Photocurrent Polarity Controlled by Light Wavelength in Self-Powered ZnO Nanowires/SnS Photodetector System.
ABSTRACT: Self-powered photodetectors are expected to play a crucial role in future nano-optoelectronic devices owing to their independent and sustainable operation. Based on the heterojunction between ZnO nanowires (NWs) and shuttle-like SnS, we design a self-powered photodetector exhibiting wide-range photoresponse and tunable spectral selectivity. Differently from conventional devices, a wavelength-induced photocurrent polarity is observed in the ZnO NWs/SnS photodetector, which enables the device to distinguish between photons in the UV and visible (VIS) regions. This is due to switching of the interfacial modulation by the pyroelectric-polarization potential (pyro-potential) inside ZnO NWs and thermoelectric-polarization potential (thermo-potential) inside SnS. A photocurrent enhancement of 125% and improved responsivity of 364 μA/W are obtained under the pyro-potential upon 690 nm light illumination, whereas reversed responsivity of -155 μA/W is obtained under the thermo-potential upon 365 nm light illumination. We believe the photocurrent polarity could be useful for improving resolution of dynamic light sensing/imaging.
Project description:We demonstrate that indium tin oxide nanowires (ITO NWs) and cationic polymer-modified ITO NWs configured in a network format can be used as high performing UV/vis photodetectors. The photovoltage response of ITO NWs is much higher than similarly constructed devices made from tin oxide, zinc tin oxide, and zinc oxide nanostructures. The ITO NW mesh-based devices exhibit a substantial photovoltage (31-100 mV under illumination with a 1.14 mW 543 nm laser) and photocurrent (225-325 μA at 3 V). The response time of the devices is fast with a rise time of 20-30 μs and a decay time of 1.5-3.7 ms when probed with a 355 nm pulsed laser. The photoresponsivity of the ITO NW devices ranges from 0.07 to 0.2 A/W at a 3 V bias, whose values are in the performance range of most commercial UV/vis photodetectors. Such useful photodetector characteristics from our ITO NW mesh devices are attained straightforwardly without the need for complicated fabrication procedures involving highly specialized lithographic tools. Therefore, our approach of ITO NW network-based photodetectors can serve as a convenient alternative to commercial or single NW-based devices.
Project description:Porous Si-SiO2 UV microcavities are used to modulate a broad responsivity photodetector (GVGR-T10GD) with a detection range from 300 to 510 nm. The UV microcavity filters modified the responsivity at short wavelengths, while in the visible range the filters only attenuated the responsivity. All microcavities had a localized mode close to 360 nm in the UV-A range, and this meant that porous Si-SiO2 filters cut off the photodetection range of the photodetector from 300 to 350 nm, where microcavities showed low transmission. In the short-wavelength range, the photons were absorbed and did not contribute to the photocurrent. Therefore, the density of recombination centers was very high, and the photodetector sensitivity with a filter was lower than the photodetector without a filter. The maximum transmission measured at the localized mode (between 356 and 364 nm) was dominant in the UV-A range and enabled the flow of high energy photons. Moreover, the filters favored light transmission with a wavelength from 390 nm to 510 nm, where photons contributed to the photocurrent. Our filters made the photodetector more selective inside the specific UV range of wavelengths. This was a novel result to the best of our knowledge.
Project description:A graphene photodetector decorated with Bi<sub>2</sub>Te<sub>3</sub> nanowires (NWs) with a high gain of up to 3 × 10<sup>4</sup> and wide bandwidth window (400-2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to the gain of a photodetector using a graphene/Bi<sub>2</sub>Te<sub>3</sub> nanoplate junction. Additionally, the position of photocurrent generation was investigated at the graphene/Bi<sub>2</sub>Te<sub>3</sub> NWs junction. Eventually, with low bandgap Bi<sub>2</sub>Te<sub>3</sub> NWs and a graphene junction, the photoresponsivity improved by 200% at 2200 nm (~0.09 mA/W).
Project description:Hierarchical Si/ZnO trunk-branch nanostructures (NSs) have been synthesized by hot wire assisted chemical vapor deposition method for trunk Si nanowires (NWs) on indium tin oxide (ITO) substrate and followed by the vapor transport condensation (VTC) method for zinc oxide (ZnO) nanorods (NRs) which was laterally grown from each Si nanowires (NWs). A spin coating method has been used for zinc oxide (ZnO) seeding. This method is better compared with other group where they used sputtering method for the same process. The sputtering method only results in the growth of ZnO NRs on top of the Si trunk. Our method shows improvement by having the growth evenly distributed on the lateral sides and caps of the Si trunks, resulting in pine-leave-like NSs. Field emission scanning electron microscope image shows the hierarchical nanostructures resembling the shape of the leaves of pine trees. Single crystalline structure for the ZnO branch grown laterally from the crystalline Si trunk has been identified by using a lattice-resolved transmission electron microscope. A preliminary photoelectrochemical (PEC) cell testing has been setup to characterize the photocurrent of sole array of ZnO NR growth by both hydrothermal-grown (HTG) method and VTC method on ITO substrates. VTC-grown ZnO NRs showed greater photocurrent effect due to its better structural properties. The measured photocurrent was also compared with the array of hierarchical Si/ZnO trunk-branch NSs. The cell with the array of Si/ZnO trunk-branch NSs revealed four-fold magnitude enhancement in photocurrent density compared with the sole array of ZnO NRs obtain from VTC processes.
