intensity (2%, 0.5 mW cm−2) under 450 nm, the photodetector exhibited a high responsivity and reached at 1.23 × 104 A W−1 with the bias voltages of 2 V. The good crystallinity and large surface of CdS nanorod are the reasons of this excellent performance of CdS based photodetector. The strategy proposed herein appears to hold great potential for a high responsivity with low illumination intensity.

Enhanced photoelectrochemical photocatalytic activities in hydrothermal synthesized SrTiO3/TiO2 heterostructure thin films

Heterostructured SrTiO3/TiO2 nanofibers were fabricated, under various doping times, by two steps in situ hydrothermal method using TiO2 nanofibers as both template and reactant. The as-fabricated heterostructure composite included SrTiO3 nanocubes or nanoparticles assembled uniformly on the surface of TiO2 nanofibers undergoes a huge photoelectric performance, evaluated by the photo-to-dark current ratio, which reaches three orders of magnitude of that observed in TiO2. The results presented here can be owing to the improvement of charge separation derived from the coupling effect of TiO2 and SrTiO3 nanocomposites and demonstrate the potential prospects of heterostructures with smaller nanostructure size in fabricating high-response UV detectors. Furthermore, SrTiO3/TiO2 nanofibers exhibit enhanced photocatalytic activity in the decomposition of the methylene blue aqueous solution under ultraviolet light, which could be attributed to the improvement of charge separation derived from the coupling effect of TiO2 and SrTiO3 nanocomposites.

High performance ultraviolet detector based on SrTiO3/TiO2 heterostructure fabricated by two steps in situ hydrothermal method

Heterostructured SrTiO3/TiO2 nanocomposites have been fabricated by two steps in situ hydrothermal method with high photoelectric performance. Especially, TiO2 plays the role of the resultant in first step reaction and the reactant in second synthesis. After the second hydrothermal method, apart from SrTiO3 particles assembling on the surface of TiO2, we observe a web-linked composite of SrTiO3 connecting TiO2 nanowires above the middle of them and making up the void space. Consequently, a higher photoelectric performance is evaluated by the photo-to-dark current ratio which reaches to three orders of magnitude. The results presented here can be owing to the improvement of charge separation derived from the coupling effect of TiO2 and SrTiO3 nanocomposites. These experiments demonstrate the potential prospects of heterostructure with smaller nanostructure size in fabricating high-response UV detectors.

High-responsivity UV detectors based on MgNiO films grown by magnetron sputtering

We have grown high-quality MgNiO films at and by the radio frequency magnetron sputtering. Transmittance measurements show that the absorption edges of the films grown at and are at 251 nm and 227 nm, respectively. We have deduced that the MgNiO film grown at a higher temperature has a higher Mg content and bigger bandgap. The XRD results confirm the deduction. Based on those films, we have fabricated UV detectors and measured the spectral response. The peak responsivities of the detectors with MgNiO films grown at and are located at 260 nm and 230 nm and are about 2.56 A/W and 2.3 A/W, respectively. The corresponding UV to visible rejection ratios (250 nm/500 nm) are 640 and 530, respectively. The large UV to visible rejection ratio and the high responsivity make the MgNiO-based detector a very encouraging candidate in the application of visible-blind and solar-blind UV light detection.