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A self-powered UV sensor with high responsivity was developed by coupling ZnO based piezoelectric nanogenerator and photodetector for uninterrupted real-time monitoring of UV radiation. Unlike conventional UV photodetectors, our approach couples a ZnO based metal-semiconductor-metal photodetector as a variable load resistor with a flexible ZnO:PVDF piezoelectric nanogenerator through impedance matching to realize self-powering of photodetector. The as fabricated UV photodetector exhibits a dark resistance of approximately 55 MΩ and change of resistance from 12 to 2 MΩ in response to UV illumination ranging from 1.5 to 14.5 mW/cm2. Under UV exposure of 1.5 mW/cm2, the output voltage of self-powered UV sensor drops from ∼14.6 V (dark) to ∼3.88 V. With increasing UV intensity from 1.5 to 14.5 mW/cm2, the output voltage gradually decreases from ∼3.88 to ∼1.04 V due to reduced ZnO photodetector resistance. This self-powered UV sensor exhibits excellent performance with a sensitivity of ∼93%, a voltage responsivity of 7.14 V (mW−1 cm−2), a response time of 0.67 s, and a recovery time of 4 s, which are better than the previous reports. The environmentally stable and biocompatible nature of ZnO based system makes it a promising candidate for self-powered real time ultraviolet remote sensing applications. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerators (PENG), which convert random mechanical energy into electrical energy, have attracted considerable attention due to their application potential in self-powered micro and nano electronics devices, wearable electronics, sensors etc. PENGs based on ZnO nanostructures are particularly important due to their low cost, flexibility and bio-compatibility. Flexible PENGs based on ZnO nanostructures dispersed in Polydimethylsiloxane (PDMS) in ITO/ZnO:PDMS/ITO device configuration were fabricated and characterized for vibration energy harvesting applications. Surfactant free ZnO nanostructures were grown using co-precipitation route and ZnO:PDMS nano-composite films with ZnO content varying in the range of 1.5–7.5 wt% were deposited on ITO/PET substrates for PENG fabrication. The maximum open circuit voltage and short circuit current of ~ 2.5 V and ~ 4 µA respectively were obtained in PENG fabricated with 6 wt% ZnO. The output characteristics were further enhanced to 5 V and 6 µA with flowing oxygen ambient annealing of ZnO nanostructures generating an instantaneous power density of ~9.55 µWcm−2. X-ray photoelectron spectroscopy studies confirmed reduction in oxygen vacancy and enhancement in oxygen interstitial concentrations on oxygen annealing which leads to the suppression of free carrier induced internal screening in ZnO nanostructures. This suppression of internal screening effect is the possible reason for the enhancement in output characteristics of ZnO:PDMS PENG fabricated with oxygen annealed ZnO nanostructures. The electrical energy generated by the ZnO:PDMS PENG was rectified and effectively stored in capacitors and used to power LEDs and LCD display. • ZnO nanostructures were grown by co-precipitation method with air and oxygen annealing. • ZnO:PDMS PENG with variable wt% of ZnO in PDMS were fabricated in ITO/ZnO:PDMS/ITO configuration. • The output performance of ZnO:PDMS PENG is improved significantly by annealing ZnO nanostructures in flowing oxygen ambient. • XPS established a correlation between the oxygen related point defects in ZnO and output characteristics of ZnO based PENG. • The output energy from ZnO:PDMS PENG was rectified and effectively stored in capacitor to flash LEDs and LCD display. [ABSTRACT FROM AUTHOR]

Abstract: We report valence and conduction band offset measurements in a pulsed laser deposited Ni0.07Zn0.93O/ZnO heterostructure using X-ray photoelectron spectroscopy, valence band spectroscopy and ultraviolet visible spectroscopy. Neglecting the strain effect, the valence band offset was estimated to be 0.32 eV and the conduction band offset comes out to be −0.23 eV. Ratio between conduction band and valence band offset is 0.72. Core level shifting due to Ni doping has also been explained. Magnetotransport study of Ni0.07Zn0.93O film reveals that the charge carriers might be spin polarized at the interface of the heterojunction. [Copyright &y& Elsevier]