Project description: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 × 10<sup>12</sup> Jones and 84,000% at 2 V bias, respectively. The rise time (τ<sub>r</sub>) and fall time (τ<sub>f</sub>) 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.
Project description:We report on the major improvement in UV photosensitivity and faster photoresponse from vertically aligned ZnO nanowires (NWs) by means of rapid thermal annealing (RTA). The ZnO NWs were grown by vapor-liquid-solid method and subsequently RTA treated at 700°C and 800°C for 120 s. The UV photosensitivity (photo-to-dark current ratio) is 4.5 × 103 for the as-grown NWs and after RTA treatment it is enhanced by a factor of five. The photocurrent (PC) spectra of the as-grown and RTA-treated NWs show a strong peak in the UV region and two other relatively weak peaks in the visible region. The photoresponse measurement shows a bi-exponential growth and bi-exponential decay of the PC from as-grown as well as RTA-treated ZnO NWs. The growth and decay time constants are reduced after the RTA treatment indicating a faster photoresponse. The dark current-voltage characteristics clearly show the presence of surface defects-related trap centers on the as-grown ZnO NWs and after RTA treatment it is significantly reduced. The RTA processing diminishes the surface defect-related trap centers and modifies the surface of the ZnO NWs, resulting in enhanced PC and faster photoresponse. These results demonstrated the effectiveness of RTA processing for achieving improved photosensitivity of ZnO NWs.
Project description:ZnO-based ultraviolet (UV) photodetector can be easily fabricated by using sol-gel spin-coating method, however, the crystallization of amorphous state ZnO thin films is necessary to fabricate high performance UV photodetector. Thus, we devised a thermal dissipation annealing (TDA) method in which the heat transfer to the ZnO thin films can be synchronized with the heat release from the substrate. It was found that sol-gel spin-coated ZnO thin films can be crystallized through the mobility difference of ZnO molecules placed at the surface of ZnO thin films. Also, UV photodetector based on ZnO thin films annealed with the TDA method exhibited faster rise and decay time constant (?<sub>r</sub>?=?35 ms and ?<sub>d</sub>?=?73 ms, respectively), a higher on/off current ratio, and reproducible photocurrent characteristics compared to that of the ZnO thin films annealed by using furnace and IR lamp. Therefore, these results indicated that the TDA method is a feasible alternative route for the fabrication of ZnO based high performance optoelectronic devices.
Project description:Herein, the optoelectrical investigation of cadmium zinc telluride (CZT) and indium (In) doped CZT (InCZT) single crystals-based photodetectors have been demonstrated. The grown crystals were configured into photodetector devices and recorded the current-voltage (I-V) and current-time (I-t) characteristics under different illumination intensities. It has been observed that the photocurrent generation mechanism in both photodetector devices is dominantly driven by a photogating effect. The CZT photodetector exhibits stable and reversible device performances to 632 nm light, including a promotable responsivity of 0.38 AW<sup>-1</sup>, a high photoswitch ratio of 152, specific detectivity of 6.30 × 10<sup>11</sup> Jones, and fast switching time (rise time of 210 ms and decay time of 150 ms). When doped with In, the responsivity of device increases to 0.50 AW<sup>-1</sup>, photoswitch ratio decrease to 10, specific detectivity decrease to 1.80 × 10<sup>11</sup> Jones, rise time decrease to 140 ms and decay time increase to 200 ms. Moreover, these devices show a very high external quantum efficiency of 200% for CZT and 250% for InCZT. These results demonstrate that the CZT based crystals have great potential for visible light photodetector applications.
Project description:In this study, a laterally coupled device composed of a photodiode and a Si nanowires-field-effect transistor (NWs-FET) is constructed on a plastic substrate and the coupled device is characterized. The photodiode is made of p-type Si NWs and an n-type ZnO film. The Si NWs-FET is connected electrically to the photodiode in order to enhance the latter's photocurrent efficiency by adjusting the gate voltage of the FET. When the FET is switched on by biasing a gate voltage of -9 V, the photocurrent efficiency of the photodiode is three times higher than that when the FET is switched off by biasing a gate voltage of 0 V.
Project description:CuO-ZnO core-shell radial heterojunction nanowire arrays were obtained by a simple route which implies two cost-effective methods: thermal oxidation in air for preparing CuO nanowire arrays, acting as a p-type core and RF magnetron sputtering for coating the surface of the CuO nanowires with a ZnO thin film, acting as a n-type shell. The morphological, structural, optical and compositional properties of the CuO-ZnO core-shell nanowire arrays were investigated. In order to analyse the electrical and photoelectrical properties of the metal oxide nanowires, single CuO and CuO-ZnO core-shell nanowires were contacted by employing electron beam lithography (EBL) and focused ion beam induced deposition (FIBID). The photoelectrical properties emphasize that the p-n radial heterojunction diodes based on single CuO-ZnO core-shell nanowires behave as photodetectors, evidencing a time-depending photoresponse under illumination at 520 nm and 405 nm wavelengths. The performance of the photodetector device was evaluated by assessing its key parameters: responsivity, external quantum efficiency and detectivity. The results highlighted that the obtained CuO-ZnO core-shell nanowires are emerging as potential building blocks for a next generation of photodetector devices.