The increasing demand of energy harvesting and wearable electronics applications requires the development of flexible and highly durable piezoelectric nanogenerators (PENG). In this work, We have fabricated flexible ZnO:PVDF based PENGs for vibrational energy harvesting and shoe insole pedometer application s. ZnO nanorods were grown by hydrothermal method and incorporated into PVDF matrixes in the concentration range of 5–15 wt%. These homogeneous ZnO:PVDF composite films were sandwiched between Al electrodes to realize flexible free standing PENGs. The open circuit voltage (Voc), short circuit current (Isc) and instantaneous power density of PENGs increased from ∼ 4 V, 0.4 µA and 1.6 µW/cm2 to ∼ 14.6 V, 0.6 µA and 21.3 µW/cm2 respectively when ZnO nanorods concentration in PVDF increased from 0 to 10 wt% and decreased with further increase in ZnO nanorods concentration. The enhancement in output characteristics of ZnO:PVDF PENG with increasing ZnO concentration was attributed to β-phase crystallization of PVDF, which was confirmed by XRD and FTIR measurements. The deterioration in output characteristics beyond 10 wt% of ZnO nanorods concentration was explained considering the variation of dielectric constant and remnant polarization. The rectified output of the PENGs was effectively stored in various commercially available capacitors and used to power LEDs and stopwatch displays. The PENG with 10 wt% ZnO concentration was used to develop shoe insole pedometer which was interfaced with android based mobile application via Bluetooth. The shoe insole pedometer was successfully tested for 5000 steps at different walking frequencies ranging from 0.5 Hz to 2 Hz in the speed range of ∼ 1.4 km/h to 5.5 km/h. This study not only gives an insight into the mechanism of ZnO:PVDF based PENGs but also opens up their potential in vibration energy harvesting and shoe insole pedometer applications. • ZnO:PVDF based flexible piezoelectric nanogenerators (PENGs) were fabricated with variable ZnO nanofiller concentrations. • The variation of output performance of ZnO:PVDF based PENGs was studied with ZnO nanofiller concentrations. • The PENGs were able to power capacitors, LEDs, and LCDs. • A pedometer device has been fabricated using the ZnO:PVDF based flexible PENG sensor. [ABSTRACT FROM AUTHOR]

Intrinsic epitaxial zinc oxide (epi-ZnO) thin films were grown by laser-molecular beam epitaxy (L-MBE), i.e., pulsed laser deposition (PLD) technique using Johnson Matthey “specpure”-grade ZnO pellets. The effects of substrate temperatures on ZnO thin film growth, electrical conductivity (σ), mobility (μ) and carrier concentration (n) were studied. As well as the feasibility of developing high quality conducting oxide thin films was also studied simultaneously. The highest conductivity was found for optimized epi-ZnO thin films is σ=0.06×103 ohm-1 cm-1 (n-type) (which is almost at the edge of semiconductivity range), carrier density n=0.316×1019 cm-3 and mobility μ=98 cm2/V s. The electrical studies further confirmed the semiconductor characteristics of epi-n-ZnO thin films. The relationship between the optical and electrical properties were also graphically enumerated. The electrical parameter values for the films were calculated, graphically enumerated and tabulated. As a novelty point of view, we have concluded that without doping and annealing, we have obtained optimum electrical conductivity with high optical transparency (⩾95%) for as deposited ZnO thin films using PLD. Also, this is the first time that we have applied PLD made ZnO thin films to iso-, hetero-semiconductor–insulator–semiconductor (SIS) type solar cells as transparent conducting oxide (TCO) window layer. We hope that surely these data be helpful either as a scientific or technical basis in the semiconductor processing. [Copyright &y& Elsevier]

High quality epitaxial indium zinc oxide (heavily indium oxide doped) (epi-n-IZO) thin films were optimized by laser-molecular beam epitaxy (L-MBE) i.e., pulsed laser deposition (PLD) technique for fabricating novel iso- and hetero-semiconductor–insulator–semiconductor (SIS) type solar cells using Johnson Matthey “specpure”- grade 90% In2O3 mixed 10% ZnO (as commercial indium tin oxide (ITO) composition) pellets. The effects of substrate temperatures, substrates and heavy indium oxide incorporation on IZO thin film growth, opto-electronic properties with 〈1 0 0〉 silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP) wafers were studied. As well as the feasibility of developing some novel models of iso- and hetero-SIS type solar cells using epi-IZO thin films as transparent conducting oxides (TCOs) and 〈1 0 0〉 oriented Si, GaAs and InP wafers as base substrates was also studied simultaneously. The optimized films were highly oriented, uniform, single crystalline approachment, nano-crystalline, anti-reflective (AR) and epitaxially lattice matched with 〈1 0 0〉 Si, GaAs and InP wafers without any buffer layers. The optical transmission T (max) ⩾ 95% is broader and absolute rivals that of other TCOs such as ITO. The highest conductivity observed is σ=0.47×103 Ω-1 cm-1 (n-type), carrier density n=0.168×1020 cm-3 and mobility μ=123 cm2/V s. From opto-electronic characterizations, the solar cell characteristics and feasibilities of fabricating respective epi-n-TCO/〈1 0 0〉 wafer SIS type solar cells were confirmed. Also, the essential parameters of these cells were calculated and tabulated. We hope that these data be helpful either as a scientific or technical basis in semiconductor processing. [Copyright &y& Elsevier]

We have optimised and deposited epitaxial indium zinc oxide (epi-IZO) (In2Zn2O5) thin films on 〈1 0 0〉 oriented Si, GaAs and InP by laser-molecular beam epitaxy (L-MBE) technique, i.e., pulsed laser deposition (PLD). Optimised growth conditions have been obtained for the deposition of high quality epi-IZO thin films. To our knowledge, this is the first time that the PLD deposited indium zinc oxide thin films on semiconductor wafers have been applied to semiconductor–insulator–semiconductor (SIS) iso- and hetero-type junction solar cell structures as wide band gap transparent conducting front electrode-window layers. We have carried out X-ray diffraction (XRD) and energy dispersive chemical analysis (EDAX) to determine the Structural and compositional properties of as-grown thin films. The crystalline quality of the obtained thin films is similar to that of the bulk single crystals. Increasing the deposition temperature leads the thin films to fine nano-structure nature. In the present work, the effects of various substrate temperatures, substrates and heavy indium oxide doping on indium zinc oxide thin film growth, structural and compositional properties were analysed. As well as our main aim, the feasibility of developing high quality transparent conducting oxide (TCO) thin films for opto-electronic devices was also studied simultaneously. Our novel achievement in this work is without any buffer layers, we have obtained good epitaxial lattice matching between the highly oriented IZO functional layers and the substrate materials suitable for III–V based high-speed opto-electronic and micro-electronic devices. [Copyright &y& Elsevier]

Highly textured zinc oxide (ZnO) thin films have been optimized and deposited by pulsed laser deposition (PLD), i.e., laser-molecular beam epitaxy technique on 〈100〉 Si, GaAs and InP wafers compatible with current semiconductor processing techniques. To our knowledge this is the first time that the PLD deposited zinc oxide thin films on semiconductor wafers have been applied to semiconductor–insulator–semiconductor type multi junction (homo and hetero) solar cell structures as wide band gap transparent conducting oxide (TCO) front electrode-emitter layers. In this present work, the effects of various substrate temperatures and substrates on ZnO thin film growth, structural and compositional properties were analyzed and the feasibility of developing high-quality TCO thin films for opto-electronic devices was also studied simultaneously. Increasing the deposition temperature leads the thin films to fine nano-structures. Our achievement in this work is elimination of any buffer layer like GaN and we have obtained good epitaxial lattice matching between the ZnO functional layers and the 〈100〉 substrates suitable for III–V-based high-speed opto- and micro-electronic devices. [Copyright &y& Elsevier]